When S1 is momentarily closed, the SCR turns on and remains on even when S1 is released. To turn off the circuit, it is necessary to momentarily close S2.
Observe that the tum-on current is very low (determined by R1), but the tum-off current is high (the nominal current of the load). This fact must be considered when using when choosing the appropriate switches.
The reader must consider the voltage drop of about 2 V in the SCR when it is on. The value of R1 and R2 depends on the SCR. The values given in the block are recommended for any SCR in the 106 series. The circuit can be powered with voltages in the range between 6 and 150 V (see the sufíix of the SCR).
The following table gives the recommended values for R1 and R2 according to the power supply voltage.
An interesting application for this circuit is as a one-bit memory. An incandescent lamp is used as load. If the sensor is ever closed, the lamp remains on, indicating the condition.
