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Old 15th October 2011, 08:34 AM   #1
BrianVG is offline BrianVG  Belgium
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Default SMPS with Microcontroller

Hi all,

I've read a thread where someone steps 35Vdc down to 12Vdc using a PIC.
Is it also possible to make go from 230Vac to 0Vdc-50Vdc using a microcontroller?

I think I'm going to use an Atmel Atmega to send out a PWM signal wich will trigger the MOSFETS in a halfbridge topology.

The PWM signal wil depend on a certain resistance I can control with a potmeter and will also depend on the output voltage. My program will check the output voltage to see if it is the value I set with the potmeter.

Is a transformer needed here?

Thanks
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Old 15th October 2011, 09:23 PM   #2
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I think MCP1631(?) has an oscillator which can be gotten from a PIC....and it has an internal error amp and current trip comparator too.

So you can control max duty cycle with micro or let the error amp do it.

http://ww1.microchip.com/downloads/e...Doc/22063b.pdf

woops sorry i just noticed its not got double ended drive as needed for half bridge...maybe they do one like that anyway ? somewhere

Last edited by eem2am; 15th October 2011 at 09:25 PM.
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Old 16th October 2011, 10:11 AM   #3
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Quote:
Originally Posted by BrianVG View Post
Hi all,

I've read a thread where someone steps 35Vdc down to 12Vdc using a PIC.
Is it also possible to make go from 230Vac to 0Vdc-50Vdc using a microcontroller?

I think I'm going to use an Atmel Atmega to send out a PWM signal wich will trigger the MOSFETS in a halfbridge topology.

The PWM signal wil depend on a certain resistance I can control with a potmeter and will also depend on the output voltage. My program will check the output voltage to see if it is the value I set with the potmeter.

Is a transformer needed here?

Thanks
You can use a microcontroller, a FPGA or a supercomputer to control the SMPS. An analog chip like sg3525 does the same job and it is not a hard job to mimic that chip in digital domain.
A transformer is a power transfer device giving a galvanic isolation and voltage/current transformation. Reconsider what and why you are going to do.
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Old 16th October 2011, 04:50 PM   #4
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the problem with using a PIC to drive the fet or fet driver is that they have to have a fast oscillator in order to get good duty cycle resolution.

this means they use a fair bit of power and are more expensiv........unless you have a sub 5 khz switching frequency
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Old 18th October 2011, 05:33 PM   #5
BrianVG is offline BrianVG  Belgium
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This is something new for me. I'm just figuring out the possibilities and read some technical papers.

Does anyone has a usefull pdf/website where I can learn more about SMPS.
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Old 19th October 2011, 10:27 AM   #6
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Originally Posted by BrianVG View Post
This is something new for me. I'm just figuring out the possibilities and read some technical papers.

Does anyone has a usefull pdf/website where I can learn more about SMPS.
SMPS (Switching Power Supply) Design; Circuit Diagrams is a good place to start.

Unquestionably, you will learn much more using analog chips, a microcontroller has its only big advantage of flexibility, it is also easier to re-program than re-solder, but that's all.
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Old 19th October 2011, 11:03 AM   #7
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Default SMPS, controller versus switcher-IC

Hi Brian,
I just bult a SMPS that was on the forum Page Title
(the 1kW smps project based on MicrosiM design).
Since it is too big for me, I started to design my own, smaller one, only 500W.
I'll take SG2535 as controller, EDT39 For the main transformer. To drive the gates of the power mosfets you can use transformer, or something like IR2110.
I thought about a controller (pic/AVR/...) for overvoltage-, overcurrent-, overtemperature- protection etc. This would make sense, to get rid of
a lot of comparators etc. I would suggest you to first build a 'normal' SMPS like the are described there, to learn about power switching etc. Then you can design your own, using a controller.
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Old 21st October 2011, 06:29 PM   #8
BrianVG is offline BrianVG  Belgium
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Thanks for the replies.

In a few months we need to make a project at school. It needs to contain an analog circuit and a microcontroller to control something. I'm just checking out what would be possible to make. I want to make something related to audio but a Class D amp is still to difficult and maybe a SMPS is too. We didn't really have had courses about SMPS.
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Old 1st November 2011, 12:25 PM   #9
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Hi,

I'd suggest making something less safety-critical than an SMPS.

If you intend to create an audio related circuit, maybe a simple digital volume control is a good choice.

You could use a uC, read a rotary encoder, display current volume on a 7 segment LED display, and control a volume chip (eg.:CS3310) thru SDI.

You can make it more complicated: creating a complete digitally controlled preamp with source selector and EQ (eg.: TDA7468, free samples available at ST), and you could also use an LCD display too...

Best regards.
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