Multiple output switching regulator

[Jdo300]

Hello All,

Now I'm looking for a good way to power all the chips on the control board I'm designing. It will be powered by two rechargeable 9V batteries in series for a total input voltage of about ~14V.

The interesting thing is that the chips I am using all require a wide range of voltage inputs. I need to produce 1.8, 3.3, 5, and 12 volts for the different sections of my circuit. I was thinking about just slapping some linear regulators to make all the voltages but quickly realized that these would probably drain my batteries faster than the actual circuit would.

Sooo... I am looking into switching regulators since I know they are much more efficient. In a perfect world, I would like to see if there are any out there that can make all these voltages from one input (or at least some of them anyway). The other thing is I'm trying to find a one-chip solution so that I don't have to add a bunch of external support components. Has anyone here run into anything like this before?

Thanks,
Jason O

 

[Averagesupernova]

Do need these different voltages just for biasing certain parts of your circuit? What type of current do they need to source?

 

[berkeman]

As Averagesupernova is alluding to, your current requirements from each power rail will drive how you would design your multi-output supply. For rails that require relatively little current, you will usually just use a linear regulator (often an LDO regulator) from the next higher rail. For rails that require a fair amount of current, then you will use a buck regulator off of the main supply rail. If you have several rails that need to supply a fair bit of current, then you can consider designing a multi-output flyback or feed-forward transformer-isolated switching regulator. You need to think about cross-regulation effects, though, when you have multiple outputs that can have a lot of output current variation between them. You generally only close the feedback on one rail, so if the other power rail has a wide current variation, that can cause excessive voltage droop on that rail.

 

[Jdo300]

Hi Averagesupernova,

I am using the power supplies to run the ICs on my board. The 1.8V and 3.3V power supplies are dedicated to runing to AD9959 IC. The 5V supply will run the crystal, pulse width controller chips, BASIC Stamp OEM board, and any other misc CMOS chips. The 12V supply will power the MOSFET driver chips and the high voltage power supply chip that I have.

the AD9959 uses a maximum of 680 mW worst case. most of the other chips are all just logic based. the MOSFET drivers I am using each draw a maximum of 650 mW. The high voltage chip draws 80 mA maximum when it is running. My guess is that the realiztic power draw would be somewhere in the neighborhood of 1-3W max.

Thanks,
Jason O

 

[Jdo300]

Hi Berkeman,

Good points made about the power considerations. I'm tryinng to determine the simplest way to design the setup, weather I use linear regulatrs, switched regulators, or a combination of both. My initial thought was just to use all linear regulators and then just piggyback them off each other so that the voltage drop across each one wouldn't be that bad, but I'm not sure if that is the best way to go. that's why I thought about the switching converter ICs that I have seen around. But realistically, if the efficiency of using the linear regulators wouldn't be too horrible, I wouldn't mind using those. I'm just hoping that there may be some magic switching converter out there that supplies some (or all) of the voltages that I need. The most important ones are the 1.8, and 3.3V supples since I have to drop from 9V down to those. I'm not too worried about the 5V and 12V outputs since those aren't too far off from 9V and 14V.

- Jason O