High Voltage Transistor Guide

In need of bipolar transistors that can withstand high voltage pulses ? Then go through this post to see some high voltage BJTs with breakdown voltages from up to 400V. 

Let's start with a list of high voltage transistors .

Not to mention, they are still available and often used in many devices today. You can also see some of them in old landline and cordless telephone circuits.

• MPSA92 (PNP)
• MPSA42 (NPN)
• MPSA44 (NPN)
• ZTX458 (NPN)
• FMMT558 (PNP)
• FZT658 (NPN)

So, what exactly is a high voltage transistor?

Simply put, a  high voltage transistor can handle higher voltage levels ranging from a few hundred volts to several kilovolts than standard transistors because they are designed to withstand higher voltage stresses and power levels.

Take a look at the FCX458 transistor data shown below (click image to enlarge).

According to the datasheet, it is a 400V NPN High Voltage Transistor in SOT89.

As you can see, it has an absolute maximum collector-base and collector-emitter voltage of 400V.

Remember at this point that for the very common BC547 transistor we are all familiar with, these are below 50V.

For transistors, the maximum allowable current, voltage, power dissipation and other parameters are specified as maximum ratings.

A transistor composes an input/ output circuit containing an emitter, base or collector. Since either terminal is used as a common terminal in the circuit, the collector-base voltage VCB, collector-emitter voltage VCE, and emitter-base voltage VEB ratings are specified for transistors.

There are two types of breakdown voltages that determine the voltage ratings - those inherent to a transistor such as V(BR)CBO and V(BR)CEO and those dependent on the base circuit conditions such as V(BR)CER and V(BR)CEX.

This TOSHIBA Application Note (PDF) describes the maximum ratings of bipolar transistors ↗ 

To test transistor breakdown voltage we use a small Chinese Multifunction Digital Transistor Analyzer/Tester (see below).

The Duoyi DY294 tester has a breakdown voltage V(BR) function up to 1000V and works very well without damaging a transistor under test so far.

It is also very useful for spotting fake transistors (that often comes with much lower breakdown voltage than specified in the ratings).

Well, until next time, keep on learning!