Quoted:
For example, can an MPS2907 be used in place of a 2N2907?
I have a cross-reference guide, but it's evidently too old & doesn't include MPS anything.
What led me to ask is that I noticed in a catalog that the specs are pretty much comparable and I just happen to have the MPS2907, though the schematic calls for the 2N2907. This is just experimental hobby work, no tempermental hi-tech equipment.
Can anyone explain if there is any across-the-board rule of thumb on substituting between series? What the heck is an MPS vs. a 2N, anyway?
Other question: none of my beginners' books explain what a Darlington transistor is, they just give some notes on what they're used for, not what the properties or the internal makeup is. Anyone?
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PRK:
Not sure on the first question, other than to say if the specs are similar, give it a go and see what happens. Transistor selection is often non-critical in many simple applications, and the 2N2907 is a pretty common device that can often be substituted-for. What's the application? Maybe I can give you more a more complete recommendation if you can provide a bit more info.
Regarding Darlington transistors, they are effectively TWO transistors in a single package, configured as follows:
1. Collectors of both transistors are tied together.
2. Emitter of transistor # 1 is connected to base of transistor # 2.
3. Base of transistor # 1 is effectively the "input" to the Darlington pair.
Clearly, you can build up these configurations yourself using two transistors, or buy "Darlington" transistors which do the same thing. They are often used in applications where you need lots of current-gain at relatively low frequencies (examples - driving servos, relays, audio, power supplies, etc.).
Hope this helps. Good luck with your substitution, and remember where the fire extinguisher is...
Plinker out.