Flyback switcher for electric vehicle safety designs

July 16, 2020 //By Nick Flaherty
The InnoSwitch3-AQ from Power Integrations achieves Q100 qualification and operates from 30 V to 550V DC input with ±3 percent accurac
The InnoSwitch3-AQ flyback switcher from Power Integrations achieves Q100 qualification and operates from 30 V to 550V DC input with ±3 percent accuracy

Power Integrations has launched an automotive-qualified flyback switcher with an integrated 750V MOSFET and secondary-side sensing for traction inverters, OBC (on-board charger), EMS (energy management DC-DC bus converters) and BMS (battery management systems) to provide an alternative power supply for an electric vehicle if the 12V battery fails.

“One important thing for the traction inverter is the functional safety, to be able to safe to use even in the presence of failure,” said Edward Ong, product marketing manager at Power Integrations.

The 12V battery is used to provide the gate drive voltage in the traction inverter so in the event that the 12V battery fails or is disconnected there is no 12V input to the gate drivers and the traction controllers. The functional safety requirements of the ISO26262 standared require an emergency power supply to provide the output voltage for the inverter controller system and the gate drivers to move the vehicle safely.

“This will be taking power from the HV bus which can be a wide range, as low as 30V and as high as 550V,” he said. “This is something that is really new.”

The InnoSwitch3-AQ flyback switcher uses Power Integrations’ high-speed FluxLink coupling to achieve ±3 percent accuracy for combined line and load regulation while eliminating both dedicated isolated transformer sense-windings and optocouplers. This high speed link allows the controller to maintains output voltage regulation even under the transient stress test, which is particularly challenging for PSR-based implementations.

“You need a feedback loop on the secondary side – in automotive optoisolators can’t be used as they degrade with time and this impacts the life of the power supply system so the dilemma is that you need the isolation to feed the data back to primary side,” said Ong.  

“But the FluxLink generates a magnetic coupling without the use of optoisolators,” he said. “The advantage of inductive coupling is that with magnetic coupling allows a faster response time so if

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The InnoSwitch3-AQ operates from 30 V to 550V DC input with ±3 percent accuracy

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