AU2018211234A1

AU2018211234A1 - An Alternator Surge Clipping Device

Info

Publication number: AU2018211234A1
Application number: AU2018211234A
Authority: AU
Inventors: Giuliano Res
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-07-31
Filing date: 2018-07-31
Publication date: 2019-02-14
Anticipated expiration: 2038-07-31
Also published as: ZA201805132B; AU2018211234B2

Abstract

An overvoltage surge clipping device in operable communication with a load: the device comprising: a combined switch and regulator, a circuit providing a control signal to turn the combined switch and regulator fully on, a detection and regulation circuit capable of adjusting the control signal when an output voltage from the load reaches a specified threshold. The control signal causes the combined switch and regulator to deliver an output voltage slightly higher than a normally regulated voltage output. Figure 1 Control Signal *!0 Generation Circuit Oupu Voltlage Regulated DC Alternator - Dtectiotand Field Coileulation Cirui Control Circuit s Combined switch Pos Field Stator Diode L and regulator Coil Coils Bridge -Neg

Description

AN ALTERNATOR SURGE CLIPPING DEVICE

BACKGROUND OF THE INVENTION [0001] The present invention relates to alternators and generators. An alternator is a device that converts mechanical energy into alternating current (AC) electrical energy. A generator is a device that converts mechanical energy into direct current (DC) electrical energy. The term ‘alternator’ is also commonly used to describe a device that is an alternator with circuitry to convert AC to DC, typically using a diode bridge, to deliver DC power. Alternators are commonly found in all types of vehicles; bicycles, motorbikes, cars, trucks, airplanes, tractors, earthmoving and mining equipment, boats, ships, spacecraft, etc. For devices that produce DC output the power can be measured at any point in time as the product of the DC voltage times the current. The present invention will be described with reference to and primarily relates to devices producing DC power.

[0002] Mechanical to electrical energy conversion occurs when a magnetic field and a coil are pushed past each other. This movement results in a mechanical force that resists the movement and the corresponding generation of an electrical current. The output power is a function of many parameters including the mechanical rotational speed, the strength and geometric shape of the magnetic field, the type of coil and the resistive, inductive and capacitive characteristics of the electrical load.

PRIOR ART [0003] Commonly, alternators and generators are regulated by controlling the strength of the magnetic field using a field coil. A control circuit adjusts the current through the field coil to control the magnetic field which in turn controls the output power. Typically the output voltage is monitored by the control circuit so as to deliver a relatively fixed output voltage for a wide range of loads. When there is a change of load, such as switching, for example, lights on or off the output voltage correspondingly goes down or up for a short period until the field strength can be adjusted to provide the regulated

2018211234 31 Jul 2018 voltage for the new load. When the load suddenly drops there is a brief overvoltage surge and when the load suddenly increases there is a brief undervoltage droop.

[0004] Other, less common techniques may be employed to provide output voltage regulation but these devices still exhibit overvoltage surge and under voltage droop.

[0005] Devices being powered by the alternator or generator may require protective circuitry to handle the surge and droop that may occur as other devices are switched on and off. A surge, in particular, can generate voltage levels that damage unprotected circuitry. In the automotive industry, for example, an international standard, ISO 16750 Part 2, has been written to provide agreed upon surge and droop limits so both alternator and powered device manufacturers can seek to meet the specified limits at minimal cost. An electronic clamping device is often used with the alternator which quickly acts as a compensating load to limit the output voltage during the surge. These voltage clamping devices need to absorb the excess energy being delivered during the surge, converting this energy into heat. Notably, the voltage clamping device is placed in parallel with any other loads or as the only load. Often there is also a very fast transient overvoltage as the voltage clamping device begins to draw current. Even with surge protection the product life of loads, such as lights, may be reduced due to the overvoltage surges.

[0006] An overvoltage surge is typically known in the automotive industry as load dump and can occur frequently when the load to an alternator is disconnected or varied. The load dump surge is dependent on the RPM of the alternator and the variation of the load, which could change from full load to no load or anywhere in-between .

[0007] There are surge protection devices specifically designed to clamp automotive load dump voltage spikes. They are commonly called voltage suppressors and can be electronic devices such as TVS, MOV, transorb, etc. They are inherently fast operating and can absorb or withstand a large amount of power as they are primarily designed to dissipate the excess energy generated by the alternator at the moment of the load dump.

[0008] A major drawback of all these devices is the wide voltage range between the

2018211234 31 Jul 2018 clamping voltage of a small current compared with the clamping voltage of the maximum current. For example, a 15V TVS will start to conduct in the region of 15V to 17V but when conducting the maximum surge current the voltage is over 23V. This poor clamping performance then requires that powered devices have secondary spike protection and filtering circuitry.

[0009] In hazardous environments, such as in mines, flame-proof alternators are required to ensure the device will not cause mine explosions. These alternators typically include circuitry to monitor the load and detect fault conditions and shut off their output until they are reset.

THE INVENTION [0010] The present invention provides a voltage regulated AC or DC alternator or generator providing power through an electronic component that usually operates as an electronic switch that is normally turned on but, when a surge occurs, the electronic component then regulates the output voltage to a value slightly higher than the normally regulated output voltage. The invention provides a clipping device which simply and inexpensively clamps the output voltage to a value far below the typical overvoltage limits seen in existing equipment. The present invention eliminates the need for a voltage clamping electronic device, and eliminates the need for protective circuitry in powered devices and lengthens the product life for devices sensitive to overvoltage surges. More specifically, the present invention provides a surge clipping device which is capable of regulating output voltage to a value slightly higher that the normally regulated out put voltage.

[0011] Compared with known devices that use a voltage clamping device that is placed across the output terminals of the alternator and acts to absorb the excess energy by drawing potentially very large current, the present invention is placed in series with the load and only needs to absorb a much smaller amount of energy needed to drop the overvoltage back down to a voltage just above the normally regulated output voltage.

2018211234 31 Jul 2018 [0012] The output voltage response can be measured and observed using an oscilloscope to monitor the output voltage following a sudden change in load. A typical response of existing devices is a very quick and high overvoltage spike followed by a rapid voltage rise then a slower voltage drop back down to the normally regulated output voltage. In comparison, the response of the clipping device according to the present invention is a quick and slight rise to the slightly higher voltage followed by a flat voltage as the alternator’s regulation circuit adjusts then a slower drop back to the normally regulated voltage. The overvoltage surge of existing devices has effectively been clipped to a voltage slightly higher than the normally regulated voltage.

[0013] In one broad form the present invention comprises:

a voltage surge clipping device for use with an alternator including a diode bridge, an nchannel MOSFET, a Zener diode, an NPN bipolar transistor and resistors.

[0014] In another broad form the present invention comprises:

a voltage surge clipping device for use with an alternator including a diode bridge, an nchannel MOSFET, a Zener diode, an NPN bipolar transistor and resistors; the clipping device comprising;

a combined switch and regulator, a control signal generation circuit in communication with the combined switch and regulator; and intermediate the regulator and control signal generation circuit, an output voltage detection and regulation circuit; the clipping device being responsive to an overvoltage surge to restrict the surge to a voltage slightly higher than a normally regulated operating voltage output.

[0015] When a surge overvoltage occurs the Zener diode conducts current to regulate the base current of the NPN transistor which in turn regulates the MOSET’s gate voltage which in turn regulates the output voltage to the circuit’s overvoltage limit which is, by design, slightly above the normally regulated output voltage. During normal operation there is only a very small leakage current through the Zener diode, no current through the NPN transistor base and the MOSFET is fully turned on.

2018211234 31 Jul 2018 [0016] Many flame-proof alternators currently use a MOSFET to shut off the output power after a fault is detected. According to the present invention, the addition of the electronic components is employed to use the existing MOSFET to regulate the output voltage.

[0017] The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a semiconductor device which is widely used for switching and amplifying electronic signals in the electronic devices. The MOSFET is a core of integrated circuit and it can be designed and fabricated in a single chip because of these very small sizes. The MOSFET is a four terminal device with source(S), gate (G), drain (D) and body (B) terminals. The MOSFET is very far the most common transistor and can be used in both analog and digital circuits.

[0018] The MOSFET works by electronically varying the width of a channel along which charge carriers flow (electrons or holes). The aim of the MOSFET is to be able to control the voltage and current flow between the source and drain. It works in effect as a switch.

[0019] In another broad form the present invention comprises:

an overvoltage surge clipping device in operable communication with a load: the device comprising:

a combined switch and regulator, a circuit providing a control signal to turn the combined switch and regulator fully on, a detection and regulation circuit capable of adjusting the control signal when an output voltage from the load reaches a specified threshold; wherein, the control signal causes the combined switch and regulator to deliver an output voltage slightly higher than a normally regulated voltage output [0020] it will be appreciated by persons skilled in the art that a wide range of alternative forms of circuitry can be used in various embodiments of the invention. For

2018211234 31 Jul 2018 example, the combined switch and regulator could be a MOSFET, a power transistor or an IGBT (Insulated Gate Bi polar Transistor).

BRIEF DESCRIPTION OF THE DRAWINGS [0021] The present invention will now be described in broad detail according to preferred but non limiting embodiments and with reference to the accompanying illustrations, wherein;

Figure 1 shows a block diagram of one embodiment of the invention.

Figure 2 is a circuit diagram for a circuit incorporated into the arrangement of figure 1.

Figure 3 shows an oscilloscope display indicating a result with surge clipping ON.

Figure 4 shows an oscilloscope display indicating a surge clipping device and internal clipping voltage; AND

Figure 5 shows an oscilloscope display result without a surge clipping device.

DETAILED DESCRIPTION [0022] Referring to figure 1 there is shown a schematic layout of one embodiment of the invention. The layout shown comprises a regulated DC alternator 1 wherein the positive output is connected to a combined switch and regulator 2 which is normally turned fully on by a control signal 3 generated by the control signal generation circuit 4. The output voltage detection and regulation circuit 5 monitors the output voltage to the load and, when the output voltage exceeds a voltage slightly higher than the normally regulated voltage, the output voltage detection and regulation circuit 5 adjusts the control signal 3 so the combined switch and regulator will drop the overvoltage on the alternator’s positive output so as to deliver a voltage slightly higher than the normally regulated output voltage. When the overvoltage surge ends the output voltage detection and regulation circuit 5 allows the control signal 3 to drive the combined switch and regulator 2 to be fully on.

2018211234 31 Jul 2018 [0023] Referring to figure 2 the alternator’s positive output is connected to an n-channel MOSFET 6 which is the combined switch and regulator. The gate of the MOSFET 6 is connected to the gate drive signal 7 via a resistor 8 whereby the MOSFET 6 is turned fully on whenever the NPN transistor 9 is off. During normal operation, where the output voltage is regulated by the regulated DC alternator 1 field coil control circuit, there is only a very small leakage current through the Zener diode 10, the resistor 11 and the NPN transistor 9 which is effectively off. Any current draw on the transistor 9 collector due to the small Zener leakage current through the transistor 9 base is insignificant and leaves the MOSFET 6 fully turned on. When an overvoltage surge occurs the output voltage rises to the point where the Zener diode 10 begins to conduct current which causes the transistor 9 to draw current from the control signal that in turn pulls the control signal 3 voltage down causing the MOSFET 6 to drop the excess voltage and deliver an output voltage to the load that is slightly higher than the normally regulated DC voltage.

[0024] The present invention describes the output being switched from the positive supply through the MOSFET to the load. Alternatively, the load could be connected to the positive supply and the MOSFET connected to ground.

[0025] Figure 3 shows an oscilloscope display indicating a result with surge clipping ON. This indicates when a control signal causes the combined switch and regulator to deliver an output voltage slightly higher than a normally regulated voltage output. In this case the minimum is 13.2V and the maximum is 14.6V. On the display each line division is 5 volts. If MOSFET is turned off the voltage goes back to 13.2 Volts. If the voltage is too high the MOSFET can be turned off momentarily. An extra transistor can be provided to turn off the MOSFET.

Figure 4 shows an oscilloscope display indicating a surge clipping device and internal clipping voltage which increases to a dangerous level. The output can be turned off until internal clipping voltage falls within safe levels and output is turned back on. Figure 5 shows an oscilloscope display result without a surge clipping device including a

2018211234 31 Jul 2018 minimum voltage of 13.2V to a maximum of 27.6V.

[0026] The present invention provides a useful alternative to the known devices and although the invention is described with reference to its application in alternator and generator devices it will be recognised that the invention has a variety of applications not limited to that described.

[0027] It will be recognized by persons skilled in the art that numerous variations and modifications may be made to the invention as broadly described herein without departing from the overall spirit and scope of the invention.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. An overvoltage surge clipping device in operable communication with a load: the device comprising:

a combined switch and regulator, a circuit providing a control signal to turn the combined switch and regulator fully on, a detection and regulation circuit capable of adjusting the control signal when an output voltage from the load reaches a specified threshold; wherein, the control signal causes the combined switch and regulator to deliver an output voltage slightly higher than a normally regulated voltage output.
2 A device according to claim 1 wherein, an electronic component operates as an electronic switch.
3 A device according to claim 2 wherein, when the electronic switch is turned on and when a voltage surge occurs, the electronic switch regulates the output voltage to a value slightly higher than said normally regulated output voltage.
4 A device according to claim 3 wherein the electronic switch is placed in series with the load.
5 A device according to claim 4 wherein, the output load voltage is initially created from an AC or DC generator.
6 A device according to claim 5 wherein, the device is attached to an output of a mechanical power to AC or DC electrical power converter.
7 A device according to claim 6 wherein, the switch absorbs a small amount of energy needed to drop an overvoltage back down to said voltage just above the normally regulated output voltage.

2018211234 31 Jul 2018
8 A device according to claim 7 wherein the electronic switch operates to allow a quick and slight rise to a slightly higher voltage followed by a flat voltage as the alternator’s regulation circuit adjusts, then a slower drop back to the normally regulated voltage.
9 A device according to claim 8 wherein, an overvoltage surge from a load device is clipped to a voltage slightly higher than the normally regulated voltage.
10 A device according to claim 9 wherein, the alternator includes a diode bridge, an n-channel MOSFET, a Zener diode, an NPN bipolar transistor and at least one resistor.
11. A device according to claim 10 wherein, in the event of a surge overvoltage in a load, the Zener diode conducts current to regulate a base current of the NPN bi polar transistor which in turn regulates the MOSET’s gate voltage which in turn regulates the output voltage to the circuit’s overvoltage limit.
12 A device according to claim 11 wherein, the output voltage is, slightly above the normally regulated output voltage.
13 A device according to claim 12 wherein, electronic components of the clipping device use a MOSFET to regulate the output voltage.
14 A device according to claim 13 wherein, during normal operation there is exists a small leakage current through the Zener diode, no current through the NPN transistor base and the MOSFET is fully turned on.
15 A device according to claim 14 wherein, said combined switch and regulator is a MOSFET. .
16 A device according to claim 12 wherein, said combined switch and regulator is a power transistor.
17 A device according to claim 12 wherein, said combined switch and regulator is

2018211234 31 Jul 2018 an IGBT (Insulated Gate Bipolar Transistor).
18 A voltage surge clipping device for use with an alternator including a diode bridge, an n-channel MOSFET, a Zener diode, an NPN bipolar transistor and resistors, the clipping device comprising;

a combined switch and regulator, a control signal generation circuit in communication with the combined switch and regulator; and intermediate the regulator and control signal generation circuit, an output voltage detection and regulation circuit; the clipping device being responsive to an overvoltage surge from a load to restrict the surge to a voltage slightly higher than a normally regulated operating voltage output of said load.
19 An alternator surge clipping device with an output control MOSFET that is on whenever the alternator’s output voltage is at its normally regulated voltage but that is used to regulate any output overvoltage surge typically resulting from a sudden drop in the load.