Current amplification

[Jacobk]

I am doing a project where around 750mA is need, how can i amplify the current while maintaining the voltage. I read a forum that said i should use a Darlington transistor, is this correct? And if so how would i do so?

 

[audioguru]

A darlington transistor has a voltage drop of 1.4V to 2.5V (base to emitter) when used an an emitter-follower that increases current.
An ordinary power transistor has a voltage drop of 0.7V to 1.5V when used as an emitter-follower.

An opamp can be used to reduce the voltage drop of a darlington to almost nothing if its supply voltage is a few volts more than the maximum output voltage.

 

[Jacobk]

So i should use a Darlington transistor and an op amp?
I am not that good with semiconductors

 

[colin55]

This statement does not make any sense at all:

I am doing a project where around 750mA is needed, how can I amplify the current while maintaining the voltage.

 

[crutschow]

I am doing a project where around 750mA is need (from what source?), how can i amplify the current (to what value of current?) while maintaining the voltage (what voltage?). I read a forum that said i should use a Darlington transistor, is this correct? And if so how would i do so?

Answer the questions in blue and we may understand what you are trying to do sufficiently to be of help.

 

[alec_t]

how can i amplify the current

Amplify what current?

 

[Jacobk]

I am trying to charge my phone from a nine. Volt. Battery using a 7805 and usb jack. It works Just a lot slower due to the low current, the voltage now is at 5.1v and the current at about 150 mA. Now is possible to use a op amp or transistor?

 

[Nigel Goodwin]

I am trying to charge my phone from a nine. Volt. Battery using a 7805 and usb jack. It works Just a lot slower due to the low current, the voltage now is at 5.1v and the current at about 150 mA. Now is possible to use a op amp or transistor?

No, you can't 'amplify' in that way.

The best way would be a switch-mode design, which can decrease the voltage at the same time as increasing the current (in a similar way to how a transformer does for AC).

But a 9V battery is a VERY, VERY poor choice - AA's would be much better, try the Minty Boost https://www.ladyada.net/make/mintyboost/

 

[ChrisP58]

A transistor allows a small current to control a larger current. But they cannot "make" current. The new current still needs to come from somewhere.

An audio amplifier does not make new power. It takes a small signal from your MP3 player and amplifies it to drive a lot more power into a big speaker. But the new power comes from the wall plug.

 

[Jacobk]

How does the mintyboost work? I followed the link and it didn't say how ot show a schematic.

 

[audioguru]

How does the mintyboost work? I followed the link and it didn't say how ot show a schematic.

The IC drives the inductor with a square-wave signal. The square-wave turns on and off and on and off etc.
Each time it turns off it produces a high voltage flyback spike of voltage that is rectified and filtered.
Pin 6 on the IC senses the output voltage and regulates the voltage.

You cannot get higher voltage for nothing. It increases the current from the battery so that the input and output powers are the same.

 

[ChrisP58]

How does the mintyboost work? I followed the link and it didn't say how ot show a schematic.

There is a schematic under the 'download' link at the left of the page.