US-12627236-B2 - Controller for an asymmetric half bridge flyback converter, asymmetric half bridge flyback converter and a method of controlling an asymmetric half bridge flyback converter

US12627236B2US 12627236 B2US12627236 B2US 12627236B2US-12627236-B2

Abstract

A controller for an asymmetric half bridge flyback converter as discussed herein. The control may include control logic configured to control one of a high-side switch and low-side switch of a half bridge of the asymmetric half bridge flyback converter based on a peak current control. For example, the control logic can be configured to limit an on-time of the one of the high-side switch and the low-side switch based on a threshold value.

Inventors

Alfredo Medina-Garcia

Assignees

INFINEON TECHNOLOGIES AUSTRIA AG

Dates

Publication Date: 20260512
Application Date: 20230323
Priority Date: 20220404

Claims (12)

1 . A controller operative to control a high-side switch and a low-side switch of a half bridge circuit of a flyback converter, the flyback converter operative to convert an input voltage into an output voltage, the controller comprising: control logic operative to: control one of the high-side switch and the low-side switch of the half bridge circuit of the flyback converter based on a peak current control function; for each of multiple switching cycles of controlling the high-side switch and the low-side switch, via the peak current control function, limit an on-time of the one of the high-side switch and the low-side switch based on a first threshold value; and trigger a protection mechanism when the on-time of one of the high-side switch and the low-side switch has been limited based on the first threshold value for a predetermined number of times, the predetermined number of times being greater than one; wherein the first threshold value is a time threshold value, and wherein the control logic is configured to switch off the one of the high-side switch and low-side switch during a condition in which the on-time of the one of the high-side switch and the low-side switch exceeds the time threshold value: wherein the control logic is configured to determine the time threshold value based on an on-time of the one of the high-side switch and the low-side switch in a first switching cycle during which the on-time in the first switching cycle was limited based on the peak current control function; and wherein the control logic is configured to determine the time threshold value based on the on-time in the first switching cycle plus a predefined time margin value.
2 . The controller of claim 1 , wherein the other one of the high-side switch and the low side switch of the half bridge circuit is coupled in parallel to a resonant circuit of the flyback converter.
3 . The controller of claim 1 , wherein the peak current control function comprises switching off the one of the high-side switch and the low-side switch during a condition in which a current provided via the one of the high-side switch and the low-side switch reaches a second threshold value.
4 . The controller of claim 1 , wherein the first threshold value is a voltage threshold value for a voltage at a resonant tank capacitor of the flyback converter.
5 . The controller of claim 1 , wherein the predetermined number of times is at least two.
6 . An asymmetric half bridge flyback converter, comprising: the controller of claim 1 , the half bridge circuit comprising the high-side switch and the low-side switch, and a resonant circuit including a capacitor and a primary winding of a transformer and coupled in parallel to the other one of the high-side switch and the low-side switch.
7 . An apparatus comprising: a controller in communication with a flyback converter, the flyback converter operative to convert an input voltage into an output voltage, the controller operative to: control a switch in a half bridge circuit of the flyback converter over multiple switching cycles, the switch operative to control a magnitude of current through a primary winding of a transformer of the flyback converter, a secondary winding of the transformer operative to produce the output voltage, the switch controlled based on a peak current control function; produce a count value indicating a number of times of limiting an on-time of the switch with respect to a threshold value via the peak current control function; and trigger a protection condition of controlling the switch in response to detecting that the count value indicating the number of times of limiting the on-time of the switch via the peak current control function crosses a count limit value; wherein the threshold value is a time threshold value derived from control of the switch in a first switching cycle of the multiple switching cycles: wherein the controller is operative to generate the count value to indicate multiple instances of the on-time of the switch exceeding the threshold value in a portion of the multiple switching cycles occurring later in time than the first switching cycle; wherein the time threshold value is a first threshold value; wherein the controller is further operative to: generate the time threshold value based on a first time duration measured between activation of the switch at a first instant of time and deactivation of the switch at a second instant of time in the first switching cycle; and wherein the controller is further operative to: determine the second instant of time based on detection that the magnitude of the current through the primary winding of the flyback converter crosses a second threshold; and set the magnitude of the time threshold value to be the first time duration plus a predefined delta time value.
8 . The apparatus as in claim 7 , wherein the controller is operative to: compare the magnitude of the current through the primary winding for each respective switching cycle in the portion of multiple switching cycles following the first switching cycle; and increment the magnitude of the count value for the respective switching cycle in response to detecting that the switch is activated to the on state for at least the time threshold value in the respective switching cycle without the magnitude of the current through the primary winding being detected as greater than the second threshold value.
9 . The apparatus as in claim 8 , wherein a magnitude of the second threshold varies over time.
10 . The apparatus as in claim 7 , wherein the flyback converter includes a capacitor disposed in series with the primary winding via a circuit node, a combination of the primary winding and the capacitor being a resonant tank circuit; wherein the threshold value is a threshold voltage value; and wherein the controller is operative to generate the count value to indicate multiple instances of a magnitude of a voltage at the circuit node being detected as exceeding the threshold voltage value in each respective switching cycle of a portion of the multiple switching cycles occurring later in time than the first switching cycle.
11 . The apparatus as in claim 10 , wherein the controller is operative to: compare the magnitude of the voltage at the circuit node to the threshold voltage value for each respective switching cycle in the portion of multiple switching cycles following the first switching cycle; and for each respective switching cycle, increment the magnitude of the count value in response to detecting that the magnitude of the voltage at the circuit node in the respective switching cycle crosses the threshold voltage value.
12 . The apparatus as in claim 11 , wherein a magnitude of the threshold voltage value is fixed over time.

Description

RELATED APPLICATION This application claims priority to earlier filed European Patent Application Serial Number EP22166456 entitled “CONTROLLER FOR AN ASYMMETRIC HALF BRIDGE FLYBACK CONVERTER, ASYMMETRIC HALF BRIDGE FLYBACK CONVERTER AND A METHOD OF CONTROLLING AN ASYMMETRIC HALF BRIDGE FLYBACK CONVERTER,” filed on Apr. 4, 2022, the entire teachings of which are incorporated herein by this reference. BACKGROUND Flyback converters are a type of voltage converters which provide galvanic isolation between an input and any output. A specific type of flyback converter is an asymmetric half bridge flyback converter, also sometimes referred to as asymmetric pulse-width modulation (PWM) half bridge flyback converter, also referred to as AHB flyback converter herein. An AHB flyback converter is essentially a converter with an inductor of the converter being split to form a transformer, such that voltage ratios are multiplied based on a winding ratio of the transformer with an additional advantage of isolation. Such a flyback converter includes a half bridge circuit (i.e., half bridge) comprising a high-side switch and a low-side switch. One of the high-side switch and low-side switch is coupled in parallel to what is sometimes referred to as resonant tank, the resonant tank including at least stray inductances of the transformer and a resonant capacitor, and sometimes an additional inductor. The high-side switch and the low-side switch are alternatingly switched on and off. In a first phase the switch of the half bridge not coupled in parallel to the resonant tank is switched on, and energy is transferred from an input voltage source to the resonant tank. Then, in a second phase when the switch parallel to the resonant tank is switched on and the other switch of the half bridge is switched on, energy is transferred to a secondary side of the transformer to provide an output voltage. A switching cycle consists of a first phase powered by a second phase. After a switching cycle, the next switching cycle starts again, with a first phase and a second phase. The above-mentioned first phase, where energy is transferred to the resonant tank, also referred to as charge phase, is usually controlled based on a peak current control scheme. In such a scheme, the current for the resonant tank is monitored, and when a peak is reached or a threshold current is reached, the switch which is not parallel to the resonant tank is switched off. However, under some conditions like specific loads, load changes or the like it may happen that a predefined peak voltage is not reached or reached very late which may lead to high voltages across a capacitor of the resonant tank. This may for example lead to too high voltages present in the converter. BRIEF DESCRIPTION According to an embodiment, a controller for an asymmetric half bridge flyback converter is provided, comprising: a control logic configured to control one of a high-side switch and low-side switch of a half bridge of the flyback converter based on a peak current control scheme (i.e., peak current control function), andfurther configured to limit an on-time of the one of the high-side switch and the low-side switch based on a threshold value. According to a further embodiment, an asymmetric half bridge flyback converter is provided, comprising the controller as defined above, a half bridge comprising the high-side switch and the low-side switch, anda resonant circuit including a capacitor and a primary winding of a transformer coupled in parallel to the other one of the high-side switch and the low-side switch. According to a further embodiment, a method for controlling an asymmetric half bridge flyback converter is provided, comprising: controlling one of a high-side switch and a low-side switch of a half bridge of the flyback converter based on a peak current control scheme, andfurther limiting an on-time of the one of the high-side switch and the low-side switch based on a threshold value. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a flyback converter according to an embodiment. FIG. 2 illustrates part of the flyback converter of FIG. 1 for illustrating a charging phase. FIG. 3 illustrates voltages and currents in the flyback converter of FIG. 1. FIG. 4 is a flowchart illustrating a method according to an embodiment. FIG. 5 is a signal diagram illustrating an implementation possibility of the method of FIG. 4. FIG. 6 is a signal diagram illustrating another implementation possibility of the method of FIG. 4. FIG. 7 illustrates a flyback converter according to another embodiment. DETAILED DESCRIPTION In the following, various embodiments will be described in detail referring to the attached drawings. These embodiments are given as examples only and are not to be construed as limiting in any way. For example, while embodiments may be described as comprising a plurality of features (e.g. components, devices, elements, acts, events etc.), this is not to be con