NE555 PWM Buck Driver

Hi, I meant to do this type of driver for my new projects.It is very simple and very efficient.With this driver you can regulate output power from 5-95%.So you can adjust power output for laser diode which she need.Just worries me what will happen if the batteries are for example discharged to half, and here is no feedback circuit to regulate the PWM(ofc. you can manually do this with potentiometer P1,but it is not practical).What do you think if this is a smart solution for using as laser driver.

That's not a buck driver. It just pulses the LEDs, and it doesn't even have feedback or constant current operation. It isn't even constant voltage, since the pulse width will vary with the input voltage. It's about the same as using a pot as a driver.

^^A very fancy pot none the less.

ok dude you are almost there. instead of driving the diode with this circuit, use the mosfet to switch current to the negative of a DRIVER. then hook the driver to your diode. the problem you have is the PWM is not regulating current. hence the need for a driver. make sure you pick your capacitor such that the frequency isn't too high. 100hz is good. if your pot is adjustable you will have a nice dimmable laser.

Using PWM does have the benefit of linearizing the brightness of the output instead of relying on just regulating current--though it can add flicker. Then again, a lot of the diode's output power is linear with respect to current.

Look if you can dim led why not to dim laser diode.I never care about current regulation,I only care about maximal diode current.Good cooler resolve thermal runway so I dont need constant current driver.My problem is that I use 3x1.5v batteries (4.5V) to drive blue laser diode @ 4.8v.So I cant use buck or boost converter because such a small difference in voltage.Linear driver have big voltage drop for this use.
I think use this "driver" because she can regulate output power without significant voltage drop(Rds on mosfet is low).I use this driver to regulate DC motors so why not laser diode.Ofc. I put capacitor on output so there is no flicker.

EXO said:

I never care about current regulation

Click to expand...

Lasers don't take abuse like LEDs do. You have a lesson to learn here. If you want to learn it the expensive way, so be it.

EXO said:

Hi, I meant to do this type of driver for my new projects.It is very simple and very efficient.With this driver you can regulate output power from 5-95%.So you can adjust power output for laser diode which she need.Just worries me what will happen if the batteries are for example discharged to half, and here is no feedback circuit to regulate the PWM(ofc. you can manually do this with potentiometer P1,but it is not practical).What do you think if this is a smart solution for using as laser driver.

Click to expand...

If you use the Current limiting Resistors as are used on the
LEDs to limit the maximum current to the LD depending on
your MAX supply voltage to the 555 circuit there should be
no problem to use that circuit for brightness control.


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Lasers don't take abuse like LEDs do. You have a lesson to learn here. If you want to learn it the expensive way, so be it.

Click to expand...

In previous laser projects, I never used the constant current driver.I always(ultra) use constant voltage control (i.e. LM1117,MC34063).Because if is laser diode rated for example 3V @ 100mA,they will not pull more current if you apply 3V.Ofc. they will pull more current if heatsink is bad(thermal runway) or you apply more voltage.So I regulate current with voltage.I have not a single diode destroyed in this way.
But in this project problem is very little difference in voltage.

EXO said:

In previous laser projects, I never used the constant current driver.I always(ultra) use constant voltage control (i.e. LM1117,MC34063).Because if is laser diode rated for example 3V @ 100mA,they will not pull more current if you apply 3V.Ofc. they will pull more current if heatsink is bad(thermal runway) or you apply more voltage.So I regulate current with voltage.I have not a single diode destroyed in this way.
But in this project problem is very little difference in voltage.

Click to expand...

Because ratings are always accurate?

A) We don't have clear spec sheets for most of the 445s out there, because we're generally not buying them as virgin diodes.

B) Even if we did, they vary from diode to diode. Some 445s have substantially higher Vf ratings (+/- as much as 0.5V in some of the tests I've seen) than others.

C) When your Voltage curve is relatively flat, a very small variance in voltage can produce a relatively larger variance in current.

D) It's questionable to use Voltage regulation with a pot. But it's downright nuts to use Voltage regulation with fixed resistors. With a pot, at least you're adjusting the voltage, while (hopefully) monitoring current, and then leaving it set at a setting that produces an appropriate mA figure. With fixed resistors, you're just praying that the IV curve of your particular diode matches what you're planning for based on a datasheet, and that your voltage, set with fixed resistors, corresponds to an appropriate current on your specific diode's curve.

EXO said:

In previous laser projects, I never used the constant current driver.I always(ultra) use constant voltage control (i.e. LM1117,MC34063).Because if is laser diode rated for example 3V @ 100mA,they will not pull more current if you apply 3V.Ofc. they will pull more current if heatsink is bad(thermal runway) or you apply more voltage.So I regulate current with voltage.I have not a single diode destroyed in this way.
But in this project problem is very little difference in voltage.

Click to expand...

So let me get this straight: you're going to rely on the non-linear, temperature-dependent I-V curves of a diode and regulate the voltage with millivolt or even microvolt precision to regulate the current (the important parameter affecting output power), and all this without active temperature control, or feedback for that matter (assuming it even converges)?

Well good luck with that dude.

This all reminds me of Jeff Goldblum explaining chaos theory in Jurassic Park.

Yes.I dont know what is so heavy.Simply use lm1117 linear regulator and connect it in voltage regulation.Turn trimmer on lowest output voltage and connect laser diode(in heatsink).Then simply increase voltage and in same time monitor current.When I reach desired current for laser diode I stop increase voltage.And that's it.

But temperature will change as current flows through the diode, which also affects its Vf/A "ratings". Seriously, electrical conduction through the junction of a diode is much more complicated than by regulating some voltage. Small LEDs and LDs don't deal with this sort of thing as much since they do not generate very much heat.

This diode you're trying to run is sinking over 1000mA across a junction with a 4.5V voltage drop. You CANNOT regulate the dissipation of 5W of heat without some kind of active cooling mechanism in such a small space.

You come here and ask us if this is a smart solution to driving a laser diode, and we tell you the truth - now all you want to do is fight the truth instead of accepting what you asked for. You can either admit that the circuit is not adequate, and you could let us help you make a better one, or you can ignore the entire forum of hobbiests that do this stuff all the time, and then come back asking us for help when your device stops working the way you wanted it to.

Either take what we have to offer you, or run without it. Your argument has no weight on this one.

Well... some people have to stare into the sun to learn that they can become blind...

EXO said:

In previous laser projects, I never used the constant current driver.I always(ultra) use constant voltage control (i.e. LM1117,MC34063).Because if is laser diode rated for example 3V @ 100mA,they will not pull more current if you apply 3V.Ofc. they will pull more current if heatsink is bad(thermal runway) or you apply more voltage.So I regulate current with voltage.I have not a single diode destroyed in this way.
But in this project problem is very little difference in voltage.

Click to expand...

It seems you don't really grasp the reasons why a Current Regulated
Driver is preferred to a Volage Regulated driver that you seem to beleive
is a better choice.

I'll try to explain the problems with a Voltage regulated driver in basic
terms.
Lets say that......

1) you have a regulated Voltage driver outputting 4 Volts to a Laser
Diode and it runs fine when first turned "on".

2) as the LD warms up the internal resistance decreases and at 4 volts
now draws more current reducing the Voltage that the Regulator sees.

3) to compensate the Voltage regulator increases its voltage to maintain
the original 4Volts to the increased LD load (decreased internal resistance)
due to internal heating.

4) this now increases the internal heat of the LD even more... and you
are now in a loop to item 2)

This continues until there is a catastrophic failure or power is turned off
to cool the LD and return it to its original cold internal resistance.

I've been on the Forum for 4 years and have heard all the reasons why
Voltage regulators work best.

Simple Answer............

A Laser Diode is a sensitive Current Device and needs/requires a Current
Regulated Driver.


Jerry

You can contact us at any time on our Website: J.BAUER Electronics

Meatball said:

But temperature will change as current flows through the diode, which also affects its Vf/A "ratings". Seriously, electrical conduction through the junction of a diode is much more complicated than by regulating some voltage. Small LEDs and LDs don't deal with this sort of thing as much since they do not generate very much heat.

This diode you're trying to run is sinking over 1000mA across a junction with a 4.5V voltage drop. You CANNOT regulate the dissipation of 5W of heat without some kind of active cooling mechanism in such a small space.

You come here and ask us if this is a smart solution to driving a laser diode, and we tell you the truth - now all you want to do is fight the truth instead of accepting what you asked for. You can either admit that the circuit is not adequate, and you could let us help you make a better one, or you can ignore the entire forum of hobbiests that do this stuff all the time, and then come back asking us for help when your device stops working the way you wanted it to.

Either take what we have to offer you, or run without it. Your argument has no weight on this one.

Click to expand...

My diode have 300mW not 5W.I talk about my experience with constant voltage regulators.I have tested constant current drivers and have and I have not noticed any difference between.I prefer constant voltage because it is simple to make and is more efficiency(no sensing resistors).
And if is so bad constant voltage because any of my laser pointer dont die?I have many of them an no one die from over heating or thermal runway.