CAUTION: HIGH VOLTAGE (100 - 200 V DC)
This is a simple boost converter circuit. It takes in a low voltage input of around 3 to 9 volts and gives an output of 100 to 200 volts. You cannot use it to power anything though, since the voltage is right across the capacitor, and it falls rapidly with loading. However it can shock a person.
I made this using material easily available in any electrical shop, and some special electronic components.
Step 1: Theory
There are 2 circuits used in a boost converter.
- The boost circuit- It has an inducter, a switch, a diode and a capacitor. A quick change in current through the inducter due to the switch results in a huge voltage across it. This huge voltage creates a huge current which charges up the capacitor. The diode doesn't let the capacitor discharge, and the voltage keeps building up.
- The switch- I have used a 555 timer with BJT power transistor 2N6292. The 555 generates a square wave which rapidly turns the transistor ON and OFF.
Usually is boost power supplies a MOSFET is used as a switch, and also their is a feedback mechanism which stops the switching (or what i like to call, pumping) once the desired voltage has been attained. In this circuit however, I have not included that, since I just wanted a high voltage.
For more details, refer to this link.
Step 2: The Boost Circuit
We are upgrading the tubelights in our home to LEDs. So I had a lot of choke coils lying around. I used one of them for this circuit. The internal resistance as measured by the multi-meter was 120 ohm.
I bought a high voltage capacitor from a local electrical store. This capacitor is generally used in ceiling fans, as it is part of the single phase induction motor circuit. I used it here because it was rated at 440V.
The diode is a regular 1N4007.
Step 3: The Switch Circuit
I used a 2N6292 NPN power transistor. Initially I wanted to use a BC547 transistor, but I didn't get any switching action with it. So I used this one.
As for my square wave generator circuit,
Duty Cycle 66.7%
At first I tried to generate a high voltage by using the rated frequency of the choke coil (~50Hz). But for some reason the high voltage was not building up. So I tried manually switching it ON and OFF. I found out that a satisfactorily high voltage (~200V) was building up. So I setup the 555 to mimic the speed of my manual switching.
Step 4: Components-
1. 3 Resistors-
- 2 1kohm resistors. R3 and R1
- 1 100 ohm resistor R2
2. 4 capacitors-
- 1 100uF electrolytic capacitor, C1
- 2 10uF electrolytic capacitors, C2, C3
- 1 2.5uf 440V capacitor, C4
3. 1 NE555, U1
4. 1 2N6292 NPN Power BJT, Q1
5. 1 diode 1N4007, D1
5. 1 choke coil/ inducter, L1
Step 5: Breadboard Prototyping
Make the circuit first on a breadboard to make sure everything works. If it doesn't, troubleshoot. Mostly, the fault will lie in the switching circuit. Try and change the transistor. Play around with the frequency of the 555 until you get the high voltage you want.
Step 6: Designing and Soldering
Before soldering, I usually use eagle cad to place the components and see where I need to place the jumpers. I refer to these images while soldering.
Carefully solder all the components into place while referring to the eagle cad image or schematic.
After soldering, mount the perfboard on the choke coil and secure it with tape. Then mount the capacitor on the choke coil too. connect the wires to the choke with the screws. The main weight and shape of the circuit is from the choke coil only.
Step 7: Testing
I setup my multi-meter to test the circuit.
I tested my 5 V power supply (those green and grey jumper wires) and got an output of 5.21 volts.
I then switched on my circuit. I could hear a faint tick-tock inside the choke coil which told me it was working. This was because the frequency was only around 5 Hz. I connected my multi-meter at 200 V settings and saw an output of 198.8 V which fluctuated wildly, but was still at a high voltage level.
I then shorted the output terminals to discharge the capacitor. It sparked.