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Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Do you have some batteries? If you take for example 4 AA batteries in series, connect the - terminal of cell 1 to the V- pin on the op amp, the + terminal of cell 4 to the V+ terminal on the op amp, then use the point where cell 2 connects to cell 3 as ground you will have a +/- 3V supply, often referred to as a bipolar power supply.
You can fake it by using two resistors (DC or AC signal) or two capacitors (AC only) in series to create a false ground, but in the case of resistors you will be wasting power, not desirable with batteries.
You can also get ICs from Maxim and others specifically intended to generate the negative supply rail from a single positive supply.
Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
I am not using batteries in the final design. I would get a regulator IC or a polarity inverter IC. For now I will test with the batteries, ofcourse.
A voltage divider output voltage will fluctuate with load? Am I correct? I will have to use a current draw of the opamp to pick the right voltage divider resistor values. Am I right? Voltage dividers are only good for designs with negatable current draw or a constant current draw. I prefer to use a resistive divider only on a signals and other low power applications.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Use a bipolar supply and you don't have to worry about voltage dividers. If you really need to operate it from a single ended supply there are tricks to make it work, but get it working on a standard bipolar supply first and then get fancy if you have to.
Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
I am not using batteries in the final design. I would get a regulator IC or a polarity inverter IC. For now I will test with the batteries, ofcourse.
A voltage divider output voltage will fluctuate with load? Am I correct? I will have to use a current draw of the opamp to pick the right voltage divider resistor values. Am I right? Voltage dividers are only good for designs with negatable current draw or a constant current draw. I prefer to use a resistive divider only on a signals and other low power applications.
Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
I am not using batteries in the final design. I would get a regulator IC or a polarity inverter IC. For now I will test with the batteries, ofcourse.
A voltage divider output voltage will fluctuate with load? Am I correct? I will have to use a current draw of the opamp to pick the right voltage divider resistor values. Am I right? Voltage dividers are only good for designs with negatable current draw or a constant current draw. I prefer to use a resistive divider only on a signals and other low power applications.
Registered Member #3859
Joined: Sun May 01 2011, 03:47PM
Location:
Posts: 179
I rebuilt the circuit with the two two AA battery holders as the sources of +3 and -3 VDC. It doesn't work. I get approx. 1.4 volts on the output when there is no input and i get 1.8 when I input +3V. if i input -3 than amp output goes slightly below zero.
Changing feedback and input limit resistor values doesn't seem to effect anything. Swapping an op amp for another identical one gives the same results. What shall I do?
By the way, I use a 100 ohm resistor for feedback, not 150. I don't have one. I had used 200 ohm negative feedback and got the same results so I don't know what negative feedback really effects.
This circuit is an expirimental circuit built on a breadboard. After that I will print a PCB with this circuit as an amp for a microcontroller ADC.
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Problems with a circuit prototype for voltage clamping amp with 1 gain based on AD8036 amp.
