- Published: Friday, 30 December 2011
- Written by Jon Chandler
In Power Protection Circuits, I outlined some methods of circuit protection. In this article, I'll take a closer look at the practical aspects of using a series diode for reverse polarity protection.
A series diode is about the simplest form of protection again a power supply being connected incorrectly. For some applications it will work well but with others, the voltage drop across the diode in normal operation will create problems.
A series diode will conduct when the power supply is correctly connected but will block the current flow if the power supply is connected with reverse polarity, protecting the circuit from damage. The downside of this simple circuit is the voltage drop across the diode. Depending on the power supply and circuit arrangement, this may or may not be a problem.
Let's start by examining the voltage drop. For this experiment, I used a common 1N4001 silicon diode (which is available at RadioShack). The diode will handle up to 1 amp and 50 volts PIV (peak inverse voltage). I used my bench power supply set to 5.0 volts as the power supply for this test and my adjustable dummy load to vary the output current. A Fluke 45 was used to measure the output voltage across the "circuit." The plot below shows the results.Discuss this article in the forums (3 replies).