New diodes combine high efficiency and low emi

1 min read

Advanced diodes that use a silicon based process to combine a low reverse recovery charge with a soft recovery platform have been unveiled by Power Integrations.

The Qspeed range has been developed to help designers to optimise the efficiency and emi performance of power conversion units. Suitable for continuous conduction mode boost power factor correction circuits, and as output diodes for hard switching applications. According to Power Integrations, in PFC circuits, Qspeed diodes can provide an overall switching performance comparable to silicon carbide diodes and at a lower cost. When a silicon PN diode is reverse biased 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 (the area under a plot of instantaneous current versus time during commutation) is defined as reverse recovery charge, or QRR. The QRR flows to ground through other devices in the system and the energy is wasted as heat, reducing efficiency and possibly raising the temperature of costly associated components, such as mosfets. Power Integrations says that Qspeed diodes have the lowest QRR of any low cost, silicon based diode. They are designed to supplant ultrafast silicon diodes in PFC and rectifier applications targeting increased efficiency or temperature reduction, and replace silicon carbide diodes in applications with aggressive cost goals. The reverse recovery waveform of a diode generates emi which must be filtered to low levels to prevent conduction to the ac mains, the power supply load, or radiation to nearby systems. Qspeed diodes incorporate a sinusoidal recovery waveform, which contains no high frequency harmonics and are said to reduce conducted and radiated emi emissions. The 600V diodes are available in three ranges. The X Series is optimised for efficiency at switching frequencies below 80kHz, and the Q and H Series are designed for use above 80kHz. Stuart Hodge, product marketing manager at Power Integrations said: "In addition to power factor correction circuits, Qspeed diodes are also well suited for use as output diodes – replacing Schottky diodes – particularly in high current, high voltage power supplies such as telecom and audio. In these applications, Qspeed diodes deliver a dramatic reduction in peak inverse voltage and the soft recovery often allows designers to completely remove snubber circuits, lowering design cost and complexity while increasing efficiency."