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

Mon Nov 20 10:34:48 CST 2006

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>