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integrator output to drive a load

 
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Richard
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integrator output to drive a load
PostPosted: Fri Aug 20, 2004 9:22 am     Reply with quote
Hi,

I have a problem, I need to drive the output of an op-amp into a
DC bulb.

The bulb requires 100mA, at 6v maximum.

How do I provide the the exact same voltage from the opamp, but with more current?

I was thinking of a using a NPN transistor as a switch, but this would
only provide +vcc and 0v, I need all the voltages in between


Any links or thoughts
I am truly in a pickle
Ttelmah
Guest
Re: integrator output to drive a load
PostPosted: Fri Aug 20, 2004 9:42 am     Reply with quote
Richard wrote:
Hi,

I have a problem, I need to drive the output of an op-amp into a
DC bulb.

The bulb requires 100mA, at 6v maximum.

How do I provide the the exact same voltage from the opamp, but with more current?

I was thinking of a using a NPN transistor as a switch, but this would
only provide +vcc and 0v, I need all the voltages in between


Any links or thoughts
I am truly in a pickle

Get a power op-amp.
Look at devices like the LM675 (overkill for the power you need, but very good). Also consider some of the audio amplifier chips. For the low power you need, I'd probably look at the LM386, which is simple to use, and migh be able to replace your op-amp, and give the required output. This behaves rather like an op-amp, but with an internal feedback resistor that programs the gain. Provided your circuit does not need more gain than it provides, you can add an external feedback circuit and use it like an op-amp.

Best Wishes
SherpaDoug



Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA

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Re: integrator output to drive a load
PostPosted: Fri Aug 20, 2004 11:47 am     Reply with quote
Richard wrote:
Hi,
I was thinking of a using a NPN transistor as a switch, but this would
only provide +vcc and 0v, I need all the voltages in between


Consider using your NPN transistor as an "Emitter Follower." You will lose a diode drop so for a op amp signal of 0 to 5V you would get 0 to 4.3V but this may be close enough and it is dirt cheap. Simply connect the op amp to the NPN base through about 100 ohms. Connect the NPN collector to +vcc. Connect the bulb from the NPN emitter to ground. Note that at worst case (half brightness) the NPN power dissapation could be 0.1A x 3V = 0.3W

The base resistor is needed to prevent VHF oscillations.
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