Isolated power rail generator for gate drivers

For the gate drivers of high-power IGBTs, mosfets, SiC mosfets and GaN hemts, Infineon has introduced an isolated power supply IC that can generate asymmetric output voltage rails.

Each member of the 2EP1xxR family, as it will be known, has a full bridge of mosfets at its output for driving both ends of a transformer primary, whose secondary can be configured in various ways.

Depending on that transformer output configuration, the input voltage, the primary/secondary turns ratio and the mark/space ratio of the drive signal, a variety of dual output voltages can be generated, symmetrical or asymmetrical, and single output voltages are also possible.

These are open-loop devices – there is no feedback or regulation.

Suggested arrangements include:

• Direct-coupled transformer and voltage-doubler output rectification.
• Direct-coupled transformer and peak rectification for symmetric outputs.
• Capacitor-coupled transformer and peak rectification for asymmetric outputs: +15 and -7.5V, for example.

Loosely, the family members are:

• 2EP100R and 2EP101R have a choice of fixed ratios for IGBT and SiC mosfet gate driver supplies.
• 2EP110R has fine duty-cycle adjustment for SiC and GaN gate drivers.
  2EP130R is a much more flexible device with 41 selectable switching frequencies, 41 selectable duty-cycles (or external PWM synchronisation) and 5 over-current limits.

Configuration is via pin strapping or resistors, with these read at power-up and stored until power-down.

“A duty-cycle setting other than 50% is mainly used in application circuits with a series capacitor at the primary side and peak rectification at the secondary side of the transformer,” according to the company. “Such a configuration allows users to adjust the ratio of the positive to the negative isolated output voltage. The transfer ratio of the transformer defines the relation between the transformer’s input and output voltages. Both measures together enable the adjustment of the output voltage for positive and negative rail in a wide voltage range.”

Operation is across 4.5 to 20V and ambients of -40 to +125°C.

Protections include: under-voltage lock-out, over-temperature, output short-circuit and over-current.

Features include soft-start and a ‘ready’ output.

Packaging is 0.65 mm pitch 3 x 5mm TSSOP-8-1.

In addition, the evaluation boards EVAL-2EP130R-VD, EVAL-2EP130R-PR and EVAL-2EP130R-Evaluation board exist and applications are expeted in solar power, electric vehicle charging, energy storage, welding, uninterruptible power supplies and drives.

The 2EP1xxR  data sheet is worth a look as its application section is a good backgrounder on asymmetric voltage generation using transformers