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Power Op AMp

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jmarmontgomery

New Member
I Was wondering about using a Power Op Amp to Directly Control a small Hobby DC Motor( Film Canister Width). I would be using a Dual Power Supply (+6V and -6V) to allow for bidirectional Motor Control. Not worried about speed, as I am running the motor through a high reduction gearbox. Would my motor be able to run?
 

Hero999

Banned
This isn't the best way to do it, PWM (Pulse Width Modulation) is a much better way of doing it because it's more efficient and the motor has resonable torque even at low speeds.
 

silvarblade

Member
The motor would be able to run but it would as mentioned by hero not give you any control over its speed.For dc motors direction is easy but for your application(gears) i think the position is equally important.Also which power op-amp are you using?
 

KMoffett

Well-Known Member
...to allow for bidirectional Motor Control...

For electronic directional control you will need an H-bridge circuit. To select the right one, you need to find out how much current the motor draws at start-up and run in both directions, as this may vary under your particular mechanical load. There are off the shelf units that include both the H-bridge and PWM speed control.

Ken
 

jmarmontgomery

New Member
The motor would be able to run but it would as mentioned by hero not give you any control over its speed.For dc motors direction is easy but for your application(gears) i think the position is equally important.Also which power op-amp are you using?

Well, Im not worried about position, my sensors going into the input are gonna take care of that. Also, im not concerned about speed because my gear train takes care of that. I'm currently trying to figure out what power op amp options i have. I need it to provide at least 1A
 

KMoffett

Well-Known Member
Well, Im not worried about position, my sensors going into the input are gonna take care of that. Also, im not concerned about speed because my gear train takes care of that. I'm currently trying to figure out what power op amp options i have. I need it to provide at least 1A

Power opamps are expensive and relays are cheap. If speed is not an issue and position is controlled by something else, why not an H-bridge of two SPDT relays. Two inputs: ON/ON full stop+braking. ON/OFF=forward, OFF/ON=reverse, OFF/OFF full stop+braking. Or is there more that we need to know?

Ken
 

jmarmontgomery

New Member
Im Making A Solar Tracker. And I Want To drive The Motor just using an power op amp and a dual power supply... The motor's direction will be changed depending on the input from two sensors. Need a power op amp that wil provide the current needed to drive the motor directly. Dont really want to deal with transistors or H-Bridges if i don't have to.
 

silvarblade

Member
an LM1877 wont be able to give 1a 6v the max power for an 8ohm laod is 2w which i guess is more then your o/p impedence.Relays will be better for a current that high unless you use an other opamp available in your area(which you have not specified)
 

KMoffett

Well-Known Member

Hero999

Banned
Those are audio amplifier ICs but can be used as operational amplifiers if you add a suitable low op-amp such as the TL081.
 

silvarblade

Member
if you are using an op amp to dive a motor and no control then why dont you use a proper driver(more current at less voltage)!
 

mneary

New Member
The size of the "small" hobby motor has me concerned. Motors the size of a film can will draw 12V at 8A (100W) for short periods. I would go with relays unless you really need speed control. Relays are cheap and really hard to burn out.
 

nos_joel

New Member
I suppose you are using a subtractor for measuring position using a sensor. I made a solar tracker. The way I did it was using a AB class amplifier after the op amps for giving the needed current for the motor. Use TIP 31npn and TIP 42pnp.
 

teyew

New Member
I'm using OPA541 to control dc motor in order to run in bidirectional but my problem is how to configure the input(by using PWM) for the pin +In and -In in order to produce the -Iout and +Iout.Could anyone can give me advice for that.....thanks.
 

bountyhunter

Well-Known Member
Well, Im not worried about position, my sensors going into the input are gonna take care of that. Also, im not concerned about speed because my gear train takes care of that. I'm currently trying to figure out what power op amp options i have. I need it to provide at least 1A
A cheaper way to make a power op amp is to use a generic op-amp and put a PFET/NFET transistor on the output inside the feedback loop. Use logic level FETs that turn on with only a few volts of gate drive if your rails are +/- 6V.
 
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bountyhunter

Well-Known Member
The size of the "small" hobby motor has me concerned. Motors the size of a film can will draw 12V at 8A (100W) for short periods. I would go with relays unless you really need speed control. Relays are cheap and really hard to burn out.
Hmmm, not the ones that have crossed my path. They like to freeze in position, the contacts sometimes "arc weld" themselves together...... first part to fail on my new Chevy was the fan control relay in the middle of summer (and one month past the 12 month warranty expired).:mad:
 
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