This section provides overview, applications, and principles of fast recovery diodes. Also, please take a look at the list of 36 fast recovery diode manufacturers and their company rankings.
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Fast recovery diodes (FRDs), also called fast diodes, are PN junction diodes capable of high-speed operation.
Their structure and functions are the same as those of the general rectifier diode. Still, while rectifier diodes are suitable for low-frequency rectification below 500 Hz, fast recovery diodes are ideal for high-frequency rectification from several kHz to 100 kHz.
Fast recovery diodes have measures to reduce the reverse recovery time trr from the on the state to the complete off stat. While the trr of rectifier diodes is about 5 to 10 us, the trr of fast recovery diodes is about 50 to 100ns.
Fast recovery diodes are used in switching power supplies by being incorporated into power factor correction (PFC) circuits that suppress high-frequency currents.
A PFC circuit consists of a diode, an inductor, and a MOSFET in the continuous operation mode of a PFC circuit, the MOSFET is turned on before the inductor current reaches 0A, forcing the diode to turn off while current is still flowing through it, causing a recovery current to flow and generating switching noise. This causes the recovery current to flow, resulting in switching noise. To prevent this noise, a fast recovery diode with a small reverse recovery time trr is used.
Fast recovery diodes are also used in AC/DC converters and inverter circuits.
Fast-recovery diodes are PN junction diodes. The electrode terminal from the P layer is called the anode, and the electrode terminal from the N layer is called the cathode, allowing only forward current to flow from the anode to the cathode, and almost no reverse current. The first recovery diode can convert alternating current to direct current by utilizing this property.
The structure and function of fast recovery diodes are the same as those of general rectifier diodes. Still, measures are taken to reduce the reverse recovery time trr in fast recovery diodes.
When a diode is suddenly reverse-biased while it is forward-biased with current flowing through it, the holes in the P layer move to the anode side, and the electrons in the N layer move to the cathode side, causing the recovery current to flow in the opposite direction of the forward current. The time until the holes and electrons move completely, a depletion layer is formed near the PN junction, and no more recovery current flows are trr.
If the forward current is high, holes and electrons will pass through the PN junction surface and penetrate to the opposite region. If a steep reverse bias is applied here, it takes time for the holes that have entered the N layer to return to the anode, and this time determines trr.
In a fast recovery diode, a carrier trap is created by irradiating electron beams or diffusing noble metal near the PN junction. Holes entering the N layer are trapped in the carrier trap on their way to the anode side and disappear, shortening the time for hole migration and reducing trr.
In a fast-recovery diode, ringing (fluctuation) caused by the sudden convergence of the recovery current when a reverse bias is applied can cause noise. Therefore, the fast recovery diode must have not only a short reverse recovery time but also the characteristic of the gradual recovery of the recovery current.
*Including some distributors, etc.
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