What Factors Determine the Selection of a High-Voltage NPN Transistor?

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When selecting a high-voltage NPN transistor for a 1000V, 4mA application with a peak inductance current of 1A, key parameters include Vce, which should be rated for 1000V, and Vce(sat) for accurate performance under load. It's crucial to consider the worst-case peak current for current ratings and to evaluate the Safe Operating Area (SOA) for transient loads. The circuit design may require adjustments to accommodate the new voltage and current specifications, including changes to the diode and other components. Heat-sinking will be necessary to manage thermal performance effectively. Understanding the signal characteristics, such as bandwidth and rise/fall times, will further inform the selection process.
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Say you want to choose a npn transistor which works for 1000V and 4mA (Peak inductance current is around 1A) in the collector side while emitter is grounded.

Which parameters should I look into to select a suitable transistor ? for the voltage should I be looking into Vbe ? or is Vce enough ? I'm thinking in this case Vce should be 1000V. For Vce (Sat) how would I calculate it when it's given for test condition (max or minimum sometimes both). For the current I should be looking into the worst case (peak current) ?

Will there be a problem if transistor which is designed for much higher voltage/current used for much lower values other than cost ?
 
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Khalid said:
Say you want to choose a npn transistor which works for 1000V and 4mA (Peak inductance current is around 1A) in the collector side while emitter is grounded.
Can you post the circuit schematic? With transient loads, things like Safe Operating Area (SOA) come into play.

https://www.sciencedirect.com/topics/engineering/operating-area
Also, if you can give us an idea of the signals that will be handled (bandwidth, rise/fall time, etc.), that will also help.

Will you be heat-sinking this transistor?
 
berkeman said:
Can you post the circuit schematic? With transient loads, things like Safe Operating Area (SOA) come into play.

https://www.sciencedirect.com/topics/engineering/operating-area
Also, if you can give us an idea of the signals that will be handled (bandwidth, rise/fall time, etc.), that will also help.
I have attached the diagram. I haven't designed the circuit so i do not fully understand every part of it but I get the jest of it, its from a project I found online which is HVDC power supply using DC to DC converter. The project is based on using a 12V battery to get 500V 2mA DC. The project also had a calculator which can measure the value of the components based on the output you desire. (You need to enter Vce sat of T1,Vin,Vout,Current,Diode voltage drop, and timing capacitor value). However I would like to adjust it to 1000V 4mA which means that I would have to change the transistor (T1) and find its Vce (sat). Diode used in the diagram will change too however I don't think will affect the calculations much if at all since the small voltage drop is small. I can link the project page if its allowed here.

berkeman said:
Will you be heat-sinking this transistor?
Yes.
 

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