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Old 17th July 2017, 12:00 AM   #71
ontoaba is offline ontoaba  Indonesia
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Ok, I'll try help redesign the mosfet and its sensing. About the MCU I'm not good at it, usually I have my friend did it. and looks like 8bit and 16bit mcu is no more supported by him. he said that today ARM based MCU is cheaper at the end, easier, and quicker to hand the project because its also very good with RTOS, and M4 can also run some linux app.

I did some quick search and found stm32f373 was cheap ($5@digikey and $3+@aliexpress), it has precise 12bit ADC, +-0.7LSB of INL. and 3x16bit SDADC (sdadc isn't good for dc but it may still worth).

You can choose which best MCU for $6 margin, I can order it and start with the mosfets. I need some specific information about its limitation and operating range. Will message you about it later.
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Old 17th July 2017, 12:44 AM   #72
Reactance is offline Reactance  South Africa
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Quote:
Originally Posted by ontoaba View Post
Ok, I'll try help redesign the mosfet and its sensing. About the MCU I'm not good at it, usually I have my friend did it. and looks like 8bit and 16bit mcu is no more supported by him. he said that today ARM based MCU is cheaper at the end, easier, and quicker to hand the project because its also very good with RTOS, and M4 can also run some linux app.

I did some quick search and found stm32f373 was cheap ($5@digikey and $3+@aliexpress), it has precise 12bit ADC, +-0.7LSB of INL. and 3x16bit SDADC (sdadc isn't good for dc but it may still worth).

You can choose which best MCU for $6 margin, I can order it and start with the mosfets. I need some specific information about its limitation and operating range. Will message you about it later.
http://docs-europe.electrocomponents...6b814f4531.pdf

Perfect MCU choice! it even has a 12bit DAC, one less part to deal with. looks like the only external parts remaining is an external reference and spi flash memory to store the data logging, store settings and calibration data.

2.5Vref, 12bit ADC, 610uV per step, 4096 Quantization levels.

I will stay clear of any rtos for now, a state machine is simple enough. I have a licenced copy of keil V5 and a programmer header. I have a uncompleted STM32F4 DSP subwoofer project on my desk .
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Last edited by Reactance; 17th July 2017 at 12:56 AM.
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Old 17th July 2017, 02:35 AM   #73
ontoaba is offline ontoaba  Indonesia
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which one you prefer? f3 or f4? f4 will be best for DSP, it has +-1.5LSB of INL. its decent 12bit ADC as well.
and it has more features.
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Old 17th July 2017, 09:28 AM   #74
Reactance is offline Reactance  South Africa
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Originally Posted by ontoaba View Post
which one you prefer? f3 or f4? f4 will be best for DSP, it has +-1.5LSB of INL. its decent 12bit ADC as well.
and it has more features.
I got both on order.
STM32F373V8T6, 32bit ARM Cortex M4 MCU, 72MHz, 256 kB Flash, 100-Pin LQFP
STM32F373R8T6, 32bit ARM Cortex M4 MCU, 72MHz, 64 kB Flash, 64-Pin LQFP

It turns out a 100PIN may still be attractive, user input buttons take alot of I/O and these devices are not badly priced, but I2C I/O expander is cheap as well.

As a reference this will come in handy.

How to filter the input of a high-side current sensing.
http://www.st.com/content/ccc/resour...DM00086777.pdf

Precision improvement techniques
for the A/D converter of the STM8 microcontroller
http://www.st.com/content/ccc/resour...CD00186359.pdf

UNDERSTANDING AND MINIMISING ADC CONVERSION
ERRORS
http://www.st.com/content/ccc/resour...CD00004444.pdf

How to get the best ADC accuracy (here they talk about the white noise trick eva explained)

in STM32 microcontrollers
http://www.st.com/content/ccc/resour...CD00211314.pdf
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There’s nothing worse than the smell of burned output transistors!!

Last edited by Reactance; 17th July 2017 at 09:31 AM.
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Old 17th July 2017, 11:42 PM   #75
ontoaba is offline ontoaba  Indonesia
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I did some changes to the mosfet and I need adjustment detail. load sharing between upper and lower mosfet and slope limit isn't implemented yet. will add later.
it has some advantage like short spike free from unstable source, and has quicker response.
it able to hold 100w by paralelling the main load with source resistor.
if you need ac 220v protection it required high voltage mosfet as the main load. but protecting from 220a isn't necessary.
the current sensing, since irfp250 max current in 30A it will safe to limit it at 15A. and the value of resistor can be adjusted to what you already have.

ok will order stm32f373 64pin. I ask my friend also and he recommend it.

any suggestion everyone is welcome.
it will be great project, isn't it?
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Old 18th July 2017, 07:43 AM   #76
ontoaba is offline ontoaba  Indonesia
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Should I make it switchable to AC load mode?
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Old 18th July 2017, 12:48 PM   #77
ontoaba is offline ontoaba  Indonesia
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also work this way. and will make it simpler 1st.
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Old 18th July 2017, 01:10 PM   #78
Reactance is offline Reactance  South Africa
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Quote:
Originally Posted by ontoaba View Post
I did some changes to the mosfet and I need adjustment detail. load sharing between upper and lower mosfet and slope limit isn't implemented yet. will add later.
it has some advantage like short spike free from unstable source, and has quicker response.
it able to hold 100w by paralelling the main load with source resistor.
if you need ac 220v protection it required high voltage mosfet as the main load. but protecting from 220a isn't necessary.
the current sensing, since irfp250 max current in 30A it will safe to limit it at 15A. and the value of resistor can be adjusted to what you already have.

ok will order stm32f373 64pin. I ask my friend also and he recommend it.

any suggestion everyone is welcome.
it will be great project, isn't it?
Hi, good attempt thus far, I'm lagging behind these few days, I started work today and some of my parts only arrived today, but they did arrive

I'm settled with the STM32f373, lets keep this conversation for later and jump into the analog stuff for now.

I see you have two servo amplifiers did you really need two ? or is the IRFP250 Qg placing to much demand on the outputs for a single servo amplifier. I have 20 pieces of 072 smd amplifiers I'm going to use for my prototype's servo stage.

Oh the question about shutdown, yes shutdown is important, it is used to turn off the load electronically (without using mechanical) relays, it will just mute the power mosfets, either from a user input (turn off/mute) or system shutdown command.
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There’s nothing worse than the smell of burned output transistors!!

Last edited by Reactance; 18th July 2017 at 01:12 PM.
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Old 19th July 2017, 04:30 AM   #79
ontoaba is offline ontoaba  Indonesia
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looks like its ok this way, 4 of irfp250n. and simulated @2v, they draw 50A+. slow but stable with a tl072 servo.
next will be current sensing, voltage sensing (easiest way is resistor divider but always draw minor current). after that a power converters. then PCB. I can take care of them.
can you re map the port? and choose how to sense the current and voltage? the source resistors can be ignored since it is used for servo feedback.
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Old 19th July 2017, 04:37 AM   #80
ontoaba is offline ontoaba  Indonesia
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My currently project is almost finished and normally I take a month or so free vacation. but don't know if I got my pc go with me. I'll have more time.
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