switching regulator:

You need to design for the whole range. In the case of something like this that means sizing the inductor (and choosing the chip) for the maximum current, then verifying that the thing will stay in regulation and otherwise work satisfactorily at the minimum current.

NOT, you need to design for what you think you want and then take care of what happens when something else tries to exceed it.

Example.

You want one shag a week.... You know that one shag a week kind of keeps the relationship happy and gives you enough time for Xbox and a day down the pub with your mates. You would like to do a bit more of philosiphising down the pub with your mates but there are more variables invoved in that scenario.

Actually, you could do without the shag, bloody hard work, but if you want clean underware without having to pick up the dirty ones then that might be one of the absolute minimum ratings according to the specification.

So it's all sorted. But what if shag day is Wednesday and he also wants one on Thursday?

That's engineering

DNA

"Genome" schreef in bericht news:3SJBg.3931$ snipped-for-privacy@newsfe5-win.ntli.net...

Including the deadline of 2-3 days ;)

Tim is right,

Use webbench on the national.com website and put in the max and min battery voltage. A reasonable range for a 12 volts battery is 16 volts down to ~9 volts at full discharge.

model with a min and max current to cover your range and you should be fine.

Hello Mook,

Yes.

For some reason the design parameters I entered usually resulted in a "can't be done" message. I then calculated them by hand and it's all in production now. So I haven't used WebBench in a while. And probably won't for a while.

I do like their idea with forums. Hasn't become popular though and I wish they had chosen a newsreader compatible format or at least provided one in parallel.

That's because they don't include "A handful of discretes" as a switcher IC in their WebBench :)

Mook Johnson schrieb:

I tried SMS 6.24 (Switchers Made Simple) the software from national website and it gave me for each current the follwoing values: Vin Max=12V

What do I do now? Should I just pick the max current values?

JJ

Yup. use the 2 amp design

Be sure you provide the minimum current to keep it regulated when there is no load on the output.

you can go to the simulator and run a sim with min load and then your max load to see what the input current and output voltages look like.