I am trying to convert 5V to a constant current source
for op amp I use AD822. for 250 ohm I use 180 ohm, so I should get a current of 28 mA. I verified when Rload = 0, 28 mA across negative terminal to ground.
But when I put Rload to circuit, 680 ohm, my current exceeds 28mA as Vcc increase.
Can anyone please point where might be the error?
Answer
The "operating output current" for an AD822 on a supply voltage of +/-15V is limited to 20mA (see page 9 of the data sheet).
Absolute maximum rating for the device is +/- 18V.
Either lower your expectations for this device or choose a more appropriate op-amp or an op-amp BJT combination.
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