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FrozenGate by Avery

5A linear current regulator?

That doesn't make sense.

The MOSFET will drop voltage, and throw of your current regulation formula.

Why not just use a traditional setup, but put a P-MOSFET before the reg?
 





Actually, the circuit does make sense. P mosfets have higher Rdson, higher gate capacitance and smaller choices compared to N fets. N fets are easier to drive too as the gate is ground referenced.

Though, I would connect the ADJ pin to the mosfet drain rather than ground and PWM the mosfet directly rather than use a RC filter. Use a totem pole driver since the arduino output will not have enough current capability to switch the fet fast enough.
 
Your way would work, but I haven't seen any mode diode, including C mount, of
course-Tried to turn my laser back in 2009, I only have partial data for
these diodes, are running the SSY-2 has its own trigger circuit into the
bank, NOW - I need to understand enough about the system So the
difference is in the tube.
 
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rhd said:
How does it make sense to put a second element that drops voltage in the feedback path?!?
Click to expand...

That was exactly why I put it there, to drop voltage.
I put the MOSFET there to act as a variable resistor, just like when you'd put a POT in there, to act as a current dial. (So NOT like a switch)

The MOSFET will thus be used in it's linear part of the characteristic.



The Lightning Stalker said:
Here is what I'm thinking about doing for one of my builds. Take one of these and wipe off the
transistor and resistor. Then in their place, solder in a TO220 or TO247 transistor that has
enough gain and a low resistance shunt. Then route all high current wiring around the board
and bingo, a small high current liner driver.
Click to expand...

It looks like you replied in the wrong thread ;)
 
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FalloutBe said:
That was exactly why I put it there, to drop voltage.
I put the MOSFET there to act as a variable resistor, just like when you'd put a POT in there, to act as a current dial. (So NOT like a switch)

The MOSFET will thus be used in it's linear part of the characteristic.
Click to expand...

So you're really looking to vary the current rapidly, rather than actually turn it on and off?
 
No, none of both.
I don't want to quickly vary the current, I want to have a Constant DC current.

Why don't you understand :( I think the whole PWM thing of the Arduino output got you confused.
The only reason why there is a PWM output, is because the Arduino doesn't have analog voltage outputs! so I have to use a PWM signal, and filter that into a DC signal.
 
This is goofy. If the insistence is on a 5V regulated PSU, you might as well use a 0.6ohm power resistor and be done with it. The diode's Vf variation is negligible in this case. If you need PWM, add a FET just before ground. Cheap, simple, effective, and just as efficient as any linear driver out there.
 
I just received my diode and regulator; built the circuit and it works perfectly ;)

The current through the diode is constant, and regulatable by changing the conductivity of the MOSFET.
 
The temperature of the MOSFET changes it's resistance drastically if the gate voltage is held constant, which makes this unusable :/

I went looking for buck converters which regulate a constant current, but I can't find any which can provide over 5Amps of current, and also has an enable input or PWM input.
Does anyone know a good buck converter which can do this?



EDIT:
Since this idea is now totally different from what I suggested in the previous posts, I'll sum up all the things I require here once again, just to make things more clearly:

Diode:
- 5W optical output, 5A@2V CW C-Mount IR 808nm diode, in a TO3 package.
(already have the diode)

Supply:
- a 5V, 8A switching PSU (already have this one)
(I can tune up the voltage to about 6V, if necessary)

Driver: //This is what I'm still looking for
- Preferred driver type: Buck
- Output current: >= 5A
- Output voltage: minimum 0V, max about 3V or higher
- Current regulation!
- Current Set Value input, will also be controlled from Arduino, to set the current value anywhere between 0 and Ioutmax.
- Enable input, to be able to turn the diode on and off from an Arduino
 
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FalloutBe said:
Diode:
- 10A (5A-2V) CW C-Mount IR 808nm diode, in a TO3 package.
(already have the diode)
Click to expand...

Don't you mean 10 Watts? (5 * 2) Anyway,
laser diodes are rated in light output, not
input power like LEDs. To get 10W of light
output, an 808nm diode would need to run
at around 9A.

The way to set current with a
microcontroller is to use a D/A converter,
which a regular Arduino does not have. The
Arduino Due does have them, just make sure
you know how to use them.
 
Yes sorry, I was mistaking about the diode.
It's power output is 5W. Electrical input is 10W (5A at 2V)

I can use a capacitor with series resistor on a PWM output to acheive an analog output of 0-5V. Will that be good enough?
If I take a large capacitor, there will be nearly no ripple, and I don't need the current set value to change rapidly, so that'd be fine.
I do however need to be able to switch it on and off at high rates. (enable pin?)
 
In theory that will work, yes, but why take
the chance when there are options out
there with real D/A converters?

Using the enable pin would switch it
completely off and on. You could also use
the current setting to bring it below
threshold and back up again. That is how
it's done in projectors.
 
Well, technically, yes, 0mA is below
threshold. The idea is to reduce the output
down to a level where it is no longer visible,
but still above zero.

Using the enable pin will force a restart cycle
thus delay. This may not be a problem
depending on your application.
 
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Oh so switching between full power and threshold has nothing to do with extending diode life time, or getting better diode performance; but only with driver startup?

The application is an engraver, moving at slow speeds. I might want to switch the diode on and off every few 100 milliseconds, but not faster than that.

Or would switching it Fully on and Fully off, affect diode lifetime?
 
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