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Soft-Start Driver

Autist

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Hi All,

Does anyone know of, or has anyone made / make a soft-start driver ?

As most of us overdrive our diodes, I'm sure that they would last longer and be more reliable, if, when they were switched on, they would be ramped up to full power in 3 or 4 seconds, instead of max power instantly.

(Whenever I use the search facility, I click on a result link and it leads back to the LPF home page. Is it me ?)

Regards

David
 

HIMNL9

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There are some drivers that can be considered soft-start, but not actually in very small sizes for lasers (except maybe flexdrive, if modified)

Anyway, there is always a way for simulate an "almost soft start" from common drivers ..... place a 47uF 10V capacitor in parallel to the diode ..... it don't make a real soft-start, but anyway protect the LD taking care about the possibles high peak of the usual on-off operations, and also making the rise of the power slow down of some fractions of second, also half second with some settings (and for a LD that is planned for be used normally in drivers that turn on and off it in MHz range, this can be considered slow ;))
 

Autist

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Hi HIMNL9,

What a quick reply.

I had thought of using a capacitor, but I was not sure whether to use electrolytic or normal, and what material capacitor, as there are so many types.

Thanks for the input and advice.

Best wishes

David
 

HIMNL9

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Well, if you can get tantalium capacitors, they are better than the others, also if for constructive reasons, is always better to choose, for tantalium ones, a working voltage that is at least the double of the one you need (like, if you're planning to use it in a circuit that can go til 12V, choose a 25V one, not a 16V one, and so on) ..... normal electrolitics works good too, but they are usually more big than tantalium ones ..... and for the very quick spikes, a 100nF ceramic one in parallel to the electrolitic one, take care also of them ;)

Basically, is all matter of how much space you have available.
 

billg519

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The tantalum cap is a good idea, follow the recommendation of 2x the expected voltage. Tantalum caps like to explode if they see an overvoltage situation. They go off like a small firecracker (ladyfinger). I use 47uf tantalums in many of my lasers. Like HIMNL9 said, it's a matter of space in your build. Where space is a problem, I have used SMT caps, these can be quite small.
 

Cyparagon

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I'm sure that they would last longer and be more reliable, if, when they were switched on, they would be ramped up to full power in 3 or 4 seconds, instead of max power instantly.
The laser in a DVD burner is turned on and off MILLIONS of times a second under normal operation. I think our meager 20 times a day isn't going to hurt it. If you want long life, run it at it's rated power or lower.
 

Hemlock_Mike

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Those diodes in intended service turn and off in the MHz range but at much less power than we push them. A 47 mfd cap can't hurt so long as its low inrush impedance doesn't cause the driver to poop all over.

HMike
 

Autist

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Thanks for the replies.
I am looking to run a 1 watt 9mm IR at around 1,000 mA utilising a FlexDrive V.5.
DrLava recommends a schottky diode in series as the voltage of the diode may be lower than the FlexDrive goes.
I do not have the specs of the diode.

Thanks again for the info.

David
 
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Protecting from peaks is a good idea, but slowing down the start isn't going to help. As others said, laser diodes are used for optical storage because of that, they can turn on and off without getting damaged as fast as you want (no petaherz I guess, but you got it, right?)
 




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