Problems matching npn, pnp

lardom · 2012-10-15 08:53

I'm trying to design a 3 1/2 H-bridge circuit to do some tests on a sensorless bldc motor. It would have been ideal to find high side and low side transistors with matching specs...that I could find at RadioShack. Building an H-bridge is a new experience for me. I hope that 'high side / low side' emitter-collector outputs match if I choose biasing resistors for the pnp transistor which has lower specs.For those who've built H-bridges are the differences between a pnp / npn a big problem?
In the schematic I'm using 6 2N2222 npn's to switch high-side TIP42 and low-side TIP31 power transistors.

LoopyByteloose · 2012-10-15 09:06

Take a look at Futurelec.com for their transistor listing as it has all the PDFs linked. The TIPxx series are matched power transistors. The TIP1xx are matched darlington power transistors with protective diodes and can be driven direct from a micro-controller in many cases.

http://www.futurlec.com/TransPowerTIP.shtml

BTW, using darlingtons doubles the voltage drop of the item. Normal power transistors will have a saturation voltage drop listed of 1 - 2 volts, while darlingtons will have 2 - 4 volts drop at saturation.

You will notice that the TIP series all have the matching PNP/NPN pair cross-referenced.

lardom · 2012-10-15 09:29

@Loopy Byteloose, thanks for the link. Wow! there is a big improvement in price too.

LoopyByteloose · 2012-10-15 11:19

Some people on this forum dislike Futurelec. I used them and found them okay for me. They can be slow on delivery. Others have claimed some parts are phony, but I've not run into that. Maybe I just don't know how to tell.

But the really good thing is that they making shopping by PDF comparison quite easy.

PJAllen · 2012-10-15 11:31

Those high-side PNPs need to be pulled up.

http://incredulist.blogspot.com/2012/10/high-side-switching.html

rwgast_logicdesign · 2012-10-15 11:54

wow this is the first time ive ever been to futurlec, its so cheap the LED matrix are 2 bucks and under and closer to 15 at places like sparkfun. Whats there deal why are they soo cheap

RDL2004 · 2012-10-15 12:58

While they have "sales offices" around the world, I believe they are based in Thailand. I've heard they're pretty reliable but shipping times can be very long (worse than coming from China). I wouldn't buy anything from them if you need it in a hurry.

LoopyByteloose · 2012-10-15 13:32

I only got one order from them and it did come from Thailand. It took about 3 weeks for delivery.

The local post office here had me do something very odd. They made me go around the counter and go to the back of the general post office to pick up the package that was obviously opened for inspection. I got the impression that they wanted me on the postal office's video cameras in case I was making a bomb or something.

Just another odd misadventure in Asia.

sam_sam_sam · 2012-10-15 14:26

Loopy Byteloose wrote: »

Some people on this forum dislike Futurelec. I used them and found them okay for me. They can be slow on delivery .

I have ordered from them from time time I would say that if you have PayPal account I would use it with them just in case you do not get your order which almost happen to me once
I have bought there 5 volt power boards and they are very well made and easy to use

lardom · 2012-10-15 18:52

@PJ Allen, thanks for the tip. I saw a schematic with 10K pull ups on the pnp's. I didn't know if they made a difference. I will add them.
@sam_sam_sam, Paypal sounds like a good idea. I can stock up on components I use a lot of.

Problems matching npn, pnp

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