Claims:We Claim:
1. An energy-harvesting electronic switch comprising:
an non-neutral power supply;
an AC switch arrangement connected across the non-neutral power supply;
at least one rectifier diode connected in anti-series across the AC switch arrangement;
a boost converter coupled to the AC switch arrangement;
a control unit connected across the booster unit; and
an auxiliary power source connected across the AC switch arrangement.
2. The energy-harvesting electronic switch of claim 1, wherein the AC switch arrangement comprises of
at least two MOSFETs connected in series; and
a diode connected across each MOSFET.
3. The AC switch arrangement of claim 2, wherein the series connection of the MOSFETs is achieved by
connecting the drain terminal of first MOSFET to the live terminal of the AC power supply;
connecting the drain terminal of second MOSFET to the terminal of an electrical appliance;
connecting the source terminal of the MOSFETs to ground; and
connecting the gate terminal of the first MOSFET to the gate terminal of the second MOSFET.

4. The AC switch arrangement of claim 1, wherein additionally a DC load is connected to the MOSFET’s gate terminal.
5. The switch of claim 1, wherein the DC load is at least one selected from a list comprising of sensors, actuators, transducers and switches.
6. The switch of claim 1, wherein the boost converter is configured to control the two MOSFETs.
7. The switch of claim 1, wherein the connection of the boost converter results in self-oscillation of the energy-harvesting electronic switch during the ON state of the AC switch arrangement.
8. The switch of claim1, wherein the control unit comprises of at least two relays; a zero cross detector; an edge triggered flip-flop; and a control interface.
9. The control unit of claim 8, wherein the relays are configured to operate complementarily to yield DC power.
10. The control unit of claim 8, wherein the control interface is at least one selected from a list comprising of sensors, transducers, signal interfaces, microprocessors, timers and switches.
11. The energy-harvesting electronic switch of claim1, wherein an auxiliary power source is connected across the AC switch arrangement and coupled to the boost converter.
12. The auxiliary power source of claim 11, wherein the auxiliary power source is configured to supply power during OFF state of the AC switch arrangement.
13. The auxiliary power source of claim 11, wherein the auxiliary power source is additionally configured to maintain self-oscillation frequency at higher temperature and threshold voltage of the MOSFETs respectively.
14. The switch of claim 1, wherein the energy-harvesting electronic switch is capable of full angle conduction to yield DC power.
, Description:ENERGY-HARVESTING ELECTRONIC SWITCH
FIELD OF INVENTION
The invention generally relates to the field of circuits and particularly to a method for energy harvesting.
BACKGROUND
A switch is a device that is included in an electrical and/or electronic circuit to activate or deactivate either a part of the circuit or the entire circuit. The electrical and/or electronic circuit contains at least one switch to activate or deactivate the whole or certain part of the circuit. The switches are categorized into mechanical switches and electrical or electronic switches. The mechanical switch is further categorized on basis of their operation. The categories include but are not limited to single pole single throw switch, SPST; single pole double throw switch SPDT; double pole single throw switch, DPST; double pole double throw switch, DPDT and two pole six throw switch, 2P6T. The electrical and/or electronic switches are categorized on the basis of current and voltage rating like mechanical switches. The most widely used electronic switches are transistors, MOSFETs and relays.
Generally, household and commercial power distribution wiring is controlled through mechanical switches. The mechanical switches are positioned in one line of a two line AC distribution system. Mechanical switches are manually operated by user. The electrical and/or electronic switch is controlled automatically by microcontroller or microprocessor. The mechanical switches have one significant disadvantage of inability to support automatic function activating devices. Examples of automatic function activation devices include but are not limited to sensors, actuators, knobs, sliders, transducers and electronic switches. In order to use automatic functions mechanical switches are substituted by electronic switching devices. Examples for automatic function includes but are not limited to turning on the lights when a person enters a room, controlling home appliances remotely and adjusting light intensity, temperature and music level in a room as preference of a person detecting the person’s presence. The electronic switching devices used for enabling automatic functions are not self powered. They need to be powered using the power line. Therefore, additional wirings are done to the conventional system to adopt the automatic functions. The disadvantages are the costs, the disruption in the installing a wired system and the potential complexity.
Numerous self-powered AC switches are known to exist that predominantly employs TRIACs to obtain the auxiliary power supply. The self-powered AC switches employing TRIACs is single gate controls conduction in both directions. One method known to exist employs the dV/dT method to self-power an AC switch. One advantage of the dV/dT method is that the rate of change of voltage across the AC switch can be varied to turn ON the switch, even if the voltage across the switch is small. One significant disadvantage of the method is the non operability of the method during static-ON operation of the switch. A further disadvantage of the method is the restriction of the application of the switch to AC-AC converters. Further, the TRIAC based self powered AC switches exhibit high power losses and often yield distorted load current waveforms due to the use of phase-control.
Hence, a need exists for an electronic switch yielding DC power capable of powering smart functions for controlling alternating current (AC) load. Further, there is a need for an electronic switch enabling operation of power devices that can retrofit into existing conventional mechanical switches used in households and commercial power distribution wiring.

BRIEF DESCRIPTION OF DRAWINGS
So that the manner in which the recited features of the invention is understood in detail, some of the embodiments are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
FIG.1 shows a detailed schematic diagram representation of the energy harvesting electronic switch for AC application, according to an embodiment of the invention.
FIG.2 shows the circuit for control unit of the energy harvesting electronic switch for AC application, according to an embodiment of the invention.
FIG.3 shows the circuit for switch arrangement and boost converter of the energy harvesting electronic switch for AC application, according to an embodiment of the invention.
FIG.4 shows the circuit for generation of auxiliary power supplies within the switch, according to an embodiment of the invention.
FIG 5(a) shows the voltage drop across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG 5(b) shows the gate-drive voltage across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG 5(c) shows the auxiliary power source voltage across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG 5(d) shows the voltage drop across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG 5(e) shows the gate-drive voltage across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG 5(f) shows the auxiliary power source voltage across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention.
FIG. 6(a) shows the voltage drop across the MOSFETs for resistive load of 5k? during OFF state of the electronic switch, according to an embodiment of the invention.
FIG. 6(b) shows the voltage drop across the MOSFETs at a temperature of 90º for resistive load of 50? during OFF state of the electronic switch, according to an embodiment of the invention.
SUMMARY OF THE INVENTION
One aspect of the invention provides an energy harvesting electronic switch circuit. The energy harvesting electronic switch circuit includes a non- neutral power supply. The energy is harvested using the non-neutral power supply. An AC switch arrangement is connected across the non-neutral power supply. The AC switch arrangement includes two MOSFETs. Rectifier diodes in anti-series across the AC switch arrangement. A boost converter is coupled to the AC switch arrangement. The boost converter is capable of controlling the two MOSFETs together with the rectifier diodes. The boost converter connection results in self-oscillation of the energy-harvesting electronic switch during the ON state of the AC switch arrangement. A control unit is connected across the boost converter. The auxiliary power source is connected across the AC switch arrangement and coupled to the boost converter. The auxiliary power source is used to supply power during OFF state of the AC switch arrangement. The energy-harvesting electronic switch is capable of full angle conduction to yield DC power.

DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide an energy harvesting electronic switch circuit that advantageously employs MOSFET for harvesting energy. The construction, operation and application of the switch shall be described in detail herein below. FIG.1 shows a block diagram representation of the energy harvesting electronic switch, according to an embodiment of the invention.
The electronic switch 100 has two terminals 101 and 103. The first terminal 101 is connected to phase line of an AC power supply (not shown). In one example of the invention, the AC power supply is non-neutral power supply. The second terminal 103 is connected in series with an AC load 105. An AC switch arrangement 107 is connected across the terminals 101 and 103. Two diodes 109 and 111 are connected in series across the AC switch arrangement 107. Further, the diodes 109 and 111 are in an anti-series arrangement. A boost converter 113 is connected to the AC switch arrangement 107. A control unit 115 is connected across the boost converter 113. An auxiliary power source 117 is connected across the AC switch arrangement 107. The auxiliary power source 117 is also coupled to the boost converter 113. The boost converter 113 is capable of amplifying the threshold voltage.
The boost converter 113 is capable to self-oscillate the electronic switch 100 during ON state of the AC switch arrangement 107. The boost converter 113 initiates the auxiliary power supply 117 generation. The boost converter 113 is discussed in detail later in the description. The voltage drop across the AC switch arrangement 107 is rectified by the diodes 109, 111. The rectified voltage is availed across the common point of the diodes 109,111 and the electronic switch 100 circuit ground. The electronic switch circuit 100 described herein briefly shall be explained in detail below.
FIG.2 shows the circuit for control unit of the energy harvesting electronic switch for AC application, according to an embodiment of the invention.
The control unit 115 is connected across the boost converter 113. The control unit 115 includes means for controlling energy flow 115a 115b, a zero cross-detector 115c, an edge-triggered flip-flop 115d, and a control interface 115e. In one embodiment of the invention relays are employed as means for controlling energy flow. Examples of components that are capable of controlling energy flow include but are not limited to toggle switch, ON/OFF switch, knob, slide and any controllable electronic switch. The first terminal of the first relay 115a is connected to the first terminal of the boost converter 113. The second terminal of the first relay 115a is connected to ground. The first terminal of the second relay 115b is connected to the second terminal of the boost converter 113. The second terminal of the second relay 115b is connected to a common point on the connection between the rectifier diodes 109,111. The relay 115a used is a low-voltage device with a high peak current capability. The relay 115b used is a high-voltage low-current device. The zero-cross detector 115c is connected across the non-neutral power supply. The ON-OFF and OFF-ON state of the AC switch 107 is carried at zero-crossing instant of the voltage across the non-neutral power supply and the AC load 105 current respectively. The zero crossing timing is obtained by comparing the voltage across the AC switch arrangement with respect to the electronic ground.
The edge-triggered flip-flop 115d is coupled to the zero-cross detector 115c. Further, one terminal of the edge-triggered flip-flop 115d is connected to the relay 115a and another terminal is connected to the relay 115b. The edge-triggered flip-flop 115d used is including but not limited to positive edge triggered flip-flop, negative edge triggered flip-flop, J-K flip-flop and S-R flip-flop. The edge-triggered flip-flop 115d triggers the relays 115a, 115b to operate complementarily. The edge-triggered flip-flop 115d is clocked by the output from the zero crossing detector115c. The output from the zero crossing detector 115d is the zero-crossing time obtained by the comparison of the voltage across the AC switch arrangement 107 with respect to the electronic ground. The ON-OFF and OFF-ON state of the AC switch 107 is carried at zero-crossing instant of the voltage across the AC non-neutral power supply.
The control interface 115e is coupled to the edge-triggered flip-flop 115d. The control interface 115e is connected to the data input of the edge-triggered flip-flop 115d. The control interface 115e is capable to detect the state of the AC load 105, wherein the state may be defined as the operational condition of the AC load 105 connected to the electronic switch 100 which includes but is not limited to ON condition, OFF condition and variation in parameters (such as light intensity, temperature, humidity and so on). Examples for the control interface 115e include but are not limited to sensors, transducers, signal interfaces, microprocessors, timers, knobs, sliders and switches.

FIG.3 shows the circuit for switch arrangement and boost converter of the energy harvesting electronic switch for AC application, according to an embodiment of the invention. The energy harvesting electronic switch 100 includes the AC switch arrangement 107 and the boost converter 113. The AC switch arrangement 107 further includes two MOSFETs 301,303 connected in common-source configuration. In one embodiment of the invention, the MOSFET used is an n-channel MOSFET. The drain terminal of the first MOSFET 301 is connected to the live 101 terminal of the AC power supply. The drain terminal of the second MOSFET 303 is connected to the AC load 105. The gate terminal of the first MOSFET 301 is connected to the gate terminal of the second MOSFET 303. The source terminals of the MOSFETs 301,303 are connected to the ground. Additionally, a direct current (DC) load 309 is connected to the MOSFETs 301,303.
Two diodes 305,307 are connected across each MOSFET. The diodes 305 and 307 are connected across each MOSFET 301 and 303 respectively by connecting the anode of the diode to the source terminal of the MOSFET and cathode of the diode to the drain terminal of the MOSFET. Examples of the diode 305,307 include but are not limited to snubber diode, TVS diode, Schottky diode and freewheeling diode. The diodes connected across MOSFET provide protection against overvoltage and dV/dT.
The MOSFETs 301,303 are controlled with addition of two rectifier diodes 109,111. The two rectifier diode 109,111 rectifies the voltage drop across the MOSFETs 201,202. The rectified output is availed across the common point of the diodes 109,111 and the electronic switch 100 ground. While the first MOSFET 301 may be forward-conducting and moves into saturation during recharge periods, the second MOSFET 303 may remain entirely in linear region, performing synchronous rectification and thereby reduces the conduction losses within the AC switch 107. A DC load 309 is connected on a common point on the connection between the gate terminals of the MOSFETs 301,303 and the electronic switch 100 ground. The DC load 309 is a device including but not limited to microcontrollers, microprocessors, sensors, actuators, transducers and switches. A minimum voltage equal to the threshold voltage of the MOSFETs 301,303 is availed for the DC load 309.
The boost converter 113 includes a storage capacitor 311, a diode 313, an emitter resistor 315, one bipolar junction transistor (BJT) 317, an inductor 319 and a voltage source 321. The positive terminal of the voltage source 321 is connected in series to the second terminal of the relay 115b. The first terminal of the inductor 319 is also connected in series with the second terminal of the relay 115b. The collector pin of the BJT 315 is connected to the second terminal of the inductor 319. The base pin of the BJT 317 is connected to the second terminal of the voltage source 321. The emitter resistor 315 is connected to the emitter pin of the BJT 206. The anode of the diode 313 is connected to a common point on connection between the inductor 319 and the BJT 317. The storage capacitor 311 is connected in series to the cathode of the diode 313 and connected to the electronic switch 100 ground.
The MOSFETs 301,303 in the AC switch arrangement 107 are operated by the boost converter 113 in their linear and saturation regions alternatively to achieve self-oscillation of the electronic switch 100. The boost converter 113 is powered by the voltage drop across the MOSFETs 301,303 during ON-state of the AC switch arrangement 107 to obtain an energy harvesting or self-oscillating DC switch. The intermittent saturation and enhancement of the MOSFETs 301,303 allows the boost converter 113 to accumulate and transfer energy from across the AC switch 107 to the storage capacitor 311 and the gate of the MOSFETs 301,303 without turning off the AC switch 107. The boost converter 113 energizes the inductor 319 to peak current values varying with the square-root of the instantaneous AC load 105 current. Further regulation is applied to the threshold voltage of the MOSFETs 301,303 by means of a low-dropout (LDO) or a shunt regulator.
When the peak AC load 105 current is less than the peak inductor 319 current, the BJT 317 conducts the entire AC load 105 current through the BJT 317. The BJT 317 is turned off as soon as the intended peak inductor 319 current is reached. During the conduction of current through the transistor 317, the gate voltage and threshold voltage of the MOSFETs 301 and 303 is very less. The energy harvesting switch 100 may not be able to self-oscillate as the gate voltage and threshold voltage of the MOSFETs 301,303 is very less. The turn-off of the transistor 317 also coincides with the maximum value of the drain to source voltage of the MOSFET 301,303. The voltage source 321 enables adjustment of the peak input current in the boost converter 113. The required voltage source 321 for adjusting the peak input current in the boost converter 113 is calculated using the equation:
V_ADJ=V_T+V_D-V_(BE,cut)-I_(L_(,max) )??R_E ?
where,
VADJ= voltage of the voltage source,
VD= the forward voltage drop of a diode,
VT=the threshold voltage,
ILmax= maximum inductor current and
RE = value of resistor connected to the emitter of the transistor
The self-oscillation frequency decreases with increase in AC load 105 current. The sustaining of oscillation also needs the energy released by the inductor to result in a maximum gate to source voltage of the MOSFET 301,303. To ensure oscillation of the electronic switch 100 at the lightest AC load 105 condition, the peak inductor current chosen is less than or equal to the minimum AC load 105 current. The energy released by the inductor is large enough to enhance the MOSFETs 301,303 and reduce drain to source voltage of the MOSFET 301,303 to a small value. The minimum value for the inductor 319 to sustain oscillation is obtained by the equation:
L>C_eq ((V_(GS,max??- ?)^2 V_T^2)/(I_(L,max)^2 ))
where,
L = the inductor value,
Ceq = the effective value of the capacitor and gate capacitance of the MOSFETs,
VGS, max=gate to source voltage of the MOSFET,
VT =the threshold voltage of the MOSFET and
IL,max = maximum inductor current.
During OFF condition of the AC switch 107 the energy flow to the boost converter 113 is interrupted resulting in gate discharge of the MOSFETs 301,303. The restoration of energy flow to the boost converter 113 can help in turning on the AC switch 107.The restoration of energy flow to the boost converter 113 is done using the two relays 115a, 115b. The relays 115a, 115b are operated complementarily. The relays 115a, 115b are static switches. During OFF state of the AC switch 107, due to leakage current, voltage can develop across the switch 107. During OFF condition of the AC switch 107, to provide an auxiliary power source 117, power is obtained from the voltage blocked across the AC switch 107.
During ON state of the relay 115b and OFF state of the relay 115a, the AC switch 102 is conducting or ON. During OFF state of the relay 104b and ON state of the relay 115a, the AC switch 107 is blocking or OFF. During ON state of the AC switch 107, power supply is obtained from the gates of the MOSFET 301,303. The power obtained is supplied to the boost converter 113, auxiliary loads and control unit 115. Examples for auxiliary loads include but are not limited to relays, control interface, DC load and zero-crossing detector.

FIG.4 shows the circuit for generation of auxiliary power supplies within the switch, according to an embodiment of the invention.
The energy harvesting electronic switch 100 contains an auxiliary power source 105 within the switch 100. The auxiliary power source 117 is connected across the AC switch arrangement 107 and coupled to the boost converter 113. In one example of the invention, the auxiliary power source 105 includes of an arrangement of diodes and capacitors 401,402. Examples for the auxiliary power source 117 includes but are not limited to rechargeable batteries, capacitors and any other circuits or devices that can store electrical energy. The switch 100 operates without additional external power source. Examples for the external power source includes but are not limited to rechargeable batteries, capacitors and any other circuits or devices that can store electrical energy.
The auxiliary power source 117 supplies power to the control unit 115 devices and auxiliary loads. Examples for the auxiliary load include but are not limited to zero-crossing detector, sensors, transducers, signal interfaces, microprocessors, timers, knobs, sliders and switches. The auxiliary power source 117 also supplies power during OFF state of the AC switch arrangement 107. The auxiliary power source 117 derives power from the non neutral power supply. During OFF state of the AC switch arrangement 107 the voltage drop across the switch 107 can be stored to the auxiliary power source 117.
The self-oscillating capacity of the electronic switch 100 enables charge pump to be driven without additional clock sources. A charge pump is defined as a DC to DC converter using capacitors to store energy for creating higher or lower voltage power source. The diode and capacitor arrangement 401,402 is capable to generate negative power supply. The discharging of current by the capacitors regulated by the diodes in the diode and capacitor arrangement 401,402 supplies power to the control unit 104 devices and auxiliary loads during OFF state of the AC switch 107.
In one example of the invention, an energy harvesting electronic switch is supplied with a non neutral power supply. The non-neutral power is supplied by connecting one terminal of the switch to the live line of an AC power supply of 250Volts at 50Hertz. The other terminal of the switch is connected to a load. The load connected is a resistive load of 50? (maximum load) or 5k? (minimum load). The ON-OFF state of the load is controlled by the electronic switch. MOSFET used within an AC switch arrangement is SPW47N60C3. Rectifier diodes used are MUR460. The boost converter uses BJT BD139. The value of inductor within boost converter is adjusted to provide a switching frequency of 1 kHz at maximum AC load current. The minimum peak inductor current used is 50mA. The value for the voltage source within the boost converter is 3V. It is obtained by connection of diode, an IRFZ44 MOSFET. A DC load is connected to the output of the boost converter is a TSOP34383, 38 kHz IR sensor. The IR sensor is employed to turn-ON and turn-OFF the switch remotely. The emitter resistor, RE and DC load are at 22? and 3.3k? respectively. The capacitor connected is of the value 1microFarad. An LED (light emitting diode) is connected with the DC load for power-ON indication.
The control unit uses negative-edge triggering dual JK flip-flop with reset, 74HC73. IRFU9310 and MMBF170 MOSFETs are used as relays for regulating energy flow to the boost converter. The zero crossing detector is constructed using four BC847BL transistors. The auxiliary power source includes an arrangement of diodes and capacitors. The diodes used are 1N4148 and capacitors used are of 1microFarad.
The energy harvesting switch of the above mentioned and illustrated embodiment is built and tested. An oscilloscope is used to record the values exhibited during ON-state and OFF-state of the electronic switch. The oscillogram of values for AC switch voltage drop, gate-drive voltage and load current for a resistive load of 50? (maximum load) and 5k? (minimum load) during ON-state of the electronic switch are recorded. The oscillogram of the voltage drop across the MOSFETs for resistive load of 5k? during OFF state of the electronic switch is recorded. Further, the oscillogram of the voltage drop across the MOSFETs at a temperature of 90º for resistive load of 50? during ON state of the electronic switch is also recorded.
FIG 5(a) shows the voltage drop across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention. The waveform in fig.5 (a) depicts the voltage drop across the AC switch for 50? exhibited a sinusoidal waveform of 1.65VPP. The sinusoidal waveform of 1.65VPP shows the superiority of usage of the MOSFETs in the AC switch compared to usage of TRIACs. TRIACs of similar size exhibits voltage drop of 4 VPP. The waveform also exhibited occasional recharge spikes of 10V at switching frequency of the MOSFETs close to 1 kHz.
FIG 5(b) shows the gate-drive voltage across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention. The waveform in fig.5 (b) depicts the gate-drive voltage of the MOSFET regulated to 4.5V±1V. The value of minimum gate-drive voltage follows the square root of the AC load current. The gate-drive voltage is hysterically regulated.
FIG 5(c) shows the auxiliary power source voltage across the MOSFETs for resistive load of 50? during ON state of the energy harvesting, according to an embodiment of the invention. The waveform in fig.5 (c) depicts the voltage of the auxiliary power source regulated at a voltage of 4.5V±200mV. The auxiliary power source is maintained at a constant value.
FIG 5(d) shows the voltage drop across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention. Fig 5(c) shows almost rectangular envelope of the voltage drop across the MOSFETs. The oscillations begin approximately 2.5ms after a zero crossing, when AC load current equals the maximum inductor current and remains same for another 5ms within each fundamental half cycle. The recharge spikes peak at 4V, with a switching frequency of approximately 5 kHz.
FIG 5(e) shows the gate-drive voltage across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention. The waveform in fig 5 (e) depicts the gate-drive voltage of the MOSFETs reaches the threshold voltage 2.7V during oscillations. A minimum voltage equivalent to the threshold voltage is available for powering the auxiliary load.
FIG 5(f) shows the auxiliary power source voltage across the MOSFETs for resistive load of 5k? during ON state of the energy harvesting, according to an embodiment of the invention. The waveform in fig.5 (f) depicts the voltage of the auxiliary power source regulated at a voltage of 2.9V±200mV. The auxiliary power source is maintained at a constant value.
Fig. 6(a) shows the voltage drop across the MOSFETs for resistive load of 5k? during OFF state of the electronic switch, according to an embodiment of the invention. The waveform in fig.6 (a) shows the voltage developed across a 5k load during the OFF-state of the AC switch, due to leakage current that amounts to approximately 2mA. The leakage current is low even with the addition of protective features. Examples for protective features include but are not limited to snubber diode, TVS diode, freewheeling diode and dV/dT.
Fig. 6(b) shows the voltage drop across the MOSFETs at a temperature of 90º for resistive load of 50? during ON state of the electronic switch, according to an embodiment of the invention. The waveform of fig 6(b) shows the sinusoidal portion of the waveform having increased to 2.75Vpp compared to 1.65Vpp at 30°C (Fig. 5a), indicating a 66% rise in the channel resistance of the MOSFETs. However, the recharge spikes and switching frequency are more or less the same as in Fig. 5a, proving the robustness of the energy harvesting electronic switches against higher temperature.
The results from the experiment shows the superiority of usage of the MOSFETs in the AC switch compared to usage of TRIACs. The gate-drive voltage is hysterically regulated.The invention is capable of static –ON, non-neutral operation of the switch. The switch handles resistive, capacitive and inductive loads.The auxiliary power source is maintained at a constant value. A minimum voltage equivalent to the threshold voltage is available for powering the auxiliary load. The leakage current is low even with the addition of protective features. The losses and distortion are reduced by variable switching frequency. The energy harvesting electronic switch is robust against higher temperatures. The features of the invention make it relevant to the area of load automation.
The energy harvesting switch as described herein above is capable of performing ON/OFF control of an AC load. Examples for the AC load includes but are not limited to lamps, fan, heaters, coolers and refrigerators. The energy harvesting switch is capable of operating without additional external power source. Examples for the power source include but are not limited to batteries, oscillators and capacitor banks. The energy harvesting switch handles a wide AC load ranging from 10Watts to 1000Watts of power. The range of AC load 108 current is varied from 50mA to 5A for apparent power ranging from 10VA to 1kVA. The switch circuit harvests the energy required for the operation of all devices within the switch, in addition to its own gate-drive.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.