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AC Power Control Circuits / Schematics

AC Line Powered LED Strings -This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line.  The circuit was designed by Ken Schultz

The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load. Published in Electronic Design, Nov. 8, 1990.

This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR, the circuit can control about 600 watts of power to load while providing full isolation and transient protection. Published in Electronic Design, Dec 2, 1996.

Circuit level shifts ac signals: AC signals can emanate from many sources, and many of these sources are incompatible with the most popular interface voltages, such as TTL. A temptation always exists to coactively couple the ac signals because capacitive coupling strips off the dc level. Capacitive coupling sometimes doesn't work, because the coupled signal's voltage swings around ground, so you have to add dc offset to make....

Why limit your power supply's input range?: EDN-Design Ideas /  Taking only a cursory look at the input-voltage ratings of your power-supply IC can limit the usable input-voltage range. With careful examination of an IC's operating specifications and circuit topology, you may be able to work around that input-voltage limitation.

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