A Test Set for Nondestructive Safe-Area Measurements - diyAudio
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Old 7th February 2008, 05:43 PM   #1
Tarzan is offline Tarzan  Belgium
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Default A Test Set for Nondestructive Safe-Area Measurements

Hi all,
To the newcomer:
This tread is set up with the aim to build a A Test Set for "Nondestructive Safe-Area Measurements under High-Voltage, High-Current Conditions" for transistors.
It is a well known fact that there are many counterfeit power transistors that do not live up to the code they carry.
Look here: http://sound.westhost.com/counterfeit.htm

It is obvious that such a batch, built in a new project or the repair of a beast of an amp can create havoc and cost a lot of money.
Not only that; you still have to find replacements that are genuine.

A search in to my memory brought up some Application Notes from RCA dating back to the early seventies.
See here:
http://www.diyaudio.com/forums/showt...35#post1402235


I finally found one of the few I was looking for.
Look here for the AN-6145:
http://www.diyaudio.com/forums/showt...66#post1421066

This will be the subject of this tread.
We will analyze the circuit (by the many great thinkers, better as I am) and build a modern instrument that will help our fight against fake transistors.

Now have a look at the AN-6145.
Start with proposing circuit changes so that actual components can be used.
Make parts of the instrument simpler.
Let's make it usable for not only NPN but also for PNP power transistors.
Is it possible to add a sort of curve tracer?
Controlled by a computer?
etc, etc.

Let's make something out of it.

Thanks and see ya on this tread....

Tarzan[B]
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Old 8th February 2008, 06:48 PM   #2
Tarzan is offline Tarzan  Belgium
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Thanks to Small Boy who converted the huge sand seperate pages in to one document.
Here is the link for the 923KB PDF document:
http://www.yuntaa.com/FileManager/Do...40A8C003025250

Tarzan
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Old 8th February 2008, 07:51 PM   #3
poynton is offline poynton  United Kingdom
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Default Re: A Test Set for Nondestructive Safe-Area Measurements

Quote:
Originally posted by Tarzan
[B]...................
Start with proposing circuit changes so that actual components can be used.
Make parts of the instrument simpler.
Let's make it usable for not only NPN but also for PNP power transistors.
Is it possible to add a sort of curve tracer?
Controlled by a computer?
.................

Obviously, it would have to be made with components which are available now.

NPN and PNP would be better but the power supplies would need careful thought to avoid complication / duplication.

Curve tracer and computer control.... nice ideas but let's get the basic thing going first !!
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Old 18th February 2008, 11:14 AM   #4
Tarzan is offline Tarzan  Belgium
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Not much response I must say.

RCA AN 6145 One File.pdf
http://www.yuntaa.com/FileManager/Do...40A8C003025250

I tried to analyze the schematics and came up with a simplified block diagram.

Simplified.jpg
http://www.yuntaa.com/Photomanager/S...40A8C003027DCA

The whole test setup can be made up of 5 main blocks.

1. An adjustable Collector voltage source.
This can be a 0 .. 150 or 300V source / 5 .. 20 Amps

2. An adjustable load for the transistor under test. Must be able to withstand the full VCC at reasonable current (.. 20 Amps)

3. An adjustable Bias supply for the load under 2.

4. A fast flip Flop and Crowbar that removes the bias in the event of a failure of the DUT

5. A pulse source that can drive the Load circuit.

It would be nice to treat each part on his own and later on combine them to complete the test setup.

An exception could be the different power supplies.
They can all be brought together on one board.
Some voltage are not known because some blocks aren't worked out yet.
I would say we stuck with + 12 V for logic and relais to stay with commonly available parts.

Cheers and hints are welcome
Tarzan
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Old 18th February 2008, 12:24 PM   #5
Eva is offline Eva  Spain
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Interesting....

With modern stuff like MOSFET, SMPS, microcontrollers, high speed gates and comparators, I think that a compact portable automatic tester for both NPN and PNP is not that hard to achieve. It may be funny as a future project

I hadn't figured out that non-destructive testing could be achieved by removing power within a few hundred nanoseconds in case of overcurrent. With nowadays components I think that power can be removed within less than 100ns of fault detection.
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Old 18th February 2008, 12:37 PM   #6
Tarzan is offline Tarzan  Belgium
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I think this link is better:
http://www.yuntaa.com/FileManager/Do...40A8C003020971
Cheers
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Old 18th February 2008, 01:00 PM   #7
PB2 is offline PB2  United States
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Looking at your block diagram, it seems to me that Rload would be better in the collector lead of the Load Switch transistor, then the base drive is simplified. Seems that Load Switch should be built as a switched current source so that the test current can be easily set.

You might want to consider running the logic on 5V so that you can take advantage of the advanced high speed logic families, AC for example.

I would have the main collector supply be an external power supply so that a bench type unit can be used with precise voltage and current control. It offers more flexibility.

I've been thinking about building a SOA test system for some time now.

Pete B.
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Old 18th February 2008, 01:48 PM   #8
PB2 is offline PB2  United States
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Just noticed that Rload and the switch have, essentially no voltage to work with, since the DUT emitter is at or below ground.
Didn't look closely at the article was there a negative supply?

Pete B.
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Old 19th February 2008, 09:10 AM   #9
Tarzan is offline Tarzan  Belgium
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Yep PB2, there is indeed a negative supply towards the emittors of the load switching transistors.
I attached a new drawing with the changes.

I have a problem attaching it to this message. Find it here:
Simplified 080219-1.jpg
http://www.yuntaa.com/Photomanager/S...40A8C0030215AE

RLoad is now connected to a -14V supply and not to the ground.

I do have a problem with understanding the use of the Vbb (0..20V) that goes to the puls generator.
Can some one explain me that?


Your comments PB2:
"Looking at your block diagram, it seems to me that Rload would be better in the collector lead of the Load Switch transistor, then the base drive is simplified. Seems that Load Switch should be built as a switched current source so that the test current can be easily set."
Can be looked at.
I recall the RCA rep telling me that he knew of an engineer in Belgium who built this unit and was very happy with it.
But that's more then 30 years ago...
So the original setup should work.

"You might want to consider running the logic on 5V so that you can take advantage of the advanced high speed logic families, AC for example."

That's a good proposal. The pulse generator and flip Flop-crowbar can be made of these.

"I would have the main collector supply be an external power supply so that a bench type unit can be used with precise voltage and current control. It offers more flexibility."

Yes can be. Allthough a test set-up that stands on his own is very handy to. I think the HV supply is the most problematic.
Some schematics show a simple HV supply. Not powerfull enough but that can be done.

Tonight I try to upload all I've found and leave a notice here.

Cheers,
Tarzan
Attached Files
File Type: pdf simplified 080219-1.pdf (55.0 KB, 139 views)
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Old 20th February 2008, 10:46 PM   #10
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Hi Tarzan

I wonder if a MOSFET would be better as the switch in the emitter of the test transistor?

Might be faster.... but there again, perhaps the switch transistor could be an MJL3281A which would be fine up to ~5A and two for 10A...

I think your blocks pretty much sum up the RCA circuit.

I guess the Vbb supply is just for the pulse circuit. Probably could run from the same psu as the negative load supply.

Need to protect the switch circuit against high voltage pulses ...in case ... maybe discrete instead of 5V logic ?



cheers
John
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