Why does this boost converter circuit not work?

I tried this circuit using a 3.7v supply and instead of a 12v Zener I used a 5v Zener. I also used a 22uH inductor. I get 5v no load but when I add a load the voltage drops a bit and the current is 50ma max. Why is this not working and what could I change to make it work? If this is the wrong circuit altogether, then what discrete circuit would work?

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Well you should only get 5 volts with a 5 volt Zener and what is the 3.7 volt supply IE a NI battery what MAH?

Davis Lambert (author)  Josehf Murchison2 years ago

it's a 3.7v lithium ion battery 2800mah

Battery is small for that booster, the booster draws 2 amps and you have less than 3 amp hours for that booster you need 8 to 10 amp hours battery or the power will just die when you load it. (8000 mah to 10000 mah)

Davis Lambert (author)  Josehf Murchison2 years ago


iceng2 years ago

The resistance values are all wrong for that low an input voltage.

And the inductor core may be wrong too .

Usually start to make a direct copy to verify you got it wired right and then experiment.

Brake the connect at R6 and see if that Q1, Q2 oscillator is a stable SQ wave as a start.

Davis Lambert (author)  iceng2 years ago

what do you think the resistor values should be?

Your reducing the voltage by 63%

Try 2.2K => 1.5K .... 4.7K => 3K and see if it oscillates.

BTW change that SQ wave to a narrow pulse wave because of values.

The inductance seems high.

Davis Lambert (author)  iceng2 years ago

it is oscillating with the original resistor values and the circuit is boosting the voltage to 5v, but if I add a load, the voltage will drop because the current output is so low

Surely you know you said that before.

Ever consider the lower R values may give you the power your wanting.

And the 0.5mm is .019" which is a 24 gauge magnet wire but not enough to calc the real inductance...

Davis Lambert (author)  iceng2 years ago

ok thank you

kmossman2 years ago

It is not working because you are using an entirely differentg voltage input, and changed a major component - without adjusting any of the other components.

Would a diesel engine work on gasoline?

Would you walk normally if suddenly one femur was 10cm shorter?

Best to look for a circuit than fits your requirements.