The presented circuit has been taken from an old elektor electronic magazine which describes a neat little circuit for converting 220V mains input to 110V AC. Let's learn more about the circuit details.
The shown circuit diagram of a transformerless 220v to 110v converter utilizes a triac and a thyristor arrangement for making the circuit successfully work as a 220v to 110v converter.
The right end of the circuit consists of a triac switching configuration where the triac becomes the main switching element.
The resistors and the capacitors around the triac is kept for presenting perfect driving parameters to the triac.
The left section of the diagram shows another switching circuit which is used to control the switching of the right hand side triac and consequently the load.
The transistors at the extreme right of the diagram are simply there to trigger the SCR Th1 at the right moment.
The supply to the entire circuit is applied across the terminals K1, via the load RL1 which is in fact a 110V specified load.
Initially the half wave DC derived through the bridge network compels the triac to conduct the full 220V across the load.
However in the course, the bridge starts getting activated causing an appropriate level of voltage to reach the right hand section of the configuration.
The DC thus generated instantly activates the transistors which in turn activates the SCR Th1.
This causes short circuiting of the bridge output, choking the entire trigger voltage to the triac, which finally ceases to conduct, switching off itself and the entire circuit.
The above situation reverts and restores the original state of the circuit and initiates a fresh cycle and the system repeats, resulting in a controlled voltage across the load and itself.
The transistors configuration components are so selected that the triac is never allowed to reach above the 110V mark thus keeping the load voltage well within the intended limits.
The shown "REMOTE" points must be kept joined normally.
The circuit is recommended for operating resistive loads only, rated at 110V, below 200 watts.