[GreenKeys] Re: Rheostat

[Don Robert House]

"If necessity is the mother of invention, then simplicity is the  
father of design"  --- Henry Drefus

Don
K9TTY

On 9 Apr 2007, at 11:11 PM, WA5CAB at cs.com wrote:

And the fourth scheme is to replace the fragile transistor with a 25K  
25W EMP
and spike proof rheostat.  And never have to worry about it again.   
First
rule of fail-safe design - never use an active component when a  
passive one will
serve, work as well, and produce no more heat.

In a message dated 4/9/2007 10:00:34 PM Central Standard Time,
jhhaynes at earthlink.net writes:
> You have to snub to protect the transistor.
>
> One scheme is an R-C series circuit, where you choose the R and C
> so that it snubs adequately and dissipates the energy in the resistor.
>
> Another scheme is to run the R-C series circuit from colletor to
> base of the switching transistor, so the inductive spike keeps the
> transistor conducting until it dies out.
>
> And another scheme is to use a Zener diode or a MOV device to
> absorb the transient.
>

Robert & Susan Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
<wa5cab at cs.com> (Primary email)
<wa5cab at houston.rr.com> (Backup email)

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