Best Way To Amplify Current
Best Way To Amplify Current
(OP)
What is the best method of amplifying output current of op-amp. I need a cheap solution without using power amps.
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Best Way To Amplify Current
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Best Way To Amplify CurrentBest Way To Amplify Current(OP)
What is the best method of amplifying output current of op-amp. I need a cheap solution without using power amps.
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RE: Best Way To Amplify Current
Depending on the accuracy and other characteristics required, you could get away with driving a push-pull stage directly from the op amp output and wrapping the feedback to the output of the push-pull stage.
TTFN
RE: Best Way To Amplify Current
There are single chip power op-amps..
RE: Best Way To Amplify Current
Basically I am using a 5 or 10 volt reference to excite a resistive sensor with sense (feedback) lines. Since the voltage references provides only small currents I am using an opamp to pass the reference voltage. I need to be able to source about 150 mA. The op-amps I am working with generally output about 12-20 mA. I tried using a single NPN transistor (C = Power, B = Op amp output, E = Load) E feedbacks to (-) input of op-amp. This approach only seems to work with certain conditions. For instance it would work with 10 VDC, but not 5 VDC. If I change the transistor to another type it would work for 5 but not 10.
RE: Best Way To Amplify Current
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Click "View Table" and note the second column.
or:
http://w
And look at the 5th column.
RE: Best Way To Amplify Current
These seem to be reasonably priced, cost was the main issue with not getting a power amp. These amps say they have a "minimum" output. Does that mean they will not operate at less than the specified output current?
RE: Best Way To Amplify Current
1. The transistor may not have enough gain for the current you want and a darlington output may be appropriate.
2. Your supply does not have enough voltage for 10V considering the op-amp will not go up to the rail voltage.
3. You could make a circuit change, but I'm not here to do your homework!
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
I'm not sure what you mean by a "complementary emitter follower". Did you mean an emitter follower using a PNP transistor, and then resistively sourcing say 200mA from the positive power rail? Ugh!
I could see one using a PNP common emitter hung from the positive rail, but the designer would have to take care of the increased loop gain to prevent it oscillating.
RE: Best Way To Amplify Current
Gunnar Englund
www.gke.org
RE: Best Way To Amplify Current
ok a standard Class B output stage.
Well that won't help the problem of the output range of the opamp. The load is static so the complementary output stage won't help at all.
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
There is a pull-push using a common emitter configuration using 741's powerpins to drive the bases, which was published in Popular Electronics about 30 yrs ago. Pretty cool concept; claimed 30 watts from complementary MJE2955/3055, a 741, and a handful of resistors.
TTFN
RE: Best Way To Amplify Current
To solve the headroom issue we need either a PNP emitter follower biassed by a resistive pullup, or we need a common-emiiter PNP hung from the positive power rail, or we need a higher power rail.
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
Source to +ve, drain to load, and the gate voltage should operate well within the output range of most op amps.
That will obviously require inversion of the inverting and non inverting inputs of the op amp. High frequency stability may be an issue, but that will depend on the particular components used, and is not going to be a difficult problem to solve if it occurs.
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
RE: Best Way To Amplify Current
I realize this is an old topic, but thought it might still be useful.
One simple way to boost output current is to place a resistor in series with the op-amp's +V supply pin. A PNP transistor is added with the emitter on the +V rail, the base on the op-amp's +V pin, and the collector on the op-amp's output. The resistor is sized to turn on the PNP at an output current somewhat below the maximum available from the op-amp's output. The +V supply current, which is through the resistor in the PNP's base circuit, includes the output current plus the op-amp's operating current.
This also allows the output voltage to swing as positive as with the unassisted output.
Works only with single amp IC's, of course.
Same circuit can be used to boost current from regulators.
RE: Best Way To Amplify Current
Anyway, it works if you can tolerate the reduced swing.
RE: Best Way To Amplify Current
I still give you a star for a creative idea. I love 3 pin regulator circuits - they can even be turned into oscillators (not just by forgetting the cap!).