# Help understanding the function of my circuit. (Bug swatter)

The important thing is the image below. I want to know how it works. Here's what I understand so far.

First I'll identify the pieces:

-The blue "packet" is a capacitor. Its a $0.030 \mu F$ with 400 V Capacitor.

-The resistance near to LED is a $560 \Omega$ resistor.

-The resistor closest to the black diode (close to the capacitor) is a $22M\Omega$ resistor; so is the one next to it.

-The resistor next to the transformer is a $1.2 k \Omega$ resistor.

-There is a resistor of $1.2k\Omega$ stuffed in between the transformer and the diode.

-There is a transistor below the transformer.

-There is a diode between the capacitor and the transformer.

My theory of how this works:

The batteries provide a voltage and this is fed to the transistor. The transistor provides an alternating voltage which is crucial to the transformer. The transformer then intensifies the voltage but this comes out as an alternating current, which is why we need a diode. The diode is connecting to the capacitor. That's all I can tell.

My questions:

What is the function of the capacitor in this circuit and why is it connected to the diode?

My two copper rackets (see first figure) discharge when they hit each other. How does this work?

What function do the resistors have? Are they in series or in parallel?

The product says it could generate a >1000V. Why isn't this harmful to a human being?

Those are my main questions up to now.

What is the function of the capacitor in this circuit and why is it connected to the diode?

My guess would be the diode is half wave rectifying the output of the transformer and charging the capacitor up. The capacitor provides the energy storage need for the racket to do the deed of dispatching the poor insect which has provide the connection to short the two copper rackets.

My two copper rackets (see first figure) discharge when they hit each other. How does this work?

Again, my best guess is the capacitor is connected across the copper rackets so touching them together shorts out the capacitor.

What function do the resistors have? Are they in series or in parallel?

They'll be for current limiting on the output of the transformer so when the rackets are shorted together you don't damage the diode / transformer / transistor (depending on how the components are rated and sized). Some of them will also probably be for tuning the self-oscillating circuit that drives the input side of the transformer.

The product says it could generate a >1000V. Why isn't this harmful to a human being?

Although it can develop high voltage, more than enough to hurt someone, it does so at such low current and energy levels it might give you a superficial burn at worst.

• @David Without having the circuit schematic it's hard to tell. My instinct is to think it's a flyback converter in which case the capacitor should be rated at the output voltage. The two rackets complete the circuit when they touch, therefore, it discharges. So i'm not sure about the claimed output voltage. Sustained current output i'd say is in uA, maybe mA at a push. Instantaneous current output is based on the energy storage, voltage and discharge time. By 'discharge' do you mean the arc / flash you see? – hooskworks Nov 28 '14 at 0:07
• @David Well, yes, because the capacitor is storing the energy that goes into creating the arc and causing the breakdown of the air / plasma formation. As i said, i'd be very suspicious of the claimed >1000V. If the two 'rackets' connect to either side of the capacitor then it simply can't be. If there were more components (more diodes and capacitors) then they could have used a voltage multiplier to boost the output but there aren't so I'm going to stick with it being unlikely the output is >1000V. – hooskworks Nov 28 '14 at 0:14
• The 'W' could mean something about the dielectric used inside it but it's not a common one i recognize and a quick bit of googling hasn't shown anything either. – hooskworks Nov 28 '14 at 0:35
• Not at all, a 1000V ~30nF in that sort of physical size and package is pretty reasonable. If you could reverse engineer the circuit and make even a basic schematic it would be interesting to see. If you read the Wikipedia article it says it can be between 500V and 1500V too. It simply gives an example with 1000V. – hooskworks Nov 28 '14 at 0:56
• – hooskworks Nov 28 '14 at 12:00