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Old 27th Nov 2017, 4:10 pm   #2
orbanp1
Heptode
 
Join Date: Nov 2009
Location: London, Ontario, Canada
Posts: 672
Default Re: Mini-drill; Speed Controller Problem

Just a quick note.
The schematics does not show how the op-amp is powered (neither the web-page).
The LM1458 is not a rail-to-rail op-amp, the inputs should be higher by 2V than VEE, the minus supply to the op-amp, so you need to provide negative supply as well, below the ground potential of the power to the drill (the +12V - +16V).
If you want to power the op-amp from the same source as the drill (just the +12V - +16V) you need a rail-to-rail op-amp, like an LM358.

PS
I have not looked at the other aspects of the circuit, but there is a Spice model of the LM1084 on the TI web-site.

Good luck, Peter

Last edited by orbanp1; 27th Nov 2017 at 4:19 pm.
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