Time relay on thyristors. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches
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The device, the scheme of which is shown in the figure, ensures that the load is turned off after a strictly defined period of time after it is turned on.
The device is turned on by a pulse applied to its input. In the initial state, in the absence of an input signal, the thyristor D1 is closed and, therefore, the current does not flow through the load. Capacitor C2 through resistors R3 - R4 is charged to the breakdown voltage of the zener diode D4. At the same time, thyristor D3 opens and shunts its control circuit. Capacitor C1 is charged to the voltage of the power source. In this state, the device can be indefinitely long.
When a pulse is received at the input, the thyristor D1 opens, connecting the load to the power source. Capacitor C1 is recharged through an open thyristor D1, thyristor D2 is turned off at the moment of discharge of capacitor C1. After the thyristor D2 closes, the capacitor C1 starts charging again. As soon as the voltage on it exceeds the breakdown voltage of the zener diode D4, the thyristor D3 opens and the capacitor C1 is discharged through it. Thyristor D1 turns off and the device returns to its original state.
Thus, the time during which the load is turned on is determined by the charge time of the capacitor C2 to the breakdown voltage of the Zener diode D4.
Diode D3 provides a quick discharge of capacitor C2 when thyristor D2 is opened. Zener diode D5 stabilizes the supply voltage of the timing circuit.
When using the elements indicated in the schematic diagram, the device provides an exposure of about 1 s.
In the time relay, you can use any low-voltage thyristors, two D810 (D5) zener diodes connected in series and a KS168A (D4) zener diode.
Since the polarity of the voltage across the capacitor C1 changes during operation, a paper capacitor should be used as the latter.
Literature
- "Popular Electronics" (USA). 1974. v.5. No. 4
Publication: N. Bolshakov, rf.atnn.ru
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