Hi all.
I have been working on designing a basic constant current sink circuit, based on the one in the attachements. My question is about how to select the correct heatsink and power transistor. First I'll try to explain the circuit specs and requirements:
R1 is a 33Ω resistor, Vs goes from 0 to 3.3V in order to generate a current from 0 to 100mA(maximum) in R1, which would be aprox I_RLOAD since Ic≈Ie. The +HV source goes anywhere from 0-200V, which allow RLOAD to vary from 0 to 2kΩ and still maintain the constant current (ideally).
The current will be applied for very small periods of time, say pulse width range from 0 to 500µs, and a frequency of 20 to 100Hz (As the sample figure attached).
Therefore I believe that my worst case scenario, would be when the transistor "sees" 100mA(max current) at the full voltage range of 200V, which turns to be a 20 W power dissipation.
Now, I could use some help with selecting the correct power transistor and heat sink. Where do I start the analysis to select the correct components (transistor and heat sink)? Would a mosfet be a better choice? Any help would be greatly aprecciated.
Jay Pe.
Thanks!
I have been working on designing a basic constant current sink circuit, based on the one in the attachements. My question is about how to select the correct heatsink and power transistor. First I'll try to explain the circuit specs and requirements:
R1 is a 33Ω resistor, Vs goes from 0 to 3.3V in order to generate a current from 0 to 100mA(maximum) in R1, which would be aprox I_RLOAD since Ic≈Ie. The +HV source goes anywhere from 0-200V, which allow RLOAD to vary from 0 to 2kΩ and still maintain the constant current (ideally).
The current will be applied for very small periods of time, say pulse width range from 0 to 500µs, and a frequency of 20 to 100Hz (As the sample figure attached).
Therefore I believe that my worst case scenario, would be when the transistor "sees" 100mA(max current) at the full voltage range of 200V, which turns to be a 20 W power dissipation.
Now, I could use some help with selecting the correct power transistor and heat sink. Where do I start the analysis to select the correct components (transistor and heat sink)? Would a mosfet be a better choice? Any help would be greatly aprecciated.
Jay Pe.
Thanks!
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