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Utility of a Bat85 diode in this particular circuit

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Tito1337:
Hi everyone,

I'm working on a circuit that takes a 0-15V pulse-width modulation signal and converts it to the same signal but in the 0-5V range. It's based on a 5V zener diode, which I understand quite well, but it has another diode, here is the schematic (sorry for French legend, MLI means PWM  :P ) :


Does anybody understand the use of a Bat85 here? Thanks!

Alex:
It looks like it has some sort of bidirectional function. The current path backwards is via a smaller resistance, possibly discharging or clamping something.

You can use a simple divider to turn 0-15 to 0-5. My guess is that the input signal is an analogue signal 0-15V (not digital 0 or 15) then clamped at about 5V. What is connected around the circuit?

Rufus:
Without seeing the other circuitry either side it is hard to say.

Basically the output PWM is driven high with +15v and 10k and driven low with 0v less a Schottky diode drop and 1k.

Probably because the load on the output sources current and needs a low impedance drive which would be too low for the input PWM to drive at +15v or wastes too much power. You might want something like this if the output is driving an LS TTL input.

It could also be to speed up the PWM falling edges.

Tito1337:
The left part is connected to the PWM-generator (based on a LM311 comparator, 0 or 15V) and the right side to something like a relay controller (with two switches, one when input=0 and the other when input>0)

So if I understand it right, it helps the output to fall faster to 0V than through the 10k ? Or it's standard circuitry before a relay controller ?

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