To use depletion mode MOSFETS simply reverse the circuits where an N-channel depletion mode MOSFET will use a variation of the P-channel enhancement mode circuit.In a depletion mode MOSFET gate voltage closes off the conductive channel from source (S) to drain (D).With an enhancement mode MOSFETs gate voltage opens the conductive channel from source to drain.
In the case of the N-channel such as the IRF630 when the gate (G) is greater than 5-volts the LED cuts on. The resistor on the gate of the N-channel MOSFET is used to bleed-off the electric charge from the gate and turn off the MOSFET. In the case of IRF630 and IRF9630 MOSFETs that value is 20-volts. Not all power MOSFETs have those so check the specifications sheets. They are used in conjunction with N-channel MOSFET switches. Gate Drive Circuit For Mosfet Driver And OutputIf the Hin pin is low this turns OFF the high side driver and output at HO is equal to Vs. It was mentioned in the previous tutorial that the H-bridge MOSFET circuit of the quasi sine wave inverter cannot be directly interfaced with the microcontroller circuit. The H-bridge MOSFET circuit generates a modified sine wave by switching the MOSFETs in a sequential manner with predetermined delay. After adding the gate driver circuitry, the resultant circuit will be able to generate a modified sine wave having a peak to peak voltage of 12 V. In the next tutorial, then, the inverter circuit will be completed by adding a switching mechanism and step up transformer. For driving the high side MOSFET the microcontroller cannot be directly interfaced to its gate terminal. There must be a gate driver circuit for switching the high side MOSFETs contrary to the low-side MOSFETs which can be directly operated without need of any external circuitry. So, it is first important to understand the half bridge circuit and its driving method. As high side MOSFET cannot be normally operated like low side MOSFETs, there are two methods of driving the high side MOSFET one is through dual power supply and another is by using bootstrap circuit. In circuit designed here, bootstrap method is used to drive to the high side MOSFET. That extra circuit can be incorporated by using some IC having the circuit inbuilt or by designing the circuit explicitly. Gate Drive Circuit For Mosfet Full Bridge ConfigurationSo for full bridge configuration, there needs two IR2110 ICs. So, this IC suits best as per the requirement of the circuit. Now its time to design the switching mechanism and gate driver circuitry. It is a high speed (operational at high frequency) power MOSFET and IGBT driver with independent high and low side referenced output channels. The IC is 3.3V logic compatible that is why it can be used with any microcontroller. The VDD is the logic voltage for working of the internal circuitry of the IC. The VDD should range in between 3 V to 20 V (with reference to Vss). The actual voltage of VDD is decided by the input supply of Lin and Hin pin. The Lin and Hin pins are the input logic supply pins for driving the low or high side driver. When the input at Lin is high then this drives the low side driver and output at LO is equal to VCC. If the Lin pin is low this turns OFF the low side driver and output at LO is equal to COM (ground). Similarly, when the input at Hin is high then this drives the high side driver and output at HO is equal to VB.
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