Adjustable current stabilizer, 16 volts 7 amps. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Adjustable current stabilizer, 16 volts 7 amps. 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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When charging car batteries, it is recommended to maintain the average charging current at a constant level. Usually, in current stabilizers, a transistor is used as a regulating element.

In the process of operation, a lot of power is dissipated on it, and in connection with this, bulky heat sinks have to be used. The efficiency of such devices is very low.

A similar device with higher efficiency is described below.

The schematic diagram of the device is shown in fig. 2.68, and time diagrams at its characteristic points - in fig. 2.67.

Adjustable current stabilizer, 16 volts 7 amps
Fig. 2.67

Rice. 2.68 (click to enlarge)

Main technical characteristics.

maximum load current, A ..... 7;
maximum load voltage, V.....16;
load current stabilization coefficient, not less than ..... 200;
Efficiency, %, not less than.....70.

A sawtooth voltage generator is assembled on the transistor VT2.

Through resistor R3, an opening voltage is applied to the base of transistor VT2 (diagram A), and through resistor R2, a closing pulsating voltage (B) is supplied from a full-wave rectifier on diodes VD5 - VD8. The total voltage at the base of the transistor VT2 is shown by a dashed line (B). Diode VD11 limits the amplitude of the closing voltage.

The resistance of resistors R2 and R3 is chosen such that the transistor is closed most of the time. Capacitor C4 is charged through resistor R5. But at the moment the mains voltage approaches zero, the transistor VT2 opens, discharging the capacitor C4.

A voltage close in shape to a sawtooth is formed on the collector of the transistor (diagram B). Through resistor R6, it enters one input of a differential amplifier assembled on transistors VT4, VT5, and voltage (G) is applied to the other input from the output of the operational amplifier DA1, which depends on the position of the resistor R14 slider.

As soon as the voltage values on the basis of transistors VT4 and VT5 are equal, the transistor VT4 will open. Following it, the transistor VT3 will open and form a current pulse (D) that opens the thyristor VS1. From this moment of the half-cycle, the rectified voltage will be supplied to the load from the 1U winding of the transformer T1 (diagram E). The higher the voltage at the base of the transistor VT5, the later pulses will appear that open the trinistor, and the lower the average current through the load.

The current stabilization function is performed by the node on the operational amplifier DA1. The current sensor is resistor R12. The voltage taken from this resistor is proportional to the load current. Through the resistor R16, it is connected to the non-inverting input DA1.

If for some reason the current through the load has increased, then the voltage at the non-inverting input of the operational amplifier DA1 also increases. This leads to a corresponding increase in voltage at the base of the transistor VT5 and an increase in the opening angle of the thyristor VS1 - the current through the load decreases. Thus, negative feedback on the load current maintains the load current at a given level.

Capacitors C5, C7 smooth out the voltage ripple at the output. Resistors R11, R15 provide a small negative voltage to the inverting input of the op-amp in the lower position of the resistor R14 engine according to the diagram. This allows you to adjust the load current almost from zero.

Capacitor C6 increases the stability of the operational amplifier. The elements of the device are powered by two stabilizers (VD9, VD1 and VD12, R4).

Adjustment

To establish the device, a wire resistor with a resistance of 1 - 2 ohms and a power of at least 100 W is connected to its output (nichrome wire with a diameter of 0,5 - 1 mm can be used).

The engine of the variable resistor R14 is set to the upper position according to the diagram and the current through the load of 13 A is set by selecting the resistor R7. When the knob of the variable resistor is rotated, the current should gradually decrease to zero.

In some cases, it is required to install an additional resistor R18 and select resistors R3 and R5. Resistor R3 regulates the delay time between the beginning and end of the signal (see diagram B in Fig. 1.1), R5 regulates the slope of the rise and fall of the signal (the resistance range, when adjusted, lies within 2,7 kOhm + 27 kOhm).

Whether a large current will stabilize depends on the amplitude of the signal based on VT1.

Details

Transformer T1 is made on a ribbon magnetic circuit ShL25X32.

Winding I contains 1100 turns of wire PEV-2 0,57; Winding II - 160 turns of wire PEV-2 0,21 with a tap from the middle; Winding III - 120 turns of wire PEV-2 1,95.

The operational amplifier K140UD1B can be replaced by K140UD5, K140UD6, K140UD7, K153UD2 (with the appropriate correction circuit). Transistor KT801B - is replaced by any of the series KT603, KT608 KT801, KT807, KT815; KT315V - on KT312, KT315, KT316, KT201; KT814B - on KT814, KT208.

Capacitors C1, C2, C3, C5, C7 - type K50-6 or K50-3; C4, C6 - KM-b or K10-7v, KLS. Resistor R12 is formed by two 5 ohm resistors C16-0,1B connected in parallel.

Ammeter RA1 - M5-2 with a full deflection current of the needle 10 A.

Diodes VD1 - VD4 - can be replaced with any of the D242 - D248 series, but in this case the power dissipated on each diode will increase and the dimensions of the body taps will have to be increased. Diodes VD1 - VD4 are installed on heat sinks with an area of 30 - 40 cm2 each.

Thyristor VS1 is installed on a heat sink with an area of at least 100 cm!

Author: Shelestov I.P.

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Comments on the article:

s.zbroy
Great scheme, works well. Made a few pieces - for myself and friends. The first publications of this scheme were in 85-89.

Arthur
Many inaccuracies, for example: an error connecting R1, instead of an emitter to a collector.

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