Pulsed Laser Driver

FrostyTheDadMan said:

You are on the correct track but a Lm555 is not fast enough I have found that the LM555 max stable pulse wave is around 1Mhz to 1.25Mhz which is about 100ns depending on the manufacture some only pulse at a rate of 500Khz
and the DVD burning diodes need a PW of 10ns which = 25Mhz to achieve the max pulse power and maintain the life of the Diode.

DSCF5935.jpg picture by FrostyTheDadMan - Photobucket

I have what you are talking about and LaserBee is correct its in testing
I have averaged using a PHR803t running at 150Khz @ 209 mA and have had 244 mA and that's a PHR
Here is a pic of a phr803t running at 209 mA for 58 minutes with out fail but my battery pack lost charge after the 58 minutes past we will be doing a longevity test to see how long the Diode will last.
Its called The Mighty Micro Drive.
DSCF6066.jpg picture by FrostyTheDadMan - Photobucket
When Testing is complete you will be able to get your MMD at LSP Paten Pending #61000221
Read all about it at LE Forum Under The Mighty Micro Drive

Click to expand...

I know the datasheet says the diode needs 30ns for pulsed behaviour, but do we really need the 30ns? Can't we use a 1 micro second or less? Maybe I'm plain wrong, can it be that they don't lase if a higher than 30ns pulse is driven into the LD?

Hey Niko... in theory...
If you take a 100 Watt Light Bulb and want to apply 500volts to it...
It can be done... but not at a 100% duty cycle..
You would need to decrease your "ON" pulse to a shorter time... and the "OFF"
pulse to a longer time...
That is duty cycle.... the higher the input voltage to the 100 watt bulb the shorter
the duty cycle or "ON" period...
to prevent burnig out the 100 Watt light bulb...


Jerry

lasersbee said:

Hey Niko... in theory...
If you take a 100 Watt Light Bulb and want to apply 500volts to it...
It can be done... but not at a 100% duty cycle..
You would need to decrease your "ON" pulse to a shorter time... and the "OFF"
pulse to a longer time...
That is duty cycle.... the higher the input voltage to the 100 watt bulb the shorter
the duty cycle or "ON" period...
to prevent burnig out the 100 Watt light bulb...


Jerry

Click to expand...

I know that, have you read the last posts? (Sorry if this sounds aggressive, I'm not trying to be aggressive).
What I'd like to achieve would be getting more beam visibility (with more pulsed power), the "off" periods will be determined by the pulsing frequency. The duty cycle would be the same or a little bit longer than the one drived on CW because the diode would lase for the same amount of time or less than a CW drived. However I could be wrong and those peaks of power could heat the diode faster than on CW.


Also, I could get a 100W bulb and drive it at 300V ; 0,33 A which would equal 100W... but this is not the case

EDIT: I just re-read what you said. Do you mean we would need to create a circuit that will drive the LD for, say (big values just for the example): 1 second on, 10 seconds off?
It is possible...and at a high frequency it shouldn't be noticeable either.

I'm still not buying the better beam visibility due to pulsed driving (with higher peak power, but lower average power). Things that can happen on the time frame of one pulse, such as burning bits on a disc, or your TV sensing the IR signal from a remote I suppose, can benefit from the higher peak power, but the human eye is going to pick up the average power unless the pulses are slow enough for you to register them as pulses (dozens of Hz), and that defeats the purpose, not to mention as far as the laser is concerned, such a slow pulse rate would be pretty much CW operation.

maxh said:

I'm still not buying the better beam visibility due to pulsed driving (with higher peak power, but lower average power). Things that can happen on the time frame of one pulse, such as burning bits on a disc, or your TV sensing the IR signal from a remote I suppose, can benefit from the higher peak power, but the human eye is going to pick up the average power unless the pulses are slow enough for you to register them as pulses (dozens of Hz), and that defeats the purpose, not to mention as far as the laser is concerned, such a slow pulse rate would be pretty much CW operation.

Click to expand...

Okay, but let's suppose we could have a slow pulse rate (not CW). We could get at least a couple of mW's more from an LD.

Regarding what you said about the human eye, I think they would register short repeated pulses. See, lots and LOTS of lightbulbs and fluorescent lamps are pulsed and you don't even know it because we just can't see the pulse rate. I know it could also mean that they're driving a 100W lamp to 110W (or less) but you know where I'm going...


EDIT: I don't know about the dragonlasers 473nm pulsed laser but I don't know if the "dots" are visible to the human eye... are they?

They should be if you scanned the Laser's beam across a wall...
You should see dots or dashes of laser light..

BTW... you were not coming off aggressive..... :gun:
:crackup::crackup:

Jerry

nikokapo said:

Okay, but let's suppose we could have a slow pulse rate (not CW). We could get at least a couple of mW's more from an LD.

Regarding what you said about the human eye, I think they would register short repeated pulses. See, lots and LOTS of lightbulbs and fluorescent lamps are pulsed and you don't even know it because we just can't see the pulse rate. I know it could also mean that they're driving a 100W lamp to 110W (or less) but you know where I'm going...


EDIT: I don't know about the dragonlasers 473nm pulsed laser but I don't know if the "dots" are visible to the human eye... are they?

Click to expand...

You will be shorting Life of the diode for more on time and that is what people do with the cw driver
The MMD will preserve the life of the diode and still allow you to run it at its max power

lasersbee said:

They should be if you scanned the Laser's beam across a wall...
You should see dosts or dashes of laser light..

BTW... you were not coming off aggressive..... :gun:
:crackup::crackup:

Jerry

Click to expand...

if you slow it down to much, up around 150Khz that's to fast for the human eye to catch and the electronic components wont be over worked
The hard part is finding a happy medium between power (mA ) and the pulse rate and limits of the semiconductors
If the data sheet says 30ns then 10ns would be just fine in fact 10ns is what I have seen most.

maxh said:

I'm still not buying the better beam visibility due to pulsed driving (with higher peak power, but lower average power). Things that can happen on the time frame of one pulse, such as burning bits on a disc, or your TV sensing the IR signal from a remote I suppose, can benefit from the higher peak power, but the human eye is going to pick up the average power unless the pulses are slow enough for you to register them as pulses (dozens of Hz), and that defeats the purpose, not to mention as far as the laser is concerned, such a slow pulse rate would be pretty much CW operation.

Click to expand...

Man you and Dugin must be brothers because that what he said
Laser power is ether their or its not and when pulsed at 25 Mhz that means it turns on and off 25 million times a second.
you will never know its off and the more intense pulses will be the focus of attention.

That would be nice if a handheld could effectively act like a laser show projector.

FrostyTheDadMan said:

you will never know its off and the more intense pulses will be the focus of attention.

Click to expand...

THIS ^ is what I'm trying to explain here, thanks man! That is exactly what I mean when I talk about improving beam visibility.

Ive got some diodes from chris and he recommends pulsing them...so thats what i will do, i like the mosfet layout over the 555 so ill c what results i get.
I think the beam would look a liitle brighter pulsed, but you would compromise life because at 25 Mhz it would be just like running the diode with a little more current at CW!

If the average power isn't higher than the power at CW it wont be any brighter.
Lets say you have one 100mW cw diode and one 200mW pulsed diode (insert x kHz here), duty cycle 50%. Both will be the same brightness. Remember LEDs use dimmers based on this. The eye don't see just the on time, it sees both the on- and off time. But it happens so fast that we see an average output. If you try to slow down till you can see the pulses brighter, it will be flickering and be VERY annoying aka a puke-light. But also that's way to slow for pulsed operation anyway.

Well, i made a test, right now ..... built on-the-fly a pwm driver, and took my labby heatsink, and 2 PHR from 2 sleds (same lot, so probably they are identical)

Putting both them in aixiz modules and driving the first one with 100 mA through the LM317 driver, hooked the second one to the PWM driver and an oscilloscope, and made some measures.

The PWM driver is powered at 12V, with the resistor in series to the LD at 27 ohm, that, considering 5V of FV of the LD, do 260mA of current (used a mosfet for the switch).

at 500 Hz, with 0,75mS on/1,25mS off, i get the same spots appearence (can't see the beam, no smoke here ) ..... then tried at 166 Hz, 33% duty cycle (2ms on/4ms off) and got the same spot appearence again (this mean, theorically, there's a little increase in visibility, cause i was with duty cycle 1 on 3, when for the same power, i have to go with duty cycle 1 on 2,6, with 100mA on the fixed one and 260mA on the pulsed one)

Anyway, the result is really subjective, and can change from person to person, and unfortunately i have no time for continue the tests at the moment, sorry (had to open the shop)

Maybe with some group of tests, made with different persons with the same circuit and diodes, we can have a better idea about how it work, and if someone notice it better than others, for different individual sensitivity (also to be considered that i made the tests only with PHR, maybe with red ones the results can give some diferent data)

If someone want to do that, i can draw a better circuit that anyone can duplicate, so all can use also the same circuits (as example, fixed values for frequencies, for have a sorta of "grid of values" that can be reproduced also from those that don't have instruments at home, and so on).

I was also thinking about it, and came up with smth like this:

http://obrazki.elektroda.net/15_1225723672.jpg

In theory it should work, and it's quite good idea.

Uhm, i suggest you to be careful with that schematic.

In that configuration, for turn off the LD, you put in short circuit the LM317, and also if is true that in the current regulation configuration it's almost self-protected, i'm not too much sure about the lifetime of a similar schematic in long periods