Do-it-yourself projects and technology updates

Voltage Divider

The Voltage divider is an important circuit to use in several applications. It can be used in a power supply where you need a + and a – voltage. In the CMOY pocket amplifier, the two 10K resistors are used in conjunction with the 2 9v batteries to make a 0V, or ground pin, as well as a +9V, and a -9V. This is used to give the opamp the +9v and -9v that it needs. This voltage divider is also used in the one-watt amplifier. The base of the transistor is connected to the 0v pin, and this keeps the transistor centered at 0V.

There are some problems with the Voltage Divider. It causes a continuous loop of current that is always running. This shortens the life of the batteries, and the current is released as heat. The CMOY pocket amplifier uses the 10K resistors at 18 Volts. From Ohm’s law, we know that voltage is equal to the current times the resistance, or V=IR. The voltage accross these two resistors is 18V. When resistors are added in series, you simply add the resistance, so you have 20,000 ohms. The current through these resistors is simply I=V/R, or 18/20,000, which is 0.9 mA (milliAmps). This is a significant amount of current loss in a battery powered device.

This can be corrected in two ways. One way is to use a higher resistor power, like 100K, or maybe 1M. These have a very small amount of current loss. This can be used in the 1-watt amplifier. A better way for the CMOY pocket headphone amplifier is to use this circuit below. With the two batteries connected in series, and the ground between the two points the loop is eliminated. The Opamp can still get its power, and ground, but there is no loss in power through the voltage divider anymore. The only drawback to this is that in order to use a switch, you have to connect one to the +9v, and the -9v lines. This ensures that neither of the two batteris are connected to the circuit via ground. This can be done using a double pole single throw (DPST) switch.

This entry was posted on Friday, December 30th, 2005 at 9:32 am and is filed under Circuits. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.