Why is there no voltage at the drain of the mosfet when in DC mode

[tastychickenwings69]

Hi.
 I have a normal Mosfet Switch which is turned on by VDD with a resistor.
Can someone explain why there practically no voltage present at drain of the mosfet if the gate is turned on with DC?
If the switch turns on via pwm signal there is 12V but with DC its only 10mV.

I get that there is still full current and power at RD but I dont get why theres no voltage.

[ledtester]

When the gate voltage is low, the MOSFET becomes a very high resistor. In the diagram below I made a 1 gigaohm resistor -- essentially it is an open circuit. The voltage at OUT is then +12V.

When the gate voltage is high enough the resistance between the drain and gate will be very small (less than 1 ohm and usually a lot lower). This will pull the output voltage close to ground -- it's just voltage divider with a very small lower leg. You'll find a more in-depth explanation of how to analyze voltage dividers here: https://learn.sparkfun.com/tutorials/voltage-dividers/

If the switch turns on via pwm signal there is 12V but with DC its only 10mV.

If the gate is driven by a separate PWM signal then output will oscillate between +12V and 0V.