duffy
Well-Known Member
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?
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?
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