84072| Datasheet

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Vishay Semiconductors

Physical Explanation
General Terminology
Semiconductor diodes are used as rectifiers, switchers, Varicaps and voltage stabilizers (see chapter `Voltage Regulator and Z-diodes'). Semiconductor diodes are two-terminal solid-state devices having asymmetrical voltage-current characteristics. Unless otherwise stated, this means a device has single pn-junction corresponding to the characteristics shown in figure 65.
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Diode capacitance, CD Total capacitance between the diode terminals due to case, junction and parasitic capacitances. Breakdown voltage, V(BR) Reverse voltage at which a small increase in voltage results in a sharp rise of reverse current. It is given in the technical data sheet for a specified current. Forward voltage, VF The voltage across the diode terminals which results from the flow of current in the forward direction. Forward current, IF The current flowing through the diode in the direction of lower resistance. Forward resistance, rF The quotient of dc forward voltage across the diode and the corresponding dc forward current.

Figure 65.

An application of the voltage current curve is given by I + I S exp V 1 VT where I S + saturation current V T + k q T + temperature potential If the diode is forward-biased (anode positive with respect to cathode), its forward current (I = IF) increases rapidly with increasing voltage. That is, its resistance becomes very low. If the diode is reverse-biased (anode negative with respect to cathode), its reverse current ( I = IR) is extremely low. This is only valid until the breakdown voltage V(BR) has been reached. When the reverse voltage is slightly higher than the breakdown voltage, a sharp rise in reverse current results. Bulk resistance Resistance of the bulk material between junction and the diode terminals. Parallel resistance, rP Diode resistance resulting from HF rectification which acts as a damping resistance to the pre-tuned demodulation circuit.

Forward resistance, differential rf The differential resistance measured between the terminals of a diode under specified conditions of measurement, i.e., for small-signal ac voltages or currents at a point of forward direction V-I characteristic. Case capacitance, Ccase Capacitance of a case without a semiconductor crystal. Integration time, tav With certain limitations, absolute maximum ratings given in technical data sheets may be exceeded for a short time. The mean value of current or voltage is decisive over a specified time interval termed integration time. These mean values over time interval, tav, should not exceed the absolute maximum ratings. Average rectified output current, IFAV The average value of the forward current when using the diode as a rectifier. The maximum allowable average rectified output current depends on the peak value of the applied reverse voltage during the time interval at which no current is flowing. In the absolute maximum ratings, one or both of the following are given: D T
he maximum permissible average rectified output current for zero diode voltage (reverse) D The maximum permissible average rectified output current for the maximum value of URRM during the time interval at which no current is flowing.

Document Number 84072 01-02

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