Choke input power supply, capacitor ratings

[Wavebourn]

Is a bleeding resistor after a choke obsolete today?

[DougL]

Is a bleeding resistor after a choke obsolete today?

I do not think so.
However, I am designing an amp with choke input. The design used 30 ma into bleeder resistors order to protect the caps with no tubes inserted. 30 ma at 330V is a bunch of heat and used 10% of the chokes current rating. Seemed excessive.

A lower current bleeder (1-2 mA) and the zener diode over-voltage protection seems "better" to me.

Doug

[Will]

Originally posted by woody
That mur860 is verry likely to fail. The voltage rating is far to low.
Let me illistrate just with a cap input filter. Take a 10v transformer use one diode to rectify it and a cap filter you get 14.1 V less the ~1v lost in the diode or 13.1V then on the other half cycle when the cap is not charging the diode sees -14.1v from the transformer + 13.1v from the charged capacitor for a total of 27.2v across the diode. I believe in your case your
diode rated at 600v will be exposed to ~760v !

Hi,
Perhaps to overcome this issue of underrated diode is to use 2 in series ?

cheers.

[AndrewT]

Hi,
since the choke input supply requires a defined load to ensure it gives the correct voltage (0.9 * Vac) then consider a shunt regulator instead of the Zener string. It can be fitted between the choke and the capacitors or after the capacitors.

There are some HV shunt regulators posted on the Forum.

If the output current drops to near zero then the capacitor voltage could rise to 1.4 * Vac * {1+reg/100}.
That will be instant explosion.
Maybe a belt and braces over-voltage crow bar set to 384Vdc?

[Tom Bavis]

Even if you can find a 1400V rectifier, you may have problems with transients at turn-off. I would suggest an MOV or a small cap across the rectifier output (I think .3 uF will be enough). I HAVE seen 1400V /160A rectifiers fail in industrial use when not so protected.