Dynamic power control circuit

An apparatus, comprising:

• a system circuit comprising a positive lead for receiving power at a first node from a first output of an external power source;
• at least one battery comprising a positive lead for receiving power at a second node from a second output of the external power source;
• a controlled resistor comprising a first lead coupled to the first node and a second lead coupled to the second node, the controlled resistor causing a high impedance path between the first node and the second node when the controlled resistor is off, the controlled resistor controlling a level of impedance between the first node and the second node when the controlled resistor is on, the controlled resistor further comprising an input for controlling the level of impedance and turning the controlled resistor on or off;
• and
• a control circuit comprising a first input coupled to the first node, a second input coupled to the second node, a logical input coupled to a component configured to cause a logical signal at the logical input indicating that the external power source is active or inactive, and the control circuit comprising a control output coupled to the input of the controlled resistor, and the control circuit is configured to cause the controlled resistor to vary the level of impedance between the first node and the second node to maintain a predetermined voltage difference between a voltage of a first signal at the first input and a voltage of a second signal at the second input, when the logical signal at the logical input indicates that the external power source is active and when the voltage of the first signal at the first input is lower than the voltage of the second signal at the second input by a threshold.

A method for controlling level of impedance between a first node for receiving power from a first output of an external power source and a second node for receiving power from a second output of the external power source, the method comprising:

• receiving a signal from the first node coupled to a positive lead of a system circuit;
• receiving a signal from the second node coupled to a positive lead of at least one battery;
• receiving a logic signal from the external power source, the logic signal indicating activation or deactivation of the external power source;
• regulating the level of impedance between the first node and the second node to maintain a voltage difference between the first node and the second node based, at least in part on, the signal from the first node, the signal from the second node, and the logic signal.