The ability to turn off the SCR via a signal or using low-power switches can be important in many robotics and mechatronic projects. The block shown in Figure 1 can accomplish that.
The SCR is turned on by momentarily pressing S1 (Which can be replaced with any sensor). To turn off the circuit, it is sufficient to press SZ momentarily.
When SCR1 is on, the capacitor remains charged, since the side of SCR1 is at ground potential, and the side of SCR2 is at the positive voltage.
When S2 is pressed, SCR2 turns on, and the capacitor is discharged. The discharge current acts as a short between the anode and cathode of SCR1, turning it off. To turn it on, press S1. Now, SCR1 turns on, and the discharge current of C1 acts as a short for SCR2, turning it off.
The value of the capacitor depends on the application and, in general, is in the range between 1 and 10 µF. Polarized types need not be used for this function. The same principle used to turn off this circuit can be used in other blocks.
