GaN-based Class D power amps
merrillaudio Would you say that it's needed to get you there at the very front, and without it your just an also-ran? (for the time being) Cheers George |
This is in response to MerrillAudio statement " GaN transistors – first commercially available in 2010, will certainly become more pervasive as the costs come down. GaN material was used in LED’s for over 2 decades. GaN transistors can be used for any class of amplifier. It is not limited to Class D or other switching designs. " Actually the first part is true 100% (I was in the team at IR that actually did it in 2010, maybe a bit too early ;)) The second part it seems to me not completely accurate. As far as I know, all GaN devices available in the market, sold by IFX, EPC, GaNSystem, Transphorm and few minor others, are designed 100% as switching devices and cannot operate well at all (meaning they will most likely blow up), if operated in linear region (Class A/B or Class A amps). Moreover, in order to make anything with a full symmetrical configuration, needed for A/B or A topology, one would also need a P type device, something that does not exist, as far as I know, with GaN. But again, GaN Mosfets are a massive improvement in the power semiconductor technology because they offer a F.O.M (figure of merit) much better than any Silicon based devices (this is true however in the voltage range between 100~600V, not much advantage yet below 60V at all, at least in power conversion) GaN is ideal for CLASS-D , because, as Merrill pointed out in his comment, designer can actually virtually eliminate the deadtime issue (reduced to mere few nanoseconds) and thanks to the transition time so much faster, be able to transfer a much wider harmonic content of the input signal to the output. Remember the 3D feeling in the comments of some that has actually listened to the GaN amps vs. traditional amps? However GaN alone cannot provide all the benefits, designs that operate at high frequency require a complete different PCB layout attention, extremely reduced parasitic, and as always in Audio applications, a careful selection of passive components, even more critical with GaN. So there are a lot of challenges, but not so intrinsically different than the one engineers encountered 30 years ago when the first power MOSFETs started to replace old bipolar transistors (and 30 years before when the bipolar transistors replaced the vacuum tubes). Eventually, lesson will be learnt and all the improvements will end up to benefit the customers/users of the new advanced products. |
Regarding power output of the in production GaN-based class D amps, I’ve been criticized for posting what is from the manufacturers’ own websites. So this is my last attempt to compare their respective outputs: ADG Vivace: 200W into 4 ohms with 0.1% THD using a 1kHz signal Technics SE-R1: 300WPC into 4 ohms with 0.5% THD using a 1kHz signal Merrill 118: 800W into 4 ohms (no THD or frequency signal data specified). |
Some more info that come to the net, also i may have mentioned, that TI Texas Instruments (who also own Burr Brown) have now the rights to manufacture GaN semiconductors. "EPC’s enhancement-mode GaN (eGaN) transistors switch up to ten times faster than silicon MOSFETs, with ‘zero’ stored charge. The increased switching speed of eGaN FETs allows amplifier designers to increase PWM switching frequencies, reduce dead-time, and drastically reduce feedback; producing a sound quality previously limited to large, complex, heavy Class-A amplifier systems. https://m.eet.com/images/planetanalog/2016/10/564363/Image-4.jpg
Cheers George |
