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Pc817 optocoupler amd igbt high side switching decay
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elektronJack:
In the attached circuit I get the result that the globe initially lights brightly then after1-3 seconds  the brightness diminishes in a 0.5 -1sec pulsating manner until eventually there is no light emitted. If I switch it off then on again it will pulsate immediately until nil emission. The igbt also gets quite hot.  Without the pc187 the light emits continously with no diminishing.
Any suggestions on how to overcome this problem is appreciated.
I have attached a slightly altered schematic showing a resistor and an LED connected to the pc817.
ledtester:
How much current is going through pins 1 and 2 of the PC817? That's the opto-coupler's LED, and usually a resistor is used to limit the current to around 10 mA. More than 50 mA for an extended period of time can burn it out.

Also, you usually want a resistor between the IGBT gate and emitter - otherwise it can stay on. This video explains why and also has some other good info on using IGBTs:



Update: Also try putting your load on the high side of the IGBT - i.e. between Vcc and C.


krish2487:
You need a high side driver. I am assuming the output side of the PC817 which is pulled up through the resistor is a seperate isolated supply from the rest of the circuit?


Also, are you trying to run the IGBT in a linear mode or switching it?
If you are trying to run the IGBT in a linear mode then it will get hot and burn out.


And what is the supply voltage on the Collector of the IGBT?


IGBTs are  most useful at high-ish voltages... they suck for low to medium voltages. :-)
T3sl4co1l:
It's only getting 3V Vgs(on), which isn't enough.  Get rid of R1.

The supplies are specified differentially, but are they really isolated?  Voo has to be isolated.

Are they really constant-voltage supplies?  Is the voltage drooping under load or anything?

There's no current limiting resistor on the LED?

Tim
elektronJack:
Why dispose of R1?
The supply Voo is isolated as i understand "isolated ".If I'm incorrect can u enlighten me?
I have measured Voo when the circuit is operating and  there is no v droop.
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