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/etc... Amplifiers & Other Linear Forum
Driving MOSFET with Op Amp
I am driving a MOSFET with a typical input capacitance of around 2800pF with an LM324 R-R op amp in the linear mode using a standard function generator. Unfortunately, the LM324 cannot drive the MOSFET much beyond 10Khz because the MOSFET gate starts drawing current past 10Khz. I want to drive the MOSFET up to 100Khz plus. The Op Amp/MOSFET circuit is configured much like a Howland Current Pump for current limiting purposes as the load needs to be current-limited.
Can someone suggest a R-R OpAmp with high-drive capability that will drive a typical N-Chan MOSFET with a typical gate capacitance of 2800pF up around 100Khz in the linear mode?
The LM7321/22 and LM7331/2 series of 30V R-R I/O op amps are designed for driving high capacitence loads. Unfortunately, they do not have a quad in this series.
Remember that even though they say "unlimited" capacitive drive, there is still a limit to the amount of peak current they can deliver into the capacitive load...which can add up pretty fast.
Integrated Signal Chain Applications, SVA
Thanks for your response. Will the LM7322 work as a drop-in replacement for an LM324 in a single-supply circuit?? I'm concerned whether the input can be grounded like the LM324.
The LM7322 is not a physical drop-in replacement, as the LM324 is a quad and the other LM7322 devices are singles or duals (different pinouts) - but electrically it is equivalent or better.
The LM7322 is a rail-to-rail input device, so the input range is from V+ to V-, so in a single supply app, the input can be "grounded".
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