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I have a source that can deliver 20mA and 4.5V (MAXIMUM). I need to boost the current to 1 A without using any further source. Also, the voltage should be maintained constant at 4.5V. is that possible with emitter- follower configuration\? if not is there any other solution

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    \$\begingroup\$ No, the law of conservation of energy applies. You want to take out more energy then you put in. \$\endgroup\$ – Oldfart Apr 22 at 10:09
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    \$\begingroup\$ Energy is the product of voltage, current, and time. If you need 4.5W constantly, then you can't get the needed power output. If you only need it sometimes, then you could charge a large capacitor from your low power source. Say you need 4.5W for 1 second. That's 4.5J of energy. You could store that amount in a large capacitor. It would take over 50 seconds to store up that amount of energy from your battery. So, high power for one second once a minute. \$\endgroup\$ – JRE Apr 22 at 10:17
  • \$\begingroup\$ You need a constant current of 1A? \$\endgroup\$ – Niteesh Shanbog Apr 22 at 10:18
  • \$\begingroup\$ what about if I boost the current and reduce the voltage at stage 1 , then at satage 2 I boost the voltage and then combine the output current of stage one with the output volltage of stage 2? \$\endgroup\$ – bondj Apr 22 at 10:22
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    \$\begingroup\$ If you only need the power intermittently you can look at the chance of adding a storage device like a capacitor, super-capacitor or a battery but this will not magically create more stored energy. \$\endgroup\$ – KalleMP Apr 22 at 10:50
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Short answer: NO

Electrical power, which is the rate at which electrical energy is transferred by an electric circuit is given by \$P = V*I\$.

The law of conservation of energy states that the total energy of an isolated system stays constant. Now you want to have an input power of 90mW and an output power of 4.5W which is clearly not possible.

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Input current 20mA, output current 1A, at the same voltage, that's a power ratio of 50:1. If you are happy with a small output duty cycle, you could achieve it with energy storage.

The size of energy store depends on the length of pulse you need. If you want a 1s pulse every minute, then that's quite a large capacitor, but a very small battery indeed. For 1mS every 100mS, a small capacitor would do. For one day every two months, a large battery.

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