Power source switchover apparatus and method
An apparatus for switching from a first power supply to a second power supply. The embodiment may detect the charge or voltage of both the first and second power supply, and power a device from the power supply having the greatest voltage or charge. A single boost converter is used regardless of which power supply is providing power.
1. A battery-switching apparatus for switching between at least a first battery and a second battery, comprising:
a first battery compartment operative to house a first battery and having a first positive terminal and a first negative terminal;
a second battery compartment operative to house a second battery and having a second positive terminal and a second negative terminal;
a single boost converter connected to each of the first and second battery compartments; wherein
the boost converter is operative to draw power from one of the first and second battery compartments having the highest voltage;
a first capacitor, wherein the first capacitor is enabled when a voltage of the first battery exceeds a voltage of the second battery; and
a second capacitor, wherein the second capacitor is enabled when a voltage of the second battery exceeds a voltage of the first battery;
the first positive terminal of the first battery compartment is connected directly to a first common node;
the second positive terminal of the second battery compartment is connected directly to the first common node;
the first negative terminal of the first battery compartment is connected to a first input of a comparator through a second common node; and
the second negative terminal of the second battery compartment is connected to a second input of the comparator through a third common node.
2. The battery-switching apparatus of claim 1 , wherein:
the comparator is electrically connected to each of the first and second battery compartments; further wherein
the comparator is operative to switch to the one of the first and second battery compartments having the highest voltage in order to supply power to the boost converter.
3. The battery-switching apparatus of claim 2 , further comprising:
a first transistor operatively connected to the comparator; and
a second transistor operatively connected to the comparator; wherein
the first and second transistors switch states according to an output of the comparator.
4. The battery-switching apparatus of claim 3 , wherein:
the first and second transistors are each electrically connected to the output of the comparator; and
the first transistor switches off when the second transistor switches on.
5. The battery-switching apparatus of claim 1 , wherein:
a voltage at the second common node exceeds a voltage at the third common node when a cell voltage of a first battery in the first battery compartment exceeds a cell voltage of the second battery in the second battery compartment.
6. The battery-switching apparatus of claim 1 , wherein:
a voltage at the third common node exceeds a voltage at the second common node when a cell voltage of the second battery exceeds a cell voltage of the first battery.
7. The battery-switching apparatus of claim 1 , further comprising:
a first capacitor electrically connected to the second common node at a first side and electrically connected to a ground at a second side; and
a second capacitor electrically connected to the third common node at a first side and electrically connected to the ground at a second side.
8. The battery-switching apparatus of claim 7 , wherein:
the first capacitor is operative to charge from a cell voltage of the first battery; and
the second capacitor is operative to charge from a cell voltage of the second battery.
9. The battery-switching apparatus of claim 8 , wherein:
as the first capacitor charges, a voltage of the second common node rises; and
as the second capacitor charges, a voltage of the third common node rises.
10. The battery-switching apparatus of claim 9 , wherein:
as the cell voltage of the first battery drops, the charge of the first capacitor drops and the voltage of the second common node drops; and
as the cell voltage of the second battery drops, the charge of the second capacitor drops and the voltage of the third common node drops.
11. The battery-switching apparatus of claim 1 , further comprising an output transistor operatively connected to an output of the boost converter.
12. The battery-switching apparatus of claim 11 , further comprising:
a peak detector operatively connected to the output of the boost converter; and
a voltage detector operatively connected to the output of the peak detector.
13. The battery-switching apparatus of claim 12 , wherein:
the output transistor is operative to switch on when the voltage detector outputs a voltage above a voltage threshold;
an output voltage at an output node is zero until the output transistor switches on; and
the output voltage at the output node exceeds zero after the output transistor switches on.
14. The battery-switching apparatus of claim 1 , wherein the boost converter is operative to draw power from the one of the first and second battery compartments having the highest voltage until the voltages of both the first and second battery compartments are below 0.9 volts.
15. The battery-switching apparatus of claim 1 , wherein the output of the boost converter supplies a bias voltage for operation of at least one transistor operatively connected thereto.
16. A method for switching between at least a first battery and a second battery, comprising:
detecting a first voltage across the first battery;
detecting a second voltage across the second battery;
determining which of the first voltage and second voltage is greatest, further comprising:
enabling a first capacitor and disabling a second capacitor in the event the first voltage exceeds the second voltage, wherein the operation of disabling the second capacitor comprises:
enabling a third capacitor; and
employing an output of the third capacitor to disable the second capacitor;
disabling the first capacitor and enabling the second capacitor in the event the second voltage exceeds the first voltage; and
in response to determining which of the first voltage and second voltage is greatest, supplying power from the greatest voltage to a single boost converter.
17. The method of claim 16 , wherein the single boost converter is electrically connected to both the first battery and second battery.
18. The method of claim 17 , wherein the operation of supplying power from the greatest voltage to a single boost converter comprises disabling the one of the first and second voltages not supplying power to the single boost converter.
19. The method of claim 18 , wherein at least one transistor is used to disable the one of the first and second voltage not supplying power to the single boost converter.
20. The method of claim 19 , further comprising:
detecting a bias voltage;
in the event the bias voltage exceeds a threshold, activating an output transistor; and
in response to activating the output transistor, outputting an output voltage.
21. The method of claim 18 , further comprising:
charging a peak detector capacitor from an output of the boost converter; and
once the peak detector capacitor is fully charged, detecting the bias voltage.
22. The method of claim 18 , wherein the operation of determining which of the first voltage and second voltage is greatest is executed by a comparator.
23. The method of claim 20 , further comprising the operation of charging an output capacitor from the output voltage after activating the output transistor.
24. The method of claim 19 , further comprising:
detecting when the greatest voltage falls below the one of the first and second voltages that is not the greatest voltage;
in response to detecting when the greatest voltage falls below the one of the first and second voltages that is not the greatest voltage, disabling the one of the first and second voltages corresponding to the greatest voltage; and
further in response to detecting when the greatest voltage falls below the one of the first and second voltages that is not the greatest voltage, enabling the one of the first and second voltages not corresponding to the greatest voltage.
25. The apparatus of claim 1 , wherein:
the first capacitor charges from the first battery only when enabled; and
the second capacitor charges from the second battery only when enabled.