Static Circuit Breaker / RFI Eliminator

This is the circuit diagram of Static Circuit Breaker.  Many a times you must have heard an undesired sharp sound emanating from the speaker, when any power appliance, like an electric iron, is switched ON of OFF. This problem is known as the Radio Frequency Interference (RFI). Some of the musical light, models, which employ SCR’s, also generate RFI. Therefore one finds it difficult to use the music lights and the sound equipment simultaneously. The rate of RFI depends upon the amount of current and the rate of switching. By using this gadget (Static Circuit Breaker), the RFI can be minimized, if not completely eliminated.

This is the circuit diagram of the Radio Frequency Interference (RFI) eliminator:

Components List:

SCR       : 600 PIV with current rating depending upon load (2x)
Diode     : BY127 (2x)
Resistor  : 1K (x2) ; 3.3K
Swirch    : General purpose switch

The two SCR’s (Silicon Controlled Rectifier), SCR1 and SCR2 are connected, such that, a complete AC cycle can pass through the load. When the switch S is closed, SCR1 fires at the start of the positive half cycle, and it then switches OFF when the current goes down to zero. At this stage SCR2 becomes forward biased and at the same time receives a sufficient gate current, which result in the firing of SCR2. Thus during the positive half cycle, SCR1 conducts and during the negative half cycle, SCR2 conducts. To break the circuit i.e to stop the flow of current through load, switch S is opened. Now since the current through the switch S is small (gate current), opening of the gate circuit results in the minimizing of RFI.

However, one may use only one SCR if one half of cycle is required.