JP7594608B2 - Two-wire electronic switches and dimmers - Google Patents

Description

The present invention relates to a power management system and a method for providing electronic switches and dimming control.

CROSS-REFERENCE TO RELATED APPLICATIONS
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's electrical system. These outlets are protected from excessive electrical loads and potentially dangerous ground faults using electromechanical devices such as fuses and circuit breakers. Similarly, control of traditional indoor electrical equipment (such as lights and ceiling fans) is achieved using electromechanical switches. These essentially mechanical control elements provide simple on-off control and 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 can interrupt the AC mains waveform on a cycle-by-cycle basis (so-called phase control). Triacs are significantly more efficient than the predecessor rheostats and autotransformers, but are still too inefficient to be used effectively in small enclosures to control large electrical loads, and can emit electrical noise into a facility's electrical system. Furthermore, they can cause flicker in modern light-emitting diode (LED) lamps, which has been linked to 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 incorporate an AC/DC power source and transistorized control circuitry that requires access to all three wires in a typical single-phase circuit: the hot lead from the AC mains, the lead to the load being switched, and the common neutral lead. Examples of such state-of-the-art three-wire systems include WO 2019/133110 (Electronic Switches and Dimmers, Telefus et al., International Application Published November 7, 2018).

There is a need for improved electronic AC control systems that provide a wide range of more reliable and highly efficient control options for a wide range of applications in facility electrical systems. Furthermore, there is a need for such control systems that can be realized using semiconductor devices that can be integrated with other circuits for advanced power control functions, can be manufactured at low cost, and can be easily installed using only two wires (the hot AC mains lead and the load).

[Brief summary of the invention]
The present invention relates to novel approaches for the control of AC power (e.g., dimming lights) through a 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 functionality that, in one embodiment, provides both on/off and phase control of the AC mains waveform.

One embodiment uses power metal-oxide-semiconductor field-effect transistors (MOSFETs) as electronic switches with very low "on" resistance connected between the AC mains power source and the desired load. A typical power MOSFET inherently incorporates a body diode in parallel with the conduction channel, so that pairs of devices are connected in a back-to-back configuration with a common source terminal to provide a truly bidirectional (AC) switch configuration. To control the switching action of the power MOSFETs, a novel floating AC/DC power supply is included that is periodically refreshed in synchronization with the AC mains power waveform through the action of the MOSFET switches. The specific examples are not intended to limit the inventive concept to the application. Other aspects and advantages of the present invention will become apparent from the accompanying drawings and detailed description.

Block diagram of a basic conventional three-wire switch/dimmer circuit. 1 is a schematic diagram of a conventional switched AC/DC power supply. Schematic diagram of the basic elements of a conventional bidirectional switch. A variation of the circuit of FIG. 3A including an additional load 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. 2 is a block diagram of an embodiment of a two-wire switch/dimmer circuit. FIG. 3 is a schematic diagram of an embodiment of the AC/DC power supply of FIG. 2 using MOSFETs. 6 is a schematic diagram of an embodiment of the three-wire circuit of FIG. 1 using the AC/DC power supply of FIG. 5 and a variation of 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. 7 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 hot line. 7 shows the effective configuration of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "off" and the hot line is positive with respect to the neutral line. 8 shows the effective configuration of the circuit of FIG. 7 when each MOSFET in the bidirectional switch is "on." 8 shows the circuit of FIG. 7 with additional subcircuits for overcurrent protection and output DC voltage control. Details of the ballast circuit used in FIG. 10 are shown.

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

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). A comparator circuit 203 has an inverting input connected to the voltage divider output node 204 and a voltage reference 205 connected to the non-inverting input and having a reference voltage V _R. The comparator 203 controls a series switch 206 which disconnects the hot input 103 from the subsequent circuitry (opens switch 206) when the voltage divider output voltage V _D exceeds the reference voltage V _R. When switch 206 is closed, a capacitor 208 is charged through a series diode 207. The diode 207 prevents the capacitor 208 from charging back through switch 206 if the voltage divider output voltage drops. Thus, the combination of diode 207 and capacitor 208 forms a "peak detector" circuit, which stores energy during each half of the AC mains cycle for supplying the downstream regulator circuit and load 209. The voltage across capacitor 208 only needs to be large enough to satisfy the energy requirements of the downstream regulator circuit and load 209. The input voltage to the downstream regulator 209 is substantially reduced compared to the rms value of the AC mains. The operation of the "peak detector" circuit ensures that the steady state voltage stored in capacitor 208 will always be V _R , regardless of fluctuations in the peak voltage of the AC mains, as long as the voltage at the voltage divider output 204 remains greater than V _R. This embodiment of the switching circuit operates as a voltage regulator circuit itself.

3A is a schematic diagram showing the basic elements of a prior art bidirectional switch 108 that uses power MOSFETs to create a bidirectional electronic switch that controls power transferred from an AC power source 101 to a load 102. 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 greater than the threshold voltage of each power MOSFET (typically 5-10 volts), forming an inversion layer and 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 R _ds . As long as the voltage drop between the drain and source remains below about 0.6 volts, the body diode remains non-conducting and can be neglected. In the "on" state, the circuit of Figure 3A is equivalent to a load 102 connected to an AC power source 101 through a series resistor with a value of _2Rds .

In the "off" 308 position of 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 conduction channel disappears as long as the drain-to-source voltage remains below the breakdown voltage of each body diode. In the "off" state, the circuit of FIG. 1 is equivalent to a load 102 connected to an AC power source 101 through back-to-back body diodes 303 and 304, effectively isolating the load 102 from the power source 101.

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

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

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

It is well known in the art that the breakdown voltage of the body diode can be favorably traded off against the value of _Rds by varying the device structure and doping levels. In particular, it has been shown that the value of _Rds is proportional to _Vbr ^2.5 . Thus, for example, cutting _Vbr in half results in a reduction in _Rds by a factor of 5.7.

The circuit of FIG. 3A shows a conceptual bias switching circuit with switch 306 and voltage source 305 electrically floating with the common source terminals of back-to-back power MOSFETs 301 and 302 varying in voltage over the entire peak-to-peak range of power supply 101. While conceptually simple, this floating bias circuit can be difficult to implement at low cost.

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

Figure 4 is a block diagram of an embodiment of a two-wire switch/dimmer 400. In contrast to Figure 1, the electronic switch and dimmer 400 requires only two wires 103, 104 for connection and operation. An electronic switch element 401 connects the AC mains 101 directly to a load 102. AC power is provided to an 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. A control circuit 107 is supplied with DC power via input lines 406, 407, and a control signal for controlling the state of the switch 401 is provided via control lines 408, 409. Like the circuit of Figure 1, in dimmer mode:
The operating bias for switch 401 is provided by control circuit 107 as pulses synchronized with the AC mains 101 waveform, and the duty cycle of these pulses establishes the percentage of total power applied to the load. Continuous full power operation in switched mode requires that switch 401 be periodically opened to refresh AC/DC power supply 106, which must incorporate sufficient energy storage to provide operating DC power between refresh operations.

5 is a schematic diagram of an embodiment of the AC/DC power supply of FIG. 2 using MOSFETs, one MOSFET 503 with input/gate 510 and output 511 to form a simple comparator circuit (203 in FIG. 2) and one MOSFET 506 with input/gate 512 and 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. 2 becomes the threshold voltage of MOSFET 503. Both MOSFETs 503 and 506 incorporate body diodes, identified as 504 and 507, respectively. Rather than appearing across the AC mains supply 101, a voltage divider with resistors 501 and 502 effectively appears across DC output node 514. Thus, when the 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 switches on, thereby switching switch MOSFET 506 off. It should be noted that this circuit operates as described above when the hot lead 103 of the AC mains supply 101 is positive with respect to the neutral lead 105. When the neutral lead 105 is positive with respect to the hot lead 103, current flows through the parallel network of body diode 504, current limiting resistor 505, Zener diode 508 and capacitor 509, and returns to the AC mains supply 101 via body diode 507. This charges capacitor 509 to a Zener voltage (selected to be sufficiently above the threshold voltage of switch MOSFET 506 to ensure that switch MOSFET 506 is fully on if the polarity of the AC mains supply 101 reverses. This circuit configuration substantially reduces the power dissipated in the switch MOSFET 506 in forward conduction mode, thereby substantially increasing the efficiency of the circuit.

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

Figure 7 is a schematic diagram of the embodiment of Figure 6 with the elements alternatively connected to produce the two-wire circuit 400 of Figure 4. This new configuration primarily involves reconnecting the hot lead 103 of the AC power source 101 to what was previously the neutral line 105, reconnecting the load from what was previously the AC mains 101 hot lead 103 to the AC mains 101 neutral lead 105, reconnecting the drain 701 of MOSFET 506 from what was previously the AC mains 101 hot lead 103 to the bidirectional switch output node 702, and isolating the floating 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 previously the AC mains 101 neutral line 105. As shown in Figure 6, the control circuit 107 provides floating control outputs 408 and 409. In summary, a bidirectional electronic switch system 400 for switching current in an alternating current (AC) circuit between an AC power source 101 having a first terminal and a second terminal, and a load 102 having a first terminal and a second terminal, the bidirectional electronic switch system having an input terminal 103 connected to the first terminal of the AC power source 101 and an output terminal 104 connected to the first terminal of the load 102, the second terminal of the AC power source 101 and the second terminal of the load 102 being interconnected external to the bidirectional switch system, and further comprising:
a. an AC/DC conversion system 106 having first (402) and second (403) input terminals for providing energy from an AC power source 101 in the form of direct current (DC) to first (404) and second (405) output terminals connected to a control circuit system 107;
b. a control circuit system 107 having first (406) and second (407) DC input terminals respectively connected to the first (404) and second (405) outputs of said AC/DC conversion system 106, and first (408) and second (409) output terminals for providing control signals to an electronic switch 401;
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 control system output terminals 408, 409 determines the state of the switch.

Figure 8A shows the effective configuration of the circuit of Figure 7 when the MOSFETs 301 and 302 in the bidirectional switch are "off" and the AC mains 101 hot line 103 is positive with respect to the AC mains 101 neutral line 105. Current flows through the parallel network of body diode 504, current limiting resistor 505, Zener diode 508 and capacitor 509, and returns to the AC mains 101 through body diode 507 and the load 102. This charges capacitor 509 to the Zener voltage (selected to be sufficiently above the threshold voltage of switch MOSFET 506 to ensure that switch MOSFET 506 is fully on if the polarity of the AC mains 101 reverses).

Figure 8B shows the effective configuration of the circuit of Figure 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. Current flows through the load 102, through the channel of MOSFET 506, through the peak detector diode 207, charging the capacitor 208 to a voltage determined by the threshold voltage of MOSFET 503 and the voltage divider comprising resistors 501 and 502, and back to the AC mains 101 through the forward biased body diode 303.

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

10 shows the circuit of FIG. 7 with additional subcircuits for overcurrent protection and output DC voltage control to provide a ballast for LED lighting. A current sampling resistor 1002 and an npn bipolar transistor 1001 form the 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 about 0.6V (for a silicon transistor), bipolar transistor 1001 conducts, connecting the gate of MOSFET 506 to its source, reducing the current. The series goes through MOSFET 1003, bias resistor 1004, Zener diode 1005 and filter capacitor 1006, which form a simple voltage control circuit. The 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 further control of the load current. The circuit 1007 is connected in series with the switches 301, 302. The ballast circuit 1007 is controlled by the control circuit 107 and is connected to the switch control circuit 107 via 1108. The connection 1008 can be a wired or wireless connection to the control circuit 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, switch 1102 is normally closed and opens when dimming to 0% output, causing ballast resistor 1101 to reduce the current through the connected LED load 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 bidirectional switch and dimmer for controlling power from an AC source to a load is described. The approach uses power MOSFETs in a bidirectional switch subcircuit configuration that includes a solid-state bipolar switch and a floating AC/DC power source that alternates between connecting the AC source to the load and cyclically connecting the AC source to the AC/DC power source. The switch and dimmer circuit configuration allows insertion into an existing single-phase circuit using only two wires. The design allows the entire circuit to be fabricated on a single chip.

Claims (10)

A bidirectional electronic switch system (400) for switching current in an alternating current (AC) circuit between an AC power source (101) having a first terminal and a second terminal, and a load (102) having a first terminal and a second terminal, comprising:
a) the bidirectional electronic switch system is connected only between the first terminal of the A.C. power source and the first terminal of the load, and only conductors not connected to the bidirectional electronic switch system are connected between the second terminal of the load and the second terminal of the A.C. power source;
The bidirectional electronic switch system comprises:
b . 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), wherein a second terminal (105) of the AC power source (101) and the second terminal of the load (102) are interconnected outside the bidirectional switch system;
c . an electronic switch (401) including two MOSFETs (301, 302) connected in a back-to-back configuration with a common source terminal;
d . an AC/DC conversion system (106) having first (402) and second (403) input terminals for providing energy from said AC power source (101) in the form of direct current (DC) to first (404) and second (405) output terminals connected to a control circuit system (107);
e . the control circuit system (107) having first (408) and second (409) output terminals for providing a control signal to the electronic switch (401);
Power to the AC/DC conversion system is refreshed via operation of the electronic switch (401);
The AC/DC conversion system includes:
(i) a voltage divider (501, 502) connected across said control circuit system (107);
(ii) a first MOSFET switch (503) having an input (510) and an output (511), connected to the voltage divider via its input (510);
(iii) a second MOSFET switch (506) having an input (512) and an output (513), the input (512) being connected to the output (511) of the first MOSFET (503) through a current limiting resistor (505);
(iv) a storage capacitor (208) connected to the output (513) of the second MOSFET switch (506) through a diode (207);
(v) a Zener diode (508) having a Zener voltage connected between the input (512) and output (513) of the second MOSFET switch (506), with a shunt capacitor (509) connected in parallel with the Zener diode (508) thereby clamping the voltage between the input (512) and the output (513) of the second MOSFET switch (506) to the Zener voltage of the Zener diode (508);
(vi) the control circuit system (107) connected to the storage capacitor (208),
f . the electronic switch (401) is 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 electronic switch (401);
g . A bidirectional electronic switch system, wherein power to the AC/DC conversion system is ON when the electronic switch (401) is OFF and the AC/DC conversion system is bypassed, and full current flows from the AC power source (101) through the load (102) when the electronic switch (401) is ON. 2. The bidirectional electronic switch system of claim 1,
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 ) connected across the bias resistor, thereby maintaining an output voltage to the control circuit system (107) at V _Z -V _T . 3. The bidirectional electronic switch system of claim 2,
a current limiting electronic circuit interposed between the second MOSFET switch (506) and the storage capacitor (208) for limiting the current flowing through the second MOSFET switch (506);
The current limiting electronic circuit includes:
a. a sense resistor (1002) connected between the output (513) of the second MOSFET switch (506) and the control circuit system (107);
b. a bipolar transistor (1001) connected between said control circuit system and said input (512) of said second MOSFET switch (506);
A two-way electronic switch system including: The bidirectional electronic switch system of claim 1, wherein all semiconductor devices are fabricated on a single integrated circuit chip. The bidirectional electronic switch system of claim 2, wherein all semiconductor devices are fabricated on a single integrated circuit chip. The bidirectional electronic switch system of claim 3, wherein all semiconductor devices are fabricated on a single integrated circuit chip. The bidirectional electronic switch system of claim 1, wherein the switch control circuit (107) output signal (408, 409) is pulsed in synchronization with the AC power source (101) to provide phase control of the AC power delivered to the load (102). 2. The bidirectional electronic switch system of claim 1,
the control circuit system (107) output signal (408, 409) comprises a pulse train synchronized with the AC power source (101);
the pulse train having an adjustable pulse width for effectively controlling the average current/power delivered to the load (102);
This provides dimming effect for light source loads and speed control for AC motor loads.
Two-way electronic switch system. 2. The bidirectional electronic switch system of claim 1,
The electronic switch (401)
a. a third MOSFET (301) and a fourth MOSFET (302) connected in series;
Each of the third MOSFET and the fourth MOSFET has a drain terminal (309, 310), a source terminal (311, 312) and a gate terminal (313, 314);
each of the third and fourth MOSFETs having a characteristic threshold voltage between the gate terminal (313, 314) and the source terminal (311, 312);
the drain terminal (309) of the third MOSFET (301) comprises the first terminal of the solid-state bidirectional electronic switch system (400);
a drain terminal (310) of the fourth MOSFET (302) comprises the second terminal of the solid-state bidirectional electronic switch system (400);
the source terminals (311, 312) of the first and second MOSFETs (301, 302) are interconnected at a first control terminal (315);
the gate terminals (313, 314) of the first and second MOSFETs (301, 302) are interconnected at a second control terminal (316);
Two-way electronic switch system. 10. The bidirectional electronic switch system of claim 9,
a ballast circuit (1007) connected between the drain terminal (309) of the MOSFET (301) and the input terminal (103);
The ballast circuit includes a fifth switch (1102) and a ballast resistor (1101);
the ballast resistor and the fifth switch are connected in parallel;
The fifth switch is controlled by the electronic control system (107);
This means,
the fifth switch is closed in a first state such that current through the bidirectional electronic switch system (400) to the load (102) bypasses the ballast resistor (1101);
the fifth switch is open in a second state and the current through the bidirectional electronic switch system (400) to the load (102) is limited by the ballast resistor (1101);
Two-way electronic switch system.

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