Stable Load Current and Voltage in a Simple MOSFET Driver Circuit

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SUMMARY

The discussion centers on modeling the load voltage and current in a MOSFET driver circuit, specifically under conditions of 18V intended load voltage and 1A load current. When the MOSFET is activated, the load voltage approaches 48V, accounting for the FET's voltage drop. The load current remains stable at approximately 1A due to the high inductance and frequency of 1MHz. The load voltage oscillates between two values depending on whether the FET or the flyback diode is conducting, with the relevant equation being VL = L · di / dt.

PREREQUISITES
  • Understanding of MOSFET operation and characteristics
  • Knowledge of inductance and its effects in circuits
  • Familiarity with flyback diodes and their role in switching circuits
  • Basic grasp of duty cycle calculations in PWM applications
NEXT STEPS
  • Study the effects of duty cycle on average voltage in PWM circuits
  • Learn about MOSFET switching losses and their impact on circuit performance
  • Investigate the role of inductance in current stability and transient response
  • Explore advanced modeling techniques for switching power supplies
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Electrical engineers, circuit designers, and students studying power electronics who are interested in understanding MOSFET driver circuits and their behavior under varying load conditions.

Forcefedglas
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Homework Statement


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Homework Equations

The Attempt at a Solution


I know what the transients should generally look like, the only part that's throwing me off is how to model the intended load voltage of 18V. I'm guessing that when the switch is on (after transients) the load voltage will be close to 48V (minus the FET voltage drop) since there's nothing in place regulating it, is it safe to assume that the load current stays at 1A in this case? And if the FET is off (after transients), the flyback diode will be forward biased and the voltage across the load will be -0.46V? If that's the case, what's the effect of the 'intended' load voltage if any?

Thanks in advance.
 

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Forcefedglas said:
I'm guessing that when the switch is on (after transients) the load voltage will be close to 48V (minus the FET voltage drop) since there's nothing in place regulating it, is it safe to assume that the load current stays at 1A in this case?
Inductor current will remain very close to 1 amp because inductance is large and frequency is high at 1MHz.

The load current will switch between the diode and the FET. Load voltage will change between two values.
While the FET is on the load current will rise slowly, while the diode is on current will fall slowly.
Relevant equation? VL = L · di / dt
For a stable current, Irise must equal Ifall.

What will the duty cycle be?
What will the average voltage across the load be?
 

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