DC-DC controllers

Go To Last Post
13 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi guys,

im building a regulated bench top power supply which im going to interface with my micro.

Ive been thnking of using a tl494, but its output PWM duty is limited to like 0-70% or so. Do you guys know of an equivalent, with a full 100% duty cycle range.

cheers
-Tony.

- Tony B. Sydney, Australia.
tbaz2679@mail.usyd.edu.au

Status: Supporting the GNU

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Found simular problem (90% max) with MC34063. So now I have an AVR doing that task. No limitations, except your imagination.

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

In a previous project I had running I also used an AVR to do the PWM. Like Nard says, the only limiting factor is your imagination.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I made a multi-output flyback converter with a tiny25. As the load is fairly constant (just a couple of opamps) and the input voltage is constant too, it works quite well but transient response is ghastly, and due to the limited number of bits, accuracy isn't that superb either.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

TL494 has duty cycle up to 96% in single-ended configuration and up to 48% in push-pull mode.

Attachment(s): 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Is it practical to use PWM for variable voltage and current loads? I always fancied doing one with an AVR but was never sure how good the regulation would be?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
Is it practical to use PWM for variable voltage and current loads? I always fancied doing one with an AVR but was never sure how good the regulation would be?

You can do it, but as alluded to above, the challenge is getting suitable transient response and maybe even more important, input ripple rejection. I tried them in a couple simple battery management applications but have since abandoned the concept. What I do now is use the Avr to "command" a switching regulator IC, which provides flexible and wide range voltage or current selection whilst providing the excellent regulation of the dedicated purpose regulator chip. Actual parts count, board area, and even total cost can wind up being less, too.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I have already tried using an AVR directly for regulation. It works, however, as mentioned above the transient response is very bad.

What i am doing now is exactly like what tom is doing, using the AVR's PWM (with filtration) to command a standard regulator.

All works well, however, before i finalize my project, i though it would of been good to have 100% duty range.

Although the specs mention 95% duty range, its actually like 70-80%. ive tested this with the scope.

This means if i have 12volt input (a car battery for example) the highest possible output would 9.5volts or so. This is why i wanted to solve this problem.

- Tony B. Sydney, Australia.
tbaz2679@mail.usyd.edu.au

Status: Supporting the GNU

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
This means if i have 12volt input (a car battery for example) the highest possible output would 9.5volts or so. This is why i wanted to solve this problem.

If you're using a boost topology, you can have the regulator output any voltage you want!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Also consider using the SEPIC topology, which permits an output higher, lower, or same as the regulator input.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
What i am doing now is exactly like what tom is doing, using the AVR's PWM (with filtration) to command a standard regulator.

I'm thinking about doing just this on a future project. Tried the AVR only way myself, and like others discovered some transient response problems.

What's the simplest technique to control a switching regulator? Do you sum the feedback voltage and the AVR's pwm signal with an opamp? Or do you just use the pwm signal as the switching regulator's reference voltage.

I'm having some trouble finding any online examples of adjusting a switching regulators output with a voltage.

Thanks,
-carl

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
What's the simplest technique to control a switching regulator? Do you sum the feedback voltage and the AVR's pwm signal with an opamp? Or do you just use the pwm signal as the switching regulator's reference voltage.

A regulator such as a LM2671 (like may others) has a "feedback" input that is compared with the internal 1.2 volt reference. Output voltage is determined by the ratio of a voltage divider from "output" to ground, with the tap connected to the feedback pin. Simply add a third resistor from the feedback pin to the output end of your pwm's lowpass filter network. Varying the pwm output from 0-5 volts, for example, will influence the output voltage of the regulator. With some simple Ohm's law calculations for the values of the three resistors, you can set the output span of the power supply most anywhere you like. If the pwm filter is not buffered with say, a unity gain op amp stage, then the values of the lowpass filter resistors will add to the "third" resistor value.

Tom Pappano
Tulsa, Oklahoma

Tom Pappano
Tulsa, Oklahoma

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:
Simply add a third resistor from the feedback pin to the output end of your pwm's lowpass filter network.

Even with buffering it's simpler then I thought.
Thanks.

-carl