700W/channel Class-D audio amp design with GaN output

EPC9192 Class-D GaN audio amp

EPC has used GaN transistors to create a high-power Class-D two-channel audio power amplifier design.

Instantiated in evaluation kit EPC9192, it is capable of pushing 700W/channel into 4Ω (or 2Ω) or 350W/channel into 8Ω. Bridging the two channels results in 1.4kW drive into 4 to 8Ω.

Key components, per channel, are a pair of 200V EPC2307 GaN transistors on a daughter card, controlled by an Onsemi NCP51820 gate driver, and a PWM on a different daughter card.

Hats off to to EPC because the PWM is not an off-the-shelf IC but a self-oscillating design (~600kHz) put together from op-amps and comparators, and more so because, in the data sheet, the company takes the time to credits designs from Williamson (Carver) and Veltman for inspiration.

EPC claims <0.005% THD+N, >120dB signal/noise ratio, 40µV noise floor and flat to 0.5 dB from 5Hz to 20kHz “regardless of load”.

Looking at the data sheet, <0.05% THD+N is true over a wider range of frequencies and power outputs, even up to 600W at 1kHz into 4Ω.

Input and output are ground-referenced, and two input rails are required at between ±42V and ±85V – with no heatsinks needed  at the bottom end, and a pair of heatsinks plus forced air required at the top end. There is no accompanying PSU design.

Protections include: under-voltage, over-voltage, over-temperature and over-current.

Find the product page here, which includes links to circuit diagrams (take a look at the PWM), and the data sheet here, which includes performance plots and enough thermal data for it to count as a reference design.

Digikey has the kit for sale here, but don’t get too excited if you are thinking ‘that will do for my living room’ as these cost around £900.

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