Making a driver - help is needed

lasersbee said:

Hey Eudaimonium,

There is no need to be a Smart A$$ answering question to a well
known member that has been on the Forum for a while...:tsk:

Just because you read Data Sheets does not mean that all other
members do or can...
A little respect goes a long way in our community.... IMO

@ SeNNHeISeR.... Soldeing connections is always the way to go
with Laser Diode circuits... especially the very sensitive Blu-Ray types..
As was posted above (1.25V /22 Ohms) will give you aporox. 59mA
of current from your driver... Be sure to test your driver with a Dummy
Test Load..


Jerry

Click to expand...

Hey sorry, I was just trying to make a joke here,
Well known member who has been around for a while is asking why is it 1.25 V ref, not 1.35.
I just could not resist to be a smart a$$ :crackup:

It is like asking, "why a bluray diode, not the IR one? "

No offence, Flaminpyro!

I am not actually reading the datasheets as you may guess, I just knew that it was explicitly 1.25 V, so I looked up if the same info is in the datasheet to prove my point, since my word against a veteran in not that good standing.

Sorry Flamin, again! Nothing personal!


@SeNNHeISeR: Why two resistors in series? Only one is needed, totalling 11 ohms, not 22.

You will underpower your laser diode greatly.

Flaminpyro said:

OK I'll restate my question, I know what the forumila dose, what I want to know is why is 1.25 volts used, why not 1.35672 volts ?

Click to expand...

Because, using an LM317, is the voltage that you have as reference voltage ..... but i think i have understood what you mean, and this explanation can confuse, so, let me try to state it in a more clear way (and forgive me for the bad English )

The LM317 serie, is a voltage regulator, where the output voltage is stabilized and regulated from a voltage controlled loopback ..... the reference voltage generated inside the chip, is 1,25V, and the IC act in this way (in voltage mode): you set the output voltage with a resistor network that take part of the output and give it back to the ADJ pin, that is connected to the comparator ..... when at the ADJ pin there's 1,25V, the output voltage is kept stable ..... if the output voltage increase, the VADJ (through the resistor network) increase, so the chip decrease the output voltage until the VADJ is 1,25V again, and ofcourse, the opposite when the output voltage decrease (hope it's clear til this point )

Now, we use this regulator as CURRENT stabilizer, that is not its main use (but it still work), but the regulation is still made with a VOLTAGE loopback system ..... this means that, connected in the current regulation mode, the chip increase and decrease the output voltage for keep the difference of voltage between the output and ADJ pin at 1,25V, and this voltage is the difference of voltage at the sides of the resistor, that is produced from the current circulating through the resistor itself (and, cause it's a serie circuit, also through the load, in this case our LDs)

So, for calculate the current that you want to get from the LM317, you must use the 1,25V value, that is the reference voltage, because you need to keep this voltage (and no others) at the sides of the resistor ..... as example, for 100mA, you need to use 1,25/0,1 (V/R) = 12,5 ohm resistor, cause this resistance value is the one that keep 1,25V at the sides of the resistor, when a current of 100mA flow through it ..... if you use a different value, like as example the one that you said (1.35672), you get for 100mA a value of 13,56 ohm ..... but this value don't give you 100mA, cause the reference voltage IS 1,25V, and with 13,56 ohm, this give you 92mA only .....

Hope this is clear enough (if not, please don't shoot me, ok ? )



EDIT: LOL, i know i type slowly, but not imagined that i took enough time for start a war (just kidding, Eudaimonium and Jerry, no offenses )

HIMNL9 said:

EDIT: LOL, i know i type slowly, but not imagined that i took enough time for start a war (just kidding, Eudaimonium and Jerry, no offenses )

Click to expand...

War? Where?

We are just having a ... friendly disagreement

I was not actually trying to be a smartass, just joking around.
If ANYBODY took offence, I humbly apologise :yabbem:

so guys i am little confused now.i wired everything correctly.Then i soldered it all up and decided to check the readings.i was reading 9.60V out and 63.7A directly.i am using a nine volt battery wich measured 10.37V so whats happening?is that ok? and waht si the problem ?

SeNNHeISeR said:

so guys i am little confused now.i wired everything correctly.Then i soldered it all up and decided to check the readings.i was reading 9.60V out and 63.7A directly.i am using a nine volt battery wich measured 10.37V so whats happening?is that ok? and waht si the problem ?

Click to expand...

You arent using a test load are you?

9.6V @63.7A will turn a diode into a puff of smoke. are you sure you had the right range selected for testing amps maybe it should be mA...

umm sorry i meant mA. now i removed one of the 11ohm resistors and now i got readings 126.8 mA and 9.28v i could add an 1ohm resistor wich i have next to me.Should i add it?

Probably yes, total of 11 ohms will be very nice for a PHR diode.

Although personally I use 12 ohms for 100mA flat.
11 or 12 ohms will do nicely.

I think your voltage is a little high. IIRC it needs to be around 5V for the PHR. (someone correct me if im wrong)

KiLLrB said:

I think your voltage is a little high. IIRC it needs to be around 5V for the PHR. (someone correct me if im wrong)

Click to expand...

He is probably measuring open circuit.

Never mind that actually, when you connect PHR, the LM317 will give exactly as much needed for PHR, no more no less.
What matters is that you set the current right, because that is not auto-sensed like voltage.

Eudaimonium said:

He is probably measuring open circuit.

Never mind that actually, when you connect PHR, the LM317 will give exactly as much needed for PHR, no more no less.
What matters is that you set the current right, because that is not auto-sensed like voltage.

Click to expand...

Gotcha...

@OP You really need to invest in a test load when you can it is a HUGE asset in situations like this.

Eudaimonium said:

Probably yes, total of 11 ohms will be very nice for a PHR diode.

Although personally I use 12 ohms for 100mA flat.
11 or 12 ohms will do nicely.

Click to expand...

yeah im gonna add it for safety.I dont wanna burn a diode because of one 1ohm resistor.Also i think that the LM317T isnt doing its job.How do i lower the voltage without lowering the current?

SeNNHeISeR said:

yeah im gonna add it for safety.I dont wanna burn a diode because of one 1ohm resistor.Also i think that the LM317T isnt doing its job.How do i lower the voltage without lowering the current?

Click to expand...

Like Euda said the voltage will "regulate" itself. With the current being hard set the diode will take the voltage it needs.

Thank you all guys for the help, i soon will asume making a test load and when i get diode in a module from modwerx i am going to enjoy my first diy blu-ray laser.

KiLLrB said:

Like Euda said the voltage will "regulate" itself. With the current being hard set the diode will take the voltage it needs.

Click to expand...

Don't forget, if you feel like typing my nickname takes long time, just punch in 'JZ' or 'Z' or whatever you feel like. JZ as of my real name initials, get it? :wave:

SeNNHeISeR said:

Thank you all guys for the help, i soon will asume making a test load and when i get diode in a module from modwerx i am going to enjoy my first diy blu-ray laser.

Click to expand...

Don't worry about it, that is what this forum is for!

Also, it is more important to check and double check your output connections as they are most important.
Make apsolutely sure that there is no way a capacitor can disconnect in operation, as it will result in death of LD when cap is connected again (it will discharge over the LD, which is not good).

Make a nice shiny permanent solder connections, don't make a breadboard setup.

I wish you the best of luck in yoru laser build!

thanks JZ i already soldered the components on a veroboard but my sodlering skills suck because im still learning.about the cap i soldered it very good. if you think that i'm gonna forget to discharge it before connecting the LD i won't

SeNNHeISeR said:

thanks JZ i already soldered the components on a veroboard but my sodlering skills suck because im still learning.about the cap i soldered it very good. if you think that i'm gonna forget to discharge it before connecting the LD i won't

Click to expand...

Your skill will come with time. Takes about a week to get nice shiny solder points.
I have a nice PDF tutorial on professional soldering, if you want I can mail it to you , it will get you started (with all the pics explanations and everything)

BTW, if you think you will forget to discharge the cap, you can solder a ~470 ohm resistor in parralel with the capacitor, it will not affect the current output at all, but it is enogh to discharge the capacitor every time.
This is called a 'cap bleeder'.