dc-dc boost convetter cascade (series)

[tural_h]

hello everyone, i made a cascade dc dc converter using mc34063 but using an external transistor, my main goal is to charge the capacitor at the 2200uf output in about 5-8 seconds, the input voltage is 3.7 ideally when the voltage is 6-7V for this I used two step up circuits first increased to 10V and then I need to get 80V but when I connect the second dc converter, the voltage at the output where it should be 10V drops to 3, the problem is how can I organize a cascade amplification circuit and what could be my problem? thanks for helping

[Andy Chee]

The source pin of the MOSFET should be connected to GND.

[PGPG]

I have Motorola Databook (Linear and Interface Integrated Circuits) from 1987 and MC34063 is there. But I'm sure that several years earlier I had xero of μA78S40 (=MC34063+OpAmp). It was first DCDC IC I have read about.
20+ years ago someone specializing in DCDC told me that this IC is so old and so bad that it is waste of time to try to use it.
Just have it in mind.

[tural_h]

hello, yes you are right, it works with a frequency of 100 kHz maximum and uses a Darlington pair, which is an additional loss and slow switching, I will have to look for another option

[PGPG]

I'm not sure, but bigger problem than these mentioned by you is its IC control scheme not ensuring even close to stable frequency.

In my opinion good ICs are those with current mode control loop (easier to stabilize than voltage mode as have one pole less in feedback loop).
I use only step-down ICs and I like the best COT (Constant On Time) control (see LM5017) as it reacts to load change in one pulse (while current mode needs 5..10 pulses to notice that load has changed).