A Chopper is a (static) device, used to obtain variable DC Voltage from a constant voltage source. The variable DC is obtained by ON / OFF operation of chopping device, which can be treated as switch. This device (Chopper) is triggered (Gated) periodically and is kept conducting for a period Ton, and is kept off for a period Toff. Therefore output at load side is pulsating (generally rectangular wave) DC voltage, which is equal to VL = Vs {Ton / {Ton + Toff)} where Vs is input source voltages.
The MOSFET, is such a device, which can be used for this operation successfully, as this diode not required commutation circuitry. In present set – up, a DC series wound motor (1/12 HP) used as load, and to control the speed MOSFET chopper is used. The set – up has builtin gate drive circuit with pulse generator, regulated DC supply and sockets given to observe / measure the waveforms / voltages.
1.1 THE D.C. SUPPLY :
A regulated DC voltage obtained by thyristor half controlled bridge rectifier, which is smoothed by capacitive filter. The controlled rectifier is in close loop to obtain DC voltage about 150 ± 5 Volt D.C.
1.2 THE GATE DRIVE SIGNAL GENERATOR :
In present type of control straregy, the on time (Ton) period is varied, but the total period T (/ton + Toff) is kept constant. A ramp generator produce/
EXPERIMENTS :
- To study MOSFET Chopper operation.
ACCESSORIES REQUIRED :
- Digital Multimeter.
- Dual Trace, Oscilloscope.
- D.C. Motor Unit, Capacity : 1 HP.
There may be any change in specification due to continuous R & D without notice.
