Emitter follower using the NPN bipolar junction transistor, outputs 0.6V less than the input voltage that we give it. The input voltage just needs to provide a very small amount of current. The voltage will be held really well no matter how much current the load needs. The BJT will provide the power needed for demanding loads. Of course the BJT gets it’s power from the power supply, but the BJT is what regulates the power as far as the load is concerned.

Diagram

Emitter resistor and the load builds up a voltage that is the base voltage minus the approx. 0.6V B-E diode drop.

Practically all of the current that goes through the load will come from the power supply and through the collector to emitter. Hardly any current being provided by the signal voltage through the base to emitter.

The transistor will self regulate to make sure only enough current flows from collector to emitter to hold the emitter voltage to 0.6V less than the base voltage.

The extra emitter resistor is not always needed. Some loads however will throw off the voltage without the emitter resistor, so it is best to just always use one.

Video

Quick NPN BJT emitter follower set with trimpot voltage divider using 2N3904 transistor







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Portable solar panel with 5V USB output. I find it better to use the panel to charge a portable power bank, which can then be used to charge a cell phone, than to try to charge a cell phone directly.



One of my favorite portable power banks, this one has a better display than my version.

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