EP3594979A1

EP3594979A1 - Apparatus to switch a led

Info

Publication number: EP3594979A1
Application number: EP18182431.9A
Authority: EP
Inventors: Thierry Delachaux; Pierre Corfdir; Rudolf Gati
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2018-07-09
Filing date: 2018-07-09
Publication date: 2020-01-15
Also published as: EP3594980B1; EP3594980A1

Abstract

An apparatus (1, 1a-c) to switch a light-emitting diode (2) or another load, comprising a mechanical switch (3), which comprises a moving electrode (4), wherein the moving electrode (4) is a contact, which electrically gets in connection with a further contact or electrode to enable a current flow while a closing phase and while an operation time and which moving electrode (4) can be separated from the further contact or electrode to interrupt current flow while a breaking phase of the mechanical switch (3), characterized in that the apparatus (1, 1a-c) comprises a solid-state-device (5), which is arranged in such a manner that current at least partially flows through the solid-state-device (5) while a closing or breaking phase and that current at least partially flows through the mechanical switch (3) in closed position while the operation time, achieves the object to drastically limit the arcing duration during the inrush current phase or switching on phase as well as during the breaking current phase or even to avoid any arcing.

Description

The invention is related to an apparatus to switch a light-emitting diode (LED) or another load, comprising a mechanical switch, which comprises a moving electrode, wherein the moving electrode is a contact, which electrically gets in connection with a further contact or electrode to enable a current flow while a closing phase and while an operation time and which moving electrode can be separated from the further contact to interrupt current flow while a breaking phase of the mechanical switch.
Nowadays LED lamps are replacing the traditional light bulbs for the sake of their more efficient conversion of electricity into light. This change is even enforced by regulation in most of the countries worldwide.
However, when switching on a LED lamp, a high inrush current occurs during the first milliseconds due to the sudden charge of capacitors located in the LED driver (AC/DC converter), as illustrated in Fig. 1. Typical inrush peak currents are ranging about 10 times higher than then rated current.
One of the issues of mechanical switches is that there is a certain bouncing of the moving electrode during the closing or making phase. The kinetic energy of the moving electrode can not be dissipated efficiently, which generates a bouncing.
The main problem comes when mechanical switches are used to switch on LEDs, for instance. Since the bounces occur while the current flows, then an arc forms between the two contacts. Due to the very high inrush current that can be reached in switching on LEDs, this can lead to an accelerating contact ageing, or even to a welding of the two contacts.
The object of the invention therefore is to drastically limit the arcing duration during the inrush current phase or switching on phase as well as during the breaking current phase or even to avoid any arcing.
The object of the invention is achieved by means of the features of claim 1.
According to this claim the apparatus comprises a solid-state-device, which is arranged in such a manner that current at least partially flows through the solid-state-device while a closing or breaking phase and that current at least partially flows through the mechanical switch in closed position while the operation time.
According to the invention it has been found that to drastically limit the arcing duration during the inrush current phase or switching on phase as well as during the breaking current phase, or even to avoid any arcing, the proposed solution is to combine a solid-state-device in parallel to a mechanical switch.
The main idea is to have the current flow through the solid-state-device, preferably a triac, during the making and breaking phases, which last a few milliseconds, while the current flows through the switch in its closed position during all the rest of the time.
The advantage of this system is to have a quasi arc-free switching during the on and off phases, which prevent an excessive erosion of the contacts. In addition, in closed position the mechanical switch ensures very low electrical losses, compared to a fully solid-state solution.
Advantageously the solid-state-device is a semi-conductor-device, which is paralleled to the mechanical switch. Semi-conductor-devices are highly reliable.
Further advantageously the solid-state-device is a triac, namely a triode for alternating current, which is paralleled to the mechanical switch. A triac is an electronic element having a structure of sheets comprising semi-conductors. A triac comprises two thyristors in anti-parallel configuration. Through this it is possible to switch alternating current, whereas a single thyristor only can switch in one direction and in activated modus functions like a diode. The triac may be fired over a gate and stay conductive as long as a holding current is undershoot.
Advantageously the mechanical switch is a rocker light switch. Such mechanical switches are highly reliable and are cost effective.
Further advantageously the apparatus comprises a disconnector. A disconnector has to be added in series in order to insure a galvanic insulation.
Advantageously the apparatus comprises a triggering system for the solid-state-device. An appropriate triggering system can switch the solid-state-device.
Further advantageously the triggering system electronically controls the gate of the solid-state-device.
Advantageously the triggering system controls the gate of the solid-state-device by a difference of a voltage on the switch.
In the drawings:

Fig. 1: shows an inrush current which occurs, when the switch closes with a LED load, it is shown that a fast transient phase occurs, which is smaller than 2ms, with a peak inrush current reaching up to about ten times the rated current,
Fig. 2: shows an illustration of the combined system, comprising a mechanical switch and a semi-conductor-device, made to drastically limit the arcing duration during the current making and breaking phases by using a triac, while ensuring low electrical losses in closed position by using the switch,
Fig. 3: shows an illustration of the combined system, comprising a mechanical switch and a solid-state-device, with two controlling possibilities, the possibility A schematically shows, that the gate of the solid-state-device is controlled electronically, and the possibility B schematically shows, that the gate of the solid-state-device is controlled by the difference of voltage on the mechanical switch, which is activated mechanically, when the switch closes, and is deactivated mechanically when the switch opens,
Fig. 4: shows an illustration of the simplest hybrid switch system, this includes the concept of triggering of a triac, the mechanical switch is a rocker light switch and further a triac gate switch is given, in the closed position, the gate of the triac is connected, so that the triac can be fired as soon as the minimum current is reached, in an open position, it ensures that the rated current is stopped to flow through the triac, resistors are chosen so, that the triac is fired only, when the voltage drop in the rocker light switch is higher than a certain threshold, typically around 10 V, which would correspond to arcing into the switch,
Fig. 5: shows an illustration of an improved triggering system for a triac including resistors and diodes, the diodes enforce the triggering current to the triac's and limit the current flowing from one side to the other of the switch via the resistors, only the diode leakage current may flow, and
Fig. 6: shows an alternative electrical diagram of the hybrid switch, it contains varistors, or Zener diodes, between the gate and the triac electrodes in order to insure a voltage drop in the specifications of the triac, as well as to protect the triac's gate from over-currents.

Fig. 1 illustrates, that a high inrush current occurs during the first milliseconds due to the sudden charge of capacitors located in a LED driver (AC/DC converter), when switching on a LED lamp. Typical inrush peak currents are ranging about 10 times higher than then rated current.
Fig. 2 schematically shows an apparatus 1 to switch a light-emitting diode (LED) 2, comprising a mechanical switch 3, which comprises a moving electrode 4.
The moving electrode 4 is a contact, which electrically gets in connection with a further contact or electrode to enable a current flow while a closing phase and while an operation time and which moving electrode 4 can be separated from the further contact to interrupt current flow while a breaking phase of the mechanical switch 3.
The apparatus 1 comprises a solid-state-device 5, which is arranged in such a manner that current flows through the solid-state-device 5 while a closing or breaking phase and that current flows through the mechanical switch 3 in closed position while the operation time.
The solid-state-device 5 is a semi-conductor-device, which is paralleled to the mechanical switch 3. The solid-state-device 5 is a triac, namely a triode for alternating current, which is paralleled to the mechanical switch 3. The mechanical switch 3 is a rocker light switch. The apparatus 1 also comprises a disconnector 6.
The working principle of the apparatus 1 is a follows:
In a switching on phase (current make), first the mechanical switch 3 is in open position and the disconnector 6 is closed. At this point no current flows into the apparatus 1. While the mechanical switch 3 is closing, the triac, namely the solid-state-device 5, is fired either slightly before the contacts' touch, or slightly after.
In case the triac is fired before the switch contacts' touch, then the inrush current is initiated through the triac, arcing-less. As soon as the contacts of the mechanical switch 3 are in closed position, the current commutes from the triac to the mechanical switch 3 due to the much lower resistance path. The voltage drop is about 10 mV into the mechanical switch 3 for 10A/16A, while the on-state voltage drop is in the range of 1 V into the triac.
In case the triac is fired after the switch contacts' touch, the inrush current flows through the contacts in closed position of the mechanical switch 3. In case of bouncing of the contacts, an arc voltage will appear, which is usually > 10 V. The scheme protected with this description, as one part of this invention, is described hereafter.
However, it is such that as soon as a 10 V voltage drop appears on the mechanical switch 3, a current commutation through the triac is initiated. Typical commutation times expected are in the range of 1 µs for 1A and 10 µs for 100 A. Within this duration, limited damages are done to the switch electrodes. Eventually, when the contacts are in a stable closed position after about 1 ms, the current commutates from the triac to mechanical switch 3.
In a switching off phase (current break), to break the current, the mechanical switch 3 is opened first. As soon as the arc appears between the two contacts, e.g. when a voltage drop > 10 V is given, then the current commutes into the triac. When the current reaches a current zero, the current is stopped. At this point the disconnector 6 opens in order to insure the galvanic insulation of the system.
For both phases described above (current make and current break), only a very short arc duration appears into the mechanical switch 3, which allows a quasi-arc free rocker light switch.
Fig. 3 schematically shows that the apparatus 1 comprises a triggering system 12 for the solid-state-device 5. The triggering system 12 electronically controls the gate of the solid-state-device 5 or the triggering system 12 controls the gate of the solid-state-device 5 by a difference of a voltage on the switch 3.
The triggering system 12 of the solid-state-device 5 works as follows:
The triggering of the solid-state device 5 and its synchronization with the mechanical switch 3 is very important. There are essentially two schemes shown in Fig. 3 that can be used to control the solid-state-device's gate.
Fig. 3 shows an illustration of the combined system, comprising the mechanical switch 3 and the solid-state-device 5, with two controlling possibilities A and B.
The possibility A schematically shows, that the gate of the solid-state-device 5 is controlled electronically, and the possibility B schematically shows, that the gate of the solid-state-device 5 is controlled by the difference of voltage on the mechanical switch 3, which is activated mechanically, when the switch 3 closes, and is deactivated mechanically when the switch 3 opens.
The first scheme on the left side of Fig. 3 is to control the solid-state-device's gate by electronic only, using rectifiers, transistors, operational amplifiers, and/or a microcontroller.
The second scheme on the right side of Fig. 3 controls the solid-state-device's gate with a mechanical connection to the mechanical switch 3.
With respect to Fig.4 it becomes clear, that this allows to synchronize the mechanical switch 3 of apparatus 1a in Fig. 4 with the gate switch 7. Because the current flowing through the triac gate has to be limited in a range between 10 - 50 mA, the exact values depend on the triac specifications, the gate switch 7 can be small in comparison to mechanical switch 3.
Additionally, it will carry this current only for a limited time, usually for a time shorter than 10 ms during the making and breaking phases, so that it does not have to be specially optimized to limit electrical losses or to avoid overheating, unlike the main switch 3. Therefore, the gate switch 7 can be very simple in design.
It also means that the triac can be chosen for a current lower than the rated current, since it does not have to carry it continuously, which may help to lower the costs. The triggering system 12 is developed such, that, when a voltage difference is larger than a few volts, namely about 10 V, which corresponds to an arc in the main switch 3.
This can be done easily by choosing the appropriate resistances of the current path to the triac gate. The role of the disconnector 6 is to ensure the galvanic insulation of the system. Without disconnector 6, the leakage current through the triac would continue to flow.
Fig. 4 shows an illustration of the simplest hybrid switch system, this includes the concept of triggering of a triac, the mechanical switch 3 is a rocker light switch and further a triac gate switch 7 is given. In the closed position, the gate of the triac is connected, so that the triac can be fired as soon as the minimum current is reached.
In an open position, it ensures that the rated current is stopped to flow through the triac, resistors 13, 14 are chosen so, that the triac is fired only, when the voltage drop in the rocker light switch is higher than a certain threshold, typically around 10 V, which would correspond to arcing into the switch 3.
The scheme concerning apparatus 1a proposed in Fig. 4 is, however, a bit too simplified. During the breaking phase, once the current is interrupted, there is still some current able to flow through the resistors 13, 14 controlling the gate current. This one can reach up to 1 A, so that the disconnector 6 may have trouble, or should be designed specifically, if it shall open with this current.
A good alternative to solve that potential issue and to make sure, at the same time, that the gate current is really going to the triac's gate, is to add diodes 8, 9 as shown in Fig. 5. The diodes 8, 9 are in series with the resistors 13, 14.
Finally, an alternative electrical scheme concerning apparatus 1c is proposed that protects the triac's gate in case of over-current and over-voltage. It is shown in Fig. 6 and uses Zener diodes 10,11 or varistors to fulfil this task.
The concept of a mechanical switch 3 in parallel to a triac shown here implies that the switching on and off sequences are done by relays, and not by a rocker light switch. Further it is implied that the solid-state device 5 must not be controlled with a microprocessor and/ or transistors, i.e. microelectronically. Further the controlling aspect of the triac implies to use the energy of the electrical network directly and to mechanically synchronize the triac with the switch. Some systems of the state of the art must have a permanent DC supply to operate their equipment synchronously.

The field of the invention relates to mechanical switches 3, in particular to mechanical switches 3 at low voltages, namely smaller 1 kV, such as rocker light switches. The invention relates to applications of light switches with LED lamps, or any other type of loads with high inrush currents occurring during the making of the current.

Reference numbers

1, 1a, 1b, 1c	Apparatus
2	Light emitting diode (LED)
3	Mechanical switch
4	Moving electrode
5	Solid-state-device
6	Disconnector
7	Gate switch
8, 9	Diode
10, 11	Zener diode
12	Triggering system
13, 14	Resistor

Claims

Apparatus (1, 1a-c) to switch a light-emitting diode (2) or another load, comprising a mechanical switch (3), which comprises a moving electrode (4), wherein the moving electrode (4) is a contact, which electrically gets in connection with a further contact or electrode to enable a current flow while a closing phase and while an operation time and which moving electrode (4) can be separated from the further contact or electrode to interrupt current flow while a breaking phase of the mechanical switch (3),
characterized in that the apparatus (1, 1a-c) comprises a solid-state-device (5), which is arranged in such a manner that current at least partially flows through the solid-state-device (5) while a closing or breaking phase and that current at least partially flows through the mechanical switch (3) in closed position while the operation time.
Apparatus according to claim 1, characterized in that the solid-state-device (5) is a semi-conductor-device, which is paralleled to the mechanical switch (3).
Apparatus according to claim 1 or 2, characterized in that the solid-state-device (5) is a triac, namely a triode for alternating current, which is paralleled to the mechanical switch (3).
Apparatus according to one of the preceding claims, characterized in that the mechanical switch (3) is a rocker light switch.
Apparatus according to one of the preceding claims, characterized in that the apparatus (1, 1a-c) comprises a disconnector (6).
Apparatus according to one of the preceding claims, characterized in that the apparatus (1, 1a-c) comprises a triggering system (12) for the solid-state-device (5).
Apparatus according to claim 6, characterized in that the triggering system (12) electronically controls the gate of the solid-state-device (5).
Apparatus according to claim 6, characterized in that the triggering system (12) controls the gate of the solid-state-device (5) by a difference of a voltage on the mechanical switch (3).
Method of use of an apparatus (1, 1a-c) according to one of the preceding claims to avoid any arcing in the mechanical switch (3).