Power Integrations has expanded its Qspeed series of diodes with the edition of the LQ10N200CQ and LQ20N200CQ common cathode diodes. Employing Merged-Pin technologies, the new AEC-Q101 qualified devices are able to balance soft switching with low reverse recovery charge (Qrr). The resulting reduced output noise and lowered EMI emissions make these units a great choice for OEMs producing in-vehicle audio systems.
Image from Power Integrations
Both of the new diodes feature a peak repetitive reverse voltage of 200 volts at 25 °C (TJ = 25 °C). Also offered are what Power Integrations claims is the industry’s lowest typical reverse recovery charge at 32.4 nC (TJ of 125°C).
Edward Ong, Product Marketing Manager at Power Integrations, comments, “The automotive audio industry has been clamoring for an alternative to Schottky diodes with their ‘snappy’ reverse recovery, which causes ringing that generates EMI and noise in sensitive Class D amplifiers. Our automotive-qualified 200 V QSpeed diodes are the perfect solution for in-car audio amplification applications.”
Important Diode Characteristics
The common cathode package can serve to reduce the amount of mounting hardware required in interleaved and bridgeless topologies.
Both Q-series diodes include two common cathode diodes. Image from Power Integrations
The LQ10N100CQ is a 10 amp device (5 amps per diode.) It has the aforementioned QRR of 32.4 nC. Typical IRRM (maximum reverse recovery current per diode) at 25 °C is 2.6 amps.
This LQ20N200CQ is a 20 amp device (10 amps per diode.) The QRR for this device is a bit higher at 48.4 nC. Typical IRRM at 25 °C is 3.29 amps.
The Softness Ratio
Both devices also feature a “diode softness” ratio of 0.39. This is what minimizes high-frequency EMI inherent in the Schottky rectifiers that are often used in Class-D power amplifier output stages.
This can be a contentious issue. As described by Lonnie Mays in All About Circuits, "we might be tempted to think that we could define the 'softness' of our recovery characteristic as a simple ratio of trrr to trrf." But there is also the slope of the curve, di/dt to consider. A high rate of current change in a given period of time, of course, will contribute to EMI.
Soft recovery waveforms. Image adapted and redrawn from JEDEC Standard No. JESD282B.01, Figure 6.1. Image from Lonne Mays, All About Circuits
For that reason, JEDEC also defines the reverse recovery softness factor (RRSF) for rectifiers as the ratio of the “maximum absolute magnitude of dI/dt within the trrr region to that in the trrf region.”
There are many issues to consider when choosing the right diode for a particular application, and one size definitely does not fit all. Power Integrations’ Paul Lacy offers important guidance to consider when exploring these complex issues.
Important Note to Component Engineers
Q-Series diodes employ Schottky technologies in their design and construction. Therefore, component engineers should plan their test setups to be similar to traditional Schottky test setups.
Both units are:
- AEC-Q101 qualified
- Fab, assembly, and test certified to IATF 16949
- ESD HBM classification H0
- RoHS Compliant
- Halogen-free per IEC 61249-2-21
They are available in a TO-252 DPAK package.
Other Qspeed Diodes from Power Integrations
While the Q-series subset of the Qspeed diode extended family has the highest softness, and therefore the lowest EMI profile.
- X-Series Diodes are optimized for frequencies below 80 kHz, have very low forward voltage drop.
- The H-Series has the lowest QRR and provides the highest efficiency.