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Old 09-20-2007, 03:56 PM #17
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Any news on the circuit?

Is pulsed actually better than CW? Or for all intents and purposes is CW easier to throw together in a MagLite?


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Old 09-20-2007, 05:38 PM #18
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I doubt pulsed operation would be of any benefit to us, really. For burning holes or lighting matches, it is the average output that matters. In CW operation this is equal to power, but in pulsed operation it has to be multiplied by the duty cycle.

The datasheet doesnt have much on that, but assuming you'd drive it at 250 mW with 50% duty cycle, its burining power and visibility would be equal to 125 mW CW.

Designing a current source with good regulation that can be switched at 12.5 MHz (40 ns pulses 50%) is not an easy feat either. These frequencies are way beyond what any LM317 or similar can handle, and even pose problems for modern opamps and power transistors (unless you pick them for these specs, resulting in rare and expensive components).
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Old 09-20-2007, 11:42 PM #19
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I made one :P

Obviously it uses 3 chips... but it still works

I'm not going to go into detail because I don't want to confuse anyone anymore that I already did... but I'm using a comparator with an RC circuit to power a MOSFET that passes the current through a regulator. All together it works nicely and outputs a very nice curve, but I can't justify putting it up online because of how much confusion it'd create.

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Old 09-20-2007, 11:57 PM #20
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

But does it actually allow greater average power than you can get from a constant current source?

I could probably mod my current driver to do it using a high slew-rate opamp and faster transistor, but it seems like a lot of designing - only worth it if there is real gain in this.
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Old 09-21-2007, 05:30 AM #21
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Exactly... the one I made is graphed right here though

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Old 09-21-2007, 05:32 AM #22
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Just for the record... that's going at 1MHz or so... :

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Old 09-21-2007, 01:11 PM #23
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

nice work but yes if your useing a 1-1 ratio 1mhz square or dirty square wave you will get 250mw pulses BUT 125 over time ( half on half off) but i think that 125mw avarage pulsed will have a better duty cycle and lifetime than a overdriven 125mw CW
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Old 09-21-2007, 01:55 PM #24
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Lol DDL, you are a clever chap ;D ;D

Jase
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Old 09-21-2007, 02:19 PM #25
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

alright, so I put some thinking into this, and although I am relaively new to ics and stuff, here is what I came up with (as an idea):

I think someone once said "40ns on/off". So that means, pulse length 80ns = 12,5 MHz. Now I take a 12MHz oscillator, hook it up to a fast-acting transistor and voilą, I have my pulsed source. For current control, I would use the DDL-circuit. Don't know if that will work, though.

alternatively, if that signal is not squary enough, I might also use a 25MHz oscillator and hook it up to a t-flipflop, and then send that to the diode/transistor.
Cost: around 3$.

Maybe use a thyristor instead of the transistor.

Could that work? Will the LM317 react badly to the 12MHz pulsing?

Also, is faster = better? Like 20ns switching?
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Old 09-21-2007, 03:15 PM #26
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Quote:
Originally Posted by philguy
alright, so I put some thinking into this, and although I am relaively new to ics and stuff, here is what I came up with (as an idea):

I think someone once said "40ns on/off". So that means, pulse length 80ns = 12,5 MHz. Now I take a 12MHz oscillator, hook it up to a fast-acting transistor and voilą, I have my pulsed source. For current control, I would use the DDL-circuit. Don't know if that will work, though.

alternatively, if that signal is not squary enough, I might also use a 25MHz oscillator and hook it up to a t-flipflop, and then send that to the diode/transistor.
Cost: around 3$.

Maybe use a thyristor instead of the transistor.

Could that work? Will the LM317 react badly to the 12MHz pulsing?

Also, is faster = better? Like 20ns switching?
I was kind of going down the same line as you Philguy but you need to take into consideration. Will the t-flipflop be able to respond at the 12.5MHz range? its quite fast.
What i was thinking about is just using something like a 555 timer and turning it into a PWM and have that follow your driver. Mind you im pretty novie at the whole electronics game and still need alota spaces filled, Actually 555 might be a bad idea... maybe a PWM using an op amp ? anyone wanna give that a try and see how it goes on a cro ... oh hang on that wont work either :/ no ideas from me then :-X


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Old 09-21-2007, 03:38 PM #27
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

A LM317 will react very badly to being switched like that, and cannot be operated stably at all... I doubt a 555 would make it to 12.5 MHz, but your average CMOS (inverting) gates will, even when operated as a crystal or LC oscillator. No problem there.

It's conceivablet to switch the reference in an opamp based circuit this fast, but i doub't it would still give decent current regulation this fast. Perhaps a more blunt 2-diodes-and-a-transistor current sink would be the better option. With fast components that should be able to keep up easily.

The advantage is in the steep power-vs-current curve of these diodes, which could be something like 80 mW @ 130 mA, but 250 @ 260 mA. Running it a 50% cycled 260 mA would produce the same heat in the diode, but would yield 125 mW of average light output. All of that is only usefull if the failure mode of the diode is thermal though, it won't protect against optical failure.
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Old 09-21-2007, 08:07 PM #28
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I had also considered a 555 before, but as far as I saw, no chance.

I found JK-Flipflops (short JK to get T) up to 30 MHz (at acceptable prices), so that should be no problem.


But that would mean I need to either use a resistor as voltage control, or hook the LM317 before the switching circuit... well, gotta try that.
A wise choice in transistor might also help with the current-limiting issue.
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Old 09-21-2007, 11:40 PM #29
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

I guess you could use a regulated known voltage and appropriate series resistor, and then switch between voltage source and LD.

Also, I wonder if it is at all required to use frequencies in the MHz range. The datasheet states figures at 40 ns, but perhaps that's just a practical time for a dvd writer, not so much related to the performace of the LD itself?
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Old 09-22-2007, 12:09 AM #30
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Wow, I just sit back, look at this and go
HUH?!?!?!?
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Old 09-22-2007, 12:27 AM #31
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

HEY!! KENOM
Why do you get to be a (YaBB)Ya Ba Da, Ba Do, Moderator already ;D ;D ;D

I want to be a moderator too, so I can edit negative LC members or exmem. posts!

Nobody gets hurt here on LASER P. Forum!!!!! " No FLASHING allowed >"

No potty mouth allowed either!

I don't get it. How did U get yaBB moderator status ???

MOST IMPORTANT: The right timing/modulation is everything when it comes down to a clean blast(ablastation)!! 8-) 8-) 8-)

Hey: let's start a LASER scull & bones cult just like......

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Old 09-22-2007, 02:00 AM #32
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Default Re: Pulsed Mode Driver circuit for SONY DVD 16x La

Quote:
Originally Posted by Benm
Also, I wonder if it is at all required to use frequencies in the MHz range. The datasheet states figures at 40 ns, but perhaps that's just a practical time for a dvd writer, not so much related to the performace of the LD itself?
Benm, as you stated, it probably has a lot to do with the pulse width required to write at 16x on a DVD. However, the rest period of the duty cycle has some will allow for cooling of the die and we don't know the longest pulse width at 250mW before the diode suffers serious damage. And, of course, Sony does not seem very forthcoming with a "substantial" data sheet or testing information on these.
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