Recently I tried using an LM324, thinking it would work where a negative supply wasn't readily available. Without getting too detailed, the circuit must be able to operate from a 9-12 V supply, and output a DC level that might be anywhere between 0 and about 3 volts. All looked well on the scope and with a meter, but I failed to take into account that I would be driving a circuit that had an existing voltage bias 0f about 1.5 volts. That bias is extremely "light", so that any typical OP-AMP that had the backing of a dual polarity supply would be able to easily over-ride the bias. But since the 324 outputs are all driven by ordinary UJTs inside the chip, the OP-AM is powerless to "pull" the voltage below .6 volts.
GRRR!!! This was a serious setback. previously I had worked with a complicated circuit using bi-polar op-amps, and a separate OP AMP package to implement an oscillator and charge pump to provide negative voltage to the original circuit. I had hoped all that would become unnecessary now having the LM324, which I'd hoped could work as needed without a negative supply. Can anyone recommend another OP-AMP, available in a quad package, that can drive closer to 0 VOLTS?