On Fri, 2012-01-20 at 10:42 +0200, Viesturs Lācis wrote: ... snip > Kirk, I repasted Your scheme here: > http://picpaste.com/scheme-3V0w43QM.png > > Do I understand that includes also Steve's and Przemek's sugestions, > if R2 is 200 ohm? > > The optoisolator is 4N25, the transistor is BD139. > > Gene, I think that I have spare 330 or 470 ohm resistors to replace > the 1K ohm R1, I will try to test it. > > Viesturs
BTW, the parts in my drawing where just the symbols I had handy and don't suggest what should be used. It looks like the 4N25 can pass 50mA with a forward voltage around 1.3 Volts. The BD139 looks like it turns fully ON with the base at .5 Volts. Following the circuit from the supply through the opto and Q1, to ground... 12Vsupply - .5Vsat4N25 - Vr2 - .5Vbd139 = 0 Vr2 = 11V Vr2 = I x R = .05A x R2 R2 = 11 / .05 = 220 Ohms (this will push the opto to its limit but should be okay) Watts = V x I = 112Vr2 x .05Ar2 = .55 Watts, so a half Watt resistor should be used. The BD139 gain is 40 or better, so 40 x .05A = 2 Amps The BD139 collector-emitter ON voltage is .5 Volts so the laser will see 11.5 Volts. What is used to modulate the laser? For some applications, the laser will need to be turned on and off at a high rate, which makes life more interesting. For the Mesa side, the 4N25 LED looks like it can take up to 60mA, so you can drive it pretty hard. My guess is that the Mesa output can sink up to 24mA, so this will be the limiting factor. I'd shoot for 15mA. Also the LED reverse voltage is 5 Volts, so it is common to have a general purpose diode (with a high reverse voltage) in series with the opto diode. 5Vsupply - VrInput - Vgendiode - VoptoLED - VmesaPin = 0 5 - VrInput - 1 - 1.3 - 1? = 0 VrInput = 1.7 Volts V = I x R, Rinput = 1.7VrInput / .015 Amps = 113 Ohms Corrections to any of the above are welcomed. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
