WEBENCH® Tools: Multi output power supply design

Hi Ken,

I would recommend first trying the WEBENCH power architect tool ( webench.ti.com/.../webench5.cgi ) to design these output voltages. You can define your input voltage range, "Add Load" and specify the voltage/current requirements for each output. Alternatively, you can also try finding some reference designs that may meet your requirements here: www.ti.com/.../index.html I am also notifying a power expert of this message to further support with any details on the frequency choice and synchronization.

Regards,
Amod

Hello Ken,
You need need to supply +15, -15, +5, and +48 volts.
What is the input voltage range? Is it AC or DC input?
If AC then can I assume you need isolation?
What is the maximum and minimum current on each rail?

Synchronization.
In general, if using multiple converters then they will "find" themselves and try to sync together.
So synchronization should be included in the initial design.
In the end phases of testing, you may find that removing synchronization still allows the converters to work fine, but will also tend to spread out the EMI impact.

Syncing converters allows a common frequency to address in EMI filtering.
On the other hand, converters operating at different frequencies, or slightly different frequencies, will result in less EMI energy concentrated at one frequency. You may want to experiment to see which is better for your electrical and physical scenario.


For an isolated supply the "loop" will usually be closed on the highest power output.
+48Vout at xxxAmps will likely be the highest power output.
+5 may have a heavy logic load and may have tight tolerances.
In this case, if the 48V has a somewhat loose tolerance, then closing the loop on +5V may be better.

+-15V are usually low current, but may need low noise for analog circuits.
PI filters are common for low noise converters.
Webench allows adding extra filters on outputs and inputs of converters.


More insights can be provided once you provide a few more details, Vin, Iout, critical noise requirements, etc.

Hi Ed,

Thanks for the advice. I’ve selected 4 supplies using the Webench tool and have built 2 of them so far with mixed results so I’m looking for some advice.

The first supply I built was the -15 volt @ 200mA and as I powered it up slowly it went into regulation but when I applied a load it was only able to deliver 22mA instead of the designed 200mA. As I increased the load the supply slowly fell out of regulation and then died. It also wouldn’t start up with even the 22mA load on, I had to turn on the input supply and then apply the load. I tried to make the cleanest prototype I could using all surface mount parts as it would be once it’s committed to a PCB so I guess the question is, is this behavior symptomatic of layout problems, if so any suggestions on the best prototyping methods?

The second supply I built was the +48 volt @ 100mA and when it powered up it just sent my input supply into current limiting. As I went thru the design, I found that disconnecting the inductor, MOSFET, or sense resistor alleviated the short but of course defeated the purpose of troubleshooting the circuit. So, I guess the question is, is there a way to test the switching controller without the higher current external components connected? If there is a recommended troubleshooting procedure, I’d love to get my hands on it.

Finally, I want to build the +15 volt @ 200mA supply using the LM5155DSSR switching controller but the only package it’s available in is a WSON which I can’t find a prototype board for any suggestions?

I have to say that in the past I’ve built a few other supplies using the Webench tool and they’ve all worked right off the bat with no problems, so I'm quite surprised with the results, or lack thereof this time around.

 

Any help would be greatly appreciated,

Ken Dabek

West End Recording