# are there limits for the number of buck converters I can run off a single power supply

I am trying to design an led array that includes 4 different types of leds. I am thinking of using several adjustable (cccv) buck converters in parallel on a single set of daisy chained PSU 24v 10A. In the design I could end up using up to 4 converters, 1 set to 19.2v @ 0.7A, 2 set to 19.2v @ 1.4A with PWM dimmer, and 1 set to 24v @ 1.05A. Those are the raw numbers using the Fv and Fc for the leds, I will likely end up slightly under current on all sets. What if any issues are there with this type of set up? Thank You

• Could, thinking, several, trying, likely, slightly = freaking show a circuit/picture cause nobody here reads minds or tarot cards. In answer to the question in your title, yes there is a limit. – Andy aka Sep 27 '16 at 23:15
• What does "cccv" mean? You can have either constant current supplies or constant voltage ones. Why do you need 3 buck converters set to 19.2V instead of 1? – Wesley Lee Sep 28 '16 at 5:14
• Having a single source of 24v all inputs for converters would be connected in parallel to it. – Fiveapes Sep 29 '16 at 10:25
• Wesley, there are sold converters with the capacity to provide adjustable constant current and adjustable constant voltage. the reason for 3 converters set to 19.2 is to allow blocks of leds to be dimmed independent of the other blocks. – Fiveapes Sep 29 '16 at 10:28

I have had boards with 12 different power rails, including two negative (half of the voltages were dedicated to an LCD), but not as much current.

You have 240 watts to begin with. Total up the values for the buck converters, perhaps conservatively using only 70% efficiency, and you get

$${(19.2\times 0.7)\over 0.7} + {2\times (19.2\times 1.4)\over 0.7} + 24\times 1.05$$

and you get a total of:

$$19.2 + 76.8 + 25.2 = 121.2 \space watts,$$

which is about half of your budget. So you should be okay. I wouldn't go more than 3/4 of your maximum, or 180 watts.

Be sure to follow the datasheet's recommendations for whatever caps you may need at the input to the buck converters, and locate them close to the IC's.

Short answer: No issues, but needs some consideration.

There are some triple converters (TPS65266 f.e.) on the market, because that is what is required on TV sets with LED backlights. If you can get around with one of these, it will reduce you BOM.

If you need to employ multiple converters, each converter will require its own input capacitance. When selecting components, follow datasheet recommendations and take care of maximum allowed ripple current and bias derating.

Multiple converters will cause quite an inrush current that can blow your PSUs fuse. You need to limit it with a thermistor (or oversize your PSU accordingly). You will also want to use soft-start/ramping on the converters and sequence the converters by connecting PGOOD to the next converters ENABLE.

Last but not least: A ferrite bead keeps the converters switching noise from the PSU cable.

• Thank You, so as long as I respect the limits of capacity for the PSU I should be ok. I will only be drawing 4.5A at any given time. – Fiveapes Sep 29 '16 at 10:32