Enhancement Mosfet Working with Zener regulation

Hi All

The drain pin of mosfet is connected to Source voltage via Series Resistor and from Drain pin junction a 6.2V zener is connected in reverse biased to Gate of Mosfet and Source pin is connected to 100K load. Can anyone help me in working of the mosfet.

Hi,

Draw and show us your circuit.

You don´t give any information about power supply. Without it it won´t work...

Klaus

KlausST said:

Hi,

Draw and show us your circuit.

You don´t give any information about power supply. Without it it won´t work...

Klaus

Click to expand...

I have attached the image file.

Hi,

and what is the problem now?

Please don´t give informations piece by piece!

What do you want to achieve?
How do you expect it to operate?
And what do you see instead?

Klaus

pavan611 said:

Hi All

The drain pin of mosfet is connected to Source voltage via Series Resistor and from Drain pin junction a 6.2V zener is connected in reverse biased to Gate of Mosfet and Source pin is connected to 100K load. Can anyone help me in working of the mosfet.

Click to expand...

This written description does not correspond to the schematic shown later.

I want to achieve- I need to understand how the circuit works.

The input voltage is applied varying from 5V to 200V which is connected to drain pin. The source pin is connected to zener voltage with zener voltage of 5.1V with Zener test current at 1mA.

Since the mosfet will turn ON only when Vgs > Vth , but in this circuit the voltage at Vs is not known. Can you guide me in understanding the working of circuit.

The output of voltage (5.1V) will be connected to LDO input pin to get the output voltage(3.3V) which can be connected to controller Vdd pin.

I am expecting the voltage to turn on the LDO, instead am not seeing any voltage at the Source pin.

Hi,

The input voltage is applied varying from 5V to 200V

Click to expand...

You are very late with this information.

--> then the circuit is a voltage limiter.

It limits the output voltage to: V_Zener - V_GS_TH

How it works:
the ABSOLUTE gate voltage is limited by the zener to about 5.1V
if the MOSFET needs about 2V (I didnßt read datasheet) V_GS_TH
* then at absoulte source voltage below 3V the MOSFET is conductive and current is suppled to the load.
* with absoulte source voltage above 3V the MOSFET becomes high impedance and thus the voltage to the load is limited
(because the resistance of the MOSFET regulates itself ... only to supply enough current to keep the voltage at baout 3V.)

Klaus

It limits the output voltage to: V_Zener - V_GS_TH

----How, Can i consider the voltage at source pin to be zero when the Source pin is connected to Input pin of LDO.

How it works:
the ABSOLUTE gate voltage is limited by the zener to about 5.1V
if the MOSFET needs about 2V (I didnßt read datasheet) V_GS_TH
* then at absoulte source voltage below 3V the MOSFET is conductive and current is suppled to the load.

----The mosfet is enhancement type & mosfet turns on only when vgs is greater than Vth.

* with absoulte source voltage above 3V the MOSFET becomes high impedance and thus the voltage to the load is limited
(because the resistance of the MOSFET regulates itself ... only to supply enough current to keep the voltage at baout 3V.)

Klaus[/QUOTE]