Pic18f452 nine dc motors control.

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Hey everyone,
currently am trying to build dc motor control, pic18f452 based, i am using irf740 Mosfets for switching. i got nine motors to control thier speed. well my question is this. if my control frequency will swing between 100hz ~20khz and the all circuit components are common ground. so what i need now is some device or component that act like optocoupler so that i can use it as abuffer to gurantee that the irfs will not consume power through the pic and at the same time this device can followup with my desired frequency. what i know that; since the circuit is common ground so no use to use optocouplers.. so any ideas?

Many Thanks for your attention.
 

i think it depend to the type of your optocoupler.. whether it NPN or PNP type..if i am rite(not really sure), u can use NPN type for common ground..
 
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Thanks for your reply, is 4N25 optosolator could withstand frequency upto 20khz . and what if i want to know the maximum frequency that any optocoupler could withstand and gives perfect o/p?. what exactly i have to look on to in the datasheet to know this particular issue.

Many Thanks For Your Attention
 

My advice is not to use common ground for this project.

9 motors is good enough to drive your pic crazy, so have separate powersupply for your pic.

Regarding 4n25 check out the terms slew rate to verify the working frequency
 
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Thx for your reply, firstly, yeah i'll do that, but can't find any thing called slew rate. what i only got is Trise, Tfall, turn on delay time, turn off delay time.
is that useful? i mean is there any equation to calculate the maximum frequency that the IC will withstand from this data?.

Many Thanks )
 

You can calculate (get an approximate) maximum frequency using on delay time and off delay time. Try it out.

It is better to test is practically using a good DSO
 
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can you post your schematic?
 
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okay, i'll post it as soon as possible. but my question was.. is there an optocupler that can withstand upto 25khz as switching speed? or there is other ics that can do same task and withstand same frequency?.

Thx.

---------- Post added at 14:14 ---------- Previous post was at 14:07 ----------

also. in 4n25 datasheet it says that the bandwidth is 300khz... <-- is this is the maximum frequency?.
 

If you need high Speed Optocoupler , you can use 6N135
1 Mbd, Photodiode With Transistor Output
 
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thx )...................................
 

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