Circuit building: stop using antique parts (2014)

Sigh.

I like FETs as much as the next engineer but if you're going to write about them, try to not make things worse.

In particular, this made me sad: the 10K resistor to ground isn't strictly necessary, but it ensures that the MOSFET remains OFF if the arduino is disconnected or it's pin is not an OUTPUT.

I was helping a high school student with a transistor project and he was complaining that "half the FETs he bought were 'bad'". And they weren't really bad, but they were destroyed. They were destroyed because, like our author, the student had no understanding of how the FET worked and so didn't realize that when you exceed the maximum Gate voltage on a FET it generally causes a current to "jump the gap" to the source and that permanently breaks it. What is even more, since the gate is essentially a capacitor, you can just touch the gate with your finger and pass enough charge (without feeling a shock or anything) to greatly exceed the gate voltage. Pick up the FET without being grounded and "boom!" dead FET.

Now there is almost no way to generate enough current by touching a Bipolar transistor to kill it, and so they continue to work for a long time while plugging them in and out of breadboards.

Do they dissipate more power? Absolutely. Are they difficult to run in parallel? Sure. But they are pretty robust parts. Sort of like the difference between alkaline batteries and LiON rechargeable batteries. Sure the latter are a "better" choice, you can recharge them after all, but if you use them wrong they catch on fire, if you short an alkaline battery it gets hot but doesn't go ballistic on you.

So those "antique" parts are generally very cost effective, very robust, and easy to get. So they make excellent tools to teach you the basics. Do you want to stay with them as you get more advanced? Probably not, but you're probably not skiing on the same skis you learned on either.

/endrant

I build a lot of guitar effects, and that community is even worse when it comes to attachement to obsolete components. The discontinuation of J201 JFETs (in TO-92 through hole package at least) by Fairchild has caused a lot of upset. My perspective, not widely shared, is that JFETs in general have been made obsolete by depletion-mode MOSFETs, at least in audio circuits.

Part of the reason, I think, is that a lot of "designers" of guitar pedals don't understand the math that determines component values for a particular transistor in a particular circuit so they don't know how to either select a modern transistor to replace an obsolete one based on datasheet parameters or to change the collector / emitter / source / drain / etc resistor values to work right with a new part.

The article seems mostly right when it's about interfacing logic circuits with loads that require even moderate currents. FET is king in this field.

I've a little aquarium and I've noticed how fish always get scared when lights turn suddenly on or off. So I took an Arduino and wrote a timer app for it, using PWM to slowly drive the output up over 60 minutes (sunrise), keep it at max for a few hours, then drive it down slowly over 60 minutes (sunset). I used a MOS-FET to drive the power LEDs directly from the Arduino. Works fantastic, and the FET is cold at all times. A 2N3055 would have been pretty hot most of the time.

I've been playing with electronics for a few decades now, so I can't be accused of change for the sake of change. The old stuff still works, sure, but there are new toys which are better in some cases.

JFETs main application these days is for when you need very low noise, usually for precise measurements. A depletion mode MOSFET has similar behavior, but not specs.

If you properly drive a 2N3055 (so all the way to 'on' or all the way to 'off') you'd have to put a pretty good current through it to get it to get hot. The trick is to use the highest voltage you can get away with (most power for the least amount of current). .6V * quite a few amps before you overcome the housings capacity to get rid of the heat.

You'll need to properly drive it though and not at too high a frequency (and for obvious reasons, not too low either because you'll notice the flicker).