DIY boost converter

[qpla]

I saw the post abt boost converter on

[url]http://www.ladyada.net/library/diyboostcalc.html\[/url]

It said it can use a 555 to generate the PWM, but there is no feedback. I know all boost converter chips have FB. Will that be a problem?

Thanks

[adafruit_support_bill]

It depends on what you want to use the boost output for. The boost converter that drives the VFD on the Ice-Tube clock has no feedback.

[adafruit_support_bill]

The phone is going to want to see a fairly stable voltage. You could either boost beyond 5v and regulate it back down, or build in some feedback. The feedback approach would likely result in a more efficient circuit.

[qpla]

Actually....I am making the thing like the miniboost, but i got another strp up chip. However, it seems that the output current is tiny, not 500mA even i have add resistance t the D+ and D- USB pins. And there is some Volt drop at Vout. Is this the problem of the chip, the inductor, or something more i have to add to the circuit??

[Zener]

To further answer your first question (which AF already answered) any REGULATOR will have feedback, whether boost, buck, linear, whatever. It needs the feedback to regulate the output. But some devices don't need an exact output so then they are unregulated and have no feedback.

As for your second question, how much current does the datasheet say it can put out? Can you post the schematic you are using?

[qpla]

the datasheet said it can provide up to 2A. I hv attached the schematic.

I cant upload the datasheet in pdf so i post the dropbox link
https://www.dropbox.com/s/duo385g1pgq4y4m/LSD91%20Spec.pdf

[Zener]

Who makes that IC? I have never seen a data sheet with no mfg info at all.

Anyway, I think the trouble is with those mosfets you have on each end. What are you trying to do with those? I would just use the curcuit from the data sheet and I am guessing that will work OK.

[qpla]

THX, but I tried not to connect those mosfet but still not good. I am just putting them on breadboard, will this affect the output?
Btw, can i change the SS24 and use some other diode?

[Zener]

Switcher circuits don't do well on breadboards. There needs to be a very low impedance path from the input capacitors. There are high peak currents at high frequencies there. Generally the manufacturer will supply a development board you can use. But does that thing have a manufacturer?

[qpla]

Haha I dun know...i think i will make my own PCB to try it.
thanks!

[Zener]

Be sure to read "Layout Consideration" on page 6 of the data sheet and follow the rules they give!