DPRG mailing list archives: [DPRG] calculating diode protection in snubber circuit.

Mon Nov 20 11:48:24 CST 2006

Hi Bill, et al,

>From my very limited experience (1 partially successful DC-DC
converter design, about 7 years ago), I seem to remember that using
fast-recovery diodes was important.

Here's an application note that may help, if you want to throw some
math at the problem:

http://www.maxim-ic.com/appnotes.cfm/appnote_number/849

Unitrode (bought by TI, I think) had a pretty good app note that
explained snubber networks.  Maybe it's on TI's site now.

Good Luck!
-Jeff

On 11/20/06, Kipton Moravec <kip at kdream.com> wrote:
> I agree with Rick. The diode should be able to handle the coil current.
> Most diodes also list their spike current which is many times the rated
> constant current. That gives you your margin.
>
> As a general rule I also like to use fast diodes because the voltage
> spike is very fast rising. You can see it with an oscilloscope.
>
> The diode is a flyback-diode in this case.
>
> A snubber is a resistor and a capacitor in series. It is used to suck up
> the same spike energy into a capacitor. The resistor tries to burn it
> off as heat.
>
> Kip
>
>
> On Mon, 2006-11-20 at 09:55 -0600, Rick Bickle wrote:
> > Bill
> >
> > I would think that the diode should at least be able to handle the coil
> > current. When the coil is turned off, it will continue the same current
> > flow for a short time. The voltage rating should be the coil voltage
> > plus a safety margin. Sounds like You're OK with 1A diodes.
> >
> > Rick
> >
> > -----Original Message-----
> > From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On
> > Behalf Of William James
> > Sent: Monday, November 20, 2006 8:37 AM
> > To: DPRG
> > Subject: [DPRG] calculating diode protection in snubber circuit.
> >
> > I am checking out some diodes in a snubber circuit and would like to
> > know if they are hefty enough. Does anyone know the calculations or rule
> > of thumb for calculating what size a diode needs to be.
> >
> > The schotsky diode are placed across the coil in a relay. The resistance
> > of the coil is 1.3kOhms and the voltage is 24 volts. That means that the
> > coil is drawing 18mA.  The diodes are rated for 1 amp. I don't know the
> > inductance of the coil.
> >
> > Thanks
> >
> > Bill
> >
> >
> >
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> --
> Kipton Moravec <kip at kdream.com>
>
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