Energy supply circuit
A circuit portion is provided which includes an energy harvesting device producing a DC output; a DC-DC converter having an input connected to the DC output of the energy harvesting device; an output for connection to a load; and a monitoring module including a non-ohmic semiconductor element. The monitoring module is arranged to derive information relating to an output current flowing from the DC-DC converter by measuring a current through the non-ohmic semiconductor element. The monitoring module is arranged to adjust one or more parameters of the DC-DC converter based on the information relating to said output current flowing from the DC-DC converter.
1. A circuit portion comprising:
an energy harvesting device producing a DC output;
a DC-DC converter having an input connected to said DC output of the energy harvesting device;
an output for connection to a load; and
a monitoring module comprising a non-ohmic semiconductor element and arranged to derive information relating to an output current flowing from the DC-DC converter by measuring a current through said non-ohmic semiconductor element,
wherein the monitoring module is arranged to adjust one or more parameters of the DC-DC converter based on the information relating to said output current flowing from the DC-DC converter.
2. The circuit portion as claimed in claim 1 , wherein the non-ohmic semiconductor element comprises at least one transistor.
3. The circuit portion as claimed in claim 2 , wherein the transistor is configured selectively to disconnect the load.
4. The circuit portion as claimed in claim 2 , wherein the transistor is a first transistor and the monitoring module further comprises at least a second transistor arranged to pass a fixed proportion of the DC-DC converter output current passed by the first transistor.
5. The circuit portion as claimed in claim 1 , wherein the transistor forms part of a load switch.
6. The circuit portion as claimed in claim 1 , wherein the circuit portion comprises two or more load switches, each load switch providing a connection to a respective load.
7. The circuit portion as claimed in claim 6 , comprising two or more power paths, wherein the monitoring module is configured to monitor a sum of currents for the two or more power paths.
8. The circuit portion as claimed in claim 1 , wherein the DC-DC converter is a capacitor-based inductor-less DC-DC converter.
9. The circuit portion as claimed in claim 1 , wherein the DC-DC converter comprises a plurality of capacitors.
10. The circuit portion as claimed in claim 1 , wherein the adjustable parameters of the DC-DC converter comprise frequency and/or input impedance.
11. The circuit portion as claimed in claim 1 , wherein the monitoring module comprises a comparator in a comparator arrangement comprising a feedback loop.
12. The circuit portion as claimed in claim 11 , wherein the comparator arrangement comprises a Schmitt-trigger comparator.
13. The circuit portion as claimed in claim 11 , wherein the comparator receives one input derived from the current through the non-ohmic semiconductor element and another input from a variable reference voltage.
14. The circuit portion as claimed in claim 11 , wherein the feedback loop is arranged so that the monitoring module adjusts the one or more parameters of the DC-DC converter to maximise the current through the non-ohmic semiconductor element.