pass transistors are nothing but controlled switches (gate is used for control). NMOS with high gate input is ON and PMOS with low gate signal is OFF. they are used extensively (for example S/H circuits to determine when the input signal is passed on to ADC).
rk
I believe the formal definition of a pass transistor is
one in which the transistor is biased into its active
region in order to control the current at its output.
The voltage difference will appear as heat.
This is a common arrangement in analog power
suppies, and is often an addition to IC-based
voltage regulators to add current capability.
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