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Various semiconductor diodes. Left: A four-diode bridge rectifier.Next to it is a 1N4148 signal diode.On the far right is a Zener diode.In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting.
The diode can be treated as switch that conducts significantly only when forward biased and is otherwise effectively disconnected (high impedance). Specific diode types that can change switching state quickly, such as the Schottky diode and the 1N4148, are called "switching diodes". Vacuum tubes can be used in high voltage applications.
ASCRs are used where either a reverse conducting diode is applied in parallel (for example, in voltage-source inverters) or where reverse voltage would never occur (for example, in switching power supplies or DC traction choppers). Asymmetrical SCRs can be fabricated with a reverse conducting diode in the same package.
The reverse bias rating of the N-drift region to collector P+ diode is usually only of tens of volts, so if the circuit application applies a reverse voltage to the IGBT, an additional series diode must be used. The minority carriers injected into the N-drift region take time to enter and exit or recombine at turn-on and turn-off.
Three 1N4148 diodes in glass DO-35 axial package. The black band on the right is the cathode side. Diode schematic symbol vs cathode marking on the package. The 1N4148 is a standard silicon switching signal diode. It is one of the most popular and long-lived switching diodes because of its dependable specifications and low cost.
Fig.2 : Current/Voltage/switching frequency domains of the main power electronics switches. The trade-offs between voltage, current, and frequency ratings also exist for a switch. In fact, any power semiconductor relies on a PIN diode structure in order to sustain voltage; this can be seen in figure 2.
The switching time is ~100 ps for the small-signal diodes, and up to tens of nanoseconds for special high-capacity power diodes. With p–n-junction switching, there is also a reverse recovery current, which in high-power semiconductors brings increased EMI noise. With Schottky diodes, switching is essentially "instantaneous" with only a slight ...
Switching losses happen in the transistor and diode when the voltage and the current overlap during the transitions between closed and open states. A schottky diode can be used to minimize the switching losses caused by the reverse recovery of a regular PN diode. [11] The switching losses are proportional to the switching frequency.
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