I couldn't find any opamps that will take and output 15v. I only need 12, but I don't want my circuit to die if it goes over. I have the above schematic wired up with an lm339 quad comparator and I only get 3v output. I could wire up all the comparators but that seems like overkill. Can someone recommend an opamp?
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I did a parametric search on TI and found this: http://focus.ti.com/docs/prod/folders/print/opa251.html
The opa251 is single supply, can handle 36v, and has rail to rail output. (meaning that the output should go to the same voltages as the supply.) Apparently you can get free samples of this chip from TI. If you are worried about overvolting it you can always use a resistor and a zener diode to protect it. |
Vector86, you could also use a voltage divider to use an opamp with a smaller range on input. Spike protection isn't a bad idea either, though
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Thanks mogwai, I ordered a free sample from TI so we'll see how that works out.
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When I have the opa251 wired in, the output doesn't behave as expected. When the input voltage reaches the refference voltage, the output stays high instead of going low. What am I doing wrong?
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Does your input signal, vref, and the op amp have a common ground?
When the voltage is higher on the - input than on the + input the output should be low. |
yes, they all have a common ground.
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I think I need to drop the input signal b about 1 volt. It seems that the comparator won't function properly if the input signal is within .8 volts of the supply voltage.
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