Hi,
I am wanting to control a voltage range of 0-10v across a 10k load with PWM from a micro. Now I was told to use this circuit with an n channel mosfet:
This is what I understand so far: R1 is to reduce current flowing into the base R2 is used to pull mosfet closed when its not conducting

I was wondering if I could have help understanding what R3 is doing?

Any help would be great.

Cheers

 

Hi,

(That's a single transistor inverter - high input is low output/sinking, low input is high output.) R3 is a pull-up to Vsupply, it's also limiting the current going through the NMOS when it is on. It's a voltage divider, so consideration must be made about the value R3 is given, e.g. 10k + 10k load = 5V when the NMOS is off, 1k + 10k load = 9V at junction of R3 and Rload.

 

Since this is Homework, a couple of suggestions which are a bit picky but might score you more marks:
1) Get into the habit of giving all components a designator, so that discussing the circuit is easier. So, let's call the 10k resistor R4 or Rload.
2) MOSFET transistors have a gate, not a base. The transistor shown is N-channel, not NPN.

 

Hi,

(That's a single transistor inverter - high input is low output/sinking, low input is high output.) R3 is a pull-up to Vsupply, it's also limiting the current going through the NMOS when it is on. It's a voltage divider, so consideration must be made about the value R3 is given, e.g. 10k + 10k load = 5V when the NMOS is off, 1k + 10k load = 9V at junction of R3 and Rload.

What is input voltage. No Velu showing R-1,R-2 & R-3 i need output 0 to 10 volt veritable so please send complete circuit diagram.

 

To get a 10v output with that circuit you need a greater than 10v supply because of the voltage-divider formed by R3 and the 10k load. It's also inefficient and wastes energy at lower output voltages through heating of R3.

Whoever advised you to do it this way is ill-informed.
The correct way to do this, for a ground-referenced load, is with a P-channel MOSFET.

 

Do you want a linear analogue voltage variable from 0-10V range across the load, or do you want a PWM signal that is 10V peak?

 

Hmm. This thread is 3 years old. Methinks the Homework should have been handed in by now.

 

Darn, another newbie necro-poster strikes again.

 

Some forums warn that you are looking at an old thread. Why doesn't this one?

 

It does. But probably only to the first new poster. After that, it is not old any more.