Quite often, when repairing or converting an ATX computer power supply into a charger or laboratory source, a diagram of this unit is required. Considering that there are a great many models from such sources, we decided to collect a collection of this topic in one place.
In it you will find typical power supply circuits for computers, both modern ATX type and already noticeably outdated ATX. It is clear that newer and more relevant options appear every day, so we will try to quickly replenish the collection of schemes with newer options. By the way, you can help us with this.
Collection of circuit diagrams for ATX and AT power supplies
ATX 310T, ATX-300P4-PFC, ATX-P6; Octek X25D AP-3-1 250W; Sunny ATX-230;
BESTEC ATX-300-12ES on UC3842, 3510 and A6351 chips; BESTEC ATX-400W(PFC) on ICE1PCS01, UC3842, 6848, 3510, LM358 chips
Chieftec computer power supply diagram CFT-500A-12S, CFT-560A-12S, CFT-620A-12S (CM6800G, PS222S, SG6858 or SG6848) APS-1000C, TNY278PN, CM6800TX; Chieftec 850W CFT-850G-DF; 350W GPS-350EB-101A; 350W GPS-350FB-101A; 500W GPS-500AB-A; 550W GPS-550AB-A; 650W GPS-650AB-A and Chieftec 650W CFT-650A-12B; 1000W CFT-1000G-DF and Chieftec 1200W CFT-1200G-DF; CFT-600-14CS, CFT-650-14CS, CFT-700-14CS, CFT-750-14CS on LD7550B
Chip Goal 250W, (with CG8010DX)
Codegen QORI 200xa at 350W on the SG6105 chip
Colors-It computer block diagram 300W 300U-FNM (sg6105 and sg6848); 330W - 330U PWM SG6105 duty station on TDA865; 330U IW-P300A2-0 R1.2 sg6105; 330U PWM SG6105 and duty station M605; 340W - 340U PWM SG6105; 350U-SCE- KA339, M605, 3842; 350-FCH PWM 3842, LM339 and M605; 340U SG6105 and 5H0165R; 400U SG6105 and 5H0165R; 400PT, 400U SCH 3842, LM339 and M605; 500T SG6105 and 5H0165R; 600PT(ATX12V-13), WT7525, 3B0365
ComStars 400W KT-400EX-12A1 on UC3543A circuit
CWT PUH400W
Delta Electronics circuit diagram of a computer power supply DPS-210EP, DPS-260-2A 260W on microassemblies NE556, PQ05RF11, ML4824-1, LM358, LM339D, PQ30R21; DPS-470 AB A 500W, APFC and PWM DNA1005A or DNA1005;
DELUX ATX-350W P4 on AZ7500BP and LP7510 circuit
FSP Epsilon 600W FX600-GLN duty circuit, assembled on the FSDM0265R IC; FSP145-60SP KA3511, duty room KA1N0165R; FSP250-50PLA, APFC on CM6800, field effect transistors STP12NM50, TOP243Y, control PS223; FSP ATX-350PNR DM311 and main PWM FSP3528; FSP ATX-300PAF and ATX-350 on DA311; 350W FSP350-60THA-P And 460W FX500-A FSP3529Z (similar to SG6105; ATX-400 400W, DM311; ATX-400PNF,; OPS550-80GLN, APFC on field-effect transistors 20N60C3, duty on DM311; OPS550-80GLN, APFC+PWM control module on CM6800G; Epsilon 600W FX600-GLN(scheme); ATX-300GTF on field truck 02N60
Green Tech circuit diagram of a 300W computer power supply model MAV-300W-P4 on a TL494CN and WT7510 chip
Hiper HPU-4S425-PU 425W APFC, based on CM6805, VIPer22A, LM393, PS229 chips
iMAC G5 A1058, APFC on 4863G, duty station on TOP245YN, main power supply on 3845B
J.N.C. 250W lc-b250 atx
Krauler ATX-450 450W (with TL3845, LD7660, WT7510)
LWT 2005 on LM339N chip
M-Tech 450W KOB-AP4450XA microassembly SG6105Z
Maxpower PX-300W chip SG6105D
Microlab circuit diagram of a computer power supply 420W, on WT7510, PWM TL3842 duty station - 5H0165R; M-ATX-420W based on UC3842, supervisor 3510 and LM393
PowerLink 300W LPJ2-18 on LPG-899 microassembly
Powerman IP-P550DJ2-0, 350W IP-P350AJ, 350W IP-P350AJ2-0 ver.2.2 on supervisor W7510, 450W IP-S450T7-0, 450W IP-S450T7-0 rev:1.3 (3845, WT7510 and A6259H)
Power Master 230W model LP-8, 250W FA-5-2, 250W AP-3-1, PM30006-02 ATX 300W
Power Mini P4,Model PM-300W. Main micro assembly SG6105
Both 230 and 250 watt power supplies are based on the very popular TL494 chip. The video repair instructions tell you how to troubleshoot and safety precautions when repairing any switching power supplies, which includes computer ones.
SevenTeam ST-200HRK (IC: LM339, UTC51494, UC3843AN)
ShenShon circuit diagram of a computer power supply 400W model SZ-400L and 450W model SZ450L, duty station on C3150, AT2005; 350w on AT2005, aka WT7520, or LPG899
Sparkman SM-400W on KA3842A, WT7510 circuit
SPS: SPS-1804-2(M1) and SPS-1804E
Personal computer power supply - used to supply power to all components and components of the system unit. A standard ATX power supply must provide the following voltages: +5, -5 V; +12, -12 V; +3.3 V; Almost any standard power supply has a powerful fan located at the bottom. On the rear panel there is a socket for connecting a network cable and a button to turn off the power supply, but on cheap Chinese versions it may not be available. From the opposite side comes a huge pile of wires with connectors for connecting the motherboard and all other components of the system unit. Installing the power supply into the case is usually quite simple. Installing a computer power supply into the system unit case To do this, insert it into the upper part of the system unit, and then secure it with three or four screws to the rear panel of the system unit. There are designs of the system unit case in which the power supply is placed in the lower part. In general, if anything, I hope you can get your bearings
Cases of breakdowns of computer power supplies are not uncommon. The causes of malfunctions can be: Voltage surges in the AC network; Poor workmanship, especially for cheap Chinese power supplies; Unsuccessful circuit design solutions; Use of low-quality components in manufacturing; Overheating of radio components due to contamination of the power supply or fan stoppage.
Most often, when a computer power supply breaks down, there are no signs of life in the system unit, the LED indication does not light up, there are no sound signals, and the fans do not spin. In other cases of malfunction, the motherboard does not start. At the same time, the fans are spinning, the indicator lights up, the drives and hard drive show signs of life, but there is nothing on the monitor display, only a dark screen.
Problems and defects can be completely different - from complete inoperability to permanent or temporary failures. As soon as you begin the repair, make sure that all contacts and radio components are visually in order, the power cords are not damaged, the fuse and switch are working, and there are no short circuits to ground. Of course, the power supplies of modern equipment, although they have common principles of operation, are quite different in their circuitry. Try to find a diagram on a computer source, this will speed up the repair.
The heart of any computer power supply circuit, ATX format, is a half-bridge converter. Its operation and operating principle are based on the use of push-pull mode. Stabilization of the device's output parameters is carried out using control signals.
Pulse sources often use the well-known TL494 PWM controller chip, which has a number of positive characteristics:
ease of use in electronic designs
good operating technical parameters, such as low starting current and, most importantly, speed
availability of universal internal protective components
The operating principle of a typical computer power supply can be seen in the block diagram below:
The voltage converter converts this value from variable to constant. It is made in the form of a diode bridge that converts voltage and a capacitance that smoothes out oscillations. In addition to these components, additional elements may be present: thermistors and a filter. The pulse generator generates pulses at a given frequency, which power the transformer winding. HE performs the main work in a computer power supply, this is the conversion of current to the required values and galvanic isolation of the circuit. Next, the alternating voltage from the windings of the transformer goes to another converter, consisting of semiconductor diodes that equalize the voltage and a filter. The latter cuts off ripple and consists of a group of inductors and capacitors.
Since many parameters of such a power supply “float” at the output due to unstable voltage and temperature. But if you carry out operational control of these parameters, for example, using a controller with a stabilizer function, then the block diagram shown above will be quite suitable for use in computer technology. Such a simplified power supply circuit using a pulse width modulation controller is shown in the following figure.
PWM controller, for example UC3843, in this case it regulates the amplitude of changes in the signals following through a low-pass filter, watch the video lesson just below:
Linear and switching power supplies
Let's start with the basics. The power supply in a computer performs three functions. First, alternating current from the household power supply must be converted to direct current. The second task of the power supply is to reduce the voltage of 110-230 V, which is excessive for computer electronics, to the standard values required by power converters of individual PC components - 12 V, 5 V and 3.3 V (as well as negative voltages, which we will talk about a little later) . Finally, the power supply plays the role of a voltage stabilizer.
There are two main types of power supplies that perform the above functions - linear and switching. The simplest linear power supply is based on a transformer, on which the alternating current voltage is reduced to the required value, and then the current is rectified by a diode bridge.
However, the power supply is also required to stabilize the output voltage, which is caused by both voltage instability in the household network and a voltage drop in response to an increase in current in the load.
To compensate for the voltage drop, in a linear power supply the transformer parameters are calculated to provide excess power. Then, at high current, the required voltage will be observed in the load. However, the increased voltage that will occur without any means of compensation at low current in the payload is also unacceptable. Excess voltage is eliminated by including a non-useful load in the circuit. In the simplest case, this is a resistor or transistor connected through a Zener diode. In a more advanced version, the transistor is controlled by a microcircuit with a comparator. Be that as it may, excess power is simply dissipated as heat, which negatively affects the efficiency of the device.
In the switching power supply circuit, one more variable appears, on which the output voltage depends, in addition to the two already existing: input voltage and load resistance. There is a switch in series with the load (which in the case we are interested in is a transistor), controlled by a microcontroller in pulse width modulation (PWM) mode. The higher the duration of the open states of the transistor in relation to their period (this parameter is called duty cycle, in Russian terminology the inverse value is used - duty cycle), the higher the output voltage. Due to the presence of a switch, a switching power supply is also called Switched-Mode Power Supply (SMPS).
No current flows through a closed transistor, and the resistance of an open transistor is ideally negligible. In reality, an open transistor has resistance and dissipates some of the power as heat. In addition, the transition between transistor states is not perfectly discrete. And yet, the efficiency of a pulsed current source can exceed 90%, while the efficiency of a linear power supply with a stabilizer reaches 50% at best.
Another advantage of switching power supplies is the radical reduction in the size and weight of the transformer compared to linear power supplies of the same power. It is known that the higher the frequency of alternating current in the primary winding of a transformer, the smaller the required core size and the number of winding turns. Therefore, the key transistor in the circuit is placed not after, but before the transformer and, in addition to voltage stabilization, is used to produce high-frequency alternating current (for computer power supplies this is from 30 to 100 kHz and higher, and as a rule - about 60 kHz). A transformer operating at a power supply frequency of 50-60 Hz would be tens of times more massive for the power required by a standard computer.
Linear power supplies today are used mainly in the case of low-power applications, where the relatively complex electronics required for a switching power supply constitute a more sensitive cost item compared to a transformer. These are, for example, 9 V power supplies, which are used for guitar effects pedals, and once for game consoles, etc. But chargers for smartphones are already entirely pulsed - here the costs are justified. Due to the significantly lower amplitude of voltage ripple at the output, linear power supplies are also used in those areas where this quality is in demand.
⇡ General diagram of an ATX power supply
A desktop computer's power supply is a switching power supply, the input of which is supplied with household voltage with parameters of 110/230 V, 50-60 Hz, and the output has a number of DC lines, the main ones of which are rated 12, 5 and 3.3 V In addition, the power supply provides a voltage of -12 V, and sometime also a voltage of -5 V, necessary for the ISA bus. But the latter was at some point excluded from the ATX standard due to the end of support for the ISA itself.
In the simplified diagram of a standard switching power supply presented above, four main stages can be distinguished. In the same order, we consider the components of power supplies in the reviews, namely:
- EMI filter - electromagnetic interference (RFI filter);
- primary circuit - input rectifier (rectifier), key transistors (switcher), creating high-frequency alternating current on the primary winding of the transformer;
- main transformer;
- secondary circuit - current rectifiers from the secondary winding of the transformer (rectifiers), smoothing filters at the output (filtering).
⇡ EMF filter
The filter at the power supply input is used to suppress two types of electromagnetic interference: differential (differential-mode) - when the interference current flows in different directions in the power lines, and common-mode - when the current flows in one direction.
Differential noise is suppressed by capacitor CX (the large yellow film capacitor in the photo above) connected in parallel with the load. Sometimes a choke is additionally attached to each wire, which performs the same function (not on the diagram).
The common mode filter is formed by CY capacitors (blue drop-shaped ceramic capacitors in the photo), connecting the power lines to ground at a common point, etc. a common-mode choke (LF1 in the diagram), the current in the two windings of which flows in the same direction, which creates resistance for common-mode interference.
In cheap models, a minimum set of filter parts is installed; in more expensive ones, the described circuits form repeating (in whole or in part) links. In the past, it was not uncommon to see power supplies without any EMI filter at all. Now this is rather a curious exception, although if you buy a very cheap power supply, you can still run into such a surprise. As a result, not only and not so much the computer itself will suffer, but other equipment connected to the household network - switching power supplies are a powerful source of interference.
In the filter area of a good power supply, you can find several parts that protect the device itself or its owner from damage. There is almost always a simple fuse for short circuit protection (F1 in the diagram). Note that when the fuse trips, the protected object is no longer the power supply. If a short circuit occurs, it means that the key transistors have already broken through, and it is important to at least prevent the electrical wiring from catching fire. If a fuse in the power supply suddenly burns out, then replacing it with a new one is most likely pointless.
Separate protection is provided against short-term surges using a varistor (MOV - Metal Oxide Varistor). But there are no means of protection against prolonged voltage increases in computer power supplies. This function is performed by external stabilizers with their own transformer inside.
The capacitor in the PFC circuit after the rectifier can retain a significant charge after being disconnected from power. To prevent a careless person who sticks his finger into the power connector from receiving an electric shock, a high-value discharge resistor (bleeder resistor) is installed between the wires. In a more sophisticated version - together with a control circuit that prevents charge from leaking when the device is operating.
By the way, the presence of a filter in the PC power supply (and the power supply of a monitor and almost any computer equipment also has one) means that buying a separate “surge filter” instead of a regular extension cord is, in general, pointless. Everything is the same inside him. The only condition in any case is normal three-pin wiring with grounding. Otherwise, the CY capacitors connected to ground simply will not be able to perform their function.
⇡ Input rectifier
After the filter, the alternating current is converted into direct current using a diode bridge - usually in the form of an assembly in a common housing. A separate radiator for cooling the bridge is highly welcome. A bridge assembled from four discrete diodes is an attribute of cheap power supplies. You can also ask what current the bridge is designed for to determine whether it matches the power of the power supply itself. Although, as a rule, there is a good margin for this parameter.
⇡ Active PFC block
In an AC circuit with a linear load (such as an incandescent light bulb or an electric stove), the current flow follows the same sine wave as the voltage. But this is not the case with devices that have an input rectifier, such as switching power supplies. The power supply passes current in short pulses, approximately coinciding in time with the peaks of the voltage sine wave (that is, the maximum instantaneous voltage) when the smoothing capacitor of the rectifier is recharged.
The distorted current signal is decomposed into several harmonic oscillations in the sum of a sinusoid of a given amplitude (the ideal signal that would occur with a linear load).
The power used to perform useful work (which, in fact, is heating the PC components) is indicated in the characteristics of the power supply and is called active. The remaining power generated by harmonic oscillations of the current is called reactive. It does not produce useful work, but heats the wires and creates a load on transformers and other power equipment.
The vector sum of reactive and active power is called apparent power. And the ratio of active power to total power is called power factor - not to be confused with efficiency!
A switching power supply initially has a rather low power factor - about 0.7. For a private consumer, reactive power is not a problem (fortunately, it is not taken into account by electricity meters), unless he uses a UPS. The uninterruptible power supply is responsible for the full power of the load. At the scale of an office or city network, excess reactive power created by switching power supplies already significantly reduces the quality of power supply and causes costs, so it is being actively combated.
In particular, the vast majority of computer power supplies are equipped with active power factor correction (Active PFC) circuits. A unit with an active PFC is easily identified by a single large capacitor and inductor installed after the rectifier. In essence, Active PFC is another pulse converter that maintains a constant charge on the capacitor with a voltage of about 400 V. In this case, current from the supply network is consumed in short pulses, the width of which is selected so that the signal is approximated by a sine wave - which is required to simulate a linear load . To synchronize the current consumption signal with the voltage sinusoid, the PFC controller has special logic.
The active PFC circuit contains one or two key transistors and a powerful diode, which are placed on the same heatsink with the key transistors of the main power supply converter. As a rule, the PWM controller of the main converter key and the Active PFC key are one chip (PWM/PFC Combo).
The power factor of switching power supplies with active PFC reaches 0.95 and higher. In addition, they have one additional advantage - they do not require a 110/230 V mains switch and a corresponding voltage doubler inside the power supply. Most PFC circuits handle voltages from 85 to 265 V. In addition, the sensitivity of the power supply to short-term voltage dips is reduced.
By the way, in addition to active PFC correction, there is also a passive one, which involves installing a high-inductance inductor in series with the load. Its efficiency is low, and you are unlikely to find this in a modern power supply.
⇡ Main converter
The general principle of operation for all pulse power supplies of an isolated topology (with a transformer) is the same: a key transistor (or transistors) creates alternating current on the primary winding of the transformer, and the PWM controller controls the duty cycle of their switching. Specific circuits, however, differ both in the number of key transistors and other elements, and in qualitative characteristics: efficiency, signal shape, noise, etc. But here too much depends on the specific implementation for this to be worth focusing on. For those interested, we provide a set of diagrams and a table that will allow you to identify them in specific devices based on the composition of the parts.
| Transistors | Diodes | Capacitors | Transformer primary legs | |
| Single-Transistor Forward | 1 | 1 | 1 | 4 |
| 2 | 2 | 0 | 2 | |
| 2 | 0 | 2 | 2 | |
| 4 | 0 | 0 | 2 | |
| 2 | 0 | 0 | 3 |
In addition to the listed topologies, in expensive power supplies there are resonant versions of Half Bridge, which are easily identified by an additional large inductor (or two) and a capacitor forming an oscillatory circuit.
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Single-Transistor Forward |
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⇡ Secondary circuit
The secondary circuit is everything that comes after the secondary winding of the transformer. In most modern power supplies, the transformer has two windings: 12 V is removed from one of them, and 5 V from the other. The current is first rectified using an assembly of two Schottky diodes - one or more per bus (on the highest loaded bus - 12 V - in powerful power supplies there are four assemblies). More efficient in terms of efficiency are synchronous rectifiers, which use field-effect transistors instead of diodes. But this is the prerogative of truly advanced and expensive power supplies that claim the 80 PLUS Platinum certificate.
The 3.3V rail is typically driven from the same winding as the 5V rail, only the voltage is stepped down using a saturable inductor (Mag Amp). A special winding on a transformer for a voltage of 3.3 V is an exotic option. Of the negative voltages in the current ATX standard, only -12 V remains, which is removed from the secondary winding under the 12 V bus through separate low-current diodes.
PWM control of the converter key changes the voltage on the primary winding of the transformer, and therefore on all secondary windings at once. At the same time, the computer's current consumption is by no means evenly distributed between the power supply buses. In modern hardware, the most loaded bus is 12-V.
To separately stabilize voltages on different buses, additional measures are required. The classic method involves using a group stabilization choke. Three main buses are passed through its windings, and as a result, if the current increases on one bus, the voltage drops on the others. Let's say the current on the 12 V bus has increased, and in order to prevent a voltage drop, the PWM controller has reduced the duty cycle of the key transistors. As a result, the voltage on the 5 V bus could go beyond the permissible limits, but was suppressed by the group stabilization choke.
The voltage on the 3.3 V bus is additionally regulated by another saturable inductor.
A more advanced version provides separate stabilization of the 5 and 12 V buses due to saturable chokes, but now this design has given way to DC-DC converters in expensive high-quality power supplies. In the latter case, the transformer has a single secondary winding with a voltage of 12 V, and the voltages of 5 V and 3.3 V are obtained thanks to DC-DC converters. This method is most favorable for voltage stability.
Output filter
The final stage on each bus is a filter that smoothes out voltage ripple caused by the key transistors. In addition, the pulsations of the input rectifier, whose frequency is equal to twice the frequency of the supply network, penetrate to one degree or another into the secondary circuit of the power supply.
The ripple filter includes a choke and large capacitors. High-quality power supplies are characterized by a capacitance of at least 2,000 uF, but manufacturers of cheap models have reserves for savings when they install capacitors, for example, of half the nominal value, which inevitably affects the ripple amplitude.
⇡ Standby power +5VSB
A description of the power supply components would be incomplete without mentioning the 5 V standby voltage source, which makes the PC sleep mode possible and ensures the operation of all devices that must be turned on at all times. The “duty room” is powered by a separate pulse converter with a low-power transformer. In some power supplies, there is also a third transformer, which is used in the feedback circuit to isolate the PWM controller from the primary circuit of the main converter. In other cases, this function is performed by optocouplers (an LED and a phototransistor in one package).
⇡ Methodology for testing power supplies
One of the main parameters of the power supply is voltage stability, which is reflected in the so-called. cross-load characteristic. KNH is a diagram in which the current or power on the 12 V bus is plotted on one axis, and the total current or power on the 3.3 and 5 V buses is plotted on the other. At the intersection points for different values of both variables, the voltage deviation from the nominal value is determined one tire or another. Accordingly, we publish two different KNHs - for the 12 V bus and for the 5/3.3 V bus.
The color of the dot indicates the percentage of deviation:
- green: ≤ 1%;
- light green: ≤ 2%;
- yellow: ≤ 3%;
- orange: ≤ 4%;
- red: ≤ 5%.
- white: > 5% (not allowed by ATX standard).
To obtain KNH, a custom-made power supply test bench is used, which creates a load by dissipating heat on powerful field-effect transistors.
Another equally important test is determining the ripple amplitude at the power supply output. The ATX standard allows ripple within 120 mV for a 12 V bus and 50 mV for a 5 V bus. A distinction is made between high-frequency ripple (at double the frequency of the main converter switch) and low-frequency (at double the frequency of the supply network).
We measure this parameter using a Hantek DSO-6022BE USB oscilloscope at the maximum load on the power supply specified by the specifications. In the oscillogram below, the green graph corresponds to the 12 V bus, the yellow graph corresponds to 5 V. It can be seen that the ripples are within normal limits, and even with a margin.
For comparison, we present a picture of ripples at the output of the power supply of an old computer. This block wasn't great to begin with, but it certainly hasn't improved over time. Judging by the magnitude of the low-frequency ripple (note that the voltage sweep division is increased to 50 mV to fit the oscillations on the screen), the smoothing capacitor at the input has already become unusable. High-frequency ripple on the 5 V bus is on the verge of permissible 50 mV.
The following test determines the efficiency of the unit at a load from 10 to 100% of rated power (by comparing the output power with the input power measured using a household wattmeter). For comparison, the graph shows the criteria for the various 80 PLUS categories. However, this does not cause much interest these days. The graph shows the results of the top-end Corsair PSU in comparison with the very cheap Antec, and the difference is not that great.
A more pressing issue for the user is the noise from the built-in fan. It is impossible to directly measure it close to the roaring power supply testing stand, so we measure the rotation speed of the impeller with a laser tachometer - also at power from 10 to 100%. The graph below shows that when the load on this power supply is low, the 135mm fan remains at low speed and is hardly audible at all. At maximum load the noise can already be discerned, but the level is still quite acceptable.
Very often you have to look under the power supply cover: inspect its components, measure voltages, and sometimes resolder components.
Computer power supplies, being high-voltage power devices, fail much more often than other computer components. Regardless of manufacturer and price, device and principle of operation of the ATX power supply unchangeable. Schematically, the design of a computer power supply can be divided into:
- Input circuit (1)
- Mains rectifier (2)
- Self-generating power supply (3)
- Power stage (4)
- Secondary rectifiers (5)
IN internal ATX power supply device
The input circuit consists of a network filter that suppresses interference in the network from the operation of the power supply. The network rectifier of the computer power supply includes a diode assembly (bridge) and rectifier capacitors. The self-oscillating power supply works when the computer is turned off (not from the network, of course, but with the Power button), it supplies a standby supply voltage of +5VStb to the motherboard controllers. A voltage of +310V is supplied to the power stage from the rectifier. The transistors of the power stage of the ATX power supply operate in a push-pull circuit together with a power transformer and are controlled by a PWM chip. From the secondary windings of the power transformer, voltage is supplied to secondary low-voltage rectifiers. The PWM chip is triggered by a signal from the motherboard “Power On”, triggering, accordingly, the transistor-transformer converter and applying voltage to its secondary windings. In the secondary windings of the computer power supply, in addition to diode assemblies (on radiators), chokes are used.
Block diagram of a computer power supply
Computer power supply is a pulse device. Unlike linear ones, switching power supplies are more compact and have high efficiency and lower heat losses. The 220V mains voltage is supplied through a surge filter to a rectifier consisting of diodes and two series-connected electrolytic capacitors. The self-generating power supply is also powered, generating a standby voltage of +5v stb. From the rectifier, a voltage of 310V is supplied to a power stage implemented using powerful transistor switches and a transformer. The power stage is controlled by pulses coming from a PWM (Pulse Width Modulation) generator microcircuit through a matching transformer to the key bases. The generated pulse voltage is removed from the secondary windings of the power transformer and rectified by diodes and capacitors. The output voltage is controlled by a special protection circuit that generates a Power-Ok (Power-Good) signal. If the output voltages deviate from the nominal values, the Power-Ok signal is not supplied to the motherboard controller, thereby blocking the computer from starting.
Schematic diagrams of ATX power supplies
ATX power supply output voltages
Pinout of ATX power supply connectors
Repair of computer power supplies
Repair of computer power supplies You should start by checking the supply of ~220V mains voltage to the rectifier. Next, you need to check the presence of +310V at the output of the rectifier (do not forget that the capacitors of the rectifier of the computer power supply are connected in series and the voltage at their terminals will be approximately 150-160V). Make sure there is voltage +5v stb and Power-Ok (pink and green wires). If they are missing, you should check the standby power supply and the PWM chip (if there is no Power-Ok voltage). If the generation of standby voltage +5v stb and Power-Ok is normal, focus your attention on the power switches and the secondary rectifier of the power supply. Do not forget that to test semiconductors and capacitors, it is better to remove them from the circuit.
This page contains several dozen electrical circuit diagrams and useful links to resources related to the topic of equipment repair. Mainly computer. Remembering how much effort and time sometimes had to be spent searching for the necessary information, a reference book or a diagram, I have collected here almost everything that I used during repairs and that was available in electronic form. I hope this is of some use to someone.
Utilities and reference books.
The program is designed to determine the capacitance of a capacitor by color marking (12 types of capacitors).
startcopy.ru - in my opinion, this is one of the best sites on the RuNet dedicated to the repair of printers, copiers, and multifunctional devices. You can find techniques and recommendations for fixing almost any problem with any printer.
Power supplies.
Power supply circuits for ATX 250 SG6105, IW-P300A2, and 2 circuits of unknown origin.
NUITEK (COLORS iT) 330U power supply circuit.
Codegen 250w mod power supply circuit. 200XA1 mod. 250XA1.
Codegen 300w mod power supply circuit. 300X.
PSU diagram Delta Electronics Inc. model DPS-200-59 H REV:00.
PSU diagram Delta Electronics Inc. model DPS-260-2A.
DTK PTP-2038 200W power supply circuit.
Power supply diagram FSP Group Inc. model FSP145-60SP.
Green Tech power supply diagram. model MAV-300W-P4.
Power supply circuits HIPER HPU-4K580
Power supply diagram SIRTEC INTERNATIONAL CO. LTD. HPC-360-302 DF REV:C0
Power supply diagram SIRTEC INTERNATIONAL CO. LTD. HPC-420-302 DF REV:C0
Power supply circuits INWIN IW-P300A2-0 R1.2.
INWIN IW-P300A3-1 Powerman power supply diagrams.
JNC Computer Co. LTD LC-B250ATX
JNC Computer Co. LTD. SY-300ATX power supply diagram
Presumably manufactured by JNC Computer Co. LTD. Power supply SY-300ATX. The diagram is hand-drawn, comments and recommendations for improvement.
Power supply circuits Key Mouse Electronics Co Ltd model PM-230W
Power supply circuits Power Master model LP-8 ver 2.03 230W (AP-5-E v1.1).
Power supply circuits Power Master model FA-5-2 ver 3.2 250W.
Maxpower PX-300W power supply circuit
Test results First of all, we present a table with measurements of the output voltages of power supplies at three different loads - at a current of 10A on the +5V bus, 20A on the +5V bus and, finally, the maximum possible, 20A on the +5V bus and 8A on the +12V bus. An exception was made only for the 250W Samsung PSU and the 235W L&C PSU, because for the first, the maximum permissible current on the +12V bus is only 6A, and for the second, the current on the +5V bus should not exceed 19A. The results that fit into the table are highlighted in purple ATX 2.03, but do not fit into ATX 2.01 (as mentioned above, this only applies to the -12V and -5V buses). Although most of the tested power supplies must comply with the ATX 2.01 specification (you can turn a blind eye to going beyond it), these voltages, generally speaking, are not very critical for the well-being of the computer, and therefore in ATX 2.03 the tolerances for them were doubled. However, there is a limit to everything, and going beyond the ATX 2.03 specifications, which are indicated in the table in red, should be treated with the utmost severity, and the place for such power supplies is in a box labeled “Reject”.
Voltages
| +3.3V | +5V | +12V | -12V | -5V |
|
| Genius, 235W | 3,32 | 4,88 | 12,24 | -12,99 | -5,09 |
| L&C, 235W | 3,27 | 4,84 | 12,44 | -12,89 | -5,52
|
| L&C, 250W | 3,34 | 5,06 | 12,53 | -11,98 | -5,2 |
| fki 250W (ATX-250W) | 3,37 | 4,69 | 12,29 | -12,04 | -5,08 |
| fki 250W (FV-250N20) | 3,31 | 4,96 | 12,29 | -12,05 | -4,97 |
| PowerMan 250W | 3,31 | 5 | 11,97 | -11,78 | -5 |
| Samsung 250W | 3,3 | 4,92 | 11,87 | -12,07 | -5,12 |
| PowerOne 250W | 3,41 | 5,02 | 12,43 | -11,8 | -4,95 |
| KME 250W | 3,33 | 5,03 | 12,36 | -11,86 | -4,98 |
| KME 300W | 3,35 | 5,08 | 12,52 | -12,06 | -5,07 |
| MEC 250W | 3,33 | 5 | 12,16 | -11,73 | -5,34 |
| High Power 250W (101) | 3,22 | 5 | 12,35 | -12,24 | -5,11 |
| High Power 250W (102) | 3,32 | 4,91 | 12,34 | -11,97 | -5,02 |
| High Power 300W | 3,27 | 4,93 | 12,27 | -11,84 | -5,07 |
| PowerMaster 300W | 3,39 | 4,96 | 12,26 | -11,92 | -4,99 |
| Genius, 235W | 3,26 | 4,75 | 12,56 | -13,50 | -5,14 |
| L&C, 235W | 3,23 | 4,70 | 12,90 | -13,71 | -5,87
|
| L&C, 250W | 3,34 | 5,01 | 12,90 | -12,43 | -5,43
|
| fki 250W (ATX-250W) | 3,36 | 4,44 | 12,64 | -12,47 | -5,25 |
| fki 250W (FV-250N20) | 3,26 | 4,86 | 12,51 | -12,37 | -5,11 |
| PowerMan 250W | 3,28 | 4,89 | 12,15 | -12,17 | -5,17 |
| Samsung 250W | 3,28 | 4,75 | 12,03 | -12,1 | -5,15 |
| PowerOne 250W | 3,41 | 4,95 | 12,76 | -12,18 | -5,11 |
| KME 250W | 3,32 | 4,92 | 12,58 | -12,2 | -5,04 |
| KME 300W | 3,35 | 4,99 | 12,76 | -12,36 | -5,1 |
| MEC 250W | 3,31 | 4,88 | 12,58 | -12,3 | -5,60
|
| High Power 250W (101) | 3,15 | 4,85 | 12,59 | -12,69 | -5,19 |
| High Power 250W (102) | 3,32 | 4,68 | 12,72 | -12,36 | -5,03 |
| High Power 300W | 3,24 | 4,83 | 12,55 | -12,28 | -5,09 |
| PowerMaster 300W | 3,37 | 4,88 | 12,51 | -12,27 | -5,13 |
| Genius, 235W | 3,23 | 4,84 | 12,19 | -14,03 | -5,19
|
| L&C, 235W | 3,2 | 4,76 | 12,19 | -14,55 | -6,16
|
| L&C, 250W | 3,34 | 5,07 | 12,51 | -12,67 | -5,61
|
| fki 250W (ATX-250W) | 3,36 | 4,53 | 12,15 | -12,90 | -5,49
|
| fki 250W (FV-250N20) | 3,24 | 4,92 | 12,16 | -12,62 | -5,25 |
| PowerMan 250W | 3,28 | 4,98 | 11,88 | -12,66 | -5,40
|
| Samsung 250W | 3,29 | 4,81 | 11,73 | -12,12 | -5,17 |
| PowerOne 250W | 3,41 | 5,01 | 12,33 | -12,45 | -5,25 |
| KME 250W | 3,26 | 4,98 | 12,22 | -12,69 | -5,18 |
| KME 300W | 3,34 | 5,1 | 12,45 | -12,75 | -5,2 |
| MEC 250W | 3,22 | 4,85 | 12,15 | -12,76 | -5,84
|
| High Power 250W (101) | 3,15 | 4,96 | 12,13 | -13,11 | -5,21 |
| High Power 250W (102) | 3,32 | 4,88 | 12,59 | -12,51 | -5,07 |
| High Power 300W | 3,23 | 4,91 | 12,16 | -12,67 | -5,1 |
| PowerMaster 300W | 3,35 | 4,93 | 12,09 | -12,47 | -5,26
|
Genius, 235W
From visual impressions, this is an average power supply that doesn’t stand out in any way. There is no power switch, instead there is a 220V output connector - naturally, when the computer is turned off, the voltage remains on it. The input filter contains both chokes and all capacitors.Oscillograms of output voltages:
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I won’t say that the picture is pleasing to the eye - when connecting a variable load, that is, fans, the amplitude of voltage ripples increases noticeably, and on oscillograms with a sweep of 4 μs/div, high voltage surges when switching the transistors of the unit are clearly visible. However, among other blocks, these results turned out to be quite average.
Well, with tests on the level of output voltages, he was not at all lucky: at full load, the output voltage, instead of the required 12V, exceeded 14V, exceeding all specifications.
So, all of the above forces us to consider this power supply as having failed testing.
L&C, 235W
Here they are, traces of Chinese engineering:
There is no place on the board for one of the chokes at all; instead of the second there are two jumpers. There is a transistor nearby, from the picture on the board around which you can guess that it should actually be on a radiator... There are radiators on the neighboring transistors, but from This is hardly easier for them - after ten minutes of operation of the unit at full load, it is better not to touch the radiators to avoid burns. Sad picture! Moreover, the oscillograms were not encouraging either - look at the strong ripples even with the fans turned off:
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
Well, the last nail in the coffin of this power supply was its output voltages - in total, for all three stages of the test, out of five voltages, four did not meet the specifications. In addition, for almost all voltages the unit showed the worst result ever seen... In connection with which we are sending it to the trash bin.
L&C, 250W
I wonder how different this unit is from its less powerful predecessor? Although there are changes for the better - for example, radiators no longer burn our fingers - but instead of chokes we see the same jumpers. And the large inscription “With fan sensor control” on the lid turns out to be an ordinary lie - no adjustment of the fan speed in the unit was noticed.
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
But the oscillograms already show obvious improvements: a relatively decent picture, except that turning on the fans slightly unbalanced the unit, increasing the ripple to a large, but still tolerable level.
The first voltage measurements inspire optimism - the +5V and +3.3V outputs show enviable stability, but... the -12V and, more critically, +12V outputs again go beyond the permissible limits, and the new product from L&C repeats the fate of the old one - the power supply is unsuitable for use.
fki, 250W - model ATX-250W
This is a completely different matter - neat assembly, all the parts are in place. Do you see the board soldered to the 220V connector? An honest surge protector is mounted right on its reverse side:
There is also a power switch, although it is mounted, contrary to Intel recommendations, below the 220V connector, and not above.
But the oscillograms brought less joy - on the 4ms/div sweep, strong ripples are visible even with the fans turned off:
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
And the voltage measurements are not at all encouraging - for two of them the power supply could not fit into the requirements. Alas, we are forced to admit that this power supply failed the tests.
fki, 250W - model FV-250N20
A model from the same company, slightly different in appearance, actually showed more than significant differences:
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
In many ways, we were also pleased with the results of voltage measurements - the model was able to fit into the requirements and, thus, turn out to be the first usable power supply :-) Although the voltage results of +3.3V are alarming. If in the previous model it remained very stable, now it drops noticeably as the load increases. Unfortunately, at the time of testing there was no suitable load for this output, and it is difficult to assess how it behaves in conditions closer to real ones. Here it is, an example of the lack of savings on details! Take a look at the dimensions of the radiators:
Do you see a small board mounted on the left radiator? This is the same fan speed controller that was promised to us back in the L&C unit. A thermal sensor is pressed directly to the radiator - and the more the transistors heat up, the faster the cooling unit fan rotates. By the way, the radiators in PowerMan were warm, but not hot.
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
The oscillograms turned out to be somewhat ambiguous. On the one hand, there is a high level of pulsation at a constant load, on the other hand, when a pulsating load (fans) is connected, only the shape of the pulsations changes, but not their amplitude (which, as testing has shown, is a pleasant rarity - in most units the amplitude only increased).
Only one thing can be said about the output voltage values - everything is within acceptable limits, moreover, the main voltages (i.e. +3.3V, +5V and +12V) show good stability. So, already two power supplies are not dangerous for your computer :-) Two things immediately catch your attention about this unit - the almost empty rear panel (there is neither a power switch nor an output connector) and a non-standard fan location. Remember Intel's recommendation to place the fan on the bottom wall of the unit, so that it blows directly on the processor? Samsung followed these recommendations only partially - the fan is hidden deep inside, but it blows from the system unit to the outside, that is, from the processor:
There is a surge protector in the unit, but Samsung cheated with one of its chokes: it is only a few turns of power wire around a ferrite ring, in contrast to the usually used inductor made of a large number of turns of enameled wire:
But here is a more significant fly in the ointment - the block turned out to be very susceptible to variable load. If, under constant load, the oscillograms, although not ideal, are quite good, then when the fans are turned on, we see the “song about the petrel”, already familiar from cheap units, and with a relatively large amplitude of emissions:
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
And here is the ointment that has just been thrown in the ointment: measurements of output voltages. The power supply from Samsung turned out to be the only one that, in all tested modes, fully complied with all specifications, including ATX 2.01. Although the voltage drop from +5V to +4.75V gives rise to some concerns (because this is already the limit, and the power supply was still loaded not at full power), but look at the behavior of voltages -12V and -5V: they change only by hundredths of a volt. This was achieved very simply - these two outputs are stabilized by separate linear compensation stabilizers of relatively low power.
PowerOne, 250W
Externally, it is a completely average power supply, made without skimping on parts, but also without any special frills. The filter is present in full, there is no power switch, but there is a 220V output. The unit is equipped with five output connectors at once, which is rare for 250W - usually there are four connectors
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
Like Samsung, this power supply turned out to be sensitive to pulsating load. But, unlike Samsung, there will be no “barrel of honey” here - the unit did not fit into the requirements, producing a voltage higher than permissible at the +12V output and, thus, failing the testing. This power supply excels in two ways. Firstly, he turned out to be the only victim of the experiments - when one was turned on, a click was heard, a small spark flashed in the block, and he did not want to work anymore. Secondly, he took first place in the number of missing parts. Rate:
Not only are there no chokes, but even the penny-worth of capacitors are missing - just an empty corner of the board.
Naturally, after something like this, it’s stupid to expect any good results, and indeed, see for yourself - the oscillogram with a sweep of 4 μsec/div and the fans on is impressive, right?
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
In terms of voltage, the unit managed to fit into the requirements, however, in connection with the above, this is more an accident than a rule... Do you remember this children's game - “Find the Ten Differences”? Let's play it one more time - look at this photo, then at the photo of a 250W block from the same KME, and be surprised:
Compared to its predecessor, many new parts have appeared - a fully assembled filter, and in the area of the stabilizer the board has become noticeably tighter (I wonder what they saved on in the 250W block? On protection, or what?). As in the previous block, there is a switch on the back wall (accordingly, there is no 220V output), but the number of output connectors has increased from four to six.
Timebase 4ms/div, fans on
Timebase 4µsec/div, fans on
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
Yes, the oscillograms no longer resemble the less powerful predecessor at all - there are no complaints about them.
But the situation with voltages is worse - +12V, which was already raised by more than half a volt, increased even more under load, and as a result, we are forced to consider the unit to have failed testing.
Timebase 4ms/div, fans off
Timebase 4µsec/div, fans off
We look at the results of voltage measurements - and another unit is recognized as failing the test: this time due to the voltage on the -5V line being outside the permissible limits. In addition, noticeable voltage fluctuations of +3.3V are cause for concern. Apparently, it’s not without reason that for this unit the maximum current consumption on the +3.3V line should not exceed 6A (remember that this is the lowest figure among all the power supplies described here), it’s not without reason...
High Power, 250W
Two such power supplies were tested, differing only in the model number, and even then in the last digit: HPS-250-101 and HPS-250-102. A later revision was distinguished, first of all, by the presence of a fan speed thermostat, which until now only PowerMan could boast of. Here it is, in the photo - a small board hanging on the left radiator:
Timebase 4µsec/div, fans off
Take a look at the waveforms with a 4ms/div sweep. “The beating of a proud heart, a song about a petrel and the ninth wave” (V. Erofeev) somehow poorly correlate with normal ideas about an expensive power supply.
The second thing that distinguished these two blocks after the thermostat was the results of voltage measurements. If the HPS-250-101 passed the tests without serious complaints, then we again recognize the HPS-250-102 as unsuitable for use - it did not fit into two voltages at once, which are critical for a computer - +5V and +12V.
High Power, 300W
Unlike less successful predecessors, this unit has a fully assembled surge protector, and there is also a power off button. However, the oscillograms immediately make you remember the previous two blocks:PowerMaster, 300W
Remember the cheaper throttle from Samsung? Specialists from Jou Jye Electronic Co have gone even further - in power supplies sold under the PowerMaster brand, we see approximately the same inductor, but on a very tiny ring, which literally fits one turn of the network wire:
However, the savings end there, and only PowerMan can compete with it in terms of its solid appearance:
Oscillograms of output voltages are no less pleasing to the eye than huge radiators:
Timebase 4ms/div, fans on
Summarizing
As you can see, not everything is so simple in the world of power supplies. On the one hand, for cheap power supplies there is a very clear relationship between quality and price - models from KME, L&C and MEC simply did not pass testing, and they were the cheapest units that came under the knife. The same dependence is very clearly visible in the example of the two participating models from KME - the more expensive unit was assembled much more carefully, while all the parts without which it still somehow worked were thrown out of the cheaper one. Everything is clear here - we get exactly what we pay, and nothing more.On the other hand, when choosing from expensive models, you cannot unambiguously judge quality only by price - just look at the mediocre results of expensive units from HighPower and the excellent results of the noticeably cheaper PowerMaster unit. Although, of course, any of these power supplies are noticeably better than units in the lower price group.
The overall testing results are not impressive (or, on the contrary, impressive?) - out of a dozen and a half power supplies, only six were tested - less than half! And this is despite the fact that the only reason for withdrawal from the race was considered to be only the output voltage exceeding the tolerances of the ATX 2.03 specification (except for the 250W power supply from KME, in which the manufacturer decided not to put a lot of “extra” parts, but which still somehow miraculously fell within voltage tolerances). And if you do more complex research, for example, measuring peak voltage surges at the power supply outputs or studying the behavior of the power supply at maximum load (that is, all 235, 250 or 300 W) - I’m afraid that a number of blocks will not reach the finish line.