Electronics > Beginners

How to add soft-start feature to a PSU?

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Arjunan M R:

--- Quote from: TheHolyHorse on June 22, 2019, 06:29:46 pm ---
--- Quote from: Arjunan M R on June 22, 2019, 03:29:08 pm ---
--- Quote from: TheHolyHorse on June 22, 2019, 03:02:58 pm ---As for the topic, can't you just set the voltage slowly. I assume you're gonna control everything with some micro so doing that in software will be ezpz.

--- End quote ---
Yeah, but the code is already complicated enough for me.With 3 devices on I²C and 1 on SPI :phew:.
I am trying to do most of the things in the hardware side as possible.

--- End quote ---

I see, I'm more experienced with software dev than electronics so that just seemed obvious to me.

You could do a simple RC thing with a large time constant, but that's gonna affect it all the time not only during start up. I think I'm to much of a noob to come with any meaningful advise when it comes to doing it in hardware ;D

BTW out of curiosity what micro are you using?

--- End quote ---
Yes I am going to RC things to make softstart.
Just to simplify things a bit I am using an off the shelf arduino uno(ATmega328P).
I first decided to use just a MCU IC but it consumes a lot of space with the oscillators and all the things it needs to work.
When using a board like arduino uno I can just put it near the pcb and connect.That simplifies the board design and
Makes sure that I don't blow  up something because i am programming it when everything is connected.

Arjunan M R:
Just using Arduino uno because I have three of them sitting here without any use.

exe:
Q6 doesn't look right to me, too big for the job, imho. Why not using something smaller? Gate capacitance can be a stability problem if PSU supports CC mode.

I think paralelling D2 and D8 is redundant, imho. A uni-directional TVS would work the same, imho. What was the reason behind it?

As for MCU, for my PSU I chose stm32f373 as it has three DACs and and two or so 16bit ADC (datasheet claims 14bits noise-free). This way I reduced BOM, and avoided i2c/spi devices (and writing drivers for them). But I'm yet to finish the project, so not sure how the MCU is good for the job.

Btw, LT3080xST, afaik, has a minimal load specification. You should pull 1mA from it or so, or it will not regulate well small currents.

Arjunan M R:

--- Quote from: exe on June 23, 2019, 07:29:10 am ---Btw, LT3080xST, afaik, has a minimal load specification. You should pull 1mA from it or so, or it will not regulate well small currents.

--- End quote ---
I have a constant current source in the schematic.
It's a current mirror.

Arjunan M R:

--- Quote from: exe on June 23, 2019, 07:29:10 am ---Q6 doesn't look right to me, too big for the job, imho. Why not using something smaller? Gate capacitance can be a stability problem if PSU supports CC mode.

--- End quote ---
Just using IRFZ44N for the same reason as arduino uno.

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