Mc33167 step up converter

[jackbob]

I'm looking to make a dc to dc step up converter and bought two mc33167's. I need to go from 12 to 24 volt. I have been trying to get them to work but it hasn't gone smoothly, all the do is step down.  They are called step up/down converters so they better work. This is the second pair of switching converters I bought that pulled the crap of being called step up converters but don't step up. Any help on how to get these things to do their job? Thanks,

Jacob.

[amspire]

If you look at the circuits on pages 11 and 14 of this datasheet, you will see it in the step-up mode.

http://www.datasheetcatalog.org/datasheet2/5/0wlywx1749qxhup1c776g52uy3ky.pdf

It needs an extra fet or transistor to short one end of the inductor to ground during the ON cycle.

Richard

[Psi]

You have to connect the IC up differently for the different modes,  stepup, stepdown, inverting.

The on semi datasheet for the MC33167 has a example circuit that will go from 12v to 28V on page 11 which is a good place to start.
http://www.datasheetcatalog.org/datasheet2/5/0wlywx1749qxhup1c776g52uy3ky.pdf

The circuit is only 0.9A so if you need more current you'll have to replace some parts with ones that handle it.
Mainly the fet, diode and inductor.

To adjust the voltage from 28 to 24 you'll need to change the R1 and R2 resistors. Ive only skimmed the datasheet but it looks like the reference is 5V, so you need to spec R1 and R2 to divide the output voltage so there is 5V on pin1 at 24V instead of 28V.

[joelby]

If you're already following the step up configuration from the datasheet, perhaps you could post a schematic diagram of the circuit you're using and maybe a photo showing your construction?

[jackbob]

Erg.. It's not working so well but I don't have all those parts on hand so I'm substituting parts. I love how it says 'few' external parts. I love electronics but sometimes it is more than enough to drive me crazy. I did however build a successful boost converter from raw parts. It's ok but you need a huge huge inductor because the small ones make kv outputs not just volts. Wew those things will light you up. If only I had no homework I could build much more.

[joelby]

Yeah, the main reason I mentioned taking a photo was so that we could exactly see what sort of inductor you're using!

[jackbob]

I tried all sorts of inductors but one thing I don't have and should have is an rlc meter. I have not a clue of the sizes of the inductors. I need a meter to read their values. Another thing is diodes, you put 12v in and get 11 out! How annoying it's not new to me but it never fails to push my buttons. For those who are still waiting on that big pwm motor control I'm building... Well china has slow shipping but it's still in the works, as long as nothing blows up   

[Psi]

The inductor needs to be the right core material for the switchmode frequency. (in your case 72kHz)
Some inductors are just not suited to switchmode supplies.