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00:00Why is the load connected to the power supply side for NMOS
00:03while the load is connected to the ground side for PMOS?
00:06Welcome to YB's Science Corner.
00:09Taking NMOS as an example, its conduction condition is VG's VG's.
00:14If the load is connected to the power supply side and the source is grounded,
00:18the gate voltage only needs to reach 5 volts to satisfy the condition.
00:23For instance, if the buzzer's voltage drop changes from 1 volt to 1.2 volt,
00:27the transistor remains stably conductive as long as the gate voltage remains 5V
00:32and does not exceed its rated value.
00:34However, if the NMOS load is connected to ground, the situation changes.
00:40VG's must overcome the load voltage drop to meet the threshold voltage.
00:43For example, with a 1 volt load voltage drop,
00:46the gate voltage must reach 5 volts plus 1 volt, totaling 6 volts.
00:50For conduction to occur, if the load impedance increases,
00:53causing a 1.2 volt voltage drop,
00:55then 6.2 volts is required for conduction.
00:58Now consider the PMOS transistor.
01:01Its conduction condition is VG's VG's,
01:03meaning the source voltage must be at least the threshold voltage higher than the gate voltage,
01:07for example, at 5 volts,
01:09if the load is connected to ground and the source is connected to the power supply.
01:13When the gate voltage decreases,
01:15the voltage difference between source and gate more readily reaches the conduction threshold.
01:19If the PMOS load is connected to the power supply terminal,
01:22the load voltage drop will reduce the voltage difference between the source and gate.
01:27This may prevent VG's from reaching the negative threshold required for conduction,
01:31causing the transistor to fail to turn on or operate unstable.
01:35That wraps up this episode's video content.
01:38If you have any questions, feel free to leave a comment below.
01:42Goodbye!
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