Here is the very popular electronics ballast.
Tuesday, December 2, 2008
The given circuit is based on popular PWM control circuit TL494. The beauty of the circuit lies in the free self start like using self oscillation and secondly the prepotional base drive to transistors. Magnetic amplifier is used in one out put for cross regulation.
This is a simple three phase sine wave generator circuit using switched capacitor filter. The input to switched capacitor filter is three phase square wave which is generated using flip flop logic driven by a ring counter. The input of ring counter is given by a PLL which is used for frequency and phase Synchrnisation. There is a feed back for controlling output ampliude by controlling square wave amplitude to switched capacitor filter.
Controll circuits implemented here is same as popular IC UC3875. Feed back is provided for both current and voltage for constant current current constant voltage application. Isolated outputs are provided using pulse transformer for driving MOSFET or IGBT. Fault current trip is also provided for protection appart from constant current limitting