Comparator circuit for generating a control signal corresponding to a difference voltage between a battery voltage and a power supply voltage

A comparator circuit for controlling a switch that couples a battery and a power supply to a circuit, the comparator circuit comprising:

• a first transistor having a first electrode for receiving a first power supply voltage, a control electrode for receiving a battery voltage, and a second electrode wherein said first transistor is configured as a voltage follower;
• a second transistor having a first electrode and a control electrode coupled in common to said second electrode of said first transistor, and a second electrode;
• a third transistor having a first electrode and a control electrode coupled in common for receiving said first power supply voltage, and a second electrode;
• a fourth transistor having a first electrode coupled to said second electrode of said third transistor, a control electrode coupled to said control electrode of said second transistor, and a second electrode coupled to said second electrode of said second transistor;
• a current source having a first terminal coupled to said second electrode of said second transistor and a second terminal for receiving a second power supply voltage;
• an amplification stage having an input coupled to said second electrode of said second transistor and an output;
• a Schmitt trigger having an input coupled to said output of said amplification stage and an output;
• and
• the switch having a first input for receiving said first power supply voltage, a second input for receiving said battery voltage, a control input coupled to said output of said Schmitt trigger, and an output coupled to the circuit wherein the comparator circuit enables the switch to couple said first power supply voltage to the circuit when said first power supply voltage is greater than said battery voltage and wherein the comparator circuit enables the switch to couple said battery voltage to the circuit when said battery voltage is greater than said first power supply voltage.