Comment by Animats | Hacker News Reader

Comment by Animats | Hacker News Reader

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If you want to switch power, MOSFETs are the way to go today. Voltage drop is near zero. Digi-Key has over a thousand MOSFETs in TO-220 packages. Here's one of the cheapest with a low gate threshold.[1] Probably good enough for most Arduino on/off applications.

MOSFETs do have some problems. They can draw large gate currents for the first few nanoseconds of turn-on, which can overload whatever is driving them. The gate input is very vulnerable to electrostatic discharge during handling. Device failure tends to be into the ON state.

I just went through a big struggle with MOSFET selection for a special purpose switching power supply. The big through-hole parts have too much gate capacitance and need too much drive at turn-on. Only in surface-mount could I get something that would work.

That's the real problem with antique parts. The new stuff is surface-mount only.

[1] https://www.fairchildsemi.com/datasheets/FQ/FQP4N20L.pdf

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 components go end-of-life, so you have to replace them.

I personally like to graph the cost-efficiency curve so I actually have to tabulate lots of mosfets, inductors, and caps, then simulate them in a spreadsheet.

I know about the specialized design tools done by each manufacturer that will recommend parts and do a design for you based on your criteria. I want something that does a much broader search for parts though.

Maybe I should write one. :)

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.)

Is the Octopart search engine still running? Or something like it?

it is, https://octopart.com/search?q=

Mouser does have a column for gate charge that you can sort by.

There are definitely still new through-hole parts, but the selection is limited. It seems like maybe 20% of new transistors get a TO-92 or TO-220 version.

> If you want to switch power, MOSFETs are the way to go today.

But, even the mosfet is old. IGBT (depending on loads, but especially for slower switching)

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