An active clamp circuit applied to a secondary side of a switching power supply, a peak energy absorption control method and a switching power supply

Abstract

This application discloses an active clamping circuit, a peak energy absorption control method, and a switching power supply applied to the secondary side of a switching power supply. The power supply includes a clamping branch, a pre-charging circuit, an energy conversion circuit, and a stable voltage point. The pre-charging circuit charges capacitor C1 before the voltage peak arrives, allowing the use of a larger capacitance value for C1 to significantly enhance peak absorption capability. Simultaneously, the energy conversion circuit, controlled by an MCU, efficiently converts and recovers the peak energy absorbed by C1 to the stable voltage point. This application resolves the contradiction between absorption effect and efficiency loss in traditional solutions, achieving energy recovery while efficiently suppressing stress peaks, thus optimizing system heat distribution and overall efficiency.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, specifically to an active clamping circuit applied to the secondary side of a switching power supply, a peak energy absorption and control method, and a switching power supply. Background Technology

[0002] In switching power supplies, the secondary rectifier diode (usually a MOSFET or diode) experiences a high voltage stress spike at turn-off due to transformer leakage inductance and parasitic parameters in the circuit. This spike not only threatens the safe operation of the rectifier diode but also generates severe electromagnetic interference.

[0003] To suppress this voltage spike, a common method is to use a passive RC snubber circuit or an active clamping circuit.

[0004] Passive RC snubber circuit: Although simple in structure, all the absorbed energy is consumed in the resistor, leading to decreased efficiency, especially in high-voltage and high-frequency applications where losses are particularly severe. Increasing the capacitance of the snubber capacitor can enhance the absorption effect, but it will increase the inrush current and losses in the resistor, creating a contradiction.

[0005] Conventional active clamping circuits typically consist of a clamping capacitor and a clamping switch connected in parallel with the rectifier diode. When the switch experiences increased stress, it opens, allowing the peak energy to charge and discharge within the clamping capacitor. This process results in significant losses and heat generation in the clamping switch. Furthermore, to facilitate control of the clamping switch, a PMOS transistor is usually used, which has a small inrush current. However, this limits the capacitance of the clamping capacitor, restricting its ability to absorb extreme peaks. Using an NMOS transistor as the switch, on the other hand, leads to complex floating-ground drive control. In high-power topology applications, both of these clamping schemes further result in high capacitor charging and discharging energy, severe switch overheating, and generally poor reliability.

[0006] Therefore, there is a common problem in the existing technology: it is difficult to achieve efficient and strong stress absorption while recovering and utilizing the absorbed energy with low loss, and to avoid additional losses caused by the absorption circuit itself. Summary of the Invention

[0007] To overcome the problem of difficulty in balancing absorption capacity and efficiency loss in existing technologies, this application breaks through the limitation of the dramatic increase in loss caused by increasing the capacitance value in traditional absorption circuits, significantly improves the absorption capacity for voltage stress peaks, changes the traditional path of energy dissipation in the form of heat, and realizes efficient recovery and reuse of peak energy; optimizes the thermal distribution of power devices, and improves the power density and long-term reliability of switching power supplies.

[0008] In one embodiment, this application provides an active clamping circuit applied to the secondary side of a switching power supply. The active clamping circuit is connected in parallel with the secondary rectifier of the switching power supply. It includes a clamping branch 10, a pre-charging circuit 20, an energy conversion circuit 30, and a stable voltage point. The clamping branch 10 includes a unidirectional conductive device D1 and a first capacitor C1 connected in series. The anode of the unidirectional conductive device D1 is connected to the high-voltage end of the secondary rectifier, and the cathode of the unidirectional conductive device D1 is connected to the first end of the first capacitor C1 to form a first node. The second end of the first capacitor C1 is connected to the low-voltage end of the secondary rectifier. The first end of the pre-charging circuit 20 is connected to a pre-charging voltage source, and the second end of the pre-charging circuit 20 is connected to the first node. The pre-charging circuit is used to charge the first capacitor C1 before the stress peak of the turn-off voltage of the secondary rectifier arrives. The input end of the energy conversion circuit 30 is connected to the first node, and the output end of the energy conversion circuit 30 is connected to the stable voltage point. The energy conversion circuit 30 is configured to transfer the energy stored in the first capacitor C1 to the stable voltage point after the first capacitor C1 absorbs energy.

[0009] In one alternative embodiment, the pre-charge circuit 20 includes a unidirectional conductive device and a pre-charge voltage source, wherein the pre-charge voltage source is a DC auxiliary power supply, the anode of the unidirectional conductive device is connected to the DC auxiliary power supply, and the cathode of the unidirectional conductive device is connected to the first node.

[0010] In one alternative embodiment, the pre-charge circuit 20 includes resistors R1 and R2, and capacitor C3. The pre-charge voltage source is the input voltage of the switching power supply. Resistor R1 and capacitor C3 are connected in parallel. The first end of resistor R1 is connected to the input voltage, and the second end of resistor R1 is connected to the first node and one end of resistor R2. Resistor R2 is connected in parallel with capacitor C1 of clamping branch 10.

[0011] In one alternative, the energy conversion circuit 30 is a BUCK circuit, BOOST circuit, BUCK-BOOST circuit, or SEPIC circuit.

[0012] In one alternative, the stable voltage point is the DC input voltage bus, DC output voltage terminal, or stable voltage point of the main power supply of the switching power supply.

[0013] In one alternative, the unidirectional conductive device D1 is a diode or a MOSFET.

[0014] In one alternative embodiment, the secondary rectifier is a MOSFET, the high-voltage end of the secondary rectifier is the drain of the MOSFET, the low-voltage end of the secondary rectifier is the source of the MOSFET, the anode of the unidirectional conductive device D1 is connected to the drain of the MOSFET, and the second terminal of the first capacitor C1 is connected to the source of the MOSFET.

[0015] In another embodiment, this application provides a method for absorbing peak energy in the aforementioned active clamping circuit, wherein before the voltage peak of the secondary rectifier arrives, charge is actively injected into the first capacitor C1, so that its terminal voltage is pre-raised to a preset potential.

[0016] In another embodiment, this application provides a switching power supply having the aforementioned active clamping circuit.

[0017] In one alternative, the switching power supply of this application employs the aforementioned method for absorbing peak energy.

[0018] Compared with the prior art, this application has the following beneficial effects: A qualitative leap in peak absorption capability: Through a pre-charging mechanism, the initial voltage of the absorption capacitor C1 is significantly higher than that of traditional circuits (typically 0V). This not only reduces the huge current surge and losses through the unidirectional conductive device D1 when peaks arrive, but more importantly, it allows for a substantial increase in the capacitance of the absorption capacitor C1 without significantly increasing losses. This increase in capacitance directly translates into stronger charge storage and voltage "smoothing" capabilities, fundamentally enhancing the suppression of high-voltage peaks.

[0019] Significantly improved energy efficiency: This application abandons the traditional practice of consuming absorbed energy as heat, and innovatively integrates a high-efficiency energy conversion circuit to actively and controllably recover the peak energy stored in capacitor C1 to the main power path. This process transforms the original "loss" into "usable energy", directly amortizing system losses and improving the overall conversion efficiency.

[0020] System thermal distribution and reliability optimization: Because energy is recovered rather than centrally dissipated, localized high-temperature hotspots on the MOSFETs in traditional active clamping absorption circuits are completely avoided. The total system heat loss is reduced and more evenly distributed, which is beneficial for optimizing PCB layout and heat dissipation design, thereby improving the power density and long-term operational reliability of the power supply.

[0021] This application introduces an independent pre-charging circuit, allowing the absorption capacitor to safely employ a larger capacitance value, thereby achieving stronger peak absorption. Subsequently, through an independent and controllable energy conversion circuit, the stored energy is efficiently and controllably released to a stable voltage point in the system, completing energy recovery. This optimization addresses both the absorption mechanism and energy path, fundamentally resolving the contradiction between absorption capacity, recovery efficiency, and additional losses. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the active clamping circuit control principle in some embodiments of this application; Figure 2 This is a schematic diagram of the application of this application in some embodiments to the secondary-side rectifier circuit of an isolated product; Figure 3 This is a schematic diagram of the application of this application in some embodiments of a secondary rectifier circuit of a non-isolated product; Figure 4 This is a schematic diagram of the circuit principle in some embodiments of this application; Figure 5 This is a schematic diagram of the circuit principle in some embodiments of this application; Figure 6 This is a schematic diagram of the circuit principle in some embodiments of this application. Detailed Implementation

[0023] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application. Similarly, the following examples are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0025] In this application, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly, meaning electrical connection or intercommunication, or connection through other equivalent means; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal connection of two elements or the interaction between two elements, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0026] In some implementations, please refer to Figure 1 , Figure 2 and Figure 4 This application provides an active clamping circuit for the secondary side of a switching power supply. The active clamping circuit is connected in parallel with the secondary rectifier of the switching power supply and includes a clamping branch 10, a pre-charging circuit 20, an energy conversion circuit 30, and a stable voltage point.

[0027] The clamping branch 10 includes a unidirectional conductive device D1 and a first capacitor C1 connected in series. The anode of the unidirectional conductive device D1 is connected to the high-voltage end of the secondary rectifier tube, the cathode of the unidirectional conductive device D1 is connected to the first end of the first capacitor C1 to form a first node, and the second end of the first capacitor C1 is connected to the low-voltage end of the secondary rectifier tube, thereby forming a complete parallel clamping circuit.

[0028] The first terminal of the pre-charge circuit 20 is connected to a pre-charge voltage source, and the second terminal is connected to the first node. The pre-charge circuit charges the first capacitor C1 before the voltage stress spike of the secondary rectifier diode's turn-off voltage arrives, raising its terminal voltage to a preset potential. This fundamentally changes the circuit's spike absorption capability: through the pre-charge mechanism, the initial voltage of the absorption capacitor C1 is much higher than in traditional circuits (typically 0V). This not only reduces the huge current surge and losses through the unidirectional conductive device D1 when the spike arrives, but more importantly, it allows for a significant increase in the capacitance of the absorption capacitor C1 without significantly increasing losses. This increase in capacitance directly translates into stronger charge storage and voltage "smoothing" capabilities, fundamentally enhancing the suppression effect of high-voltage spikes.

[0029] The input terminal of the energy conversion circuit 30 is connected to the first node, and the output terminal of the energy conversion circuit 30 is connected to the stable voltage point, which can be the input bus or output terminal of the switching power supply. The energy conversion circuit 30 is configured to efficiently transfer the excess energy stored in the first capacitor C1 to the stable voltage point through power electronic conversion after the first capacitor C1 absorbs energy. This significantly improves energy efficiency: compared to the traditional method of consuming absorbed energy as heat, by integrating a highly efficient energy conversion circuit, the peak energy stored in capacitor C1 is actively and controllably recovered to the main power path. This process converts the original "loss" into "usable energy," directly distributing system losses and improving the overall conversion efficiency.

[0030] Furthermore, the system's thermal distribution and reliability have been optimized: because energy is recovered rather than concentratedly dissipated, localized high-temperature hotspots on the MOSFETs in traditional active clamping absorption circuits are completely avoided. The system's total heat loss is reduced and more evenly distributed, which is beneficial for optimizing PCB layout and heat dissipation design, thereby improving the power density and long-term operational reliability of the power supply.

[0031] This application introduces an independent pre-charging circuit, allowing the absorption capacitor to safely employ a larger capacitance value, thereby achieving stronger peak absorption. Subsequently, through an independent and controllable energy conversion circuit, the stored energy is efficiently and controllably released to a stable voltage point in the system, completing energy recovery. This optimization addresses both the absorption mechanism and energy path, fundamentally resolving the contradiction between absorption capacity, recovery efficiency, and additional losses.

[0032] In some embodiments, the pre-charge circuit 20 includes a unidirectional conductive device and a pre-charge voltage source, the pre-charge voltage source being a DC auxiliary power supply, the anode of the unidirectional conductive device being connected to the DC auxiliary power supply, and the cathode of the unidirectional conductive device being connected to the first node.

[0033] In some implementations, the unidirectional conductive device D2 may be a diode or a MOSFET.

[0034] In one example, see Figure 4The energy conversion circuit in this embodiment can be a controlled DC-DC converter. This embodiment is a SEPIC circuit, including inductors L1 and L2, capacitors C2 and C3, diode D3, and switching transistor Q1. One end of inductor L1 is the input terminal of the energy conversion circuit, connected to the first node. The other end of inductor L1 is connected to the first terminal of switching transistor Q1 and one end of capacitor C3. One end of capacitor C3 is connected to one end of inductor L2 and the anode of diode D3. The cathode of diode D3 is the output terminal of the energy conversion circuit, connected to one end of capacitor C2 and the stable voltage output voltage. The other end of inductor L2 is connected to the second terminal of switching transistor Q1, the other end of capacitor C2, and the output voltage ground.

[0035] In practical applications, before the main power operates, the auxiliary source VCC pre-charges capacitor C1 through diode D2. This ensures that when the main power operates, capacitor C1 maintains a certain voltage level before the stress spike of the rectifier diode in the secondary rectifier circuit rises. When the stress spike is higher than the capacitor voltage, the charging branch of capacitor C1 will not generate a large inrush current through the unidirectional conductive device D1. The SEPIC circuit detects the voltage of capacitor C1 and provides an appropriate duty cycle to transfer the stress energy exceeding the rectifier diode stress plateau to the output terminal. In this way, the charging and discharging of the clamping branch 10 are separated, allowing for a larger charging capacitor, resulting in better peak voltage suppression. The discharging branch feeds back to the output capacitor, greatly optimizing the efficiency of the absorption circuit.

[0036] In some implementations, please refer to Figure 1 and Figure 5 The active clamping circuit is used in isolated switching power supplies and consists of four parts: a clamping branch 10, a pre-charging circuit 20, an energy conversion circuit 30, and a voltage stabilization point. The clamping branch is composed of a unidirectional conductive device D1 and a first capacitor C1 connected in series. The secondary rectifier is a MOSFET, with its high-voltage terminal being the drain and its low-voltage terminal being the source. The anode of the unidirectional conductive device D1 is connected to the drain of the MOSFET, and D1 is connected to the first capacitor C1 to form the first node. The second terminal of the first capacitor C1 is connected to the source of the MOSFET, thus forming a complete parallel clamping loop.

[0037] A pre-charge circuit is connected between a pre-charge voltage source and the first node. It is used to actively inject charge into the first capacitor C1 before the voltage spike of the secondary rectifier arrives, so that its terminal voltage is pre-raised to a preset potential.

[0038] The input of the energy conversion circuit is connected to the first node, and the output is connected to a stable voltage point (e.g., the input bus or the output) in the main power circuit of the switching power supply. The circuit is configured to start operating after the first capacitor C1 has absorbed the energy of a voltage spike, efficiently transferring excess energy stored in the first capacitor C1 to the stable voltage point through power electronic conversion.

[0039] As an example, the energy conversion circuit in this embodiment can be a controlled DC-DC converter. In this embodiment, it is a BUCK circuit, including an inductor L1, a diode D3, a switch Q1, and a capacitor C2. The first terminal of the switch Q1 is the input terminal of the energy conversion circuit, connected to the first node. The second terminal of the switch Q1 is connected to one end of the inductor L1 and the cathode of the diode D3. The other end of the inductor L1 is the output terminal of the energy conversion circuit, connected to one end of the capacitor C2 and the stable voltage point output voltage. The anode of the diode D2 and the other end of the capacitor C2 are connected to the output voltage ground.

[0040] In practical applications, before the main power operates, the auxiliary source VCC pre-charges capacitor C1 through diode D2. This ensures that when the main power operates, capacitor C1 maintains a certain voltage level before the stress spike of the rectifier diode in the secondary rectifier circuit rises. When the stress spike is higher than the capacitor voltage, the charging branch of capacitor C1 will not generate a large inrush current through the unidirectional conductive device D1. The BUCK circuit provides an appropriate duty cycle by detecting the voltage of capacitor C1, transferring the stress energy exceeding the rectifier diode stress plateau to the output terminal. In this way, the charging and discharging of the clamping branch are separated, allowing for a larger charging capacitor and better suppression of the voltage spike. The discharging branch feeds back to the output capacitor, greatly optimizing the efficiency of the absorption circuit.

[0041] In some implementations, please refer to Figure 1 and Figure 6 An active clamping circuit is applied to a non-isolated switching power supply, which consists of four parts: clamping branch 10, pre-charging circuit 20, energy conversion circuit 30, and stabilizing voltage point.

[0042] The clamping branch consists of a unidirectional conductive device D1 and a first capacitor C1 connected in series. The anode of the unidirectional conductive device D1 is connected to the high-voltage terminal of the secondary rectifier (such as the drain of a MOSFET), and its cathode is connected to the first terminal of the first capacitor C1, forming a critical first node. The second terminal of the first capacitor C1 is connected to the low-voltage terminal of the secondary rectifier (such as the source of a MOSFET), thus forming a complete parallel clamping circuit.

[0043] A pre-charge circuit is connected between a pre-charge voltage source and the first node. It is used to actively inject charge into the first capacitor C1 before the voltage spike of the secondary rectifier arrives, so that its terminal voltage is pre-raised to a preset potential.

[0044] The input of the energy conversion circuit is connected to the first node, and the output is connected to a stable voltage point (such as the input bus or the output) in the main power circuit of the switching power supply. The circuit is configured to start working after the first capacitor C1 has absorbed the energy of the voltage spike, and to efficiently transfer the excess energy stored in the first capacitor C1 to the stable voltage point through power electronic conversion.

[0045] The pre-charge circuit 20 includes resistors R1 and R2, and capacitor C3. The pre-charge voltage source is the input voltage of the switching power supply. Resistor R1 and capacitor C3 are connected in parallel. The first end of resistor R1 is connected to the input voltage. The second end of resistor R1 is connected to the first node and one end of resistor R2. Resistor R2 is connected in parallel with capacitor C1 of clamping branch 10.

[0046] As an example, the energy conversion circuit in this embodiment can be a controlled DC-DC converter. For example... Figure 6 As shown, this embodiment is a SEPIC circuit, including inductors L1 and L2, capacitors C2 and C3, diode D3, and switching transistor Q1. One end of inductor L1 is the input terminal of the energy conversion circuit, connected to the first node. The other end of inductor L1 is connected to the first terminal of switching transistor Q1 and one end of capacitor C3. One end of capacitor C3 is connected to one end of inductor L2 and the anode of diode D3. The cathode of diode D3 is the output terminal of the energy conversion circuit, connected to one end of capacitor C2 and the stable voltage output voltage. The other end of inductor L2 is connected to the second terminal of switching transistor Q1, the other end of capacitor C2, and the input voltage ground.

[0047] In practical applications, before the main power operates, the input voltage is divided by resistors R1 and R2 and capacitors C3 and C1, pre-charging capacitor C1. This ensures that when the main power operates, capacitor C1 maintains a certain voltage level before the stress spike of the rectifier diode in the secondary rectifier circuit rises. When the stress spike is higher than the capacitor voltage, the charging branch of capacitor C1 will not generate a large inrush current through the unidirectional conductive device D1. The SEPIC circuit provides an appropriate duty cycle by detecting the voltage of capacitor C1, transferring the stress energy higher than the rectifier diode stress plateau to the input terminal. In this way, the charging and discharging of the clamping branch are separated, and the charging capacitor can be relatively large, resulting in good peak voltage suppression. The discharging branch feeds back to the input capacitor, greatly optimizing the efficiency of the absorption circuit.

[0048] In some implementations, the energy conversion circuit 30 may be a BUCK circuit, BOOST circuit, BUCK-BOOST circuit, or SEPIC circuit.

[0049] In some implementations, the stabilization voltage point can be selected from the DC input voltage bus, the DC output voltage terminal, or the stabilization voltage point of the main power supply.

[0050] In some embodiments, this application provides a method for absorbing peak energy for the above-mentioned active clamping circuit, which actively injects charge into the first capacitor C1 before the voltage peak of the secondary rectifier arrives, so that its terminal voltage is pre-raised to a preset potential.

[0051] In some embodiments, this application provides a switching power supply having the above-described active clamping circuit.

[0052] In some embodiments, the switching power supply of this application employs the above-described method for absorbing peak energy.

[0053] The above embodiments are merely preferred embodiments of this application. It should be noted that the above preferred embodiments should not be considered as limitations on this application. Several improvements and modifications can be made without departing from the spirit and scope of this application. These improvements and modifications are obvious from existing well-known technologies and should also be considered within the protection scope of this application. They will not be elaborated further here using examples.

Claims

1. An active clamping circuit applied to the secondary side of a switching power supply, characterized in that: The active clamping circuit is connected in parallel with the secondary rectifier of the switching power supply, and includes a clamping branch (10), a pre-charging circuit (20), an energy conversion circuit (30), and a stable voltage point. The clamping branch (10) includes a unidirectional conductive device D1 and a first capacitor C1 connected in series. The anode of the unidirectional conductive device D1 is connected to the high-voltage end of the secondary rectifier tube. The cathode of the unidirectional conductive device D1 is connected to the first end of the first capacitor C1 to form a first node. The second end of the first capacitor C1 is connected to the low-voltage end of the secondary rectifier tube. The first end of the pre-charging circuit (20) is connected to a pre-charging voltage source, and the second end of the pre-charging circuit (20) is connected to the first node. The pre-charging circuit is used to charge the first capacitor C1 before the stress peak of the turn-off voltage of the secondary rectifier arrives. The input terminal of the energy conversion circuit (30) is connected to the first node, and the output terminal of the energy conversion circuit (30) is connected to the stable voltage point. The energy conversion circuit (30) is configured to transfer the energy stored in the first capacitor C1 to the stable voltage point after the first capacitor C1 absorbs energy.

2. The active clamping circuit according to claim 1, characterized in that: The pre-charge circuit (20) includes a unidirectional conductive device and a pre-charge voltage source. The pre-charge voltage source is a DC auxiliary power source. The anode of the unidirectional conductive device is connected to the DC auxiliary power source, and the cathode of the unidirectional conductive device is connected to the first node.

3. The active clamping circuit according to claim 1, characterized in that: The pre-charge circuit (20) includes resistors R1 and R2, and capacitor C3. The pre-charge voltage source is the input voltage of the switching power supply. Resistor R1 and capacitor C3 are connected in parallel. The first end of resistor R1 is connected to the input voltage. The second end of resistor R1 is connected to the first node and one end of resistor R2. Resistor R2 is connected in parallel with capacitor C1 of clamping branch (10).

4. The active clamping circuit according to claim 1; characterized in that, The energy conversion circuit (30) is a BUCK circuit, BOOST circuit, BUCK-BOOST circuit or SEPIC circuit.

5. The active clamping circuit according to claim 1, characterized in that, The stable voltage point is the DC input voltage bus, DC output voltage terminal, or stable voltage point of the main power supply of the switching power supply.

6. The active clamping circuit according to claim 1, characterized in that, The unidirectional conductive device D1 is a diode or a MOSFET.

7. The active clamping circuit according to claim 1, characterized in that: The secondary rectifier is a MOSFET, the high-voltage end of the secondary rectifier is the drain of the MOSFET, the low-voltage end of the secondary rectifier is the source of the MOSFET, the anode of the unidirectional conductive device D1 is connected to the drain of the MOSFET, and the second end of the first capacitor C1 is connected to the source of the MOSFET.

8. A method for controlling the absorption of peak energy, used in the active clamping circuit according to any one of claims 1 to 7, characterized in that, Before the voltage spike of the secondary rectifier arrives, charge is actively injected into the first capacitor C1, so that its terminal voltage is pre-raised to a preset potential.

9. A switching power supply having an active clamping circuit as described in any one of claims 1 to 7.

10. The switching power supply according to claim 9 employs the peak energy absorption control method as described in claim 8.

Images