Here is a very useful circuit suggested by ICOTRON (Siemens) capable of eliminating the two-voltage switch that many devices operating on the 110 V and 220 V network have. Avoiding connection errors, which can cause the equipment to burn, this circuit automatically switches the voltage. If the 110 V device is plugged into a 220 V outlet, the voltage is automatically switched to 110 V. The base of the circuit is the integrated TLB3102 and the system can only operate on resistive circuits or universal type motors. To adjust the device, a 60 W x 220 V lamp is placed at the output as RL and the circuit is connected to 220 V. The trimmer P1 is then adjusted to have a voltage of 110 V dc RMS in the load. The voltmeter used to measure this output voltage must be of the “True RMS” scale type, as the waveform found there is not pure sinusoidal, and the common multimeters have voltage scales only for sinusoidal forms in alternating values. The circuit in dotted lines is for an option of shutdown by temperature, which can be used in appliances such as hair dryers, etc. The use of an NTC allows a maximum operating temperature to be programmed when the load is then disconnected. Trigger pulses will only be released when the device has cooled down enough to do so.
