I wouldn’t try to find exact Ib current that produces Ic=70mA @ Vce<0.3V as if you use different transistor the values will be different ..
Try to use decent Ib current that will for sure produce saturation and then limit the Ic current to whatever level you need (70mA or so) with a resistor connected between [C] and [Vcc] ..
IanP
:wink:
please give the following data:
Vcc
min/typ/max hfe of the transistor.
(Ic=70mA as given)
You really should read the replies in your other thread:https://www.edaboard.com/posts/810145/#post810145
A CONSTANT CURRENT/VOLTAGE IS NOT THE WAY TO DRIVE THOSE LASERS.
Keith.
Well, I don't know what to say. I have been designing laser drive circuits for over 20 years and have used two types - ones with internal monitor photodiodes which need a closed loop optical power control circuit and high power pulsed ones which can be driven with a high current pulse. Yours is the first type and needs an optical feedback loop using the internal photodiode. If you don't, you will blow them up. You need an optical power meter to set them, if I haven't already mentioned that.
That is it.
Keith
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