Wondering if my protective diode is sufficent

2018-02-23 08:00:02

First off, since this is my first post (I am a long time answer seeker), I would like to thank the SE EE community for all the answers I got here over the years! Thanks!

Being self-taught, I've always gotten by on research and reading but this time I am stalled.

I want to build a DC-DC step-down powering a light sensing op-amp Schmitt trigger turning on a linear LDO reg for a fan (powered by the step-down). There is also another LDO powered by the step-down for some LEDs.

I drew up my schematics, put a protective diode across the fan reg, out of habit but now I am wondering if this is enough. This is the first time I am building something with electronics before the volt regs.

Anyway here are my schematics as they stand right now (they are not fully completed yet but you should get the jist of it) :

As you can see, I put a 1n4001 across the fan volt reg. Now, do I need to do something to protect the LM741 and/or the LM2575? The LED volt reg shouldn't need anything,

  • The protection looks adequate but the If for the LEDs looks sub-optimal with 3 pots. Did you want it as a dimmer?

    What is the purpose of the light sensing fan? Why do you have so many pots?

    Why not use the LED series R to ADJ to regulate as a CC source.

    Unlike the LM317 which uses 1.25V referenced to Vout (non-inverting) this ADJ input is inverting with Vref=1.275V. So to design a CC LED regulator move the Rs to the ground side and choose a ground side LED Rs for If*Rs=1.275 V for the desired the LED forward current. With 12V-9V, you would have had a ~3V drop, now using the LM2941 as a current regulator, you expect a 1.275V drop on the ground side series R and thus a slightly greater drop on the LM2941 to drive three LED's with constant current. If power Pd is an issue in IC, then adding another Rs to dump 1.5W can be done.

    2018-02-23 10:36:30