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LTC3780 buck boost converter

mgurpreet — Thu, 09 Jan 2020 11:04:09 GMT

I am trying to make lab bench power supply with buck boost converter, I am using LTC3780 buck boost converter which is easily available in Chinese market. Now the buck boost converter has three variable resistors namely vout-set, cc-set, uv-set. uv-set is under voltage protection which is not necessary for my project. I need to replace vout-set and cc-set with bigger potentiometer. Vout is 500k which is available in market but cc-set is 200k which is not easily in market. So can i use any other pot instead of 200 ?[View:/resized-image/__size/620x827/__key/communityserver-discussions-components-files/198/2744.contentimage_5F00_127634.jpg:620:827]

RE: LTC3780 buck boost converter

michaelkellett — Fri, 10 Jan 2020 10:02:56 GMT

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.

RE: LTC3780 buck boost converter

mgurpreet — Fri, 10 Jan 2020 04:01:14 GMT

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

RE: LTC3780 buck boost converter

dougw — Fri, 10 Jan 2020 03:54:50 GMT

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

RE: LTC3780 buck boost converter

mgurpreet — Fri, 10 Jan 2020 03:42:54 GMT

Ok, please trace and then let me know.

RE: LTC3780 buck boost converter

dougw — Thu, 09 Jan 2020 15:17:35 GMT

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.

RE: LTC3780 buck boost converter

michaelkellett — Thu, 09 Jan 2020 14:10:33 GMT

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.

RE: LTC3780 buck boost converter

shabaz — Thu, 09 Jan 2020 12:28:36 GMT

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.

RE: LTC3780 buck boost converter

mgurpreet — Thu, 09 Jan 2020 12:25:26 GMT

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.

RE: LTC3780 buck boost converter

shabaz — Thu, 09 Jan 2020 11:40:32 GMT

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).