# Power supply for ~170 VDC

Discussion in 'Electronic Design' started by lsiu, Jan 17, 2004.

1. ### lsiuGuest

Hello,

I am trying to build a DC power supply by simply using a bridge rectifier
and a capacity. The circuit is shown here:

http://lsiu.dyndns.org/static/circuits/supply01.png

However, when I pluged it in, the rectifier blew up on me. Since then I have

Any idea while the circuit doesn't work? The recitifier I used is RS206
(http://www.rectron.com/data_sheets/rs201l-rs207l.pdf), which should be able
to withstand 800 VAC.

I notice that when I tried out the bridge rectifier with a function
generation giving 20 Vpp sine waves, the output is not full wave rectifier,
rather, the supposing inverted bottom half of the sine wave is a "shaky
almost 0 V" curve on my oscilloscope.

Thanks for helping.

Leonard

2. ### Rene TschaggelarGuest

Whoa,
Never do that with line power without a transformer in between.
The line impedance is just too low. The transformer limits the current
amonst other stuff. Plus an additional resistor limiting the current
into the cap would help.

Rene

3. ### Fred BloggsGuest

It is ***EXTREMELY*** important that you ***NOT*** place your scope GND
probe at the negative terminal of the capacitor- this will create a
short circuit in the rectifier, and you cannot GND any terminal of the
then you will need to find an isolation transformer for the 120VAC line
voltage, or use a handheld voltmeter.

5. ### Gary LecomteGuest

In a Circuit like this you need a Current Limiting Resistor. The
In-Rush current to initally charge the capacitor is VERY HIGH.

I don't know the load current you expect to get, but I would suggest a
25 to 50 ohm resistor, Quite high wattage!

Gary

6. ### John WoodgateGuest

You have nothing to limit the inrush current into the uncharged
capacitor. So your current is limited only by the resistance in the
rectifier and the ESR of the capacitor - perhaps 1 ohm in total - giving
a potential 170 A peak!

7. ### John WoodgateGuest

I read in sci.electronics.design that John Woodgate <
But the primary cause of your burn-up may well be that you connected the
scope ground to the negative DC line, as given in another post.

8. ### N. ThorntonGuest

Both output wires will be live. Its a circuit to be avoided.

Regards, NT

9. ### lsiuGuest

Thank you very much for your help.

Leonard