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How do I build a DC-DC boost converter? Answered

Hey Guys!
I want some advice regarding boost converters.
I want to charge a capacitor rated for 450v 1150uF using a boost converter with input voltage >12 volts.
What kind of inductor values will I need?
What should be the duty cycle and frequency of the square wave generator?
And is there any formula to calculate this or a calculator?
Thanks in advance,



3 years ago

I would go really complicated and salvage a disposable falsh camera.
All you need on the circuit board and only 1.5V required ;)
Keep in mind you have to charge your cap to the specs.
You can't just feed it 450V and unlimited amps as it will act as a short circuit when empty.


Answer 3 years ago

Well, for starters I live in India. Disposable cameras here are a dream! Well, so is any transformer based charger, actually. The only thing I can get is parts and I don't know how to put them together :-(


3 years ago

The question is too vague to answer. As it stands, just about anything could work. All you really need to do is utilize the flyback effect of inductors to boost voltage.


All boost converters work like this. They allow current to start flowing from the low voltage power supply through a switching element, directly to ground. The current grows larger and larger but soon the switching element is switched off, and no more current is allowed to flow through that switching element. The magnetic field that has been produced collapses and you get a insane voltage spike where the end of the inductor is. This is because you cannot change the flow of current through an inductor simultaneously.

Inductors are analogous to hammers. when you bring a hammer to a sudden stop, the force that it produces is enormous, allowing huge pressures to be applied to, say, a nail.

If the current has nowhere to go, it will likely destroy something. So you stick a diode from the inductor to a storage capacitor, so that the voltage spike can only climb as high as the whatever voltage is currently stored in the capacitor at that time, plus the diode voltage drop. When it reaches that voltage, the current can continue to flow through the diode and charge the capacitor until the energy that was stored in the inductor has been fully released.

REAL switchmode converters have much more circuitry built in to vary the frequency, duty cycle, etc. of the pass transistor to regulate the output voltage. (In the most basic sense, they just turn off once the output voltage needed has been reached.) Without that, the voltage on the capacitor will just continue to increase over time until something fails. I had this happen to me when I made a 40V boost converter, and my feedback resistors were the wrong values. The voltage on my capacitor got up to 180V, and the chip actually exploded!!! :-O A chunk of it hit me in the face!


As long as the switching frequency is high enough that you don't saturate the inductor's core, and that the voltage spikes where the switching element is don't exceed the maximum voltage of the switching element, you should be fine. A larger inductor generally means that you can use a lower switching frequency. Real switchmode converters operate in the 100's of KHz, upwards into the MHz range.