Power regulator of wide application. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Power regulator of wide application. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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The author of the article claims that the electronic device proposed by him can be successfully used to regulate the operating temperature of the tip of an electric soldering iron, electric stove, electric furnace and other similar loads with high thermal inertia.

The proposed device differs from similar power regulators described earlier in "Radio" by the simplicity of controlling trinistors that switch loads operating in intermittent mode. This mode is characterized by the fact that the duration of the control cycle is constant, and the duration of the load and pause changes or, in other words, the duty cycle changes - the ratio of the load on time to the duration of the control cycle. In the variant of the controller in question, the cycle time is chosen to be 45 s, and the range of smooth power control in the load is from 5 to 95%. The maximum load power is 2 kW.

The power regulator (Fig. 1) consists of a symmetrical multivibrator on transistors VT2 - VT5, a multivibrator current amplifier on a VT1 transistor, an electromagnetic relay K1 and trinistors VS1 and VS2, which act as electronic switches. The resistor R13 changes the duty cycle of the control pulses on the collector of the transistor VT2, and, consequently, the power in the load connected to the X1 connector. In this case, the repetition period of the multivibrator pulses changes insignificantly. Resistors R12 and R14 limit the current in the base circuits of transistors VT3, VT4 at the extreme positions of the variable resistor R13 engine.

(click to enlarge)

The diode bridge VD3, the resistor R7, which dampens the excess voltage of the network, the capacitor C3, which smoothes the ripple of the rectified voltage, is a transformerless power supply of the device. Zener diode VD4 limits the voltage at the output of the rectifier to 25 ... 28 V, when the transistor VT1 is closed and relay K1 in its collector circuit is de-energized.

Load switching is carried out by contacts K1.1 and K1.2 of relay K1 in the trigger circuits of trinistors VS1, VS2. The trigger node of the trinistor VS1 is formed by the contacts K1.1 of the relay, the resistor R3, the capacitor C1, the dynistor VD1 and the resistors R2, R1, and the trigger node of the trinistor VS2 is formed by the contacts K1.2, the resistor R4, the capacitor C2, the dinistor VD2 and the resistors R5, R6.

When the relay winding is de-energized and contacts K1.1 and K1.2 are open, both trinistors are in the closed state and the power in the load is zero. When the control pulse opens the transistor VT1, the relay K1 is activated and the closed contacts K1.1 and K1.2 turn on the trigger circuits of the trinistors. From this moment, the trinistor VS1 begins to pass a positive half-wave of the mains voltage, and VS2 - negative.

The trinistor VS1 opens with a pulse of the discharge current of the capacitor C1, supplied to its control electrode through the dinistor VD1. The capacitor C1 is charged by the mains voltage through the resistor R3 until the dinistor is turned on. Resistor R2 - current-limiting. Resistor R1 is necessary for reliable closing of the trinistor VS1. As long as the SCR is open, the voltage drop across it has no effect on the start circuit until the end of the mains voltage half cycle.

The trinistor VS2 works similarly, but with a negative half-wave of the mains voltage. And since the turn-on voltage of the VD1 dinistor is approximately 20 V, the load is switched at the same voltage with a low level of interference that does not significantly affect the operation of other electrical appliances powered by the same AC network. When the transistor VT1 is closed, the relay winding K1 is de-energized, the contacts K1.1 and K1.2 open and the load is disconnected from the network.

With the arrival of the next control pulse of the multivibrator at the base VT1, the cycle of power control in the load is repeated.

The principle of operation of the regulator is illustrated by the timing diagrams shown in fig. 2. On it, diagrams a correspond to the minimum power mode, and diagrams b correspond to the maximum.

Power regulator for a wide range of applications

The details of the control unit are mounted on a printed circuit board with dimensions of 110x42 mm (Fig. 3), made of one-sided foil fiberglass. The rest - on a breadboard (the printed circuit board was not developed), the dimensions of which were dictated by the dimensions of the selected parts. Oxide capacitors - K50-6. Resistor R7 is composed of three PEV-10 or PEV-7,5 resistors connected in series with a resistance of 2,2 kOhm each. We will replace it with a capacitor with a capacity of 0,47 microfarads with a rated voltage of at least 400 V. In parallel with this capacitor, a resistor with a resistance of 510 kOhm 0,5 W should be connected, in series with a capacitor - 36 Ohms of the same power. Variable resistor R13 - SP-1 group A, the rest - MLT.

Power regulator for a wide range of applications

VT5 - any n-p-n silicon structures with a static base current transfer coefficient of at least 30. The VT1 transistor can be KT815 or KT817 with the letter index B - G. Instead of KU202N trinistors (VS1, VS2), KU202M, KU202K, KU202L are suitable. Relay K1 - RES47 for operation voltage 24 V.

Structurally, the regulator is made in a housing from a subscriber loudspeaker. Variable resistor R13 is installed in place of the volume control. If it is group A, then the power control scale is linear. SCRs VS1, VS2 and zener diode VD4 are mounted on finned heat sinks.

An unmistakably assembled regulator requires no adjustment. To check its performance, it is necessary to connect an incandescent lamp with a power of 1 ... 100 W to the X200 connector. The change in the duration of the glow of the lamp and the pause between its inclusions when the knob of the resistor R13 "Power" is rotated indicates the correct operation of the device.

For more than two years, the load of the described regulator has been an electric stove, in which the bimetallic heating temperature controller has failed. The average daily duration of operation is 3...4 hours. During the entire period of operation there was not a single failure, problems with the contacts of the bimetallic thermostat completely disappeared.

Author: Yu.Nigmatulin, Novopetropavlovskoye village, Kurgan region.

See other articles Section Power regulators, thermometers, heat stabilizers.

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