Please help identify unmark glass diode

[debugtimog]

Hi Guys,
Please help identify this diode, as shown in the diagram below. I have check in the microscope, it really does not have any marking at all. It is used in power regulator unit.

[R_J]

Re: Please help identify unmark glass diode

maybe pictures of the board or a model number might help, If its not a zener, I would guess a 1n4148 would work

[budm]

Re: Please help identify unmark glass diode

If that circuit is correct, then yes, 1N4148 should be fine.
Is it tested bad?

[debugtimog]

Re: Please help identify unmark glass diode

It is missing on my board, but the other similar board still have it. I need to order but I dont know the PN. Thanks you all. I will go for 1N4148 then.

[MHTSOS]

Re: Please help identify unmark glass diode

Why would it have a reverse biased diode in the ISENSE pin of UC3854?

[petehall347]

Re: Please help identify unmark glass diode

Why would it have a reverse biased diode in the ISENSE pin of UC3854?

thermal tracking ?

[MHTSOS]

Re: Please help identify unmark glass diode

I don't know. In the darasheet of UC3854 is doesn't say anything about it. In other ICs (i.e. Cm6800) I have seen zener diodes reverse biased to Isense pin in order to protect the IC in case the primary mosfet shorts and you get a huge current through the current sense resistor and a very big voltage drop across it. I have a psu with CM6800, the mosfets were shorted, there was no zener in parallel with the sense resistor even though the darasheet shows it, the sense resistor was open/blown and the Isense pin of CM6800 got 380V and as a result it was blown too. I made some tests and I installed a 12V zener in parallel to the sense resistor. During the tests one mosfet blew again but this time only the mosfet and the zener died before the fuse blew. That's why a zener diode would make more sense to me in that place.