Switch with electronic trip unit

Abstract

The invention relates to a switch with an electronic trip unit. The invention relates to a switch (LS) having an electronic trip unit (ETU) and a supply circuit (NT) for supplying energy to the electronic trip unit (ETU) from a monitored circuit. In the case of a switch according to the present invention, a supply circuit (NT) is configured using a linear regulator (LDO) and a switching regulator (DCDC). The linear regulator (LDO) and the switching regulator (DCDC) are connected in parallel. The switching regulator (DCDC) has a power good output (PG / SS), and the linear regulator (LDO) has a disabling input (SHDN) connected to each other. Such a device is inexpensive and, when building a voltage supply, results in a fast supply of an output voltage by a linear regulator and deactivation of the linear regulator via a disabled input if a switching regulator operating with lower loss is able to ensure the voltage supply. The supply is automatically taken over by the switching regulator without external additional elements or signaling.

Description

Technical Field

[0001] The invention relates to a switch having an electronic tripping unit and a supply circuit for supplying the electronic tripping unit with energy from a monitored circuit. Background Art

[0002] A circuit breaker introduced into an electrical circuit provides protection for the circuit that functions similarly to a fuse. Protection is achieved by monitoring the current flowing through the conductors of the circuit. Typically, the current or energy flow is diverted through the circuit to an energy sink or consumer. The circuit breaker monitors protection parameters for the presence of conditions for interrupting the circuit by opening the switch (also referred to herein as tripping the switch). This protection function typically involves short-circuit current (monitoring the absolute value of the current) and overcurrent (monitoring for exceeding a current threshold within a predetermined time interval). Furthermore, tripping according to more complex criteria can be provided in the event of an arc fault.

[0003] For example, the interruption occurs by opening contacts of a circuit breaker. Unlike fuses, these protection parameters or response values are adjustable in circuit breakers. To adjust these parameters and verify the tripping criteria, modern circuit breakers usually have a control unit, also known as an electronic trip unit or ETU (electronic trip unit) or an overcurrent trip unit.

[0004] In particular, for low-voltage circuits or low-voltage power grids, there are various types of circuit breakers, depending on the level of the current provided in the circuit. A circuit breaker in the sense of the present application is particularly a switch used for currents of 25 to 6300 amperes, as used in low-voltage installations. More particularly, enclosed circuit breakers are used for currents of 63 to 1600 amperes, in particular 125 to 630 or 1200 amperes. Open circuit breakers are used, in particular, for currents of 630 to 6300 amperes, more particularly 1200 to 6300 amperes. Open circuit breakers are also known as air circuit breakers, or ACBs for short, and enclosed circuit breakers are known as molded case circuit breakers or compact circuit breakers, or MCCBs for short.

[0005] Low voltage refers to voltages up to 1000 V AC or 1500 V DC. Low voltage also refers to voltages greater than a low voltage having a value of 50 V AC or 120 V DC.

[0006] exist Figure 1 An example of a circuit breaker LS with an electronic trip unit or ETU serving as a control unit is shown. The circuit breaker is configured to interrupt electrical conductors L1, L2, and L3 of an electrical circuit, for example a three-phase AC circuit, wherein first conductor L1 forms a first phase of the three-phase AC circuit, second conductor L2 forms a second phase, and third conductor L3 forms a third phase. A neutral conductor may also be provided.

[0007] In accordance with Figure 1 In the example, the third conductor L3 is connected to an energy converter EW, so that at least a portion of the current, i.e., a portion of the conductor current or the total current of the third conductor, flows through the primary side of the energy converter EW. The energy converter EW is typically a transformer with an iron core. Alternatively, an energy converter EW can be provided in each phase or conductor of the circuit. The secondary side of the energy converter EW is connected to a power supply NT, which typically provides energy to the electronic trip unit ETU in the form of a supply voltage. A sensor unit SE is provided, which utilizes at least one sensor element, such as a Rogowski coil, for determining the current level. In a common expansion variant, the current level of each phase conductor or conductor of the circuit is determined.

[0008] The sensor unit SE is connected to the control unit ETU and transmits the level of the current in the conductors L1 - L3 of the circuit to said control unit.

[0009] In the electronic trip unit (ETU), the transmitted current value is compared with a current limit value and / or a current time interval limit value, which constitutes a tripping cause. If these current limit values and / or current time interval limit values are exceeded, the circuit is interrupted. This is achieved with the aid of an interruption unit (UE), which is connected to the electronic trip unit (ETU) and has contacts for interrupting conductors L1, L2, L3, or other conductors of the circuit. In this case, the interruption unit (UE) receives an interruption signal for opening the contacts.

[0010] The electronic trip unit ETU is equipped with a display AZ on which the values of system-related variables, such as current, voltage, energy, power, phase angle, etc., can be displayed. These variables are partially measured and partially calculated from the measured values. A communication interface KS (e.g., a Zigbee, Wi-Fi, or BLE radio interface or a cable interface, e.g., for a LAN cable) is also included, via which the detected system-related values can be transmitted, for example, to a monitoring point for display or analysis.

[0011] Since the electronic trip unit (ETU) is supplied with energy from the monitored circuit, it is inactive as long as no current to be monitored is flowing. At the end of this idle state, the ETU must firstly wake up very quickly and secondly efficiently convert the (limited) available energy.

[0012] A solution for a switch is known from IN354091-B, which uses two regulators (50a, 50b) which are controlled by a control logic (60) which in turn receives control commands via a controller (90). By using the regulators, the voltage supply can be adapted so that the switch operates quickly when waking up from a standstill phase. Summary of the Invention

[0013] The object of the present invention is to provide a cost-optimized energy supply for an ETU of a circuit breaker, which takes into account the requirements for rapid functional capability during the wake-up phase and for an efficient energy supply during normal operation.

[0014] This object is achieved by a switch, such as a low-voltage power circuit breaker, having an electronic trip unit and a supply circuit for supplying the electronic trip unit with energy from a monitored circuit. In the switch according to the invention, the supply circuit is formed by a linear voltage regulator (hereinafter referred to as a "linear regulator") and a switching regulator connected in parallel. The switching regulator has a power good output, and the linear regulator has a disable input, which are connected to each other.

[0015] In most cases, a supply voltage is generated for the switched ETU that is lower than the supply voltage. The supply voltage is then regulated downward for voltage supply. For this purpose, a step-down converter or a so-called SEPIC converter (single-ended primary inductance converter) can be used as a switching regulator. However, the present invention is also applicable in scenarios where voltage regulation is required. In these scenarios, a booster, for example, can also be used as a switching regulator.

[0016] The device according to the invention is low-cost and, when setting up the voltage supply, ensures that the output voltage is quickly provided by a linear regulator and, if a switching regulator operating with lower losses can ensure the voltage supply, the linear regulator is deactivated via a disable input. The switching regulator automatically takes over the supply without any external additional components or signaling.

[0017] According to one refinement, a diode or a circuit that mimics the behavior of a diode (an "ideal diode" type circuit) is connected in series with the output of the switching regulator. This prevents the influence of the typically present output-side capacitive elements of the switching regulator during voltage conversion by the linear converter, and thus prevents any resulting delays in establishing the target output voltage. For example, a corresponding circuit that mimics the behavior of a diode, constructed using at least one switching transistor (e.g., MOSFET), can be designed and connected to the power-good output of the switching regulator so that it becomes conductive when a power-good signal is applied.

[0018] According to a preferred embodiment, the supply circuit of the switch according to the invention is designed for supplying energy (typically voltage) to an electronic trip unit or ETU using energy extracted from the monitored circuit by means of an energy converter.

[0019] The supply circuit can contain components connected in series for rectification, for filtering or smoothing and for voltage conversion. In this case, the components or stages for voltage conversion can be formed using linear regulators and switching regulators. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be explained in more detail below within the scope of exemplary embodiments with reference to the accompanying drawings.

[0021] Figure 1 Shown is the power switch,

[0022] Figure 2 Show Figure 1 The power switching components,

[0023] Figure 3 shows a linear regulator,

[0024] Figure 4 shows a buck converter,

[0025] Figure 5 shows the behavior of a linear regulator and a buck converter in establishing the output voltage.

[0026] Figure 6 shows connecting a linear regulator and a buck regulator in parallel with the aid of a microcontroller,

[0027] Figure 7 Shown in accordance with Figure 6 The effect of the capacitor on the buck regulator under the Konstellation condition,

[0028] Figure 8 The arrangement according to the invention shows a linear regulator and a buck converter,

[0029] Figure 9 shows the signal progression in the case of the device according to the invention, and

[0030] Figure 10 A circuit diagram of the arrangement according to the invention showing a linear regulator and a buck converter. DETAILED DESCRIPTION

[0031] Figure 2 A more detailed representation of the principle structure of the power supply section NT is shown in FIG. Figure 1 The power supply section is composed of three components NT1-NT3 arranged in series. Typically (when fed with AC power), the voltage is first rectified by NT1, then filtered or smoothed by NT2, and finally converted down to a value of 3.3V suitable for the ETU by NT3.

[0032] For step-down transformation, different solutions exist. Figure 3 Figure 1 shows a linear voltage regulator (also known as LDO or "Low Drop Out"), which regulates the available voltage (e.g., 12 V) down to a lower voltage, such as 3.3 V. The LDO topology offers the advantage that the desired output voltage is already achieved with the LDO at a slightly higher voltage (above the selected output voltage (3.3 V)). However, a disadvantage is that at higher input voltages, the difference between the input and output voltages is lost as heat and is therefore no longer available for the actually required output power, meaning that low efficiency is tolerated.

[0033] Another solution is to Figure 4 The step-down converter or step-down converter DCDC for voltage conversion shown in FIG. The main advantage here is that the available energy is converted with high efficiency, ie very good efficiency is achieved.

[0034] However, disadvantages that should be mentioned are that a buck converter requires a significantly longer time to adjust the output voltage and requires a larger difference between the input voltage and the output voltage.

[0035] exist Figure 5 The figure shows the behavior of the two converters used to step down the 12V voltage to the 3.3V input value required by the ETU during the wake-up phase of the ETU. Figure 1The voltage that builds up at the converter input when the power switch LS is supplied with energy again via the energy converter EW after a period in which the circuit is not conducting current. The middle curve shows the voltage provided at the output of the LDO, while the lower curve shows the voltage at the output of the step-down converter DCDC. The LDO provides the target voltage of 3.3V significantly faster.

[0036] In order to overcome the power loss disadvantage of LDO, a buck converter DCDC is combined with LDO, that is, in order to combine the advantages of the two converters, a linear regulator or LDO is connected in parallel with the buck converter DCDC. During the startup phase, the LDO should first quickly bring the output voltage to the target value so that the buck converter DCDC with better efficiency can then take over. The switch from LDO to buck converter DCDC can be performed by a microprocessor uC, such as in Figure 6 However, this solution not only has the disadvantage of relatively high costs (additional microprocessor). Another disadvantage is that the step-down converter DCDC has a capacitor at the output, which is an additional (capacitive) load for the LDO during voltage buildup (see Figure 7 ).

[0037] Therefore, according to the present invention, after reaching the output voltage of the step-down converter DCDC, switching is automatically performed via a power-good output, which is connected to a disable input of the LDO. When the target output voltage is within its tolerance range after oscillation or after the start-up phase, an electrical signal (power-good signal) is applied to the power-good output. This signal deactivates the LDO via the disable input. In this case, switching is performed without interrupting or reducing the output voltage. This solution is Figure 8 Furthermore, a diode or a circuit simulating the function of a diode is connected downstream of the buck converter DCDC, which prevents the capacitor at the output end of the buck converter DCDC from being charged by the LDO during voltage buildup and thus slows down the voltage buildup.

[0038] exist Figure 9 The signal change process is shown in FIG. From top to bottom: the voltage at the input of the parallel circuit of converters, the voltage at the output of the LDO, the voltage at the output of the buck converter, the signal at the power good output of the buck converter or the disable input of the LDO, and the output voltage provided to the ETU. As shown in FIG. Figure 9As can be seen in the graph, the LDO follows the input voltage almost synchronously and already provides the desired output voltage of 3.3V after reaching the input voltage of ~3.4V. The buck converter starts operating from a voltage of ~8V. Once the desired output voltage is reached, the buck converter issues a shutdown command to the LDO, which then stops "supplying." The buck converter now fully takes over the 3.3V voltage generation.

[0039] exist Figure 10 A more detailed diagram of the parallel connection according to the invention of an LDO and a buck converter DCDC is shown in FIG. The buck converter DCDC has a power good output PG / SS, which is connected to the disable input SHDN of the LDO. Instead of a downstream diode, a MOSFET is located at the output of the buck converter DCDC (see FIG. Figure 10 ), the Mosfet is an "ideal" diode. This "ideal" diode has two tasks:

[0040] 1. Reduce the peak current load (inrush current) of the LDO caused by the capacitive load (output capacitor of the buck converter DCDC) during the voltage buildup phase, and

[0041] 2. When the buck converter DCDC is active, conduction losses are minimized, thereby achieving a stable output voltage under different output currents.

[0042] A so-called "ideal" diode is a circuit that mimics the behavior of a diode. Such circuits are known from the prior art (wherein, depending on the implementation, the behavior is more or less "ideal"). Figure 10 In FIG, the ideal diode ID is formed by two MOSFETs M1 and M2 and is controlled by a power good (disable) signal, for which the power good output PG / SS of the step-down converter DCDC is connected to the gate electrode of the transistor M2.

[0043] Relative to the basis Figure 6 or Figure 7 The main advantage of the solution is that the switching takes place automatically without additional components (such as a microprocessor) and without the need for firmware commands. The capacitive load of the LDO during startup is reduced by the MOSFET circuit.

[0044] This embodiment merely describes a specific case of the solution according to the present invention. This specific case should not be construed as limiting. Those skilled in the art will readily appreciate that many other design solutions fall within the scope of protection of this application. For example, a SEPIC converter or a boost converter may be used as the switching regulator, depending on the scenario, rather than a buck converter.

Claims

1. A switch (LS) having an electronic trip unit (ETU) and a supply circuit (NT) for supplying energy to the electronic trip unit (ETU) from a monitored circuit, wherein - The supply circuit (NT) is composed of a linear regulator (LDO) and a switching regulator (DCDC), wherein - the linear regulator (LDO) and the switching regulator (DCDC) are connected in parallel, - the switching regulator (DCDC) has a power good output terminal (PG / SS), - the linear regulator (LDO) has a disable input (SHDN), and A power good output terminal (PG / SS) of the switching regulator (DCDC) is connected to a disable input terminal (SHDN) of the linear regulator (LDO).

2. The switch according to claim 1, wherein: The switching regulator (DCDC) is a buck converter, a SEPIC converter, or a boost converter.

3. The switch (LS) according to claim 1 or 2, characterized in that A diode or a circuit (ID) that mimics the behavior of a diode is connected in series with the output terminal of the switching regulator (DCDC).

4. The switch (LS) according to claim 3, characterized in that - a circuit (ID) that mimics the behavior of a diode is connected in series with the output of the switching regulator (DCDC), and - A circuit that mimics the behavior of a diode (ID) is designed and connected to the power good output terminal (PG / SS) of the switching regulator (DCDC) so that when a power good signal is applied, the circuit that mimics the behavior of a diode (ID) becomes conductive.

5. The switch (LS) according to claim 4, characterized in that A circuit (ID) emulating the behavior of a diode is formed using at least one switching transistor (M1, M2).

6. The switch (LS) according to claim 5, characterized in that The at least one switching transistor (M1, M2) is a Mosfet.

7. A switch (LS) according to any one of the preceding claims, characterized in that The supply circuit (NT) is designed to supply the electronic trip unit (ETU) with energy extracted from the monitored circuit by means of an energy converter (EW).

8. The switch (LS) according to claim 7, characterized in that The supply circuit (NT) comprises components for rectification (NT1), for filtering or smoothing (NT2) and for voltage conversion (NT3) connected in series.

9. The switch (LS) according to claim 8, characterized in that The components (stages) for voltage conversion (NT3) are formed using the linear regulator (LDO) and the switching regulator (DCDC).

10. The switch (NS) according to any one of the preceding claims, characterized in that The switch (NS) is a low voltage power switch.

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