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?

MPS is Motorola's version of these mostly generic transistors. You can usually use an MPS2907 in place of a 2N2907, or vice-versa. Also, the PN2907 is an even lower-cost version that usually substitutes well. About the only place where you might run into problems is when using the 2907 at pretty close to its maximum voltage or collector current ratings — some of the generic versions are just a tad less robust under these conditions. Also, note that some manufacturers offer several grades (with an A,B or C suffix) of this  part, with slightly different maximum ratings. Metal cased versions are still also available, although they don't offer any advantages in most applications. In probably 95% of all circuits, you can use any of them interchangably.

A Darlington pair uses two transistors (usually inside the same package), interconnected so as to multiply the current gain obtained by either transistor alone. They are often used as pass transistors in linear power supplies, allowing large amounts of current to be controlled directly by an integrated circuit or op-amp. The main disadvantage of a Darlington pair is that it can't be turned on as completely as a discrete transistor, resulting in higher power losses when used as a saturated switch.

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.

The Darlington transistor , is a two transistor setup usually in common-emitter and common-collector configurations.  

The amp consists of two trans. that are connected in such a way as to provide dc and ac beta values that are equal to the product of the individual transistor beta's.

Now then , any small to medium signal transistor, with voltage specs and beta in either NPN spec should or could be made to work. What is the project.

The 2907 if I remember correctly can be run up to about 12/15 volts ? is this correct. Just find something close...

Here's a general cross reference to NTE components.  You can play with criss-crossing part numbers to see what's compatible with what.

[url]www.action-electronics.com/nte.htm[/url]

A Darlington transistor is two or more transistors cascaded in a single package in order to increase gain and current handling.

[img]junior.apk.net/~scotts/darx.JPG[/img]

OK, thanks everyone.  One application on the 2N2907 is to control a relay that switches a battery powered lamp on and off.

The other circuit is an led flasher.  Nothing spectacular here, but as I work thorough this book of circuits, I may run into a more interesting project where I have to do this this substitution again.

I had good results in the past when I used a more robust component in place of one I didn't have, but that was within the same series.  In this case, I didn't know if it was even comparable, or a different technology.


Thanks for the help, and the Darlington explanation.

One application on the 2N2907 is to control a relay that switches a battery powered lamp on and off.

If I am not mistaken then, any transistor should work.  Is the transistor either baised in Saturation or Cutoff and merely acting as a switch???

Ben

Sure can. Same device.

And Darlington is not a type of transistor but a configuration. Skibane knows his Small-Signal switching devices.

Motorola Semi is now operated as "On Semiconductor". Their site has the old Mot device datasheets.