Simple Adjustable Laser driver (V. 2) It Works!!!

Re: Simple Adjustable Laser driver (V. 2) It Works

ooh, well this works for phr-803Ts? thats relevant to my interest
ill be watching for the smt version, my electronics savvy coach could most likely help me build it

Re: Simple Adjustable Laser driver (V. 2) It Works

Omega said:

ooh, well this works for phr-803Ts? thats relevant to my interest
ill be watching for the smt version, my electronics savvy coach could most likely help me build it

Click to expand...

Thanks for the interest. I've actually done the second build of this circuit. The first one broke a lead while I had it apart to measure current. Then I created a solder-bridge trying to repair it and blew a diode... Being a prototype I'd already soldered many of the components more than once playing with the layout. So rather than try to repair it and risk another diode, I built another one.

As for performance, I've taken PHR803T's up to 155mA without ill effects. But after adjusting one to 165mA while warm, it died on the next cold start. This leads me to believe that the cold-start delay could be increased to allow higher current settings.

Also, I've got stuff coming from digi-key and some experimental layout art for the SMT version. I can definitely make it small enough. I'll likely focus on the P-channel version as it could be used for blu-ray or 650nm. (I'm going to try etching the PCB using a 70W laser cutter/engraver so that'll be an experiment in itself.) If it works I'll post the PCB art on this thread for anyone who's interested.

cheers,
kernelpanic

Re: Simple Adjustable Laser driver (V. 2) It Works

Remember, with a P-channel mosfet, you'll need an opamp that with a working range including the positive supply like TL081. The LM358 won't work

Also, watch out for those spikes. USE AN OSCILLOSCOPE. I've had two PHR-803T survive and one dead in one of my test suites. They were driven at 250mA for 360+ cold starts and 7.5 seconds duty. Afterwards, I discovered the spikes with my oscilloscope as being 10us with a peak of 315mA.

Re: Simple Adjustable Laser driver (V. 2) It Works

Zom-B said:

I've tried with the cap like you suggested and it creates hella big ringing pulses (>150% of signal) at each rising edge.

I tried to play with the values of both resistors and the cap between the output and input and found out that with a certain range of caps and resistors it works better. The cap is now 10nF and the resistors both <1k Ohm. I'm still working on improving the values.

Click to expand...

The ideal values I found for these parts are

C8 = 10nF (as found earlier)
R10 = 1 kOhm
R11 = 390 Ohm or more (I took 470 Ohm)

These values work best in my case, that is to say, with an LM324 opamp and the BUZ11 MOSFET. Other opamps and other MOSFETs might create different situations (especially the MOSFET).

Increasing the value of R11 dampens the signal and slows down the slopes. Decreasing it on the other hand creates overshoot. The slope with the ideal value is around 10 microseconds.

Re: Simple Adjustable Laser driver (V. 2) It Works

Zom-B said:

[quote author=Zom-B link=1220866048/20#31 date=1224181082]I've tried with the cap like you suggested and it creates hella big ringing pulses (>150% of signal) at each rising edge.

I tried to play with the values of both resistors and the cap between the output and input and found out that with a certain range of caps and resistors it works better. The cap is now 10nF and the resistors both <1k Ohm. I'm still working on improving the values.

Click to expand...

The ideal values I found for these parts are

C8 = 10nF (as found earlier)
R10 = 1 kOhm
R11 = 390 Ohm or more (I took 470 Ohm)

These values work best in my case, that is to say, with an LM324 opamp and the BUZ11 MOSFET. Other opamps and other MOSFETs might create different situations (especially the MOSFET).

Increasing the value of R11 dampens the signal and slows down the slopes. Decreasing it on the other hand creates overshoot. The slope with the ideal value is around 10 microseconds.
[/quote]

Thanks for the info on this. BTW are you using my circuit or yours? I've mostly gone at the start up delay by increasing the values of the cap on the pot and the cap across the LD, thus increasing turn on time. But I like your approach. Mind if I incorporate it into my driver?

cheers,
kernelpanic

Re: Simple Adjustable Laser driver (V. 2) It Works

See here for the entire circuit: http://www.laserpointerforums.com/forums/YaBB.pl?num=1224769382/0

Re: Simple Adjustable Laser driver (V. 2) It Works

Zom-B said:

The ideal values I found for these parts are

C8 = 10nF (as found earlier)
R10 = 1 kOhm
R11 = 390 Ohm or more (I took 470 Ohm)

These values work best in my case, that is to say, with an LM324 opamp and the BUZ11 MOSFET. Other opamps and other MOSFETs might create different situations (especially the MOSFET).

Click to expand...

The resistors will definitely depend on the mosfet. C8 should depend more on the op-amp's level of internal compensation than the mosfet used.

Increasing the value of R11 dampens the signal and slows down the slopes. Decreasing it on the other hand creates overshoot. The slope with the ideal value is around 10 microseconds.

Click to expand...

That part I got.

Thanks,
kernelpanic

Re: Simple Adjustable Laser driver (V. 2) It Works

Kernel great driver... going to buy the parts as asap... TTL modulation would be really really great! hint hint

Re: Simple Adjustable Laser driver (V. 2) It Works

anything new of the modulation mod of the circuit?

Re: Simple Adjustable Laser driver (V. 2) It Works

kendon said:

anything new of the modulation mod of the circuit?

Click to expand...

Andrea87 posted one here-
http://www.laserpointerforums.com/forums/YaBB.pl?num=1231275597

cheers,
kernelpanic

Re: Simple Adjustable Laser driver (V. 2) It Works

thanks. seems a little bit more complicated, but i will look into it.