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I have a battery pack at ~9VDC wired to a buck converter which steps down the voltage to 5VDC to power an electronic device.

The problem is that it sometimes supplies enough current on the device start-up to prevent the voltage from dropping too low and at other times it does not. Usually it does not, but the fact that it's fine sometimes makes me think I'm borderline on having enough power.

Is it possible to add a capacitor or other component somewhere into the layout in order to supply some additional current momentarily to get past the start-up peak draw at which point the current from the battery pack may be sufficient?

====EDIT Oct 15 2020====

For more details as requested:

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    \$\begingroup\$ Maybe. But it would be good to get a definite idea of what is going wrong first. Do you have an oscilloscope so you can probe the 9V power and the 5V power and capture exactly what is happening when you connect the battery? Does the DC-DC regulator have any "enable" pins on it? Are there already a lot of capacitors on the 9V rail? One thing that might be happening is that the 5V rail is crashing due to 5V inrush. It might not be the 9V at all. Reducing capacitance on 5V could help. \$\endgroup\$ – mkeith Oct 15 at 3:30
  • \$\begingroup\$ If you could share a lot more information I think you would have a better chance of getting a good answer. Like what is the DC-DC converter? What is on the 5V rail? How much power does it use? How about a schematic? What kind of 9V batter do you have? Have you tried powering it with a power supply? Does it behave any differently? \$\endgroup\$ – mkeith Oct 15 at 3:32
  • \$\begingroup\$ The switched input inductor changes the input impedance and with a soft start Reference voltage for PWM, you can prevent UVP shutdown. Look for ways to do that so that your battery is not overloaded. all batteries have ESR which creates that voltage drop by the transient load. learn to regulate it or try an ICL from Digikey, but these are less accurate and have hysteresis. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Oct 15 at 4:55
  • \$\begingroup\$ @mkeith I've added more details to the question - thanks. I'm not skilled in EE so don't fully understand what you and Tony posted. I do not have an oscilloscope, but I can see the voltage readout on the buck converter dropping during boot up. \$\endgroup\$ – g491 Oct 15 at 7:56

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