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555 as boost regulator controller.

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s3c

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I've come across a number of related articles but haven't seen one implemented in this fashion, I'm trying to create a real cheap boost regulator, all the other attempts I've seen use the 555 in astable mode with the timing determined by a rc pair.

Simple 12-180V boost converter using the 555 as controller | Circuit Project Electronic

the problem with this approach is that the timing has to be set up perfectly to be efficient. Using the 555 to measure the current through the inductor would make for a far better design and allow easy current limiting for battery operations which is what I'm after. After a bit of fiddling about I created the following, when simulating in orcad it gives rather good results but building it posed problems, the circuit gets stuck in a certain state and doesn't oscillate.

Anyone up for building it to confirm that I'm not just screwing something up or have any idea why it would deviate from my simulated model? Any comments and suggestions would be appreciated.

(The transistor and inductor was chosen because that's what I had at hand)
 

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Mr RB

Well-Known Member
Your circuit is really inefficient due to needing such a high voltage across the current sense resistor to operate the 555 times.

You can find a input current regulated boost converter here;
+5v to +12v converter

which is a proven design. Output voltage is fixed by a zener. It regulates around average input current which at regulated 5v equals average input power.
 

s3c

New Member
I came across that post when I first thought up this idea, adding a zener would provide the same voltage limiting in my circuit but I'm not at that point yet, want to get a working prototype before moving on.

Any Ideas as to why It isn't operating like the simulated model? :)

[EDIT]

Got it working, guess I had a faulty part, still doesn't perform like it's simulated counterpart but at least now I have something to go on. Trying to derive some equations now but not real sure where to begin, anyone have any ideas?
 
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smanches

New Member
Use the 555 as a sawtooth generator instead. Then use an opamp to create your PWM signal with another one as the error multiplier. Much easier than trying to use the 555 directly to generate the PWM signal.

Tried for a couple days with only the 555 before I gave up. I could not find a way to keep it's frequency constant and vary the duty cycle.
 
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