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General => General Technical Chat => Topic started by: ferdieCX on June 15, 2018, 08:10:48 pm

Title: Does the BF840 have an internal diode ?
Post by: ferdieCX on June 15, 2018, 08:10:48 pm

Hi, I have just measured some BF840 with the DMM, and it seems that they have an emitter-collector protection diode. In the data sheet there is no mention about an internal diode, so I am a little surprised.
They are SOT23 packages marked NCW, so they should be BF840 made in China for NXP-Philips.
Does anyone know about that ?

Title: Re: Does the BF840 have an internal diode ?
Post by: David Hess on June 16, 2018, 03:21:47 am

I agree with blueskull; newer DMMs use a higher test voltage to support testing of blue LEDs and this might be enough to exceeded the 4 volt base-emitter breakdown voltage of the BF840.  There is no way that transistor has a parallel collector-emitter diode.

Note that base-emitter (or collector-emitter) breakdown damages the transistors lowering hfe which may or may not matter in the intended application.

Title: Re: Does the BF840 have an internal diode ?
Post by: ferdieCX on June 16, 2018, 12:41:00 pm

Thank you very much for your answers. I have used a Fluke 179, and it puts out 7 V in the diode mode   :palm:
I took 2 NEW transistors and repeated the measurement with a Simpson VOM that uses a 1.5 V battery.
In both transistors, the direct resistance base-emitter and base collector are both 20 ohms and the resistance between collector (-) and emitter (+) is 26 ohm
So, there must be another reason for this strange behavior :-//