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DDL schematic mod

MLZ

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I haven't been using my Bluray laser sinds the diode blew up again at 100mA... (those suckers are expensive).

What do you guys think of my circuit? And why do you think it blew again?
I think it's safer to place the diode this way then parallel with the capacitor.
And I've placed a risistor parallel with the capacitor to drain it as quick as possible.
(I haven't built in the main switch.)

 

Cyparagon

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Several things I see that might be a problem.

1. 100 ohm is rather large (unless it's a 15-turn) and you won't see any change in output until the edge.

2. Better to put the 1N4001 parallel to the laser diode (but facing the other way) so it doesn't drop any voltage under normal operation.

3. The blue indicator should be in parallel with the main laser circuit. Otherwise, the regulator is trying to pull all of its supply current through the indicator. Indicators need low current, lasers need high current.

It would work as is as long as the indicator is capable of eating 100mA. ~3V for the regulator, ~3.2V for the indicator, ~5.5V for the laser diode, and 0.7V for the rectifier just means it probably won't operate at the full 100mA. The indicator is the biggest problem.
 
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Yes exactly what he said !!!

Other wise you might get away with the indacator
in that possition in the ckt if you were to use a PHAT led
which can handel AMPS of current.
 
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MLZ

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1. You're right. The potmeter starts letting more amps through at the end of the turns.
2. I'll rebuild the circuit with the diode in DDL's original designed spot.
3. And the LM317T gets pretty hot with 12V passing through it.
4. I want to buy one of Mohrenberg's beautifully crafted hosts with heatsink and do it the right way.
Luckily I have one PHR-308-T diode left.
 

MLZ

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I've ordered a Mohrenberg Guidesman kit the other day and I'm going to rebuild my driver so the IC makes contact with the host, with a little heat guiding paste between it.
Can't wait to get crackin'!
 

Cyparagon

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Only 6mA will leak across the resistor. That is a very small portion of the power dissipated by the driver.
 

Benm

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I've ordered a Mohrenberg Guidesman kit the other day and I'm going to rebuild my driver so the IC makes contact with the host, with a little heat guiding paste between it.
Can't wait to get crackin'!
Make sure it does not make -electrical- contact with the host though!

I assume the host is connected to battery ground, and the metal tab on the lm317 is connected to its output pin, so that'll short things out. The proper way to mount it is using a mica pad and plastic screw with some thermal paste on both sides. Alternatively you can use a sort of rubbery pads that don't need paste.
 

MLZ

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The last time I ordered a PHR-803-T it costed me around 25 euro's (sending included).

So the capacitor did fry the diode... now I know why.
Is my 47uF diode big enough for the job?
With this info my next build can't go wrong. *knock on wood*

The ground of my current build is attached directly to the batteries because it was built into a plastic casing.
I thought that the metal tab's only purpose was for heatsinking.
 

Benm

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The purpose of the tab IS heatsinking, but it is electrically connected to the middle pin in this type of chip casing.

I have no idea what fried your diode. The capacitor is fine as it is, just make sure that the connections between the capacitor and laser diode are solid. The only way this type of driver blows up diodes is when the driver is powerd with the diode disconnected, and then connecting the diode. This would obviously happen if the wiring was dodgy, giving an intermittant connection. Make sure your solderwork is good on that connection!
 




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