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Blown Up Anytone AT-6666
- Thread starter TheRATT
- Start date
I say the same thing about my Swiss army knife if people laugh. I tell them to imagine it stuck in their eye and then they shut up.
It affects the turn on time. Maybe not that important as far as matching goes but you can find variances in the same part number by another manufacturer. All other parameters the same but the capacitance is way off.Not the gate capacitance, no.
But it will for Vgs.
The people matching these and selling them are only interested in Vgs.
They don't care about gate capacitance. It's a gimmick, remember?
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When designing no item is considered a "Gimmick."
That "Gimmick" will affect the input impedance of a tuned input.
Are we talking about MOSFETs in general or the fantastic properties of matched ERF2030s?
There is no datasheet, remember. We have no idea what the gate capacitance is unless I sit here and characterize a few of them and I don't feel the need to bother with it, tbh.
Well, the sad part of all this is I see the Capacitance (with gate off) going up on every new part that shows up to supersedes the one it replaces.
What used to be about 1000pF has gone up now to about nearly 0.01uF (~8000pF!) so yeah...considerably higher finagling of tuning requirements...
What used to be about 1000pF has gone up now to about nearly 0.01uF (~8000pF!) so yeah...considerably higher finagling of tuning requirements...
Well if we are just swapping out the same parts, okay no problem. But if you are changing it to another type of fet then it matters.
That's what I mean - they have a larger gate "trigger" plate. So that equates to a leverage issue of applying enough bias current to "wash" the plate clean after each use and keep it from staying on or latching up...
I agree. It does matter.
But keep in mind these gimmick parts with no datasheets like the ERFs have mystical properties I liken to the unicorn and we have no real way of knowing what these things really are. Obviously they were binned to be close enough to work for either of the prevailing MOSFETs in use. (The IRF520 and 13N10)
These people that swap these MOSFETs do not care about such things. All they want to see is Vgs being the same when that's only part of the story.
I had a design in which occasionally the fets would latch on. I put a 100K resistor from gate to source. Fixed it right up. It was one of those deals where purchasing bought a similar part but the gate capacitance was double of the originally specified part.
So noted! Worth re-quoting so others don't miss this...
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That's a more common mistake than people realize and on the EE portion of stackoverflow all the time.
They don't understand why the MOSFET they connected directly to their GPIO (BAD) just stays on all the time.... surprise! gate capacitance and not ensuring the state of your GPIO with a pullup/down
