Driver for the new 505nm and 480nm diodes

[deadshadow]

This is Paul's daughter. He is still in the hospital and will be there until next month. He wanted me to let you all know that he hasn't forgotten anyone.

He'll be back ASAP

thanks for the update about him,so from your writting "he'll be back soon" i assume everything goes well with his health.i wish the best and easier-quickest recovery to him :yh:

 

[diachi]

This is Paul's daughter. He is still in the hospital and will be there until next month. He wanted me to let you all know that he hasn't forgotten anyone.

He'll be back ASAP

Thanks for the update! :beer: Nice of him to be worrying about us when he's the one we should be worrying about!

Hopefully he has a speedy recovery.

 

[CurtisOliver]

Yep, that’s Paul. ^^

 

[Atomicrox]

Only got around to scoping it again today, this time powered by 3 14500 batts.

Seems clean when turned on with pot on max:

Added a 1uF ceramic to the output and the ripple lowered a bit, to around 36mA pk-pk.

Unfortunately the huge noise when touching the pot's knob is back, it's not caused by the extra cap, I tested.

Not sure what to do.
Maybe increase the capacitance between SET and GND? Can you suggest a value?

I'm starting to geat fearful of using this with a rare diode (the 480nm one). Really wish I could find a commercial driver with analog modulation.

 

[Astralist]

BUT, that noise exist only when touching the pot's knob right??

Are you by any chance creating a long connection along the 20k pot and 100 ohm resistor?? that could cause additional noise pickup.

how about adding some more bulk ceramic capacitor at output?
like 3x 22uF ceramic (3x 22uF is better than 1x 66uF because of paralleled ESR)

 

[Atomicrox]

Yes, only while touching the knob.
The 100ohm resistor is soldered directly to the pot. The wire from the regulator to them isn't short (maybe 4cm?). Maybe I could lower it a bit, but I need some wire to position it correcly.

Unfortunately I don't have any high value ceramics here. Could buy some online, but it'll take long to arrive and I'm not really looking forward to waiting another 3 months to build this.

 

[Ferton]

47 uF i classic. But it not require a fet basics transistor?

 

[Rivem]

47 uF i classic. But it not require a fet basics transistor?

You need to fill out your profile and post a thread in the welcome section.

 

[Atomicrox]

I just discovered the oscilloscope is (part of?) what's causing the strange oscillation when touching the knob.
When the oscillation is happening a DMM will read lower across the dummy load resistor. This only happens with the scope attached. Without it the output current seems stable.

Any ideas why? Am I using the scope incorrectly?

Maybe this driver is safe after all.

 

[paul1598419]

Might be the earth ground for the scope is floating, not actually grounded. This could introduce noise into your output.

 

[Atomicrox]

The outlet I used should be properly grounded, is there an easy way to test it?

 

[paul1598419]

Sure. It should measure 110 VAC from ground to the high side of the outlet. If not, the ground is floating and you have no earth ground.

 

[Atomicrox]

Measured, it's correct. Any other ideas?

 

[paul1598419]

You might also check for stay AC between the earth ground prong and something grounded like plumbing. If you find none there, check the same places with an ohmmeter to see it has a good earth ground connection.

 

[Atomicrox]

Checked, ground seems fine. Must be something else.

 

[Atomicrox]

Decided to try the driver on the 505nm diode anyways. It's working well, analog modulation is great.

Will keep testing it for a few weeks before I decide if I'll use it on the 480nm.

Here's the final schematic with all the caps:

PS: still unsure why the oscillation was being induced by the scope (or was it?) Any tips are welcome.