Alternating ON-OFF Switch, #2
Parts List
Resistors are 1/4 Watt, 5%
R3,R5,R6 = 1K (brown-black-red) R1,R7 = 2K7 (red-violet-red) R4 = 100K (brown-black-yellow) R2 = 180K (brown-gray-yellow) C1 = 10uF/16V, electrolytic C2 = 220uF/16V, electrolytic C3 = 1uF/16V, electrolytic D1 = 1N4148 Led1 = Led, red Q1,Q2 = BC557B (or 2N3906) Q3 = BC337-40 (or 2N3904) S1 = Momentary on-switch Ry1 = Relay (see text)
Description:
This circuit is the transistor version of the 4069 cmos type. Every press of the push-button will activate or
de-activate the relay.
On power-up, the voltage on the base of Q1 and Q2 is equal with the supply voltage. The base of Q3 is at ground
potential. So, all three transistors are blocking. Relay Ry1 not energized and the Led is off.
Pressing momentary switch S1, Q2 is biased. After a small delay, caused by capacitor C1, Q3 is also biased. The
collector of Q3 is now put to ground potential, which causes relay Ry1 to energize and light the led at the same time.
At this time Q1 is biased and the circuit stabilized, because the base of Q2 is now connected to ground potential via R1.
This keeps Q2 biased when S1 is released (like a latch). C1 is recharged via R3, close to the supply voltage.
If S1 is pressed again, Q2's base gets biased with a positive voltage instead of being put to ground potential. Q2 will
block and the whole sequence will repeat itself. This circuit works like a thyristor. In fact, Q2 and Q3 are together
a discrete thyristor.
This circuit can be used in many applications by selecting different relays.
The coil of Ry1 should be capable of handling 5 to 12V at 250mA maximum or Q3 will go up in smoke!
The prototype used 70mA and less than 0.1uA when idle.
Labels: All, Other
Parts List
Resistors are 1/4 Watt, 5%
R3,R5,R6 = 1K (brown-black-red) R1,R7 = 2K7 (red-violet-red) R4 = 100K (brown-black-yellow) R2 = 180K (brown-gray-yellow) C1 = 10uF/16V, electrolytic C2 = 220uF/16V, electrolytic C3 = 1uF/16V, electrolytic D1 = 1N4148 Led1 = Led, red Q1,Q2 = BC557B (or 2N3906) Q3 = BC337-40 (or 2N3904) S1 = Momentary on-switch Ry1 = Relay (see text)
Description:
This circuit is the transistor version of the 4069 cmos type. Every press of the push-button will activate or
de-activate the relay.
On power-up, the voltage on the base of Q1 and Q2 is equal with the supply voltage. The base of Q3 is at ground
potential. So, all three transistors are blocking. Relay Ry1 not energized and the Led is off.
Pressing momentary switch S1, Q2 is biased. After a small delay, caused by capacitor C1, Q3 is also biased. The
collector of Q3 is now put to ground potential, which causes relay Ry1 to energize and light the led at the same time.
At this time Q1 is biased and the circuit stabilized, because the base of Q2 is now connected to ground potential via R1.
This keeps Q2 biased when S1 is released (like a latch). C1 is recharged via R3, close to the supply voltage.
If S1 is pressed again, Q2's base gets biased with a positive voltage instead of being put to ground potential. Q2 will
block and the whole sequence will repeat itself. This circuit works like a thyristor. In fact, Q2 and Q3 are together
a discrete thyristor.
This circuit can be used in many applications by selecting different relays.
The coil of Ry1 should be capable of handling 5 to 12V at 250mA maximum or Q3 will go up in smoke!
The prototype used 70mA and less than 0.1uA when idle.
Labels: All, Other
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