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Circuit building: stop using antique parts (2014)

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Re: Circuit building: stop using antique parts (2014)

#91

Post by vvanders »

ChuckMcM wrote: post #12

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 boug…

Yeah, The Art of Electronics does a great job at covering the practical side of transistor choices and some of the trade-offs involved.

Re: Circuit building: stop using antique parts (2014)

#92

Post by wbl »

AceJohnny2 wrote: post #83

I've recently gotten back into hobby electronics, trying to revive all that EE knowledge I haven't used in 15 years, and one thing I sorely lack is knowledge of common components to use. Online electronics stores are no help because of the overload of possible components. Is there some sort of Cookbook out there I could refer to for up-to-date examples of common circuits and electronic tasks? I mean, I otherwise tota…

Horowitz and Hill third edition.

Re: Circuit building: stop using antique parts (2014)

#93

Post by mindslight »

ChuckMcM wrote: post #37
pravda wrote: post #34

Earlier quoted context omitted.

>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. Not sure why that made you sad (extraneous ' in its?). But I agree about the static-sensitive disadvantage of MOSFETs. Also, the author mentions that a TIP120 is not a transistor but a darlington pair (two transistors in one) but…

It wasn't the grammar :-) it was that the author considered the 10K resistor to ground as "not strictly necessary". It is critical if the microprocessor pin can float (tri-state). Without it, and a floating gate, not only will the FET eventually turn on, it can be damaged by excess charge build up.

nit: It's not wrong to assert that the microcontroller software will prevent the output pin from ever floating. And the gate's voltage will be constrained between Vdd and Vss due to the output pin's likely body diodes. Is it worth it to save a penny part, especially in a hobby/prototype design? No.

Also if you throw away all your BJTs, what do you use to drive the gate capacitance of your fancy FETs?

Re: Circuit building: stop using antique parts (2014)

#94

Post by Florin_Andrei »

jacquesm wrote: post #77
cr0sh wrote: post #62

Earlier quoted context omitted.

> before you overcome the housings capacity to get rid of the heat. The thing is, most of these larger BJT parts were designed to be used with heatsinks, not usually standalone. IMHO, there's nothing wrong with dropping some voltage and dumping some heat. Sure, it isn't efficient, but if you size everything properly, and your project can accommodate the heatsink - then where's the problem? Heck, a long time ago you c…

> outside of the L298's weird footprint, and the fact that heatsinks for them are almost unobtanium In a pinch: any piece of aluminum U profile will do, just drill a hole in it and use some heat conducting paste.

It could not possibly be easier. It's literally a flat piece of metal with a hole in it. Add a drop of heat goo in between for extra coolness.

Re: Circuit building: stop using antique parts (2014)

#95

Post by sounds »

TD-Linux wrote: post #74
sounds wrote: post #29

Earlier quoted context omitted.

I would love to see something on digikey or mouser that allowed me to search for MOSFETs in a way that was less painful. Let's say you wanted to do a special purpose switching power supply. Digikey doesn't have a column for gate capacitance (for the mosfet), or Q (for the inductor). All that manual work to read datasheets is terrible, especially if your design takes a little while to perfect and some of the component…

Digikey does have the gate capacitance, just specified in a weird way - gate charge @ voltage. Most higher power FETs are always specified @ 10V gate, so it's directly equivalent.

Thanks! I wasn't able to figure out if it really was directly equivalent. (Thanks also to sibling comment pointing out Mouser has the same.)

Re: Circuit building: stop using antique parts (2014)

#99

Post by guitarbill »

earlz wrote: post #36
PeanutNore wrote: post #14

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 "…

I'm a noob builder (constructed my first pedal a week ago, woo) but I can kinda understand this. Most effects tend to overdrive their components. This by definition means that they operate beyond what a datasheet and the manufacturer specifies. Tiny differences that aren't noticeable when going by the specs can become much more obvious when hearing it overdriven. Yes, the community is really based in "older is always…

> (though the resistor bit I'm not sure on why they don't just buy high precision ones for a few cents more)

high precision resistors can get expensive, aren't always readily available (depending on your volume), or simply might not be available in the power rating you need. especially if you don't need absolute precision you might consider it wasteful. so it's good to know how to match resistors when you're designing/prototyping the circuit.

because of that, it's probably become hearsay and superstition, and is consequently overused.

Re: Circuit building: stop using antique parts (2014)

#100

Post by zw123456 »

TD-Linux wrote: post #79
zw123456 wrote: post #59

While we are on the topic of using more modern parts, if you are controlling a motor as shown in the example, why not use an H-Bridge chip ?

You might only need to spin the motor in one direction.

Yes, but even so, they also have half bridge chips, all the biasing and compensation, the correct diodes etc. The point is, a motor controller chip is more modern way that the old transistor or MOSFET way. unless you are designing some cheapo thing that will be produced in the millions and have to scrape every penny out of the design, it is better and easier to simply use a motor controller chip in my view.
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