Chip ULN2003 (ULN2003a) is essentially a set of powerful composite switches for use in inductive load circuits. Can be used to control loads of significant power, including electromagnetic relays, DC motors, solenoid valves, in various control circuits and others.
Brief description of ULN2003a. The ULN2003a microcircuit is a Darlington transistor assembly with high-power output switches, which has protective diodes at the outputs, which are designed to protect control electrical circuits from reverse voltage surge from an inductive load.
Each channel (Darlington pair) in the ULN2003 is rated at 500 mA and can handle a maximum current of up to 600 mA. The inputs and outputs are located opposite each other in the microcircuit housing, which greatly facilitates the layout of the printed circuit board.
ULN2003 belongs to the ULN200X family of chips. Different versions of this chip are designed for specific logic. In particular, the ULN2003 chip is designed to work with TTL logic (5V) and CMOS logic devices. ULN2003 is widely used in control circuits for a wide range of loads, such as relay drivers, display drivers, linear drivers, etc. ULN2003 is also used in stepper motor drivers.
Below is a list of what can replace ULN2003 (ULN2003a):
Often the ULN2003 chip is used to control a stepper motor. Below is the wiring diagram for ULN2003a and stepper motor.
DIY charger from a computer power supply
Different situations require power supplies of different voltages and power. Therefore, many people buy or make one so that it is enough for all occasions.
And the easiest way is to use a computer as a basis. This laboratory power supply with characteristics 0-22 V 20 A remade with minor modifications from computer ATX to PWM 2003. For the conversion I used JNC mod. LC-B250ATX. The idea is not new and there are many similar solutions on the Internet, some were studied, but the final one turned out to be the same. I am very pleased with the result. Now I am waiting for a parcel from China with combined voltage and current indicators, and, accordingly, I will replace it. Then it will be possible to call my development LBP - charger for car batteries.
Adjustable power supply diagram:
First of all, I unsoldered all the output voltage wires +12, -12, +5, -5 and 3.3 V. I unsoldered everything except +12 V diodes, capacitors, load resistors.
I replaced the input high-voltage electrolytes 220 x 200 with 470 x 200. If there is one, it is better to install a larger capacity. Sometimes the manufacturer saves on the input power filter - accordingly, I recommend soldering it if it is missing.
The +12 V output choke has been rewound. New - 50 turns of wire with a diameter of 1 mm, removing the old windings. The capacitor was replaced with 4700 uF x 35 V.
Since the unit has standby power supply with voltages of 5 and 17 volts, I used them to power the 2003 and the voltage testing unit.
Pin 4 was supplied with a direct voltage of +5 volts from the “duty room” (i.e., connected to pin 1). Using a resistor 1.5 and 3 kOhm voltage divider from 5 volts of standby power, I made 3.2 and applied it to input 3 and to the right terminal of resistor R56, which then goes to pin 11 of the microcircuit.
Having installed the 7812 microcircuit on the 17 volt output from the control room (capacitor C15), I received 12 volts and connected it to a 1 Kohm resistor (without a number on the diagram), which at the left end is connected to pin 6 of the microcircuit. Also, a cooling fan was powered through a 33 Ohm resistor, which was simply turned over so that it blew inward. The resistor is needed to reduce the speed and noise of the fan.
The entire chain of resistors and negative voltage diodes (R63, 64, 35, 411, 42, 43, C20, D11, 24, 27) was removed from the board, pin 5 of the microcircuit was shorted to ground.
Added adjustment voltage and output voltage indicator from a Chinese online store. You just need to power the latter from the standby +5 V, and not from the measured voltage (it starts working from +3 V). Power supply tests
Tests were carried out simultaneous connection of several car lamps (55+60+60) W.
This is approximately 15 Amps at 14 V. It worked for about 15 minutes without problems. Some sources recommend isolating the common 12 V output wire from the case, but then a whistle appears. Using a car radio as a power source, I did not notice any interference either on the radio or in other modes, and 4*40 W pulls perfectly. Best regards, Petrovsky Andrey.
The article presents a simple design of a PWM regulator, with which you can easily convert a computer power supply, assembled on a controller other than the popular tl494, in particular, dr-b2002, dr-b2003, sg6105 and others, into a laboratory one with an adjustable output voltage and limiting the current in the load. Also here I will share my experience in redesigning computer power supplies and describe proven ways to increase their maximum output voltage.
In the amateur radio literature there are many schemes for converting outdated computer power supplies (PSUs) into chargers and laboratory power supplies (LPs). But they all relate to those power supplies in which the control unit is built on the basis of a PWM controller chip of type tl494, or its analogues dbl494, kia494, KA7500, KR114EU4. We have redesigned more than a dozen such power supplies. Chargers made according to the scheme described by M. Shumilov in the article “Simple built-in ampere-voltmeter on pic16f676” performed well.
But all good things must come to an end, and recently we have increasingly come across computer power supplies in which other PWM controllers were installed, in particular, dr-b2002, dr-b2003, sg6105. The question arose: how can these BPs be used for the manufacture of laboratory PIs? The search for diagrams and communication with radio amateurs did not allow us to move forward in this direction, although we managed to find a brief description and connection diagram for such PWM controllers in the article “PWM controllers sg6105 and dr-b2002 in computer IP.” From the description it became clear that these controllers tl494 is much more complicated and trying to control them externally to regulate the output voltage is hardly possible. Therefore, it was decided to abandon this idea. However, when studying the circuits of the “new” power supplies, it was noted that the construction of the control circuit of the push-pull half-bridge converter was carried out similarly to the “old” power supplies - on two transistors and an isolation transformer.
An attempt was made to install tl494 with its standard wiring instead of the dr-b2002 microcircuit, connecting the collectors of the tl494 output transistors to the transistor bases of the power supply converter control circuit. The repeatedly tested above-mentioned M. Shumilov circuit was chosen as the tl494 harness to ensure regulation of the output voltage. Enabling the PWM controller in this way allows you to disable all the blocking and protection circuits in the power supply; moreover, this circuit is very simple.
An attempt to replace the PWM controller was successful - the power supply started working, the output voltage adjustment and current limitation also worked, as in the converted power supply of the “old” model.
The PWM controller unit is assembled on a printed circuit board made of one-sided foil-coated fiberglass laminate measuring 40x45 mm. The drawing of the printed circuit board and the layout of the elements are shown in the figure. The drawing is shown from the installation side of the components.
The board is designed for the installation of output components. There are no special requirements for them. Transistor vt1 can be replaced with any other direct bipolar transistor with similar parameters. The board provides for the installation of trimming resistors r5 of different sizes.
The board is secured in a convenient place with one screw closer to the installation site of the PWM controller. The author found it convenient to attach the board to one of the PSU heatsinks. The outputs pwm1, pwm2 are soldered directly into the corresponding holes of the previously installed PWM controller - the outputs of which go to the bases of the converter control transistors (pins 7 and 8 of the dr-b2002 microcircuit). The vcc pin is connected to the point at which there is an output voltage of the standby power supply circuit, the value of which can be in the range of 13...24V.
The output voltage of the IP is adjusted using potentiometer r5, the minimum output voltage depends on the value of resistor r7. Resistor r8 can be used to limit the maximum output voltage. The value of the maximum output current is regulated by selecting the value of resistor r3 - the lower its resistance, the greater the maximum output current of the power supply will be.
The work of remaking the power supply involves working in high-voltage circuits, so it is strongly recommended to connect the power supply to the network through an isolation transformer with a power of at least 100 W. In addition, to avoid failure of key transistors during the process of setting up the IP, it should be connected to the network through a 220V 100W “safety” incandescent lamp. It can be soldered to the power supply instead of the mains fuse.
Before you begin remaking a computer power supply, it is advisable to make sure that it is in good working order. Before switching on, you should connect 12V car bulbs with a power of up to 25 W to the +5V and +12V output circuits. Then connect the power supply to the network and connect the ps-on pin (usually green) to the common wire. If the power supply is working properly, the “safety” lamp will flash briefly, the power supply will start working and the lamps in the +5V, +12V load will light up. If, after switching on, the “safety” lamp lights up at full intensity, a breakdown of power transistors, rectifier bridge diodes, etc. is possible.
Next, you should find the point on the power supply board at which there is an output voltage of the standby power supply circuit. Its value can be within 13...24V. From this point we will later take power for the PWM controller unit and the cooling fan.
Then you should unsolder the standard PWM controller and connect the PWM controller unit to the power supply board according to the diagram (Fig. 1). The p_in input is connected to the 12-volt output of the PSU. Now you need to check the operation of the regulator. To do this, you should connect a load in the form of a car light bulb to the p_out output, turn the resistor r5 slider all the way to the left (to the position of minimum resistance) and connect the power supply to the network (again through a “safety” lamp). If the load lamp lights up, you should make sure that the adjustment circuit is working properly. To do this, you need to carefully turn the slider of resistor r5 to the right, while it is advisable to control the output voltage with a voltmeter so as not to burn the load lamp. If the output voltage is regulated, then the PWM regulator unit is working and you can continue upgrading the power supply.
We solder all the power supply load wires, leaving one wire in the +12 V circuits and a common one for connecting the PWM controller unit. We solder: diodes (diode assemblies) in +3.3 V, +5 V circuits; rectifier diodes -5 V, -12 V; all filter capacitors. The electrolytic capacitors of the +12 V circuit filter should be replaced with capacitors of similar capacity, but with a permissible voltage of 25 V or more, depending on the expected maximum output voltage of the laboratory power supply being manufactured. Next, you should install the load resistor shown in the diagram in Fig. 1 as r2, necessary to ensure stable operation of the power supply without external load. The load power should be about 1 W. The resistance of resistor r2 can be calculated based on the maximum output voltage of the power supply. In the simplest case, a 2-watt resistor with a resistance of 200-300 Ohms will do.
Next, you can unsolder the wiring elements of the old PWM controller and other radio components from the unused output circuits of the power supply. In order not to accidentally unsolder something “useful”, it is recommended to unsolder the parts not completely, but one terminal at a time, and only after making sure that the IP is working, remove the part completely. Regarding the filter choke l1, the author usually does nothing with it and uses the standard winding of the +12 V circuit. This is due to the fact that, for safety reasons, the maximum output current of a laboratory power supply is usually limited to a level not exceeding the rating for the +12 V power supply circuit .
After cleaning the installation, it is recommended to increase the capacitance of the filter capacitor C1 of the standby power supply, replacing it with a capacitor rated 50 V/100 µF. In addition, if the diode vd1 installed in the circuit is low-power (in a glass case), it is recommended to replace it with a more powerful one, soldered from the -5 V or -12 V circuit rectifier. You should also select the resistance of resistor r1 for comfortable operation of the cooling fan M1.
Experience in redesigning computer power supplies has shown that with the use of various PWM controller control circuits, the maximum output voltage of the power supply will be within 21...22 V. This is more than enough for the manufacture of chargers for car batteries, but it is still not enough for a laboratory power source. To obtain an increased output voltage, many radio amateurs suggest using a bridge circuit for rectifying the output voltage, but this is due to the installation of additional diodes, the cost of which is quite high. I consider this method irrational and use another method of increasing the output voltage of the IP - upgrading the power transformer.
There are two main ways to modernize an IP power transformer. The first method is convenient in that its implementation does not require disassembling the transformer. It is based on the fact that usually the secondary winding is wound in several wires and it is possible to “stratify” it. The secondary windings of the power transformer are shown schematically in Fig. A). This is the most common scheme. Typically, a 5-volt winding has 3 turns wound in 3-4 wires (windings “3.4” - “general” and “general” - “5.6”), and a 12-volt winding has an additional 4 turns. in one wire (windings “1” - “3.4” and “5.6” - “2”).
To do this, the transformer is unsoldered, the taps of the 5-volt winding are carefully unsoldered, and the “braid” of the common wire is unraveled. The task is to disconnect the parallel-connected 5-volt windings and connect all or part of them in series, as shown in the diagram in Fig. b).
Selecting the windings is not difficult, but phasing them correctly is quite difficult. The author uses for this purpose a low-frequency sine wave generator and an oscilloscope or AC millivoltmeter. By connecting the output of a generator set to a frequency of 30...35 kHz to the primary winding of the transformer, use an oscilloscope or millivoltmeter to monitor the voltage on the secondary windings. By combining the connection of 5-volt windings, they achieve an increase in the output voltage compared to the original one by the required amount. In this way, you can increase the output voltage of the power supply to 30...40 V.
The second way to modernize a power transformer is to rewind it. This is the only way to get a power output voltage greater than 40V. The most difficult task here is to disconnect the ferrite core. The author adopted a method of boiling a transformer in water for 30-40 minutes. But before boiling down the transformer, you should carefully consider the method of disconnecting the core, taking into account the fact that after boiling down it will be very hot, and besides, hot ferrite becomes very fragile. To do this, it is proposed to cut two wedge-shaped strips from tin, which can then be inserted into the gap between the core and the frame, and with their help, separate the halves of the core. If parts of the ferrite core break or chip off, you shouldn’t be too upset, since it can be successfully glued together with cyacrylane (the so-called “superglue”).
After releasing the transformer coil, it is necessary to wind the secondary winding. Pulse transformers have one unpleasant feature - the primary winding is wound in two layers. First, the first part of the primary winding is wound on the frame, then the screen, then all the secondary windings, again the screen and the second part of the primary winding. Therefore, you need to carefully wind the second part of the primary winding, while being sure to remember its connection and winding direction. Then remove the screen, made in the form of a layer of copper foil with a soldered wire leading to the terminal of the transformer, which must first be unsoldered. And finally, wind the secondary windings to the next screen. Now you definitely need to dry the coil thoroughly with a stream of hot air to evaporate the water that penetrated into the winding during boiling.
The number of turns of the secondary winding will depend on the required maximum output voltage of the power supply at the rate of approximately 0.33 turns/V (that is, 1 turn - 3 V). For example, the author wound 2x18 turns of PEV-0.8 wire and obtained a maximum output voltage of the power supply of about 53 V. The cross-section of the wire will depend on the requirement for the maximum output current of the power supply, as well as on the dimensions of the transformer frame.
The secondary winding is wound in 2 wires. The end of one wire is immediately soldered to the first terminal of the frame, and the second is left with a margin of 5 cm to form a “pigtail” of the zero terminal. Having finished winding, solder the end of the second wire to the second terminal of the frame and form a “pigtail” in such a way that the number of turns of both half-windings is necessarily the same.
Now you should restore the screen, wind the previously wound second part of the primary winding of the transformer, observing the original connection and winding direction, and assemble the transformer magnetic circuit. If the wiring of the secondary winding is soldered correctly (to the terminals of the 12-volt winding), then you can solder the transformer to the PSU board and check its performance.
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Introduction
The big advantage of a computer power supply is that it works stably when the mains voltage varies from 180 to 250 V, and some units also work with a greater voltage variation. From a 200 W unit it is possible to obtain a useful load current of 15-17 A, and in a pulsed (short-term high load mode) - up to 22 A. Computer power supplies of the standard range that comply with the ATX12 standard and are intended for use in PCs based on Intel Pentium IV processors and below, most often made on microcircuits 2003, AT2005Z, SG6105, KA3511, LPG-899, DR-B2002, IW1688. Such devices contain a smaller number of discrete elements on the board and have a lower cost than those built on the basis of the popular PWM chip TL494. In this material we will look at several approaches to repairing the above-mentioned power supplies and give some practical advice.
Blocks and diagrams
A computer power supply can be used not only for its intended purpose, but also as a source for a wide range of electronic designs for the home that require a constant voltage of 5 and 12 V for their operation. With the minor modification described below, this is not at all difficult to do. And you can purchase a PC power supply separately either in a store or a used one at any radio market (if you don’t have enough of your own “bins”) for a symbolic price.
This makes the computer power supply stand out from all other industrial options when it comes to being used in a radio technician's home laboratory. For example, we will take JNC blocks of the LC-B250ATX and LC-B350ATX models, as well as InWin IP-P300AQ2, IP-P350AQ2, IP-P400AQ2, IP-P350GJ20, which use the 2003 IFF LFS 0237E chip in their design. In some others there are BAZ7822041H or 2003 BAY05370332H. All these microcircuits are structurally different from each other in the purpose of the pins and the “filling”, but their operating principle is the same. So the 2003 IFF LFS 0237E chip (hereinafter we will call it 2003) is a PWM (pulse width modulator of signals) in a DIP-16 package. Until recently, most budget computer power supplies produced by Chinese companies were based on the TL494 PWM controller chip from Texas Instruments (http://www.ti.com) or its analogues from other manufacturers, such as Motorola, Fairchild, Samsung and others. The same microcircuit has a domestic analogue KR1114EU4 and KR1114EU3 (the pinouts in the domestic version are different). Let's first learn methods for diagnosing and testing problems.
How to change the input voltage
The signal, the level of which is proportional to the load power of the converter, is removed from the middle point of the primary winding of the isolation transformer T3, then through diode D11 and resistor R35 it is supplied to the correction circuit R42R43R65C33, after which it is supplied to the PR pin of the microcircuit. Therefore, in this circuit it is difficult to set protection priority for any one voltage. Here we would have to greatly change the scheme, which is unprofitable in terms of time.
In other computer power supply circuits, for example, in the LPK-2-4 (300 W), the voltage from the cathode of a dual Schottky diode type S30D40C, a +5 V output voltage rectifier, is supplied to the UVac input of the U2 chip and is used to control the input AC supply voltage BP. Adjustable output voltage is useful for a home laboratory. For example, to power electronic devices for a passenger car from a computer power supply unit, where the voltage in the on-board network (with the engine running) is 12.5-14 V. The higher the voltage level, the greater the useful power of the electronic device. This is especially important for radio stations. For example, let's look at adapting a popular radio station (transceiver) to our LC-B250ATX power supply - increasing the voltage on the 12 V bus to 13.5-13.8 V.
We solder a tuning resistor, for example, SP5-28V (preferably with the index “B” in the designation - a sign of linearity of the characteristic) with a resistance of 18-22 kOhm between pin 6 of the U2 microcircuit and the +12 V bus. At the +12 V output we install a 5- 12 W as a load equivalent (you can also connect a constant 5-10 Ohm resistor with a dissipation power of 5 W and higher). After the considered minor modification of the power supply unit, the fan does not need to be connected and the board itself does not need to be inserted into the case. We start the power supply, connect a voltmeter to the +12 V bus and monitor the voltage. By rotating the variable resistor slider, we set the output voltage to 13.8 V.
Turn off the power and measure the resulting resistance of the trimming resistor with an ohmmeter. Now, between the +12 V bus and pin 6 of the U2 chip, we solder a constant resistor of the appropriate resistance. In the same way, you can adjust the voltage at the +5 V output. The limiting resistor itself is connected to pin 4 of the 2003 IFF LFS 0237E microcircuit.
How the circuit works 2003
The supply voltage Vcc (pin 1) to the U2 chip comes from the standby voltage source +5V_SB. The negative input of the error amplifier IN of the microcircuit (pin 4) receives the sum of the output voltages of the IP +3.3 V, +5 V and +12 V. The adder is made respectively on resistors R57, R60, R62. The controlled zener diode of the U2 microcircuit is used in the optocoupler feedback circuit in the standby voltage source +5V_SB, the second zener diode is used in the +3.3V output voltage stabilization circuit. The control circuit of the output half-bridge converter BP is made according to a push-pull circuit using transistors Q1, Q2 (designation on the printed circuit board) type E13009 and transformer T3 type EL33-ASH according to the standard circuit used in computer units.
Interchangeable transistors - MJE13005, MJE13007, Motorola MJE13009 are produced by many foreign manufacturers, so instead of the abbreviation MJE, the transistor marking may contain the symbols ST, PHE, KSE, HA, MJF and others. To power the circuit, a separate winding of the standby mode transformer T2 type EE-19N is used. The greater the power of transformer T3 (the thicker the wire used in the windings), the greater the output current of the power supply itself. In some printed circuit boards that I had to repair, the “swinging” transistors were named 2SC945 and H945P, 2SC3447, 2SC3451, 2SC3457, 2SC3460(61), 2SC3866, 2SC4706, 2SC4744, BUT11A, BUT12A, BUT18A, BUV46 , MJE13005, and the designation is on the board was indicated as Q5 and Q6. And at the same time there were only 3 transistors on the board! The 2003 IFF LFS 0237E chip itself was designated U2, and there is not a single U1 or U3 designation on the board. However, let’s leave this oddity in the designation of elements on printed circuit boards to the conscience of the Chinese manufacturer. The designations themselves are not important. The main difference between the LC-B250ATX type power supplies under consideration is the presence on the board of one type 2003 IFF LFS 0237E chip and the appearance of the board.
The microcircuit uses a controlled zener diode (pins 10, 11), similar to TL431. It is used to stabilize the 3.3 V power circuit. I note that in my practice of repairing power supplies, the above circuit is the weakest point in a computer power supply. However, before changing the 2003 chip, I recommend that you first check the circuit itself.
Diagnostics of ATX power supplies on a 2003 chip
If the power supply does not start, you must first remove the housing cover and check the oxide capacitors and other elements on the printed circuit board by external inspection. Oxide (electrolytic) capacitors clearly need to be replaced if their cases are swollen and if they have a resistance of less than 100 kOhms. This is determined by “continuity” with an ohmmeter, for example, model M830 in the appropriate measurement mode. One of the most common malfunctions of power supplies based on the 2003 chip is the lack of stable startup. The launch is performed by the Power button on the front panel of the system unit, while the contacts of the button are closed, and pin 9 of the U2 microcircuit (2003 and similar) is connected to the “case” by a common wire.
In a "braid" these are usually green and black wires. In order to quickly restore the functionality of the device, it is enough to disconnect pin 9 of the U2 chip from the printed circuit board. Now the power supply should turn on stably by pressing the button on the rear panel of the system unit. This method is good because it allows you to continue to use an obsolete computer power supply without repairs, which is not always financially beneficial, or when the unit is used for other purposes, for example, to power electronic structures in a home amateur radio laboratory.
If you hold down the “reset” button before turning on the power and release it after a few seconds, the system will simulate an increase in the delay of the Power Good signal. This way you can check the reasons for the malfunction of data loss in CMOS (after all, the battery is not always “to blame”). If data, such as time, is periodically lost, then the shutdown delay should be checked. To do this, “reset” is pressed before turning off the power and held for a few more seconds, simulating the acceleration of the Power Good signal. If the data is saved during such a shutdown, the problem is a large delay during shutdown.
Power increase
Two high-voltage electrolytic capacitors with a capacity of 220 μF are installed on the printed circuit board. To improve filtering, reduce impulse noise, and ultimately ensure the stability of the computer power supply to maximum loads, these capacitors are replaced with analogues of higher capacity, for example, 680 μF for an operating voltage of 350 V. A breakdown, loss of capacitance, or breakage of the oxide capacitor in the power supply circuit reduces or negates filtering of supply voltage. The voltage on the plates of the oxide capacitor in power supply devices is about 200 V, and the capacitance is in the range of 200-400 μF. Chinese manufacturers (VITO, Feron and others) usually install the cheapest film capacitors, without much concern for either the temperature regime or the reliability of the device. The oxide capacitor in this case is used in the power supply device as a high-voltage power supply filter, and therefore must be high-temperature. Despite the operating voltage indicated on such a capacitor is 250-400 V (with a margin, as expected), it still “fails” due to its low quality.
For replacement, I recommend oxide capacitors from KX, CapXon, namely HCY CD11GH and ASH-ELB043 - these are high-voltage oxide capacitors specially designed for use in electronic power devices. Even if an external inspection did not allow us to find faulty capacitors, the next step is still to unsolder the capacitors on the +12 V bus and instead install analogues of higher capacity: 4700 µF for an operating voltage of 25 V. The section of the PC power supply circuit board itself with oxide capacitors for power supply, to be replaced is shown in Figure 4. We carefully remove the fan and install it in reverse - so that it blows inward and not outward. This modernization improves the cooling of radio elements and ultimately increases the reliability of the device during long-term operation. A drop of machine or household oil in the mechanical parts of the fan (between the impeller and the electric motor axis) will not hurt. In my experience, it can be said that the noise of the supercharger during operation is significantly reduced.
Replacing diode assemblies with more powerful ones
On the printed circuit board of the power supply, diode assemblies are installed on radiators. In the center there is a UF1002G assembly (12 V power supply), on the right side of this radiator there is a D92-02 diode assembly, providing a -5 V power supply. If such a voltage is not needed in a home laboratory, this type assembly can be permanently desoldered. In general, D92-02 is designed for a current of up to 20 A and a voltage of 200 V (in pulsed short-term mode, many times higher), so it is quite suitable for installation instead of UF1002G (current up to 10 A).
The Fuji D92-02 diode assembly can be replaced, for example, with S16C40C, S15D40C or S30D40C. All of them, in this case, are suitable for replacement. Diodes with a Schottky barrier have a lower voltage drop and, accordingly, heating.
The peculiarity of the replacement is that the “standard” output diode assembly (12 V bus) UF1002G has a completely plastic composite housing, therefore it is attached to a common radiator or current-conducting plate using thermal paste. And the Fuji D92-02 diode assembly (and similar ones) has a metal plate in the housing, which requires special care when installing it on a radiator, that is, through the obligatory insulating gasket and a dielectric washer under a screw. The reason for the failure of UF1002G diode assemblies is voltage surges on the diodes with an amplitude that increases when the power supply operates under load. At the slightest excess of the permissible reverse voltage, Schottky diodes receive an irreversible breakdown, so the recommended replacement with more powerful diode assemblies in the case of future use of a power supply with a powerful load is completely justified. Finally, there is one tip that will allow you to check the functionality of the protective mechanism. Let's short-circuit the +12 V bus to the body (common wire) with a thin wire, for example, MGTF-0.8. This way the tension should disappear completely. To restore it, turn off the power supply for a couple of minutes to discharge the high-voltage capacitors, remove the shunt (jumper), remove the equivalent load and turn on the power supply again; it will work normally. Computer power supplies converted in this way work for years at 24 hours at full load.
Power pin
Suppose you need to use the power supply for domestic purposes and you need to remove two terminals from the block. I did this using two (equal length) pieces of waste wire from the computer power supply and connected all three pre-soldered wires in each conductor to the terminal block. To reduce power loss in the conductors coming from the power supply to the load, another electrical cable with a copper (less loss) multi-core cable is also suitable - for example, PVSN 2x2.5, where 2.5 is the cross-section of one conductor. You can also not lead the wires to the terminal block, but connect the 12 V output in the PC power supply housing to an unused connector of the PC monitor network cable.
Pin assignment of the 2003 microcircuit
PSon 2 - PS_ON signal input that controls the operation of the power supply: PSon=0, the power supply is turned on, all output voltages are present; PSon=1, power supply is turned off, only standby voltage +5V_SB is present
V33-3 - Voltage input +3.3 V
V5-4 - Voltage input +5 V
V12-6 - Voltage input +12 V
OP1/OP2-8/7 - Control outputs of a push-pull half-bridge converter PSU
PG-9 - Testing. Open collector output PG signal (Power Good): PG=0, one or more output voltages are not normal; PG=1, power supply output voltages are within specified limits
Vref1-11 - Control electrode of controlled zener diode
Fb1-10 - Cathode of controlled zener diode
GND-12 - Common wire
COMP-13 - Error amplifier output and negative input of PWM comparator
IN-14 - Error amplifier negative input
SS-15 - Positive input of the error amplifier, connected to the internal source Uref = 2.5 V. The output is used to organize a “soft start” of the converter
Ri-16 - Input for connecting an external 75 kOhm resistor
Vcc-1 - Supply voltage, connected to standby source +5V_SB
PR-5 - Input for organizing power supply protection
