Apparently every TO-92 BJT I own is backwards?

[midwayfair]

I was double checking a layout just now and noticed this ... I checked a bunch of dozen different ways, but with the pins facing me, flat side up:

2N5088: Collector on the left (should be on the right)
2N3904: " "

BC549C (Fairchild from Mouser): Collector on the right. (Should be on the left)

Etc.

It's not just a couple things from a few suppliers, it's every single TO-92 I have is backwards according to the datasheets.

Everything I have with an emitter tab is correct, though ...

[Mark Hammer]

I find a great many datasheets are rather ambiguous in the way they describe the pinout.  Am I looking at the top of the transistor?  Up from the bottom?  That's why I use my meter to confirm.  I look for a plausible hfe, and let that tell me what pin is what.

[midwayfair]

I find a great many datasheets are rather ambiguous in the way they describe the pinout.  Am I looking at the top of the transistor?  Up from the bottom?  That's why I use my meter to confirm.  I look for a plausible hfe, and let that tell me what pin is what.

I'm so used to just knowing the pinout of the ones I use all the time that I haven't looked at the datasheets in a long time. That's why I was so surprised when I looked up a 2N5088 and it was backwards from what I expected.

[Kipper4]

Perhaps you'd like to share how you check them please Jon.
I wouldn't have a clue and I'd appreciate knowing so I can put it in my little book.
Thanks

[midwayfair]

Perhaps you'd like to share how you check them please Jon.
I wouldn't have a clue and I'd appreciate knowing so I can put it in my little book.
Thanks

Just plug them into a buffer or booster circuit.

[akc1973]

Using your hfe setting on your DMM is a good way to verify pinouts, I find...especially when it's hard to read which manufacturer's transistor you have.

[R.G.]

All bipolar transistors work with collector and emitter swapped - kind of. 

In the reverse mode, Hfe is dramatically reduced.

[PRR]

If you are really befuddled.... in addition to the low Hfe in backward mode, as you go above 7V the Collector junction will stand-up, the emitter junction will break down.

A 24V supply and a 22K resistor in series, and a voltmeter, can tell. Apply the resistored voltage to two pins. Measure the voltage on those pins. If 0.6V, you found a forward junction, flip the leads. If 7V, you found a reverse Base-Emitter junction. If 23.9V, there's a reverse Collector junction in there. Six measurements will find ALL the breakdown voltages, forward and backward.

[UKToecutter]

I personally use an inexpensive Peak tester (DCA55).
It tells you which leads are which and gives you a full set of specs for your individual device.

The more expensive DCA75 will even draw you graphs!!

You don't want to get caught out by using a datasheet and either a) reading it wrong, or b) using the wrong datasheet

[duck_arse]

jon, all those transistors are backwards. only the bc5xx series is correct.

anyway, I always draw the 3d, isometric (?) view on my circuits. still, I have a couple of way old PN3564's, which I would expect to be backwards to start with, except they have a preformed base lead bent towards the flat. so now I don't know what is where, except the base, obviously.

[midwayfair]

PRR, thanks for the testing regimen.

I did some more testing today, and it looks like my confusion arose from the weird biasing network I used in a couple different circuits. I had the base biasing resistor going to +9v instead of the collector. Apparently when you do that, the transistor works better backwards ... I guess I'll redo a bunch of layouts now to fix that.

However, it also looks like my Eagle library might be backwards, too? Here's a layout I did where the schematic part was BC549C, but the collector is flipped.

[Kipper4]

Yes thanks PPR that's one for the book. And print page.

[pinkjimiphoton]

i told you guys sometimes stuff sounds better backwards. i guess this is why!!!
i don't bother with the data sheets anymore after getting so much stuff wrong, i check everything on my meter to see what's what, and even then, sometimes the reverse beta will sound better, especially with germaniums.

weird planet!!!

[PRR]

> weird biasing network I used in a couple different circuits. I had the base biasing resistor going to +9v instead of the collector. Apparently when you do that, the transistor works better backwards...

No. Both are valid. Optimum resistor values will be different. Some voltage-tests and comparison may bring clarity.

If it "works better" with C and E reversed, it probably isn't much of an Amplifier.
____________________________

> especially with germaniums.

Ah. Yes, Ge does not have the trustworthy 7V emitter breakdown, and may not have a low reverse Hfe. Some Ge parts were quite symmetrical.

[pinkjimiphoton]

very true... particularly nte ones, some of which have the same gain no matter what way ya turn them.