Power Integrations’ 600-Volt 12-Amp Qspeed Diode Features a Qrr of 14nC

The QH12TZ600Q from Power Integrations (PI) employs a merged PiN and Schottky diode technology to achieve its smooth reverse recovery current transition characteristics.

Image courtesy of Power Integrations

The smooth reverse recovery current transitions enabled by the QH12TZ600Q not only serve to increase efficiency but also reduces electromagnetic interference  (EMI) generation. 
 

The Benefits of Qspeed Diodes’ Qrr

Qspeed diodes offer very low Qrr, and exhibit soft recovery characteristics, which makes them well suited for use in continuous conduction mode (CCM) boost power factor correction (PFC) circuitry and as output diodes in hard switching applications. 

As described in a PI video, when a silicon diode gets turned off and reverse-biased, the current rapidly falls off and then begins falling backward as it recovers from forward conduction. The integration of negative current over time is the reverse recovery charge (Qrr). This energy is repetitively lost with each switching cycle.

Qrr of Qspeed diodes vs Ultrafast diodes. Image taken from PI video

As illustrated above, much less energy is lost by the Qspeed diode because of its low Qrr.

Diode “Softness” as Related to EMI

Ultrafast diodes exhibit a choppy waveform with sharp edges which will generate EMI. In the illustration below, note that for the Qspeed diode, the time it takes for the negative voltage to get to its’ lowest point is about equal to the time it takes to get back to zero. This denotes a “soft” diode, and note the lack of EMI generating choppy waves exhibited.

Diode recovery. Image taken from PI video

The ultrafast diode takes way more time getting to zero than it does recover, and note the choppiness of the subsequent part of the waveform

Application to On-Board Chargers

The reduced Qrr reduces MOSFET switching losses and allows designers to opt for higher switching frequencies. This, in turn, reduces the required size for magnetic filtering components. When employed in onboard chargers, the low EMI can also serve to eliminate the need for snubber circuitry. 

As noted by Edward Ong, senior product marketing manager at Power Integrations said: “The Qrr of these new Qspeed diodes is half that of the next best ultra-fast silicon diodes, resulting in very high system efficiency. This is particularly important for automotive on-board charger applications that require higher switching frequency to reduce volume and weight, and enables the Qspeed diodes to replace SiC devices.” 

In a recent trial, PI switched out an ultrafast diode and replaced with a Qspeed family member. The reduced switching losses translated into a cooler running MOSFET. The heat energy saved translated into enough useful energy to effect an overall 1% increase in efficiency

Applications 

• Power Factor Correction (PFC) boost diode for on-board chargers
• Output rectifiers for on-board chargers

Physical

• The  QH12TZ600Q is available in a TO-220 package, which allows for the unit to be directly mounted to metal heat sinking. This helps enable superior thermal performance. 

Regulatory and Safety

• The diode is AEC-Q101 qualified
• Electrostatic discharge (ESD) Human body model (HBM) classification H0
• IATF 16949 qualified for fabrication, assembly and testing
• Isolation is 2500 volts