9V/1kV DC/DC converter

Currently I'm working on a device to electrocute home insects like cockroaches, progress is small because they are smarter than I thought, but that's a different story. For that project I had to find a source of sufficient high voltage and output power. Presented in previous post 5V/400V converter had insufficient voltage and power, another option, flyback transformer was too dangerous to be used here.

Finally, I have made a new high voltage supply based on an inverter transformer and voltage doubler. It seems to be ok for this job, but it can be used in various other applications so I'm presenting it in a separate entry.

Warning! the device produces high voltage that can be lethal, if you want to build it, please take cautions.

The transformer was salvaged from old LCD monitor, it was used there to power fluorescent tube. It costs around 6$, so they are not expensive. Unfortunately I couldn't find Eagle component library for it, so I had to make a new one. Q1 initially hasn't had a radiator, but later I added a small one because it was getting warm.

Full output voltage is present on R11, so it was protected against accidental touch by using a shrink tube. It's not the best way, but it's still better than nothing. All connectors have latches to avoid accidental slip out - important, especially for high voltage ones.

High voltage traces have bigger clearance to prevent spark gaps. Positive power supply rail has bigger width, because the current is around 330mA.

As visible on the rendering, by an accident I swapped top/bottom layer of two diodes. Opss!

A square generator is made from IC1A and IC1B, frequency depends on C1, R3, R4, pulse width depends on an R3 and R4 ratio. The signal is buffered by using IC1C and IC1D. Voltage doubler is made from C9, C10, D4, D5.

Output voltage = 1kV is at frequency around 11-14kHz, to minimize power consumption, I decided reduce output voltage to around 850V, this is equivalent to 5kHz from the generator.

If nothing is connected to the output, then even after power was turned off, C9, C10 can store enough power to provide unpleasant shock. To protect against that, discharge resistor R5 was added. C9 doesn't have one, so it keeps a high charge even after the device was powered off.

Input voltage = 9V DC, power consumption = 3W.

R3, R4, C1 may be chosen differently in order to provide a a bit lower/higher voltage and smaller power consumption.

Below is the signal on Q1 gate.

Output voltage changes over time, room temperature, no load.

Please ignore SV1 and R1 - this part is completely wrong - pin 1 of IC1A should be connected to Vdd or to pin 2 of the same gate. This area was supposed to turn on or off the generator by using an external control module, but it should be connected with pin 8 of IC1C and 12 of IC1D. In the current implementation, when the generator is disabled, t1 is fully opened. Dummy error.

Eagle files for this project can be downloaded from my GitHub repository.

At the end, just to show what I'm working on now, below is a movie of an electrocuted cockroach. Don't watch if you are sensitive!

4 comments:

  1. Very robust circuit, but no feedback loop - voltage will go up and down.

    ReplyDelete
  2. Hi. I will not comment the circuit, just the task.

    I have had a long waiting idea similar to yours, but it was not devised as a trap for roaming insects, but as a protective barrier for e.g. furniture or doorways. After all, I don't have anything against little buggers as long as they don't foul my food, dishware, clothings and body. Besides, their cleverness then works for you instead of against you: they will learn to avoid places where you specifically especially don't want them!

    Therefore I suggest you to make your concept geometry such that it achieves easily defined goals: prevent cockroaches from crossing certain lines, like passing between rooms A and B, entering a cabinet, climbing the legs of the table to access the table top or (in case of bedbugs) bed surface. Orient your active surfaces in such a way that they can't give shock to people or pets, e.g for doorways and other long barriers place tracks inside gaps too wide for insects to cross, but too narrow for fingers or animal tongue (you don't keep anteaters for pets?), and for tables and beds put tracks on ring plates encircling furniture legs, tracks facing downwards, with neutral ring being the outermost one.

    Another thing, from the video it seems your bugs are not zapped instantly, they perhaps suffer for a prolonged time. I wonder if a higher voltage peak would kill them instantly? If the resistance of their, quite thin, extremities is high (and I suppose that chitin which makes their exoskeletons is mostly a dielectric) you certainly would need more voltage to achieve amount of current surge lethal to them.

    ReplyDelete
  3. I have a device I bought from Home Depot that allows you to zap rats. It only take 4 AA batteries. They enter, eat some peanut butter and it zaps them. The LED turns from green to red to indicate that you got one. These are around $45. What kind of circuit do you think this uses? I could tear it apart but I don't want to. Do you think the circuit would be lethal to humans and how could I modify your design to make a similar circuit to what they probably use?

    ReplyDelete