Boost Converter

This is the first time I am using inductor and with it I tried making a boost converter. The problem is that the voltage across the capacitor is not going above the supply voltage of 5v . I am using a axial inductor of 100uH in this circuit. I even checked the voltage across the inductor and found that it hardly gives a voltage increase of 1v . Is this due to the fact that I am using an axial inductor? What type of inductor should I use and of what value?

Schematic?

Bit of pragmatic advice here: Given that you can probably get a ready-manufactured boost converter to your omitted specification, using that makes much more sense than attempting to design your own.

Otherwise put - if you were going to design a boost converter into a PCB for commercialisation of tens, hundreds or thousands of units, you would not be asking here. :astonished:

Sorry, but that is reality. :roll_eyes:

santam: This is the first time I am using inductor and with it I tried making a boost converter.

Do you have a 'scope? Its really difficult to work with this kind of circuit blind.

The problem is that the voltage across the capacitor is not going above the supply voltage of 5v . I am using a axial inductor of 100uH in this circuit. I even checked the voltage across the inductor and found that it hardly gives a voltage increase of 1v . Is this due to the fact that I am using an axial inductor?

No, the shape isn't important, the electrical characteristics are, and inductors have lots of specs that matter, inductance, saturation, frequency range, series resistance, self-resonant frequency, etc

What type of inductor should I use and of what value?

Follow the recommendations of the datasheet of the converter chip to the letter for all components, inductor, capacitors, diode, and PCB layout.

Well, gotta say it's an interesting exercise to try. Just don't expect great efficiency.

I was quite impressed to see how a circuit as simple as a Joule thief manages to have a single pretty much empty alkaline battery (producing maybe 1.2V open circuit) light up a white LED fairly brightly!

MarkT: Follow the recommendations of the datasheet of the converter chip to the letter for all components, inductor, capacitors, diode, and PCB layout.

+1 to that. Don't forget that "PCB layout" thing. Yes, for any halfway decent converter you need a PCB.

I have attached the schematic of my circuit. Please tell me what is wrong with it and why is the circuit not boosting the voltage?

the boost converter does not convert dc voltages! you need to provide an ac , ideally square wave signal.

OP's circuit, posted properly:

Please tell me what is wrong with it and why is the circuit not boosting the voltage?

How rapidly are you operating the switch?

You get a "boost" only very briefly after the switch is opened. When the switch is closed, you are mostly short circuiting the power supply to ground, so it should be closed for not much longer than the LR time constant.

In a commercial boost converter, that switch would be a MOSFET, opened and closed perhaps 50,000 times each second.

jremington: In a commercial boost converter, that switch would be a MOSFET, opened and closed perhaps 50,000 times each second.

I think you lost a zero there.

The el-cheapo buck converter I use a lot is supposedly switching at 1-1.4 MHz.

50 kHz is still fairly common, and I did say "perhaps".

Here is a hand crank switched 500V boost converter for a "retro" Geiger counter.

If you use the output transformer from an old tube radio instead, a single 1.5V cell will generate > 600V.

I have used arduino to manage the switching process. The code is as follows:

setup()
{
pinMode(6,OUTPUT);
}
loop()
{
digitalWrite(6,HIGH);
delayMicroseconds(1);
digitalWrite(6,LOW);
delayMicroseconds(1);
}

I have attached the pin 6 to the base of the transistor as shown in the circuit diagram in the attachment.
But the problem is I am getting hardly 9v output with a 5v input voltage. How do I increase the output to like around 30v?

Hi,
OPs circuit;


Where did you get the basic diagram from and the component values?
How are you driving the transistor?
Do you have a base resistor fitted?
Have you got the gnd of the Arduino connected to the gnd of the boost circuit?
PLEASE MARK INPUT and OUTPUT voltage points.

Using a 1N4148 is probably not big enough, but its the basic boost circuit.

Tom.. :slight_smile:

The transistor i am using is 2n2222. The transistor is driven by the arduino and I am not using the arduino as a power source. I am using a external 5v power supply as the input. Only the digital pin 6 of the arduino is connected to the circuit to the base of the transistor.

santam: delayMicroseconds(1);

From the delayMicrosecons() manual page:

This function works very accurately in the range 3 microseconds and up. We cannot assure that delayMicroseconds will perform precisely for smaller delay-times.

That's an issue.

For the schematic: D1 is which exact type? 1N4148 will work (but not much current indeed). 1N400x not due to it's sluggish reverse recovery. Usually a Schottky is used in these circuits.

Power conversion circuitry stresses every component's performance to the limit, unless you are happy to live with 50% efficiency then every component's details will matter - ESR and ESL in the capacitors are hugely important, ESR and self-resonance in the inductor matter, switching speed and losses need careful attention, circuit layout is important, and protection circuitry is mandatory to stop the circuit self-destructing (inductors saturate and turn into short-circuits, without rapid protection circuitry to detect this and turn off the switch, then pop - the switch device vaporizes)

Its fun to experiment with such circuitry, but if you want reliable power, use a prebuilt switching converter designed from the manufacturer's datasheet for the chip involved, and using the exact pcb layout recommendations.

MarkT: Its fun to experiment with such circuitry, but if you want reliable power, use a prebuilt switching converter designed from the manufacturer's datasheet for the chip involved, and using the exact PCB layout recommendations.

See reply #2.

santam: The transistor i am using is 2n2222. The transistor is driven by the arduino and I am not using the arduino as a power source. I am using a external 5v power supply as the input. Only the digital pin 6 of the arduino is connected to the circuit to the base of the transistor.

What about the 5V supply gnd and the Arduino gnd? Have you got a series base resistor fitted? It doesn't look like it, fit one before you destroy the 2222. Try about 1K to start with. Tom... :)