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I’ve seen the term “voltage divider” used a lot lately. What exactly is a voltage divider, and what is it used for?
A voltage divider does what it sounds like: it creates an output voltage less than the input voltage. A potentiometer can be used as a voltage divider, as can two resistors in series. It’s often used as a reference voltage, where little current is drawn over the connection. Op-amps use reference voltages to change signal output, so you can use a pot as a voltage divider to change attributes of sound in a synthesizer, for example. The op-amp outputs current that is proportional to the difference in voltage between it’s two inputs, so the resistor divider is used to make the output voltage a multiple of the input voltage- basically a resistor divider in reverse.
Many sensors respond to their respective input by producing a corresponding change in resistance. For instance, a light sensor might have a high resistance when it’s bright out, and a low resistance in darkness. Sensors can be used in one of the positions pictured above (R1 or R2; the diagram is a resistive voltage divider) to invert the output. For example, a light-sensitive resistor (LDR) in a voltage divider could be changed from its normal high-when-light state to high-when-dark. Sure, you could invert that output in software, too, but what if you’re not using a programmable microcontroller? With just an extra resistor, you’ve inverted the sensor’s function.
Here’s some more reading material on voltage dividers:
- Doctronics voltage divider page
- All about circuits – voltage dividers
- Voltage divider Wikipedia page
Where do you use voltage dividers? Post up your experiences in the comments.
This week’s Ask MAKE has been sponsored by Jameco Electronics.
2 thoughts on “Ask MAKE: Voltage divider”
My scariest divider is the 6666/1 divider in my CRT monitor. It provides a scaled sample of the CRT anode high voltage to the regulation circuit. If the “bottom” resistor fails then 27,500 volts are present on a low voltage wire+board.
A designer caution: when designing voltage dividers be aware of the load which the output is connected to. It is usually in parallel with the “bottom” resistor.
[…] that, if you use a cable, you’ll also need to use a 3.3V regulator, or go ahead and build a voltage divider out of resistors, as the FTDI cable runs at 5V and the ESP8266 runs at just […]
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