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Casio driver

Tech_Junkie

Tech_Junkie

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I've asked a few time if multiple diodes could be hooked up to one driver. I was told it was possible, but if a diode failed, the rest would probably blow 'cause of the spike. And its not a good idea to do it. Well how does Casio do it with 24 diodes? You can see they are connected in parallel. What stops the other diodes from frying if one goes down? Or are they run parallel in 4 banks, and if one blows the other banks are not effective?

p1012603.jpg
 





i think there is a monitor chip on the driver that can detect if one blow and adjust accordingly. or it just over drives the other laser to compensate the dead laser diode. plus when one dies they still take current just dont emit much light.
 
Tech Junkie;

Looking at the circuit in the 1st post, I would say it is 4 strings of 6 laser diodes in series.

If one laser diode shorts, the other 5 will probably still work with constant current for the string.

Plenty of fan cooling also improves the reliability.

Regardless, these diodes have proven pretty rugged with only limited failures.

LarryDFW
 
LarryDFW said:
Tech Junkie;

Looking at the circuit in the 1st post, I would say it is 4 strings of 6 laser diodes in series.

If one laser diode shorts, the other 5 will probably still work with constant current for the string.

Plenty of fan cooling also improves the reliability.

Regardless, these diodes have proven pretty rugged with only limited failures.

LarryDFW
Click to expand...


One other thing to keep in mind is with the current that these LD's see,
it is more likely that diodes would fail from COD rather than the leads
to the die completely blowing out...

That in mind, as along as the LD remain in an 'LED' state, it will continue
to draw the same current and voltage, just no real output of light.

The other LD's in that 'string' would continue to see the same current.

Cant remember if these are series or parallel, but if series, the 'string'
would go out if one failed, and only if the lead on the die 'popped'.
IIRC these are in parallel..

The LD's ive blown were all around 2A or just a hair above. In my case,
there was no 'LED' output, just an open circuit with blown out leads.
 
Casio driver have also safety checks ..... the driver power the array for half second at the minimum power, when you turn it on, and in this time it do a complete check, for voltages and currents ..... if the microchip find a string opened, or a diode shorted out, or a temp sensor blowed, it cut off immediately the power, and send a "lamp fault" to the system, locking all .....
 
wannaburn said:
That in mind, as along as the LD remain in an 'LED' state, it will continue
to draw the same current and voltage, just no real output of light.
Click to expand...

I've noticed with red diodes that the Vf for a given current is slightly lower when they are blown to leds. I'm not sure if this is also true for the 445 diodes, but if it were, the whole bank would dim if one diode in it was leded.

I suppose the simple answer is that they just don't die that easily when run at their rated specs in the projector. Putting them in banks rather than all-paralel is probably a practical consideration - those copper traces wouldn't handle the full current of the array, for example.

Also, i reckon they are binned on Vf, so that all diodes behave virtually identical, and driving them in paralel is feasible.
 
If it is supplying 6A per bank you could loose two and still be running 1.5A per which is certainly doable.

But I would think that they are like Christmas tree lights. Since they are in series one going out would stop the entire bank from working.

Good to see my pictures are being useful.:beer:



Harvesting the Casio Projector
[/QUOTE]
 
I agree with DTR, if they're run in a series and you lose one then the rest in that series would simply stop functioning until it was replaced or bypassed. And I don't think the spike from a single diode going would be enough to push these over the edge and blow the entire series. The possibility would obviously still be there as with any spike, but I think it would be unlikely that it would blow the whole series.
 
As said before, failure modes vary with laser diodes. If one failed LED-style, there would be no problem if they were connected in series. Its only when they go open circuit it would matter: in series the whole bank would go out, in paralel the remaining 5 diodes divide the excess current.

I don't know what the design consideration at casio was, but it would be reasonable to assume they designed it such that the device would still work reasonably well when a single diode fails. The paralel configuration probably does that quite well: if one fails LED it would just be a 1/24th reduction in light, and if one failed open circuit it would be less of a reduction since the other 5 are driven harder. Probably neither condition would make a consumer send the product back for a repair, while they just might if power dropped 25% instantly.
 
The 4 banks have 6 diodes in series. Each bank has it's own driver (I don't actually KNOW this but I'm very sure it's true).
 
series-parallel averages out the pros and cons of series and parallel. If all were paralleled, you'd need a bunch of current (think 24 times the current of a single diode).
If all were in series, you'd need a very high voltage (24 times Vf).

Series-parallel means you can have a lower voltage and lower current. On top of that, if one device fails, the worst it would do is knock out the other devices that are in series with it. If you had a single driver that just pumped otu current without caring where it goes, your other series strings would end up sharing the extra current.

Are you planning something big?
 
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