ARCHITECTURE FOR AC/DC SMPS WITH PFC AND MULTI-MODE LLC DC/DC CONVERTER

Abstract

An AC/DC Switching Mode Power Supply (SMPS) comprises a PFC stage, an isolated LLC DC/DC converter stage, and a control circuit that provides feedback/control signals to PFC and LLC controllers, to enable a plurality of operating modes, dependent on a sensed peak AC input voltage and required output voltage Vo. The PFC provides a first DC bus voltage Vdc (e.g. 200V) for low line AC input and a second DC bus voltage (e.g. 400V) for high line or universal AC input. A multi-mode LLC converter is operable in a half-bridge mode or a full-bridge mode. For low line AC input, output voltage Vo, and PFC output Vdc, the LLC operates in full-bridge mode; for high line input, output voltage Vo and PFC output 2×Vdc, the LLC operates in half-bridge mode; for universal AC input, output voltage 2×Vo, and PFC output 2×Vdc, the LLC operates in full-bridge mode.

Claims

1. An AC input AC/DC Switching Mode Power Supply (SMPS) comprising: a first stage comprising a non-isolated AC/DC converter comprising a power factor correction (PFC) stage which receives an AC input voltage and provides a DC bus voltage; and a PFC controller; a second stage comprising an isolated DC/DC converter comprising an LLC resonant DC/DC converter which receives the DC bus voltage and provides an output voltage; and an LLC controller; the LLC resonant DC/DC converter comprising first and second half-bridge legs, which are operable in a half-bridge mode and in a full-bridge mode; and a control circuit configured to: sense the AC input voltage, provide a first control signal, comprising a voltage feedback control signal, to the PFC controller to regulate an output of the PFC to provide the DC bus voltage, dependent on the AC input voltage; provide a second control signal, comprising one of a full-bridge mode signal and a half-bridge mode control signal, to the LLC controller to operate the LLC resonant DC/DC converter in the full-bridge mode or the half-bridge mode, dependent on the AC input voltage; in a first operating mode, for a low line AC input at or below a threshold value, the PFC stage regulates the DC bus voltage to a first value and LLC resonant DC/DC converter operates in the full-bridge mode to provide a first output voltage; and in a second operating mode, for a high line AC input above the threshold value, the PFC stage regulates the DC bus voltage to a second value, which is twice the first value, and the LLC resonant DC/DC converter operates in the half-bridge mode to provide the first output voltage.

2. The AC/DC SMPS of claim 1, wherein: in a third operating mode, for universal AC input, the PFC stage regulates the DC bus voltage to the second value and the LLC resonant DC/DC converter operates in the full-bridge mode to provide a second output voltage which is twice the first output voltage.

3. The AC/DC SMPS of claim 1, which is configured as a Power Supply Unit which is operable in said first and second operating modes to provide the first output voltage having a fixed value.

4. The AC/DC SMPS of claim 2, configured as power delivery (PD) adapter comprising a plurality of output ports, each output port comprising a buck converter; and an output port controller, wherein each buck converter receives the first output voltage or the second output voltage from the LLC resonant DC/DC converter, and provides an output voltage to a corresponding output port, wherein the output port controller provides an output mode definition signal to the control circuit to control the output voltage: in the first and second operating modes, each buck converter receives the first output voltage and the output voltage of the output ports is selected from a first group of output voltages for a first power range; in the third operating mode, each buck converter receives the second output voltage and the output voltage of the output ports is selected from a second group of output voltages for a second power range, the second power range being higher than the first power range.

5. The AC/DC SMPS of claim 2, configured as USB power delivery adapter comprising a plurality of output ports, each output port comprising a buck converter and a USB port; and an output port controller; wherein each buck converter receives the first output voltage or the second output voltage from the LLC resonant DC/DC converter, and provides an output voltage to a corresponding USB port, wherein the output port controller provides an output mode definition signal to the control circuit to control the output voltage, so that: in the first and second operating modes, each buck converter receives the first output voltage and the output voltage is selected from a Standard Power Range (SPR) consisting of output voltages of 5V, 9V, 15V and 20V; in the third operating mode, each buck converter receives the second output voltage and the output voltage of the output ports is selected from an Extended Power Range (EPR) or Adjustable Voltage Supply (AVS) consisting of output voltages of 28V, 36V and 48V; wherein the SPR, EPR and AVS are compliant with USB Power Delivery Specification Revision 3.1.

6. The AC/DC SMPS of claim 5, wherein the first output voltage is 25V and the second output voltage is 50V.

7. The AC/DC SMPS of claim 1, wherein the non-isolated AC/DC converter comprising the PFC stage comprises a bridge rectifier PFC or a bridgeless totem pole PFC.

8. The AC/DC SMPS of claim 1, wherein switches of the first and second half-bridge legs of the LLC resonant DC/DC converter comprise any one of: GaN transistors; SiC transistors; and Si transistors.

9. The AC/DC SMPS of claim 1, wherein switches of the first half-bridge leg comprise GaN transistors and switches of the second half-bridge leg comprise Si transistors.

10. The AC/DC SMPS of claim 1, wherein switches of the first half-bridge leg comprise SiC transistors and switches of the second half-bridge leg comprise Si transistors.

11. A method of operating an AC input AC/DC Switching Mode Power Supply (SMPS) the AC/DC SMPS comprising: a first stage comprising a non-isolated AC/DC converter comprising a power factor correction (PFC) stage which receives an AC input voltage and provides a DC bus voltage; and a PFC controller; a second stage comprising an isolated DC/DC converter comprising an LLC resonant DC/DC converter which receives the DC bus voltage and provides an output voltage, and an LLC controller; the LLC resonant DC/DC converter comprising first and second half-bridge legs, which are operable m a half-bridge mode and in a full-bridge mode; and a control circuit; the method comprising, in the control circuit, sensing the AC input voltage, providing a first control signal, comprising a voltage feedback signal, to the PFC controller to regulate the output voltage of the PFC to provide a DC bus voltage, dependent on the AC input voltage; providing a second control signal, comprising one of a full-bridge mode control signal and a half-bridge mode control signal, to the LLC controller to operate the LLC resonant DC/DC converter in the full-bridge mode or the half-bridge mode, dependent on the AC input voltage; and in a first operating mode, for a low line AC input at or below a threshold value, controlling the PFC stage to regulate the DC bus voltage to a first value and controlling the LLC resonant DC/DC converter to operate in full-bridge mode to provide a first output voltage; and in a second operating mode, for a high line AC input above the threshold value, controlling the PFC stage to regulate the DC bus voltage to a second value, which is twice the first value, and controlling the LLC resonant DC/DC converter to operate in the half-bridge mode to provide the first output voltage.

12. The method of claim 11, comprising: in a third operating mode, for universal AC input, controlling the PFC to regulate the DC bus voltage to the second value and controlling the LLC resonant DC/DC converter to operate in the full-bridge mode to provide a second output voltage, which is twice the first output voltage.

13. The method of claim 12, comprising receiving from an output port controller an output mode definition signal to enable the control circuit to select one of said first, second and third operating modes to provide an appropriate one of the first output voltage and the second output voltage.

14. A control circuit for an AC input AC/DC Switching Mode Power Supply (SMPS), the AC/DC SMPS comprising: a first stage comprising a non-isolated AC/DC converter comprising a power factor correction (PFC) stage which receives an AC input voltage and provides a DC bus voltage, and a PFC controller; a second stage comprising an isolated DC/DC converter comprising an LLC resonant DC/DC converter which receives the DC bus voltage and provides an output voltage; and an LLC controller; the LLC resonant DC/DC converter comprising first and second half-bridge legs, which are operable in a half-bridge mode and in a full-bridge mode; the control circuit being configured for implementing a method comprising: sensing the AC input voltage, providing a first control signal, comprising a voltage feedback signal, to the PFC controller to regulate the output voltage of the PFC to provide the DC bus voltage, dependent on the AC input voltage; providing a second control signal, comprising one of a full-bridge mode and a half-bridge mode control signal, to the LLC controller to operate the LLC resonant DC/DC converter in the full-bridge mode or the half-bridge mode, dependent on the AC input voltage; in a first operating mode, for a low line AC input at or below a threshold value, controlling the PFC to regulates the DC bus voltage to a first value and controlling the LLC resonant DC/DC converter to operate in full-bridge mode to provide a first output voltage; and in a second operating mode, for a high line AC input above the threshold value, controlling the PFC to regulates the DC bus voltage to a second value, which is twice the first value, and controlling the LLC resonant DC/DC converter to operate in the half-bridge mode to provide the first output voltage.

15. The control circuit of claim 14 comprising: an input for receiving the AC input voltage and means for generating an input voltage sense signal indicative of any one of a low line AC input, a high line AC input and a Universal AC input; an input for receiving an output voltage mode definition signal to define a specified output voltage value; means for comparing the input voltage sense signal with a reference voltage and generating the first control signal and the second control signal, dependent on the AC input voltage and the specified output voltage value; the first control signal being output to the PFC controller to regulate the PFC to provide an output Vdc having the first value or the second value; the second control signal being a output to the LLC controller to select the half-bridge mode or the full-bridge mode of the LLC resonant DC/DC converter and to regulate an output voltage of the LLC resonant DC/DC converter to a first value (Vo) or a second value (2×Vo).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 shows a table listing requirements for 80 Plus test categories;

[0029] FIG. 2 shows a simplified functional block diagram for an AC input AC/DC Switching Mode Power Supply comprising a non-isolated AC/DC converter with PFC and an isolated DC/DC converter;

[0030] FIG. 3 shows a simplified functional block diagram for an AC input AC/DC Switching Mode Power Supply, comprising a non-isolated AC/DC converter with PFC and an isolated DC/DC converter comprising an LLC DC/DC converter;

[0031] FIG. 4 shows a circuit schematic for an example AC input AC/DC Switching Mode Power Supply wherein the first stage comprises a Bridgeless Totem Pole (BTP) PFC, and the second stage comprises a full-bridge LLC DC/DC converter;

[0032] FIG. 5 shows a functional block diagram for AC input AC/DC SMPS of example embodiments comprising an active PFC stage, a DC/DC converter stage comprising a multi-mode LLC topology, and a control circuit providing voltage feedback and LLC mode control signals;

[0033] FIGS. 6A, 6B and 6C show circuit schematics to illustrate, respectively, operational modes 1, 2 and 3 of an example SMPS comprising a multi-mode LLC converter with voltage feedback and LLC mode control;

[0034] FIG. 7 is a table comparing parameters for operation in modes 1, 2 and 3;

[0035] FIG. 8 shows a circuit schematic for an AC input AC/DC SMPS of an example embodiment for a 1 kW fixed output voltage Vo datacenter PSU comprising a BTP PFC stage, a multi-mode full-bridge SR LLC DC/DC converter and a control circuit for providing control signals for voltage feedback and multi-mode LLC operation;

[0036] FIG. 9A shows a circuit schematic and gate-source voltage (Vgs) waveforms for each transistor switch of the LLC converter, configured for operation in mode 1, for low line AC input;

[0037] FIG. 9B shows a circuit schematic and gate-source voltage (Vgs) waveforms for each transistor switch of the LLC converter, configured for operation in mode 2, for high line AC input;

[0038] FIG. 10 shows a table of simulated data for a 1 kW datacenter PSU of an example embodiment comprising a SMPS with a BTP PFC and multi-mode LLC converter for full load at low line AC input;

[0039] FIG. 11 shows a table of simulated data for the 1 kW datacenter PSU of the example embodiment comprising a SMPS with BTP PFC and multi-mode LLC converter for light load (10% load) at low line AC input;

[0040] FIG. 12 shows a table of data comparing performance of the example BTP PFC for different operational modes, for low line AC input and for 1 kW full load;

[0041] FIG. 13 (Prior Art) shows a circuit schematic for an example SMPS for a USB PD 3.1 adapter using a conventional topology;

[0042] FIG. 14 shows a circuit schematic for an example SMPS for a USB PD 3.1 adapter of an example embodiment comprising a rectifier PFC, a multi-mode SR LLC converter and a control circuit for multi-mode operation, dependent on AC input voltage and defined PD3.1 protocol output voltage;

[0043] FIGS. 15A, 15B, 15C show circuit schematics to illustrate, respectively, operational modes 1, 2 and 3 of the example SMPS illustrated in FIG. 14; and

[0044] FIG. 16 shows a table comparing parameters for operation in modes 1, 2 and 3 of an example SMPS with PFC and multi-mode LLC for a USB PD3.1 adapter.

[0045] The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of some embodiments of the invention, which description is by way of example only.

DETAILED DESCRIPTION

[0046] A simplified circuit block diagram for an example AC input AC/DC Switching Mode Power Supply (SMPS) comprising a PFC stage and an LLC DC/DC converter stage is shown in FIG. 3. In an example implementation illustrated in FIG. 4, the first stage comprises a Bridgeless Totem Pole (BTP) PFC, and the second stage comprises a full-bridge SR LLC DC/DC converter. The BTP PFC comprises inductor L and switches Sa1 and Sa2 and switches Sa3 and Sa4. The full bridge of the SR LLC comprises switches S1 and S2, and S3 and S4. Sb1 and Sb2 are SR MOSFETs. Conventionally, the DC bus voltage (Vdc) is fixed at ˜400Vdc. The losses PFC are very large, especially at low line AC input, creating heat and resulting in high temperature and poor efficiency. Another drawback is that it is difficult to support a wider range of output voltages Vo using an LLC converter.

[0047] A simplified circuit block diagram for an example AC input AC/DC Switching Mode Power Supply (SMPS) for example embodiments comprising a PFC stage, a multi-mode LLC resonant DC/DC converter stage, and a control circuit for input AC voltage sense and LLC mode control shown in FIG. 5. (For brevity, the multi-mode LLC resonant DC/DC converter may be referred to simply as the “multi-mode LLC converter”” or “LLC converter”). The PFC stage may be any suitable active PFC topology, e.g., a bridge diode boost PFC topology or a BTP PFC topology, which can provide a de bus voltage Vdc of a first value Vdc.sub.1, e.g. 200Vdc for low line AC input and a second value Vdc.sub.2=2×V.sub.dc1, e.g. 400V for high line AC input. The control circuit is configured to sense the input AC voltage, e.g. sense the peak AC input voltage, and provide a Vdc voltage feedback control signal to the PFC controller to control the dc bus voltage Vdc dependent on the peak input AC voltage. The multi-mode LLC converter is an LLC converter that can be operated in a plurality of modes, e.g. a half-bridge mode and a full-bridge mode, dependent on the sensed AC line input. The control circuit is configured to provide an LLC mode control signal to the LLC controller to operate in one of the plurality of modes, dependent on the sensed AC line input. The multi-mode LLC converter can also operate in first and second output modes, to provide an output voltage Vo of a first value Vo.sub.1 or a second value Vo.sub.2, where Vo.sub.2=2×Vo.sub.1.

[0048] FIGS. 6A, 6B and 6C show circuit schematics to illustrate, respectively, operational modes 1, 2 and 3 of a SMPS comprising an active power factor correction stage and a multi-mode LLC stage which is operable in full-bridge and half-bridge modes. The active PFC stage may have any suitable topology which can provide control of the dc bus voltage Vdc to provide first and second bus voltages Vdc.sub.1 and 2×Vdc.sub.1, which in this example are 200V and 400V, respectively. In the first operational mode, FIG. 6A, for low line AC input, the control circuit senses the peak AC input voltage and outputs a first (voltage feedback) control signal to the PFC, to operate the PFC to set Vdc at Vdc.sub.1=200V, and outputs a second (FB/HB mode) control signal to the LLC controller to operate the LLC in full-bridge mode and to provide a first output voltage Vo. In the second operational mode, FIG. 6B, for high line AC input, the control circuit senses the peak AC input voltage and outputs a first (voltage feedback) control signal to the PFC, to operate the PFC to set Vdc as 2×Vdc.sub.1=400V, and outputs a second (FB/HB mode) control signal to the LLC controller to operate the LLC in half-bridge mode, and to provide a first output voltage Vo. The control circuit may also be configured to receive an output mode definition, which defines first and second output voltages, and provide first and second control signals for a third operational mode. In the third operational mode, FIG. 6C, for Universal AC input, the control circuit outputs a first (voltage feedback) control signal to the PFC controller to select Vdc to 2×Vdc.sub.1=400V, and outputs a second (FB/HB mode) control signal to the LLC controller so that the LLC converter operates in full-bridge mode and provides a second output voltage 2×Vo, which is twice the first output voltage.

[0049] A table comparing parameters for operation in modes 1, 2 and 3 is shown in FIG. 7.

Example I: SMPS for 1 kW Datacenter PSU

[0050] A circuit schematic for an example implementation of an SMPS of an embodiment configured for 1 kW datacenter PSU, with fixed output voltage Vo, is shown in FIG. 8. The SMPS comprises a Bridgeless Totem Pole (BTP) PFC, a multi-mode LLC converter which is operable in full-bridge and half-bridge modes, and a control circuit for voltage feedback and LLC mode control.

[0051] Operation of Control Circuit for Voltage Feedback & Mode control: Resistor R3, capacitor C1 and resistor R4 form a voltage divider to sense peak AC input voltage and compare it with a 5V reference voltage using differential comparator. The comparator output voltage Va controls a voltage feedback control signal * to the BTP PFC controller and a mode control signal ** to the LLC controller to select full-bridge (FB) mode or half-bridge (HB) mode operation of the LLC converter.

[0052] At low line AC input, the comparator output voltage Va is “low”, and transistor Qa is in the off-state. The resistors R1 and R2 form a voltage divider to provide a first (voltage feedback) control signal to PFC controller, which regulates Vdc to Vdc.sub.1=200V. The comparator output voltage Va being “low” also provides a second (FB/HB mode) control signal to the LLC controller, which makes the LLC converter operate in full-bridge mode.

[0053] At high line AC input, the comparator output voltage Va is “high”, and transistor Qa is in the on-state. The resistor R1 and resistors R2 and R5 form a voltage divider to provide a voltage feedback control signal to the PFC controller, which regulates Vdc to 2×Vdc.sub.1=400V. The voltage Va being “high” also provides a FB/HB mode control signal to the LLC controller, which makes the LLC converter operate in half-bridge mode.

[0054] By way of example only, the PSU of the embodiment shown in FIG. 8 is a GaN/Silicon hybrid implementation. The switches Q1 and Q2 of the BTP PFC comprise GaN transistors and the switches Q3 and Q4 of the BTP PFC comprises Si MOSFETs. The multi-mode LLC converter is a full-bridge SR LLC converter wherein the first half-bridge leg comprises switches Q5 and Q6, which comprise GaN transistors, and the second half-bridge leg comprises switches Q7 and Q8, which comprise Si MOSFETs. Using GaN transistors, instead of silicon power transistors provides several advantages. Compared to silicon MOSFETs, GaN transistors have lower on-resistance, higher breakdown voltage, no reverse-recovery characteristics. GaN devices have much lower switching losses, so they can operate at higher switching frequencies. For example, in a PSU or Universal AC/DC adapter, which uses GaN devices, higher switching frequencies allow for the use of smaller capacitors and inductors, which can significantly reduce the power converter size, weight and cost.

[0055] A GaN/Si hybrid implementation may be used to take advantage of different characteristics of both GaN transistors and Si transistors, e.g. to optimize performance and cost. The switches of multi-mode LLC may be implemented with other combinations of power semiconductor technologies. For example, both half-bridge legs comprise GaN transistors, or both half-bridge legs comprise SiC transistors, or both half-bridge legs comprise Si transistors. In another example, the first half-bridge leg comprises wide-bandgap transistors, e.g. SiC transistors and the second half-bridge leg comprises Si transistors.

[0056] FIG. 9A shows a circuit schematic and gate-source voltage (Vgs) waveforms for each transistor switch of the LLC converter, configured for operation in mode 1, for low line AC input, e.g. 90Vac to 160Vac, with a DC link voltage Vdc=200V. In this mode the switches Q5 and Q6 (GaN transistors) and switches Q7 and Q8 (Si transistors) operate in a full-bridge mode with 200V voltage stress. This mode enables the PFC to operate with higher efficiency, and the LLC converter operates with lower switching losses. FIG. 9B shows a circuit schematic and gate-source voltage (Vgs) waveforms for each transistor switch of the LLC converter, configured for operation in mode 2, for high line AC input, e.g. 160Vac to 277Vac with a DC link voltage Vdc=400V. Switches Q5 and Q6 (GaN transistors) operate with 400V voltage stress. For switches Q7 and Q8 (silicon transistors), Q7 is constantly off and Q8 is constantly on, so the LLC converter operates in a half-bridge mode.

[0057] FIG. 10 shows a table of simulated data for an example 1 kW datacenter PSU of an embodiment 1 comprising a SMPS with a BTP PFC and half-bridge LLC converter, and corresponding data for a SMPS of embodiments 2 and 3 comprising a BTP PFC and a multi-mode LLC converter for two different switching frequencies (fs=100 kHz and 200 kHz) for the PFC, for full load, at low line AC input. FIG. 11 shows corresponding data for light load (10%), at low line AC input. In SMPS for PSU of these example embodiments, for low line AC input, efficiency is improved by 0.6% for full load and by 1.3% to 2.3% for light load.

[0058] The PSU can support full rated power for universal AC input, for both low line AC input and high line AC input.

[0059] Comparative performance data for the BTP PFC, for full-load, low line AC input, are summarized in the table in FIG. 12. By using a PFC switching frequency of 200 kHz instead of 100 kHz, the size (volume) of the PFC inductor can be reduced by 50%. A smaller size inductor provides for a SMPS with a higher power density. The design provides the same ripple current on the PFC inductor, with different inductance values. The losses are transistor losses only, and do not include the PFC inductor losses. Data is simulated for an ambient temperature of 40 C, a thermal resistance (Rth) of the case to heatsink of 2.5K/W and a Rth of the heatsink to ambient of 0.5K/W.

Example II: SMPS for a USB PD 3.1 Adapter

[0060] The USB Power Delivery Specification Revision 3.1 (PD3.1) May 2021 defines a choice of three new fixed higher voltages: 28V (above 100 W), 36V (above 140 W) and 48V (above 180 W) compared to previous PD3.0. The previously defined standard power range (SPR) comprised fixed voltages of 5V, 9V, 15V and 20V. A new adjustable voltage supply (AVS) mode provides for a range from 15V to one of three maximum voltages (28V, 36V, or 48V) depending on the available power.

[0061] A circuit schematic for an example SMPS for a USB PD 3.1 adapter using a conventional topology comprising a PFC stage, a synchronous-LLC DC/DC converter stage, which provides an output bus voltage of 50V to buck converters for each USB-C output port is shown in FIG. 13. The efficiency of the PFC stage is low when the dc bus voltage Vdc is fixed at 400Vdc and the AC line input is low, e.g. in the range of 90Vac to 120Vac. The efficiency of a buck DC/DC converter supplied by a 50V bus voltage input to provide outputs to the USB ports of 5V, 9V and 15V is very low.

[0062] A circuit schematic for an example SMPS for a USB PD 3.1 adapter of an example embodiment comprising a PFC, a multimode LLC DC/DC converter and a control circuit for voltage feedback and multi-mode LLC operation, dependent on AC line input voltage, is shown in FIG. 14. The PFC stage can use any active PFC topology, such as a bridge rectifier boost PFC or bridgeless totem pole PFC. In FIG. 14, a bridge rectifier boost PFC is illustrated by way of example. The isolated DC/DC stage comprises a multi-mode LLC which can be configured to operate in full-bridge mode or half-bridge mode. As described above, with reference to the control circuit of the embodiment shown in FIG. 8, the control circuit senses the peak AC input voltage and provides a first (voltage feedback) control signal to the PFC controller to operate the PFC to provide a first DC bus voltage Vdc=Vdc.sub.1, e.g. 200V, for low line AC input, and to provide a second DC bus voltage Vdc=2×Vdc.sub.1, e.g. 400V, for high line AC input. The control circuit also provides a second (FB/HB mode) control signal to the LLC controller, to enable the LLC to operate in full-bridge mode or in half-bridge mode, dependent on the sensed AC line input and defined PD3.1 protocol output voltage. The control circuit also receives an output mode control signal from the controller of the buck DC/DC converters (labelled PD3.1& MCU) which defines the required output mode, e.g. PD3.1 SPR, or EPR/AVS, to control the output voltage.

[0063] FIGS. 15A, 15B and 15C show circuit schematics to illustrate, respectively, operational modes 1, 2 and 3. In the first operational mode, FIG. 15A, for low line AC input the control circuit outputs a first (voltage feedback) control signal to the PFC controller to operate the PFC stage to provide a first DC bus voltage Vdc.sub.1, e.g. 200V and outputs a second (FB/HB mode) control signal to the LLC controller to operate the multi-mode LLC in full-bridge mode, to provide a first DC output voltage Vo. In the second operational mode, FIG. 15B, for high line AC input, the control circuit sends a first control signal to the PFC controller to operate the PFC stage to provide a second DC bus voltage 2×Vdc.sub.1, e.g. 400V, and sends a second control signal to the LLC controller to operate the multi-mode LLC in half-bridge mode to provide the DC output voltage Vo. In the third operational mode, FIG. 15C, for universal AC input, the control circuit provides control signals to operate the PFC to provide the second DC bus voltage 2×Vdc.sub.1, e.g. 400V and to operate the multi-mode LLC in half-bridge mode to provide a DC output voltage 2×Vo.

[0064] FIG. 18 shows a table comparing parameters for operation in modes 1, 2 and 3 for providing example power outputs for PD3.1. Mode 1 and mode 2 support PD3.1 SPR mode with PD output voltage 5V, 9V, 15V and 20V. The DC bus voltage is set at 25V as an input to the buck DC/DC stage to increase the efficiency of buck DC/DC stage compared to a conventional fixed 50V bus voltage. Mode 1 is used for low line AC input voltage, and the PFC output voltage is set at Vdc (e.g. 200V) to increase PFC efficiency at low line AC input and the multi-mode LLC converter operates in full-bridge mode. Mode 2 is used for high line AC input voltage, and the PFC output voltage is set at 2×Vdc (e.g. 400V) and the multi-mode LLC converter operates in half-bridge mode. Mode 3 supports PD3.1 EPR or AVS mode with PD output voltages at 28V, 36V and 48V. The DC bus voltage supplied by the multi-mode LLC is set at 50V as an input voltage of buck DC/DC stage. The PFC output voltage is set at 2×Vdc (e.g. 400V) and the multi-mode LLC converter operates in full-bridge mode when the AC line input voltage is a universal input for both low line and high line AC input.

[0065] For example, when the SMPS PD output voltage is SPR output (e.g. 5V, 9V, 15V and 20V), the DC bus voltage is set at 25V and multi-mode LLC converter operates in mode 1 (full-bridge) or mode 2 (half-bridge), according to the AC input voltage. When the PD output voltage is EPR or AVS (e.g. 28V, 36V and 48V), the DC bus voltage is set at 50V and multi-mode LLC converter operates in at full-bridge mode at universal AC input voltage. By changing the DC bus voltage according to PD output voltage, the buck DC/DC converter efficiency is dramatically increased because of a smaller difference between DC bus voltage and output voltage. The multi-mode LLC converter enables support for wider range of voltage outputs, such as to meet PD3.1 requirements for an output voltage range from 5V to 48V.

[0066] Although some SMPS of example embodiments have been described in detail, these are provided by way of example only. DC bus voltages and DC output voltages may be selected to meet requirements for different target applications. It will be appreciated that target applications may include, for example: higher power adapters which require PFC, e.g. ≥75 W and future PD3.1 adapters; datacenter or server PSU, PSU for telecom and industrial applications, LED lighting drivers, and other AC/DC SMPS applications.

[0067] Although embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and not to be taken by way of limitation, the scope of the present invention being limited only by the appended claims.