JP2023525754A - Two-wire electronic switch and dimmer - Google Patents

Abstract

A bi-directional switch and dimmer for controlling power from an AC power source to a load is described. The present approach converts power MOSFETs into bi-directional switch sub-circuit configurations (including floating AC/DC power supplies and solid state bipolar switches) (connecting AC power to loads and periodically connecting AC power to AC/DC power supplies). alternate between). The switch and dimmer configuration allows insertion into existing single phase circuits using only two wires. This design allows the entire circuit to be fabricated on a single chip. [Selection drawing] Fig. 7

Description

The present invention relates to power management systems and methods of providing electronic switches and dimming controls.

[Cross reference to related application]
Not applicable.

[STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT]
Not applicable.

[Related Background Art]
Traditionally, access to alternating current (AC) power in homes and business environments is provided by mechanical outlets that are hardwired into the facility electrical system. These outlets are protected from excessive electrical loads and potentially dangerous ground faults with electromechanical devices such as fuses and circuit breakers. Similarly, control of conventional indoor electrical appliances (such as lights and ceiling fans) is accomplished using electromechanical switches. These primarily mechanical control elements, which provide simple on/off control, inevitably wear out and over time can cause short circuits and potentially dangerous arcing.

More nuanced control of common electrical equipment is typically provided by electronic elements such as triacs that allow the AC main waveform to be interrupted on a cycle-by-cycle basis (so-called phase control). Although triacs are significantly more efficient than their predecessors, rheostats and autotransformers, they are still inefficient for effective use in small enclosures for controlling large electrical loads. over, can generate electrical noise into the facility electrical system. Additionally, they can cause flickering in modern light-emitting diode (LED) lamps responsible for adverse health effects.

State-of-the-art AC switches employ high voltage semiconductor devices (such as bipolar transistors or MOSFETs) to control the application of AC power to the desired load. These modern circuits consist of an AC/DC power supply and a transistorized control circuit (three wires in a typical single-phase circuit: a hot lead from the AC mains, a lead to a switched load, and a Incorporates a common neutral lead) and those that require access to all. Examples of such state-of-the-art three-wire systems include WO2019/133110 (Electronic Switches and Dimmers, Telefus et al., International filed November 7, 2018).

There is a need for an improved electronic AC control system that provides a wide range of more reliable and highly efficient control options for a wide variety of applications in facility electrical systems. Moreover, such a control system can be implemented using semiconductor devices that can be incorporated into other circuits for advanced power control functions, can be manufactured at low cost, and two wires ( What is needed is a control system that can be easily installed using only hot AC mains leads and loads.

[Brief summary of the invention]
The present invention relates to novel techniques for controlling AC power (e.g., dimming lights) through the facility electrical system, ranging from simple outlet on/off switching to continuous variation of applied AC power. . More particularly, the present invention relates to a combination of functions that, in one embodiment, provide both on/off and phase control of the AC main waveform.

One embodiment uses a power MOS field effect transistor (MOSFET) as an electronic switch with a very low "on" resistance connected between the AC mains and the desired load. A typical power MOSFET essentially incorporates a body diode parallel to the conducting channel, thus connecting pairs of devices in a back-to-back configuration with a common source terminal for a true bidirectional (AC) switch configuration. is provided. To control the switching action of the power MOSFETs, a novel floating AC/DC power supply is included, which is periodically refreshed through the action of the MOSFET switches in synchronism with the AC mains waveform. Individual examples are not intended to limit the application of the concepts of the present invention. Other aspects and benefits of the invention will become apparent from the accompanying drawings and detailed description.

1 is a block diagram of a basic conventional three-wire switch/dimmer circuit; FIG. 1 is a schematic diagram of a conventional switched AC/DC power supply; FIG. Schematic diagram of the basic elements of a conventional bidirectional switch. A variation of the circuit of FIG. 3A that includes additional loading across all switch devices. 3C is the circuit of FIG. 3B showing the current through the additional load when each switch device is "off"; FIG. 3 is a block diagram of an embodiment of a two-wire switch/dimmer circuit; 3 is a schematic diagram of an embodiment of the AC/DC power supply of FIG. 2 using MOSFETs; FIG. FIG. 5 is a schematic diagram of an embodiment of the three-wire circuit of FIG. 1 using a variation of the AC/DC power supply of FIG. 5 and the basic switch circuit of FIG. 3A; 7 is a schematic diagram of the embodiment of FIG. 6 with the elements reconnected to produce the two-wire circuit of FIG. 4; FIG. 8 shows the effective configuration of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "off" and the neutral line is positive with respect to the hotline; 8 shows an effective configuration of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "off" and the hotline is positive with respect to the neutral line; Figure 8 shows the effective configuration of the circuit of Figure 7 when each MOSFET in the bidirectional switch is "on"; 8 shows the circuit of FIG. 7 with additional sub-circuits for overcurrent protection and output DC voltage control; Figure 11 shows details of the ballast circuit used in Figure 10;

FIG. 1 is a block diagram of a basic prior art three wire switch/dimmer unit 100 employing solid state switch devices. AC mains 101 provides hot 103 and neutral 105 input connections through switch/dimmer circuit 100 to load 102 connected to load 104 and neutral 105 output connections. The switch device 108 is driven by a switch control circuit 107 comprising a DC power supply powered by an AC/DC power supply 106 . In switch mode, a continuous DC bias is supplied to switch device 108 by control circuit 107 to maintain closure. In dimmer mode, the operating bias is provided by the control circuit 107 as pulses synchronous with the AC mains 101 waveform, the duty cycle of these pulses establishing the ratio of the total power delivered to the load. For dimmer operation, the controller 107 includes a pulse generation circuit and synchronizes with the AC mains power as is known in the art. The controller may include a user interface for inputting desired power to the load. In one embodiment, the user interface is physically embedded within control circuitry 107 . In another embodiment, the control circuitry includes wireless communication circuitry and the user interface is located physically remote from the control circuitry 107 . It should be noted that a minimum of three connections (103-105) are required to install the switch/dimmer unit.

FIG. 2 is a schematic diagram of a prior art switched AC/DC power supply 106 . The circuit includes a voltage divider network 201, 202 (having an output node 204 and connected across the AC mains power supply 101). Comparator circuit 203 has an inverting input connected to voltage divider output node 204, and a voltage reference 205 having a reference voltage _VR connected to a non-inverting input. Comparator 203 controls series switch 206, which disconnects hot input 103 from subsequent circuitry (opens switch 206) when voltage divider output voltage V _D exceeds reference voltage V _R . When switch 206 is closed, capacitor 208 is charged through series diode 207 . Diode 207 prevents back charging of capacitor 208 through switch 206 when the voltage divider output voltage drops. The combination of diode 207 and capacitor 208 thus forms a “peak detector” circuit that stores energy in each half of the AC mains cycle for supply to subsequent regulator circuitry and load 209 . The voltage across capacitor 208 need only be large enough to satisfy the energy requirements of subsequent regulator circuitry and load 209 . The input voltage to subsequent regulator 209 is substantially reduced compared to the rms value of the AC mains supply. Due to the operation of the "peak detector" circuit, as long as the voltage at the voltage divider output 204 remains greater than V _R , the steady-state voltage stored on capacitor 208 will always be V _R , regardless of the AC mains peak voltage fluctuations. is guaranteed to be This embodiment of the switching circuit operates as a voltage regulator circuit itself.

FIG. 3A is a schematic diagram showing the basic elements of a prior art bidirectional switch 108 using power MOSFETs to create a bidirectional electronic switch that controls power transferred from AC power source 101 to load 102. FIG. . Power MOSFETs 301 and 302 include body diodes 303 and 304, respectively. Switch 306 controls the gate-source bias voltage applied to power MOSFETs 301 and 302 . In the "on" 307 position, a bias voltage 305 is applied to the gate terminals 313,314 of each power MOSFET 301,302. Voltage 305 is above the threshold voltage of each power MOSFET (typically 5-10 volts) and forms an inversion layer, creating a conductive channel extending from the drain 309, 310 to the source 311, 312 of each device. In this "on" state, the drain-to-source behavior of each power MOSFET can be modeled as a low value resistor _Rds . As long as the voltage drop between drain and source remains less than about 0.6 volts, the body diode remains non-conducting and negligible. In the "on" state, the circuit of FIG. 3A is equivalent to a load 102 connected to an AC power source 101 through a series resistor of 2R _ds value.

In the "off" 308 position of the switch 306, the gate terminals 313, 314 of each power MOSFET 301, 302 are shorted to the source terminals 311, 312 and the drain-to-source voltage remains low as long as the drain-to-source voltage remains below the breakdown voltage of the respective body diode. The conductive channel between sources disappears. In the "off" state, the circuit of FIG.

In the "off" state, the requirement that the drain-to-source voltage of each power MOSFET remain below the body diode _Vbr breakdown voltage requires that the body diode breakdown voltage exceed the AC power source 101 peak voltage. Thus, for example, assuming power supply 101 corresponds to a typical 120 volt (rms) AC mains supply, the breakdown voltage of each body diode must exceed the peak supply voltage of 170 volts.

A more detailed analysis of the power MOSFET structure shows that the body diode is essentially the base-collector junction of a bipolar transistor connected in parallel with the MOSFET channel. Additional parasitics are base-collector junction capacitance and base-emitter parasitic resistance. This AC-coupled circuit imposes a constraint on the rate of change dV _ds /dt of the drain-source voltage to avoid forward biasing of the base-emitter junction, thereby causing Makes the bipolar transistor conductive. The resulting leakage current may be insufficient to power the load 102, but may be large enough to create additional efficiency and safety concerns.

Similarly, constraint considerations in the "on" state require that the drain-to-source voltage drop (given by R _ds *Iload) of each power MOSFET be less than about 0.6 volts. Potentially more important is that the power dissipated in each power MOSFET in the "on" state (given by R _ds *Iload ² ) must stay below a few watts to avoid excessive temperature rise. . Thus, for example, switching a typical home circuit from a 120 volt AC mains supply, which has a typical limit of 20 amps, each power MOSFET has an R _ds of less than 0.005 ohms (5 milliohms). demand that

It is well known in the prior art that the body diode breakdown voltage can be advantageously traded off against the value of _Rds by varying the device structure and doping level. In particular, the value of R _ds has been shown to be proportional to V _br ^2.5 . So, for example, cutting V _br in half results in a decrease in R _ds by a factor of 5.7.

According to the circuit of FIG. 3A, a conceptual bias switching circuit comprising switch 306 and voltage source 305 is shown electrically floating with the common source terminal of back-to-back power MOSFETs 301 and 302, This varies in voltage over the peak-to-peak range of power supply 101 . Although conceptually simple, this floating bias circuit can be difficult to implement at low cost.

FIG. 3B shows a modification of the circuit of FIG. 3A in which an additional load device 317 is connected in parallel with power MOSFETs 301 and 302 and control switch 306 is in the "on" position, switching power MOSFET gates 313, 314 to Connect to voltage 305 . Current flows from the AC source 101 through the power MOSFET channel to the load 102 and follows path 318 , effectively bypassing the additional load device 317 . FIG. 3C shows the circuit of FIG. 3B with control switch 306 changed to the "off" position, connecting power MOSFET gate electrodes 313, 314 to source terminals 311, 312. FIG. In this case, each power MOSFET device does not conduct and current flows from AC power source 101 through additional load 317 . Current follows path 319 and flows through additional load 317 and load 102 and back to AC power source 101 . In this way, the bi-directional switch circuit acts like a two-pole switch, supplying full current to the load 102 when each power MOSFET is "on" and full current when each power MOSFET is "off". Provides reduced power to additional load 317 .

FIG. 4 is a block diagram of an embodiment of a two-wire switch/dimmer 400. As shown in FIG. In contrast to FIG. 1, electronic switch and dimmer 400 requires only two wires 103, 104 for connection and operation. Electronic switch element 401 connects AC mains power supply 101 directly to load 102 . AC power is provided to AC/DC converter 106 via supply lines 402, 403, and filtered and regulated DC power is provided to subsequent circuitry via DC output lines 404, 405. Control circuit 107 is supplied with DC power via input lines 406 and 407 and control signals for controlling the state of switch 401 are provided via control lines 408 and 409 . As in the circuit of Figure 1, in dimmer mode,
The operating bias for switch 401 is provided from control circuit 107 as pulses synchronous with the AC mains 101 waveform, the duty cycle of these pulses establishing the ratio of total power applied to the load. For continuous full power operation in switch mode, the switch 401 is periodically opened to allow the AC/DC power supply 106 (sufficient energy storage to provide operating DC power between refresh operations). must be built in) need to be refreshed.

FIG. 5 is a schematic diagram of an embodiment of the AC/DC power supply of FIG. 2 using MOSFETs, one MOSFET 503 having an input/gate 510 and an output 511 for a simple comparator circuit (203 in FIG. 2). and one MOSFET 506 has an input/gate 512 and an output 513 as a switch (206 in FIG. 2). The input to the comparator is the gate 510 of MOSFET 503 and the analog of voltage reference 205 in FIG. Both MOSFETs 503 and 506 incorporate body diodes identified as 504 and 507 respectively. Rather than appearing across AC mains 101 , a voltage divider comprising resistors 501 and 502 effectively appears across DC output node 514 . Thus, when DC output 514 reaches a value determined by the threshold voltage of MOSFET 503 and the voltage divider ratio established by resistors 501 and 502, MOSFET 503 turns on, thereby turning switch MOSFET 506 off. . Note that this circuit operates as described above when the hot lead 103 of the AC mains 101 is positive with respect to the neutral lead 105 . When neutral lead 105 is positive with respect to hot lead 103 , current flows through body diode 504 , current limiting resistor 505 , Zener diode 508 and the parallel network of capacitor 509 to body diode 507 . to the AC mains power supply 101 via. Thereby, capacitor 509 is selected to exceed the zener voltage (the threshold voltage of switch MOSFET 506 sufficiently to ensure that switch MOSFET 506 is fully turned on when the polarity of AC mains 101 is reversed). ). This circuit configuration substantially reduces the power dissipated in switch MOSFET 506 in forward conduction mode, thereby substantially increasing the efficiency of the circuit.

FIG. 6 is a schematic diagram of an embodiment of the three wire circuit 100 of FIG. 1 using a variation of the AC/DC power supply of FIG. 5 and the basic switch circuit of FIG. 3A. A switch circuit, comprising power MOSFETs 301 and 302 (including body diodes 303 and 304, respectively), connects AC mains 101 neutral line 105 to allow for multiple control voltage levels provided by the AC/DC power supply. rearranged. The function of switch 306 in FIG. 3 is accomplished directly by using control circuit 107 (which provides floating control outputs 408 and 409 and is powered by the AC/DC power supply circuit shown in FIG. 5).

FIG. 7 is a schematic diagram of the embodiment of FIG. 6 with the elements alternatively connected to produce the two wire circuit 400 of FIG. This new configuration consists primarily of reconnecting the hot lead 103 of the AC power supply 101 to what was formerly the neutral line 105 and connecting the load to what was formerly the AC mains 101 hot lead 103. Reconnect the drain 701 of MOSFET 506 from what was the hot lead 103 of the AC mains 101 to the bi-directional switch output node 702; Isolating the neutral 404 line (connected to capacitor 208, control circuit 107, and the common source connection of MOSFET switch devices 301 and 302) from what was AC mains 101 neutral line 105. . As shown in FIG. 6, control circuit 107 provides floating control outputs 408 and 409 . In summary, a bidirectional electronic switch system for switching current in an alternating current (AC) circuit between an AC power source 101 having first and second terminals and a load 102 having first and second terminals. 400, having an input terminal 103 connected to a first terminal of an AC power source 101 and an output terminal 104 connected to a first terminal of a load 102; is interconnected externally of the bidirectional switch system with the second terminal of
a. First (402) and second (403) inputs for providing energy from the AC power source 101 in direct current (DC) to first (404) and second (405) output terminals connected to the control circuit system 107; an AC/DC conversion system 106 having terminals;
b. First (406) and second (407) DC input terminals respectively connected to first (404) and second (405) outputs of said AC/DC conversion system 106 and providing control signals to electronic switch 401; a control circuit system 107 having first (408) and second (409) output terminals for
c. an electronic switch 401 connected between the input terminal 103 and the bidirectional switch output terminal 104;
and the state of the control signal appearing between the control system output terminals 408, 409 determines the state of the switch.

FIG. 8A shows the performance of the circuit of FIG. 7 when MOSFETs 301 and 302 in the bidirectional switch are "off" and AC mains 101 hot line 103 is positive with respect to AC mains 101 neutral line 105. configuration. Current flows through body diode 504 , current limiting resistor 505 , a parallel network of Zener diode 508 and capacitor 509 , through body diode 507 and load 102 back to AC mains 101 . Thereby, capacitor 509 is selected to exceed the zener voltage (the threshold voltage of switch MOSFET 506 sufficiently to ensure that switch MOSFET 506 is fully turned on when the polarity of AC mains 101 is reversed). ).

FIG. 8B shows the effective operation of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "off" and the AC mains 101 neutral line 105 is positive with respect to the AC mains 101 hot line 103. Show configuration. Current flows through load 102, through the channel of MOSFET 506, and through peak detector diode 207, capacitor 208 as determined by the threshold voltage of MOSFET 503 and the voltage divider comprising resistors 501 and 502. voltage and returns to the AC mains supply 101 through a forward biased body diode 303 .

FIG. 9 shows the effective configuration of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "on". The AC/DC power supply circuit is bypassed and all current flows from the AC mains supply 101 through the load 102 .

FIG. 10 shows the circuit of FIG. 7 with additional sub-circuits for overcurrent protection and output DC voltage control to provide a ballast for LED lighting. Current sampling resistor 1002 and npn bipolar transistor 1001 form an overcurrent protection circuit. Resistor 1002 has a very small value (much less than 1 ohm) determined by the maximum current rating of power MOSFET 506 . When the voltage drop across resistor 1002 exceeds approximately 0.6V (for silicon transistors), bipolar transistor 1001 conducts, connecting the gate of MOSFET 506 to its source and reducing current flow. The series passes through MOSFET 1003, bias resistor 1004, Zener diode 1005 and filter capacitor 1006 which form a simple voltage control circuit. Output voltage 514 is controlled to a value given by the Zener voltage of diode 1005 minus the threshold voltage of pass MOSFET 1003 . In one embodiment, the two-wire switch further includes a ballast circuit 1007 that provides additional control of load current. Circuit 1007 is connected in series with switches 301 and 302 . Ballast circuit 1007 is controlled by control circuit 107 and is connected to switch control circuit 107 via 1108 . Connection 1008 can be a wired or wireless connection to control circuitry 107 .

In one embodiment shown in FIG. 11, ballast circuit 1007 includes ballast resistor 1101 and switch 1102 wired in parallel. Switch 1102 is controlled by control circuit 107 via connection 1008 . In one embodiment for dimming LED lighting, the switch 1102 is normally closed and opens when dimmed to 0% output, which causes the ballast resistor 1101 to adjust to the connected LED load. reduces the current through to below the threshold required to light the LED. In one embodiment, switch 1102 is a relay switch. In another embodiment, control line 1008 is a wireless connection to control circuit 107 .

[summary]
A bi-directional switch and dimmer for control of power from an AC power source to a load is described. The present approach employs a power MOSFET in a bi-directional switch sub-circuit configuration including a solid state bipolar switch and a floating AC/DC power supply that alternates the connection of the AC power supply to the load and the periodic connection of the AC power supply to the AC/DC power supply. use. The switch and dimmer circuitry allows for insertion into existing single phase circuits using only two wires. This design allows the entire circuit to be fabricated on a single chip.

Claims (13)

Bidirectional for switching current in an alternating current (AC) circuit between an AC source (101) having first and second terminals and a load (102) having first and second terminals An electronic switch system (400) comprising:
a. An input terminal (103) connected to a first terminal of an AC power source (101), an output terminal (104) connected to a first terminal of a load (102), and a second terminal of the AC power source (101). (105) and said second terminals of load (102) are interconnected external to said bidirectional switch system;
b. first (402) and for providing energy from said AC power supply (101) in direct current (DC) to first (404) and second (405) output terminals connected to a control circuit system (107); an AC/DC conversion system (106) having a second (403) input terminal;
c. said control circuit system (107) having first (408) and second (409) output terminals for providing control signals to an electronic switch (401);
d. said electronic switch (401) connected between said input terminal (103) and a bi-directional switch output terminal (104), wherein the state of said control signal appearing between control system output terminals (408, 409) determines said determine the state of the switch,
Bi-directional electronic switch system. The bi-directional electronic switch system of claim 1, comprising:
The AC/DC conversion system is
a. a voltage divider (501, 502) connected across the control circuit system (107);
b. a first switch (503) having an input (510) and an output (511) and connected to said voltage divider via its input (510);
c. A second switch (506) having an input (512) and an output (513), the input (512) being coupled to said output of said first switch (503) through a current limiting resistor (505). a second switch (506) connected to (511);
d. a storage capacitor (208) connected through a diode (207) to said output (513) of said second switch (506);
e. A Zener diode (508) having a Zener voltage, connected between the input (512) and the output (513) of the second switch (506), a shunt capacitor (509) being coupled to the Zener diode (508). A Zener diode ( 508) and
f. said control circuit system (107) connected to said storage capacitor (208);
A two-way electronic switch system comprising: The AC/DC conversion system according to claim 2,
further comprising a series voltage control circuit interposed between the storage capacitor (208) and the control circuit system (107);
The series voltage control circuit comprises a pass transistor (1003) having a characteristic threshold voltage (V _T ) connected to the control circuit system (107) and a bias resistor (1004) connected across the pass transistor. a Zener diode (1005) having a Zener voltage (V _Z ) is connected to said bias resistor so that the output voltage to said control circuit system (107) is maintained at V _Z −V _T /DC conversion system. The AC/DC conversion system according to claim 2,
further comprising a current limiting electronic circuit interposed between said second switch (506) and said storage capacitor (208) for limiting the current flowing through said second switch (506);
The current limiting electronic circuit comprises:
a. a sensing resistor (1002) connected between said output (513) of said second switch (506) and said control circuitry system (107);
b. a bipolar transistor (1001) connected between said control circuitry system and said input (512) of said second switch (506);
An AC/DC conversion system comprising: 3. The AC/DC conversion system according to claim 2, wherein both said first switch and said second switch are N-MOSFETs. 3. The AC/DC conversion system according to claim 2, wherein both said first switch and said second switch are bipolar transistors. 2. The AC/DC conversion system of claim 1, wherein all semiconductor devices are fabricated on a single integrated circuit chip. 3. The AC/DC conversion system of claim 2, wherein all semiconductor devices are fabricated on a single integrated circuit chip. 5. The AC/DC conversion system of claim 4, wherein all semiconductor devices are fabricated on a single integrated circuit chip. The bi-directional electronic switch system of claim 1, wherein said switch control circuit (107) output signals (408, 409) are pulsed synchronously with said AC power source (101) to provide said load (102) with a A bi-directional electronic switch system that provides phase control of transmitted AC power. The bi-directional electronic switch system of claim 1, comprising:
said control circuit system (107) output signals (408, 409) comprising pulse trains synchronized with said AC power source (101);
said pulse train has an adjustable pulse width to effectively control the average current/power delivered to said load (102);
This provides a dimming effect for light source loads and speed control for AC motor loads.
Bi-directional electronic switch system. The bi-directional electronic switch system of claim 1, comprising:
The electronic switch (401) comprises:
a. comprising a third (301) and a fourth (302) electronic switch device connected in series;
each switch device has a drain terminal (309, 310), a source terminal (311, 312) and a gate terminal (313, 314);
each of said third and fourth switch devices connected in series has a characteristic threshold voltage between said gate terminals (313, 314) and said source terminals (311, 312);
said drain terminal (309) of said third switch device (301) comprising said first input terminal of said solid state bidirectional switch (400);
a drain terminal (310) of said fourth switch device (302) comprises said first output terminal of said solid state bidirectional switch (400);
said source terminals (311, 312) of said first and second switch devices (301, 302) are interconnected at a first control terminal (315);
said gate terminals (313, 314) of said first and second switch devices are interconnected at a second control terminal (316);
Bi-directional electronic switch system. A bi-directional electronic switch system according to claim 12, comprising:
further comprising a ballast circuit (1007) connected between said drain terminal (309) and said input terminal (103) of said third switch device (301);
said ballast circuit comprising a fifth switch (1102) and a ballast resistor (1101);
the ballast resistor and the fifth switch are connected in parallel;
said fifth switch is controlled by said electronic control system (107);
by this,
said fifth switch is closed in a first state and current through said bi-directional electronic switch system (400) to said load (102) bypasses said ballast resistor (1101);
said fifth switch is opened in a second state and current through said bi-directional electronic switch system (400) to said load (102) is limited by said ballast resistor (1101);
Bi-directional electronic switch system.

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