Elektor-based 35 W self-oscillating boost converter

[Bootstrapper]

Hi,

I found an interesting article on self-oscillating boost converter from Elektor 2001 summer circuits collection. The title is "12V-to-24V Converter", author G.Baars.

The schematic for my slighly modificated version is shown as an attachment: the semiconductor components shown are not final, I have recently ordered more capable ones from the Ebay. I intend to have a 12V to 25V @ 1.5A converter so that if higher power is required, these individual converters could be parallelled. The most significant change is that I will use SMD parts (except the output caps), mostly 0805 resistor&caps.

This converter works with constant duty cycle defined by the astable multivibrator capacitances C1&C3. If a change in the duty cycle is needed, the value of C3 can be altered. The operating frequency is set by R1&C1. I came to these values after some simulations with a stepping current load. Anyway, the multivibrator provides the gate drive pulses. The difference amplifier Q3&Q4 compares the output voltage (divided by R10&Rtrim) with the zener voltage and shuts down the FET via Q5 when needed. The rest of the converter is a typical boost output stage with LC filter.

Has anyone experimented with this converter or any similar, non-isolated self-oscillating one? I'll post measurement results here as soon as I get the converter up and running.

[sawreyrw]

The astable operating frequency is set by R2*C1. Note that the ratio R2/R1 must be quite a bit less than the transistor current gain.

[Bootstrapper]

Correct, I wrote the post too hastily.