Author Topic: How to add soft-start feature to a PSU?  (Read 6726 times)

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Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #25 on: June 23, 2019, 08:03:50 am »
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.
Stm32 is expensive.
I will stick with what i have to keep the cost down.
 

Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #26 on: June 23, 2019, 08:08:10 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.

Yeah I might want to change the MOSFET.
Its input capacitance is 1470pF :-\.
I have a pull down resistor of 4K7 at the input.
So, it will take 4 µs to turn on or off the MOSFET. It's a lot. I will change the MOSFET.
 

Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #27 on: June 23, 2019, 08:10:34 am »
I think paralelling D2 and D8 is redundant, imho. A uni-directional TVS would work the same, imho. What was the reason behind it?
Yes a unidirectional TVS would work fine |O.
 

Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #28 on: June 23, 2019, 10:09:23 am »
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.
Stm32 is expensive.
I will stick with what i have to keep the cost down.

Well not really, the STM32F373 cost less than MCP3421A0T-ECH and MCP4922 combined and you'll get everything in one package. And as exe stated higher precision SDADC and IIRC the internal DACs are also better.
 
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Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #29 on: June 23, 2019, 10:13:59 am »
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.
Stm32 is expensive.
I will stick with what i have to keep the cost down.

Well not really, the STM32F373 cost less than MCP3421A0T-ECH and MCP4922 combined and you'll get everything in one package. And as exe stated higher precision SDADC and IIRC the internal DACs are also better.
Yeah , but then I have to buy the programmer and learn how to programm it.
 

Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #30 on: June 23, 2019, 10:14:59 am »
Yes, it's cheaper than arduino.
 

Offline Siwastaja

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Re: How to add soft-start feature to a PSU?
« Reply #31 on: June 23, 2019, 10:18:26 am »
Yeah , but then I have to buy the programmer

$1.42:
https://www.ebay.com/itm/USB-To-RS232-TTL-UART-PL2303HX-Auto-Converter-USB-to-COM-Cable-Adapter-Module/201539573206?hash=item2eecb1d5d6:g:sUoAAOSwyXVbaQjC

(using the bootloader. I have never used anything else than the built-in UART bootloader, or my own bootloaders written later. This is just fine, ignore the naysayers.)

Quote
learn how to programm it.

This is true, there's quite a bit of learning curve involved. The bright side is, it's going to be a very universal skill, over wide range of projects.

I jumped in the STM32 world (from 8-bit AVR) by directly designing it in in an actual customer project and promising delivery in one month :-DD. Funny times. In the end, the customer was satisfied despite delays (took two months to have anything work at all), and I learned a lot, but it happened quickly, and with the customer, we designed a proper V2 (using STM32 as well) a year later, with more realistic schedules.
« Last Edit: June 23, 2019, 10:22:32 am by Siwastaja »
 
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Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #32 on: June 23, 2019, 10:19:09 am »
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.
Stm32 is expensive.
I will stick with what i have to keep the cost down.

Well not really, the STM32F373 cost less than MCP3421A0T-ECH and MCP4922 combined and you'll get everything in one package. And as exe stated higher precision SDADC and IIRC the internal DACs are also better.
Yeah , but then I have to buy the programmer and learn how to programm it.

You can just plug in the usb download the DFU tool from st and flash it real easy. As for the programming it will probably be a bit more complicated, but that all depends on programming experience. The arduino will by far be easier, so if you're more comfortable with that go for it.
 
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Offline TheHolyHorse

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Offline Siwastaja

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Re: How to add soft-start feature to a PSU?
« Reply #34 on: June 23, 2019, 10:24:19 am »
Yeah, some indeed have the USB bootloader. UART works for the smaller STM32's not equipped with the USB peripheral or factory bootloader functionality for it.
 
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Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #35 on: June 23, 2019, 10:44:02 am »
I jumped in the STM32 world (from 8-bit AVR) by directly designing it in in an actual customer project and promising delivery in one month :-DD. Funny times. In the end, the customer was satisfied despite delays (took two months to have anything work at all), and I learned a lot, but it happened quickly, and with the customer, we designed a proper V2 (using STM32 as well) a year later, with more realistic schedules.

Yeah I've only played with some AVR stuff before as well so this will be my first project with the STM32 ;D
 

Offline exe

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Re: How to add soft-start feature to a PSU?
« Reply #36 on: June 23, 2019, 11:06:24 am »
To me stm32 has a huge learning curve (may be because I'm on Linux). But I don't know an alternative that would be that universal. I use Chibios for firmware. I don't use CubeMX because the code and API it generates is absolutely not to my liking. It's fine for led blinking, but when I tried more sophisticated programs I found Chibios much easier to use. Still difficult nonetheless.

BTW, I'm giving esp32+8Mb psram + micropython a chance. But it doesn't have many IO pins, so I'm stuck with SPI displays.
 
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Offline Kleinstein

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Re: How to add soft-start feature to a PSU?
« Reply #37 on: June 23, 2019, 11:15:10 am »
The choice of µC is probably the least problem. One difficulty with the STM32 is that they come in really small cases only. Not everybody can solder this, especially on a board with limited quality. One can do  something like AVR or PIC18 on a prototype board - the STM32 essentially needs a professional made board with solder mask.

A big problem of the circuit shown is that it starts with a voltage regulator and kind of adds a poor current limit as a an afterthought. This sytems tends to oscillate.  For the same reason Dave's 1 st Version of the µ-supply never got finished.  Designing a lab supply (combined voltage and current regulation) is not that easy as it sounds. Using a voltage regulator chips usually does not really help - it is more like making things more difficult.
 
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Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #38 on: June 23, 2019, 11:21:48 am »
The choice of µC is probably the least problem. One difficulty with the STM32 is that they come in really small cases only. Not everybody can solder this, especially on a board with limited quality. One can do  something like AVR or PIC18 on a prototype board - the STM32 essentially needs a professional made board with solder mask.

You can get boards from JLC for almost nothing and solder LQFP with 0.5mm pitch.
 

Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #39 on: June 23, 2019, 11:22:37 am »
 Then what is the best way to add current limiting?
 

Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #40 on: June 23, 2019, 11:24:09 am »
The choice of µC is probably the least problem. One difficulty with the STM32 is that they come in really small cases only. Not everybody can solder this, especially on a board with limited quality. One can do  something like AVR or PIC18 on a prototype board - the STM32 essentially needs a professional made board with solder mask.

You can get boards from JLC for almost nothing and solder LQFP with 0.5mm pitch.
But in my country i can't order from JLC.(that's not a problem)
 

Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #41 on: June 23, 2019, 11:26:47 am »
To me stm32 has a huge learning curve (may be because I'm on Linux). But I don't know an alternative that would be that universal. I use Chibios for firmware. I don't use CubeMX because the code and API it generates is absolutely not to my liking. It's fine for led blinking, but when I tried more sophisticated programs I found Chibios much easier to use. Still difficult nonetheless.

I'm gonna do everything from scratch, that's all part of the fun(for me at least). If you just wanna get things running you'll probably be better of using something like Chibios like you're doing. But I've never been a fan of that, not that there's anything wrong with em I just like programming :)
 

Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #42 on: June 23, 2019, 11:28:05 am »
The choice of µC is probably the least problem. One difficulty with the STM32 is that they come in really small cases only. Not everybody can solder this, especially on a board with limited quality. One can do  something like AVR or PIC18 on a prototype board - the STM32 essentially needs a professional made board with solder mask.

You can get boards from JLC for almost nothing and solder LQFP with 0.5mm pitch.
But in my country i can't order from JLC.(that's not a problem)

There are other cheap chines pcb manufacturer that will do the job.
 
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Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #43 on: June 23, 2019, 11:31:42 am »
Then what is the best way to add current limiting?

Mine is just using some mosfet as pass transistor. It's basically doing what the voltage regulator is doing internally.
 
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Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #44 on: June 23, 2019, 11:34:51 am »
Then what is the best way to add current limiting?

Mine is just using some mosfet as pass transistor. It's basically doing what the voltage regulator is doing internally.
Yeah, thats much simpler :phew:.
Can you post the schematic.
 

Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #45 on: June 23, 2019, 11:38:14 am »
Then what is the best way to add current limiting?

Mine is just using some mosfet as pass transistor. It's basically doing what the voltage regulator is doing internally.
Yeah, thats much simpler :phew:.
Can you post the schematic.

you can download the entire project from https://github.com/JeppeSRC/PowerSupply
 
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Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #46 on: June 23, 2019, 12:00:02 pm »
Here is mine.
 
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Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #47 on: June 23, 2019, 12:06:38 pm »
Here is mine.

BTW if you're making your own symbols and footprints save them in a project specific library and include that library with the project files. RN some symbols are missing.
 

Offline TheHolyHorse

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Re: How to add soft-start feature to a PSU?
« Reply #48 on: June 23, 2019, 12:20:51 pm »
Also "a trap for you players" like dave would've said. Check the minimum soldermask width. If you look at the attached images you'll see that on one image it's just two big blocks instead of each individual pad. It's gonna be real difficult to solder if you don't get that soldermask between the pads.
 
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Offline Arjunan M RTopic starter

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Re: How to add soft-start feature to a PSU?
« Reply #49 on: June 23, 2019, 12:30:22 pm »
Here is mine.

BTW if you're making your own symbols and footprints save them in a project specific library and include that library with the project files. RN some symbols are missing.
Sorry.I didn't save it into project specific library.What can I do.
Are you having problems with footprints.
 


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