A diode is a semiconductor device with two terminals: an anode and a cathode. The direction in which a diode “goes” or conducts current depends on the polarity of the voltage applied to its terminals. Typically, current flows through a diode from the anode (positive terminal) to the cathode (negative terminal) when the diode is forward-biased. In this state, the diode offers low resistance to current flow. Conversely, when the voltage polarity is reversed (reverse bias), the diode blocks current flow and offers high resistance.
To determine which way a diode goes or its polarity:
- Markings: Diodes often have markings such as a band around one end or a line near the cathode terminal. The band or line indicates the cathode side, while the other terminal is the anode.
- Datasheet: Referring to the diode’s datasheet is crucial for identifying its polarity and orientation. The datasheet provides information on the physical configuration of the diode, including terminal identification and electrical characteristics.
- Multimeter Test: Using a multimeter in diode mode can help identify the forward and reverse directions of a diode. When the multimeter probes are connected in one direction across the diode, it should show a low resistance reading (forward bias), indicating current flow. In the opposite direction, it should show a high resistance reading (reverse bias), indicating no current flow.
The forward direction of a diode refers to the direction in which current flows easily from the anode to the cathode. This direction corresponds to the diode’s low-resistance state when a forward voltage is applied.
In a real diode, the anode is typically marked with a positive symbol (+) or a longer lead compared to the cathode. The cathode is marked with a negative symbol (-) or a shorter lead. Identifying these markings or lead lengths helps determine which side of the diode is positive and which is negative, aiding correct orientation in a circuit to ensure proper operation according to the diode’s specifications.