In this PSU I'm working on, in the PWM gate drive, I found this sot23 thing, that seemed to be an N-ch JFET. It's marked NAN, searching around for NAN sot23, IDK what that is. The 1st 2 things that show up are in fact JFET listings, but they don't match the pinout.
https://www.google.com/search?client=firefox-b-d&q=NAN+sot23Out of circuit, in a device tester, that I don't think makes a negative rail, it said it was an N-ch, with Idss=2.7mA and Vgsoff=63.8V. So IDK what it does to get that. But it said the pinout, with the middle pin pointing away from me, is from left to right, G-D-S.
On a breadboard, it seemed to turn on around -1.6Vgs, and had no gate current, and was having around 10-15mA Id for 10-20Vdd from a 1k resistor. But then between my DMM changing ranges, possibly bad banana plug connections, stopping all current, and me turning up the Vdd to ~24V, I seemed to have zapped it, and now some current flows into the gate. Sometimes the tester sill says the same info tho.
The circuit is below, as the way it should be wired, if in fact the tester is right. But it is setup up more like a MOSFET, with the source on GND, the drain sinking the primary side L1 inductor current, along with a parallel SMD diode marked D1. And the gate is connected to the PWM, but like a MOSFET, taking it higher than the source.
In the sim, with a JFET with Vgsoff=-1.8V, the circuits works pretty much the same if I swap D and S, thats typical I know. And not much worse, if I GND the gate, put PWM on the drain, and inductor on the source. I guess because that diode is there too. A BJT works almost exactly the same too, almost the same current in the main switching inductor L4.
Another thing tho, with the JFET, (and a zero output resistance PWM source), I see the gate current is ~0.73A peak. So with an on time of 10us, that's 7.3uC, and with Vgs=1.6Vp, that would be 4.6uF if it was a normal capacitor. So how is that gate current actually so high? And if typical gate source capacitance is a few pF, how is the current so high for so long ?? Vdg is also about 1.8Vp. Is this the Miller effect, is it really that big ? ?
Also the diode current from the gate drive inductor L1 seems crazy at an average ~1.43A . I wonder what it is IRL. But thats basically the circuit (IDK the C4 and C15 values, or the exact diodes/FETs)