Performance foldback depending on temperature

Abstract

A control circuit is presented. This circuit can be configured to control the operation of a power converter. It can be configured to receive a temperature reading from a temperature sensor and to control the power converter's output current based on that temperature reading. The power converter can include a transformer with a primary and secondary side, and the control circuit can be configured to control the output current by controlling the switching behavior of switching elements coupled to the transformer's primary side. A battery charger incorporating the control circuit and the power converter is also presented.

Description

TECHNICAL AREA

[0001] This document relates to overtemperature protection (OTP) in battery chargers. Specifically, it relates to OTP in hybrid flyback power converters that can be used in battery chargers. background

[0002] In battery charger applications, the chargers are often rigidly enclosed in a plastic housing without any airflow. This can pose thermal challenges, especially in small form factors. The temperature of the power supply unit (PSU) is roughly proportional to the power losses. As power losses increase, controlling the housing temperature to meet specifications can become more difficult.

[0003] The patent application (US 2024 / 0120821A1) discloses a power conversion device comprising: a voltage regulator circuit for regulating the power of a power source to a desired voltage; an inverter for converting the output power of the voltage regulator circuit into alternating current power; a resonant circuit with inductance and capacitance; a high-frequency transformer for converting the alternating current power of the inverter; a rectifier for converting the alternating current power output by the high-frequency transformer into direct current power; a temperature sensor for detecting the temperature of the resonant circuit; and a control unit for detecting an anomalous resonant frequency when the temperature reaches or exceeds a predetermined threshold in order to control an anomalous condition.

[0004] The publication (US 2022 / 0216792A1) discloses a device comprising a power converter that can be operated in buck or boost mode, a sensor for detecting a temperature-related parameter of the power converter, and a control unit that determines whether the parameter exceeds a threshold, sets the operating mode, and reduces the output power of the power converter depending on this parameter and the operating mode. Summary

[0005] According to one aspect, a control circuit is presented. The control circuit can be configured to control the operation of a power converter. The control circuit can be configured to receive a temperature value from a temperature sensor. The control circuit can be configured to control an output current of the power converter based on the temperature value. The control circuit can include one or more processors for implementing or at least initiating the functional features described in this document. In particular, the control circuit can include a microcontroller (MCU) for executing the described functions. Furthermore, the control circuit can include a memory unit.

[0006] The control circuit can be configured to control the switching of the power converter's switching elements. The switching elements can be implemented using any suitable devices, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), insulated-gate bipolar transistors (IGBTs), MOS-controlled thyristors, or other suitable power devices. For example, the switching elements can be implemented using a III-V composite semiconductor material, such as high-electron-mobility GaN transistors (HEMTs). Each switching element can have a control terminal (e.g., a gate) to which an appropriate control signal (e.g., drive voltage / current) can be applied to turn the switching element on (i.e., close the switching element) or turn the switching element off (i.e., open the switching element).

[0007] The features of the control circuit described in this document, in particular its functional characteristics, can be implemented by appropriate software or hardware units, or by a combination of both. Hardware units can be implemented with digital or analog circuit elements, or by a combination of both. The power converter can be a DC / DC power converter or an AC / DC power converter. The temperature sensor can be external or internal to the control circuit.

[0008] The control circuit can be configured to reduce the output current or power of the power converter when the temperature exceeds a first threshold. Specifically, the control circuit can be configured to reduce the output current of the power converter only when the temperature exceeds the first threshold. The control circuit can be configured to reduce the output current linearly with respect to temperature between the first threshold and a second threshold. Alternatively, the control circuit can be configured to reduce the output current non-linearly with respect to temperature between the first and second thresholds.

[0009] The control circuit can be configured to keep the output current below an upper current limit. The control circuit can also be configured to reduce the upper current limit when the temperature exceeds a first threshold. For example, the control circuit can be configured to keep the upper current limit constant when the temperature is below the first threshold. In other words, when the temperature is below the first threshold, the control circuit can perform overcurrent protection (OCP) using the constant upper current limit. In this way, the control circuit can control / regulate the output current according to control objectives (e.g., based on one or more feedback variables from the power converter) while simultaneously preventing the output current from exceeding the upper current limit.If the temperature rises above the first threshold, the control circuit can continue to regulate the output current according to the specified control objectives. However, the upper current limit can be reduced if the temperature exceeds the first threshold.

[0010] The control circuit can be configured to linearly reduce the upper current limit across the temperature between the first threshold and a second threshold. Alternatively, the control circuit can be configured to reduce the upper current limit solely based on the temperature value and independently of other feedback variables from the power converter. Such feedback variables might include, for example, the input voltage, output voltage, or output current of the power converter.

[0011] The control circuit can be configured to receive an additional feedback parameter indicating the output current or voltage of the power converter. The control circuit can also be configured to control the output current based on this additional feedback parameter, provided that the output current does not exceed the upper current limit.

[0012] The control circuit can be configured to switch to protection mode and shut down the power converter when the temperature exceeds a second threshold. The control circuit can also be configured to no longer generate control signals for the power converter's switching elements while in protection mode.

[0013] The power converter can comprise a transformer with a primary and a secondary side. The control circuitry can be configured to control the output current of the power converter based on the temperature by controlling the switching behavior of the switching elements coupled to the primary side of the transformer. In other words, the switching elements can be electrically isolated from the secondary side of the transformer. The power converter can include a resonant capacitor and a half-bridge coupled to the primary side of the transformer. The switching elements can form the half-bridge. The power converter can also be referred to as a hybrid flyback power converter or a power converter based on a resonant asymmetric half-bridge flyback topology. Alternatively, the power converter can be based on an inductor-inductor-capacitor (LLC) topology.

[0014] The control circuit can be configured, based on a feedback voltage indicating the output voltage of the power converter, to ignore or disable an overcurrent protection function when the temperature exceeds a first threshold. Specifically, the control circuit can be configured to ignore the feedback voltage when the temperature exceeds the first threshold. The temperature sensor can be located outside the control circuit and may include a thermistor, and the temperature value can include a voltage across the thermistor. The thermistor, also known as a thermal resistor, can be, for example, an NTC thermistor (NTC, negative temperature coefficient) or a PTC thermistor (PCT, positive temperature coefficient).

[0015] According to another aspect, a battery charger is presented. The battery charger may include the control circuit and the power converter described in this document. The power converter may comprise a transformer with a primary and a secondary side. The control circuit may be configured to control the output current of the power converter based on the temperature by controlling the switching behavior of the switching elements coupled to the primary side of the transformer. The control circuit may be galvanically isolated from the electrical signals of the secondary side of the transformer.

[0016] Another aspect presented is a method for controlling a power converter. This method can involve receiving a temperature value from a temperature sensor via a control circuit. The method can then control the output current of the power converter based on this temperature value using the control circuit.

[0017] The method can include reducing the output current of the power converter by the control circuit when the temperature exceeds a first threshold. The method can also include linearly reducing the output current across the temperature range between the first threshold and a second threshold.

[0018] The method can, in particular, include keeping the output current below an upper current limit. The method can include reducing the upper current limit when the temperature exceeds the first threshold. The method can include linearly reducing the upper current limit across the temperature between the first and second thresholds. The method can include reducing the upper current limit based solely on the temperature value and independently of other feedback variables of the power converter.

[0019] The procedure may include switching to protection mode and shutting down the operation of the power converter when the temperature value exceeds the second threshold.

[0020] The power converter can comprise a transformer with a primary and a secondary side. The method can include controlling the output current of the power converter based on the temperature value by controlling the switching behavior of the switching elements coupled to the primary side of the transformer. The power converter can include a resonant capacitor and a half-bridge coupled to the primary side of the transformer, and the switching elements can form the half-bridge.

[0021] The method can include disabling an overcurrent protection function based on a feedback voltage that indicates an output voltage of the power converter when the temperature exceeds a first threshold. The external temperature sensor can include a thermistor, and the temperature value can include a voltage across the thermistor.

[0022] According to another aspect, a computer program is presented. The computer program may include instructions which, when executed by one or more processors of the control circuit, cause the control circuit to perform the operations described in this document.

[0023] The computer program can, for example, be software / firmware loaded into the memory of the control circuit. For this purpose, the computer program can be transmitted over a network, and the control circuit can include a network interface for receiving the computer program. Alternatively, the computer program can be distributed on a data carrier and downloaded into the control circuit. More generally, the computer program can be stored on a non-transient, computer-readable medium. This document discloses and claims a non-transient, computer-readable medium that stores instructions which, when executed by one or more processors of a control circuit, cause the control circuit to perform the steps described herein.

[0024] It should be noted that the methods and systems, including their preferred embodiments, as described in this document can be used independently or in combination with other methods and systems disclosed herein. Furthermore, the features described in connection with a system are also applicable to a corresponding method. Moreover, all aspects of the methods and systems described in this document can be combined as desired. In particular, the features of the claims can be combined with one another as desired.

[0025] In this document, the terms "couple" or "coupled" refer to elements that are in electrical communication with each other, either through a direct connection, e.g., via wires, or an indirect connection via other circuit elements in between. For example, two elements can be said to be coupled even if a circuit element (which can be switched on and off) lies between them. On the other hand, the term "connect" or "connected" refers to elements that are directly electrically connected to each other, e.g., via wires, and there are no circuit elements between them. Brief description of the characters

[0026] The present invention is illustrated by way of example and without limitation in the figures, in which the same reference numerals refer to similar or identical elements and in which: Fig. 1 shows an exemplary power converter topology, Fig. 2 an exemplary flowchart of a current reduction process shows, Fig. 3 An example diagram of the upper current limit versus the measured temperature shows, Fig. Figure 4 shows an exemplary implementation of a temperature measurement using an NTC thermistor and corresponding signal waveforms, and Fig. Figure 5 shows another example diagram of the upper current limit versus the measured temperature with hysteresis. Detailed description

[0027] Typically, the most unfavorable operating condition for thermal performance occurs at maximum output power and minimum input voltage. These applications are usually designed to operate over a wide range of universal input voltages from 85Vac to 265Vac. In this case, 85Vac at maximum load power is usually the most unfavorable condition for meeting thermal requirements. At lower input voltages, line losses at the bridge rectifier, power factor correction stage, and isolated DC-DC converter become dominant, resulting in decreased PSU efficiency and increased temperature. As the input voltage increases towards the nominal input voltage conditions of approximately 115V / 230Vac, efficiency and thermal performance improve compared to the minimum input voltage.At the highest input voltage of ~265Vac, the power losses usually increase again depending on the PSU topology used, and in some designs the total losses would be at their highest level.

[0028] A common design practice is to ensure thermal compliance at this worst-case input voltage, taking into account the maximum output power. This requires proper sizing along with correct thermal management, such as the use of heat sinks, thermal pads, and thicker plastic enclosures to prevent hotspots and meet enclosure temperature requirements. However, this increases system costs and necessitates a larger power supply.

[0029] Fig. Figure 1 shows an exemplary power converter topology that can be controlled by a controller (control circuit) proposed in this document. The power converter 1 includes a transformer 11, which divides the power converter 1 into a primary and a secondary side. On the primary side, the power converter 1 includes an input capacitor 12, a high-side switching element 13, a low-side switching element 14, and a resonant capacitor 15. The switching element 13 and the switching element 14 form a half-bridge. This half-bridge, together with its specific drive circuit arrangement, is also referred to in this document as a power stage or power supply unit (PSU). On the secondary side, the power converter 1 includes a rectifier diode 16, an output capacitor 17, and an output resistor 18.

[0030] It should be noted that the power converter 1 shown is exemplary and many variations exist. For example, the primary winding of the transformer 11 and the resonant capacitor 15 can be connected in series with the high-side switching element 13, instead of being in series with the low-side switching element 14 as shown. Alternatively, the rectifier diode 16 can be replaced by a synchronous rectification switching element controlled by an additional, secondary-side control circuit, often referred to as a synchronous rectification control circuit. The control circuit presented in this document can be configured to control the switching elements 13 and 14 on the primary side. Furthermore, this control circuit can be galvanically isolated from the signals originating from the secondary side of the power converter 1.

[0031] Fig. Figure 2 shows an example flowchart of a current reduction method. The method can be implemented in the controller based on two temperature thresholds, which are detected by a thermistor in the PSU. As the temperature rises and falls between these two thresholds, the output current is reduced depending on the temperature. In particular, Figure 2 shows... Fig. 2, that the output current is reduced when the detected temperature is between a release temperature Tr (referred to in the claims as the first threshold) and a trip temperature Tt (referred to in the claims as the second threshold), and that the protection mode is switched when the detected temperature exceeds the trip temperature Tt. This scheme can make it possible to meet thermal specifications without having to oversize components.

[0032] The ambient temperature (T) of the power supply can be measured using a negative temperature coefficient (NTC) thermistor (or another temperature sensor). As mentioned earlier, there are two temperature thresholds: the lower limit Tr (enable temperature) and the upper limit Tt (trigger temperature). When T is below the lower limit Tr, the power supply is switched on and operates normally. This means the output can reach 100% of the maximum rated current. As T rises and reaches Tr, the current is reduced, for example, linearly depending on the temperature, as shown in Fig. 3 shown. Fig. Figure 3 shows an example diagram of the upper current limit versus the measured temperature. Here, the current is controlled and can depend on four variables: Iout_limit, Id, Tt, and Tr. These last two variables determine the slope of the upper current limit during the current foldback (i.e., between Tr and Tt). Temperature monitoring continues, and if the temperature reaches the upper threshold Tt, the power supply may be switched off for specific reasons. This ensures the protection of the power supply against potential unusual events. The power supply can then be switched back on once the temperature falls below Tr.

[0033] Fig. Figure 4 shows an exemplary implementation of temperature measurement using an NTC thermistor and corresponding signal waveforms. In this example, temperature sensing is achieved by measuring the voltage across a multifunction input / output (MFIO) pin. Tt is represented by the MFIO voltage, OTP_trigger_th, while Tr is represented by the MFIO voltage, OTP_release_th. Since the primary-side current limit can be set to a lower value than that required by the feedback, the feedback signal is expected to rise and saturate. To provide the power reduction function, the primary controller may need to disable the overcurrent protection (OCP) limits (based on a feedback voltage Vfb) when it detects T > Tr.

[0034] For example, reducing the output charging current when the temperature exceeds a certain threshold would not affect the operation of the power supply, but would limit the amount of heat dissipated internally. Therefore, by continuously monitoring the PSU temperature and linearly reducing the output current or power as a function of temperature once it exceeds a specific threshold, a more optimized, smaller, and more cost-effective design can be achieved.

[0035] Fig. Figure 5 shows another example diagram of the upper current limit versus the measured temperature with hysteresis. For this purpose, a third threshold temperature T3 is introduced to prevent possible fluctuations in power supply operation between power foldback and normal operation.

Claims

[1] Control circuit configured to control the operation of a power converter (1), wherein the control circuit is configured to receive a temperature value (T, Temp) from a temperature sensor (NTC) and to control an output current of the power converter (1) based on the temperature value (T, Temp), wherein the control circuit is configured to reduce the output current of the power converter (1) when the temperature value (T, Temp) exceeds a first threshold value (Tr, T1), wherein the control circuit is configured to ignore an overcurrent protection function based on a feedback voltage indicating an output voltage of the power converter (1) if the temperature value (T, Temp) exceeds the first threshold (Tr, T1). [2] Control circuit according to claim 1, wherein the control circuit is configured to linearly reduce the output current over the temperature between the first threshold (Tr, T1) and a second threshold (Tt, T2). [3] Control circuit according to claim 1, wherein the control circuit is configured to keep the output current below an upper current limit (I out_lim ) to maintain, and wherein the control circuit is configured to maintain the upper current limit (I out_lim ) to reduce when the temperature value (T, Temp) exceeds the first threshold value (Tr, T1). [4] Control circuit according to claim 3, wherein the control circuit is configured to set the upper current limit (I out_lim ) to reduce linearly over the temperature between the first threshold (Tr, T1) and a second threshold (Tt, T2). [5] Control circuit according to claim 3 or 4, wherein the control circuit is configured to set the upper current limit (Iout_lim ) only based on the temperature value (T, Temp) and independent of other feedback variables of the power converter (1). [6] Control circuit according to any one of claims 3 to 5, wherein the control circuit is configured to receive another feedback variable indicating the output current or output voltage of the power converter (1), and wherein the control circuit is configured to adjust the output current based on the other feedback variable, provided that the output current does not exceed the upper current limit (I out_lim ) not exceeding, to control. [7] Control circuit according to one of the preceding claims, wherein the control circuit is configured to switch to a protection mode and shut off the operation of the power converter (1) when the temperature value (T, Temp) exceeds a second threshold value (Tt, T2). [8] Control circuit according to one of the preceding claims, wherein the power converter (1) comprises a transformer (11) having a primary side and a secondary side, and wherein the control circuit is configured to control the output current of the power converter (1) based on the temperature value (T, Temp) by controlling the switching behavior of switching elements (13, 14) coupled to the primary side of the transformer (11). [9] Control circuit according to claim 8, wherein the power converter (1) comprises a resonant capacitor (15) and a half-bridge coupled to the primary side of the transformer (11), and wherein the switching elements (13, 14) form the half-bridge. [10] Control circuit according to one of the preceding claims, wherein the temperature sensor (NTC) comprises a thermistor and wherein the temperature value (T, Temp) is represented by a voltage across the thermistor. [11] Battery charger comprising a control circuit and a power converter (1) according to any of the preceding claims. [12] Battery charger according to claim 11, wherein the power converter (1) comprises a transformer (11) with a primary side and a secondary side, and wherein the control circuit is configured to control the output current of the power converter (1) based on the temperature value (T, Temp) by controlling the switching behavior of switching elements (13, 14) coupled to the primary side of the transformer (11), and wherein the control circuit is galvanically isolated from electrical signals of the secondary side of the transformer (11). [13] Method for controlling a power converter (1) wherein the method comprises: - Receiving a temperature value (T, Temp) from a temperature sensor (NTC) by a control circuit; and - Control of an output current of the power converter (1) based on the temperature value (T, Temp) by the control circuit - Reducing the output current of the power converter (1) when the temperature value (T, Temp) exceeds a first threshold value (Tr, T1), - Ignoring an overcurrent protection function based on a feedback voltage indicating an output voltage of the power converter (1) if the temperature value (T, Temp) exceeds the first threshold (Tr, T1). [14] Computer program comprising instructions which, when executed by one or more processors of a control circuit, cause the control circuit to perform operations according to any one of claims 1 to 10.

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