My 803t theory...the reason for all the power.

[brtaman]

Hey guys,

Ever since I started reading the forums, and learning about the massive power of just a "reader diode" the 803t, I have wondered why engineers would place such a powerful diode inside a 2.4x reader. Well after a discussion in gooeygus's GGC thread I believe that I have come to a definitive theory.


The 803t diodes, are harvested from earlier HD-DVD drives. These were in a way pioneers in the HD-DVD field of consumer electronics, it is my belief that the main reason that such powerful diodes were used in these drives is a "prototype" or first generation of read sensor (the thinga-majig, that takes the flashes of laser and turns it into code for it to be read). As these were the begining products I believe that it is safe to assume, that they were not very "good" and probably struggled to supply a steady stream of data, with a lower powered laser diode. This is what I believe was the main driving force behind the usage of such a high powered diode in there reader drives.

This theory is somewhat supported by the newer drives which have the 811t diode's installed. In time toshiba engineers were able to make a much more efficient and precise read sensor (evolution of HD-DVD technology). These newer sensors enabled the drives to use a less powerful diode while at the same time still provide all the performance of the previous older and less efficient drives.


Well this is my theory on the factors behind the use of practically a burner diode in a reader.

Hope you enjoyed reading through this ;D, please feel free to comment and add your opinion.


brtaman

 

[Murudai]

The general theory of why they use such powerful diodes is because of the use.

When we take them out for use in pointers, we sometimes blow them. We overdrive them, and push them to their limits. Now if you just bought a blu-ray drive and the diode blew 1 hour in to the movie, you'd be pretty pissed.

Thus they are such a high power so at their really safe operating range, they are still powerful enough to do lots of things.

 

[brtaman]

Yes murudai that is true, diodes in components usually/always run under or at exact specs in order to increase life.

But the point of the post was to explain the reason behind the insanely powerful 803t which was then replaced by the much weaker 811t. The culprit IMO was the sensor...in the original drives, it wasn't too efficient and needed a really strong beam to be able to stream data from the disc...It would seem that this sensor chip was upgraded (through development of HD-DVD technology) to the point where it needed a much less powerful beam to stream data successfully, which would explain the reason behind all newer drives having the low-power diode.


brtaman

 

[Murudai]

Oh, I see. I didn't know the 803ts were being replaced.

In that case, your theory sounds plausible

 

[brtaman]

I am pretty sure thats the case, I mean from what ive read it seems that the 803t's are found in older sleds, while newer sleds all have the 811t??

LOL@plausible...this aint no mythbusters ;D


brtaman

 

[GooeyGus]

well.. the newer sleds on the HD-DVD xbox360 drives have the DT0811, but it seems they were all the PHR-803T in the hd-dvd drives for PC's

AND... even the DT0811 can do way more than it should... it will still do like 80mW.

It's plausible ( ;D ) but who really knows with these wacky sled manufacturers. I mean, the PS3 (which can read blu-ray) was out before these HD-DVD drives for the xbox, and they only use a ~15mW 405nm laser.

I think what may be more likely, is that they haven't gottan the manufacturing process of the 405nm diodes perfect yet. This way, they get diodes which are rated slightly higher and they can still use them if they under-perform. With the lower power ones, they would throw quite a few away if they didn't put out the power they needed. With the higher power diodes, they just turn up the current a bit, and the diode still lasts a long time.

 

[pseudolobster]

well there's one way to test if this is even remotely plausible... find out what current the diode is running at while it's reading a hd-dvd!

I'm guessing that these are being used at much, much lower than what we're driving them at.. The PS3's nichia diodes are run in the playstation at <5mW, and as far as I know the differences between HD-DVD and BluRay involve the logical data structure of the disc, while the physical reading of the disc is the same mechanics between the two. I see no reason to believe they're being read at more than 5-10mW.

The 803t's have roughly the same power as a 4x burner, so I'm sure if they were being run at full juice within the drives, they would be *burning* writable media when they tried to read it.

 

[IgorT]

The reading sensor can not be the culprit. It's 100x easier to create a more sensitive pickup sensor, than to create a more powerful 405nm diode. And cheaper...

I think one of the reasons the diodes in the PHR sleds ended up being used as reader, is diodes because of their large inconsistencies in power.

But the DT0811 sled also uses quite a powerful diode.. So in both cases, i think another reason are the high losses in the plastic optics inside the sleds. Those are UV improoved acrylics with a 405nm AR coating, but the light still has to travel through many of them.

The PS3 sled used a much less powerful diode, and managed to read just fine with it's sensor.


So we have:
- higher reading speed
- high losses in the optics
- big power inconsistencies (with the PHR sled diode)

 

[IgorT]

I'm guessing that these are being used at much, much lower than what we're driving them at.. The PS3's nichia diodes are run in the playstation at <5mW

There is no need to guess, all diodes are driven much lower in drives, than what we are driving them at.. We are driving them at close to or over their pulsed ratings, but CW!

This diode was never meant to reach such powers, which is another reason for the inconsistencies.. Everything it can reach above the power used in the sleds, is just a safety margin for a longer lifetime...

Every part is made to withstand much more than it has to for this reason. But this one seems like it can take more..


It would be interesting to find out the current use in the drive tho. But you can't do that with a DMM...



Oh, and if i remember correctly, in the PS3 sled, the power after all the optics was 0.5mW, so around 10% of what the diode is doing.

 

[pseudolobster]

Well, what I meant is I think they're being used at like 5mW, compared to the nearly 200mW they're capable of (40x their rating)... Compare that to a 16x red burner diode, rated at like ~80-100mW CW, we're only able to drive them to ~200mW before they start to die (2x their rating)... This is much more than a safety margin, I'm guessing these diodes were meant to be in burners but they're from a bin that failed QA... They're not capable of running reliably at such high currents, but at ~5mW they're very reliable.

BTW, why couldn't we measure the current using a DMM? Is it pulsed?

edit: hehehe my 405th post is on the bluray board.. nice.

 

[IgorT]

I'm guessing these diodes were meant to be in burners but they're from a bin that failed QA...

Well, yeah, that's what i meant, when i mentioned the large power inconsistencies at high currents.

This could have resulted in these ending up in reader sleds. It could have been down to either doing that or throwing them all away.

But if you check their datasheet (if it really is their datasheet) their max CW power is listed as 100mW.. So it's not that far away from 16x red's specs and what we're getting out of them.


I don't know if it's pulsed when reading. If it is, a DMM couldn't measure it, yes. But it may not be pulsed... Pulses are required for burning. Reading would work with CW.



Another reason can be the price.. Sometimes it's cheaper to order a large quantity of one model, than two smaller quantity of different models.

Just look at the price of these diodes in small quantities, never mind sample quantities...


This is also the reason some people are suspecting the 6x Blue Ray reader drive could contain the same diode as the writer.. If true, it could be a good source for it. But someone has to risk $160 and then the diode, to find out..

 

[brtaman]

Very good points guys, however I would be really interested in what the diode in older style sleds is putting out when they are in use.

Though I have concluded that the sensor might not be the culprit (reasons provided by IgorT), I am sure some aspect of the sled design must have been some sort of driving factor in the use of such a powerful diode. Perhaps all the optics as IgorT suggested, maybe surplus diodes (using whats at hand), maybe the 803t's were the only feasible (cost wise) diode for use in the HD-DVD drives, (sony's is probably propriety), who knows but I still believe it has something to do with the technology that was at hand at the beginning of round X of the transfer media wars...???


(BTW thanks for completely demolishing my theory ;D)


brtaman

 

[IgorT]

Haha, well you asked for other oppinions...

 

[daguin]

A couple of the members with more electronics experience than me were discussing these sleds. (Of course I can't find the thread now) They saw the needed components to hook up for burning in the electronics of the 803 sled. They didn't look at the 0811.

Peace,
dave