Charger from computer unit DIY food

Different situations require power supplies of different voltage and power. Therefore, many people buy or make one that is enough for all occasions.

And the easiest way is to take the computer as a basis. This laboratory power supply unit with characteristics 0-22 V 20 A redesigned with a little tweak from computer ATX on PWM 2003. For rework 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 turned out to be its own. I am very pleased with the result. Now I'm waiting for a package 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.

Scheme regulated unit power supply:

First of all, I removed all the wires of the output voltages +12, -12, +5, -5 and 3.3 V. I removed all diodes, capacitors, load resistors except +12 V.

Replaced input high-voltage electrolytes 220 x 200 by 470 x 200. If there is, then it is better to put a larger capacity. Sometimes the manufacturer saves on the input filter for power supply - accordingly, I recommend re-soldering if not available.

Output choke + 12V rewound. New - 50 turns with a wire with a diameter of 1 mm, removing the old windings. The capacitor was replaced by 4700 microfarads x 35 V.

Since the unit has a standby power supply with voltages of 5 and 17 volts, I used them to power the 2003 and for the voltage test unit.

I applied a direct voltage of +5 volts to pin 4 from the "duty room" (that is, I connected it to pin 1). Using a resistor 1.5 and 3 kΩ voltage divider from 5 volts of the standby power, I made 3.2 and applied it to input 3 and to the right terminal of the resistor R56, which then goes to pin 11 of the microcircuit.

Having installed the 7812 microcircuit at the 17 volt output from the duty room (capacitor C15), I received 12 volts and connected it to a 1 Kom resistor (without a number in the diagram), which is connected with the left end to pin 6 of the microcircuit. Also, through a 33 Ohm resistor, I fed the cooling fan, which I simply turned it over so that it blew inside. The resistor is needed in order to reduce the speed and noise of the fan.

The entire chain of resistors and diodes of negative voltages (R63, 64, 35, 411, 42, 43, C20, D11, 24, 27) was dropped from the board, pin 5 of the microcircuit was short-circuited to ground.

Added adjustment voltage and output voltage indicator from a Chinese online store. It is only necessary to power the latter from the duty room +5 V, and not from the measured voltage (it starts to work from +3 V). Power supply tests

The tests were carried out simultaneous connection of several car lamps (55 + 60 + 60) W.

This is about 15 Amperes at 14 V. I worked for 15 minutes without problems. Some sources recommend isolating the common 12 V output wire from the case, but then a whistle appears. Using the 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, Andrey Petrovsky.

Chip ULN2003 (ULN2003a) is essentially a set of powerful composite keys for use in inductive load circuits. Can be used to control large loads, including electromagnetic relays, motors direct current, solenoid valves, in various control circuits and others.

Chip ULN2003 - 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 the control electrical circuits from the reverse voltage surge from the inductive load.

Each channel (Darlington pair) in ULN2003 is rated for 500mA load and can handle a maximum current of 600mA. Inputs and outputs are located opposite each other in the microcircuit case, which greatly facilitates wiring printed circuit board.

ULN2003 belongs to the ULN200X family of microcircuits. Different versions of this IC are designed for specific logic. In particular, the ULN2003 microcircuit is designed to work with TTL logic (5V) and CMOS logic devices. ULN2003 is widely used in control circuits of a wide range of loads, as relay drivers, display drivers, line drivers, etc. ULN2003 is also used in stepper motor drivers.

Block diagram of ULN2003

Schematic diagram

Specifications

• Nominal collector current of one key - 0.5A;
• Maximum output voltage up to 50 V;
• Protective diodes at the outputs;
• The input is adapted to all kinds of logic;
• Possibility of using for relay control.

Analogue ULN2003

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

• Foreign analogue of ULN2003 - L203, MC1413, SG2003, TD62003.
• The domestic analogue of ULN2003a is a microcircuit.

Microcircuit ULN2003 - connection diagram

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

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 the experience of reworking computer power supplies and describe the 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 power supply (IP). But they all relate to those power supplies in which the control unit is built on the basis of a tl494 type PWM controller chip, or its analogs dbl494, kia494, КА7500, KR114EU4. We have reworked more than a dozen of these power supplies. Chargers made according to the scheme described by M. Shumilov in the article "A simple built-in ammeter on pic16f676" have shown themselves well.

But all good things come to an end someday and recently more and more computer power supplies began to come across, in which other PWM controllers were installed, in particular, dr-b2002, dr-b2003, sg6105. The question arose: how can these PSUs be used for the manufacture of laboratory IPs? The search for circuits and communication with radio amateurs did not allow progress in this direction, although it was possible to find a brief description and a diagram of the inclusion of such PWM controllers in the article "PWM controllers sg6105 and dr-b2002 in computer power supplies." From the description it became clear that these controllers much more difficult tl494 and trying to control them from the outside 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 supply units, it was noted that the construction of the control circuit for a push-pull half-bridge converter was carried out similarly to the "old" power supply unit - on two transistors and an isolation transformer.

An attempt was made to install the tl494 with its standard strapping 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. As a strapping tl494 to ensure regulation of the output voltage, the aforementioned M. Shumilov's circuit was repeatedly tested. This inclusion of the PWM controller allows you to disable all interlocks and protection schemes available in the power supply, besides, this scheme is very simple.

An attempt to replace the PWM controller was crowned with success - the power supply unit worked, the output voltage adjustment and current limiting also worked, as in the converted “old” power supply units.

Description of the device diagram

Construction and details

The PWM regulator block is assembled on a printed circuit board from one-sided foil-coated fiberglass with a size of 40x45 mm. The printed circuit board drawing and the layout of the elements are shown in the figure. The drawing is shown from the component installation side.

The board is designed for the installation of output components. There are no special requirements for them. The vt1 transistor can be replaced with any other direct conduction bipolar transistor of similar parameters. The board provides for the installation of trimming resistors r5 of different standard sizes.

Installation and commissioning

The board is fastened 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 pwm1, pwm2 outputs are soldered directly into the corresponding holes of the previously installed PWM controller - the leads of which go to the bases of the converter control transistors (pins 7 and 8 of the dr-b2002 microcircuit). The vcc pin connections are made to the point at which there is output voltage standby power supply circuits, the value of which can be in the range of 13 ... 24V.

Adjustment of the MT output voltage is carried out by potentiometer r5, the minimum output voltage depends on the value of the resistor r7. The r8 resistor can be used to limit the maximum output voltage. The value of the maximum output current is regulated by the selection of the value of the resistor r3 - the lower its resistance, the greater the maximum output current of the power supply unit.

The procedure for converting a computer power supply unit into a laboratory IP

The work on alteration of the power supply unit is associated with work in circuits with high voltage, therefore, it is strongly recommended to connect the power supply unit to the network through an isolation transformer with a capacity of at least 100W. In addition, to prevent the failure of key transistors in the process of setting up the IP, it should be connected to the network through a "safety" incandescent lamp for 220V with a power of 100W. It can be soldered to the PSU instead of the mains fuse.

Before proceeding with the alteration of a computer power supply, it is advisable to make sure that it is working properly. Before switching on, 12V car bulbs with a power of up to 25W should be connected to the + 5V and + 12V output circuits. Then connect the power supply unit to the network and connect the ps-on pin (usually green) to the common wire. If the power supply unit is working properly, the "safety" lamp will briefly flash, the power supply unit 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 heat, a breakdown of power transistors, rectifier bridge diodes, etc. is possible.

Next, you should find on the power supply board the point at which there is the output voltage of the standby power circuit. Its value can be in the range of 13 ... 24V. From this point in the future we will take power for the PWM controller unit and the cooling fan.

Then you should unsolder the standard PWM controller and connect the PWM regulator unit to the power supply board according to the diagram (Fig. 1). The p_in input is connected to the 12-volt power supply output. Now you need to check the operation of the regulator. To do this, connect a load in the form of a car light bulb to the p_out output, bring the r5 resistor slider to the left (to the minimum resistance position) and connect the power supply unit to the network (again through a “safety” lamp). If the load lamp lights up, make sure that the adjustment circuit is working properly. To do this, you need to carefully turn the slider of the 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 to upgrade the power supply unit.

We solder all the load wires of the power supply unit, leaving one wire in the +12 V circuits and a common one for connecting the PWM controller unit. We solder: diodes (diode assemblies) in circuits +3.3 V, +5 V; rectifier diodes -5 V, -12 V; all filter capacitors. Electrolytic capacitors the filter of the +12 V circuit should be replaced with capacitors of the same capacity, but with an allowable voltage of 25 V or more, depending on the expected maximum output voltage of the manufactured laboratory power supply. Next, install the load resistor shown in the diagram in Fig. 1 as r2 required to ensure stable operation of the MT without external load. The load power should be about 1W. The resistance of the resistor r2 can be calculated based on the maximum output voltage of the power supply. In the simplest case, a 2-watt 200-300 ohm resistor is suitable.

Next, you can remove the piping elements of the old PWM controller and other radio components from the unused output circuits of the power supply unit. In order not to accidentally drop out something "useful", it is recommended to unsolder the parts not completely, but one by one, and only after making sure that the MT is working, remove the part completely. Regarding the filter choke l1, the author usually does not do anything with it and uses the standard +12 V circuit winding.This is due to the fact that, for safety reasons, the maximum output current of the 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 by replacing it with a capacitor with a nominal value of 50 V / 100 μF. In addition, if the vd1 diode 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 rectifier of the -5 V or -12 V circuit. You should also select the resistance of the resistor r1 for comfortable operation of the cooling fan M1.

The experience of reworking computer power supplies showed that using various control schemes for a PWM controller, the maximum output voltage of the power supply will be in the range of 21 ... 22 V. This is more than enough for the manufacture of chargers for car batteries, but for a laboratory power supply it is still not enough. To obtain an increased output voltage, many radio amateurs suggest using a bridge rectifying circuit for 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 way to increase the output voltage of the power supply - modernization power transformer.

There are two main ways to upgrade a power transformer IP. 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 schematically shown in Fig. a). This is the most common pattern. Usually a 5-volt winding has 3 turns, wound in 3-4 wires (windings "3.4" - "common" and "common" - "5.6"), and a 12-volt winding - additionally 4 turns in one wire (windings "1" - "3.4" and "5.6" - "2").

To do this, the transformer is desoldered, the taps of the 5-volt winding are carefully unsoldered and the "pigtail" of the common wire is unwound. The task is to disconnect the parallel connected 5-volt windings and turn on all or part of them in series, as shown in the diagram in Fig. b).

It is not difficult to isolate the windings, but it is quite difficult to phase them correctly. For this purpose, the author uses a low-frequency sine signal generator and an oscilloscope or AC millivoltmeter. By connecting the output of the generator, tuned to a frequency of 30 ... 35 kHz, to the primary winding of the transformer, the voltage on the secondary windings is monitored using an oscilloscope or millivoltmeter. By combining the connection of 5-volt windings, they achieve an increase in the output voltage compared to the original by the required amount. In this way, you can achieve an increase in the output voltage of the PSU up to 30 ... 40 V.

The second way to upgrade a power transformer is to rewind it. This is the only way to obtain an output voltage of more than 40 V. The most difficult task here is to disconnect the ferrite core. The author has adopted a method of boiling a transformer in water for 30-40 minutes. But before you digest the transformer, you should think carefully about the method of separating the core, given the fact that after digestion it will be very hot, and besides, hot ferrite becomes very fragile. To do this, it is proposed to cut out two wedge-shaped strips from the 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. In case of breaking or chipping off parts of the ferrite core, you should not be particularly upset, since it can be successfully glued with cyacrylane (the so-called "superglue").

After freeing the coil of the transformer, it is necessary to wind up the secondary winding. Have pulse transformers there is 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 be sure to remember its connection and the direction of winding. 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. Finally, wind up the secondary windings to the next screen. Now, be sure to dry the coil well with a jet of hot air to evaporate the water that has penetrated into the winding during digestion.

The number of turns of the secondary winding will depend on the required maximum output voltage of the MT 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 received the maximum output voltage of the power supply unit of about 53 V. The wire cross-section will depend on the requirement for the maximum output current of the power supply unit, 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 sealed 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. After finishing the winding, the end of the second wire is sealed to the second terminal of the frame and a "pigtail" is formed 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 up the previously wound second part of the primary winding of the transformer, observing the original connection and the direction of winding, and assemble the magnetic core 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 performance.

ARCHIVE: Download

Section: [Power supplies (impulse)]
Save the article to: