Is there replace ment for J113 fet?

[skylly]

I cant find J113 in our country.

[greylourie]

If you can't find J113/MBFJ113, then maybe try 2N4393/MMBF4393. Or you could change some of the circuitry and use cmos switches like 4066/4053 etc.

But I am surprised in China you cant find these parts.

[skylly]

may i use a bf245?

[Davor]

Most probably you may. You may expect somewhat higher on resistance, and somewhat lower gate capacitance, but if Vgso is OK for your application - it will work.

[skylly]

ok, thanks, I'll have a try.

[skylly]

Allmost done.

[skylly]

Have problem at step 7, for Q3 and Q4, I use pn4393. I can't change the Voltage of TP4 to 500mv by adjusting R6. It always -0.03v.

[Darin]

Did you short the pin 2 to pin 1 or 3 at PL3

[skylly]

Yes, I shorted PL3 at step 6.

[greylourie]

I wonder if the gate cutoff source voltage ratings on those PN4393 could be a problem ?

Datasheet shows :
J111/PN4393 has Vgs(off) of -3v to -10v
J113 has Vgs(off) of -0.5v to -3v

[Davor]

If Vgs(off) is below the lowest voltage at gate, the FET is constantly conducting, and that is a problem. Ideally the Vgs(off) is around midpoint between high and low voltages at gate.

[skylly]

Allthough my MPP can detect metal.
I'll get J113 anyway...

[KRinAZ]

Have problem at step 7, for Q3 and Q4, I use pn4393. I can't change the Voltage of TP4 to 500mv by adjusting R6. It always -0.03v.

I have the same issue with my RevC MPP, & I have the J113 in the circuit, so I just ignored the voltage at TP4 since I used an o-scope for all calibrations - my MPP works fine regardless of the voltage at TP4.

By the way, if mouser.com delivers to CN they have the J113 in stock...

[pigeon]

Hi
It is possible to use k117
Thank you