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Old 24th September 2009, 06:23 PM   #1
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Default Transistor Testing Rig

With all the counterfeiting of transistors going on, I feel the need to test all the ones I have (as well as future purchases). I'm looking to build a test rig (or rigs) for this purpose. Ideally, I would like to be able to do 4 tests:

1. Basic hfe test
2. Device matching with in-circuit type voltage & current values
3. Variable high voltage/low current stress test for Vce (within SOA)
4. Variable low Voltage/high current stress test for power handling (within SOA)

#1 is pretty straightforward & there are circuits floating around on the internet.
#2 will be someting along the lines of Anatech's circuit.
#3 & #4 are what I'm really looking for help on. I'd love to have a single PS for both, but realize that I may need 2. I have no experience with SWPS's, but I'm open to suggestions if that is the best solution. I really want to have variable voltage so that I can control the tests (and record where the fake ones pop ). I also want to make sure that if the DUT fails, there is some protection scheme so that nothing else is damaged.

Specifically, I'm looking for pointers on the best way to approach building 1 or 2 power supplies that are variable from 0-10VDC and deliver up to 10A of current and/or be variable from 50-200VDC and deliver up to 100mA of current. Fusing is the obvious protection scheme, but is current limiting a better option (including handling a shorted transistor)? I'm thinking that using something like 1ohm resistors in the base & emiiter circuits is the best way to monitor what's happening during the tests, but I'm open to other options.

Any input would be greatly appreciated. Thanks!
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Old 24th September 2009, 06:58 PM   #2
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Instead of #3 you should measure reverse currents and break-down voltages, it is more informative.
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Old 25th September 2009, 12:08 AM   #3
Enzo is offline Enzo  United States
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Or find a curve tracer - or build one.
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Old 25th September 2009, 12:57 AM   #4
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Or find a curve tracer - or build one.
Looking at ebay, buying one is pricey. I will do some searching on building one. Thanks for the tip.
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Old 26th September 2009, 12:30 AM   #5
tessier is offline tessier  Canada
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Originally Posted by Wavebourn View Post
Instead of #3 you should measure reverse currents and break-down voltages, it is more informative.
Hi

How do we measure reverse currents and break-down voltages ?

Thanx

Paul
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Old 26th September 2009, 12:36 AM   #6
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if anyone wants a copy of my curver tracer manual and schematic (it's definitely a do-able DIY project) PM me.
My curver tracer is a Leader LTC905 with AB comparison facility
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Old 26th September 2009, 12:58 AM   #7
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The only crucial component in the LTC905 is a multitapped transformer secondary for the individual sweep voltages. As it is rectified but not filtered to provide a 100Hz (120Hz in the US) sweep frequency, I could measure the actual secondary taps and it would be easy enough to have one wound to suit. The Tx/former has 12-0-12, 12-0, & (0-10,20,30,40,50,60,80,100v) secondaries. The rest of the circuitry is bog standard components.
Output is XY to your cro for testing TR/FET/MOSFETS/SCRs/TRIACs/diodes/zener/tunnel etc.
Breakdown can be determined with this unit.
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Old 26th September 2009, 01:16 AM   #8
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Quote:
Originally Posted by tessier View Post
Hi

How do we measure reverse currents and break-down voltages ?
Directly. Open any datasheet for a clue. They specify maximal reverse currents for given voltages. Apply a voltage and measure current.
How to measure breakdown voltage I explained in my previous post: supply a voltage higher than a breakdown one, but limit it's current. How would you measure a breakdown voltage of a Zener diode? The same.

However, a curvetracer is a very convenient tool for such measurements.
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Old 26th September 2009, 01:22 AM   #9
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The advantage of the curve tracer over steady application of votage/current is that it is switched 120 times a second and that often highlights otherwise ok transistors.
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Old 26th September 2009, 03:12 AM   #10
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Originally Posted by restorer-john View Post
if anyone wants a copy of my curver tracer manual and schematic (it's definitely a do-able DIY project) PM me.
My curver tracer is a Leader LTC905 with AB comparison facility
How does the Leader compare to the B&K 501A?
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