# Fixed DC to Variable DC Using MOSFET( IXFH320N10T2)

#### Dasun Umayanga M. A.

Joined Aug 3, 2019
23

This is my circuit diagram and I am not able to receive the proper voltage wave form at load end, really need a professional advice here

#### crutschow

Joined Mar 14, 2008
26,814
First you need to state what is the "proper voltage wave form" you expect, voltage. frequency. and wave-shape.
Otherwise we are guessing.

#### Alec_t

Joined Sep 17, 2013
11,984
Your function generator needs to be able to drive the gate with a high enough voltage (well above Vgs(thr)) to turn on the FET. At high frequencies the gate current required to switch the FET quickly can be large.

#### AlbertHall

Joined Jun 4, 2014
11,147
The circuit assumes that there is no common connection between the function generator and the DC supply not even a mains earth connection. If this assumption is wrong then the circuit won't work.

#### Dasun Umayanga M. A.

Joined Aug 3, 2019
23
First you need to state what is the "proper voltage wave form" you expect, voltage. frequency. and wave-shape.
Otherwise we are guessing.
thank you sir,
DC 2
First you need to state what is the "proper voltage wave form" you expect, voltage. frequency. and wave-shape.
Otherwise we are guessing.
20v dc
10kHz to 40kHz frequency
10vda (50% duty cycle)

#### crutschow

Joined Mar 14, 2008
26,814
10vda (50% duty cycle)
What's vda?
(Please use abbreviations that we are all familiar with.)

What kind of function generator are you using?

#### Dasun Umayanga M. A.

Joined Aug 3, 2019
23
I am into say that output I am looking for is 10v dc average ( at 20v dc at supply input and gate signal is square wave of 50% duty cycle)

I am having PINTEK FG-32 3MHz function generator.

I need this to operate at 10kHz to 40kHz

#### Dasun Umayanga M. A.

Joined Aug 3, 2019
23
Your function generator needs to be able to drive the gate with a high enough voltage (well above Vgs(thr)) to turn on the FET. At high frequencies the gate current required to switch the FET quickly can be large.
Sir, I have PINTEK FG - 32 and I am looking for 10kHz to 40kHz frequency range

#### Dasun Umayanga M. A.

Joined Aug 3, 2019
23
The circuit assumes that there is no common connection between the function generator and the DC supply not even a mains earth connection. If this assumption is wrong then the circuit won't work.
There is common connection between supply and function generator

#### Alec_t

Joined Sep 17, 2013
11,984
What are the frequency generator's rated output current and voltage?
What is the load resistance/type?
Show us 'scope plots of the gate-to-source drive voltage and the voltage across the load.

#### crutschow

Joined Mar 14, 2008
26,814
Below is the LTspice simulation of your circuit (with a similar MOSFET that I had the model for).
Are you applying a 10V signal to the MOSFET gate?
What is the "proper voltage" that you want?

#### AllanGreen

Joined Jan 17, 2013
3
Please can you confirm that your oscilloscope "ground" is not directly connected to either PSU "ground" or function generator "ground"? If you aren't sure, switch off and disconnect the PSU and the function generator from your circuit, and use an AVO ohmeter between the ground terminals of each... If there is a low resistance connection (say less than 100 ohms) you are shorting bits of your circuit out. (I was once that soldier.)

Ha ha, just checked the dates of the preceding posts. No doubt this problem has long been sorted!