IGBT use in dimmer

Discussion in 'The Projects Forum' started by surpriya_7, Dec 19, 2008.

  1. surpriya_7

    Thread Starter New Member

    Jun 16, 2008
    Hello All,

    I am currently working on a bulb dimmer controlled by PWM- 0 to 80pc duty cycle. I am using STGP20NC60V. My load is a 60W incadescent bulb. My problem is that the Vge remains good 12V upto 70pc but drops to 6-5V sharp when run at 80pc. The other issue is that the IGBT when continuously kept on a run at 80pc cycle, gets damaged after a couple of hours.
    Im not sure if the two problems are related or not.

    Please help. Thanks.
  2. eblc1388

    Senior Member

    Nov 28, 2008
    Your 12V power supply capacitor can only charges up if there is voltage present after the bridge rectifier. Voltage is NOT there if the IGBT fires.

    If the IGBT is firing at high percentage, then there is very little cycle time left for the capacitor to charge via 100K+1N4007 so the capacitor voltage and ultimately the IGBT drive voltage drops.

    You need to consider another method to get a stable 12V supply, either by decreasing the value of the 100KΩ resistor and possibly increase the rating of the zener diode. Or you can also use a higher voltage zener diode but add a 12V voltage regulator to get a stable 12V. Either way, same amount of heat will be generated(wasted).

    To prove that this is really the case, change your 100K before the 1N4007 into 47K and see if the circuit works better at 80%.

    If the IGBT's drive is not sufficient, it will become hot and might be damaged after a long duration.