Two-terminal protective device using parasitic energy harvesting
A two-terminal electrical protective device operates by harvesting energy from a small but non-zero voltage drop across a closed solid-state switch. From a default, open-circuit state, the device is remotely triggered by an AC signal to enter the desired conductive state. Power scavenged by an energy harvesting circuit while the device is in the conductive state, powers a gate drive circuit to hold the device in the conductive state for as long as current flows. When current stops, the device returns to the default open-circuit state.
1. An electrical circuit comprising:
a switch having an input, output, and control gate;
an energy harvesting circuit coupled to the input and output of the switch to collect power from a voltage drop across the switch; and
a gate control circuit coupled to the energy harvesting circuit and the control gate of the switch to maintain the switch in an ‘on’ state in response to power received from the energy harvesting circuit and to latch the switch off in response to no power being collected from the energy harvesting circuit.
2. The circuit of claim 1 wherein the gate control circuit controls the switch to maintain a minimum voltage for feeding the energy harvesting circuit over a wide range of currents through the switch.
3. The circuit of claim 1 wherein the switch is in an open state with no voltage applied to the control gate.
4. The circuit of claim 1 wherein the gate control circuit controls the switch to maintain a minimum voltage for feeding the energy harvesting circuit over a wide range of currents through the input and output of the switch.
5. The circuit of claim 1 wherein the energy harvesting circuit comprises a resonant converter having a turns ratio sufficient to convert the voltage drop for the gate control circuit to keep the switch in an on state while current is flowing through the switch.
6. The circuit of any of claims 1 and further comprising a zener diode coupled between the energy harvesting circuit and the input to cause the switch to turn on prior to avalanche.
7. The circuit of any of claims 1 and further comprising a rectifier coupled to the energy harvesting circuit that activates the energy harvesting circuit in response to an AC signal across the switch.
8. The circuit of any of claims 1 and further comprising a resonant filter coupled between the energy harvesting circuit and the switch to prevent turn on due to noise.
9. The circuit of any of claims 1 wherein the switch comprises a solid-state switch.
10. The circuit of any of claims 1 wherein the switch is configured to latch to a high impedance state in response to low current across the switch resulting in a low voltage at the gate of the switch.
11. A system comprising:
a plurality of photovoltaic (PV) modules coupled in series;
a plurality of switches coupled between pairs of the PV modules in series, wherein at least one of the switches comprises:
a switch having a high impedance latchable state;
an energy harvesting circuit coupled to the switch to collect power from the voltage drop across the switch; and
a control circuit coupled to the energy harvesting circuit to maintain the solid-state switch in an ‘on’ low impedance state and to latch the switch off in the high impedance state in response to no power being collected from the energy harvesting circuit.
12. The system of claim 11 and further comprising a master switch coupled to the series string of PV modules and switches, the master switch capable of stopping current flow in the series string.
13. The system of claim 12 wherein the switches latch to the high-impedance state in response to the master switch stopping current flow.
14. A method comprising:
harvesting energy from a disconnect switch while DC current is flowing through the switch;
generating a supply voltage from the harvested energy;
applying a voltage to a control gate of the disconnect switch, the voltage being generated by a control circuit coupled to the supply voltage; and
latching the disconnect switch in a high impedance state in response to a lack of DC current flowing through the switch.
15. The method of claim 14 and further comprising placing the disconnect switch in a conductive state in response to an AC signal applied to the disconnect switch, the disconnect switch comprising a solid-state switch.