MOSFET as a high voltage/high side switch.

Thread Starter

gllorens

Joined May 12, 2020
3
Hi everyone,
I have to implement a High Voltage (150V) switch using Mosfet in high side configuration. I'm a little lost and I don't know how to choose either the MOSFET or the gate driver.
The application, as I have said, is to control a 150V source but only 1mA will flow to the load.

1589277330341.png
This is the circuit I've been using but it only works when V1 is 150V.
What I would need is for it to wirk when V1 is 3.3 or 5V

Thank you very much for your help in advance!
 

Wolframore

Joined Jan 21, 2019
1,748
to switch 150V using PFET with logic level gate voltage is not possible as you discovered. You could use another transistor to pull the gate down when activated as a simple gate driver.
 

AnalogKid

Joined Aug 1, 2013
8,464
At a minimum you will need an NPN or n-channel transistor driving the M1 gate, something rated for 200-300 V. Also, you have over 13 mA through R1 and R3, for a power dissipation of just over 2 W. R1 needs to be much larger.

ak
 

crutschow

Joined Mar 14, 2008
24,968
control a 150V source but only 1mA will flow to the load.
You show a 1k load which gives 150mA of load current.

For the high-side MOSFET you also need to limit the maximum gate-source voltage to avoid damaging the gate (typically to about 10-12V).
For example, this can be done with a Zener from gate-source, or a proper selection of the two gate resistor values.
 

Thread Starter

gllorens

Joined May 12, 2020
3
Following some of your advice, I designed this circuit and it appears to work fine to my purpose:

1589292584620.png

Thank you all very much for your help!!
 

crutschow

Joined Mar 14, 2008
24,968
You do realize that you are using the MOSFET as a source-follower, not a switch(?).
Thus the voltage across R2 will depend upon the Vsg(threshold) of the particular MOSFET you happen to buy.
 

AnalogKid

Joined Aug 1, 2013
8,464
For the circuit in post #7, the gate voltage must be 160 V to assure that the FET is fully enhances ("on" or "saturated"). While you show two different GND symbols, they must be electrically related to each other or the circuit will not function.

ak
 

Wolframore

Joined Jan 21, 2019
1,748
there's a lot that's not quite right about this design and application but we have limited information. What is 150V DC for? How much current are we talking about? Is it inductive load?..... etc. there may be better ways to do this but can't tell with limited information.
 

ronsimpson

Joined Oct 7, 2019
680
Using P mosfet. V1 is data from 3.3V logic. 3.3 volts is not much to turn many MOSFETs.
When V1 = 0V, Q2=0 current. Q1 is off.
When V1= 3.3V, Q2=about 1mA. Just under 3V on R2.
R3 is not needed but helps reduce the power loss in Q2. At 1mA there will be 75V across R3 when Q2 is on at 1mA.
1mA in Q2 causes 1mA in R1 which makes about 9 volts. This is a good voltage for the gate of Q1.
You know Q1 needs a voltage G to S to turn on. Pulling down 9V will turn it on. D1 is there for safety. Just in case the voltage is too big the voltage will be limited to 15V. That is 150-15=135.
1589316657920.png
Q2 needs to be a small 200V part. From my head 2N5550 is a 150V part. Close but not right.
 
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