Multiple power path management with micro-energy harvesting

1. A power converter circuit comprising:

an output port configured for electrical coupling to a variable circuit load;

a first input port configured for electrically coupling to an energy harvest source;

an input/output port configured for electrically coupling to a second energy source;

a first circuit path from the energy harvest source to the second energy source at the input/output port and to the variable load at the output port;

a second circuit path from the second energy source to the output port;

a cold start circuit configured to produce a first voltage level at the output port by charging a capacitor at the output port using energy of the energy harvest source; and

a main converter circuit configured to produce a second regulated voltage level at the input/output port using energy of the energy harvest source when the voltage at the output port capacitor is above a specified voltage value and to use the energy of the capacitor at the output port during startup of the main converter circuit.

2. The power converter circuit of claim 1 including:

a second input port configured for electrical coupling to a third energy source, wherein the power converter circuit includes a third circuit path from the second input port to the output port; and

a charging control circuit configured to activate energy delivery to the circuit load from the second energy source when a voltage at the second energy source is above a specified cutoff voltage value, and to activate energy delivery to the circuit load from the third energy source when the voltage at the second energy source is less than the specified cutoff voltage value.

3. The power converter circuit of claim 2 , wherein the charging control circuit includes a switch circuit configured to prevent the third energy source at the second input port from charging the second energy source.

4. The power converter circuit of claim 2 , wherein the charging control circuit includes a switch circuit configured to prevent the main converter circuit and the second energy source from charging the third energy source.

5. The power converter circuit of claim 2 , wherein the charging control circuit is configured to activate energy delivery to the circuit load from the second energy source when a voltage of the second energy source at the input/output port plus a specified offset voltage value is greater than a voltage of the third energy source at the second input port, and activate energy delivery from the third energy source when the voltage of the second energy source plus the specified offset voltage value is less than the voltage of the third energy source.

6. The power converter circuit of claim 2 , wherein the charging control circuit includes a first switch circuit to activate energy delivery to the circuit load from the third energy source when a voltage of the third energy source at the second input is greater than a voltage at the circuit load at the output port by less than a second specified voltage value, and includes a second switch circuit to activate energy delivery to the circuit load from the third energy source when the voltage of the third energy source is greater than the voltage at the circuit load by more than the second specified voltage value.

7. The power converter circuit of claim 2 , wherein the charging control circuit includes a switch circuit configured to disconnect the output port from the input/output port when a voltage at the input/output port decreases below a specified shutdown voltage.

8. The power converter circuit of claim 1 , wherein the first circuit path is configured to electrically couple an inductor to a switching circuit node of the power converter circuit, wherein the main converter circuit is configured to provide a switching cycle using the switching circuit to provide the second regulated voltage.

9. The power converter circuit of claim 8 , including a switch circuit, wherein the cold start circuit includes a charge pump circuit to charge the output port capacitor, and wherein the switch circuit is configured to provide the energy of the output port capacitor to the main converter circuit when the voltage at the output port capacitor satisfies the specified voltage value.

10. The power converter circuit of claim 8 , wherein the main converter circuit includes a boost converter topology.

11. An energy harvest system comprising:

a variable system load;

an energy harvest source, wherein the energy harvest source has an energy density insufficient to meet a peak energy requirement of the system load;

a rechargeable energy source; and

a power converter circuit, the power convert circuit including:

an output port configured for electrical coupling to the system load;

a first input port configured for electrically coupling to the energy harvest source;

an input/output port configured for electrically coupling to the rechargeable energy source;

a first circuit path from the energy harvest source to the rechargeable energy source at the input/output port and to the variable load at the output port;

a second circuit path from the rechargeable energy source to the output port;

a cold start circuit configured to produce a first voltage level at the output port by charging a capacitor at the output port using energy of the energy harvest source; and

a main converter circuit configured to produce a regulated voltage level at the input/output port using energy of the energy harvest source when the voltage at the output port capacitor is above a specified voltage value.

12. The energy harvest system of claim 11 , including a backup battery, wherein the power converter circuit includes:

a second input port configured for electrical coupling to the backup battery, wherein the power converter circuit includes a third circuit path from the second input port to the output port; and

a charging control circuit configured to activate energy delivery to the circuit load from the rechargeable energy source when a voltage at the second energy source is above a specified cutoff voltage value, and to activate energy delivery to the circuit load from the backup battery when the voltage at the rechargeable energy source is less than the specified cutoff voltage value.

13. The energy harvest system of claim 12 , wherein the charging control circuit includes a switching circuit configured to prevent the backup battery at the second input port from charging the rechargeable energy source, and to prevent the main converter circuit and the second energy source from providing charge to the backup battery.

14. The energy harvest system of claim 11 , wherein the energy harvest source includes at least one of a photovoltaic cell or a thermo-electric energy generator.

15. A method of operating an energy harvest system, the method comprising:

generating a cold start voltage level at an output port of the energy harvest system by charging a capacitor at the output port using energy of an energy harvest source electrically coupled to a first input port of the energy harvest system, wherein the output port is electrically coupled to a variable circuit load of the energy harvest system;

producing, with a power converter circuit, a regulated voltage level at an input/output port using energy of the energy harvest source when the voltage at the output port capacitor meets or exceeds a specified voltage value, wherein the input/output port is electrically coupled to a second energy source; and

starting up the power converter circuit using energy of the capacitor at the output port.

16. The method of claim 15 , including:

activating energy delivery to the circuit load from a second energy source, electrically coupled to a second input of the energy harvest system, when a voltage at the second energy source is above a specified cutoff voltage value, and

activating energy delivery to the circuit load from the third energy source when the voltage at the second energy source is less than the specified cutoff voltage value.

17. The method of claim 16 , including preventing the third energy source at the second input port from charging the second energy source.

18. The method of claim 16 , including preventing the power converter circuit and the second energy source from charging the third energy source.

19. The method of claim 16 , including:

activating energy delivery to the circuit load from the second energy source when a voltage of the second energy source at the input/output port plus a specified offset voltage value is greater than a voltage of the third energy source at the second input port; and

activating energy from the third energy source when the voltage of the second energy source plus the specified offset voltage value is less than the voltage of the third energy source.

20. The method of claim 16 , including:

activating energy delivery to the circuit load from the third energy source when a voltage of the third energy source at the second input is greater than a voltage at the circuit load at the output port by less than a second specified voltage value; and

activating energy delivery to the circuit load from the third energy source when the voltage of the third energy source is greater than the voltage at the circuit load by more than the second specified voltage value.