Is that really bad news for me? Digi-key says they have ~6K of them in stock. surely they will sell me 10 or 20 of them.

 

No, it's not bad news at all. You can buy a number of them now while they're cheap.

There will be a replacement that's better eventually, I'm sure.

They're probably having a hard time with counterfeit items giving their products a bad name. If you buy from Fairchild Direct, Mouser, Newark, or Digi-Key or another authorized distributor, you can be sure you're getting the genuine item.

 

I've prototyped the circuit, and I've run into a road block. I'm sure it's because I'm ignorant. It looks correct to me; but it is not behaving the way I think it should.


The green LED in the upper left hand corner remains lit no matter what level the output pin is at on the micro-controller. I think the LED should only be lit when the output pin is high.

The uC is upper left. The dome thing is the motion sensor. And the device with the red jumpers is the radio. The circuit above the mosfet is a voltage regulator for the radio.

I have no idea what I did wrong. I would appreciate help.

 

If your mosfet is an n-channel then the source and drain pins need to be swapped.

hgmjr

 

That did it. Thank you very much.

Another question: does n-channel mean PNP?

 

No, N-channel doesn't mean PNP.

P-channel MOSFETS are mostly used on the high side of an H-bridge.
N-channel MOSFETS are mostly used on the low side of an H-bridge.

N-channel MOSFETS are more efficient than P-channel MOSFETS.
For that reason, N-ch MOSFETS are being used on both the upper and lower sides of H-bridges with high-side driver IC's made for such purposes.

It's kind of difficult to compare MOSFETS to bipolar junction transistors, as they are completely different critters.

But if you had to make a very rough comparison, an N-ch MOSFET would be an NPN transistor.
Gate = base
Source = emitter
Drain = collector
But not really.
Transistors have hFE ratings, for gain over different Ic. You put "X" amount of current in the base, and you get "Y" amount of current out of the collector. (It's not quite that simple, but that's basically what happens.)
It's impossible to give a MOSFET an hFE rating, because after the gate is charged, there IS no more gate current - or if there is, it's in picoamperes. Instead, MOSFETs are rated for Rds(on) in Ohms (or mOhms) and peak current capacity. They're basically a switch.

 

You can learn more about the differences between bipolar transistors and MOSFETs in the AAC ebook. Here is the link to the bipolar transistor. The MOSFET section of the AAC ebook is in the process of being written so it is unavailable at this time.

hgmjr

 

I get it. It makes sense now. BJT = amplifier, MOSFET = switch.

 

I get it. It makes sense now. BJT = amplifier, MOSFET = switch.

Both of these devices can serve as amplifiers or switches. It depends on how the devices are configured in the circuit.

hgmjr

 

I guess I'll read up on them, then.