Battery powered electronic switch

Abstract

Single pole double throw and single pole single throw electronic switches may be advantageously constructed by employing at least one pair of N channel enhancement MOSFETs if each N channel enhancement MOSFET of the pair is coupled to a common drain, and logic signals generated by a sensor are either sent directly to the pair or are inverted before reaching the pair.

Description

[0001] BATTERY POWERED ELECTRONIC SWITCH CROSS-REFERENCED TO RELATED APPLICATIONS

[0002] Not applicable

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] Not applicable

[0005] BACKGROUND OF THE INVENTION

[0006] I. Field of the Invention

[0007] The present invention relates generally to switches, and more specifically to single pole double throw (SPDT) and single pole single throw (SPST) electronic switches.

[0008] IL Discussion of the Prior Art

[0009] Mechanical Switches come in many styles such as reed switches, and snap acting switches. Some mechanical switches employ a SPDT configuration where there is one Common (C) connection, one Normally Open (NO) connection, and one Normally Closed (NC) connection. Some mechanical switches employ a Single Pole Single Throw' Throw (SPST) switches where there is one C connection and one NO connection or one NC connection.. There are also Double Pole Double Throw (DPDT) mechanical switches. Mechanical switches are easy to understand and apply. For each contact, when it is in one position, full circuit current is flowing and there is no voltage across it. In the other position, the circuit physically opens, no current is flowing, and the full circuit voltage is across it. While such switches are easy to apply, many users mis-apply them. The maximum ratings can be easily understood, but many mechanical switches also require a minimum current and / or voltage applied, or they will not be as reliable. This information is not always on the data sheets related to such switches. Mechanical switches also suffer from w ear and contact corrosion due to their mechanical nature and, as such, are not as reliable as electronic switches.

[0010] Electronic switches are sometimes used to address the reliability' issues associated with mechanical sw itches. Electronic stitches have no moving parts to wear out, no contacts to corrode, and if used below' the maximum ratings, no minimum ratings to consider. However, electronic switches are often more difficult to apply since there are many different types such as 2 wire, 3 wire, NO or NC, switched positive (PNP), and switched negative (NPN), among others. Many electronic switches are polarity sensitive and are alternating current (AC) or direct current (DC) only. 2 wire switches are easiest to apply but they are only single pole single throw (SPST). Further, because the internal electronics must be powered all the time, these switches require a voltage drop when they are on and a leakage current when they are off.

[0011] Non polarity sensitive SPDT electronic switches do not appear to be available, likely because of the required NC output. For the output element, most commonly a Metal Oxide Semiconductor Field-effect Transistor (MOSFET), to be conducting when not energized, it needs to be a depletion mode MOSFET instead of an enhancement mode MOSFET. With a depletion mode MOSFET, the transistor requires a negative gate to source voltage (VGS) to be applied to switch the device “off’ and, as such, is the equivalent of a normally closed (NC) switch. The depletion mode MOSFET has much higher resistance so would not be suitable for more than a few' milliamps (mA) of current. There are some small signal relays that offer a NO output and a NC output, but they are not connected as a SPDT and are polarity sensitive.

[0012] SUMMARY OF THE INVENTION

[0013] The present invention provides switches that offer (a) the simplicity of the application and understanding of a mechanical switch, (b) universal adaptation of the SPDT or SPST function, and (c) the reliability of an electronic switch. Embodiments of the present invention can be connected in a SPDT or SPST configuration with no leakage current or voltage drop. These embodiments do so by employing a battery to power the internal circuitry of the switch. Employing a battery to power the internal circuitry of the switch ensures that adequate pow er is always available even w hen the switch is turned off. Embodiments of the present invention employ enhancement MOSFETs, a secondary advantage obtained by the use of the battery. With an enhancement MOSFET, the transistor requires a gate to source voltage (VGS) to switch the device “on” and, as such, is like a normally open (NO) switch. MOSFETs have three pins — typically but not necessarily a source pin connected to ground, a drain pin connected to a load, and a gate. An electrical field that controls the current flow through the channel between the drain and source, without any steady state cunent flowing from the gate into the MOSFET itself is created by applying a voltage to the gate.

[0014] The outputs of electronic switches made in accordance with the present invention may be configured as a solid-state relay making the switch polarity insensitive. A person of ordinary skill in the art would generally understand that both the NO and NC connections cannot be connected to make a SPDT switch using the standard relay configuration because both will turn on due to the interplay of the electronics. The present invention solves this problem in a novel way. Specifically, the output MOSFETs may be connected in a common drain configuration instead of the currently used common source configuration. This is a counterintuitive solution to the SPDT issue because use of a common drain configuration causes the MOSFETs to become more difficult to drive.

[0015] Embodiments of the present invention also ensure that the power consumption of the switch’s circuitry is low enough so that the battery will last a long enough time, typically the lifetime of the switch. This permits the battery^ to be potted with the rest of the electronics since the battery never needs to be changed. Tests have show n that circuits made in accordance with the invention are low enough in power that the battery should last over 30 years.

[0016] More specifically, switches made in accordance with the present invention comprise a sensor, an inverter, a battery, and a first pair of N channel enhancement MOSFETs coupled to a first common drain. In some embodiments, the switch may also include a buffer coupled to the sensor and step-up circuity coupled to the battery.

[0017] Switches configured as an SPDT switch typically have a second pair of N channel enhancement MOSFETs coupled to a second common drain. The first pair of N channel enhancement MOSFETs coupled to a first common drain are configured to receive first logic signals from the sensor (or the buffer if a buffer is provided). These first logic signals are also received by the inverter, which inverts then first logic signals and then transmit these inverted logic signals, i.e., second logic signals, to the second pair of N channel enhancement MOSFETs coupled to a second common drain. The first pair of N channel enhancement MOSFETs may also be coupled to a first drive circuit and the second pair of N channel enhancement MOSFETs may be coupled to a second drive circuit.

[0018] Switches configured as an SPST switch, may have a jumper (e.g., a jumper cable or three-way switch) to provide two discrete and selectable signal paths. A first selectable signal path extends between the sensor (or buffer if a buffer is employed) and the first pair of N channel enhancement MOSFETs bypassing the inverter and configured to deliver said first logic signals to the first pair of N channel enhancement MOSFETs, which are connected in the conventional common source configuration. A second selectable signal path extends through the inverter between the sensor (or buffer) and the first pair of N channel enhancement MOSFETs. The inverter is configured to invert the first logic signals to create second logic signals and deliver the second logic signals to first pair of N channel enhancement MOSFETs.

[0019] BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts:

[0021] Figure 1 is a schematic diagram of an embodiment of a wired single pole double throw (SPDT) switch made in accordance with the present invention.

[0022] Figure 2 is a schematic diagram of an embodiment of a wired single pole single throw (SPST) switch made in accordance with the present invention.

[0023] DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] This description of the preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. In the description, relative terms such as “lower’, “upper’", “horizontal’", “vertical”, “above”, “below"’, “up”, “down”, “top” and “bottom” as well as derivatives thereof (e.g., “horizontally”, “downwardly”, "‘upwardly”, etc.) should be construed to refer to the orientation as then described or as shown in the drawings under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms such as "connected", “connecting”, “attached”, “attaching”, “join” and “joining” are used interchangeably and refer to one structure or surface being secured to another structure or surface or integrally fabricated in one piece, unless expressively described otherwise.

[0025] The wired SPDT electronic switch 1 shown in Figure 1 is wired to other electronics of a device via a normally closed (NC)connector 2, a normally open (NO)connector 3, and a common (C) connector 4. The wired switch 1 comprises a battery 10 for powering the circuitry of the switch which, in some embodiments, may include step up circuitry 12. The switch 1 further comprises a sensor 14. Sensor 14 may be a magnetic proximity sensor, an optical sensor, an inductive sensor, a capacitive sensor, or any other suitable type of sensor without deviating from the invention. Figure 1 shows sensor 14 coupled to a buffer 16. This buffer may be unnecessary in other embodiments depending on the attributes of the sensor 14.

[0026] Logic signals (i.e., either a one or a zero) are generated by the buffer 16 (or sensor 14 if buffer 10 is not used) and delivered directly to MOSFETs 18 and 30. MOSFET 30 then affects MOSFET 28. These signals are also delivered to MOSFETs 22 and 24 which cooperate to act as an inverter which converts a one to a zero and a zero to a one. The inverted signal is then delivered to MOSFETs 26 and 31. As such, whatever logic signal is delivered to MOSFETs 18 and 30, the opposite logic signal is delivered MOSFETs 26 and 31. MOSFETs 18 and 20 are each connected to a first common drain. Likewise, MOSFETS 26 and 28 are each connected to a second common drain. MOSFETs 18, 20, 26 and 28 are all N channel enhancement MOSFETs. Given this arrangement, (a) if the signal generated by the buffer 16 is a zero, MOSFETS 18 and 20 are off, the signal generated by the inverter is a one, and MOSFETS 26 and 28 are on, and (b) if the signal generated by the buffer is a one, MOSFETS 18 and 20 are on, the signal generated by the inverter is a zero, and MOSFETS 26 and 28 are off.

[0027] A first drive circuit is located on the gate and source of MOSFET 28. A second substantially identical drive circuit is located on the gate and source of MOSFET 20. Each of these first and second safety circuits comprises a first flow path comprising first MOSFET 30 / 31, a first resistor 32 / 33, ajunction diode 34 / 35, and a Schottky diode 36 / 37. When the signal delivered by the buffer 16 to MOSFETS 18 and 30, and by the inverter comprising MOSFETS 22 and 24 to MOSFETS 26 and 231, current flows through MOSFETS 30 / 31, resistors 32 / 33, junction diodes 34 / 35 and the Schottky diodes 36 / 37 to the MOSFETS 28 / 20 turning them on. The two drive circuits also provide a second flow path employed when the signal delivered by the buffer 16 to MOSFETS 18 and 30, and by the inverter comprising MOSFETS 22 and 24 to MOSFETS 26 and 31 changes state causing MOSFETS 28 / 20 to turn off. The second flow path is employed to quickly discharge the gate capacitance of MOSFETS 28 / 20 to turn them off and includes MOSFET 38 / 39, MOSFET 40 / 41 , and Zener diode 42 / 43. Second, third and fourth resistors are also present in each of the two drive circuits, i.e., second resistors 44 / 45, third resistors 46 / 47 and fourth resistors 48 / 49.

[0028] The Zener diodes 42 / 43 of the two drive circuits serve to clamp the voltage between the gate and the source of MOSFETs 28 / 20, so the voltage does not get too high and damage the switch. Resistor 48 serves to keep the gate and source at the same voltage when the MOSFET 28 is turned off. Similarly, resistor 49 serves to keep the gate and source at the same voltage when MOSFET 20 is turned off. The diodes 34 and 35 are low leakage diodes and serve to block too high a voltage. Resistor 44 / 45 develops a voltage across it when the capacitance of MOSFETS 28 / 20 starts to discharge when turned off. This voltage turns on MOSFETS 38 / 39 which then turns on MOSFETS 40 / 41. This combination provides a discharge path for the gate capacitance of MOSFETS 28 / 29 and turns them off quickly. The drawing shows diodes associated with each of the MOSFETs 18, 20, 26 and 28. These are not separate diodes, but instead are intrinsic to the N channel enhancement MOSFETs employed as MOSFETs 18, 20, 26 and 28.

[0029] Various types of batteries may be employed as battery 10. An example of a suitable battery is the Model TL-4902 lithium battery made by Tadiran Batteries of Lake Success, New York. This battery has nominal capacity @ 0.5 mA, to 2 V of 1.2 AH, a rated voltage of 3.6 V, a maximum recommended continuous current of 20 mA, a maximum 1 sec. pulse capability of 50 mA, and an operating temperature range of - 55 °C to +85 °C. Significantly, this battery has discharge characteristics providing a service life of approximately thirty' years when powering a switch of the type described above. A wired single pole single throw (SPST) switch 100 is illustrated in Figure 2. The SPST electronic switch 100 is wired to other electronics of a device via a first connector 102 which in some configurations is normally open and in other configurations is normally closed. Also shown is a common (C) connector 104. The switch 100 comprises battery' 110 for pow ering the circuitry' of the switch w hich, in some embodiments, may include step up circuitry 112. This switch also employs a sensor 114. Sensor 114 may be a magnetic proximity sensor, an optical sensor, an inductive sensor, a capacitive sensor, or any other suitable type of sensor without deviating from the invention. Figure 2 shows sensor 114 coupled to a buffer 116. This buffer may be unnecessary' in other embodiments depending on the attributes of the sensor 114. Two sets of MOSFETs are shown in Figure 2. MOSFETs 122 and 124 cooperate to act as an inverter. MOSFETs 126 and 128 are N channel enhancement MOSFETs employed as the output. The diodes illustrated in conjunction w ith MOSFETs 126 and 128 are not separate diodes, but instead are intrinsic to these MOSFETs. MOSFETS 126 and 128 have a common source connection.

[0030] As noted above, connector 102 may be a NO or NC connector depending on the configuration. The configuration is determined by how ajumper 133 is connected. Herein, the term “jumper” is used generically to include any device, such as ajumper cable or three-way switch, that may be used in conjunction with the connectors 131, 132, and 133 to selectively complete two separate and discrete signal flow paths. Jumper 133 may be connected between connectors 130 and 132 as showTi or alternatively between connectors 131 and 132.

[0031] In operation, the buffer 116 will generate a “one” or a “zero” logic signal based on signals received from the sensor 114. If the jumper 133 is connecting connectors 130 and 132 as shown, this logic signal generated by buffer 116 will be delivered from buffer 116 directly to the MOSFETs 128 and 126. If, how ever, the jumper 133 is positioned to connect connector 131 with connector 132, the logic signal generated by the buffer 116 is inverted by the inverter formed by MOSFETs 122 and 124 such that the opposite of the logic signal generated by the buffer 116 is delivered to the MOSFETs 126 and 128 by the inverter.

[0032] Both the SPDT and SPST switches described herein offer important advantages. First, the electronic switches made in accordance with the present invention have virtually no leakage current or voltage drop. This is achieved by employing a battery to power the internal circuitry of the switch. Employing a battery to power the internal circuitry of the switch ensures that adequate power is always available even when the switch is turned off. The use of a battery' in this way offers the secondary advantage of enabling the use of an N channel enhancement MOSFETs. With N channel enhancement MOSFETs, the transistor requires a gate to source voltage (VGS) to switch the device “on” and, as such, is like a normally open (NO) switch. MOSFETs have three pins — a source pin, a drain pin, and a gate. An electrical field that controls the current flow through the channel between the drain and source, without any steady state cunent flowing from the gate into the MOSFET itself is created by applying a voltage to the gate.

[0033] Second, switches made in accordance with the present invention typically offer the advantage of being polarity' insensitive.

[0034] Third, the current standard relay configuration is to connect MOSFETs in a common source configuration. To solve issues associated with this standard configuration in SPDT applications, the present invention takes a very different approach, specifically connection in a common drain configuration rather than a common source configuration. Because the output MOSFETS 126 and 128 of the SPST switch illustrated in Figure 2 are not connected in a SPDT configuration, they are connected in a common source configuration. However, in the SPDT switch of Figure 1 MOSFETs 18 and 20 are connected in a first common drain configuration and MOSFETs 26 and 28 are connected in a second common drain configuration. Doing so allows these switches to have both their NO and NC connections to be connected while avoiding having them both turn on due to the interplay of the electronics as is the case with the standard relay configuration. This solution is counterintuitive because connection to a common drain rather than to a common source makes MOSFETs more difficult to drive.

[0035] Fourth, the circuit’s power consumption is low enough so that the battery will last a long enough time, essentially the lifetime of the switch. This permits the battery to be potted with the rest of the electronics since the battery never needs to be changed. Tests have shown that circuits made in accordance with the invention are low enough in power that a battery of the type described above should last over 30 years.

[0036] This invention has been described herein in considerable detail to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use embodiments of the example as required. However, it is to be understood that the invention can be carried out by specifically different devices and that various modifications can be accomplished without departing from the scope of the invention itself. By way of example, and without limitation various types of output transistors, other than MOSFETs may be used without deviating from the invention.

[0037] What is claimed is:

Claims

CLAIMS1. A wired electronic switch comprising: a. a sensor; b. an inverter; and c. a battery'.

2. The wired electronic switch of claim 1 wherein said electronic switch is a single pole single throw (SPST) switch comprising a first pair of transistors.

3. The wired electronic switch of claim 2 wherein said transistors of said first pair of transistors are each N channel enhancement MOSFETS.

4. The wired electronic sw itch of claim 2 further comprising first, second and third connectors, and a jumper, said jumper adapted to selectively connect said first and second connectors to provide a first signal path betw een the sensor and at least one transistor of the first pair of transistors bypassing the inverter, said j umper further adapted to selectively connect said first and third connectors to provide an alternative signal path through the inverter which inverts the signals and delivers inverted signals to at least one transistor of the first pair of transistors.

5. The wired electronic switch of claim 1 further comprising a buffer coupled to the sensor.

6. The wired electronic switch of claim 1 further comprising step up circuitry connected to the battery.

7. The wired electronic switch of claim 1 wherein said sensor is selected from a group consisting of magnetic sensors, optical sensors, inductive sensors, and capacitive sensors.

8. The wired electronic switch of claim 1 wherein said electronic switch is a single pole double throw (SPST) switch.

9. The wired electronic switch of claim 8 further comprising a first pair of transistors and a second pair of transistors.

10. The wired electronic switch of claim 9 w herein each of the transistors of the first pair of transistors is coupled in a first common drainconfiguration, and wherein each of the transistors of the second pair of transistors is coupled in a second common drain configuration.

11. The wired electronic switch of claim 9 wherein each of the transistors of at least one of the first pair of transistors and the second pair of transistors is an N channel enhancement MOSFET.

12. The wired electronic switch of claim 9 further comprising a a first signal path bypassing the inverter, and second signal path through the inverter.

13. A wired electronic SPDT switch comprising: a. a battery, b. step up circuitry coupled to the battery, c. a sensor coupled to a buffer, said buffer configured to generate first logic signals, d. a first pair of transistors, e. an inverter configured to receive said first logic signals and invert said first logic signals to generate second logic signals, f. a second pair of transistors configured to receive said second logic signals.

14. The wired electronic SPDT switch of claim 13 wherein each transistor of the first pair of transistors is an N channel enhancement MOSFET, and wherein s each transistor of the first pair of transistors is coupled to a first common drain.

15. The wired electronic SPDT switch of claim 14 wherein each transistor of the second pair of transistors is an N channel enhancement MOSFET, and wherein s each transistor of the second pair of transistors is coupled to a second common drain.

16. The wired electronic SPDT switch of claim 13 further comprising a first drive circuit and a second drive circuit, each of said first drive circuit and said second drive circuit separately comprising a plurality of resistors, an additional pair of MOSFETs, a junction diode, a Schottky diode, and a Zener diode.

17. The wired electronic SPDT switch of claim 16 wherein said first drivecircuit provides a first flow path and a second flow path, and wherein said second drive circuit provides a third flow path and a fourth flow path.

18. The wired electronic SPDT switch of claim 13 wherein said sensor is selected from a group consisting of magnetic sensors, optical sensors, inductive sensors, and capacitive sensors.

19. wired electronic SPST switch comprising: a. a batten . b. step up circuitry coupled to the battery, c. a sensor coupled to a buffer, said buffer configured to generate first logic signals, d. a first pair of transistors, , e. an inverter configured to receive said first logic signals and invert said first logic signals to generate second logic signals, f. a first selectable signal path extending between the buffer and at least one of the transistors of the first pair of transistors bypassing the inverter, and a second selectable signal path extending between the buffer and at least one of the transistors of the first pair of transistors through the inverter.

20. The wired electronic SPST switch of claim 19 wherein each transistor or the first pair of transistors is an N channel enhancement MOSFET.

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