Hi guys,
I am having trouble with what I assume to be a very simple problem. I am using an op-amp (LM348N) as a comparator. The chip is powered from a 50Hz, 12V source.
When the input voltage is higher than the reference, I expect close to 12V out, and otherwise, close to 0V. This is all fine except that instead of ~0V I get 3.5V. I realise that in practice the output will never reach the supply rails, but surely it can get closer than this.
Numbers:
Supply: 12V, 0V
Op-amp +: 1.5V
Op-amp -: 6V
Vout: 3.5V
When the threshold is met, Vout = 11.2V.
The 1.5V comes from a computer serial port - I have no idea what the waveform looks like. Grounding the input instead gives Vout = 2.0V. Is this as good as I'm going to get? I've tried various resistors around the place but I lack the experience to make any real educated guess.
Is the op-amp perhaps not cut out for this kind of use or are there any other issues or solutions you can see?
Thank you for your time!
Matt
I am having trouble with what I assume to be a very simple problem. I am using an op-amp (LM348N) as a comparator. The chip is powered from a 50Hz, 12V source.
When the input voltage is higher than the reference, I expect close to 12V out, and otherwise, close to 0V. This is all fine except that instead of ~0V I get 3.5V. I realise that in practice the output will never reach the supply rails, but surely it can get closer than this.
Numbers:
Supply: 12V, 0V
Op-amp +: 1.5V
Op-amp -: 6V
Vout: 3.5V
When the threshold is met, Vout = 11.2V.
The 1.5V comes from a computer serial port - I have no idea what the waveform looks like. Grounding the input instead gives Vout = 2.0V. Is this as good as I'm going to get? I've tried various resistors around the place but I lack the experience to make any real educated guess.
Is the op-amp perhaps not cut out for this kind of use or are there any other issues or solutions you can see?
Thank you for your time!
Matt
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