Using a few of electronic components, we can create a power supply with variable output  voltage from 2 volts to 15 volts. This circuit using LM317 IC component which is a positive voltage regulator. This IC has the ability to drain a small electric current, to improve its capability, the output of the IC LM317 is inserted into 2n3055 power transistor with current capability up to 15 Amperes (with using a good heat sink)

Figure 1. Simple variable power supply.

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