Understanding Mosfet Circuit with PWM to control voltage 0-10v

Thread Starter

Link068

Joined Apr 10, 2017
31
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
 

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Daniel Sala

Joined May 28, 2015
60
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.
 

Alec_t

Joined Sep 17, 2013
10,616
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.
 
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