This is a simple DC to DC Power Supply. It is from a book called "The Basics v3 Intro to Electronics". I don't understand what is the point of resistor R1. If I remove R1 the circuit still works normally. I still get the same output voltage when I turn potentiometer to max and led is just as bright.

 

Probably just a load resistor to allways draw a minimum current

 

Probably just a load resistor to allways draw a minimum current

Why does it need to draw minimum current? There is current going through led.

 

Why does it need to draw minimum current? There is current going through led.

True. If the LED is regarded as a requisite part of the regulator then R1 is superfluous.

 

Certainly the R1 resistor does provide a load, and just as certainly it provides no benefit to the operation of the circuit.

 

Resistor R1 is to prevent Q1 leakage current from causing the LED to glow.

 

R1 would maintain a load when the voltage is set below the LED threshold. If needed, probably not.

 

Leaving R1 in would not hurt.

 

Given that we do not have any specifications or description of operation of the cicuit, all of the guesses are correct.

 

Given that we do not have any specifications or description of operation of the cicuit, all of the guesses are correct.

Here is the description from the book. It just says you can regulate between 0 volts to 9 volts and led lights up when there is voltage across the output. It doesn't mention R1 at all.

 

There is no way you could output 9 volts from that circuit while inputting 9-volts.

The usage of the term "9 volts of power" makes me want to cringe.

 

There is no way you could output 9 volts from that circuit using a 9-volt battery.

That is true. It is little over 8 volts.

 

You might look for a better book, as this one appears pretty sloppy. They should definitely describe the purpose of each component, and also why the particular value was chosen.

They claim that the LED lights up whenever there is voltage at the output. This isn't true. Set the voltage to 1.5 V (a very reasonable and useful output voltage if you are trying to test circuits intended to operate off something like an AAA battery) and the LED won't be lighting up.

It also implies that you can get an output voltage all the way up to 9 V, which is not the case since if the transistor is conducting, you will have the Vbe drop and since the base voltage can't exceed 9 V, the output voltage can't get up above 8.3 V to 8.4 V.

 

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3