here is the close-up. power in on the right and power out on the left. the schottky diode is 1n5819 (1a 40v), on the top left corner.

left to the capacitor, I left some space to add an external switch to deliver more current. the resistor that sets the current is on the bottom (10ohm since ncp3065's Vfb is 230mv), and I also left more space there to add dimming or to parallel more resistors to increase the current capability.

 

so a minimal design would require one timing capacitor, one resistor to set current, one diode, one chip, and one inductor.

cannot get any simpler than that, can you?

 

the whole thing is about 1x1 without the inductor, and if you find a smaller inductor and mount it underneath the board, it would take much less space.

the lowest voltage this thing runs on is about 3v: with 3 batteries, the current is rock solid at 22ma (=24v output voltage); with 2 batteries, it fluctuates around 12ma (=14v output voltage).

 

Hello millwood,

Is it nessesary to post 12 posts afther eachother?
You can also edit a post to add or change something.
Some post only contain one line.

Greetings,
Bertus

 

Hello millwood,

Is it nessesary to post 12 posts afther eachother?
You can also edit a post to add or change something.
Some post only contain one line.

Greetings,
Bertus

is there a rule against posting certain number of posts after each other?

 

I put together a similar circuit using 3842 (in this case, ka3842b from fairchild). the basic idea is the same: use a step-up dc/dc converter and regulate the voltage drop on the pwm controller's Vfb pin to yield the desired current (in this case, 25ma).

the load is a 1k resistor + a red led (Vfwd=2.2v) -> total output on the load of 27.2v, + 5v on the Vfb = 32v. all powered by a 16v IBM ThinkPad power adapter.

the step-up converter itself uses an OnSemi mosfet (mtp20n15 I think), and a 3a Schottky diode (on the bottom of the board). no CS resistor, plus all the goodies offered by the pwm controller.