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Thyristor
Latch |
How the circuit works: The latching circuit uses a Thyristor / Silicon Controlled
Rectifier (SCR), to keep an output turned on after an input signal has
triggered the device. When a positive going voltage is briefly applied
to the input of the circuit, a current will start flowing into the Gate
(G) of the Thyristor and this triggers the device to turn on
permanently. So when the input is removed, the output will still remain switched on.
To reset the circuit, the power supply to the device needs to be removed or an open-circuit applied across its output, to prevent current flowing into the Anode (see OP1).
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Circuit Diagram
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Avoiding Problems: Comparing The Thyristor with the Transistor: The Thyristor is connected in a similar way to the transistor ( see P1 and P5). The input to the device is the Gate (equivalent to the Base), the output is connected to the Anode (equivalent to the Collector) and the Cathode is connected down to the negative power rail (like the Emitter).
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