Powerful power supply from a computer. Modification of power supplies

The article is based on 12 years of experience in repairing and maintaining computers and their power supplies.

Stable and reliable operation of a computer depends on the quality and properties of its components. With the processor, memory, motherboard, everything is more or less clear - the more megahertz, gigabyte, etc., the better. And what is the difference between power supplies for $ 15 and for, say, $ 60? Same voltages, same power on the label - why pay more? As a result, a power supply unit with a case is purchased for $ 25-35. The cost price of the same power supply unit in it, taking into account delivery from China, customs clearance and resale by 2-3 intermediaries, is only $ 5-7 !!! As a result, the computer can glitch, freeze, restart for no reason. The stability of a computer network also depends on the quality of the power supply units of the computers that make up it. When working with an uninterruptible power supply unit, and at the moment of switching it to the internal battery, reboot. But the worst thing is if, as a result of a failure, such a power supply will bury another half of the computer, including the hard drive. Recovering information from hard disks burned by a power supply often exceeds the cost of the hard drive itself by 3-5 times ... Everything is explained simply - as the quality of power supplies is difficult to control right away, especially if they are sold inside the cases, this is a reason for the Chinese uncle Li save money at the expense of quality and reliability - at our expense.

And everything is done extremely simply - by sticking new tags with a higher declared power on the old power supplies. The power on the stickers is more and more from year to year, but the filling of the blocks is still the same. Codegen, JNC, Sunny, Ultra, different "no name" are guilty of this.

Rice. 1 Typical Chinese cheap ATX power supply. Refinement is expedient.

Fact: the new Codegen 300W power supply is loaded into a balanced load of 200W. After 4 minutes of operation, its wires leading to the ATX connector began to smoke. At the same time, an imbalance of the output voltages was observed: at the + 5V source - 4, 82V, at + 12V - 13.2V.

What is the structural difference between a good power supply unit and those "no name" ones that are usually bought? Even without opening the cover, you can usually notice the difference in the weight and thickness of the wires. With rare exceptions, a good PSU is heavier.

But the main differences are inside. On the board of an expensive power supply, all the parts are in place, a fairly tight installation, the main transformer is of decent size. In contrast, the cheap one seems half empty. Instead of chokes for secondary filters, there are jumpers, some of the filter capacitors are not soldered at all, there is no mains filter, a small transformer, secondary rectifiers, too, or are made on discrete diodes. The presence of a power factor corrector is not provided at all.

Why do you need a surge protector? During its operation, any switching power supply induces high-frequency ripples both along the input (supply) line and along each of the output lines. Computer electronics are very sensitive to these ripples, so even the cheapest power supply uses simplified, minimally sufficient, but still output voltage filters. They usually save money on power filters, which is the reason for the emission of sufficiently powerful radio-frequency interference into the lighting network and into the air. What does this affect and what does it lead to? First of all, these are “inexplicable” failures in the operation of computer networks and communications. The appearance of additional noise and interference on radios and televisions, especially when receiving on an indoor antenna. This can cause malfunctions of other high-precision measuring equipment located nearby, or included in the same phase of the network.

Fact: in order to exclude the influence of different devices on each other, all medical equipment undergoes strict control for electromagnetic compatibility. A surgical unit based on a personal computer, which has always successfully passed this test with a large margin of performance, turned out to be rejected due to exceeding the maximum permissible interference level by 65 times. And only there, during the repair process, the computer's power supply was replaced with one purchased at a local store.

Another fact: a medical laboratory analyzer with a built-in personal computer out of order - as a result of the throw, the standard ATX power supply burned out. To check if something else had burned out, the first Chinese man that came across was connected to the place of the burned one (it turned out to be a JNC-LC250). We never managed to start this analyzer, although all voltages produced by the new power supply and measured with a multimeter were normal. Well, you guessed to remove and connect the ATX power supply from another device (also based on a computer).

The best option from the point of view of reliability is the initial purchase and use of a high-quality power supply unit. But what if the money is scarce? If the head and hands are in place, then good results can be obtained already by modifying the cheap Chinese. They - thrifty and prudent people - designed printed circuit boards according to the criterion of maximum versatility, that is, in such a way that, depending on the number of installed components, the quality and, accordingly, the price could be varied. In other words, if we install those parts that the manufacturer saved on, and change something else, we get a good block of the middle price category. Of course, this cannot be compared with expensive copies, where the topology of printed circuit boards and circuitry were originally calculated to obtain good quality, like all parts. But for the average home computer, this is a perfectly acceptable option.

So which block is right? The initial selection criterion is the size of the largest ferrite transformer. If he has a tag with numbers 33 or more in the beginning and has dimensions of 3x3x3 cm or more - it makes sense to mess around. Otherwise, it will not be possible to achieve an acceptable balance of voltages of + 5V and + 12V when the load changes, and in addition, the transformer will be very hot, which will significantly reduce reliability.

We replace 2 electrolytic capacitors according to the mains voltage with the maximum possible ones that can fit on the seats. Usually in cheap units their ratings are 200 µF x 200 V, 220 µF x 200 V, or at best 330 µF x 200 V. Change to 470 µF x 200 V or better to 680 µF x 200 V. These electrolytes, like any other in computer power supplies, install only from the 105 degree series!

Rice. 2 High-voltage part of the power supply unit, including rectifier, half-bridge inverter, electrolytes at 200 V (330 µF, 85 degrees). No surge protector.

Installation of capacitors and chokes of secondary circuits. The chokes can be taken from disassembly on the radio market or wound on a suitable piece of ferrite or a ring 10-15 turns of wire in enamel insulation with a diameter of 1.0-2.0 mm (more is better). Capacitors are suitable for 16 V, Low ESR type, 105 degree series. The capacity should be selected as high as possible so that the capacitor can fit in its original place. Typically 2200 µF. Observe the polarity when reeling!

Rice. 3 Low voltage part of the power supply. Secondary rectifiers, electrolytic capacitors and chokes, some of which are missing.

We change the rectifier diodes and secondary rectifier modules for more powerful ones. First of all, this concerns rectifier modules for 12 V. This is explained by the fact that in the last 5-7 years the power consumption of computers, in particular motherboards with a processor, has increased to a greater extent on the + 12 V bus.

Rice. 4 Rectifier modules for secondary sources: 1 - the most preferred modules. Installed in expensive power supplies; 2 - cheap and less reliable; 3 - 2 discrete diodes - the most economical and unreliable option, which must be replaced.

Install the line filter choke (see Fig. 2 for its installation location).

If the PSU radiators are in the form of plates with cut-out petals, bend these petals in different directions to maximize the efficiency of the radiators.
Rice. 5 ATX power supply with modified heatsinks.
With one hand we hold the radiator undergoing revision, with the other hand, using pliers with thin tips, bend the radiator petals. Do not hold onto the printed circuit board - there is a high probability of damaging the soldering of parts on and around the radiator. This damage may not be visible to the naked eye and lead to dire consequences.

Thus, by investing $ 6-10 in upgrading a cheap ATX power supply, you can get a good PSU for your home computer.

Power supplies are afraid of heat, which leads to failure of semiconductors and electrolytic capacitors. This is aggravated by the fact that air passes through the computer power supply unit already preheated by the elements of the system unit. I recommend that you clean the power supply from the inside in time and check for swollen electrolytes in one step.

Rice. 6 Failed electrolytic capacitors - swollen tops of the enclosures.

If the latter are found, we change to new ones and we are glad that everything remains intact. The same applies to the entire system unit.

Attention - defective CapXon capacitors! CapXon electrolytic capacitors of the LZ 105 o C series (installed in motherboards and computer power supplies), which had been lying in a heated living room for 1 to 6 months, swelled up, and electrolyte came out of some of them (Fig. 7). The electrolytes were not in use, were in storage, like the rest of the workshop parts. The measured equivalent series resistance (ESR) turned out to be 2 orders of magnitude on average! above the limit for this series.

Rice. 7 Defective CapXon electrolytic capacitors - bulging case tops and high equivalent series resistance (ESR).

An interesting note: probably due to the low quality, CapXon capacitors are not found in high-reliability equipment: power supplies for servers, routers, medical equipment, etc. Based on this, in our workshop, in the incoming equipment with CapXon electrolytes, they act as if they were known to be faulty - they immediately change to other.

Modification of power supplies CODEGEN and others, JNC-like ... Sasha Cherny / 04/27/2004 00:56

This article (first draft) was written for my own project, which is currently in a dying state and will be repurposed. Since I believe that the article will be useful to many people (I judge by numerous letters, including from the readers of your resource), I suggest that you post the second edition of this creation.

The good and stable performance of your computer depends on many factors. Last but not least, it depends on a correct and reliable power supply. The average user is primarily concerned with the choice of a processor, motherboard, memory and other components for his computer. Little if any attention is paid to the power supply. As a result, the main criterion for choosing a power supply unit is its cost and the declared power indicated on the label. Indeed, when 300 W is written on the label, this is certainly good, and at the same time the price of a case with a power supply unit is $ 18 - $ 20 - generally great ... But not everything is so simple.

And a year or two and three years ago, the price for cases with a power supply unit did not change and amounted to the same $ 20. And what has changed? That's right - the declared power. First 200W then 235 - 250 - 300W. Next year there will be 350 - 400 watts ... Has there been a revolution in the power supply structure? Nothing like this. You are being sold the same PSUs only with different labels. Moreover, often a 5-year-old PSU with a declared power of 200 watts produces more than a fresh 300 watt. What can you do - cheaper and more economical. If we get a case with a power supply for $ 20, then how much is its real cost, taking into account transportation from China and 2-3 intermediaries when selling? Probably $ 5-10. Can you imagine what parts Uncle Liao put in there for $ 5? And you with THIS want to power up a computer with a cost of $ 500 or more? What to do? Buying an expensive power supply for $ 60- $ 80 is, of course, a good way out when you have money. But not the best (not everyone has money and not enough). For those who do not have extra money, but have straight arms, a bright head and a soldering iron - I propose a simple revision of Chinese power supplies in order to bring them to life.

If you look at the circuitry of branded and Chinese (no name) power supplies, you can see that they are very similar. The same standard switching circuit is used based on the KA7500 PWM microcircuit or analogs on the TL494. And what is the difference between the power supplies? The difference is in the parts used, their quality and quantity. Consider a typical branded power supply:

Picture 1

It can be seen that it is quite tightly packed, there are no free spaces and all the parts are unsoldered. All filters, chokes and capacitors are included.

Now let's look at a typical JNC PSU rated at 300 watts.

Picture 2

An incomparable example of Chinese engineering! There are no filters (instead of them there are "specially trained jumpers"), no capacitors, no chokes. In principle, everything works without them too - but how! The output voltage contains switching noise of transistors, sudden voltage surges and significant voltage drop under various operating modes of the computer. What a stable job here ...

Due to the used cheap components, the operation of such a unit is very unreliable. The actually delivered safe power of such a power supply unit is 100-120 watts. With more power, it will simply burn out and take half of the computer with it. How to modify the Chinese power supply unit to a normal state and how much power do we really need?

I would like to note that the prevailing opinion about the high power consumption of modern computers is a little wrong. A packed Pentium 4-based system unit consumes less than 200 watts, while those based on AMD ATHLON XP consume less than 150 watts. Thus, if we at least provide a real power supply unit of 200-250 watts, then one weak link in our computer will be less.

The most critical details in a PSU are:

High voltage capacitors
High voltage transistors
High voltage rectifier diodes
High frequency power transformer
Low voltage diode rectifier assemblies

The Chinese brothers also manage to save here ... Instead of high-voltage capacitors 470mkf x 200 volts, they put 200mkf x 200 volts. These details affect the ability of the unit to withstand a short-term loss of mains voltage and the power of the supplied voltage of the PSU. They use small power transformers that get very hot at critical power levels. And they also save on low-voltage rectifier assemblies, replacing them with two discrete diodes soldered together. The lack of filters and smoothing capacitors has already been mentioned above.

Let's try to fix it all. First of all, you need to open the PSU and estimate the size of the transformer. If it has dimensions of 3x3x3 cm or more, then it makes sense to modify the block. First, you need to replace the large high-voltage capacitors and put at least 470 microfarads x 200 volts. It is necessary to put all the chokes in the low-voltage part of the power supply unit. The chokes can be wound by yourself on a ferrite ring with a diameter of 1-1.5 cm with a copper wire with lacquered insulation with a cross section of 1-2 mm 10 turns. You can also take chokes from a faulty power supply (a killed power supply can be bought at any computer office for $ 1-2). Next, you need to unsolder the smoothing capacitors into the empty places of the low-voltage part. It is enough to put 3 capacitors 2200μF x 16 volts (Low ESR) in the + 3.3v, + 5v, + 12V circuits.

A typical form of low-voltage rectifier diodes in cheap units is as follows:

Figure 3

or worse, like this

Figure 4

The first diode assembly provides 10 amperes at 40 volts, the second 5 amperes max. At the same time, the following data is written on the power supply cover:

Figure 5

Declared 20-30 amperes, but in reality 10 or 5 amperes are issued !!! Moreover, on the power supply board there is a place for normal assemblies, which should be there:

Figure 6

The marking shows that this is 30 amperes at 40 volts - and this is a completely different matter! These assemblies must be on the + 12V and + 5V channel. The + 3.3v channel can be performed in two ways: either on the same assembly, or on a transistor. If there is an assembly, then we change it to a normal one, if a transistor, then we leave everything as it is.

So, we run to the store or to the market and buy there 2 or 3 (depending on the power supply unit) diode assemblies MOSPEC S30D40 (for the +12 volt channel S40D60 - the last digit D - voltage - the more, the calmer in the soul or F12C20C - 200 volts ) or similar in characteristics, 3 capacitors 2200 microfarads x 16 volts, 2 capacitors 470 microfarads x 200 volts. All these parts cost about $ 5-6.

After we changed everything, the power supply unit will look something like this:

Figure 7

Figure 8

Further refinement of the power supply unit is as follows ... As you know, in the power supply unit, the +5 volt and +12 volt channels are stabilized and controlled at the same time. With +5 volts set, the actual voltage on channel +12 is 12.5 volts. If the computer has a heavy load on channel +5 (AMD-based system), then the voltage drops to 4.8 volts, while the voltage on channel +12 becomes 13 volts. In the case of a system based on Pentium 4, the +12 volt channel is heavily loaded and everything happens the other way around. Due to the fact that the +5 volt channel in the PSU is made of much better quality, even a cheap unit will power an AMD-based system without any problems. While the power consumption of the Pentium 4 is much higher (especially at +12 volts) and the cheap power supply unit must be improved.

Overestimated voltage on the 12 volt channel is very harmful for hard drives. Basically, HDD heating occurs due to increased voltage (more than 12.6 volts). In order to reduce the voltage of 13 volts, it is enough to solder a powerful diode, for example, KD213, into the break of the yellow wire supplying the HDD. As a result, the voltage will decrease by 0.6 volts and will be 11.6 volts - 12.4 volts, which is quite safe for a hard drive.

As a result, we got a normal power supply unit capable of delivering at least 250 watts to the load (normal, not Chinese!), Which, moreover, will become much less heated.

A warning!!! Everything that you will do with your power supply unit - you do at your own peril and risk! If you do not have sufficient qualifications and cannot distinguish a soldering iron from a plug, then do not read what is written here, and even more so do not !!!

Comprehensive noise reduction for computers

How to deal with noise? To do this, we must have the correct case with a horizontal power supply unit (PSU). Such a case has large dimensions, but it removes excess heat to the outside much better, since the power supply unit is located above the processor. It makes sense to put on the processor a cooler with an 80x80 fan, for example, the Titan series. As a rule, a large fan, with the same performance as a small one, runs at lower speeds and produces less noise. The next step is to lower the temperature of the processor during idle or light load.

As you know, most of the time the computer processor is idle, waiting for the response of the user or programs. At this time, the processor is simply wasting empty cycles and heats up. Coolers or soft coolers are designed to combat this phenomenon. Recently, these programs even began to be built into the BIOS of the motherboard (for example, EPOX 8KRAI) and into the Windows XP operating system. One of the simplest and most effective programs is VCOOL. This program, when the AMD processor is running, performs the Bus disconnect procedure - disconnecting the processor bus when idle and reducing heat dissipation. Since a processor idle takes 90% of the time, the cooling will be very significant.

Here we come to the understanding that we don't need to rotate the cooler fan at full speed to cool the processor. How to lower the turnover? You can take a cooler with an external speed controller. Or you can use the fan speed control program - SPEEDFAN. This program is remarkable in that it allows you to adjust the fan speed depending on the CPU heating by setting a temperature threshold. Thus, when the computer starts up, the fan rotates at full speed, and when working in Windows with documents and the Internet, the fan speed is automatically reduced to minimum.

The combination of VCOOL and SPEEDFAN programs allows you to stop the cooler altogether while working in Word and the Internet, and the processor temperature does not rise above 55C! (Athlon XP 1600). But the SPEEDFAN program has one drawback - it does not work on all motherboards. In this case, you can lower the fan speed if you switch it to work from 12 volts to 7 or even 5 volts. Usually the cooler is connected to the motherboard using a three-pin connector. The black wire is ground, red is +12, yellow is the RPM sensor. In order to transfer the cooler to a 7 volt power supply, you need to pull the black wire out of the connector and insert it into a free connector (red wire + 5 volts) coming from the power supply unit, and insert the red wire from the cooler into the power supply unit connector with a yellow wire (+12).

Figure 9

The yellow wire from the cooler can be left in the connector and inserted into the motherboard to monitor the fan speed. Thus, we get 7 volts on the cooler (the difference between +5 and +12 volts is 7 volts). To get 5 volts on the cooler, it is enough to connect only the red wire of the cooler to the red wire of the power supply unit, and leave the two remaining wires in the cooler connector.

Thus, we got a processor cooler with reduced rpm and low noise. With a significant reduction in noise, heat dissipation from the processor does not decrease or decreases slightly.

The next step is to reduce the heat dissipation of the hard drive. Since the main heating of the disk occurs due to the increased voltage on the +12 volt bus (in reality, it is always 12.6 - 13.2 volts here), everything is done very simply here. In the break of the yellow wire that feeds the hard drive, we solder a powerful diode of the KD213 type. A voltage drop of about 0.5 volts occurs across the diode, which has a beneficial effect on the temperature regime of the hard drive.

Or maybe go even further? To convert the PSU fan to 5 volts? It will not work just like that - you need a revision of the power supply unit. And it consists in the following. As you know, the main heating inside the PSU is experienced by the radiator of the low-voltage part (diode assemblies) - about 70-80 C. Moreover, the assembly + 5V and + 3.3V experiences the greatest heating. High-voltage transistors at the correct block (this part of the power supply unit is correct in almost 95% of power supply units, even in Chinese ones) are heated to 40-50 C and we will not touch them.

Obviously, one common heat sink for the three power rails is too small. And if, when the fan is running at high speeds, the radiator still cools normally, then when the speed decreases, overheating occurs. What to do? It would be wise to increase the size of the heatsink, or even split the power rails into different heatsinks. We'll do the last one.

To separate from the main radiator, a + 3.3v channel was chosen, assembled on a transistor. Why not + 5v? At first, this was done, but voltage ripples were found (the influence of the wires, which lengthened the leads of the + 5v diode assembly, had an effect). Since the channel is + 3.3v. powered by + 5V, then there are no more ripples.

For the radiator, an aluminum plate with a size of 10x10 cm was chosen, to which a + 3.3v channel transistor was screwed. The terminals of the transistor were lengthened with a thick wire 15 cm long. The plate itself was screwed through insulating bushings to the top cover of the power supply unit. It is important that the radiator plate does not come into contact with the PSU cover and radiators of power diodes and transistors.

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

After such a revision, you can safely put the PSU fan at +5 volts.

Video card. A more precise approach is needed here. If you have a video card of the GeForce2 MX400 class, then in most cases it does not need a cooler at all (which, by the way, is what many manufacturers do - they do not install a cooler at all). The same applies to video cards GeForce 4 MX440, Ati Radeon 9600 - a passive radiator is enough here. In the case of other video cards, the approach can be similar to the above - switching the fan power supply to 7 volts.

Let's summarize. We've looked at measures to reduce noise and heat generation in an AMD processor-based system. For example, I will give the following data. At the moment, this article is being written on a very powerful computer AMD Athlon XP 3200+, with 512 MB of RAM, a GeForce 4 mx440 video card, HDD WD 120 gb 7200, CD-RW and has a processor temperature of 38C, temperature inside the case 36C, temperature inside the power supply unit, measured by a digital thermometer on the radiators of power diodes - 52C, the hard drive is just cold. The maximum processor temperature during the simultaneous 3DMark test and cpuburn was 68C after 3 hours of operation. In this case, the PSU fan is connected to 5 volts, the processor fan with a TITAN cooler is connected to 5 volts all the time, the video card does not have a fan. In this mode, the computer works without any failures for 6 months, at a room temperature of 24C. Thus, a powerful computer has only two fans (operating at low speeds), stands under the table and is practically inaudible.

P.S. Perhaps in the summer (the room will be +28) you will need to install an additional case fan (with a power supply of + 5V, so to speak - for peace of mind ...), but maybe not, wait and see ...

A warning! If you do not have sufficient qualifications, and your soldering iron is similar in size to an ax, then do not read this article, and even more so do not follow the advice of its author.

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Hello, now I will tell you about the conversion of an ATX power supply of the codegen 300w 200xa model into a laboratory power supply with voltage regulation from 0 to 24 Volts, and current limiting from 0.1 A to 5 Amperes. I will lay out the scheme that I got, maybe someone can improve or add something. The box itself looks like this, although the sticker may be blue or a different color.

Moreover, the boards of the 200xa and 300x models are almost the same. Under the board itself there is an inscription CG-13C, maybe CG-13A. Perhaps there are other models similar to this one, but with different inscriptions.

Soldering unnecessary parts

Initially, the diagram looked like this:

It is necessary to remove all unnecessary, atx connector wires, unsolder and rewind unnecessary windings on the group stabilization choke. Under the choke on the board, where it says +12 volts, we leave that winding, we wind the rest. Unsolder the braid from the board (main power transformer), in no case bite it off. Remove the radiator along with the Schottky diodes, and after removing all unnecessary, it will look like this:

The final layout after rework will look like this:

In general, we solder all the wires, details.

Making a shunt

We make a shunt from which we will relieve stress. The meaning of the shunt is that the voltage drop across it tells the PWM how it is loaded by current - the power supply output. For example, the resistance of the shunt we got 0.05 (Ohm), if you measure the voltage on the shunt at the time of passage of 10 A, then the voltage on it will be:

U = I * R = 10 * 0.05 = 0.5 (Volt)

I will not write about the manganin shunt, since I did not buy it and I do not have it, I used two tracks on the board itself, we close the tracks on the board as in the photo to get the shunt. It is clear that it is better to use manganin, but even so it works more than normal.

We put the choke L2 (if any) after the shunt

In general, they need to be counted, but if anything, a program for calculating chokes was slipping somewhere on the forum.

We supply a common minus to PWM

It is possible not to serve if it is already ringing on the 7th leg of the PWM. It's just that on some boards on the 7th pin there was no general minus after the parts were soldered (I don’t know why, I could be wrong that there wasn’t :)

We solder a wire to the 16th PWM pin

We solder to the 16th PWM pin - a wire, and this wire is fed to the 1 and 5 legs of the LM358

Between 1 leg of the PWM and the plus output, solder a resistor

This resistor will limit the voltage supplied by the PSU. This resistor and R60 forms a voltage divider that will divide the output voltage and supply it to 1 leg.

The inputs of the op-amp (PWM) on the 1st and 2nd legs are used for the task of the output voltage.

The task on the output voltage of the PSU comes to the 2nd leg, since 5 volts (vref) can come to the second leg as much as possible, then the reverse voltage should come to the 1st leg also no more than 5 volts. For this, we need a voltage divider of 2 resistors, R60 and the one that we install from the output of the power supply unit to 1 leg.

How it works: let's say a variable resistor is put on the second leg of the PWM 2.5 Volts, then the PWM will give out such pulses (increase the output voltage from the PSU output) until 2.5 (volts) comes to 1 leg of the op-amp. Suppose if this resistor is not present, the power supply will reach the maximum voltage, because there is no feedback from the PSU output. The resistor value is 18.5 kOhm.

We install capacitors and a load resistor on the output of the power supply unit

The pull-up resistor can be supplied from 470 to 600 Ohm 2 Watt. Capacitors of 500 microfarads for a voltage of 35 volts. I did not have capacitors with the required voltage, I put 2 in series of 16 volts 1000 microfarads. We solder capacitors between 15-3 and 2-3 PWM legs.

Soldering the diode assembly

We put the diode assembly the one that was 16C20C or 12C20C, this diode assembly is designed for 16 amperes (12 amperes, respectively), and 200 volts of reverse peak voltage. Diode assembly 20C40 will not work for us - do not think about installing it - it will burn out (checked :)).

If you have any other diode assemblies, see that the reverse peak voltage is at least 100 V and for the current, which is higher. Conventional diodes will not work - they will burn out, these are ultra-fast diodes, just for a switching power supply.

We put a jumper for the PWM power supply

Since we removed the piece of the circuit that was responsible for supplying power to the PSON PWM, we need to power the PWM from the 18 V power supply on duty. Actually, we install a jumper instead of the Q6 transistor.

We solder the output of the power supply +

Then we cut the common minus that goes to the body. We do so that the general minus does not touch the case, otherwise, short-circuiting the plus, with the PSU case, everything will burn out.

We solder the wires, common minus and +5 Volts, power supply duty room output

We will use this voltage to power the volt-ammeter.

We solder the wires, common minus and +18 volts to the fan

We will use this wire through a 58 Ohm resistor to power the fan. Moreover, the fan must be turned so that it blew on the radiator.

We solder the wire from the braid of the transformer to a common minus

Solder 2 wires from the shunt for the LM358 op-amp

We solder the wires, as well as resistors to them. These wires will go to the LM357 op-amp through 47 ohm resistors.

We solder the wire to the 4th leg of the PWM

With a positive +5 Volt voltage at this PWM input, there is a limitation of the regulation limit at the C1 and C2 outputs, in this case, with an increase at the DT input, there is an increase in the duty cycle at C1 and C2 (you need to look at how the output transistors are connected). In a word - stopping the output of the power supply unit. This 4th PWM input (we supply +5 V there) will be used to stop the PSU output in the event of a short circuit (above 4.5 A) at the output.

Assembling the current amplification and short circuit protection circuit

Attention: this is not a complete version - for details, including photos of the rework process, see the forum.

Discuss the article LABORATORY PSU WITH PROTECTION FROM A CONVENTIONAL COMPUTER

I hope it will be of interest to you and your readers.

Best regards, Sasha Cherny.

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I needed a lightweight power supply for various tasks (expeditions, power supply of different HF and VHF transceivers or in order not to carry a transformer power supply unit when moving to another apartment)... After reading the available information on the network about the alteration of computer power supplies, I realized that I would have to figure it out myself. Everything that I found was described as somewhat chaotic and not entirely clear (for me)... Here I will tell you, in order, how I reworked several different blocks. The differences will be described separately. So, I found several PSUs from old PC386 with a power of 200W (in any case, it was written on the lid)... Usually, on the cases of such power supplies, they write something like the following: + 5V / 20A, -5V / 500mA, + 12V / 8A, -12V / 500mA

The currents indicated on the buses +5 and + 12V are pulsed. It is impossible to constantly load the PSU with such currents, high-voltage transistors will overheat and crack. Subtract 25% from the maximum impulse current and get the current that the PSU can hold constantly, in this case it is 10A and up to 14-16A for a short time (no more than 20 seconds)... Actually, here it is necessary to clarify that 200W PSUs are different, not all of them that I came across could hold 20A even for a short time! Many pulled only 15A, and some up to 10A. Keep this in mind!

I want to note that the specific PSU model does not play a role, since they are all made practically according to the same scheme with small variations. The most critical point is the presence of the DBL494 microcircuit or its analogs. I came across a power supply unit with one microcircuit 494 and with two microcircuits 7500 and 339. Everything else does not really matter. If you have the opportunity to choose a PSU from several, first of all, pay attention to the size of the pulse transformer (the bigger, the better) and the presence of a surge protector. It's good when the mains filter is already unsoldered, otherwise you will have to unsolder it yourself in order to reduce the interference. It's easy, wind 10 turns on a ferrite ring and put two capacitors, the places for these parts are already provided on the board.

PRIORITY MODIFICATIONS

To begin with, let's do a few simple things, after which you will get a well-functioning power supply with an output voltage of 13.8V, direct current up to 4 - 8A and short-term up to 12A. You will make sure that the PSU is working and decide if you need to continue the modifications.

1. We disassemble the power supply and take out the board from the case and thoroughly clean it with a brush and a vacuum cleaner. There should be no dust. After that, we solder all the bundles of wires going to the buses +12, -12, +5 and -5V.

2. You need to find (on board) chip DBL494 (in other boards it costs 7500, this is an analogue), switch the protection priority from the + 5V bus to + 12V and set the voltage we need (13 - 14V).
Two resistors depart from the 1st leg of the DBL494 microcircuit (sometimes more, but it doesn't matter), one goes to the case, the other to the + 5V bus. We need him, carefully solder one of his legs (breaking the connection).

3. Now, between the + 12V bus and the first DBL494 foot microcircuit, we solder a resistor 18 - 33kΩ. You can put a trimmer, set the voltage to + 14V and then replace it with a constant one. I recommend setting 14.0V instead of 13.8V, because most branded HF-VHF equipment works better at this voltage.

ADJUSTMENT AND ADJUSTMENT

1. It's time to turn on our power supply to check if we did everything right. The fan can be left unconnected and the board itself can be left out of the case. We turn on the power supply unit, without load, connect a voltmeter to the + 12V bus and see what kind of voltage there is. With a trimmer resistor, which stands between the first leg of the DBL494 microcircuit and the + 12V bus, we set the voltage from 13.9 to + 14.0V.

2. Now check the voltage between the first and seventh legs of the DBL494 microcircuit, it should be at least 2V and not more than 3V. If this is not the case, match the resistance of the resistor between the first leg and the body and the first leg and the + 12V rail. Pay close attention to this point, this is a key point. At a voltage higher or lower than the specified one, the power supply unit will work worse, unstable, hold a lower load.

3. Short-circuit the + 12V bus to the case with a thin wire, the voltage should disappear in order for it to recover - turn off the power supply for a couple of minutes (it is necessary for the capacities to be discharged) and turn it on again. Is there any tension? OK! As you can see, the protection works. What didn't work ?! Then we throw out this power supply unit, it does not suit us and we take another ... hee.

So, the first stage can be considered completed. Insert the board into the case, bring out the terminals for connecting the radio station. The power supply can be used! Connect the transceiver, but you can't give a load more than 12A yet! Car VHF station, will operate at full power (50W), and in the HF transceiver you will have to set 40-60% of the power. What happens if you load the PSU with high current? It's okay, protection usually works and the output voltage disappears. If the protection does not work, high-voltage transistors will overheat and burst. In this case, the voltage will simply disappear and there will be no consequences for the equipment. After replacing them, the power supply unit is operational again!

1. We turn the fan over, on the contrary, it should blow inside the case. Under the two screws of the fan, we put washers in order to unfold it a little, otherwise it blows only on high-voltage transistors, this is wrong, it is necessary that the air flow be directed both to the diode assemblies and to the ferrite ring.

Before this, it is advisable to lubricate the fan. If it makes a lot of noise, put a 60 - 150 ohm 2W resistor in series with it. or make a rotation regulator depending on the heating of the radiators, but more on that below.

2. Remove two terminals from the PSU for connecting the transceiver. From the 12V bus to the terminal, draw 5 wires from the bundle that you soldered at the beginning. Place a 1uF non-polar capacitor and an LED with a resistor between the terminals. Also lead the negative wire to the terminal with five wires.

In some power supplies, in parallel to the terminals to which the transceiver is connected, put a resistor with a resistance of 300 - 560 ohms. This is a load so that the protection does not work. The output circuit should look something like the diagram shown.

3. We power up the + 12V bus and get rid of unnecessary trash. Instead of a diode assembly or two diodes (which is often put in place of it), we put the assembly 40CPQ060, 30CPQ045 or 30CTQ060, any other options will worsen the efficiency. Nearby, on this radiator, there is a 5V assembly, we solder it and throw it away.

Under load, the following parts heat up most strongly: two radiators, a pulse transformer, an inductor on a ferrite ring, an inductor on a ferrite core. Now our task is to reduce heat transfer and increase the maximum load current. As I said earlier, it can go up to 16A (for 200W PSU).

4. Unsolder the choke on the ferrite rod from the + 5V bus and put it on the + 12V bus, the choke that was there earlier (it is taller and wound with a thin wire) evaporate and discard. Now the throttle will practically not heat up or will, but not so much. On some boards, there are simply no chokes, you can do without it, but it is desirable that it be for better filtering of possible interference.

5. A choke is wound on a large ferrite ring to filter out impulse noise. The + 12V rail is wound on it with a thinner wire, and the + 5V rail is the thickest. Solder this ring carefully and swap the windings for the + 12V and + 5V buses (or include all windings in parallel)... Now the + 12V rail goes through this choke, the thickest wire. As a result, this choke will heat up significantly less.

6. The PSU has two radiators, one for high-power high-voltage transistors, the other for diode assemblies for +5 and + 12V. I came across several types of radiators. If, in your PSU, the dimensions of both radiators are 55x53x2mm and they have fins at the top (as in the photo) - you can count on 15A. When the radiators are smaller, it is not recommended to load the PSU with a current of more than 10A. When the radiators are thicker and have an additional platform at the top - you're in luck, this is the best option, you can get 20A in a minute. If the heatsinks are small, to improve heat dissipation, you can attach a small duralumin plate or a half from the heatsink of an old processor to them. Pay attention to whether the high-voltage transistors are well screwed to the radiator, sometimes they dangle.

7. We solder electrolytic capacitors on the + 12V rail, put 4700x25V in their place. It is advisable to evaporate the capacitors on the + 5V bus, just so that there is more free space and the air from the fan blows around the parts better.

8. On the board you can see two high-voltage electrolytes, usually 220x200V. Replace them with two 680x350V, as a last resort, connect two in parallel at 220 + 220 = 440mKf. This is important and the point is not only in filtering, impulse noise will be attenuated and resistance to maximum loads will increase. The result can be viewed with an oscilloscope. In general, you must do it!

9. It is desirable that the fan changes speed depending on the heating of the power supply unit and does not spin when there is no load. This will extend the life of the fan and reduce noise. I offer two simple and reliable schemes. If you have a thermistor, look at the diagram in the middle, with a trimmer we set the temperature of the thermistor's response to about + 40C. Transistor, you need to install exactly KT503 with maximum current gain (this is important), other types of transistors work worse. A thermistor of any type of NTC, which means that when it heats up, its resistance should decrease. You can use a thermistor with a different rating. The trimmer must be multiturn, so it is easier and more accurate to adjust the fan response temperature. We fasten the circuit board to the free fan lug. We attach the thermistor to the choke on a ferrite ring, it heats up faster and stronger than the rest of the parts. You can glue the thermistor to the 12V diode assembly. It is important that none of the thermistor leads short to the radiator !!! In some PSUs, there are fans with a high current consumption, in this case, after KT503, you need to put KT815.

If you don't have a thermistor, make a second circuit, look on the right, it uses two D9 diodes as a thermoelement. With transparent flasks, glue them to the radiator on which the diode assembly is installed. Depending on the transistors used, sometimes you need to choose a 75 kΩ resistor. When the PSU is running without load, the fan should not be spinning. Everything is simple and reliable!

CONCLUSION

From a computer power supply with a power of 200W, it is possible to get 10 - 12A (if there are large transformers and radiators in the power supply unit) at constant load and 16 - 18A for a short time at an output voltage of 14.0V. This means you can safely operate SSB and CW at full power. (100W) transceiver. In SSTV, RTTY, MT63, MFSK and PSK modes, you will have to reduce the transmitter power to 30-70W, depending on the duration of the transmission.

The weight of the converted PSU is about 550g. It is convenient to take it with you on radio expeditions and various trips.

During the writing of this article and during the experiments, three PSUs were damaged (as you know, experience does not come immediately) and five PSUs have been successfully redone.

A big plus of a computer power supply unit is that it works stably when the mains voltage changes from 180 to 250V. Some specimens also operate with a wider voltage spread.

See photos of successfully converted switching power supplies: