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  #1  
Old 07-24-2010, 03:20 PM
forumito forumito is offline
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Question PNP transistor: E, C and Base

Hello to all,

I'm having trouble finding out the "pinout" of a A933 PNP transistor.
The manual says
Quote:
Transistors have 3 pins named emitter, collector, and base, from left to right with the flat side facing you. [...]
But (as far as I can see) A933 is flat on both sides!

Here is the picture of A933:

What do "S" and "R" stand for ... "Set" and "Reset" as in SR latch? And "J"? Should these tell me which pin is E, C and Base?

Or is there some convention that, no matter the transistor type/model, "flat side" is the side with label on it?

Thank you for helping a humble novice.
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Old 07-24-2010, 03:26 PM
tom66 tom66 is offline
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That's not a TO-92 case. It's a special type of flat TO-92. The numbering usually refers to left-to-right on the side which has the part number and assorted writing. I think the name is "SPT".

It is not an SR latch, you would need at least 2 pins for power, 2 inputs and 1 (or 2) outputs, more than 3 pins.

Here is the datasheet for that PNP. It's apparently the 2SA933, I guessed this and it seems to match. Datasheet is pretty poor quality but we can see that the pins are numbered emitter->collector->base. If you plug this into any multimeter with transistor test in this configuration, and it shows a valid Hfe (i.e. greater than about 30) then you know the pinout is correct. The datasheet suggests a Hfe of 120 to 560.

http://pdf1.alldatasheet.com/datashe...HM/2SA933.html

Last edited by tom66; 07-24-2010 at 03:39 PM.
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  #3  
Old 07-24-2010, 04:12 PM
forumito forumito is offline
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Quote:
Originally Posted by tom66 View Post
[...]
Here is the datasheet for that PNP. It's apparently the 2SA933, I guessed this and it seems to match. Datasheet is pretty poor quality but we can see that the pins are numbered emitter->collector->base.
I was reading this datasheet just before posting: as there are no labels in the document ... how do you know that the side with the label is the "flat side"?
Is it safe to assume that labeled side = "flat" side? That is, can PNP (or NPN) transistor get damaged if improperly connected (within reasonable current of course)?

Quote:
Originally Posted by tom66 View Post
If you plug this into any multimeter with transistor test in this configuration [...]
I've looked into multimeter manual and it says:
"Transistor tests can only be performed with the optionally available measuring adapter." That implies I need an extra device?
"No voltage may be applied and measured on the adapter." No voltage may or can't be applied?
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Old 07-24-2010, 04:24 PM
tom66 tom66 is offline
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Hmm, going and buy one of those really cheap Mastech meters for about 2.99 just for the transistor test seems like too much. One of my meters came with an external transistor tester, but your meter manufacturer may have been cheap and skimped on this. No voltage may be applied, that means if you do damage could occur to the meter.

I mentioned that the labelled side is always the "flat side". It is also usually the longest side, note that the other side has probably got little triangular cuts in it...

The low voltage/current a meter provides will generally do no harm to a transistor if connected backwards. The story is different if you are dealing with a circuit with higher voltages or currents, you can destroy transistors easily... it's usually quite spectacular, sparks n' smoke.
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  #5  
Old 07-24-2010, 04:26 PM
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I believe if you look closely, you will notice a slight beveled edge. This is the key to establishing the orientation. I believe it is along the left side of the device shown in your picture.


hgmjr
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Old 07-24-2010, 04:32 PM
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Another way to locate the base - it will be the only pin to show a junction to the collector and the emitter both. You can find that with the resistance function (the PN junction function is better) on your meter.
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Old 07-24-2010, 04:57 PM
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I read the markings to say:
Code:
A933
   _
S.RJ
Select All
I frequently use Beenthere's method to do a quick transistor check using the diode function.

Depending on how fresh your meter's battery is, a reading of around 500 to 750 is OK.
If it's under 200, that junction is likely shorted.
If it's > 750 or so, it's probably open or intermittent.

You'll only get readings from the base to the collector and emitter.
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Old 07-24-2010, 05:46 PM
forumito forumito is offline
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Wink Both sides are beveled

Now, "flat" side is the one with more or less bevel?

Thank you for handy multimeter suggestions.
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  #9  
Old 07-24-2010, 05:51 PM
tom66 tom66 is offline
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The flat side as mentioned is the side with the labelling.

Do a meter check to be certain.
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