WO2016000754A1

WO2016000754A1 - Unit and method for synchronous rectification control

Info

Publication number: WO2016000754A1
Application number: PCT/EP2014/063900
Authority: WO
Inventors: Jun Ma; Georgios TSENGENES; Grover TORRICO
Original assignee: Huawei Technologies Co.,Ltd
Priority date: 2014-07-01
Filing date: 2014-07-01
Publication date: 2016-01-07
Also published as: CN106664080B; EP3149851A1; CN106664080A

Abstract

A unit ant a method for synchronous rectification control unit is disclosed. The synchronous rectification control unit includes a voltage sensing circuit 25 configured to detect body diode conduction for a power switch 14, and to output a voltage pulse signal V_DC corresponding to the body diode conduction. The synchronous rectification control unit further includes a capture unit 24 configured to determine a time duration T_c for the voltage pulse signal V_DC, and to store the time duration T_c in a memory. The synchronous rectification control unit further includes a control algorithm circuit 26 configured to determine a turn-on time T_on and a turn-off time T_off to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Q1 during an upcoming switching cycle, wherein the determination of the turn—on T_on and turn—off T_off times is based on the stored time duration T_c. The synchronous rectification control unit further includes a PWM signal generator 32 configured to generate, by use of the determined turn-on T_on time and turn-off T_off time, the synchronous PWM control signal SQ1 for controlling switching of the power switch 14 when the power switch is in a synchronous side of a circuit; or the non-synchronous PWM control signal Q1 for controlling switching of the power switch 14 when the power switch is in a non-synchronous side of the circuit 100.

Description

UNIT AND METHOD FOR SYNCHRONOUS RECTIFICATION CONTROL

FIELD OF INVENTION

Implementations described herein relate generally to a

synchronous rectification control unit and a method for controlling synchronous rectification. In particular is herein described a mechanism for generating synchronous or non- synchronous pulse width modulation, PWM, control signals usable for controlling switching a power switch. BACKGROUND OF INVENTION

Power switches, for example switches being realised by use of MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) of other suitable types of transistors, are used in a number of circuits today. For example, such power switches are used power converters, which may be implemented as half bridge power converters or full bridge power converters. E.g. full bridge power converter circuits may include a synchronous side and a non-synchronous side. In such a circuit, the non- synchronous side is the side to which the original/non- converted signal/power is inputted, and the synchronous side is the side where the manipulated/converted signal/power is outputted. This can also be expressed as the synchronous rectification side is defined as a side of the circuit, at which side the synchronous rectification power switches are located. Correspondingly, the non synchronous rectification side is defined as side of the circuit, at which side the main power switches are located.

Thus, for a bidirectional circuit, the non-synchronous side of the circuit can correspond to different physical sides of the circuit, depending on in which direction the signal/power should be manipulated/converted, since the original

signal/power is input to the non-synchronous side.

Correspondingly, the synchronous side of the circuit can correspond to different physical sides of the circuit, depending on in which direction the signal/power should be manipulated/converted, since the manipulated/converted

signal/power is output from the synchronous side.

Circuits including such power switches, e.g. power

transforming circuits or the like, can be utilised in a large variety of units, e.g. in A User Equipment (UE) , also known as a mobile station, wireless terminal and/ or mobile terminal enabled to communicate wirelessly in a wireless communication network, sometimes also referred to as a cellular radio system. Such circuits can also be utilised in a radio network node, or base station, e.g., a Radio Base Station (RBS) , which in some networks may be referred to as "eNB", "eNodeB",

"NodeB" or "B node", depending on the technology and/ or terminology used. Switching of the power converters in such circuits aims at being as power efficient as possible. MOSFETs, and other transistors being used for realising the power switches, generally have a lower electrical resistance when the switch is closed/conducting than when the switch is open/non- conducting. As a non-limiting example can be mentioned that a MOSFET switch has a voltage drop over the switch corresponding to the body diode voltage of the MOSFET, which can be e.g. 0.7 Volt, when the switch is open. When the MOSFET switch is closed, the voltage drop over the switch is much lower, e.g. 0.01 Volt according to a non-limiting example. Therefore, to achieve as high power efficiency as possible, as much power as possible should flow through the closed switch, which has the lower voltage drop.

Conventional synchronous rectification has been suggested for improving the power efficiency of circuits by controlling switching of the power switches being included in the

circuits. Today, a number of conventional synchronous

rectification control solutions have been proposed. One such solution tunes a synchronous rectification duty cycle based on detection of a synchronous rectification body diode conduction for a power switch. If a body diode conduction is present, the duty cycle for the synchronous rectification is increased until the body diode conduction stops. On the contrary, if a body diode conduction is not present, the synchronous

rectification duty cycle is decreased until the body diode conduction starts. As a result, the body diode conduction state often alternates between on and off.

One significant drawback of this conventional method is that each update/tuning of the synchronous rectification duty cycle has to use a fixed small step. However, a small step

update/tuning of the synchronous rectification duty cycle results in serious problems when the circuit is utilized in a close loop operation, since the current shoot-through in the circuit occurrence becomes evident when SR duty cycle changes too slowly. Generally, the duty cycle decreases very slowly, which means that the power switch is still turned-on while the current reaches zero and changes to the opposite current direction. This opposite direction of the current through the same power switch is the cause for the current shoot-through phenomenon . Also, since the turn-on time of synchronous side (pulse Width Modulated) PWM signals in conventional solutions is

synchronized with non-synchronous side PWM signals, current shoot-through could occur in case of light load operation. This is because of current lags/delays for the on-edge PWM pulse, which results in a reversed direction current flow in the power switch once it is turned-on, when the synchronous side PWM signals in conventional solutions is synchronized with non- synchronous side PWM signals.

SUMMARY OF INVENTION

It is therefore an object to solve at least some of the above mentioned disadvantages and to improve the power efficiency and to lower the implementation complexity of circuits

including a synchronous side and a non-synchronous side.

According to a first aspect, the object is achieved by a synchronous rectification control unit including:

- a voltage sensing circuit configured to

- detect body diode conduction for a power switch, and - output a voltage pulse signal V_DC corresponding to said body diode conduction;

- a capture unit configured to

- determine a time duration T_c for said voltage pulse signal V_DC, and

- store said time duration T_c in a memory;

- a control algorithm circuit configured to determine a turn- on time on and a turn-off time T₀ff to be used for a

synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle, said determination of said turn-on T_on and turn-off T_0ff times being based on said stored time duration T_c; and

- a PWM signal generator configured to generate, by use of said determined turn^—on T_ori time and turn-off T_0ff time, said synchronous PWM control signal SQ1 for controlling switching of the power switch when the power switch is in a synchronous side of a circuit; or said non-synchronous PWM control signal Ql for controlling switching of the power switch when the power switch is in a non-synchronous side of the circuit. By utilisation of this synchronous rectification control unit, an exact and fast update update/tuning of the non- synchronous rectification and/or synchronous rectification duty cycle can be achieved, since larger steps can be taken during the tuning as for the conventional solutions. Thus, a power efficient switching can be achieved by the synchronous rectification control unit. Also, current shoot-through is efficiently mitigated by the fast update/tuning of the non- synchronous rectification and/or synchronous rectification duty cycle, both for changing conditions and for light load operation.

In a first possible implementation form of the synchronous rectification control unit according to the first aspect, the voltage sensing circuit is further configured to detect an on- edge body diode conduction for the power switch of said non- synchronous side and to output an on-edge voltage pulse signal Von c corresponding to said on-edge body diode conduction.

By detecting the on-edge body diode conduction time, the time that the diode start to conduct can be exactly determined.

Based on this time, it is then possible to manipulate the dead-time between the switching pulses in order to minimize the diode conduction time and improve the efficiency. In a second possible implementation form of the synchronous rectification control unit according to the first aspect as such or according to the first possible implementation form of the synchronous rectification control unit according to the first aspect, the control algorithm circuit is further

configured to update a dead time T_d to a new dead time value T_{d new} if the time duration T_c has a value greater than zero, T_c >0; said new dead time value T_{d new} being equal to an already used dead time value T_d minus a portion of the time

duration T_c, T_d__{new =}T_d-T_dm 0<Τ^<Τ_ο.

Hereby, the dead time is minimized in order to achieve a minimum diode conduction time, which results in high power efficiency .

In a third possible implementation form of the synchronous rectification control unit according to the first aspect as such or according to the synchronous rectification control unit according to the first or second possible implementation forms of the synchronous rectification control unit according to the first aspect, said control algorithm circuit is further configured to set a new dead time value T_{d new} to a

predetermined value T_{d ρΓβ(}ι T_{d new} =T_d preci if the time duration T_c has a value equal to zero, T_c =0.

If T_c=0, this means that there is a risk for current shoot- through. By this possible implementation, this situation is identified, and a predefined value for the dead time is set in order to guarantee that no shoot-through will happen.

In a fourth possible implementation form of the synchronous rectification control unit according to the first aspect, - said voltage sensing circuit is further configured to detect an on-edge body diode conduction and an off-edge body diode conduction for the power switch and to output an on-edge voltage pulse signal ν_οη and an off-edge voltage pulse signal V₀ff corresponding to said on-edge body diode conduction and said off-edge body diode conduction, respectively;

- said capture unit is further configured to determine a turn- on time duration T_{on c} as a time duration of the on-edge voltage pulse signal V_{on c}, and to determine a turn-off time duration T_off c for said synchronous PWM control signal SQ1 as a time duration of the off-edge voltage pulse signal V_{off c}.

Hereby, an exact and fast update/tuning of the synchronous rectification duty cycle can be achieved. A power efficient switching which also efficiently mitigates current shoot- through is provided by the fast update/tuning of the

synchronous rectification duty cycle.

In a fifth possible implementation form of the fourth possible implementation form of the synchronous rectification control unit according to the first aspect, the control algorithm circuit is further configured to update said turn-on time T_on to a new turn-on time T_on new if said turn-on time duration T_on c has a value greater than zero, T_on c >0; said new turn-on time Ton new being equal to an already used turn-on time T_on minus a portion T_on m of said turn-on time duration T_on c T_on new ₌T_on ^_

Ton_m/ 0^<CTon_m—Ton_c ·

By detecting the turn-on time duration T_on c, the information of the diode conduction is detected. The adaption of the turn-on time T_on to a new value T_on new based on the detected turn-on time duration T_on c is usable for minimizing the time that the diode conducts, thus for increasing the efficiency.

In a sixth possible implementation form of the fourth or fifth possible implementation forms of the synchronous rectification control unit according to the first aspect, the control algorithm circuit is further configured to set a new turn-on time on new to a predetermined value T_on preci if said turn-on time duration T_on c has a value equal to zero; T_on c=0.

If Ton c₌o, there is a risk for current shoot-through. This situation is here identified, and a predefined value for the turn-on time T_on preci time is set in order to guarantee that no shoot-through will happen.

In a seventh possible implementation form of the fourth, fifth or sixth possible implementation forms of the synchronous rectification control unit according to the first aspect, the control algorithm circuit is further configured to update said turn-off time T_off to a new turn-off time T_{off new} if said turn- off time duration T₀ff _c has a value greater than zero; T₀ff _c >0; said new turn-off time T₀ff new being equal to an already used turn-off time T₀ff plus a portion T₀ff _m of said turn-off time duration T₀ff__c; T₀ff_new =T₀ff+T₀ff__m; 0<T_Off_m-T_Off_c ·

By detecting the turn-off time duration T₀ff _cr information of the diode conduction is also detected. Here, the turn-off time T₀ff is then adapted to a new value T₀ff new based on the detected turn-off time duration T₀ff _c iⁿ order to minimize the time that diode conducts, i.e. to increase the power efficiency.

In a eighth possible implementation form of the fourth, fifth, sixth or seventh possible implementation forms of the

synchronous rectification control unit according to the first aspect, said control algorithm circuit is further configured to set said turn-off time T₀ff to a predetermined value T₀ff _preci if a turn-off time duration T₀ff _c has a value equal to zero;

If T₀ff c=0 there is a risk for current shoot-through. This risk is here identified, and a predefined value for the turn-off time T_0ff preci time is set, which guarantees that no shoot- through will happen.

In a ninth possible implementation form of the synchronous rectification control unit according to the first aspect as such or according any of the preceding implementation forms of the first aspect,

- said voltage sensing circuit is further configured to output a logic high value for said voltage pulse signal V_DC when said body diode is conducting a current; and

- said capture unit is configured to determine the time duration T_c as equal to a time duration during which said voltage pulse signal V_DC has the logic high value.

By using a capture unit, an accurate time reference for the voltage pulse signal V_DC can be captured, which is usable for increasing the power efficiency.

According to a second aspect, the object is achieved by an integrated circuit comprising at least one of the synchronous rectification control units according to the first aspect as such or according any of the preceding implementation forms of the first aspect.

The integrated circuit according to the second aspect has advantages corresponding to the advantages stated above for the first aspect.

According to a third aspect, the object is achieved by an electronic device having a power converter comprising the synchronous rectification control units according to the first aspect as such or according any of the preceding

implementation forms of the first aspect. The electronic device according to the third aspect has advantages corresponding to the advantages stated above for the first aspect.

According to a fourth aspect, the object is achieved by a method for controlling synchronous rectification, including:

- detecting body diode conduction for a power switch;

- outputting a voltage pulse signal V_DC corresponding to said body diode conduction;

- determining a time duration T_c for said voltage pulse signal V_DC;

- storing said time duration T_c in a memory;

- determining a turn-on time T_on and a turn-off time T₀ff to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle, said determination of said turn- on Ton and turn-off T₀ff times being based on said stored time duration T_c; and

- generating, by use of said determined turn-on T_on time and turn-off T₀ff time, said synchronous PWM control signal SQ1 for controlling switching of the power switch when the power switch is in a synchronous side of a circuit; or said non- synchronous PWM control signal Ql for controlling switching of the power switch when the power switch is in a non-synchronous side of the circuit. By utilisation of this synchronous rectification control method, an exact and fast update update/tuning of the

synchronous rectification duty cycle can be achieved, since larger steps can be taken during the tuning as for the

conventional solutions. Thus, a power efficient switching can be achieved by the synchronous rectification control method. Also, current shoot-through is efficiently mitigated by the fast update/tuning of the synchronous rectification duty cycle, both for changing conditions and for light load

operation .

In a first possible implementation form of the method for controlling the synchronous rectification according to the fourth aspect, an on-edge body diode conduction for the power switch of said non-synchronous side is detected, and an on- edge voltage pulse signal V_{on c} corresponding to said on-edge body diode conduction is output.

By detecting the on-edge body diode conduction time, the time that the diode start to conduct can be exactly determined. Based on this time, it is then possible to manipulate the dead-time between the switching pulses in order to minimize the diode conduction time and to improve the power efficiency.

In a second possible implementation form of the method for controlling the synchronous rectification according fourth aspect as such or according to the first possible

implementation form of the method for controlling the

synchronous rectification according to the fourth aspect, a dead time T_d is updated to a new dead time value T_{d new} if the time duration T_c has a value greater than zero, T_c >0; said new dead time value T_{d new} being equal to an already used dead time value T_d minus a portion of the time duration T_c, T_{d new =}T_d-

-L dm 0<T_dm≤T_c .

In a third possible implementation form of the method for controlling the synchronous rectification according to the fourth aspect as such, or according to the first or second possible implementation forms of the synchronous rectification control unit according to the fourth aspect, a new dead time value T_d_new is set to a predetermined value T_d__pred; T_d__new =T_d__pred; if the time duration T_c has a value equal to zero, T_c =0.

If T_c=0, there is a risk for current shoot-through. By this possible implementation, this situation is identified, and a predefined value for the dead time is set in order to

guarantee that no shoot-through will happen.

In a fourth possible implementation form of the method for controlling the synchronous rectification according to the fourth aspect,

- an on-edge body diode conduction and an off-edge body diode conduction for the power switch are detected, and an on-edge voltage pulse signal ν_οη and an off-edge voltage pulse signal V₀ff corresponding to said on-edge body diode conduction and said off-edge body diode conduction, respectively, are output;

- a turn-on time duration T_{on c} is determined as a time duration of the on-edge voltage pulse signal ν_{οη cr} and a turn-off time duration T₀ff _c for said synchronous PWM control signal SQ1 is determined as a time duration of the off-edge voltage pulse signal V₀ff _c ·

synchronous rectification duty cycle.

In a fifth possible implementation form of the fourth possible implementation form of the method for controlling the

synchronous rectification according to the fourth aspect, said turn-on time T_on is updated to a new turn-on time T_on new if said turn-on time duration T_on c has a value greater than zero, T_on c >0; said new turn-on time T_{on new} being equal to an already used turn-on time T_on minus a portion T_{on m} of said turn-on time duration T₀n_c_ T₀n_new = _ori— _on^m; O^Ton^—T₀n_c ·

By detecting the turn-on time duration T_{on c}, the information of the diode conduction is detected. The adaption of the turn-on time T_on to a new value T_{on new} based on the detected turn-on time duration T_{on c} is usable for minimizing the time that diode conducts, thus for increasing the efficiency.

In a sixth possible implementation form of the fourth or fifth possible implementation forms of the method for controlling the synchronous rectification according to the fourth aspect, a new turn-on time T_{on new} is set to a predetermined value T_{on pred} if said turn-on time duration T_{on c} has a value equal to zero;

Ton_c^—0 ·

If Ton c₌o there is a risk for current shoot-through. This situation is here identified, and predefined value for the turn-on time T_on preci time is set in order to guarantee that no shoot-through will happen.

In a seventh possible implementation form of the fourth, fifth or sixth possible implementation forms of the method for controlling the synchronous rectification according to the fourth aspect, said turn-off time T₀ff is updated to a new turn-off time T₀ff new if said turn-off time duration T₀ff _c has a value greater than zero; T₀ff _c >0; said new turn-off time

T₀ff new being equal to an already used turn-off time T₀ff plus a portion T₀ff _m of said turn-off time duration T₀ff _c Toff new

By detecting the turn-off time duration T₀ff _r information of the diode conduction is also detected. Here, the turn-off time T₀ff is then adapted to a new value T₀ff new based on the detected turn-off time duration T_{0ff c} iⁿ order to minimize the time that the diode conducts, i.e. to increase the power efficiency.

In a eighth possible implementation form of the fourth, fifth, sixth or seventh possible implementation forms of the method for controlling the synchronous rectification according to the fourth aspect, said turn-off time T_off is set to a

predetermined value T_{off pred} if a turn-off time duration T_{off c} has a value equal to zero; T_{off c}=0.

If T_{off c}=0 there is a risk for current shoot-through. This risk is here identified, and a predefined value for the turn-off time T_{off pred} time is set, which guarantees that no shoot- through will happen.

In a ninth possible implementation form of the method for controlling synchronous rectification according to the fourth aspect as such, or according to any of the above possible implementation forms of the method for controlling the

synchronous rectification according to the fourth aspect, - a logic high value is output for said voltage pulse signal V_DC when said body diode is conducting a current; and

- the time duration T_c is determined as equal to a time duration during which said voltage pulse signal V_DC has the logic high value.

According to a fifth aspect, the object is achieved by a computer program with a program code for performing a method according to the second aspect when the computer program runs on a computer. The computer program according to the fifth aspect has

advantages corresponding to the advantages stated above for the fourth aspect. Further, a computer program with a program code gives flexibility, accuracy, and robustness to

environmental conditions. Also, the program code is easily modified and updated.

In other words, a Micro Controller Unit (MCU) provides PWM signals to both non-SR side and SR side power switches. For the non-SR side switching, a delay time, i.e. the dead time, is often inserted in order to tune the turn-on time of the PWM signals, while the turn-off time remains unchanged. For the SR side switching, both the turn-on and the turn-off times of PWM signals are supposed to be tuned. These tunings aim to

minimize the body diode conduction time so that power losses are reduced.

To achieve the reduced power losses, the synchronous

rectification control unit being implemented in the MCU features event capture functionality, which facilitates saving of information corresponding to captured events in

registers/memories. In addition to the MCU, a voltage sensing circuit is used for detecting body diode conduction and to produce corresponding voltage pulse signals to be captured by the capture unit of the MCU.

For the non SR side, at least one voltage sensing circuit is required to detect the body diode conduction related to the on-time PWM signal, and at least one dedicated capture unit is assigned to capture corresponding pulse signals and to save information corresponding to the pulse signals in a

register/memory . For the SR side, at least one voltage sensing circuit is required to detect the body diode conduction related to both the SR on-time and off-time PWM signals, and at least another one dedicated capture unit is assigned to capture

corresponding the PWM signals and to save information

corresponding to the pulse signals in two registers/memories, one for the on-time PWM signals and the other for the off-time PWM signals, respectively.

When power switch body diode conduction is detected in a present switching cycle, a voltage pulse signal is generated by the voltage sensing circuit and is instantaneously captured by the capture unit of the MCU. The captured pulse width includes body diode conduction time information that is saved in a capture register/memory. The control algorithm circuit then determines a desired turn-on and/or turn-off time

instance for the next switching cycle to achieve a minimal body diode conduction time.

When power switch body diode conduction is not detected in a present switching cycle, no voltage pulse signal is generated and thus nothing is captured by the capture unit. The missing pulse width, i.e. the zero width information, here indicates that the body diode has no conduction time. The control algorithm circuit then sets a predefined turn-on and/or turn- off time instance for the next switching cycle to achieve a predefined body diode conduction time. The tuning of turn-on and turn-off time is on the basis of each switching cycle. Other objects, advantages and novel features of the embodi^¬ ments of the invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention are described in more detail with reference to attached drawings illustrating examples of embod^¬ iments of the invention in which:

Fig. 1 is a schematic block diagram illustrating a

synchronous rectification control unit according to some embodiments.

Fig. 2 is a schematic block diagram illustrating a

synchronous rectification control and one power switch according to some embodiments. Fig. 3 is a schematic block diagram illustrating a

synchronous rectification control and two power switches according to some embodiments.

Fig. 4 is a flow chart diagram illustrating some

embodiments . Fig. 5 is a block diagram illustrating some embodiments.

Fig. 6 illustrates examples of input and output signals

values according to some embodiments.

Fig. 7 illustrates examples of input and output signals

values according to some embodiments. Fig. 8 illustrates examples of input and output signals

values according to some embodiments.

Fig. 9 illustrates examples of input and output signals

values according to some embodiments.

Fig. 10 illustrates examples of input and output signals

values according to some embodiments. Fig. 11 illustrates examples of input and output signals values according to some embodiments.

Fig. 12 is a flow chart diagram illustrating the synchronous rectification control method according some embodiments .

Fig. 13 is a schematic block diagram illustrating a

processing circuit implementing the synchronous rectification control method according to some embodiments .

DETAILED DESCRIPTION OF INVENTION

Embodiments of the invention described herein are defined as a synchronous rectification control unit and a method for controlling synchronous rectification, which may be put into practice in the embodiments described below. These embodiments may, however, be exemplified and realised in many different forms and are not to be considered as limited to the embodi^¬ ments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete.

Still other objects and features may become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustr^¬ ation and not as a definition of the limits of the herein dis^¬ closed embodiments, for which reference is to be made to the appended claims. Further, the drawings are not necessarily drawn to scale and, unless otherwise indicated, they are mere^¬ ly intended to conceptually illustrate the structures and pro^¬ cedures described herein. Figure 1 schematically illustrates the inner structure of the synchronous rectification control unit 40 implementing the embodiments of the invention.

The synchronous rectification control unit 40 includes a voltage sensing circuit 25 a capture unit 24, a memory (not shown in figure l),a control algorithm circuit 26, and a pulse width modulation, PWM, signal generator 32.

A voltage difference over a power switch 14 is an input signal 30 to the synchronous rectification control unit 40, as will be described more in detail in connection with figures 2 and 3 below .

The voltage sensing circuit 25 is configured to detect body diode conduction for the power switch 14. The voltage sensing circuit 25 is also configured to output a voltage pulse signal V_DC corresponding to the detected body diode conduction.

According to an embodiment, the voltage sensing circuit 25 is further configured to output a logic high value for the voltage pulse signal V_DC when the body diode is conducting a current. Correspondingly, the voltage sensing circuit 25 is further configured to output a logic low value for the voltage pulse signal V_DC when the body diode is not conducting a current .

In other words, the voltage sensing circuit 25 is configured to consider the voltage difference over the power switch 14, e.g. between the potential points 22 and 23 in the non- limiting example in figure 2, as input 30 to the synchronous rectification control method. The voltage sensing circuit 25 outputs a voltage pulse signal which indicates the conduction time of the body diode 141 of the power switch 14 e.g in figure 2. The voltage sensing circuit 25 is connected to a Micro Controller Unit, MCU, 27. The MCU includes the capture unit 24, the memory, the control algorithm 26, and the PWM signal generator 32.

The capture unit 24 is configured to determine a time duration T_c for the voltage pulse signal V_DC being output by the voltage sensing unit 25. The capture unit 24 is also configured to store the time duration T_c in the memory (not shown) . The capture unit 24 may be included in the MCU as stated above.

According to an embodiment, the capture unit 24 is further configured to determine the time duration T_c as being equal to a time duration during which the voltage pulse signal V_DC has a logic high value.

The control algorithm circuit 26 is configured to determine a turn-on time T_on and a turn-off time T₀ff to be used for a synchronous PWM control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle. This determination of the turn—on T_ori and turn—off T₀ff times is based on the stored time duration T_c. The control algorithm circuit 26 may be included in the MCU. Thus, the capture unit 24 is configured to capture the

duration of the voltage pulse signal V_DC, then the control algorithm circuit 26 is configured to manipulate the turn-on Ton and turn-off T₀ff times, or the dead-time between the first 14 and second 13 power switches (shown in figure 3) based on the captured duration time, as is described below. In this document, dead time is a delay time inserted by one power switch at one or more edges of its switching cycles in order to provide a blank switching time in one complementary switch pair, e.g. a blank switching time between conduction for a first switch 13 and second switch 14 in figure 3. The dead time corresponds to the time period where no switching pulse is given to any of the first 14 and second 13 power switches. The dead time is utilized for preventing current shot-through, i.e. short circuit coupling in the circuits including the power switches. The PWM signal generator 32 is configured to generate PWM control signals based on the determined turn-on T_on time and on the turn-off T_off time. The PWM signal generator 32 is

configured to generate the synchronous PWM control signal SQ1 for controlling switching of the power switch 14 when the power switch is in a synchronous side of a circuit 100. The PWM signal generator 32 is configured to generate the non- synchronous PWM control signal Ql for controlling switching of the power switch 14 when the power switch is in a non- synchronous side of the circuit 100. The output signal 31 represents the desired switching pulses being based on, and corresponding to, the modified turn-on T_on and/or turn-off T_0ff times of the PWM signals.

The synchronous rectification control unit 40 according to embodiments of the invention has a number of advantages. The synchronous rectification control unit can provide a high power efficiency. Also, the synchronous rectification control unit according to embodiments of the invention presents a simple, very low complex, and still robust solution to the above stated problems. The synchronous rectification control unit 40 can provide a robust synchronous rectification control for essentially all possible working conditions, without causing current shoot-through conditions.

The synchronous rectification control unit 40 provides dead- time optimisation on the non-synchronous side power switches. The synchronous rectification control unit 40 also improves operation of the synchronous side power switches. Figure 2 illustrates a circuit diagram of a non-limiting example of a circuit 100 including a power switch and the synchronous rectification control unit 40. The synchronous rectification control unit 40 is connected across the power switch 14, which can be e.g. a MOSFET, at the points 22 and 23. Thus, the input signal 30 corresponds to the voltage difference between the potential points 22 and 23. The output signal 31 of the synchronous rectification control unit 40 is a synchronous PWM control signal SQ1 for controlling switching of the power switch 14 when the power switch is in a

synchronous side of the circuit 100, or a non-synchronous PWM control signal Ql for controlling switching of the power switch 14 when the power switch is in a non-synchronous side of the circuit 100. Figure 3 illustrates a non-limiting example of a circuit diagram for a half-bridge power converter equipped with the synchronous rectification control method in the form of a first 40 and second 41 synchronous rectification control unit. The half-bridge power converter includes two power switches 13 and 14, e.g. being MOSFETs, and a capacitor 12 being connected between terminals 10 and 11 and being fed by a rectified DC voltage. Each one of the first 40 and second 41 power switches is connected to an individual first 40 and second 41

synchronous rectification control unit, respectively. The first synchronous rectification control unit 40 is

connected across the first power switch 14 at the first potential voltage points 22 and 23. Thus, the input signal 30 to the first synchronous rectification control unit 40 is the differential voltage between the first potential voltage points 22 and 23 over the first power switch 14. The second synchronous rectification control unit 41 is connected across the second power switch 13 at the second potential voltage points 28 and 29. Thus, the input signal 30 to the second synchronous rectification control unit 41 is the differential voltage between the second potential voltage points 28 and 29 over the second power switch 13.

The output signal 31 of the first synchronous rectification control unit 40 represents the desired switching pulses for the first power switch 14 being based on, and corresponding to, the modified turn-on T_on and/or turn-off T_off time of the PWM signals. The switching pulses are thus synchronous PWM control signals SQ1 for controlling switching of the first power switch 14 when the power switch is in a synchronous side of a circuit 100, and non-synchronous PWM control signals Ql for controlling switching of the first power switch 14 when the power switch is in a non-synchronous side of the circuit 100.

The output signal 31 of the second synchronous rectification control unit 41 represents the desired switching pulses for the second power switch 13 being based on, and corresponding to, the modified turn—on T_ori and/or turn—off T_0ff time of the PWM signals. The switching pulses are thus synchronous PWM control signals SQ1 for controlling switching of the second power switch 13 when the power switch is in a synchronous side of a circuit 100, and non-synchronous PWM control signals Ql for controlling switching of the second power switch 13 when the power switch is in a non-synchronous side of the circuit 100.

Generally, when one of the first 14 and second 13 power switches is turned/switched on, the other one of the first 14 and second 13 power switches should be turned/switched off. As is illustrated in figure 3, for a half-bridge power

converter, there are two synchronous rectification control units, i.e. one for each power switch.

The synchronous rectification control units can also be utilised e.g. for full-bridge power converters, wherein four synchronous rectification control units would be utilised, one for each power switch.

When there are more than one synchronous rectification control units utilised in a circuit to control power switches, these more than one synchronous rectification control units are logically independent and separated. However, the more than one synchronous rectification control units can be either physically separated, or can be physically integrated into one common synchronous rectification control unit. Figure 4 is a flowchart illustrating a couple of embodiments for the method/algorithm/logic of the control algorithm circuit 26 for a power switch 13, 14 being located in the non- synchronous side of the circuit 100. In the following, the logic is described for the case of controlled switching of the first power switch 14. However, corresponding logic may be utilized for controlled switching of one or more of the first 14 and second 13 switches in e.g. a half-bridge circuit as the one illustrated in figure 3.

According to an embodiment, the voltage sensing circuit 25 is further configured to detect an on-edge body diode 141 conduction for the power switch 14 of the non-synchronous side and to output an on-edge voltage pulse signal ν_οη c

corresponding to the on-edge body diode 141 conduction. The control algorithm circuit 26 is further configured to

determine the new turn-on time T_on and/or a new dead time T_{d new} to be used for the synchronous pulse width modulation, PWM, control signal SQ1 or the non-synchronous PWM control signal Ql during an upcoming switching cycle.

In a first step 401, non-synchronous rectification side body diode conduction voltage pulse V_DC is input to the synchronous rectification control unit 40, 41.

In a second step 402, the time duration T_c for the voltage pulse signal V_DC is determined/measured.

In a third step 403, the time duration T_c is compared to the value zero, and the method proceeds to either of a fourth 404 step if the time duration T_c has a value higher than zero;

T_c>0; and a fifth step 405 if the time duration T_c is not longer than zero.

If the logic proceeds to the fourth step 404, i.e. if the time duration T_c has a value higher than zero, T_c >0, the control algorithm circuit 26 is further configured to update a dead time T_d to a new dead time value T_{d ne}w This new dead time value T_{d new} is here equal to an already used dead time value T_d minus a portion of the time duration T_c, T_{d new =}T_d-T_dm,

0<T_dm<T_c. If the logic proceeds to the fifth step 405, i.e. if the time duration T_c has a value equal to zero, T_c =0, the control algorithm circuit 26 is further configured to set a new dead time T_d__ne„ to a predetermined value T_d__pred; T_d__rie„=T_d_p_red .

Thus, figure 4 illustrates the logic for how the dead time T_d is optimized for non-synchronous rectification side power switches of the circuit 100. The input of the flow chart is the non-synchronous rectification side body diode conduction voltage pulse. Then, the time duration T_c of this voltage pulse is captured. If the time duration T_c is greater than zero, the control algorithm decides to decrease the new dead time T_d new- Otherwise, if the duration time T_c is zero, the control algorithm decides to restore the dead time to a predefined value T_d__pred. In other words, if the power switch 13, 14 to be controlled is located in the non-synchronous side of the circuit 100, the synchronous rectification control unit 40, 41 manipulates the dead time between the first 14 and second 13 power switches. The capture unit 24 here obtains the voltage pulse signal time duration T_c of the voltage pulse V_DC from the voltage sensing circuit. Then, the control algorithm circuit 26 analyses if this time duration T_c is greater than zero. If the time duration T_c is greater than zero, then a percentage of this time duration T_c is subtracted from the dead-time T_d. On the other hand, if the obtained voltage pulse signal time duration T_c is equal to zero then the new dead-time value T_{d new} is reset to a predefined value T_{d pred}.

Figure 5 is a flowchart illustrating a couple of embodiments for the method/algorithm/logic of the control algorithm circuit 26 for a power switch 13, 14 being located in the synchronous side of the circuit 100. In the following, the logic is described for the case of controlled switching of the first power switch 14. However, corresponding logic may be utilized for controlled switching of one or more of the first 14 and second 13 switches in e.g. a half-bridge circuit as the one illustrated in figure 3 above.

In a first step 501, the synchronous side voltage pulse signal V_DC corresponding to the body diode conduction and the non- synchronous side PWM control signals Ql are input to the voltage sensing circuit 25. In a second step 502, the voltage sensing circuit 25 is further configured to detect on-edge body diode 141 conduction for the power switch 14. The voltage sensing circuit 25 is also configured to output an on-edge voltage pulse signal ν_οη corresponding to the on-edge body diode conduction. In figure 5, the on-edge voltage pulse signal V_on is denoted as a

synchronous rectification on-edge voltage pulse signal V_sron .

The control algorithm circuit 26 is then further configured to determine the turn-on time duration T_{on c} as the time duration of the on-edge voltage pulse signal V_{on c}. In figure 5, the turn-on time duration T_{on c} is denoted as a synchronous

rectification turn-on time duration T_sronc-

In a third step 503, the turn-on time duration T_{on c} is compared to the value zero, and the logic proceeds to either of a fourth 504 step if the turn-on time duration T_{on c} has a value higher than zero; T_{on c}>0; and to a fifth step 505 if the turn- on time duration T_{on c} is not longer than zero.

If the logic proceeds to the fourth step 504, i.e. if the turn-on time duration T_{on c} has a value higher than zero,

Ton c>0, the control algorithm circuit 26 is further configured to update the turn-on time T_on to a new turn-on time T_on new, in figure 5 denoted T_sron new The new turn-on time T_on new is here equal to an already used turn-on time T_on minus a portion T_on m of the turn-on time duration T₀n__c; T_on_new =T₀n-T₀n_m; 0<T_On_m≤T_On_c; in figure 5 denoted as T_sron_new =T_sr0n^—T_sr0nm/ 0<T_sronm— Tsronc for synchronous rectification.

If the logic proceeds to the fifth step 505, i.e. if the turn- on time duration T_on c has a value equal to zero, T_on c=0, the control algorithm circuit 26 is further configured to set the new turn-on time T_on new to a predetermined value T_on pred, in figure 5 denoted T_{sron pred}. In a second step 506, the voltage sensing circuit 25 is further configured to detect off-edge body diode 141

conduction for the power switch 14. The voltage sensing circuit 25 is also configured to output an off-edge voltage pulse signal V_off corresponding to the off-edge body diode conduction. In figure 5, the off-edge voltage pulse signal V_off is denoted as a synchronous rectification off-edge voltage pulse signal V_sroff .

The control algorithm circuit 26 is also configured to

determine the turn-off time duration T_{off c} for the synchronous PWM control signal SQl by setting the turn-off time duration T₀ff c as the time duration of the off-edge voltage pulse signal V₀ff c- In figure 5, the turn-off time duration T₀ff _c is denoted as a synchronous rectification turn-off time T_sr0ff_C- In a seventh step 507, the turn-off time duration T₀ff _c is compared to the value zero, and the logic proceeds to either of an eighth 508 step if the turn-off time duration T₀ff _c has a value higher than zero; T₀ff _c>0; and to a ninth step 509 if the turn-off time duration T₀ff _c is not longer than zero. If the turn-off time duration T₀ff _c has a value greater than zero; T₀ff _c >0; the logic proceeds to the eighth step 508 and the control algorithm circuit 26 is further configured to update said turn-off time T₀ff to a new turn-off time T₀ff new being an already used turn-off time T₀ff plus a portion T₀ff _m of the time duration T₀ff__c; T_off_new =T_off+T₀ff__m; 0<T_Off_m≤T_Off_c; in figure 5 denoted as T_sr0ff_new =Tsroff+Tsroffm; 0<T_srOffm-Tsroffc ·

If the turn-off time duration T₀ff _c has a value equal to zero; T₀ff c=0; the logic proceeds to the ninth step 509 and the control algorithm circuit 26 is further configured to set the turn-off time T₀ff to a predetermined value T₀ff _prec in figure 5 denoted as T_sroff_p_red · In other words, the flow chart of figure 5 describes how the turn-on T_on and turn-off T₀ff instance is optimized for the synchronous rectification side power switch (es) 14, 13. The inputs of the flow chart are the synchronous rectification side body diode conduction voltage pulse V_DC and the non- synchronous rectification side PWM signals Ql . Then the time duration of the first turn-on voltage pulse T_{on c}/T_sronc and the time duration of the second turn-off voltage pulse T_{off c}/T_sroffc are captured. If the turn-on time duration T_{on c}/T_sronc is greater than zero the control algorithm decides to decrease the on-time of the synchronous rectification side power switch Ton new c /T_Sronc new_/ otherwise if the turn-on time duration

Ton c/Tsronc is zero, the control algorithm decides to restore the on-time of the synchronous rectification side power switch 14, 13 to a predefined value Ton_preci_c/T_Sronc_preci ·

If the time duration of the second turn-off voltage pulse T₀ff _c/T_sroffc is greater than zero, the control algorithm decides to increase the off-time of the synchronous rectification side power switch (es) 14, 13 T₀ff _c new /T_sr0ffc new, otherwise if the second turn-off voltage pulse T₀ff _C/T_sr0ffc is zero, the control algorithm decides to restore the off-time of the synchronous rectification side power switch 14, 13 to a predefined value

J- off_c_pred /Tsroffc_pred ·

According to an aspect, the synchronous rectification control unit 40, 41, and its embodiments, is included in an integrated circuit .

As described above, the synchronous rectification control unit 40, 41 may be utilised for a power converter. According to an aspect, such a power converter is included in a power

electronic device. Figure 6 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 14 power switch, and of the second Q₂ non-synchronous PWM control signal for the second 13 power switch. Figure 6 further shows plots of the first voltage V_Q1 over the first power switch 14, i.e. the voltage across the points 22 and 23 in figure 3, and of the second voltage V_Q2 over the second power switch 13, i.e. the voltage across the points 29 and 30 in figure 3. Figure 6 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 25.

According to the operation condition presented in figure 6, a voltage pulse signal is thus created and output by the voltage sensing circuit 25, i.e. T_c >0, due to the dead-time T_d being introduced in the PWM control signal scheme. Thus, figure 6 corresponds to the left branch of the flow chart of figure 4. The delayed turn-on time of power switch 14, i.e. the dead- time T_d before the first Qi PWM control signal reaches its high value, allows for a current flow through the body diode 141 of the first power switch before the first power switch is turned on by the high value for the first Qi PWM control signal.

The low to high transition of the voltage pulse signal V_DC indicates the time instant/moment when the body diode 141 starts to conduct a current. Correspondingly, the high to low transition of the voltage pulse signal V_DC indicates the time instant/moment when the body diode 141 stops to conduct a current and thus when the body of the power switch 14 starts to conduct a current .

As described above, the voltage pulse signal V_DC is captured by the capture unit 24, and information of the body diode 141 conduction time T_c is determined and stored in a memory. Obviously, the body diode 141 conduction time duration T_c is closely related to the applied PWM dead time T_d. In order to reduce the body diode 141 conduction power losses, PWM dead time is T_d therefore needed to be optimized in a way that the captured pulse width T_c is as narrow as possible. The control algorithm circuit 26 is therefore configured to modify the PWM dead-time T_d to a new value T_{d new}; T_{d new =}T_d-T_dm, 0<T_dm≤T_c. The new dead time value T_{d new} will be applied to the power switches 13 and 14 during the next switching cycle. Figure 7 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 14 power switch, and of the second Q2 non-synchronous PWM control signal for the second 13 power switch. Figure 7 further shows plots of the first voltage V_Qi over the first power switch 14, i.e. the voltage across the points 22 and 23 in figure 3, and of the second voltage V_Q2 over the second power switch 13, i.e. the voltage across the points 29 and 30 in figure 3. Figure 7 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 25.

According to the operation condition presented in figure 7, if the body diode 141 of the first power switch 14 does not conduct a current, i.e. T_c =0, then the voltage sensing circuit 25 will not create any voltage pulse signal V_DC . Thus, figure 7 corresponds to the right branch of the flow chart of figure 4.

In this case the control algorithm 26 will adjust the PWM dead time T_d to a predefined value T_{d pred}; T_{d new} =T_d preci and this new value T_{d new} will then be applied to the power switches 13 and 14 during the next switching cycle. Figures 8, 9, 10 and 11 illustrate the synchronous

rectification control method according to different embodiments applied on the synchronous rectification side of the circuit 100. In these figures, the corresponding notation as in figure 5 is used. Here, four different representative operation conditions can be analysed. In figure 8 a first operation condition is illustrated, wherein only a first on- edge voltage pulse signal V_on appears. In figure 9 a second operation condition is illustrated, wherein only a second off- edge voltage pulse signal V_off appears. In figure 10 a third operation condition is illustrated, wherein no voltage pulse signal appears. In figure 11 a fourth operation condition is illustrated, wherein both a first on-edge voltage pulse signal V_on and a second off-edge voltage pulse signal V_0ff appear.

In figures 8,9,10 and 11, the operation conditions for the synchronous rectification control method implemented in the synchronous rectification control unit 40 of figure 3 are illustrated for the case when the synchronous rectification control unit 40 is applied on the synchronous rectification side of the circuit 100 for turn-on and turn-off time

instant/moment manipulation. Thus, for the operation

conditions illustrated in figures 8,9,10 and 11, the power converter presented in figure 3 is placed/positioned on the synchronous rectification side of the circuit 100.

Figure 8 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 14 power switch on the non- synchronous rectification side of the circuit, and of the second ₂ non-synchronous PWM control signal for the second 13 power switch on the non-synchronous rectification side of the circuit. Figure 8 further shows example values and waveforms of the first SQi synchronous PWM control signal for the first 14 power switch on the synchronous rectification side of the circuit, and of the second SQ₂ synchronous PWM control signal for the second 13 power switch on the synchronous rectification side of the circuit. Figure 8 also shows a first synchronous current iSRi, which is the current being conducted by the first power switch 14 on the synchronous side, and a second synchronous current iSR₂, which is the current being conducted by the second power switch 13 on the synchronous side. Figure 8 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 25, here being a turn-on voltage pulse V_on and a turn-off voltage pulse V_off .

According to the operation condition presented in figure 8, which also corresponds to the left branch of figure 5 above, a voltage pulse signal is created by the voltage sensing circuit 25 due to the delayed turn-on time T₀n/T_Sron of the first synchronous PWM control signal SQ1 for the first synchronous power switch 14, which initiates/allows current flow through its body diode 141. The low to high transition of the voltage pulse signal V_DC indicates the instant/moment when body diode 141 starts to conduct current and the high to low transition of the voltage pulse signal V_DC indicates the instant/moment when the body of the power switch 14 starts to conduct

current, and thus indicates the instant/moment when the body diode 141 stops to conduct current. Such a pulse is captured by the capture unit 24, as described above, and information about the body diode 141 conduction time duration T_c/T_{s r0}nc is determined and stored in a memory.

Obviously, the body diode 141 conduction time duration T_c/T_{s r0}nc is closely related to the turn-on time T₀n/T_Sron of the first power switch 14. In order to reduce the body diode 141

conduction power losses, the turn-on time T₀n/T_Sron is therefore needed to be optimized in a way that the captured pulse width, i.e. the time duration T_{on c}/T_sronc, is as narrow as possible. Based on the time duration T_{on c}/Tsronc information being

determined and stored by the capture unit 24, the control algorithm circuit 26 is configured to modify the turn-on time to a new value T_on new/T_sron new such that the new turn-on time T_{on new} is equal to an already used turn-on time T_on minus a portion T_{on m} of the turn-on time duration T_{on c} ; T_{on new =}T_on-T_{ori m};

The new turn-on time duration value T_{on new}/T_{srori new} will be applied to the first 14 and second 13 power switches during the next switching cycle. According to the operation described in figure 8, no voltage pulse signal V_off/V_sroff appears after the zeroing of the synchronous PWM signal SQi. Thus, the turn- off time duration of the PWM signal SQi T_{sr0ff c}/To_ff c has a value equal to zero; T_{sr0ff C}/T_0ff c=0, and the turn-off time T_sr0ff/T_0ff will be set on a predefined value T₀ff _preci/Tsroff prec as

described above for the right branch of figure 5 .

Figure 9 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 14 power switch on the non- synchronous rectification side of the circuit, and of the second Q2 non-synchronous PWM control signal for the second 13 power switch on the non-synchronous rectification side of the circuit. Figure 9 further shows example values and waveforms of the first SQi synchronous PWM control signal for the first 14 power switch on the synchronous rectification side of the circuit, and of the second SQ2 synchronous PWM control signal for the second 13 power switch on the synchronous

rectification side of the circuit. Figure 9 also shows a first synchronous current iSRi, which is the current being conducted by the first power switch 14 on the synchronous side, and a second synchronous current iSR₂, which is the current being conducted by the second power switch 13 on the synchronous side. Figure 9 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 25, here being a turn-off voltage pulse V₀ff and a turn-on voltage pulse V₀n. According to the operation condition presented in figure 9, a voltage pulse signal V_DC is created by the voltage sensing circuit 25 due to an early turn-off time T_off/T_sroff of the first power switch 14, which allows current flow through its body diode 141. The low to high transition of the voltage pulse signal V_DC indicates the instant/moment when body of the power switch 14 stops to conduct current and the body diode 141 starts to conduct current and the high to low transition of the voltage pulse signal V_DC indicates the instant/moment when the body diode 141 stops to conduct current due to the zeroing of the first synchronous current iSRi.

Such a pulse, i.e. a turn-off voltage pulse V₀ff is captured by the capture unit 24, and information about the body diode 141 conduction time duration T_c/T_sr0ff_C is determined and stored in the memory. Obviously, the body diode 141 conduction time duration T_c/T_sr0ff_C is closely related to the turn-off time off/ groff of the power switch 14. In order to reduce the body diode 141 conduction power losses, the turn-off time T_sr0ff is therefore needed to be optimized in a way that the captured pulse width, i.e. the time duration T_c/T_sr0ff_C is as narrow as possible. Based on the time information determined and stored by of the capture unit 24, the control algorithm circuit 26 is configured to modify the turn-off time instant/moment

T₀ff new/Tsroff new such that the new turn-off time T₀ff new is equal to an already used turn-off time T₀ff plus a portion T₀ff _m of the turn-off time duration T₀ff _c Toff new =T₀ff+T₀ff _m;

The new turn-off time value T₀ff new/T_{s r}off new will be applied to the power switches 1 3 and 1 4 during the next switching cycle. According to operation described in figure 9 the first turn-on V₀n voltage pulse signal does not appear, i.e. the turn-on time duration T_{on c} has a value equal to zero; T_{on c}= 0. Thus, the turn-on time of the PWM signal S Qi will be set to a predefined

Value T on_precl / ^ sron_pred ·

Figure 1 0 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 1 4 power switch on the non- synchronous rectification side of the circuit, and of the second Q₂ non-synchronous PWM control signal for the second 1 3 power switch on the non-synchronous rectification side of the circuit. Figure 1 0 further shows example values and waveforms of the first S Qi synchronous PWM control signal for the first 1 4 power switch on the synchronous rectification side of the circuit, and of the second SQ₂ synchronous PWM control signal for the second 1 3 power switch on the synchronous

rectification side of the circuit. Figure 1 0 also shows a first synchronous current iSRi, which is the current being conducted by the first power switch 1 4 on the synchronous side, and a second synchronous current 1SR₂, which is the current being conducted by the second power switch 1 3 on the synchronous side. Figure 1 0 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 2 5 , here being a turn-off voltage pulse V₀ff and a turn-on voltage pulse V_on.

According to the operation condition presented in figure 1 0 , the body diode 1 4 1 does not conduct any current. Therefore, the voltage sensing circuit 2 5 will not create any voltage pulse signals. On other words has the turn-on time duration on c has a value equal to zero; T_{on c}= 0 ; and the turn-off time duration T₀ff _c has a value equal to zero; T₀ff _c= 0 .

In this case the control algorithm circuit 2 6 is configured to set the turn-on time instant/moment T₀n/T_Sron to a predefined value T_{on P}reci T sron preci and the turn-off time instant/moment T_off/T_sroff to a predefined value T_off__pred/T_sroff__pred . These

predefined values T_on_p_red/T_sron__pred and T_off__pred/T_sroff__pred will then be applied to the power switches 1 3 and 1 4 during the next switching cycle. Figure 1 1 is a graph having plots that illustrate example values and waveforms of the first Qi non-synchronous PWM control signal for the first 1 4 power switch on the non- synchronous rectification side of the circuit, and of the second Q₂ non-synchronous PWM control signal for the second 1 3 power switch on the non-synchronous rectification side of the circuit. Figure 1 1 further shows example values and waveforms of the first S Qi synchronous PWM control signal for the first 1 4 power switch on the synchronous rectification side of the circuit, and of the second SQ₂ synchronous PWM control signal for the second 1 3 power switch on the synchronous

rectification side of the circuit. Figure 1 1 also shows a first synchronous current iSRi, which is the current being conducted by the first power switch 1 4 on the synchronous side, and a second synchronous current 1SR₂, which is the current being conducted by the second power switch 1 3 on the synchronous side. Figure 1 1 further shows a plot for the voltage pulse signal V_DC, i.e. the output of the voltage sensing circuit 2 5 , here being a turn-off voltage pulse V₀ff and a turn-on voltage pulse ν_οη. According to the operation condition presented in figure 1 1 , two voltage pulse signals, a turn-on pulse V_on and a turn-off pulse V₀ff, are created and output by the voltage sensing circuit 25 during the same switching cycle. These turn-on V₀n and turn-off V₀ff pulses are output due to the delayed turn-on time on and the early turn-off time T₀ff of the power switch 14, that allows current flow through its body diode 141. The first turn-on pulse V_on signal appears before the synchronous PWM signal SQ1 of the first power switch 14 and the second turn-off voltage pulse V_off signal appears after the

synchronous PWM signal SQ1 of the first power switch 14. The low to high transition of the first turn-on voltage pulse signal V_on indicates the time instant/moment when the body diode 141 starts to conduct current and the high to low transition of the first turn-on voltage pulse signal V₀n indicates the moment when the body of the power switch 14 starts to conduct current and the body diode 141 stops to conduct current. The low to high transition of the second turn-off voltage pulse V₀ff signal indicates the time

instant/moment when body of the power switch 14 stops to conduct current and the body diode 141 starts to conduct current and the high to low transition of the second turn-off voltage pulse V₀ff signal indicates the time instant/moment when the body diode 141 stops to conduct current due to the zeroing of the first synchronous current iSRi.

The low to high and high to low transition of the first turn- on voltage pulse signal ν_οη is captured by the capture unit 24, and information about body diode 141 conduction time duration Ton c/Tsronc is determined and stored in the memory. In order to reduce body diode 141 conduction power losses, the turn-on time instant/moment T₀n/T_sron should be optimized in a way that the captured pulse width, i.e. the time duration T_on c/Tsronc is as narrow as possible. Based on the time duration information T_on c Tsronc determined and stored by the capture unit 24, the control algorithm circuit 26 is configured to modify the turn- on time on new/Tsron new such that the new turn-on time T_on new is equal to an already used turn-on time T_on minus a portion T_on m of said turn-on time duration T_on c T_on new =T₀n^_T₀n _m;

During the same switching cycle, the low to high and high to low transition of the second turn-off voltage pulse V_off signal is captured by the capture unit 24, and information about body diode 141 conduction time duration T_{off c}/T_sroffc is determined and stored in the memory. In order to reduce the body diode

141 conduction power losses, the turn-off time instant/moment T₀ff/T_sr0ff must be optimized in a way that the captured pulse width, i.e. the time duration T₀ff _c/T_sr0ff_C is as narrow as possible. Based on the time information determined and stored by the capture unit 24, the control algorithm circuit 26 is configured to modify the turn-off time T₀ff new/T_sroff new such that the new turn-off time T₀ff new is equal to an already used turn- off time T₀ff plus a portion T₀ff _m of the turn-off time duration T₀ff__c; T₀ff_new =Toff+T₀ff_m; 0<T_Off_m≤T_Off_c- The new and optimized turn-on time instants/moments T_on new/T_sron new and the new and optimized turn-off time instants/moments T₀ff new/T_sroff new will then be applied to the power switches 13 and 14 during next switching cycle.

Figure 12 is a flow chart illustrating actions of a method 300 method for controlling synchronous rectification.

It is however to be noted that any, some or all of the descr^¬ ibed actions 301-303, may be performed in a somewhat different chronological order than the enumeration indicates, be per^¬ formed simultaneously or even be performed in reversed order. Further, it is to be noted that some actions may be performed in a plurality of alternative manners according to different embodiments. The method 300 may comprise the following acti^¬ ons :

Action 301

In a first action 301, a body diode conduction for a power switch 14 is detected.

Action 302

In a second action 302, a voltage pulse signal V_DC

corresponding to the body diode conduction is output.

Action 303 In a third action 303, a time duration T_c for the voltage pulse signal V_DC is determined.

Action 304

In a fourth action 304, the determined time duration T_c is stored in a memory. Action 305

In a fifth action 305, a turn-on time T_on and a turn-off time T_0ff to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle are determined. The

determination of the turn—on T_ori and turn—off T_0ff times is here based on the time duration T_c being stored in the memory.

Action 306

In a sixth action 306, the synchronous PWM control signal SQ1 for controlling switching of the power switch 14 is generated when the power switch is in a synchronous side of a circuit

100. Alternatively, the non-synchronous PWM control signal Ql for controlling switching of the power switch 14 is generated when the power switch is in a non-synchronous side of the circuit 100.

Also, the method for controlling synchronous rectification may be implemented in a circuit 600 schematically illustrated in figure 13. The processing circuit 600 is configured for:

- detecting 301 body diode conduction for a power switch 14;

- outputting 302 a voltage pulse signal V_DC corresponding to the body diode conduction;

- determining 303 a time duration T_c for the voltage pulse signal V_DC;

- storing 304 the time duration T_c in a memory;

- determining 305 a turn-on time T_on and a turn-off time T_0ff to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle, wherein the determination of the turn-on T_on and turn-off T_0ff times is based on the stored time duration T_c; and

- generating 306, by use of the determined turn-on T_on time and turn-off T_0ff time, the synchronous PWM control signal SQ1 for controlling switching of the power switch 14 when the power switch is in a synchronous side of a circuit 100; or the non- synchronous PWM control signal Ql for controlling switching of the power switch 14 when the power switch is in a non- synchronous side of the circuit.

The processing circuit 600 may comprise, e.g., one or more instances of a Central Processing Unit (CPU) , a processing unit, a processing circuit, a processor, an Application Specific Integrated Circuit (ASIC) , a microprocessor, or other pro- cessing logic that may interpret and execute instructions. The herein utilised expression "processing circuit" may thus repr- esent a processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the ones enumerated above.

The processing circuit 600 may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions.

The processing circuit 600 may be connected to at least one memory 601, according to some embodiments. The memory 601 may comprise a physical device utilised to store data or programs, i.e., sequences of instructions, on a temporary or permanent basis. According to some embodiments, the memory 601 may comprise integrated circuits comprising silicon-based trans^¬ istors. Further, the memory 601 may be volatile or non-vola^¬ tile . The previously described actions 301-303 may be implemented through one or more processing circuits 600, together with computer program code for performing the functions of the actions 301-306. Thus a computer program product, comprising instructions for performing the actions 301-306 may perform the method 300 controlling synchronous rectification, when the computer program product is loaded in a processing circuit 600.

The computer program product mentioned above may be provided for instance in the form of a data carrier carrying computer program code for performing any, at least some, or all of the actions 301-306 according to some embodiments when being loaded into the processing circuit 600. The data carrier may be, e.g., a hard disk, a CD ROM disc, a memory stick, an opti^¬ cal storage device, a magnetic storage device or any other appropriate medium such as a disk or tape that may hold mach^¬ ine readable data in a non transitory manner. The computer program product may furthermore be provided as computer pro^¬ gram code on a server and may be downloaded remotely, e.g., over an Internet or an intranet connection.

The terminology used in the detailed description of the embodiments as illustrated in the accompanying drawings is not intended to be limiting of the described method 300 and/ or synchronous rectification control unit 40, which instead are limited by the enclosed claims.

As used herein, the term "and/ or" comprises any and all comb- inations of one or more of the associated listed items. In addition, the singular forms "a", "an" and "the" are to be interpreted as "at least one", thus also possibly comprising a plurality of entities of the same kind, unless expressly stated otherwise. It will be further understood that the terms "includes", "comprises", "including" and/ or "comprising", specifies the presence of stated features, actions, integers, steps, operations, elements, and/ or components, but do not preclude the presence or addition of one or more other

features, actions, integers, steps, operations, elements, components, and/ or groups thereof.

Claims

1. A synchronous rectification control unit (40, 41), including :

- a voltage sensing circuit (25) configured to

- detect body diode conduction for a power switch (14), and

- output a voltage pulse signal V_DC corresponding to said body diode conduction;

- a capture unit (24) configured to

- determine a time duration T_c for said voltage pulse signal V_DC, and

- store said time duration T_c in a memory;

- a control algorithm circuit (26) configured to determine a turn-on time T_on and a turn-off time T_0ff to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle, said determination of said turn-on T_on and turn-off T_0ff times being based on said stored time duration T_c; and

- a PWM signal generator (32) configured to generate, by use of said determined turn—on T_ori time and turn—off T_0ff time, said synchronous PWM control signal SQ1 for controlling switching of the power switch (14) when the power switch is in a

synchronous side of a circuit; or said non-synchronous PWM control signal Ql for controlling switching of the power switch (14) when the power switch is in a non-synchronous side of the circuit (100) .

2. The synchronous rectification control unit (40, 41) as claimed in claim 1, wherein the voltage sensing circuit (25) is further configured to detect an on-edge body diode

conduction for the power switch (14) of said non-synchronous side and to output an on-edge voltage pulse signal ν_οη c

corresponding to said on-edge body diode conduction.

3. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 1-2, wherein the control algorithm circuit (26) is further configured to update a dead time T_d to a new dead time value T_{d new} if the time duration T_c has a value greater than zero, T_c >0; said new dead time value T_{d new} being equal to an already used dead time value T_d minus a portion of the time duration T_c, T_d__{new =}T_d-T_dm 0<Τ^≤Τ_ο.

4. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 1-3, wherein said control

algorithm circuit (26) is further configured to set a new dead time value T_d__ne„ to a predetermined value T_d__pred; T_d__ne„ =T_d__pred; if the time duration T_c has a value equal to zero, T_c =0.

5. The synchronous rectification control unit (40, 41) as claimed in claim 1, wherein

- said voltage sensing circuit (25) is further configured to detect an on-edge body diode conduction and an off-edge body diode conduction for the power switch (14) and to output an on-edge voltage pulse signal ν_οη and an off-edge voltage pulse signal V_0ff corresponding to said on-edge body diode conduction and said off-edge body diode conduction, respectively;

- said capture unit (24) is further configured to determine a turn-on time duration T_{on c} as a time duration of the on-edge voltage pulse signal ν_{οη cr} and to determine a turn-off time duration T_{0ff c} for said synchronous PWM control signal SQ1 as a time duration of the off-edge voltage pulse signal V_{0ff c} -

6. The synchronous rectification control unit (40, 41) as claimed in claim 5, wherein the control algorithm circuit (26) is further configured to update said turn-on time T_on to a new turn-on time T_{on new} if said turn-on time duration T_{on c} has a value greater than zero, T_{on c} >0; said new turn-on time T_on new being equal to an already used turn-on time T_on minus a portion T₀n_m of said turn-on time duration T_on_c_; T_on_new = ₀n-T₀n_m;

7. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 5-6, wherein the control algorithm circuit (26) is further configured to set a new turn-on time Ton new to a predetermined value T_{on pred} if said turn-on time duration T_{on c} has a value equal to zero; T_{on c}=0.

8. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 5-7, wherein the control algorithm circuit (26) is further configured to update said turn-off time T₀ff to a new turn—off time T₀ff new if said turn-off time duration T₀ff _c has a value greater than zero; T₀ff _c >0; said new turn-off time T₀ff new being equal to an already used turn-off time T₀ff plus a portion T₀ff _m of said turn-off time duration

Toff_c/ T₀ff_new =T₀ff+T₀ff__m; 0<T₀ff_m-T₀ff_c ·

9. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 5-8, wherein said control

algorithm circuit (26) is further configured to set said turn- off time T₀ff to a predetermined value T₀ff _preci if a turn-off time duration T₀ff _c has a value equal to zero; T₀ff _c=0.

10. The synchronous rectification control unit (40, 41) as claimed in anyone of claims 1-9, wherein:

- said voltage sensing circuit (25) is further configured to output a logic high value for said voltage pulse signal V_DC when said body diode is conducting a current; and

- said capture unit (24) is configured to determine the time duration T_c as equal to a time duration during which said voltage pulse signal V_DC has the logic high value.

11. An integrated circuit comprising at least one of the synchronous rectification control unit according to any of claims 1-10.

12. A power electronic device having a power converter comprising the synchronous rectification control unit

according to any of claims 1-10.

13. A method for controlling synchronous rectification, including :

- detecting (301) body diode conduction for a power switch (14);

- outputting (302) a voltage pulse signal V_DC corresponding to said body diode conduction;

- determining (303) a time duration T_c for said voltage pulse signal V_DC;

- storing (304) said time duration T_c in a memory;

- determining (305) a turn-on time T_on and a turn-off time T_0ff to be used for a synchronous pulse width modulation, PWM, control signal SQ1 or a non-synchronous PWM control signal Ql during an upcoming switching cycle, said determination of said turn—on T_ori and turn—off T_0ff times being based on said stored time duration T_c; and

- generating (306), by use of said determined turn-on T_on time and turn-off T_0ff time, said synchronous PWM control signal SQ1 for controlling switching of the power switch (14) when the power switch is in a synchronous side of a circuit (100); or said non-synchronous PWM control signal Ql for controlling switching of the power switch (14) when the power switch is in a non-synchronous side of the circuit (100) .

14. A computer program with a program code for performing a method according to claim 13, when the computer program runs on a computer.