Switch with electronic release unit

Abstract

Circuit breaker (MCB) with an electronic trip unit (ETU) and a supply circuit (SC) for supplying energy to the electronic trip unit (ETU) from a monitored circuit, in which - the power supply circuit (PS) is formed with a linear regulator (LDO) and a switching regulator (DCDC), wherein - the linear digital output regulator (LDO) and the switching regulator (DCDC) are connected in parallel, - the switching regulator (DCDC) has a PowerGood output (PG / SS), - the linear regulator (LDO) has a disable input (SHDN), - the PowerGood output (PG / SS) of the switching regulator (DCDC) is connected to the Disable input (SHDN) of the linear regulator (LDO), and a diode or a circuit emulating the behavior of a diode (ID) is connected in series with the output of the switching regulator (DCDC).

Description

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

[0002] Circuit breakers installed in an electrical circuit provide protection for the circuit, functioning similarly to a fuse. This protection is achieved by monitoring the current flowing through a conductor in the circuit. Typically, the circuit carries an electrical current or energy flow to a power sink or consumer. The circuit breakers monitor protective parameters to ensure that conditions are met that trigger an interruption of the circuit by opening the breaker (also known as tripping). Such protective functions generally cover short-circuit current (monitoring the absolute value of the current) and overcurrent (monitoring for exceeding current thresholds for predefined time periods). Additionally, a more complex tripping mechanism based on arc faults may be provided.

[0003] The interruption occurs, for example, when the circuit breaker's contacts open. Unlike a fuse, these protection parameters or response values ​​are adjustable in a circuit breaker. Modern circuit breakers typically have a control unit, also known as an electronic trip unit (ETU) or overcurrent trip unit, for setting these parameters and verifying the tripping criteria.

[0004] Especially for low-voltage circuits and networks, there are various types of circuit breakers depending on the intended current. For the purposes of this application, "circuit breaker" refers specifically to those used in low-voltage installations for currents from 25 to 6300 amperes. More specifically, enclosed circuit breakers are used for currents from 63 to 1600 amperes, particularly from 125 to 630 or 1200 amperes. Open-circuit breakers are used primarily for currents from 630 to 6300 amperes, and more specifically from 1200 to 6300 amperes. Open-circuit breakers are also known as air circuit breakers (ACBs), and enclosed-circuit breakers as molded case circuit breakers or compact circuit breakers (MCCBs).

[0005] Low voltage refers to voltages up to 1000 volts AC or 1500 volts DC. Low voltage also includes voltages higher than extra-low voltage, defined as 50 volts AC or 120 volts DC.

[0006] An example of a circuit breaker (LS) with an electronic trip unit (ETU) serving as a control unit is shown in the Fig. Figure 1 shows the circuit breaker. It is designed to interrupt electrical conductors L1, L2, and L3 of an electrical circuit, for example, a three-phase AC circuit, where the first conductor L1 represents the first phase, the second conductor L2 the second phase, and the third conductor L3 the third phase of the three-phase AC circuit. A neutral conductor may also be included.

[0007] In the example according to Fig. 1. The third conductor L3 is connected to the energy converter EW such that at least a portion of the current, i.e., a partial conductor current, or the entire current of the third conductor flows through the primary side of the energy converter EW. The energy converter EW is typically a core-type transformer. An energy converter EW can also be provided in each phase or conductor of the electrical circuit. The secondary side of the energy converter EW is connected to a power supply unit NT, which provides power, typically in the form of a supply voltage, for the electronic trip unit ETU. A sensor unit SE is provided, which is formed with at least one sensor element, e.g., a Rogowski coil, to determine the magnitude of the electric current. In a typical configuration, the magnitude of the electric current in each phase conductor or conductor of the electrical circuit is determined.

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

[0009] The transmitted current values ​​are compared in the electronic trip unit (ETU) with current limits and / or current-time interval limits that determine the tripping triggers. If these limits are exceeded, the electrical circuit is interrupted. This is achieved by means of a breaker 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 electrical circuit. In this case, the breaker unit (UE) receives a break signal to open the contacts.

[0010] The electronic trip unit (ETU) is equipped with a display (AZ) that can show values ​​of system-relevant parameters, such as current, voltage, energy, power, phase angle, etc. These values ​​are partly measured and partly calculated from measured values. A communication interface (KS) is also shown (e.g., Zigbee, Wi-Fi, or BLE wireless interface, or wired interface, e.g., for LAN cable), through which the recorded system-relevant values ​​can be transmitted to a monitoring station for display or analysis.

[0011] Since the electronic trip unit (ETU) is powered by the monitored circuit, it is inactive as long as no current to be monitored is flowing. Upon exiting this sleep state, the ETU must wake up very quickly and efficiently utilize the (limited) available energy.

[0012] From IN354091-B, a solution for a switch is known that uses two regulators (50a, 50b) controlled by a control logic (60), which in turn receives control commands from a controller (90). The use of the regulators allows the voltage supply to be adjusted for fast operation of the switch when waking from a standby state.

[0013] DE 10 2017 214 903 A1 discloses a switch with an electronic release unit and a supply circuit for supplying energy to the electronic release unit from a monitored circuit.

[0014] EP 1 681 760 A2 discloses a power supply circuit with a linear regulator and a switching regulator connected in parallel. A logic circuit is used to switch from the operation of the linear regulator to the operation of the switching regulator when the switching regulator can supply the load on its own, i.e., when it has reached operating speed.

[0015] US 2003 / 0 234 635 A1 and the document “TEXAS INSTRUMENTS: Adding an LDO for Increased Standby Mode Efficiency”, TIDA-00393-June 2015, each show a power supply circuit with a linear regulator and switching regulator in parallel and the resulting advantages.

[0016] Publication EP 3 764 453 A1 shows the advantageous use of circuits that mimic the behavior of a diode and are arranged in series with each of the parallel-connected electrical supply circuits.

[0017] The invention aims to provide a cost-optimized energy supply for an ETU of a circuit breaker, taking into account the requirements for rapid functionality during a wake-up phase as well as an efficient energy supply during normal operation.

[0018] The problem is solved by a switch, e.g., a low-voltage circuit breaker, with an electronic trip unit and a power supply circuit for powering the electronic trip unit from a monitored circuit. In this switch according to the invention, the power supply circuit is formed with a linear voltage regulator – hereinafter referred to as the “linear regulator” – and a switching regulator, which are connected in parallel. The switching regulator has a PowerGood output and the linear regulator a Disable input, which are connected to each other. A diode or a circuit emulating the behavior of a diode is connected in series with the output of the switching regulator.

[0019] In most cases, a supply voltage is generated for the ETU (Electro-Trigger Unit) of a switch that is lower than the mains supply voltage. The mains voltage is then regulated down to provide the supply voltage. For this configuration, a buck converter or step-down converter, or a SEPIC converter (single-ended primary inductance converter), can be used as a switching regulator. However, the invention is also applicable in scenarios where voltage regulation needs to be increased. In these scenarios, a boost converter, for example, can also be used as a switching regulator.

[0020] The arrangement according to the invention is simple and, when setting up a power supply, ensures that the output voltage is quickly provided by the linear regulator and then deactivated via the disable input when the more efficient switching regulator is able to provide the power supply. The switching regulator takes over the power supply automatically without any additional external components or signaling.

[0021] A diode or a circuit emulating 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 switching regulator's typically present output capacitive elements during voltage conversion by the linear converter, thus eliminating any potential delay in the build-up of the target output voltage. A corresponding diode-emulating circuit, which may include at least one switching transistor (MOSFET, etc.), can be designed and connected to the switching regulator's PowerGood output in such a way that it becomes conductive when a PowerGood signal is applied.

[0022] According to a preferred embodiment, the supply circuit of the switch according to the invention is designed to provide energy (typically voltage supply) to the electronic trip unit or ETU by means of energy taken from the monitored circuit by means of an energy converter.

[0023] The power supply circuit can contain components for rectification, filtering or smoothing, and voltage transformation connected in series. The voltage transformation component or stage can then be formed by the linear regulator and the switching regulator.

[0024] The invention will now be explained in more detail using an exemplary embodiment and the accompanying figures. These figures show... Fig. 1: a circuit breaker, Fig. 2: Elements of the circuit breaker of Fig. 1, Fig. 3: a linear regulator, Fig. 4: a downward converter, Fig. 5: the behavior of linear regulators and buck converters when building up an output voltage, Fig. 6: a parallel circuit of a linear regulator and a step-down regulator using a microcontroller, Fig. 7: the influence of a buck converter's capacitance in a given constellation Fig. 6, Fig. 8: an arrangement of linear controller and step-down converter according to the invention, Fig. 9: Signal waveforms in an arrangement according to the invention and Fig. 10: a circuit diagram of an arrangement of linear regulator and buck converter according to the invention.

[0025] Fig. 2 shows elements of the in Fig. Figure 1 shows a power switch with a more detailed illustration of the basic structure of the power supply unit NT. This unit consists of three components NT1-NT3 arranged in series. Typically (when powered by alternating current), NT1 first rectifies the current, followed by NT2 filtering or smoothing, and finally NT3 transforms the voltage down to the appropriate value of 3.3V for the ETU.

[0026] There are different solutions for the downward transformation. In Fig. Figure 3 shows a linear voltage regulator – also known as an LDO or "Low Dropout" regulator – which reduces the available voltage (e.g., 12V) to a lower voltage of, for example, 3.3V. The LDO topology offers the advantage that the desired output voltage is achieved even at a slightly higher voltage (above the selected output voltage of 3.3V). However, the disadvantage is that at higher input voltages, the difference between the input and output voltage is dissipated as heat and is therefore no longer available for the required output power; in other words, a lower efficiency is accepted.

[0027] Another solution is a DC-DC step-down converter for voltage conversion, as used in Fig. Figure 4 shows the main advantage here, as the available energy is converted with high efficiency, i.e., a very good efficiency is achieved.

[0028] However, a disadvantage is that a step-down converter takes significantly longer to adjust the output voltage and requires a larger difference between input and output voltage.

[0029] In Fig. Figure 5 shows the behavior of both converters for the step-down transformation from a 12V voltage to the 3.3V input value required by the ETU during the ETU's wake-up phase. The uppermost curve shows the voltage that builds up at the converter's input when the power switch LS is off. Fig. 1. After a phase in which the circuit carried no current, it is again supplied with energy via the energy converter EW. The middle curve represents the voltage provided at the output of an LDO, the lower one the voltage at the output of a step-down converter DCDC. The target voltage of 3.3V is delivered by the LDO considerably faster.

[0030] To counteract the power loss disadvantage of the LDO, a step-down DC-DC converter is combined with an LDO. This means that to combine the advantages of both converters, the linear regulator (LDO) and the step-down DC-DC converter are connected in parallel. During the start-up phase, the LDO should first quickly bring the output voltage to the target value before being replaced by the more efficient step-down DC-DC converter. The switching from the LDO to the step-down DC-DC converter can be performed by a microcontroller (µC), as shown in [reference to relevant diagram]. Fig. 6 indicated. However, this solution not only has the disadvantage of relatively high complexity (additional microprocessor). Another disadvantage is that the step-down converter DCDC has a capacitor at its output, which represents an additional (capacitive) load for the LDO during voltage build-up (see ). Fig. 7).

[0031] According to the invention, the switching after the output voltage of the step-down converter DCDC is reached is therefore automated by a PowerGood output, which is connected to a Disable input on the LDO. An electrical signal (PowerGood signal) is applied to the PowerGood output when, after the settling-in or start-up phase, the target output voltage is generated within its tolerance range. This signal deactivates the LDO via the Disable input. The switching occurs without interruption or drop in the output voltage. This solution is in Fig. Figure 8 shows that a diode or a circuit simulating the diode function is connected downstream of the DCDC step-down converter, which prevents the capacitor in the output of the DCDC step-down converter from being charged during the voltage build-up by the LDO and thus slowing down the voltage build-up.

[0032] In Fig. Figure 9 shows signal waveforms. From top to bottom, the following are shown: the voltage at the input of the converter parallel circuit, the voltage at the output of the LDO, the voltage at the output of the step-down converter, the signal at the PowerGood output of the step-down converter or at the Disable input of the LDO, and the output voltage provided to the ETU. As shown in the diagram of Fig. As can be seen in diagram 9, the LDO follows the input voltage almost synchronously and delivers the desired output voltage of 3.3V as soon as the input voltage reaches -3.4V. The step-down converter begins operating at a voltage of approximately 8V. Once the desired output voltage is reached, it sends a turn-off signal to the LDO, whereupon the LDO ceases output. The step-down converter then takes over the entire 3.3V voltage generation process.

[0033] In Fig. Figure 10 shows a more detailed representation of a parallel circuit according to the invention, comprising an LDO and a step-down converter DCDC. The step-down converter DCDC has a PowerGood output PG / SS, which is connected to a Disable input SHDN of the LDO. Instead of the downstream diode, a MOSFET is located at the output of the step-down converter DCDC (see Figure 10). Fig. 10), which represents an "ideal" diode. This has two functions: 1. Reduction of the peak current load (inrush current) of the LDO caused by the capacitive load (output capacitors of the step-down converter DCDC) during the voltage build-up phase and 2. Minimizing conduction losses when the DCDC step-down converter is active, thereby achieving a stable output voltage at different output currents.

[0034] The so-called "ideal" diode is a circuit that replicates the behavior of a diode. Such circuits are known from the prior art (although the behavior varies depending on the design). Fig. 10 This ideal diode ID is formed with two MOSFETs M1 and M2 and is controlled with the PowerGood (Disable) signal, for which the PowerGood output PG / SS of the step-down converter DCDC is connected to the gate electrode of transistor M2.

[0035] A significant advantage over a solution corresponding to Fig. 6 or Fig. The advantage is that switching occurs automatically without an additional component (e.g., a microprocessor) and without the need for firmware commands. The capacitive load on the LDO during startup is reduced by the MOSFET circuit.

[0036] The exemplary embodiment describes only one specific case of a solution according to the invention. This is not to be interpreted restrictively. Numerous further embodiments, which fall within the scope of protection of the application, are immediately apparent to those skilled in the art. For example, depending on the scenario, a SEPIC converter or a boost converter can be used as the switching regulator instead of a buck converter.

Claims

[1] Circuit breaker (CB) with an electronic trip unit (ETU) and a power supply circuit (PS) for supplying energy to the electronic trip unit (ETU) from a monitored circuit, in which - the power supply circuit (PS) is formed with a linear regulator (LDO) and a switching regulator (DCDC), wherein - the linear digital output regulator (LDO) and the switching regulator (DCDC) are connected in parallel, - the switching regulator (DCDC) has a PowerGood output (PG / SS), - the linear regulator (LDO) has a disable input (SHDN), - the PowerGood output (PG / SS) of the switching regulator (DCDC) is connected to the Disable input (SHDN) of the linear regulator (LDO), and a diode or a circuit emulating the behavior of a diode (ID) is connected in series with the output of the switching regulator (DCDC). [2] Switch according to claim 1, characterized bythat the switching regulator (DCDC) is a buck converter, a SEPIC converter or a boost converter. [3] Switch (LS) according to claim 1 or 2, characterized by , that - a circuit (ID) simulating the behavior of a diode is connected in series with the output of the switching regulator (DCDC), and - the circuit (ID) that emulates the behavior of a diode is designed and connected to the PowerGood output (PG / SS) of the switching regulator (DCDC) in such a way that when a PowerGood signal is applied, the circuit (ID) that emulates the behavior of a diode becomes conductive. [4] Switch (LS) according to claim 3, characterized by , that the circuit (ID) simulating the behavior of a diode is formed with at least one switching transistor (M1, M2). [5] Switch (LS) according to claim 4, characterized by that at least one switching transistor (M1, M2) is a MOSFET. [6] Switch (LS) according to any one of the preceding claims, characterized by , that the supply circuit (NT) is designed to provide energy to the electronic release unit (ETU) by means of an energy converter (EW) taken from the monitored circuit. [7] Switch (LS) according to claim 6, characterized by , that the supply circuit (NT) contains components connected in series for rectification (NT1), for filtering or smoothing (NT2) and for voltage transformation (NT3). [8] Switch (LS) according to claim 7, characterized by , that the component (stage) for voltage transformation (NT3) is formed with the linear regulator (LDO) and the switching regulator (DCDC). [9] Switches according to any one of the preceding claims, characterized by that the switch is a low-voltage circuit breaker.

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