An active switch for electrically connecting and disconnecting a power source such as an energy harvester to a charge storage device is disclosed. The active switch allows a minimal amount of reverse back current flow from the charge storage device to the power source having a high off-resistance.
1. An energy harvesting system, comprising: an intermittent current limited power source; a device for storing charge; and an active switch comprising a positive power input, a negative power input and an output;
said active switch powered by said current limited power source, having said active switch positive and negative power input connected directly to said current limited power source and said active switch output connected in series with a charge terminal of said device for storing charge for electrically connecting and disconnecting the power source to the device wherein when disconnecting the power source from the storage device the active switch allows a minimal amount of reverse back current flow from the storage device to the power source and wherein a pull down resistor ensures said active switch shuts off when no power source is available.
2. The energy harvesting system according to claim 1 , wherein said active switch further comprises: a field effect transistor operated by a current directional detector.
3. The energy harvesting system according to claim 2 , wherein said current directional detector further comprises: a differential amplifier.
4. The energy harvesting system according to claim 2 , wherein said current directional detector further comprises: an operational amplifier.
5. The energy harvesting system according to claim 1 , further comprises: an active switch regulation/regulator circuit electrically connected between said power source and said active backflow switch.
6. The energy harvesting system according to claim 1 , wherein said device for storing charge is less than 500 mah.
7. An energy harvesting system, comprising:
an intermittent current limited power source; a device for storing charge; and
a field effect transistor comprising a gate, a drain and a source;
operated by a current directional detector comprising a positive input, a negative input and an output, having the source of the field effect transistor electrically connected to the positive input, the drain electrically connected to the negative input and the gate electrically connected to the output of said current directional detector;
said current directional detector powered by said current limited power source,
having said current directional detector positive and negative power input connected directly to said current limited power source wherein said field effect transistor and said current directional detector control electrically connects and disconnects the power source to the device wherein when disconnecting the power source from the device the combination of the field effect transistor and control current directional detector with a pull down resistor directly connected between said field effect transistor gate and source allows a minimal amount of reverse back current flow from the device to the power source.
8. The energy harvesting system according to claim 7 , wherein said current directional detector further comprises: a differential amplifier.
9. The energy harvesting system according to claim 7 , wherein said current directional detector further comprises: an operational amplifier.
10. The energy harvesting system according to claim 7 , further comprises: an active switch regulation/regulator circuit electrically connected between said power source and said device.
11. The energy harvesting system according to claim 7 , wherein said device for storing charge is less than 500 mah.
12. An active switch for use in energy harvesting systems comprising:
a field effect transistor, said field effect transistor comprising a gate, a drain and a source, said field effect transistor operated by an operational amplifier comprising a positive input, a negative input, and an output, having a pull down resistor directly connected between said field effect transistor gate and source to ensure electrically connecting and disconnecting a power source to a device, having said operational amplifier positive and negative power input connected directly to said current limited power source, whereby when disconnecting the power source from the device a minimal amount of reverse back current flow from the device to the power source is allowed.
13. The active switch according to claim 12 , wherein said current directional detector comprises: a differential amplifier.
14. The active switch according to claim 12 , wherein said current directional detector further comprises: an operational amplifier.
15. The active switch according to claim 12 , further comprises: an active switch regulation/regulator circuit.
16. The active switch according to claim 12 , wherein said power source is photovoltaic.
17. The active switch according to claim 12 , wherein said device is a battery.