| Electronics > Beginners |
| Low voltage drop transistor (or other device) |
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| electrodacus:
Yes an N-channel like MCH3484 (overkill) will work great and you will have almost no voltage drop. |
| permal:
--- Quote from: electrodacus on December 02, 2018, 07:48:37 pm ---Yes an N-channel like MCH3484 (overkill) will work great and you will have almost no voltage drop. --- End quote --- Thanks, but sadly the gate and source are switched compared to the SOT-23 so it won't fit the already existing PCB. |
| Zero999:
--- Quote from: permal on December 02, 2018, 07:03:15 pm ---3.3V, updated OP. I've never used a Mostfet before :) I'm currently using a NPN transistor, ZXTN25050DFHTA. Changing that to a Mosfet, it'd have to be a P-channel Mosfet, right? --- End quote --- That's an NPN BJT, so would need to be replaced with an N-channel MOSFET. What's wrong with the ZXTN25050DFHTA? It looks perfectly good to me. --- Quote from: permal on December 02, 2018, 07:45:38 pm --- --- Quote from: oPossum on December 02, 2018, 07:37:24 pm --- --- Quote from: permal on December 02, 2018, 07:30:08 pm ---Why is it a problem to put an NPN transistor on the high side? --- End quote --- The base voltage would have to exceed the supply voltage to get the lowest possible Vce. That is not a problem with PNP/P-channel because the base/gate is pulled towards ground. You can easily get less than 100 mV Vce at 100 mA with ordinary PNP transistors like PN2907 and 2N4403. --- End quote --- Oh, of course. Thanks for the suggestions, those are however THT mounted, I need a SOT23 to match the existing footprint. CMPDM7002AHC seems like a candidate, but what voltage is required on the gate to open it, I can't see that in the datasheet? --- End quote --- That looks reasonable, also try the IRLML2402TR. |
| T3sl4co1l:
Yeah, high side. You need a PNP or P-ch. Hack that in there (use pigtails if you have to fudge a footprint), and the enable signal will be inverted (active low). Vce(sat) is typically much lower than Vbe. Tim |
| oPossum:
If you replace the NPN with a N channel MOSFET, you will have greater voltage drop. You have to bodge in a P channel device as T3sl4co1l says. |
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