Laboratory power supply 3-30 volts 1 ampere on the K143EN3A chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies
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My working "laboratory" power supply has been serving for over 20 years. Having repeatedly repaired it after extreme loads, I came to the conclusion that adjustable current protection is necessary. About 5 years ago, I developed a power supply circuit on the K142ENZA chip, and since then I forgot about repairing it. The proposed scheme of the power supply unit (PSU) can serve as a laboratory voltage source with voltage regulation limits of 3 ... 30 V, and a charger with regulation of the battery charge current (AB).
Rice. 1. PSU schematic diagram
The K142ENZA chip is an adjustable voltage regulator with an overcurrent protection system and allows you to get an output voltage of 3 to 30 V at a load current of up to 1 A. By supplementing it with a power amplifier based on a VT1 transistor and an adjustable current protection circuit, we get a universal reliable PSU.
Transistor VT1 is an "amplifier" of the output transistor of the microcircuit and allows you to get an output current of up to 15 A with a power dissipated on it up to 100 watts. To do this, it is installed on a radiator with an area of at least 200 cm2 with good ventilation. Forced blowing by the fan is desirable.
The current control circuit works as follows. When current flows through resistor R2, the voltage drop across it through the voltage divider R3-R4 and the emitter follower VT2 affects the input of the protection circuit DA1. Resistor R3 limits the maximum protection operation current. Decreasing R3, we increase the maximum value of the current at which the protection is triggered. Resistor R4 sets the protection operation limit.
If the power supply unit is proposed to be used as a laboratory one, it is advisable to select an input voltage of about 40 V. At the same time, the voltage adjustment range at the output of the power supply unit is from 3 to 30 V. It should be borne in mind that at high load currents and low output voltage, power equal to :
Рр = (Uvh - ORO) I.н (W)
Therefore, if there is no need for high output voltages, it is desirable to reduce the input voltage to 20 ... 25 V.
The output voltage is controlled by a voltmeter. To control the current, you can turn on the ammeter. Resistor R4 should be equipped with a scale calibrated from the minimum protection operation current (I have 20 mA) to the maximum. As R4, you can use a multi-turn, or any other resistor with a vernier device.
When charging the battery, the procedure is as follows:
- engines of resistors R4 and R5 are set to a minimum;
- AB is connected according to polarity;
- the power is turned on;
- the voltage regulator (R5) sets the maximum value. There is no current;
- the current regulator (R4) smoothly increases the current to the required value;
- the voltage regulator is brought to a minimum until the current begins to decrease;
- the required charging current is finally set by the voltage regulator.
If this PSU is equipped with a timer that turns it off after the time required to charge the battery, then you get an automatic charger.
Author: K. Selyugin, Novorossiysk; Publication: cxem.net
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