When a diode is exposed to a DC (direct current) voltage, its behavior depends on the polarity of the applied voltage relative to the diode’s orientation. A diode allows current to flow in only one direction, from its anode (positive side) to its cathode (negative side), when forward biased. When a positive voltage is applied to the anode and a negative voltage to the cathode, the diode conducts current, allowing electrons to flow freely through the diode.
Conversely, when a diode is reverse biased, meaning the positive voltage is applied to the cathode and the negative voltage to the anode, the diode blocks current flow. In this state, the diode exhibits a very high resistance, preventing significant current from passing through it. Instead, a small leakage current, known as reverse leakage current, may flow due to minority charge carriers.
A diode’s primary function in a DC circuit is to control the direction of current flow. It allows current to flow in one direction (forward bias) while blocking it in the opposite direction (reverse bias). This characteristic makes diodes essential for rectification, where AC (alternating current) is converted into DC. In a rectifier circuit, diodes conduct during the positive half-cycle of the AC signal, allowing current flow in one direction only, thereby converting AC to pulsating DC.
A diode itself does not increase DC voltage; instead, it can be used in conjunction with other components in voltage multiplier circuits to achieve higher DC voltages. Diode-based voltage multiplier circuits, such as the Cockcroft-Walton voltage multiplier, use diodes and capacitors to double, triple, or quadruple the input voltage level. This method is commonly used in applications requiring high voltage DC supplies, such as in cathode ray tubes (CRTs) and particle accelerators.
Diodes are crucial in rectification circuits for changing AC to DC. By allowing current to flow only in one direction, diodes convert the alternating polarity of AC into a unidirectional flow of current in the output circuit. Half-wave rectifiers use one diode to pass only one half of the AC waveform, resulting in a pulsating DC output. Full-wave rectifiers use multiple diodes arranged in a bridge configuration to rectify both halves of the AC waveform, producing a smoother DC output suitable for powering electronic devices and circuits.