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How does an op amp work on a MOSFET?
The opamp output will start slewing towards the positive rail, since the non-inverting input is higher than the inverting input, and since the MOSFET is off, the opamp is open-loop with extremely high gain. Eventually, the opamp output voltage will reach the gate-to-source threshold of the MOSFET, and it will start conducting.
When does an op amp start to conduct?
Eventually, the opamp output voltage will reach the gate-to-source threshold of the MOSFET, and it will start conducting. One of a few things could happen now.
What’s the difference between a positive and negative op amp?
There’s now a difference of 1V between the op-amp inputs. The opamp output will start slewing towards the positive rail, since the non-inverting input is higher than the inverting input, and since the MOSFET is off, the opamp is open-loop with extremely high gain.
How does an op amp work in an OTA?
The opamp will set a voltage based on the inputs, not a current – it’s a normal opamp by the looks of the schematic symbol, not an operational transconductance amplifier (OTA) which would set a current based on the inputs.
What should the drain current be for a MOSFET?
For correct biasing the MOSFET must fully conduct at a minimum drain current of 100mA with a VGSof 3V or less. The MOSFET should be able to supply all the necessary output current at VGS= 10V with some headroom. The required output current is 5.6A peak for a 125W/8Ω output.
What are the characteristics of an enhancement mode MOSFET?
The operation of the enhancement-mode MOSFET, or e-MOSFET, can best be described using its I-V characteristics curves shown below. When the input voltage, ( VIN ) to the gate of the transistor is zero, the MOSFET conducts virtually no current and the output voltage ( VOUT ) is equal to the supply voltage VDD.
What happens when the voltage of the MOSFET is zero?
When the input voltage, (VIN) to the gate of the transistor is zero, the MOSFET conducts virtually no current and the output voltage (VOUT) is equal to the supply voltage VDD. So the MOSFET is “OFF” operating within its “cut-off” region.