Conversion of computer power supplies with PWM controllers such as DR-B2002, DR-B2003, SG6105 into laboratory power supplies. DIY charger from a computer power supply Replacing diode assemblies with more powerful ones

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, motors direct current, solenoid valves, in various control circuits and others.

ULN2003 chip - description

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 circuits. 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 wiring 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 logical devices CMOS. 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.

Block diagram of ULN2003

Schematic diagram

Characteristics

The rated collector current of one key is 0.5A;
Maximum output voltage up to 50 V;
Protective diodes at the outputs;
The input is adapted to all kinds of logic;
Can be used to control relays.

Analogue ULN2003

Below is a list of what can replace ULN2003 (ULN2003a):

Foreign analogues of ULN2003 are L203, MC1413, SG2003, TD62003.
The domestic analogue of ULN2003a is the microcircuit.

ULN2003 chip - connection diagram

Often the ULN2003 chip is used to control a stepper motor. Below is the wiring diagram for ULN2003a and stepper motor.

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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 sources nutrition (IP). 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.

Description of the device circuit

Construction and details

The PWM controller unit is assembled on a printed circuit board made of one-sided foil-coated fiberglass laminate measuring 40x45 mm. The printed circuit board drawing and the arrangement of elements are shown in the figure. The drawing is shown from the installation side of the components.

The board is designed for 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.

Installation and commissioning

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 power supply 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 where there is output voltage standby power supply circuits, the value of which can be within 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 procedure for converting a computer power supply into a laboratory power supply

The work of remaking the power supply involves working in circuits with high voltage, therefore 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 power supply. 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 remaking 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, however, 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 a low-frequency sine wave generator and an oscilloscope or millivoltmeter for this purpose. alternating current. 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 is wound onto the frame primary winding, 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 need to 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 magnetic circuit of the transformer. If the wiring of the secondary winding is soldered correctly (to the terminals of the 12-volt winding), then you can solder the transformer into the power supply board and check its functionality.

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Section: [Power supplies (switching)]
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The materials of this article were published in the magazine Radioamator - 2013, No. 11

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 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 performed well “Computer power supply – charger”,(Radio - 2009, No. 1) with the addition of an arrow measuring instrument for measuring output voltage and charging current. Based on the same circuit, the first laboratory power supplies were manufactured, until the “Universal control board for laboratory power supplies” came into view (Radio Yearbook - 2011, No. 5, p. 53). Using this scheme, it was possible to produce much more functional power supplies. A digital ampere-voltmeter was developed specifically for this regulator circuit, described in the article "A simple built-in ampere-voltmeter on PIC16F676."

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 “SG6105 and DR-B2002 PWM controllers in computer IP.” From the description it became clear that these controllers are much more complex than the TL494 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 the TL494 with its standard wiring instead of the DR-B2002 chip, 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 limiting also worked as in the converted power supply of the “old” model.

Description of the device circuit

Construction and details

The board is designed for 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.

Installation and commissioning

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 power supply 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 chip). 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 procedure for converting a computer power supply into a laboratory power supply

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.

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 power supply. 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, move 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 the 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.

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.

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.