Charger on a thyristor inverter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Charger on a thyristor inverter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells

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High-frequency thyristors, previously used in television scanners, can also be successfully used in thyristor inverters. The thyristor works like a key and has two stable states: open (conductive) and closed. To open the thyristor, a positive (relative to the cathode) voltage is applied to the control electrode (GE) (a short pulse is enough), which ensures the flow of a triggering current in the UE circuit. In this case, the current through the thyristor must exceed the holding current, otherwise the thyristor will return to the closed state after the control voltage is removed.

If the current exceeds the holding current, the thyristor remains open even after the UE is de-energized. It can be closed only by lowering the current below the holding current.

At high forward voltage slew rates, the thyristor can go into the open state even in the absence of a control signal. To reduce the rate of rise of the anode voltage, additional RC elements are used. In the proposed charger, built according to the high-frequency inverter circuit, a KU221A thyristor is used as a switching element.

The charger circuit consists of:

generator on the analog timer DA1;
emitter follower on the transistor VT1, matching the output resistance of the timer with the control input of the thyristor VS1;
thyristor inverter VS1 with switching circuits;
power rectifier bridge of the VD10 inverter;
transformerless power supply with ballast capacitor C11-VD9-C5;
voltage stabilizer DA2-VD3;
rectifier and output circuit filter VD8-С8-L-1;
output voltage stabilization circuits VU1-VD5-R9-R10;
temperature sensor RT1.

(click to enlarge)

The generator with adjustable duty cycle of pulses is made on the integrated timer DA1. To operate the circuit in the oscillator mode, pins 6 and 2 are interconnected and connected to capacitor C1.

The charge of the capacitor C1 occurs along the circuit R1-VD1-R2-C1, the discharge - along the circuit DA1 (pin 7) - R3-VD2-R2-C1. The charge time can be determined by the approximate formula t1=0,639(R1+R2)C1, the discharge time - t2=0,639(R2+R3)C1.

While the capacitor C1 is charging (up to a voltage of 2/3 Upit), output 3 of DA1 is high, then the internal trigger of the microcircuit switches, and a low level appears at output 3. The open internal transistor of the microcircuit discharges the capacitor C1 (up to a voltage of 1/3 Upit), and the charge cycle is switched on again. As a result, at the output of the timer, a continuous sequence of rectangular pulses is obtained, which are fed through the resistor R4 to the input of the emitter follower VT1. From its load R7, pulses (in the same polarity) arrive at the control electrode of the thyristor VS1 and open it. The thyristor is shunted with a parallel circuit R11-C6-VD7, which allows to extend the turn-on time.

The thyristor closes in the absence of control current, when the voltage across the resistor R13 in the circuit of its anode drops, the capacitor C9 is discharged to feed the current of the winding of the transformer T1, and the current VS1 becomes less than the holding current. To reduce the effect of the control current on the control electrode VS1, a small negative voltage is applied from the resistor R8 in the cathode circuit. Zener diode VD4 limits the reverse voltage pulse.

The mains power of the inverter is supplied from the VD10 diode bridge. Capacitor C10 performs the preparation of the operating voltage of the inverter and filters possible interference from the operation of the thyristor VS1. The energy recovery circuit of the reverse pulse of the winding of the transformer T1 is made on the VD6-R12-C7 chain. The elements of protection and switching are made on the fuse FU1 and the mains switch SA1.

Stabilization of the output voltage is carried out using a feedback circuit through the optocoupler VU1 to the control input (pin 5) DA1. With an increase in the load voltage (for example, due to an increase in its resistance), the LED turns on and the phototransistor of the optocoupler opens. The opening threshold VU1 is set by the regulator R10. The opened phototransistor shunts the control input DA5 through the resistor R1, thereby reducing the duration of the output pulses of the microcircuit (without changing the duration of the pauses), the thyristor opens for a shorter time, and the load voltage decreases. When the load voltage decreases, these processes occur in reverse. The temperature sensor RT1 in the feedback circuit allows, with an increase in the temperature of the thyristor VS1 radiator, to reduce the power in the load.

The timer chip and emitter follower are powered by an analog stabilizer DA2. The diode bridge VD9 is connected to the mains through the ballast capacitor C11, the reduced voltage after smoothing by the capacitor C5 is supplied to DA2.

The radio components used in the thyristor inverter can be replaced with similar ones indicated in the table. The power pulse transformer in the circuit is selected based on the operating frequency of the inverter and the load power. Its overall power should slightly exceed the load power (taking into account losses). It is quite difficult to make a home-made transformer at a good level, it is easier to pick up a ready-made one. Pulse transformers from computer power supplies are well suited. For analysis, one of the available transformers was dismantled. It turned out that its primary winding contains 42 turns of PEL-type wire 0,63 mm laid in two layers. The low-voltage winding is made of 2 wires 00,8 mm and contains 6 + 6 turns (with an average output). In this device, you can also use transformers from imported TV power supplies.

Adjustment. After assembling the circuit, a thorough check of the power circuits for short circuits is carried out. Instead of fuse FU1, a 220 V, 100 W light bulb is temporarily turned on, and mains voltage is applied. If the bulb lights up almost to full brightness, then there is a malfunction in the circuit. When the light bulb is lit with a weak glow, a 12 V, 50 W car light bulb can be connected to the output instead of a load. The glow of the light bulb indicates the correct operation of the circuit.

The duty cycle regulators R2 and the feedback value R10 achieve the highest brightness of the light bulb in the secondary circuit (with output voltage control). After adjusting the circuit, the fuse is put in place. After a short period of time, the device is turned off and the temperature of the radio elements is monitored. In case of overheating, increase the size of the radiators or additionally install a fan from the computer

When charging, a 4-volt car battery with a capacity of 2 ... 12 Ah is connected to the output terminals in the appropriate polarity with a wire with a cross section of at least 10 mm100. With the charge current regulator R2, a current of 0,02 C is set by the ammeter (C is the battery capacity). Charging time is 5...6 hours.

Authors: V.Konovalov, A.Vanteev, Creative Laboratory "Automation and Telemechanics", Irkutsk Center "Energy Saving Technologies", Irkutsk

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