Re: Sync gap strobe light...

• To: tesla-at-pupman-dot-com
• Subject: Re: Sync gap strobe light...
• From: Neon John <johngd-at-bellsouth-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Tue, 29 Jun 1999 05:29:30 -0600
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Tesla List wrote:
> 
> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> 
> Hi All,
> 
>         While watching the input of a switching power supply today at
work, I had
> a "brainstorm" about the sync gap strobe thing.  Then I read all the great
> suggestions many people gave and combined them into a neat little design.
> 
[snip]
> 
>         The design should be fool proof but don't change any of the values or
> things may go bad.  R1 is a current limiter and help get the pulse times
> just right.  R2 provides a load so the cap discharges just the right amount
> to need more charge at each cycle.  C1 is a cap that likes to draw spikes.
> D1 is the big LED.  T1 is a small 12.6 volt AC transformer.


I see one potentially fatal problem with this design. Let's assume
the cap charges to near the peak AC voltage minus maybe 3 volts for
the LED drop on the positive swing.  let's say 15 volts.  On the
negative swing, the LED must also serve as the blocking diode and
thus is subjected to 15 + (12.6*1.414) = 32.8 volts.  I've never
seen an LED that will withstand that kind of PRV for long.  To fix
the circuit, just put another diode, say a 1n4001, in series with
the LED and put one in reverse in parallel across the LED.  The
latter to limit the PRV on the LED to one forward diode drop.

Other than that, nifty little circuit.  Elegant in its simplicity.

John

-- 
John De Armond
johngdSPAMNOT-at-bellsouth-dot-net
Neon John's Custom Neon
Cleveland, TN
"Bendin' Glass 'n Passin' Gas"

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