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I have a 24V/40A power supply with a foldback current limiter. And I need to connect 76 buck converters of 5V and 2A each to it. Since the current of the power supply is limited and considering that the input current of the buck converters is not constant, but has peaks.

Can the sum of the currents of the buck converters exceed 40A at any time?

In such a case, what happens to the output voltage when the current protector of the power supply acts?

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  • \$\begingroup\$ Do you understand how foldback current limiting works, in a general sense? \$\endgroup\$
    – SteveSh
    Oct 28, 2022 at 15:17
  • \$\begingroup\$ You should show a schematic of your buck converter and explain how much bulk capacitance you have in total. \$\endgroup\$
    – Andy aka
    Oct 28, 2022 at 15:20
  • \$\begingroup\$ If all buck converters are loaded fully, they need at least 79.2 % efficiency in order not to overload your 24 V supply. Do they? \$\endgroup\$
    – winny
    Oct 28, 2022 at 15:23
  • \$\begingroup\$ @SteveSh If I exceed the current limit, the foldback limiter would reduce the voltage, causing the buck converter to increase the duty cycle, drawing more current, and so on until the power supply goes into hiccup mode, I think. \$\endgroup\$
    – Monty Java
    Oct 28, 2022 at 15:42

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Each amplifier will draw about 0.5A (10W/(~80% efficency)/24V) max at the input. 0.5A * 76 is 38A so you won't exceed the 40A of the supply. (this is assuming an ~80 percent efficiency of the 5V converter, you'll have to check the datasheet because it varies by current, if it gets into the 70% range you might be in trouble.)

If you do exceed the supply, and it has current foldback limiting, the supply will go into constant current mode which will lower the voltage as more current is drawn.

Some supplies can have an undervoltage lockout and will just switch off if the voltage goes below a certain point.

Either way this could have unpredictable results. It's best to make sure you have adequate current for the load.

One thing you might want to consider is inrush current and total capacitance of the supply. Buck controllers have input capacitance, the total of the 76 buck regulators must not exceed the total rated load capacitance of the supply. There is also the problem of inrush current (mostly from the capacitors) but the capacitors will probably contribute the most inrush so you could just check the capacitance spec.

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  • \$\begingroup\$ At first I thought the same as you. But then I doubted, because the input current is not constant, it is 0.5 A on average, but it has peaks greater than 0.5 A in the duty cycle. So, if the peaks were to coincide, would there be a problem using that power supply? \$\endgroup\$
    – Monty Java
    Oct 28, 2022 at 15:36
  • \$\begingroup\$ No, because you aren't exceeding 0.5A. Usually a buck controller also has input capacitors for short term storage which should smooth out \$\endgroup\$
    – Voltage Spike
    Oct 28, 2022 at 15:40

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