Home > Circuit Bricks > Voltage Reference - Variable
UPDATED:.21:15 21 October 2013
FUNCTION BLOCK
DESCRIPTION
  • This voltage reference provides an adjustable voltage level.
  • It provides a voltage proportional to the supply connected to it.
  • Must be connected to a high impedance input - such as a comparator/op-amp.
CIRCUIT DETAILS

  • Current flowing through the resistors generates a voltage accorss them
  • R1 and R2 set the higher and lower limits of the voltage range. VR1 selects a voltage within this range.
  • If you want to have the full range of supply voltage, then omit R1 and R2.
  • Voltage across any resistor


where R is either R1, R2 or VR1
Input

Circuit Diagram
This is usually the power supply.
Output

The output voltage is a proportion of the supply voltage (+V)

In the example shown if

  • +V = 12v, then range is 1v to 11v
  • +V = 9v then range is 0.75v to 8.25v
  • +V = 6v then range is 0.5v to 5.5v

Change R1 and R2 to change the range of voltage.

The output current is very low and should be buffered or connected to a high impedance input - such as a comparator.

TIP: Keep VR1 10K or less in value to keep noise on the voltage to a minimum.
DEVICE DETAILS

Carbon
Preset
Although a potentiometer can be used, voltage references are usually set once and adjusted rarely.

A carbon preset is one device that is cheap and PCB mounted.

Multi-turn
Preset

A more accurate device is a "Multi-turn preset" that can have up to 20 turns for the full range of resistance. You can hear a clicking sound if you turn them to the limits.
Written by Phil Townshend - 2008
www.edutek.ltd.uk - Working Electronics For Students & Teachers