Electrical Projects Many modern appliances, while operating on ac, use dc motors or rechargeable dc batteries that require the ac to be converted to dc at some point within the appliance. A diode is a small electronic device which can be used to convert alternating current to direct current.

Remember that a diode will allow current to flow in one direction only. Electrons can flow against the direction of the arrow in the schematic symbol or, in the case of an actual diode, electrons can flow from the end with a line or dot to the unmarked end, but not in the opposite direction. If current can flow equally well in either direction, the diode is not performing its function and should be replaced.

You can check a diode by first detaching one lead of the diode from the circuit it is in so that no current will flow through the circuit. Then, with the appliance disconnected, attach the leads from an ohmmeter to the diode and check resistance. Then reverse the ohmmeter leads and check the resistance through the diode in the opposite direction. Because an ohmmeter has a battery and a meter in slow current from the ohmmeter to flow easily in one direction, but should not allow current to flow in the opposite direction. So the resistance of the diode should be very low (typically, about 15-30 ohms) in one direction, and comparatively high in the other direction. The difference in resistances (called the front-to-back ratio of the diode) should be at least 10:1. If the front-to-back ratio is not at least 10:1, the diode should be replaced. Whenever you replace a diode, make certain that the cathode end is at the same point as it was originally.



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October 12, 2008