[1673] PNP Power Transistor Closeup

Date: November 26th, 2014 | Comments : [2] | Categories: DIY.

pnp transistor

This is a PNP power transistor that I have had in storage for years. You can see from the stamp on the metal case top that it was made in the 13th week of 1980.

pnp transistor

It says $2.17 on the price tag but I bought a box of dozens of discontinued parts for $5.00 at a local Radio Shack and several of these transistors were in it.

pnp transistor

It is more than a little crusty after many years in storage in less than ideal conditions, even though it has been sealed in the blister pack the entire time.

I though it might be interesting to cut off the top of one of these 100 watt PNP power transistors and see what is under the hood.

First, I tried to pry off the top piece with a knife blade but that seemed to be getting nowhere. So then I put the part in a vise and went around the outer rim of the top of the case with a hacksaw. I kept the cut shallow and rotated around the piece as it cut through. The hacksaw blade made short work of it and soon the top dome came off.

pnp transistor

It is surprising how thin the wires are that connect the silicon chip to the contact pins. On this transistor, the metal case of the TO-3 package is the collector connection. Sure seems small to dissipate 100w!

pnp transistor

Click on the image above to get a large view of the silicon chip. This picture was taken with a Pentax Q10 that had a +2 closeup lens screwed on the filter threads.

The question remains: does it still work? If you look closely at the chip near the left corner, it got dinged by the hacksaw blade and the base-emitter was shorted. I put the device under a magnifying lens and with some careful application of an Xacto blade, I was able to clear the space between the etched sections of the silicon. My Peak transistor tester then registered an hFE of 19, which is more than the minimum hFe of 15 that is specified for the part. So, even considering it is 34 years old, has been lobotomized with a hacksaw, and then microsurgery done to the substrate with a razor, the transistor still works properly and is in spec. Motorola made top notch transistors back in the day!


2 Responses to “PNP Power Transistor Closeup”

[425804] admin Says: 10:26 pm, December 4th, 2014

I measured the wires connecting the die to the pins and they are 0.010″ which makes them 30 gauge.

I tried to test the wire with a magnet to see if they were steel but could not determine for sure since the magnet was so strongly attracted to the base and emitter pins that extend out the bottom. Clearly the pins are steel.

The case and the round insert below the die are not magnet and are probably an aluminum alloy.

[529612] mictester Says: 1:45 am, January 19th, 2015

Did you know that your decapitated transistor will:

a: Work (slightly) as a solar cell, and will probably generate as much as 600mV in bright light (with almost no current available)

b: Work (quite well) as a photo transistor, with its gain dependant on the amount of light falling on it.

In my early days in electronics, I used to gently file the top off a BC109 to make a photo-transistor for an automatic porch light controller – I made dozens of them for friends and family!


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