Buck Converter Using UC or AS3843

How about you have a look at the National Semiconductor site.

I dialled in your parameters and wound up with these results

http://webench.national.com/webench5/power/webench5.cgi?VinMin=30.0&VinMax=60.0&O1V=24&O1I=5.0&op_TA=30

I realise it's not a solution to your immediate problem but the NS webench is a pretty cool free tool, especially if your tinkering with power supplies.

its okay, thanks for replying. and this is really interesting. thanks for sharing it :) my problem with these types of parts is that i need to have them shipped, and sadly im nearing my deadline. that's why i settled for using the 3843 controller. i originally started designing using an LT3845 but i ruined the sample chips, so i changed my design to this. have you tried this LT3845? any advice?

I live in Australia so my selection of COTS (Component Off The Shelf) devices are limited by the local suppliers whims. Needless to say I mostly rely on Element 14(Far*n#ell), RS Components and Ebay.

I've not had any dealings with the LT3845, the switchmode regulators I've been using are the LM22674, LM2574 and LM2596. For me they've been plug and play, straight out of the "Webench" recommendations. I like them because they are low component count readily available and cheap to buy.

With any luck one of the other "Gurus" will pop by and put you on the right track.

Hi there, From looking at your circuit I would suggest a few things.

0.1uF Vcc to ground, schottky diode output to ground and also the app note recommends Ct not be less than 1000pF, yours is 560pF. These measures are all to keep noise to a minimum, hope they help.

thanks, cjforum. ill try these when i get back in the lab :) have a happy new year