Re: Switch-mode supply for bug zapper (fwd)

[<sroys@xxxxxxxxxxxxxxxxx>]

---------- Forwarded message ----------
Date: Wed, 22 Sep 2004 17:22:20 -0500
From: Dr. Resonance <resonance@xxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Switch-mode supply for bug zapper (fwd)



You need the factors for the steel you intend to use.  Different types have
different losses.  You obtain this from the mfgr.

Digi-Key has some inexpensive IR type emitters & detectors.  Have the fly
crawl a distance, like 4-6 inches inside the tube, and then, he triggers the
IR beam which controls the zapper.  A small single ended NST works great for
this application.  The current will burn them right up.  The fly hits the IR
beam at the 1/2 mid-way point which energizes a small grid in each
direction.  The midpoint has a section 2 inches long with no grid.  They
become trapped and can't exit either direction without getting zapped.

You could also use a 600 Ohm to 10K audio xmfr.  They make nice HV sparks
operating in a pulsed mode.  If the time duration is short, like 1-2 sec,
they could also charge a cap rectified with a 1/2 wave diode in a short time
period.  Then the charged cap waits for the fly.   The charging cycle occurs
every 5 minutes and is controlled by a 555 IC chip --- a small relay
controls the power section.

You put sugar crystals in the tube and at the end of the tube use a small
glass test tube so you can see your accumulated flies to adjust the time
periods.  The flies will accumulate and then try to go out the charged grid
section.

Dr. Resonance

>
> Unsatisfied by the performance of our bug zapper (UV tube, HV applied
across a
> grid - flies crawl in, then crawl out again without shorting anything), I
am
> looking at alternative designs.
>
> The one we have uses a conventional laminated iron, 50Hz transformer.  The
whole
> thing gets warmer than I'd like, so I'm looking at making a switchmode
version.
>
> My idea is to use a flyback topology (only two windings to wind) with an
> integrated switcher (TOP202), which runs at 100kHz.  This will drive a
1:10
> transformer, which will be rectified and charge a small capacitor.
>
> 1) What do I need to know and what formula would I use to calculate my
primary
> turns?
>
> 2) Ditto for sizing the components for the snubber.
>
> I assume that a microwave oven diode - normally working at 50-60Hz - would
be
> too slow for the HV rectification and that I'd need a string of high-speed
diodes.
>
> Cheers
>
> M
>
>
> -- 
> Matthew Smith
> Kadina Business Consultancy
> South Australia
>
>
>