First power supply

[scumbagatheist]

You're too kind.

As far as the name goes, it's best to keep them on their toes...

 

[Lazerbeak]

in this case the LD is some distance away from the output of the driver. The purpose of this capacitor is to bypass the brief high-freq switching spikes that may be arriving at the leads of the diode. 100nF may not be enough to smooth out power-up slugs of poorly designed high current drivers, sometimes even 2uF is not enough....
Because i have them, I also slip ferrite beads on the wires leading to the laser diode. Those present high impedance to fast transients.

Thank you for posting the picture Phenol. Honestly it is a bit beyond me right now to understand what I'm seeing. I will have to go back to school with SBA, I've been trying to avoid that. Very cool Phenol :gj:

 

[Lazerbeak]

Excuse me please Phenol. How do you calculate the necessary capacitor to use for a particular diode? Is it a matter of checking voltage spikes against a test load? I have been googling and such. The practical application of the theory would help my understanding a great deal. If and when you can. Thank you The ferrite beads in the solder is a slick trick :gj:

 

[Sigurthr]

You determin what frequency the transients and switching noise are at and then choose a low enough impedance to load them down by using ohms law and then use the capacitice reactance formula to find the capacitance needed.

Capacitive reactance = 1 / (2pi x f x C)

 

[Lazerbeak]

Thank you for the reply Sigurthur. I'm sorry, I had to google to respond Before I start, I apologize for my absolute ignorance in electical theory. I took electronics in school, but there was always a deep divide between theory and practical application for me. I really do appreciate the knowledge and will understand. What kind of method or device do you use to calculate the frequency of the transients and the switching noise? Is impedance an AC term or is the calculation applicable to a DC setup? I saw an item called a laserorb, a diode to protect sensitive laser diodes from ESD. and a Zener diode was also mentioned, are these commercial methods to do what you members are doing with capacitors or is ESD entirely different from the oscillations of the switching transients and the resulting voltage spikes (don't know if I'm visualizing that right).

I actually really love Tesla coils too, but the math to calculate windings and coils always intimidated me. Resonance, wireless transmission of energy, so cool. That's why I liked you tesla coil hene vid so much Really enjoying the conversation Thanks, "How to Lase Safely" is in my signature now great contribution

 

[Sigurthr]

Always glad to help.

Resistance and reactance are forms of impedance. Impedance is the opposition to the flow of current. It is for both ac and DC.

Frequency has to be measured unfortunately, you might be able to calculate it if you designed the driver or if it is listed by the designer, but it's something you measure with an o scope.

Glad you enjoyed the vid and my safety post! Just do me a favor and spell my name right please =P .

 

[Lazerbeak]

Thank you for the Reply Sorry, name is changed

Do you design and build circuits/drivers or can you optimize a build? Cheers :beer:

 

[phenol]

calculating the exact amount of capacitance is a daunting task because there are many factors that play a role-- amplitude and freq of noise, parasitic inductance of the conductors leading to the laser diode, ESL (equivalent series inductance of the capacitor), its dissipation factor at a given frequency, etc.
it would be much easier to measure the noise, if any, and find the best value experimentally.
It should be noted that you may not need extra de-noising in this or that driver just because i was being overly precautious. if the laser diode has to have rapid response time, such as during pulsed operation, parallel capacitors would do it no good.
As for ESD, it's an entirely different phenomenon that can pack lethal (to electronics) amount of energy delivered in a matter of nanoseconds. not only does it suck big time, but it's also notoriously difficult to predict and route away from sensitive circuits due to its subnanosecond rise/fall times... Yes, there are components designed to absorb quickly up to a certain amount of esd energy or transient overvoltage events of various origin, like inductive load switching or lightnings. they come in many different varieties of sizes and breakdown voltage, those TVS parts called transzorbs. There are better suited alternatives for esd protection only in portable equipment, such as ceradiodes. of course, proper part selection and its location on the pcb are super important for their efficacy.
Do you need to protect semiconductor laser equipment and associated driver circuitry against esd? If you built a lab unit with exposed heatsink--absolutely yes...the heatsink/host needs low Z grounding, but thats a different story.

 

[Lazerbeak]

Thank you Phenol. I was up till about 3-4 this morning googling so I understand a bit. You and Sigurthr have shared what I feel is some pretty deep knowledge with me at this point. Everybody seems to have somewhat different techniques and "tolerances" for what is allowable or dangerous for the diodes.

It should be noted that you may not need extra de-noising in this or that driver just because i was being overly precautious.

I would prefer to error on the side of caution as well.
Do you use an oscilloscope then to measure noise? Your logic makes a lot of sense. Trial and error is very practical, especially for me at this point as the actual math makes my brain hurt I do have a portable build idea I have been playing with. Some basic ideas were posted here... http://laserpointerforums.com/f42/decadiode-knife-edge-pbs-405nm-idea-81889.html#post1177501 I'm just getting mirrors and learning at this point. Powering multiple diodes with a single power source. A bit beyond me technically to do "properly". I am learning so the information you and other forum members have shared is really invaluable. Hoping that some more exoerienced members will be intrigued and work with me at some point. I'll be spending the next few months buying some parts from forum members if I can. I like your avatar,btw, it makes me dizzy
Rock On!

 

[Sigurthr]

For that multiple diode build use a driver for each diode and then power all the drivers from a single source. Laser diodes have some variances in forward voltage and their Vf/I curves. The result is if you tried to make a single driver to drive them all in parallel you would have a hard time making sure they all share current evenly, and if one diode failed it would pop the rest from overcurrent. If you run them all in series then current is forced to be shared equally but you have a very high Vf to overcome, even though one failing will not blow the rest. Though, 70V @ 500mA (10 diodes seriesed) is easier to design for than 7V @ 5A. Individual drivers lets you set each diode's operation with precision, and isolates each unit from the bulk, best of all designs.

If you want to overengineer the modules and they are not being used for a pulsed application then put a 0.1uF low inductance low ESR cap across the + and - pins of the diode and the power input of the driver. Put a 10k SMD resistor across the capacitor/diode pins (to prevent charged cap diode death syndrome). Put a 1N4148 diode reverse biased across the pins of the laser diode. Place a ferrite bead (or a few) on the + line from the driver to the diode. Twist the wire pair from the driver to the diode into a tight bifiliar spiral. Last but not least keep all connections as short as possible and make sure you are grounded to a good earth ground when working with the driver and diode.

Most of that isn't needed at all. If you feel you absolutely need all that be sure not to forget your :tinfoil: hat as well.

 

[Lazerbeak]

Thank you, thank you Sigurthr. I've been researching the forum reading about drivers and this is really in depth and puts everything together with the physical circuit design. Forgive my ignorance. My uninformed logic tells me that putting something between + and - would short out the circuit, but in Le Quack's driver piece http://laserpointerforums.com/f67/how-laser-diode-drivers-work-explanatory-thread-71513.html he mentions induction coils dumping the stored magnetic charge as voltage when the regulator is turned off. So is this similar like Phenol's pic and only excess voltage goes into the cap in the event of a voltage spike? Great reply Sir oh and by the way...

 

[Sigurthr]

My uninformed logic tells me that putting something between + and - would short out the circuit, but in Le Quack's driver piece http://laserpointerforums.com/f67/how-laser-diode-drivers-work-explanatory-thread-71513.html he mentions induction coils dumping the stored magnetic charge as voltage when the regulator is turned off. So is this similar like Phenol's pic and only excess voltage goes into the cap in the event of a voltage spike?

First off; an inductor is a dead short to DC current, but for AC it resembles a resistor (not literally, but this is a vastly simplified explanation). The higher the frequency of AC the more impedance it has to current.

In switch mode power supplies (or drivers) power is applied to the inductor, and the infuctor forms a magnetic field, the power is then cut off from the inductor and the magnetic field collapses. This causes a voltage to develop across the inductor. SMPS technology uses this developed voltage to power the load connected. The inductor is only ever parallel to the load during the portion of time in which the developed voltage is powering the load, much like a battery is parallel to it's load. During this time the power to the inductor from the power source is disconnected, so there is no shorting out of the power source. Understand?

 

[Lazerbeak]

Yes, I understand now. It's fascinating how matter and energy function, especially at the micro level, the principles seem so simple at times, but then under extreme conditions things become almost counter-intuitive. Quantum mechanics and physics seem that way to me, but then I'm a layman. I appreciate you taking the time to help me. I didn't realize you were in the middle of such a major project with your new laser setup. :thanks: Wish I could help. Lase on!