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DC Amplifier op-amp

Hiya,

I have an input voltage that ranges between 0-1V, which can be at a high frequency. This output requires connection to a high-impedance load.

I need to scale this to 0-4V or 5V so I can input it into an ADC.

I'm currently looking at an Op-Amp but having difficulty getting it to work - currently have an LM358, Vee is GND, Vcc is 5V.

I copied the design at

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but subsituting

10k for R1 and 30k for R2.

The input signal is connected directly to the + input however the output I get isn't as expected.

Can anyone see anything wrong with it?

Thanks,

Ben

Reply to
google
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Check out the data sheet for the LM358

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and find the specification for output voltage swing. The is only specified for a supply voltages of 30V, but note that the output - driving a 10k load - isn't guaranteed to get within three volts of the positive rail, and typically can only get within two volts.

You want an amplifier with a rail-to-rail output - the National Semiconductor LM10 was the first one on the market, and Farnell still sell the LM10CLN for about $5 in small quantities. The Motorola MC33201P dual rail-to-rail op amp is a lot cheaper at about $1.50.

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It has a marvellous low-output impedance output stage, but in all other respects is about as cheap and nasty as the LM358.

--
Bill Sloman, Nijmegen
Reply to
bill.sloman

How high is "high"?

As you've kindly not said what you *did* see I'll assume the tops of the waveform are clipped and you never get less than a couple of ADC counts.

You should check out the maximum and minimum output levels the LM358 is capable of. It's in the datasheet. It won't quite reach its -ve supply rail and it won't get within a couple of volts of the positive supply rail. A wider supply range for the op-amp ( Vee < 0V, Vcc > 7V ) or an op-amp with rail-to-rail outputs are possible solutions.

Tim

Reply to
Tim Auton
** Groper alert !!

** Sounds like video.

Lotsa luck with a crummy LM358.

....... Phil

Reply to
Phil Allison

No one can work with that kind of description, "high frequency." You either get specific or get lost. You know so little about things, that in your mind there is little to know.

Reply to
Fred Bloggs

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