Igbt help needed..

[duffy]

The usual technique to pull up to a higher voltage than the 5V the microcontroller can supply is to drive an NPN transistor connected common-emitter (grounded emitter). The collector would be tied to a resistor that pulls up to the 15V. All the microcontroller sees is the base resistor and base-emitter drop voltage. You get your voltage off the collector, and drive it the opposite of how you normally would - a "1" out the port gives you 0V, a "0" gives you the 15V. You can add a cap to the collector and PWM it to get an intermediate voltage.

What is the size of the load on this thing - how many amps does it draw? Sounds like you want the IGBT to drop 120V of the 240V, in other words: you want it to work as a linear regulator. If the load is 1A, this means the IGBT will have to dissipate 120 watts. That's a LOT of heat to dissipate.

Additionally, IGBTs are the most non-linear drivers I've worked with. A fixed bias just isn't going to give you a reliable drop on anything more than a purely resistive load (and even that would be finicky). To get a stable voltage with a dynamic load you will need some sort of feedback from the output to hold the drop at 120V.

Would a low-tech solution like a variac work?

 

[johansen]

Im trying to use igbt as switch. In the same time, i want to reduce the voltage of Vce according to voltage of Vg. Means that, when Vg=ov, Vce=240vDc, when Vg=15v, Vce=120v. Problem now is, the voltage from microcontroller only can supply 0-5v.. Anyone know what can pull up the voltage to 15 v but in the same time, the output voltage need to be variable which is depend on input voltage..

that sounds like the deffinition of a linear device.
you can only turn an igbt off or on, anywhere in the middle and you'll let the magic smoke out lol