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how can I design high reliable 24V output

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mdamdam

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I want to replace a Siemens PLC by a microcontroler. For the 24V output I'll use some classic drivers like ulN2803.
Can somebody give me some tips and/or diagram to obtain the same reliability as professional PLC.
What kind of components I have to use to proctect for example from HVoltage spikes, short circuit, reverse current....

Thanks
Damdam
 

bunalmis

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You must use optoisolator for inputs and outputs of your microcontroller.
Industrial envirements has big electrical noise.
 

mdamdam

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I need 24 output and can not find small and multiple opto isolators. The best I could find are dual ones, in is smd package but quite as big as DIL ones :-(
Damdam
 

froggy

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mdamdanm,
Yes you are right there isn't any small optocouplers, since the whole idea about a optocoupler is to give electrical isolation, the size is given. At least the distance between the dirty, and the clean side is given,
0.3" distance gives 2.5-5kV isolation.
(I heard somewhere that the theratical voltage/distance to create a spark is close to 1kV/mm)

/Froggy
 

7rots51

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hi
for isolation check www.isol*oop.com they have several channels and are magnet*oresistive based.

I heared that there are optocouplers with logic output input(TTL) with several channels in a pack.

to tjalps:
is there a IC similar to infinion digital outputs(SPI interface,mosfet protected) for multichannel digital input (SPI or I2C interface)?

The SPI or I2C will reduce the number of optocoupler required and the IC can have diagnostic capability .


bye
 

mdamdam

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You are right Froggy, what I expected was
package even if one dimension is few mm.
Just for info: I acutlaly work on an isolation experiment . In a quasi perfect vacuum, i could obtain up to 10kV/mm !!! ( of course with a very carefull design of plates an no point effect ). I dont know values for dry air.
M
 

mdamdam

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Thank 7roots51 !
The link is interesting.
Allegromicro can provide equivalent of multi ULN2803 + shif register. So you can have in one chip serial input and 20 (?) 24V output.... but not isolated...
Damdam
 

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