TO-92 Question

hacksign23 · 2010-08-16 20:37

Hi guys;
another quick question.
I've been looking up on transistors, voltage regulators, etc, and I notice that most have either the to-92 or the to-220 in the model name.

So for a 5v regulator, it had the model name of 7805 to-92.

what exactly is the to-92?
on wiki, it says it's a tyle of transistor enclosure construction.
I don't really understand what it's saying, since the model is being used with a voltage regulator. any help :P ?
thanks.

Brian Carpenter · 2010-08-16 20:43

That is correct. To-92 is the style of package. Let me see if i can find some images for you.

It is a form factor issue as well as how much current / heat it can handle.

RDL2004 · 2010-08-16 20:53

One thing to be aware of is that pin out diagrams for the TO-92 are often drawn as if looking up at the bottom instead of down from the top like an IC package. I destroyed a couple of LM34s that way once.

hacksign23 · 2010-08-16 20:57

ohhhh. so a to-92 is just a way of packing an ic? kinda like dip ._. ?

Tubular · 2010-08-16 20:57

Also, bigger cases let the same regulator dissipate more power.
A 7805 in a TO-92 case (78L05) is typically used for currents up to 100 mA
A 7805 in a TO-220 case is typically used for currents up to 1000 mA (1 amp)
A 7805 in a TO-3 case (78H05) is typically used for currents of up to 3 or 5 amps

Nick McClick · 2010-08-16 21:44

@hacksign - correct. I usually see transistors (2n3904) in a To-92, but you can get other things, like 1-wire EEPROM's and temperature sensors.

Toby Seckshund · 2010-08-17 00:04

It pays to check the pinouts for the device that you are using as there are different lead arangements within TO-92. There are a, b, c ... sorts.

I use http://www.alldatasheet.com/ a lot for this.

hacksign23 · 2010-08-17 00:12

Tubular wrote: »

Also, bigger cases let the same regulator dissipate more power.
A 7805 in a TO-92 case (78L05) is typically used for currents up to 100 mA
A 7805 in a TO-220 case is typically used for currents up to 1000 mA (1 amp)
A 7805 in a TO-3 case (78H05) is typically used for currents of up to 3 or 5 amps

for amps, do you mean input or output?

Leon · 2010-08-17 00:23

Output current. The input current is slightly higher, of course.

Toby Seckshund · 2010-08-17 00:32

As these are linear regulators, the input current is virtually identical to the output current. The only difference is the quiesant current of the regulator's internals. For the usual 7805 sort this is about 5 - 10 mA. So for a regulator giving out 5V at 1A, but being fed from a 12V power supply, the input current would be 1.005A (or so ). The 7V (12V - 5V) would be dropped across the regulator and would be disipated as heat. 7V x 1.005A = 7.035Watts which would have to be got rid off with a substantial heatsink, hence the sort of regulator packages that can be bolted to something.

If the 5V was only to supply 5mA then the power to be disipated would only be (12V-5V) x (5mA + 5ma) = 70mW and the TO-92 sort would be smaller, cheaper ...

In the last case the 5mA quiesant current would be the same as the output current, this might be a problem if the supply were batteries as half of the energy is wasted

Good morning Leon. I saw you name on quite a few posts yesterday, whilst searching for a LC meter.

Leon · 2010-08-17 00:45

Nothing to do with this topic, but the AADE unit is very popular with radio amateurs. I was involved with a project for something that used a similar technique, and designed a nice PCB for it, but it didn't go ahead. That was probably what you found.

Cluso99 · 2010-08-17 04:47

The pins for transistors are b=base, c=collector, e=emitter. Be careful as different manufacturers sometimes have different pinouts. I got caught with the P2N2222 which uses a different pinout to the 2N2222 from different manufacturers.

Same applies to the TO220 for regulators. Just make sure you check the manufacturers datasheet on the web.

TO-92 Question

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