Phase power regulator. Encyclopedia of radio electronics and electrical engineering

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

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Many schemes have been created to adjust the power, but radio amateurs continue to experiment in search of the optimal one. The existing schemes for phase power control, although they attract with their simplicity, have one significant drawback - when the mains voltage changes, you have to re-select the triac control mode for a given power. In addition, you must admit, it is inconvenient to regulate the power with a potentiometer, especially if you have to periodically return to previously set modes.

The proposed scheme (Fig. 1) is based on the principle of phase power control in the load in a discrete way. Consider the operation of the circuit when the switch SA1 is set to position 10.

Fig.1. Schematic diagram of the power regulator

The mains voltage of 50 Hz (Fig. 2a) through the limiting resistor R1 is supplied to the diode bridge VD1 ... VD4, rectified, while the pulse frequency doubles (Fig. 2b) Clock pulses limited by resistors R4, R5 are input (pin 1) DD1.1. At the initial time, the input 1 of the DD1.1 microcircuit is logical "0", as a result, the output 3 DD1.1 will be a logical "1" (Fig. 2c), which will start the generator on the elements DD1.3, DD1.4. The generator is tuned to a frequency of 1000 Hz. When connected to the network, pulses with a frequency of 100 Hz, passing through the diode VD9, charge the capacitor C3. At this moment, the counter DD2 is reset. At the same time, capacitor C2 is charged, the voltage from which, limited by the Zener diode VD10, serves to power the microcircuits.

Fig.2. Stress graphs

Pulses from the generator fill the counter DD2. After the 10th pulse, a logical "9" appears at the output of Q2 DD1 (Fig. 2d), which, through the resistor R8, opens the transistor VT1, which switches the optodistor VU1. The latter, through the diode bridge VD5 ... VD8, turns on the triac VS1. In this case, the power in the load will be minimal, since the triac opens at the end of the half-cycle of the mains voltage (Fig. 2e).

Simultaneously with the opening of VT1, the RS-trigger DD1, DD1.1 is reset through the capacitor C1.2, and the counter DD9 is reset through the resistor R2. The duration of the reset and opening pulses of the triac depend on the ratings of R9, R11, C3.

If the switch SA1 is set to position 1, then the triac opens at the first pulse coming from the generator to the input of the counter DD2 (Fig. 2f). In this case, the power released in the load will be maximum.

The above circuit contains one switch and one counter, so the power switching resolution is approximately 10%. For a smoother change in power (reducing the resolution of adjustment), it is necessary to install additional counters and switches. All counter reset inputs are combined, from the output of the first switch, the signal is sent to the clock input (input C) of the second counter, etc. Resistors R8, R9 are connected to the last switch. It is also necessary to increase the filling frequency of the counters (2, 3, 4 kHz, etc.).

The power setting accuracy depends mainly on the frequency drift of the generator. If greater accuracy is needed, I recommend using a crystal clock generator, shown in Fig. 3. Of course, the variation in power adjustment due to the instability of the network both in voltage and in frequency remains.

Fig.3. Clock generator

The device is assembled on a printed circuit board with dimensions of 55x80 mm (Fig. 4). All parts, except for the SA1 switch, are located on the board. SA1 is mounted on the front panel of the device. The cable connecting the switch to the board must be no more than 25 cm.

Fig.4. Regulator printed circuit board

Details. The triac in this device can be used any. It only depends on the adjustable power. Zener diode VD10 - any with a stabilization voltage of 9 ... 15 V. Microcircuits of the 561 series can be replaced with the 176th. Then you need a zener diode with a stabilization voltage of 9 V. It is desirable to use capacitor C4 with the smallest temperature drift. Transistor VT1 is replaced by any of the KT315, KT3102 series. Diodes VD1 ... VD9 - with a maximum reverse voltage of 300 V and a current of 100 ... 300 mA. SA1 - any for 10 positions and one direction.

The regulator was also successfully tested with TO125-12,5 optothyristors. The LEDs of the optothyristors were connected in series, and the output thyristors were connected in anti-parallel. The value of the resistor R6 was reduced to 220 ohms.

Author: S. Abramov, Orenburg, asmoren@mail.ru; Publication: radioradar.net

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