Subelement C: Receiving Systems – 10 Key Topics – 10 Exam Questions – 4 Drawings— Topic 26: Power Supplies
Question 8-26C5
Element 8 (RADAR)When monitoring the gate voltage of a power MOSFET in the switching power supply of a modern RADAR, you would expect to see the gate voltage change from “low” to “high” by how much?
Explanation
Power MOSFETs, crucial components in modern switching power supplies like those in RADAR systems, are voltage-controlled devices. To fully turn "on" and minimize power loss, the gate-source voltage (Vgs) must be driven significantly above the device's threshold voltage (Vth).
The threshold voltage for most power MOSFETs is typically between 1V and 4V. However, to ensure the MOSFET is fully enhanced (saturated) and achieves its lowest drain-source resistance (Rds(on)), the "high" gate drive voltage needs to be much greater than the threshold. Common gate drive voltages range from 5V for "logic-level" MOSFETs, up to 10V, 12V, or even 15V for standard power MOSFETs in high-power applications.
Therefore, a gate voltage change from "low" (typically near 0V) to "high" will be *greater than 2 volts* to ensure efficient and reliable switching. Options A and B represent insufficient voltage swings for proper power MOSFET operation. While D provides a broad range, C correctly identifies the fundamental requirement for the "high" state to be substantially above a minimal threshold for effective turn-on.
Related Questions
8-26C3 The circuit shown in Fig. 8C10 is the output of a switching power supply. Measuring from the junction of CR6, CR7 and L1 to ground with an oscilloscope, what waveform would you expect to see?8-26C4 With regard to the comparator shown in Fig. 8C11, the input is a sinusoid. Nominal high level output of the comparator is 4.5 volts. Choose the most correct statement regarding the input and output.8-26C6 The nominal output high of the comparator shown in Fig. 8C11 is 4.5 volts. Choose the most correct statement which describes the trip points.8-27C1 One of the best methods of reducing noise in a RADAR receiver is?8-27C2 The primary cause of noise in a RADAR receiver can be attributed to: