LTC3780 buck boost converter

Hi Gurpreet,

I don't know anything about this module or the chip. However, if you can find a 250k potentiometer (which should be easy) then you can just place a 820k resistor across it (it will not be a perfect replacement, but the difference in effect will probably not be noticeable with the circuit).

Hi shabaz,

I can only get  10k, 100k, 500k. Is there a way to put a resistor in parallel with 500k and make it behave like 200k or any other way.

Hi,

The further you go away from 200k, the greater the difference in effect. 250k is ok, and they are available to order from many suppliers.

You could try a different value, see what the impact is. It may be fine.

This module, and indeed this chip, are not very suitable for a lab power supply.

The 3780 seems to result in staggeringly noisy power supplies - in 2016 I was helping a customer with issues related to switching noise from this chip which they were using on a new board. I tested their original board, the Linear Technology demo board, a Chinese board a bit like yours and 2 different boards that I designed. They were all quite efficient and incredibly noisy. In the end we gave up on it altogether and used a buck regulator and some other design changes on the customer's board.

I think that the buck/boost architecture, combined with the use of external MOSFETs just makes for a really noisy design.

It does depend on what you are doing but for most people low noise and repeatable behaviour are the key things you need from a lab bench supply - go for a linear design.

Just for fun I've attached some pictures from my archive of bad results with LTC3780:

Chinese board (I removed the heatsink)

First attempt

Second attempt with extra filters - which helped but not enough.

MK

I expect it would work with a 100K pot, and maybe even a 500K pot, but I would trace out the circuit to make sure.

Ok, please trace and then let me know.

I don't have the module, it is necessary to measure continuity on the card to trace the circuit and draw the circuit diagram.

I want that power supply to repair cell phones and computer motherboards. Will the noise generated by buck boost converter is acceptable or not ?

I would say that this power supply is totally unsuitable for mobile phone or motherboard repair.

You need a decent linear lab supply, ideally with simultaneous current and voltage display and with a reliable current limit.

If you can afford one the AimTTi models are good (make sure you pick a linear one) - otherwise there are several much cheaper models from other suppliers but make sure you check out reviews carefully.

MK