The circuit shown in Figure 1 can be used to control loads up to 3 A from such
low-current sensors as reed switches or home-made switches. It is a momentary control, since the load is on only during the time the sensor is open.
When the sensor is closed, we find a 1.25 V voltage in the output of the circuit. When the sensor is open, the voltage in the output rises to a value adjusted by P1. The LM350T can supply voltages up to 25 V. The input voltage must be at least 3 V higher than the desired in the output.
This circuit is recommended for applications where, in the low state (load off), the voltage can be as low as 1.25 V). If a zero-volt output is desired, a negative voltage of 1.25 V must be applied to the sensor instead to shunt it to ground. The LM350 must be mounted on a heat sink.
