c547b = to-92/2n3906 ??

[PainGypsy]

I have a bunch of transistors labeled C547B PH98. I am wondering if I can use them in place of 2N3906. I am building an El Cheapo pic programmer as found in Myke Predko book "Programming PICmicro MCU's. I believe I have some labeled 548 as well. There is also call for a 78L12 and I have a few regular 7812's but not in the package type that it calls for... I would think I can use the standard 7812 in place of the 78L12 as long as I could get it on the board... Any help is greatly appreciated!

[russlk]

The 2N3906 is a PNP transistor. If yours are PNP and have a DC current gain of 100 they will be near enuf. To find the current gain, connect the transistor common emitter with -5 volt DC supply, 100 ohms in the collector and 43K from base to -5V. The voltage drop across the 100 ohms times 100 will be approximatly equal to the current gain.
The 7812 has more current capablility than the 78L12, so that is a safe substitution.<p>[ June 20, 2003: Message edited by: Russ Kincaid ]</p>

[PainGypsy]

Thank you very much Russ!! I will use the test you described. Thank you for spelling it out a bit.

[Calcbert]

Make sure to check myke.com for the latest revisions to the "Book" version of the El Cheapo programmer. A few resistors and capacitors have been taken out, and a clarification is made about the orientation of some of the transistor packages.<p>I had mine built per the specs in the book I got the PCB in, and it didn't work until I found the modifications on the web page and deconstructed the circuit slightly.