Schottky Bridge Rectifier, Reverse Voltage Breakdown

[ACharnley]

Hi,

I have an AC source (dynamo bicycle hub) which gives low frequency AC that can potentially range from 1v to 100v without load. Amperage will be low, < 1 Amp for sure. If, for efficiency, I were to use 4x schottky diodes instead of a traditional one chip silicon bridge, would the reverse voltage, if it were high, cause the schottky to break down?

As for the load, it's a 24v zener/darlington regulator with a switch mode between + and collector. As I understand it after 24v a greater load would be applied, but only if the switch mode was consuming power, else the load would still minimal (a 1.5k resistor and 24v zener).

Thanks, Andrew

 

[ACharnley]

The 5819 is 40v reverse, so that would be 80v total?

In theory, I shouldn't hit that.

**broken link removed**

However it is to replace a kbp307 which has a voltage drop of only 1.1V. That seems identical to using 5819 Skhottkys?

 

[Diver300]

The 5819 is 40v reverse, so that would be 80v total?

No, because each leg of the rectifier has one forward biased and one reverse biased diode, so all the voltage is across the reverse biased diode.

The kbp307 is rated to 700 V, so the 40 V diode is too low and will break down. I don't know if breakdown will actually damage the diodes.

You could put a zener to limit the voltage. Alternatively you could use MOSFETs to form a synchronous rectifier.

Can you post your circuit? Switch-mode regulators can behave in odd ways when run from current-limited sources like alternators.

 

[ACharnley]

I'd post the circuit if I had it, but essentially AC into the KBP307, which goes to a TIP142 with a small buck WP1804 between + and collector, and a 1.5W/24V zener between + base and -.

There's a 25v 100uF capacitor on the circuit input and 6800uF capacitance on the 5V output side, which I've tested as working well with the dynamo.

Space is extremely limited so unless the active rectification was small or on chip it wouldn't be possible. I hadn't heard about it though and will look into it!

 

[alec_t]

There's a 25v 100uF capacitor on the circuit input

I'd replace that with one having a much higher voltage rating than the zener voltage.
Personally, I'd tolerate the small loss in efficiency and use a conventional silicon diode bridge.

 

[dr pepper]

I have seen a few times diodes in series to increase voltage ratings, in fact theres a diode stack in a tv lopty.

If you were to generate a 100v at 1a with a bike dynamo you'd soon slow down!