3842 SMPSU Odd Jobs

I don't really understand what you're trying to do here, but, I don't see any problem with repeatedly running the startup sequence for the chip.

A few observations.

The chip does not have a FET incorporated it has a totem pole output for driving a FET. Or is that what you meant?

A person can run about 20 yards in 2 seconds, I don't suppose cattle are much slower (if at all), so one of them could easily break the wire and be well out of the way before noticing anything. But you say you have a system which works so I'm probably well off track. Then again it may be possible to reduce the power used even more by making a system which only supplies a pulse when the wire comes under a bit of tension. (Just thinking aloud.)

Why not go the whole hog and use the UC3842 as a power supply, you just need a suitable FET and transformer.

First results in today!!

I have powered up the circuit and got my 1khz pulse chain although i am tempted to bring it down a little perhaps to 500hz. Also the mark space ratio needs to be got a little closer to 1:1. This is a simple potential divider from the VREF pin.

The spark is about 4mm long and that is about the size i need.

The problem is domestic cats digging up seedlings in the veg plot.

I am using this method since it is the long run is cheaper than an air rifle or poison before you even think about vet bills and any legal costs.

And yes i have an IRF840 driving the coil. I just took it for granted that all readers would assume i had fitted a FET.

The coil seems happy with 110V P/P applied.

Anyone got any idea where i can get a data sheet for a BMW ignition coil from?

That is the kind of thing i am looking for. The one i am fiddling about with does not have the integrated power stage. It is a good start though.

Cheers.

About the FET.

The FET is there to be seen by all. I had a quick look for an old one without an insulated tab as it is a bit of a waste since the duty cycle is so small that there is no need for a heat sink.

I am pretty sure it is going to be fine running from 24 volts AC with a tripler in the remote unit on the fence post as it only has to charge up the capacitors before each pulse.

Can you post a snapshot or diagram of your schematic? I wonder if this would work for the squirrels that keep trying to bury (and unsuccessfully dig up) their nuts in my garden every year???

I did change one or two values and can't remember what was final. The unit is on field test now so i have left the old values readable for reference. Remember that the DC resistance of the coil is 0.68R and the 1uf capacitor has to be similar to the type used in a CRT fly-back circuit. Those resin dipped ones split open after a while it they are used here. PF correction capacitors will also be fine for this job.

We had some footprints on the parsnip bed ending in two deep ones where the unit programmed a feral cat with a virtual air gun pellet. That feral cat may try again after it has hidden under a parked car and tried again while we are out and then we should have no more trouble.

Right.

I am now looking into the mark space ratio during the start up period.

This is important for my job.

I am going to try the 3844 or 3845 as the mark space is too high on the 3842 in my circuit or during start up.

We are almost there now!