Hello .I have a lot of BU208 & BU126
.how can i use these bu208 or bu126 ( which there VCE voltages 1500v and 800v ) as general purpose power transistors for example as instead of 2N3055 especially in 12 to 220v inverters .
thanks
High voltage transistors may have a small current gain and a high saturation voltage. Just replacing a relatively low voltage transistor will fail. You can make an inverter, but its output power will be lower. High-voltage transistors, it is advisable to use in the inverter 220V ==> 12V.
Look at the picture and pay attention to the control currents (base currents) of the transistors:
I just looked at an old datasheet from Motorola for the BU508. Minimum hFE of 2.25, That is the lowest spec I've ever seen - and to two post decimal digits. The typical gain curve peaks at less than 14. These transistors were made specifically for horizontal output for raster CRTs (television sets).