I have a battery supplying 5V@500mAh and an LED (the load) which draws 1000mA@5V (twice the current the battery supplies per hour).

I found some circuits that have NPN transistors only and other having Op-Amp and a MOSFET (for example How to design Current Amplifier circuit to amplify the signal current to 1A).

Can someone draw a circuit that can handle this boosting job?

And please in order to understand it more deeply, tell me why do I need an Op-Amp when using a MOSFET as an amplifier?

  • 2
    \$\begingroup\$ The units mAh and mA are not the same...your battery might be able to supply 1000mAh for about a half hour. On the other hand, I don't believe that you have a 5V "battery". Give us a link to the datasheet for your "battery". \$\endgroup\$ – Elliot Alderson Dec 9 '18 at 19:03
  • \$\begingroup\$ @ElliotAlderson adafruit.com/product/2078 combining adafruit.com/product/1578 \$\endgroup\$ – Danaro Dec 9 '18 at 22:19
  • \$\begingroup\$ Where would the amplifier circuit get the extra power from? \$\endgroup\$ – user253751 Dec 9 '18 at 23:51

No, the battery you plan to use will not be able to supply as much power as you want (unless you exceed the manufacturer's recommendations). You want 5W out of the power shield. With a 3.7V nominal battery voltage that means you need at least 1.35A from the battery itself...probably 1.5A after taking the efficiency of the dc/dc converter into consideration. That's a discharge rate of 3C for the battery you have selected, 3 times larger than the manufacturer's recommended current. You should probably look for a battery that can supply 2A continuously. Also, the power shield is right at the edge of it's capabilities if you ask for 1A continuously.

You can't "amplify" current and voltage from a battery. Power is conserved, so if you want 5W of power out you must provide at least 5W of power in. You can increase the voltage with a boost converter but you will get less current. Or, you can lower the voltage with a buck converter and get a larger current. In other words, there is no circuit in the known universe that can take 3.7V and 500mA input power and give you 5V and 1000mA output power.

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  • \$\begingroup\$ So can you please explain what this circuit does i.stack.imgur.com/9bx6I.jpg \$\endgroup\$ – Danaro Dec 10 '18 at 9:55
  • \$\begingroup\$ That circuit is a voltage regulator. The output voltage follows (is the same as) the input voltage. But the output voltage must always be less than the supply voltage and the output current can not be greater than the supply current. \$\endgroup\$ – Elliot Alderson Dec 10 '18 at 12:02

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