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