- Ready-Made Extension #3 -

Directing Current

The Bridge Rectifier in the LVPS circuit cleverly changes alternating current which changes direction of flow 60 times into direct current which maintains its flow in one direction. The bridge rectifier is made from diodes.

The general question of this investigation is "How does a bridge rectifier work?" The quick answer is: "It uses diodes." Of course that leads to more questions; what does a diode do, and how are diodes combined to make a rectifier?

Start by investigating diodes.

Begin with a light emitting diode (LED) and find out the effect of voltage on the current through the diode. Make graphs of current vs voltage. Drive current through the diode in one direction, slowly increasing the voltage. Be CAREFUL, the LVPS can easily burn out LEDS; they operate at quite low voltages, so stop as soon as the LED is nicely lit. Now reverse the leads of the diode and drive current through in the other direction, slowly increasing the voltage. Combine the two plots of current vs. voltage on one graph. This is the characteristic curve of the diode.

Four diodes can be connected in a way that lets current pass through a load when the applied voltage is positive, but reverses polarity when the voltage is negative. The backward negative current is the same as a positive forward current. A circuit diagram for this configuration, called a bridge rectifier, is pictured below.

Figure E4 Rectifier

To help understand how the diodes direct the current flow, you could:

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