Multi-output 9v supply using MC34063?

[matt_garman]

Alright, how about something like this:

Battery -> regulator -> multiple isolated DC-DC converters (one per output)

I'm looking at something like the MuRata NMG1209SC for the isolated DC-DC converters. 12v input, 9v output, decent ripple and noise if an inductor and capacitor is added to the output.

For the first converter, to get from battery voltage to 12v to power the isolated DC-DC converters, how about something like this: TPS61085T?

I think that checks all the boxes (except cost, those isolated DC-DC converters aren't cheap). Seems pretty simple, unless I'm overlooking something (certainly wouldn't be the first time!).

 

[FauxFrench]

The principle should work but the TPS61085T seems not to be sufficiently powerful. The switch can max. handle 2A and with 3V input that makes 6W (no margins). Then, you have the losses in the first common regulator and the losses in the isolated DC-DC converters. Not much power will be left for the loads.

 

[PRR]

why the need for isolation when in the end it's going to power a bunch of guitar pedals that are going to share a common ground via a series link chain of guitar cables?

1) It seems better to not have parallel signal and power ground commons.

2) Some pedals take *reverse* polarity power.

 

[matt_garman]

The principle should work but the TPS61085T seems not to be sufficiently powerful. The switch can max. handle 2A and with 3V input that makes 6W (no margins). Then, you have the losses in the first common regulator and the losses in the isolated DC-DC converters. Not much power will be left for the loads.

I think you're right. My read of the graphs on page 5 of the datasheet suggests it might be a little worse than that: max load current is about 0.6A with 3V supply and 9V output. That's 5.4W output. Probably OK for a couple DC-DC converters, but doesn't leave much headroom.

FWIW, I likely won't let the of the 18650 cells drop below 3.6v. (Technically they go down the 3v, but typical recommendations suggest staying above 3.6v, to extend the cell's life.)

How about this: PAM2422?

Another option maybe: TPS55340. But that looks to have a more complicated implementation.

 

[turk 182]

1)2) Some pedals take *reverse* polarity power.

i think i understand what your hinting at here but would you mind elaborating on this?

i've never known this to be a problem...or are those short polarity flip cables a lark?

 

[FauxFrench]

The PAM242X seems most promising. The TPS55340 is a versatile input voltage chip (2.9V-32V!) but the graph on the first page of the datasheet hints a quickly dropping efficiency with low input voltages. The PAM242X is designed for low input voltages, just as you want to use it for.
The PAM2423 can probably be used with your 18650 cells up to an output current of around 1A at 9V. Graphs on page 5 of 10 of the datasheet. PAM2422 should do as well.