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I am thinking about utilizing a step-down regulator chip for a synchronous buck converter. I figured a basic laptop power supply would work for this (fit some connectors on it). I have done the simulations utilizing a 12v DC supply for the chip. At max duty cycle (99%), the input current pulls just under 6 amps. Does this mean I would need a 12V 6A supply? Application is battery charging, so I'm using it to produce a consistent output current. Just a bit confused, know basic buck theory but not as familiar with chips.

Thanks

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    \$\begingroup\$ What's your output voltage? \$\endgroup\$ – Nick Johnson Nov 18 '15 at 17:17
  • \$\begingroup\$ In addition to Nick's question, what is the maximum power output (V * I) of your buck converter in the worst case? Probably the worst case would be during CC charging with the battery voltage near the highest point where CC is still allowed. \$\endgroup\$ – mkeith Nov 18 '15 at 17:31
  • \$\begingroup\$ Output voltage comes out to 4.2v at steady state (for 5 amp output). For my battery I need to have a max charge current of 5 amps. The battery can be charged to 4.1v, so I wasn't 100% if I had to then charge it at that voltage or if simply pouring current into the battery the voltage will rise. The charge current can be changed by user so I was going to use pwm to accomplish that. \$\endgroup\$ – Jacob Deen Nov 18 '15 at 17:41
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    \$\begingroup\$ 4.2 * 5 = 21 Watts. Bump that up by 20% to account for loss. So you need at least 25 Watts. Make sure you read all the fine print about cooling and temperature de-rating, etc for the supply. Your 12V 6A supply is 72W, so that is more than enough if you want to go that way. Another option is to use one of those laptop power supplies. They are usually around 20V and 45 W or more. It may not be optimal to buck down from such a high voltage. Look at the efficiency under those conditions. \$\endgroup\$ – mkeith Nov 19 '15 at 4:11
  • \$\begingroup\$ Ya that definitely makes sense with the wattage. I was just getting a bit confused on the basic theory behind it. I know the buck drops voltage increases current, but if a simulation is pulling 5.5 amps at the input I believe I would need a 12v 6A supply to be able to do the high end duty cycle stuff then. \$\endgroup\$ – Jacob Deen Nov 19 '15 at 22:29
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4.2 * 5 = 21 Watts. Bump that up by 20% to account for loss. So you need at least 25 Watts. Make sure you read all the fine print about cooling and temperature de-rating, etc for the supply. Your 12V 6A supply is 72W, so that is more than enough if you want to go that way. Another option is to use one of those laptop power supplies. They are usually around 20V and 45 W or more. It may not be optimal to buck down from such a high voltage. Look at the efficiency under those conditions to see if it will work for you.

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