Temperature dependent power flyback
By using a control circuit in the battery charger to monitor temperature and reduce output current or shut down the power converter, the thermal management problem in the sealed design is solved, achieving safe and efficient temperature control and reducing equipment costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- INFINEON TECH AUSTRIA AG
- Filing Date
- 2025-10-15
- Publication Date
- 2026-04-21
AI Technical Summary
In battery chargers, the sealed design presents challenges for thermal management, especially in small-sized designs where controlling the casing temperature becomes difficult, affecting the safety and efficiency of the device.
A control circuit is used to monitor the temperature and reduce the output current or shut down the power converter when the temperature exceeds a threshold. Temperature sensors such as NTC thermistors are used, and overcurrent protection is implemented by combining software and hardware. The switching of the control elements is controlled to regulate the output current.
Effectively controlling the temperature of the battery charger prevents overheating, improves equipment safety and efficiency, reduces excessive size requirements in the design, and lowers system costs.
Smart Images
Figure CN121906970A_ABST
Abstract
Description
Technical Field
[0001] This document relates to over-temperature protection (OTP) in battery charger equipment. Specifically, this document relates to an OTP that can be applied to hybrid flyback power converters in battery charger equipment. Background Technology
[0002] In battery charger applications, chargers are typically tightly sealed within a plastic housing with no available airflow. This can present thermal challenges, especially in small-size designs. The temperature of the power supply unit (PSU) is approximately proportional to power loss. As power loss increases, controlling the housing temperature to meet specifications can become more challenging. Summary of the Invention
[0003] 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 the output current of the power converter based on the temperature value. The control circuit may include one or more processors for implementing or at least activating the functional features of the control circuit described herein. Specifically, the control circuit may include a microcontroller (MCU) for performing the described functions. Additionally, the control circuit may include a memory unit.
[0004] The control circuit can be configured to control the switching of the switching elements of the power converter. The switching elements can be implemented using any suitable device, such as, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET), an insulated-gate bipolar transistor (IGBT), a MOS gate-controlled thyristor, or any other suitable power device. For example, the switching elements can be implemented using III-V compound semiconductor materials such as, for example, GaN high electron mobility transistors (HEMTs). Each switching element can have a control terminal (e.g., a gate) to which a corresponding 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).
[0005] The features of the control circuit described in this document, particularly its functional characteristics, can be implemented using appropriate software or hardware units, or a combination of both. The hardware units can be implemented using digital or analog circuit elements, or a combination of both. The power converter can be a DC / DC power converter or an AC / AC power converter. The temperature sensor can be external to or internal to the control circuit.
[0006] The control circuit can be configured to reduce the output current or output power of the power converter if the temperature value exceeds a first threshold. Specifically, the control circuit can be configured to reduce the output current of the power converter only if the temperature value exceeds the first threshold. The control circuit can be configured to linearly reduce the output current above a temperature between the first and second thresholds. Optionally, the control circuit can be configured to reduce the output current above the temperature in a non-linear manner between the first and second thresholds.
[0007] The control circuit can be configured to maintain the output current below the upper current limit. The control circuit can be configured to reduce the upper current limit if the temperature exceeds a first threshold. For example, the control circuit can be configured to maintain a constant upper current limit if the temperature is below the first threshold. In other words, when the temperature is below the first threshold, the control circuit can be configured to perform overcurrent protection (OCP) using the constant upper current limit. Here, the control circuit can control / regulate the output current according to an adjustment target (e.g., based on one or more feedback parameters of the power converter) while preventing the output current from exceeding the circuit's upper limit. When the temperature rises above the first threshold, the control circuit can still continue to control the output current according to the adjustment target. However, when the temperature exceeds the first threshold, the upper current limit can be reduced.
[0008] The control circuit can be configured to linearly reduce the upper current limit above a temperature between a first threshold and a second threshold. The control circuit can be configured to reduce the upper current limit based solely on the temperature value and independently of other feedback parameters of the power converter. Such feedback parameters may include, for example, the input voltage, the output voltage, or the output current of the power converter.
[0009] The control circuit can be configured to receive another feedback parameter indicating the output current or output voltage of the power converter. The control circuit can also be configured to control the output current based on this other feedback parameter, provided that the output current does not exceed the circuit's upper limit.
[0010] The control circuit can be configured to enter a protection mode and shut down the power converter if the temperature exceeds a second threshold. In protection mode, the control circuit can be configured to stop generating control signals for the switching elements of the power converter.
[0011] A power converter may include a transformer having a primary side and a secondary side. Control circuitry may be configured to control the output current of the power converter based on a temperature value by controlling the switching behavior of switching elements coupled to the primary side of the transformer. In other words, the switching elements may be electrically isolated from the secondary side of the transformer. The power converter may include a resonant capacitor and a half-bridge coupled to the primary side of the transformer. The switching elements may form the half-bridge. The power converter may also be represented as a hybrid flyback power converter, or as a power converter based on a resonant asymmetric half-bridge flyback topology. Alternatively, the power converter may be based on an inductor-inductor-capacitor LLC topology.
[0012] The control circuit can be configured to ignore or deactivate the overcurrent protection function based on a feedback voltage indicating the output voltage of the power converter if the temperature value exceeds a first threshold. Specifically, the control circuit can be configured to ignore the feedback voltage if the temperature value exceeds the first threshold. The temperature sensor can be external to the control circuit and can include a thermistor, and the temperature value can include a voltage across the thermistor. The thermistor, also known as a thermally sensitive resistor, can be, for example, a negative temperature coefficient (NTC) thermistor or a positive temperature coefficient (PTC) thermistor.
[0013] According to another aspect, a battery charger device is presented. The battery charger device may include control circuitry and a power converter as described herein. The power converter may include a transformer having a primary side and a secondary side. The control circuitry may be configured to control the output current of the power converter based on a temperature value by controlling the switching behavior of switching elements coupled to the primary side of the transformer. The control circuitry may be isolated from the electrical signal current on the secondary side of the transformer.
[0014] According to another aspect, a method for controlling a power converter is presented. The method may include: receiving a temperature value from a temperature sensor by a control circuit. The method may also include: controlling the output current of the power converter by the control circuit based on the temperature value.
[0015] The method may include: if the temperature value exceeds a first threshold, reducing the output current of the power converter by a control circuit. The method may also include: linearly reducing the output current above a temperature between the first and second thresholds.
[0016] Specifically, methods may include: maintaining the output current below a current limit. Methods may include: reducing the current limit if the temperature value exceeds a first threshold. Methods may include: linearly reducing the current limit above a temperature between a first threshold and a second threshold. Methods may include: reducing the current limit based solely on the temperature value, and independently of other feedback parameters of the power converter.
[0017] The method may include: if the temperature value exceeds a second threshold, entering a protection mode and shutting down the power converter.
[0018] A power converter may include a transformer having a primary side and a secondary side. A method may include controlling the output current of the power converter based on temperature by controlling the switching behavior of switching elements coupled to the primary side of the transformer. The power converter may include a resonant capacitor and a half-bridge coupled to the primary side of the transformer, and the switching elements may form the half-bridge.
[0019] The method may include: if the temperature value exceeds a first threshold, activating an overcurrent protection function based on a feedback voltage indicating the output voltage of the power converter. An external temperature sensor may include a thermistor, and the temperature value may include a voltage across the thermistor.
[0020] According to another aspect, a computer program is presented. The computer program may include instructions that, when executed by one or more processors of a control circuit, cause the control circuit to perform the operations described herein.
[0021] The computer program can be, for example, software / firmware loaded into the memory of the control circuitry. For this purpose, the computer program can be transmitted over a network, and the control circuitry can include a network interface device for receiving the computer program. Alternatively, the computer program can be distributed on a data carrier and can be downloaded to the control circuitry. Generally, the computer program can be stored on a non-transitory computer-readable medium. This document discloses and claims a non-transitory computer-readable medium storing instructions that, when executed by one or more processors of the control circuitry, cause the control circuitry to perform the steps described herein.
[0022] It should be noted that the methods and systems, including their preferred embodiments outlined in this document, can be used alone or in combination with other methods and systems disclosed in this document. Furthermore, the features outlined in the context of the system also apply to the corresponding methods. Moreover, all aspects of the methods and systems outlined in this document can be combined arbitrarily. In particular, the features of the claims can be combined with each other in any manner.
[0023] In this document, the term "coupled" or "coupled" refers to elements that are electrically connected to each other, such as directly via a wire or indirectly via other circuit elements between them. For example, two elements can be said to be coupled even if there is a circuit element such as a switch (which can be turned on and off) between them. On the other hand, the term "connected" or "linked" refers to elements that are directly electrically connected to each other, such as via a wire, and no circuit element is located between them. Attached Figure Description
[0024] The invention is illustrated by way of example rather than limitation. In the accompanying drawings, the same reference numerals refer to similar or identical elements, and in the drawings:
[0025] Figure 1 An exemplary power converter topology is shown.
[0026] Figure 2 An exemplary flowchart of a current reduction method is shown.
[0027] Figure 3 An exemplary graph showing the upper limit of current relative to the measured temperature is provided.
[0028] Figure 4 An exemplary implementation of temperature measurement using an NTC thermistor and a corresponding signal waveform is shown, as well as
[0029] Figure 5 Another exemplary graph shows the upper limit of current relative to the measured temperature with hysteresis. Detailed Implementation
[0030] Typically, worst-case thermal operating conditions occur during the period of maximum output power load and minimum input voltage. These applications are often designed to operate under a wide range of common input voltages from 85Vac to 265Vac. In this case, 85Vac with maximum load power is typically the worst-case condition for meeting thermal requirements. At lower input voltages, conduction-related losses dominate in the bridge rectifier, power factor correction converter stage, and isolated DC-DC stage, leading to decreased PSU efficiency and increased temperature. As the input voltage increases toward the nominal input voltage condition, efficiency and thermal performance are better at ~115V / 230Vac relative to the minimum input voltage. At higher input voltages, ~265Vac, power losses typically increase again, depending on the PSU topology used, and in some designs, total losses will be at their highest level.
[0031] A common design practice is to consider the maximum output power and ensure thermal compliance at the worst-case input voltage. In doing so, appropriate sizing must be implemented, along with proper thermal management (such as using heatsinks, thermal pads, and thicker plastic housings) to ensure no hot spots are generated and that case temperature requirements are met. However, this adds additional system cost and results in a larger power supply.
[0032] Figure 1 An exemplary power converter topology that can be controlled by the controller (control circuitry) presented in this document is shown. The power converter 1 includes a transformer 11 that separates the power converter 1 into a primary side 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. Here, the switching elements 13 and 14 form a half-bridge. In this document, this half-bridge, along with its dedicated drive circuitry, is also referred to as a power stage or a 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.
[0033] It should be noted that the power converter 1 illustrated is exemplary in nature, and many variations exist. For example, the primary winding of transformer 11 and resonant capacitor 15 may be connected in series with the high-side switching element 13 instead of the low-side switching element 14 illustrated. Alternatively, rectifier diode 16 may be replaced by a synchronous rectifier switching element controlled by an additional secondary-side controller, typically referred to as a synchronous rectifier controller. The controller (control circuitry) presented herein can be configured to control switching elements 13 and 14 on the primary side. Furthermore, this controller can be isolated from the electrical signal current originating from the secondary side of power converter 1.
[0034] Figure 2 An exemplary flowchart of a current reduction method is shown. This method can be implemented in a controller based on two temperature thresholds sensed by a thermistor within the PSU. If the temperature increases and falls between these two thresholds, the output current decreases accordingly. More specifically, Figure 2 The diagram shows that if the sensed temperature is between the release temperature Tr (represented as a first threshold in the claims) and the trigger temperature Tt (represented as a second threshold in the claims), the output current is reduced, and if the sensed temperature exceeds the trigger temperature Tt, a protection mode is entered. This scheme allows thermal specifications to be met without over-designed components.
[0035] The external temperature (T) of the power supply can be measured using a negative temperature coefficient (NTC) thermistor (or other temperature sensor). As mentioned, there are two temperature thresholds: a lower limit Tr (release temperature) and an upper limit Tt (trigger temperature). When T is below the lower limit Tr, the power supply turns on and operates in normal operating condition. That is, the output can reach 100% of the rated maximum current limit. As T increases and reaches Tr, a current reduction will occur, for example, linearly according to the current at... Figure 3 The temperature shown above. Figure 3 An exemplary graph showing the upper limit of current relative to the measured temperature is shown. Here, the current is controlled and can depend on four variables: Iout_limit, Id, Tt, and Tr. The latter variable determines the slope of the upper limit of current during current feedback (i.e., between Tr and Tt). Temperature monitoring continues, and when the temperature reaches the upper threshold Tt, the power supply can be shut off for some reason. In this way, we ensure that the power supply is protected from possible abnormal events. Once the temperature falls below Tr, the power supply is then allowed to be turned on again.
[0036] Figure 4 An exemplary implementation of temperature measurement using an NTC thermistor and the corresponding signal waveform is shown. In this example, temperature sensing is performed by measuring the voltage across the multifunction input / output (MFIO) pin. Tt is represented by the MFIO voltage as OTP_trigger_th, and Tr is represented by the MFIO voltage as OTP_release_th. Since the current limit from the primary side can be set to a lower value than the feedback requirement, the feedback signal can be expected to increase and saturate. To provide power derating, if the master controller detects T > Tr, the master controller may need to disable the overcurrent protection OCP limit (based on the feedback voltage Vfb).
[0037] For example, reducing the output charging current whenever the temperature exceeds a limit will not affect the operation of the power supply but will limit the internal heat dissipation. Therefore, if we can have continuous monitoring of the PSU temperature and linearly reduce the output current or power based on the temperature once a certain threshold is exceeded, we can have a more optimized, smaller, and cheaper design.
[0038] at last, Figure 5 Another exemplary diagram is shown showing the upper limit of current relative to the measured temperature with hysteresis. For this purpose, a third threshold temperature T3 is introduced to prevent power supply operation from power backflow and possible fluctuations in normal operation.
[0039] It should be noted that the description and accompanying drawings are merely illustrative of the principles of the proposed methods and systems. Those skilled in the art will be able to implement various steps, and although not explicitly described or shown herein, these arrangements embody the principles of the invention and are included within the spirit and scope of the invention. Furthermore, all examples and embodiments outlined in this document are primarily intended for illustrative purposes only to aid the reader in understanding the principles of the proposed methods and systems. Moreover, all statements herein providing principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to cover their equivalents.
Claims
1. A control circuit configured to control the operation of a power converter, wherein the control circuit is configured to: receive a temperature value from a temperature sensor and control the output current of the power converter based on the temperature value.
2. The control circuit of claim 1, wherein the control circuit is configured to reduce the output current of the power converter if the temperature value exceeds a first threshold.
3. The control circuit according to claim 1 or 2, wherein the control circuit is configured to linearly reduce the output current above a temperature between the first threshold and the second threshold.
4. The control circuit of claim 1, wherein the control circuit is configured to: maintain the output current below the upper current limit, and wherein the control circuit is configured to: reduce the upper current limit if the temperature value exceeds a first threshold.
5. The control circuit of claim 4, wherein the control circuit is configured to linearly reduce the upper limit of current above a temperature between the first threshold and the second threshold.
6. The control circuit according to claim 4 or 5, wherein the control circuit is configured to reduce the current limit based solely on the temperature value and independently of other feedback parameters of the power converter.
7. The control circuit according to any one of claims 4 to 6, wherein the control circuit is configured to: receive another feedback parameter indicating the output current or the output voltage of the power converter, and wherein the control circuit is configured to: control the output current based on the other feedback parameter provided that the output current does not exceed the upper limit of the current.
8. The control circuit according to any one of the preceding claims, wherein the control circuit is configured to: enter a protection mode and shut down the operation of the power converter if the temperature value exceeds a second threshold.
9. The control circuit according to any one of the preceding claims, wherein the power converter includes a transformer having a primary side and a secondary side, and wherein the control circuit is configured to control the output current of the power converter based on the temperature value by controlling the switching behavior of a switching element coupled to the primary side of the transformer.
10. The control circuit of claim 9, wherein the power converter includes a resonant capacitor and a half-bridge coupled to the primary side of the transformer, and wherein the switching element forms the half-bridge.
11. The control circuit according to any one of the preceding claims, wherein the control circuit is configured to: if the temperature value exceeds a first threshold, ignore the overcurrent protection function based on a feedback voltage indicating the output voltage of the power converter.
12. The control circuit according to any one of the preceding claims, wherein the temperature sensor comprises a thermistor, and wherein the temperature value comprises a voltage across the thermistor.
13. A battery charger device comprising a control circuit and a power converter according to any one of the preceding claims.
14. The battery charger device of claim 13, wherein the power converter includes a transformer having a primary side and a secondary side, wherein the control circuit is configured to control the output current of the power converter based on the temperature value by controlling the switching behavior of a switching element coupled to the primary side of the transformer.
15. A method for controlling a power converter, the method comprising: The control circuit receives the temperature value from the temperature sensor, and The control circuit controls the output current of the power converter based on the temperature value.
16. A computer program comprising instructions that, when executed by one or more processors of a control circuit, cause the control circuit to perform the operation of any one of claims 1 to 12.