Are BUV20s double-die?

[JeffYoung]

I got these off eBay. They look right, and the case dimensions are all within spec.

The insides looks nice and professional as well (and certainly not doctored about), but are they supposed to be double-die?



Thanks,
Jeff.

 

[JeffYoung]

Update: while nothing conclusive, the consensus over on PinkFishMedia seems to be that they are indeed double-die.

Cheers,
Jeff.

 

[davidsrsb]

Fakes have small die, those are as big as you can fit in the case.
This device is a dedicated high current (50A) switch, not an amplifier

 

[JeffYoung]

Yeah, Julian Vereker (of Naim) was of the opinion that speed was more important than linearity, and he wasn't a fan of parallel output devices. As a result all his output stages used switching transistors.

 

[davidsrsb]

In this device, the two die have some built in emitter resistance, so they share current at high current. At lower currents there is no forced sharing and this causes the poor SOA at moderate voltages, making this device poor for an audio amplifier or linear power supply.

 

[JeffYoung]

Ahhh... so that's why the SOA curve has that funny inversion in it.

I wonder if this fit in with Vereker's dislike of parallel output devices: it essentially operates as a single device until the current demands rise, at which point it becomes two. Or if he was just unaware of this.

 

[davidsrsb]

Classic JV era Naim amplifiers were run with very low quiescent current, close to optimum, which would have been hard to match across multiple devices even with the high value emitter resistors Naim liked

 

[wg_ski]

All switching transistors have a funny inversion in the SOA curve, regardless if they are double die or not. Even a lot of the higher speed FETs do now.

I think all the Motorola 50 amp TO-3 devices with the large pins are double die. Even the darlingtons, even the low voltage ones specified for linear operation. And you do not get a full doubling of the SOA, or even current capacity. Two 30 amp 200 watt die are needed to get 50 amps at 300 watts. And the second breakdown point comes back a little. Not only that, but the prices are pretty high so you might as well use two of the single die version. At least in an amplifier.