Electronics > Projects, Designs, and Technical Stuff
HOW DOES THIS WORK?? Bench light circuit has me stumped...
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engrguy42:

--- Quote from: thm_w on March 26, 2020, 10:52:26 pm ---D5 or D7 is not a zener?

Watch some of BigClives videos, he does a good job of explaining capacitive dropper circuits. Although I don't know a specific one to match that circuit.

Here is a solar/ac lead acid video: https://www.youtube.com/watch?v=IMYaWd_wuf8

C1 is the key in the front that allows a limited amount of charge to pass into the rectifier, R1 is to discharge C1 for safety.

--- End quote ---

Thanks, yeah you're right. Both the D5 and D7 are zeners, type 1N4007 (M7). So small that I missed it. I think 1 A, 1000volts or something.
Biduleohm:
Ok ;)

1N4007 is a very common rectifier diode, not a zener. And yep, 1 A and 1 kV.

And I think I know what D5 is for: allow to charge the battery but prevent D6 to be powered by the battery while not charging.
engrguy42:

--- Quote from: Biduleohm on March 27, 2020, 12:49:50 am ---Ok ;)

1N4007 is a very common rectifier diode, not a zener. And yep, 1 A and 1 kV.

And I think I know what D5 is for: allow to charge the battery but prevent D6 to be powered by the battery while not charging.

--- End quote ---

Okay. I put in the correct 1N4007's. My sim with the charging AC source on shows about 4.6 volts across the big capacitor C2, and -0.6 across D5, which means it's forward biased I guess.

Current is flowing "up" D5 towards C2, and current thru C2 is flowing down towards D5

My brain officially exploded.
Biduleohm:
That makes sense. If you redraw the schematic with the battery negative in the middle and the charger negative "-Neg" at the bottom it should make more sense to you of what's happening.
engrguy42:

--- Quote from: Biduleohm on March 27, 2020, 01:30:06 am ---That makes sense. If you redraw the schematic with the battery negative in the middle and the charger negative "-Neg" at the bottom it should make more sense to you of what's happening.

--- End quote ---

Thanks. But I'm still wrestling with the fact (?) that there should be a 120V full wave signal across the C2 at the output of the rectifier, right? But it's about 4v instead. So maybe the parallel RC at the bridge input on the AC side knocks down the 120VAC or something? And that damn D5 diode between the rectifier output and the battery negative just makes me insane.  |O
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