What about using the collector base diode in a bjt as a low leakage diode? It will be slower than the emitter base diode probably, but can handle 100+ V. I measured an MMBT5551s collector base diode leakage to be better than 1 pA @ 9V. The modern jellybean low leakage diode is the BAV199 probably.
A few reasons that the C-B junction is often a poor choice. It's got a bigger junction area, which means that it has a higher capacitance and a slower reverse recovery. Also, if you use the B-E junction with collector and base shorted, the transistor's current gain works for you to flatten out the curve of forward voltage with respect to current. Doing the same thing with base and emitter shorted is running the transistor in reverse-active mode, where the current gain is much smaller. I'll have to remember the BAV199 the next time I need such a thing. (As I said in the video, I seldom do need such a thing, but it's good to have it in my compendium of parts.)
ERRATUM: At 7:52, BD547/847/557/857 should be BC547/557/847/857.
I like the style. I appreciate your time and wealth of knowledge. I love this stuff.
Very informative, thanks for making these!
@@nicholasmascioni3333 Glad it helps!
I see you have BD547 as universal transistor, shouldn't this be BC547 instead?
@Kris_M oops! Typo in script propagated everywhere!
What about using the collector base diode in a bjt as a low leakage diode? It will be slower than the emitter base diode probably, but can handle 100+ V. I measured an MMBT5551s collector base diode leakage to be better than 1 pA @ 9V. The modern jellybean low leakage diode is the BAV199 probably.
A few reasons that the C-B junction is often a poor choice. It's got a bigger junction area, which means that it has a higher capacitance and a slower reverse recovery. Also, if you use the B-E junction with collector and base shorted, the transistor's current gain works for you to flatten out the curve of forward voltage with respect to current. Doing the same thing with base and emitter shorted is running the transistor in reverse-active mode, where the current gain is much smaller.
I'll have to remember the BAV199 the next time I need such a thing. (As I said in the video, I seldom do need such a thing, but it's good to have it in my compendium of parts.)