PI - Qspeed™ Diodes from POWER INTEGRATIONS: High Efficiency with Low EMI

Qspeed diodes use a silicon-based process to combine an extremely low reverse recovery charge (QRR) with a very soft recovery waveform. Together, these features help designers optimize the efficiency and EMI performance of their power conversion circuits. Qspeed diodes are ideal for PFC circuits that operate in continuous conduction mode (CCM), and as output diodes for hard-switching applications. In PFC circuits, Qspeed diodes can provide an overall switching performance that is comparable to silicon-carbide (SiC) diodes at considerably lower cost.

When a silicon PN diode is operated in reverse bias and turns off, the current rapidly falls to zero and then briefly flows backwards through the diode as the PN junction switches from conduction to blocking mode of operation. The product of time and negative current (i.e., the area under a plot of the instantaneous current curve, in dependence on the time during commutation) is defined as the reverse recovery charge, or QRR. The QRR flows to ground through other components in the system and the energy is wasted as heat, thus reducing efficiency and raising the temperature of costly associated components, such as MOSFETs. Qspeed diodes have the lowest QRR of any low-cost, silicon-based diode. They supplant ultra-fast silicon diodes in PFC and rectifier applications that target increased efficiency or temperature reduction, and they replace silicon-carbide diodes in applications with aggressive cost goals.

The reverse recovery waveform of a diode generates electrical noise (EMI) that must be filtered to low levels, to prevent the noise from interfering with the AC mains and power supply load through either conduction or radiation to nearby systems. Qspeed diodes feature very soft switching: The waveform is essentially sinusoidal with no high-frequency harmonics, thus reducing conducted and radiated EMI emissions. In turn, this reduces the size, cost, weight, and complexity of a power supply's EMI filter hardware, as well as the prototyping and development cost associated with EMI suppression.

Qspeed diodes deliver exceptional performance without the cost of exotic materials, thereby enabling high-efficiency, low-cost designs. Qspeed 600V diodes are available in three families: The X Series is optimized for cost effectiveness and high efficiency at switching frequencies below 80kHz, and the Q and H Series are designed for use above 80kHz. The Q Series has the highest softness and best EMI characteristics. The H Series has the lowest forward drop (VF) and QRR, while offering the highest efficiency. In addition to the 600V products, Qspeed 300V diodes provide best-in-class switching for rectifier and audio applications.

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