Yet another steve-o weird-azz idea

[steve-o]

Hey, You-all!
I need some input from you electronics gurus. I’ve been using these types of linear regulator circuits for LD drivers for quite a few years now (even built an argon supply w/ ‘em) all except the 0-5V control input. I found where somebody successfully did this type of input using a transistor in the ‘adj’ leg (possibly driven w/ an opamp; can’t remember the details.) Has anybody done or seen this? Also I’m going to hookup a high speed square-wave generator to the input to check for overshoot on the output. Also.. anybody done this?

I know a few responses may be “why don’t you just use a flexmod?” Well, I’m sure the flexmods are great (I haven’t tried them yet) I’m just used to the LM317/338 regulators, and I’ve had good luck with them . They have built –in overtemp protection , good noise/ 60 Hz rejection, and are very sturdy. Plus, I like to design and build everything in my lasers, that way if there’s a problem, I’ll be able to fix it straight-away
Thanks in advance for any and all input/ advice.




© steve-o Lasertec 2012

[dnar]

I don't see how the schematic you posted could work. You have a constant current source (2nd reg) being fed from a variable voltage regulator (1st reg).

Just use a Flexmod P3.

[steve-o]

It does work.. I've been using this configuration for years. -sigh- how much is a flexmod? The LM338s are a little over a buck a piece ..
The 1st reg feeds variable voltage to the 2nd reg until it hits the I limit then it won't overcurrent the LD ..
Ok- I'm putting a copyright on this circuit

[dnar]

It does work.. I've been using this configuration for years. -sigh- how much is a flexmod? The LM338s are a little over a buck a piece ..
The 1st reg feeds variable voltage to the 2nd reg until it hits the I limit then it won't overcurrent the LD ..
Ok- I'm putting a copyright on this circuit

Yeah, as I thought the 2nd regulator is on "drop-out" until you reach maximum current.

How linear is your modulation response? You sure you don't have a bump in the response towards the top end?

[steve-o]

Yeah, as I thought the 2nd regulator is on "drop-out" until you reach maximum current.

How linear is your modulation response? You sure you don't have a bump in the response towards the top end?

Well, it looks pretty smooth to the eye, but I can check and see .. Is the flexmod and similar circuitry linear or compensated for relative brightness such as a logarithmic slope is applied for audio circuitry?

[Fenechlaser]

Is the flexmod and similar circuitry linear or compensated for relative brightness such as a logarithmic slope is applied for audio circuitry?

Electronics experts correct me if I'm wrong. As far as I know many available drivers do not incorporate such a 'slope' i.e. they are linear. Btw if you have any old mobo's and old HDD/CD-R/RW drives you can salvage parts and build yourself a driver using op-amps and mosfets - all you need are the pots and shunts.... And patience to work with SMD + Lots of flux... Just google for current regulators using op-amps and do the rest...

I had a kit like this (and still do). As Dnar stated modulation might be a bit 'coarse', that's why good drivers don't use the 317 or 338...

[Fenechlaser]

Is the flexmod and similar circuitry linear or compensated for relative brightness such as a logarithmic slope is applied for audio circuitry?

Electronics experts correct me if I'm wrong. As far as I know many available drivers do not incorporate such a 'slope' i.e. they are linear. Some software allows for this in the sense that they can be adjusted to make the laser's output as linear as possible. There are also boards to achieve this function by conditioning the 5v analog signal to the laser.

Btw if you have any old mobo's and old HDD/CD-R/RW drives you can salvage parts and build yourself a driver using op-amps and mosfets - all you need are the pots and shunts.... And patience to work with SMD + Lots of flux... Just google for current regulators using op-amps and do the rest...

I had a driver kit using the lm350T (and still do). As Dnar stated modulation might be a bit 'coarse' due to rise times etc, that's why hi-end drivers don't use the 317, 350 or 338 which where designed with voltage stability not high frequency modulation in mind (but mind you, they do work )...

[steve-o]

I had a driver kit using the lm350T (and still do). As Dnar stated modulation might be a bit 'coarse' due to rise times etc, that's why hi-end drivers don't use the 317, 350 or 338 which where designed with voltage stability not high frequency modulation in mind (but mind you, they do work )...

The LM350 appears to be of the same design as the 317/338. Do you have a schematic of your "kit" Fenech?

[Fenechlaser]

I don't have it but the kit it is still currently being sold by cfavreau although now it is a complete RGB driver.

[steve-o]

Ok, thanks
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