A voltage regulator circuit for use with an integrated circuit (IC) chip and an external voltage source includes a first transistor and a second transistor. The first transistor has the emitter thereof electrically connected to the external voltage source and the collector thereof electrically connected to the IC chip via a power input pin. The second transistor has the collector thereof electrically connected to ground, the base thereof electrically connected to the IC chip via a voltage-regulation control pin, and the emitter electrically connected to the base of the first transistor. The voltage regulator circuit is utilized for regulating a source voltage received from the external voltage source via the first transistor in response to a current signal flowing through the voltage-regulation control pin to have the regulated voltage inputted into the integrated circuit chip via the power input pin.