Re: Power Supply Circuit

Les,

What it does is sense the 120Hz cap charge restoring current pulses.
If these are absent, such as when the AC power is shut off or if the
cap is being backdriven by a drive, a power MOSFET crowbars a wire-
wound power resistor across the supply. The resistor is sized so that
it draws the full current rating of the supply thru it.

A 10A, 80VDC supply filter cap would be 10,000uF for a 10% ripple at
max current. The crowbar resistor would be 8 Ohms, forming a time
constant of 80 milli-seconds. Three time constants would be about a
1/4 second discharge time for the supply after AC power shut-off.

A backdriven supply develops a voltage rise on its filter cap. This
biases the bridge rectifier off and no current flows thru it. The
sense circuit again places an 8 Ohm load across the supply until
rectifier current is re-established.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "Les Watts" <leswatts@r...> wrote:
> Great!
>
> I need to build up a snubber for my supply. Is yours some kind of
> zener/driver/power transistor?
>
> I am running at reduced speed and acceleration due to a too small
power
> supply.
> I recently got 3000w transformers that will give me about 60 vac.
That will
> give about
> 85 vdc which is about right for a 90vdc max amp. The combination of
line
> overvoltage
> (common here) and servo regeneration charging the cap could cause
amp
> overvoltage
> shutdown often so a snubber would be a good thing for me.
>
> Les
>
> Leslie Watts
> L M Watts Furniture
> Tiger, Georgia USA
> http://www.rabun.net/~leswatts/wattsfurniturewp.html
> engineering page:
> http://www.rabun.net/~leswatts/shop.html
> ----- Original Message -----
> From: "mariss92705" <mariss92705@y...>
> To: <CAD_CAM_EDM_DRO@y...>
> Sent: Friday, June 14, 2002 2:12 PM
> Subject: [CAD_CAM_EDM_DRO] Power Supply Circuit
>
>
> > Hi,
> >
> > I have drawn up a power supply circuit that will:
> >
> > (1) Dump the supply voltage very quickly when AC power is turned
off
> > (2) Dump "returned current" from steppers or servos
> > (3) Has a green LED "POWER ON" indicator
> > (4) Has a red LED "DUMP" indicator
> > (5) No relays. All electronic.
> >
> > I will breadboard the circuit and test it this weekend. I will
post
> > the diagram after that if anyone is interested.
> >
> > The circuit will fit on a PCB that can be mounted atop the main
> > filter capacitor via the two cap terminal screws.
> >
> > You keep your transformer, bridge rectifier and filter capacitor
as
> > is. This just sits on top of your capacitor and does its thing.
> >
> > Mariss
> >
> >
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