Driver Circuits and Capacitor Protection

well, I would consider Daedal to be an expert also!  Im sure he has built many many lasers, experiance is unbeatable. and yes, if it oscillates, its gonna die for sure!

Max

These voltage regulators can be tricky really.. sometimes you build a circuit that is stable 10 times, only to find it insnt the next.

Daedal.... Thanks for the very thorough explanation! Thanks also to Benm, chimo, Gazoo, CHP for their insight. Theory discussions such as this are healthy for airing different ideas and solidifying exactly what's going on in our regulator / diode circuits.

I learned a few things anyway, which is always a good result

This has been a very good discussion...I learn something new here every day so I will never be an expert...lol. We will all use our own methods based on what we fell is the right way to go...but most of us do agree on the basics of protecting our little gems.

I agree also! this is the best discusion forum ever!

Max

does it matter what a cap is rated to?

say a 200uF cap at 500v? or a 200uF at 50v

whats the difference if you were to put the 50v on the 500v, or vice versa? How is capacitance related to voltage?

This is what this forum is about, and I personally enjoy the learning experience I get from this place just as much. You guys are great, and the topics opened up here are very good and provocative issues that gets ones' brain moving

Cxrazy, to answer your question, it does matter what it is rated to. But the minimum you should go to is a rating of 2X that of the laser diode... and for the safest measures, go for 1.5 your input to the circuit

If you load a 50V capacitor with 500V, you start to get breakdown in the capacitor where the plates start to arc, generate heat, and proceed to permanently destroy the cap... in other situations you just get a ruined cap because it will just short-circuit. Loading any capacitor to a lower voltage that its rating is a good thing

--DDL

I forgot to mention this... For a given capacitance (say 10uF) a 10V cap would be smaller than a 50V, and both would be smaller than a 500V. 500V caps are usually HUGE... check them out on Google/eBay

--DDL

another thing to note about electrolytic capacitors: if overloaded they not only fail but can explode! I learned that one permanently, down in the basement waaaay back when... if the leads are both at one end and soldered in, the can goes flying.

and Cxrazy, yes it's ok to mix different voltage rated capacitors. The voltage rating is just the maximum working voltage, and does not affect the circuit (except if the capacitor starts to fail).

yes!

Thats all I needed to know.

I've got TONS of caps from an old PSU as well as some resistors, (i'm such a cheap bastard) so I'll probably get to building my driver sometime soon.