Microelectromechanical switch with load-dependent switching control

Abstract

The invention relates to a microelectromechanical switch comprising a micromechanical switching element (10), a load path (20) for a load signal (25), and a control path (30) for a control signal (35). The micromechanical switching element can be actuated by means of the control path and an associated electrical drive (50), and the load path can be switched by means of the micromechanical switching element. The core of the invention consists in the fact that a control device (40) is arranged in the control path, which is configured to electrically actuate the micromechanical switching element as soon as a control signal is present and the current of the load signal falls below a predetermined value.

Description

State of the art

[0001] The invention relates to a microelectromechanical switch comprising a micromechanical switching element, a load path for a load signal, and a control path for a control signal, wherein the micromechanical switching element can be actuated by means of the control path and an associated electrical drive, and the load path can be switched by means of the micromechanical switching element. Such micromechanical switches are known in the prior art as MEMS relays.

[0002] The effort to miniaturize switches contradicts the need to switch large loads.

[0003] Existing patent applications focus on monitoring maximum currents in MEMS relays, such as US patent 2013 / 0027817 A1. The patent aims to protect components connected to the MEMS relay by monitoring the current amplitude. If the maximum permissible current is exceeded, the MEMS relay disconnects the power supply. Another method for switching higher electrical loads with MEMS relays is described in US 7893799BA. The essential mechanism consists of a latching mechanism with two flexible structures. A further method for switching larger electrical loads is described in US 2012 / 0169266 A1 using a MEMS array. This method employs Hybrid Arcless Limiting Technology (HALT circuits), which reduces phase currents by connecting relays in parallel. In US 2017 / 0117110 A1 or US 2017 / 0117109 A1, another alternative for switching larger currents is described.

[0004] Switching larger electrical loads with MEMS relays leads to intensive wear of the contacts in micromechanical structures. Object of the invention

[0005] The object of the invention is to create a MEMS relay which can switch large electrical loads with low contact wear and high cycle stability. Core and advantages of the invention

[0006] The core of the invention consists in the arrangement of a control device in the control path of the micromechanical switch. This control device is configured to electrically actuate the micromechanical switching element as soon as a control signal is present and the current of the load signal falls below a predetermined value. According to the invention, switching occurs at low current or at the current zero crossing. Switching at the current zero crossing results in the lowest electrical power loss at the switching contact of the MEMS relay. This implies that the smallest arc, and thus the lowest thermal stress, occurs at the switching contact.

[0007] It is advantageous that switching at the current zero crossing, which implies detection of the current zero crossing, enables the operation of larger inductive or capacitive loads at the output of the switch according to the invention (MEMS relay).

[0008] Advantageous embodiments of the invention can be found in the dependent claims. drawing Fig. Figure 1 schematically shows a microelectromechanical switch according to the invention with load-dependent switching control as a normally open contact. Fig. Figure 2 schematically shows a microelectromechanical switch according to the invention with load-dependent switching control as a normally closed contact. Fig. Figure 3 shows the current and voltage curves of a load to be switched. Description

[0009] Fig. Figure 1 schematically shows a microelectromechanical switch according to the invention with load-dependent switching control as a normally open contact. The image shows a microelectromechanical switch 1 with a micromechanical switching element 10, a load path 20 for a load signal 25, and a control path 30 for a control signal 35. The micromechanical switching element can be actuated by means of the control path and an associated electrical actuator 50, and the load path can be switched by means of the micromechanical switching element. A control device 40 is arranged in the control path, which is configured to electrically actuate the micromechanical switching element as soon as a control signal is present and the current of the load signal falls below a predetermined value. For this purpose, the control device has a phase detector 42 with an input for the load signal 25. The phase detector detects a zero crossing of the current of the load signal 25.One output of the phase detector and the control signal 35 are each connected to an input of a signal logic circuit 44. One output of the signal logic circuit is connected to the electric drive 50. The switch is configured as a normally open contact, i.e., it is open when the micromechanical switching element is in its resting state.

[0010] Fig. Figure 2 schematically shows a microelectromechanical switch according to the invention with load-dependent switching control as a normally closed contact. In contrast to the one in Fig. In the device shown in Figure 1, this switch is designed as a normally open switch, i.e., closed when the micromechanical switching element is in its resting state.

[0011] Fig. Figure 3 shows the current and voltage waveforms of a load to be switched. A periodic voltage U and current I are depicted over time t. Voltage and current have a phase shift Φ relative to each other.

[0012] The phase detector detects a zero crossing of the current of the load signal 25. The load signal 25 is applied between an input pin 22 and an output pin 24 of the load path 20. The MEMS relay can be configured either as a normally open contact, as shown in Fig. 1 shown, or as an opener, as in Fig. Figure 2 shows how this can be implemented. Another input pin 32 of the control path 30 receives the control signal 35 to switch the MEMS relay. The internal phase detector 42 evaluates the current and voltage behavior relative to another output pin 34, a reference pin connected to an electrical ground 60, as shown in the Fig. 1 and Fig. 2 shown. At the zero crossing of the current ( Fig. 3) The phase detector 42 delivers a control signal to internal evaluation electronics, the signal processing logic 44. If a switching command 35 is present at the further input pin 32, the MEMS relay is activated by the electric actuator 50 by deflecting the micromechanical switching element 10 from a rest position and thus switching the load path 20. The actuator 50 is any drive unit of the movable micromechanical switching element of a MEMS relay. This can be, as in the Fig. 1 and Fig. 2 shown schematically, suspended in a deflectable manner by means of a suspension spring or designed in another way. Other capacitive drive types are also possible. Reference symbol list 1 microelectromechanical switch 10 micromechanical switching part 20 Load path 22 Load input 24 Load output 25 Load signal (In) 30 Control path 32 Tax input 34 Control output 35 Control Signal 40 Control unit 42 Phase detector (U / I) 44 Signal combination logic (Evaluation Logic) 50 electric drive (MEMS Drive Unit) 60 Electrical ground (GND) QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2013 / 0027817 A1

[0003] US 7893799

[0003] US 2012 / 0169266 A1

[0003] US 2017 / 0117110 A1

[0003] US 2017 / 0117109 A1

[0003]

Claims

[1] Microelectromechanical switch comprising a micromechanical switching element (10), a load path (20) for a load signal (25) and a control path (30) for a control signal (35), wherein the micromechanical switching element can be actuated by means of the control path and an associated electrical drive (50) and the load path can be switched by means of the micromechanical switching element, characterized by , that a control device (40) is arranged in the control path, which is configured to electrically actuate the micromechanical switching element as soon as a control signal is present and the current of the load signal falls below a predetermined value. [2] Microelectromechanical switch according to claim 1, characterized by , that the specified value is a zero crossing of the current of the load signal (25). [3] Microelectromechanical switch according to one of the preceding claims 1 or 2, characterized bythat the control device (40) has a phase detector (42) with an input for the load signal (25). [4] Microelectromechanical switch according to any one of the preceding claims 1 to 3, characterized by , that the load path (20) is closed when the micromechanical switching part (10) is actuated. [5] Microelectromechanical switch according to any one of the preceding claims 1 to 3, characterized by , that the load path (20) is open when the micromechanical switching part (10) is actuated.

Images