Ripple reduction circuit for use with a power supply

Abstract

The present disclosure relates to a ripple reduction circuit for use with a power supply. A ripple reduction circuit for use with an AC / DC power supply providing an output voltage to a load is presented. The ripple reduction circuit comprises an input terminal for receiving the output voltage and a low pass filter. The low pass filter is configured to filter an AC component of the output voltage to obtain a filtered DC voltage. The ripple reduction circuit generates a reference current and a control voltage having an AC component in phase with the AC component of the output voltage based on the filtered DC voltage.

Description

Technical Field

[0001] This disclosure relates to a ripple reduction circuit and a power supply with power factor correction incorporating the ripple reduction circuit. background

[0002] AC / DC power supplies convert AC input to DC output voltage. This is typically achieved using a rectifier coupled to a transformer, thus creating an isolated power supply. Isolated AC / DC switching power converters can be used to provide regulated power to electronic devices while simultaneously providing current isolation between the electronic device and the AC power supply. The transformer provides current isolation, and the components coupled to the primary winding are collectively referred to as the primary side of the power converter circuit, while the components coupled to the secondary winding are collectively referred to as the secondary side. The output provides a regulated voltage to the output load.

[0003] A crucial quality factor for this type of power supply is the power factor, defined as the ratio of real power delivered to the load to apparent power received by the converter from the input source. International organizations like the EU have established regulations specifying the minimum power factor or maximum harmonic levels that equipment must possess to be sold in the European market. Reactive circuit elements such as inductors and capacitors can lower the converter's power factor. To improve the power factor, AC / DC power supplies are typically equipped with power factor correction (PFC) and are referred to as PFC converters.

[0004] Existing AC / DC power supplies are limited by significant current oscillations and / or relatively complex designs, thus restricting their application.

[0005] The purpose of this disclosure is to address one or more of the limitations mentioned above. Overview

[0006] According to a first aspect of this disclosure, a ripple reduction circuit is provided for use with an AC / DC power supply that provides an output voltage to a load. The ripple reduction circuit includes an input terminal for receiving the output voltage; a low-pass filter adapted to filter the AC component of the output voltage to obtain a filtered DC voltage; wherein the ripple reduction circuit is adapted to generate a reference current based on the filtered DC voltage and to generate a control voltage having an AC component in phase with the AC component of the output voltage.

[0007] Optionally, the load is positioned between the first output terminal and the second output terminal, and the ripple reduction circuit includes a linear regulator adapted to regulate the voltage at the second output terminal based on the control voltage.

[0008] Alternatively, the linear regulator is a low-dropout regulator.

[0009] Optionally, the voltage at the second output terminal is equal to the control voltage.

[0010] Optionally, the low-dropout regulator includes an operational amplifier coupled to a switch.

[0011] Optionally, the ripple reduction circuit includes a current mirror circuit adapted to generate a reference current, wherein the reference current has a first current component and a second current component.

[0012] Optionally, the first current component is fixed, and the second current component is variable based on the output of the low-pass filter.

[0013] Optionally, the current mirror circuit includes a first switch coupled to a low-pass filter via a first resistor and a second switch coupled to an input terminal via a second resistor or via a load.

[0014] Optionally, the current mirror circuit includes a third resistor coupled to a voltage source configured to provide a reference voltage, wherein the third resistor is coupled to the control terminals of the first switch and the second switch.

[0015] Optionally, the low-pass filter has a time constant greater than a predetermined ripple period of the output voltage.

[0016] According to a second aspect of this disclosure, an AC / DC power supply is provided, the AC / DC power supply including a power factor correction converter coupled to a ripple reduction circuit according to the first aspect.

[0017] Optionally, the power factor correction converter includes a rectifier coupled to a transformer having a primary winding and a secondary winding, a switch coupled to the primary winding, and a power factor controller coupled to the switch, wherein the power factor correction converter can operate in at least one of a constant voltage mode and a constant current mode.

[0018] Optionally, the power factor correction converter is adapted to provide a variable output voltage.

[0019] The AC / DC power supply according to the second aspect of this disclosure may include any of the features described above associated with the ripple reduction circuit according to the first aspect of this disclosure.

[0020] According to a third aspect of this disclosure, a method is provided for reducing ripple in an AC / DC power supply that provides an output voltage to a load, the method comprising:

[0021] Receive output voltage from AC / DC power supply;

[0022] A low-pass filter is used to filter the AC component of the output voltage to obtain a filtered DC voltage.

[0023] A reference current is generated based on the filtered DC voltage; and

[0024] A control voltage is generated that has an AC component in phase with the AC component of the output voltage.

[0025] Optionally, the load is positioned between the first output terminal and the second output terminal, and the method includes adjusting the voltage at the second output terminal based on a control voltage.

[0026] Optionally, the output voltage varies within the output range, and the ripple of the load output voltage or load output current is significantly reduced or eliminated within the output range.

[0027] Optionally, the reference current has a first current component and a second current component, wherein the first current component is fixed and the second current component is variable based on the output of the low-pass filter.

[0028] Optionally, the method includes subtracting the DC component of the output voltage to obtain the control voltage.

[0029] Optionally, the method includes generating a control voltage using a reference current and an output voltage.

[0030] The third approach can share the features of the first and second aspects as described above and in this paper.

[0031] According to a fourth aspect of this disclosure, an LED driver is provided that includes an AC / DC power supply according to a second aspect of this disclosure. Attached Figure Description

[0032] The present disclosure is described in more detail below by way of example and with reference to the accompanying drawings, wherein:

[0033] Figure 1A This is a diagram of a conventional AC / DC switching converter with power factor correction;

[0034] Figure 1B It is shown Figure 1A A diagram illustrating the operation of the PFC converter;

[0035] Figure 2 yes Figure 1A Simulation of the output current and output voltage of the converter;

[0036] Figure 3 This is a diagram of an AC / DC converter with a DC-DC converter output stage, based on existing technology.

[0037] Figure 4 This is a diagram of an AC / DC converter equipped with a ripple cancellation converter according to existing technology;

[0038] Figure 5 This is a diagram of an AC / DC converter equipped with a constant current regulator, based on existing technology.

[0039] Figure 6 This is a flowchart of a method for reducing output oscillations of an AC / DC power supply according to the present disclosure;

[0040] Figure 7A This is a diagram of an AC / DC power supply equipped with a ripple reduction circuit according to the present disclosure.

[0041] Figure 7B yes Figure 7A A diagram of a ripple reduction circuit;

[0042] Figure 7C It is shown Figure 7B A diagram illustrating the operation of the ripple reduction circuit;

[0043] Figure 8 This indicates the output is not equipped with a ripple reduction circuit. Figure 7A Simulation of the output voltage and output current of the PFC converter;

[0044] Figure 9 It displays a ripple reduction circuit. Figure 7A Simulation of the waveform obtained for a 25V output voltage circuit;

[0045] Figure 10 It displays a ripple reduction circuit. Figure 7A The circuit simulation obtained for a 35V output voltage;

[0046] Figure 11 This is a diagram of another ripple reduction circuit;

[0047] Figure 12 This is a diagram of an LED driver including an AC / DC power supply according to the present disclosure.

[0048] describe

[0049] Figure 1A A conventional AC / DC disconnector converter 100 with power factor correction is shown. The PFC converter 100 has a full-bridge rectifier 110, one end of which is coupled to an AC voltage source 120, and the other end of which is coupled to a source having a primary winding N. P and secondary winding N S Transformer T130. Primary winding N POne end is coupled to rectifier 110 to receive the rectified input voltage Vin, and the primary winding N P The other end is grounded via switch S0 and resistor R. Primary-side controller 140 is coupled to switch S0. Primary-side controller 140 is configured to perform power factor correction by implementing constant current (CC) control and / or constant voltage (CV) control. Primary-side controller 140 is also referred to as a PFC controller. The secondary side N of transformer T... s The output capacitor C is coupled via diode D. To meet power factor requirements (e.g., PF > 0.9), converter 100 is designed to have a nearly zero bulk capacitor (input or filter capacitor) after the bridge rectifier.

[0050] Figure 1B It is shown Figure 1A A diagram illustrating the operation of the PFC converter. Figure 1B The output voltage Vout and output current Iout are displayed in CV mode and CC mode, respectively. Ripple is shown for both output voltage and output current. The converter output voltage and output current are regulated by the PFC controller 140 on the primary side.

[0051] Figure 2 It is a display Figure 1A The simulation focuses on the output current and output voltage of the converter. The output voltage Vout exhibits significant ripple oscillations at twice the AC line frequency (e.g., 2 × 50 Hz or 2 × 60 Hz). This ripple can affect the control and function of some devices, including LEDs, causing flickering, for example.

[0052] Figure 3 This is a diagram of an AC / DC converter with a DC-DC converter output stage, based on existing technology. Converter 300 is similar to... Figure 1A The PFC converter 100 is provided, however, in this example, a DC-DC converter 350 is provided as a second stage to provide a stable and ripple-free DC voltage.

[0053] Figure 4 This is an illustration of an AC / DC converter 400 equipped with a ripple cancellation converter (RCC) as described in US10 / 015849. In this example, the transformer has two secondary windings, providing two outputs. An active RCC buck converter 450 is used at the second output to generate an inverting ripple voltage. This method achieves output ripple compensation.

[0054] Figure 5 This is a diagram of an AC / DC converter with a constant current regulator, based on existing technology. Converter 500 is similar to... Figure 1AThe PFC converter 100, however, in this example, incorporates a constant current CC regulator 550 at the output. The CC regulator 550 is formed by an operational amplifier whose output is connected to transistor M. Circuit 500 suppresses output ripple but can only operate under specified CC conditions. Because the load voltage at the regulated current may be much lower than the converter output, transistor M may dissipate a significant amount of power. For example, if the load voltage is 30V and the converter output is 40V, transistor M will have to dissipate 10V.

[0055] Figure 6 This is a flowchart of a method for reducing output oscillation (ripple) of an AC / DC power supply according to this disclosure. The power supply is used to provide an output voltage to a load.

[0056] In step 610, an output voltage is received from an AC / DC power supply. The output voltage has a DC component and an AC component, the AC component also referred to as the residual AC component or ripple component.

[0057] In step 620, the AC component of the output voltage is filtered using a low-pass filter to obtain the filtered DC component.

[0058] In step 630, a reference current is generated based on the filtered DC voltage. For example, the reference current may have a first current component and a second current component, the first current component being fixed and the second current component being variable based on the output of the low-pass filter.

[0059] In step 640, a control voltage with an AC component in phase with the AC component of the output voltage is generated. For example, a reference current and the output voltage can be used to generate the control voltage.

[0060] Using the proposed method, a load voltage with no or significantly reduced voltage ripple can be provided across the load.

[0061] Figure 7A The following diagram illustrates the implementation. Figure 6 AC / DC power converter using this method.

[0062] The power converter 700 includes a PFC converter 710 coupled to the ripple reduction circuit 720.

[0063] Figure 7B yes Figure 7A The diagram shows a ripple reduction circuit. The ripple reduction circuit 720 includes a low-pass filter 722, a current mirror circuit 724, and a linear regulator 726.

[0064] The low-pass filter 722 is formed by an operational amplifier OPA2, two resistors R1 and R2, and a capacitor C1. Operational amplifier OPA2 has an inverting input and a non-inverting input. The inverting input is coupled to node C at its output, and the non-inverting input is coupled to ground at node B via capacitor C1. Resistor R1 is positioned between nodes A and B, and the second resistor R2 is positioned between node B and ground.

[0065] The current mirror circuit 724 includes a pair of transistors S1 and S2 having a common gate terminal at node D. Transistor S1 has a drain terminal coupled to resistor Rb and a source terminal coupled to ground. Transistor S2 has a drain terminal coupled to resistor Rcfg at node E and a source terminal coupled to ground. Resistor Rcfg is coupled to node A. The gates of S1 and S2 are coupled to a reference voltage Vref through resistor Rb1. The drain of S1 is coupled to the gates of S1 and S2 at node D.

[0066] The linear regulator 726 is implemented as a low-dropout regulator formed by an operational amplifier OPA1 and a transistor M1. The operational amplifier OPA1 has an inverting input coupled to node E, a non-inverting input coupled to the drain terminal of M1, and an output coupled to the gate terminal of M1. The load is positioned between the first output terminal (positive terminal) and the second output terminal (negative terminal). Figure 7B In the circuit, the linear regulator 726 is located at the second output terminal. It should be understood that, in an alternative embodiment, the linear regulator may be located at the first output terminal.

[0067] In operation, the PFC converter 710 generates an output voltage Vout. Since the primary side of the AC / DC converter operates in power factor correction mode, Vout has a relatively large ripple component. The voltage Vout is received at node A. A low-pass filter LPF circuit 722 filters out or averages the AC frequency component (ripple frequency component) of Vout to generate a DC voltage Vopa2 at node C. This allows the DC component of the output voltage Vout to be detected and transformed by a current mirror circuit 724 with Rcfg, where Rcfg establishes the gain factor. The current mirror circuit 724 receives Vopa2 and generates a control voltage Vc at node E. The control voltage Vc is then used as a reference voltage for the linear regulator 726. The control voltage Vc is defined by the following equation (1). The linear regulator 726 regulates the voltage Vf on the negative side of the load such that Vc = Vf.

[0068] More specifically, through R cfg Current I m With the reference current I through S1 ref Mirror image; therefore, the control voltage Vc can be expressed as:

[0069] Vc = Vout - (I ref *R cfg (1)

[0070] The control voltage Vc can be adjusted to match different Vout values.

[0071] The linear regulator 726 operates to deliver a constant voltage V at node F. M1 Voltage V M1 It is regulated to follow Vc.

[0072] The control voltage Vc should be selected to be higher than the saturation voltage level V. sat_min This allows M1 to operate in the saturated region.

[0073] Because V M1 It is regulated to follow Vc, so V M1 =Vc. Therefore, the load voltage V 负载 It can be represented as:

[0074] V 负载 =I m *R cfg =I ref *R cfg (2)

[0075] The control voltage Vc can also be expressed as V sat_min The ripple voltage V with Vout 纹波 The sum of:

[0076] Vc = V sat_min +V 纹波 (3)

[0077] Vout = V sat_min +V 纹波 +V 负载 (4)

[0078] Reference current I ref =I Rb1 +I Rb , where I Rb1 Through R b1 The current, and I Rb Through R b The current.

[0079] Current I Rb1 It is a fixed bias current, equal to V. ref / R b1 and current I Rb It is a variable current, equal to V opa2 / R b Because V opa2Proportional to Vout, then I ref Dynamically changing. If Vout increases, then V... opa2 Increase and I ref Increase.

[0080] However, the reference current I ref It does not change linearly with Vout. This is because the gate voltage Vgate of the current mirror has a constant value. Current I Rb1 It was added to compensate for this nonlinearity. Furthermore, I Rb1 It will also reduce the I caused by the low-pass filter components. ref The influence of the residual ripple component. Current I Rb1 (Therefore, the corresponding value is V) ref and R b1 It can be selected to allow the control voltage Vc to be consistent with the selected Vout output range.

[0081] The output V of the low-pass filter 722 opa2 Proportional to Vout and scaled down by a factor N. The time constant Tc = ((R1*R2) / (R1+R2)*C1 is designed to be greater than the maximum ripple period of the power factor correction (PFC) converter output ripple. For example, this can be chosen to be 5 times larger. For example, Tc > 50 milliseconds, and the LPF 722 allows frequencies below 20 Hz to pass through. This provides a stable input for the OPA2 while providing sufficient response time.

[0082] For applications including LED lighting and chargers, power converters do not require very fast response times.

[0083] Figure 7C This is a diagram showing the load voltage at different output voltage values. The oscillation (ripple) of the output voltage Vout at the positive terminal of the load is compared to the voltage V at the negative terminal of the load. M1 The oscillations are in phase. Therefore, the voltage V across the load is... 负载 The oscillations are eliminated or greatly reduced.

[0084] In the numerical example, to cover the typical Vout range of 25V to 35V, R cfg and I ref It has the following values:

[0085] R cfg =(25V-V) C ) / I ref@25V =(35V-V) C ) / I ref@35V

[0086] I ref@25V =(V ref -Vgs ) / R b1 +(25V / NV gs ) / R b

[0087] I ref@35V =(V ref -V gs ) / R b1 +(35V / NV gs ) / R b

[0088] Assuming the output range is 25V to 35V, V C Set to 2.5V, V of the current mirror gs For 1V, V ref =5V,R b =2kΩ,R b1 =10.7kΩ and N=10 (i.e., R1=9*R2), we can obtain:

[0089] R cfg =20kΩ

[0090] I ref@25V =1.124mA

[0091] I ref@35V =1.624mA

[0092] N is the shrinking factor of Vout, which is equal to R1 + R2. In the example above, R1 = 9 * R2, and Vopa2 = (R2 / (R1 + R2))Vout = Vout / 10.

[0093] Figure 8 This simulation displays the waveforms of the output voltage Vout and load current Iout of the PFC converter 710 when the ripple reduction circuit 720 is not set at the output. For an output voltage Vout = 25V, the load current Iout has a peak-to-peak ripple of 140mA.

[0094] Figure 9 It displays a ripple reduction circuit 720. Figure 7A The circuit waveforms are simulated. The simulation shows the output voltage Vout, load current Iout, control voltage Vc, and the voltage across transistor M1. For the output voltage Vout = 25V, the load current Iout has a peak-to-peak ripple of 30mA. Voltage Vc and voltage V... M1 The same. The oscillation / ripple of Vc is the same as that of V. M1 The oscillations / ripples are in phase.

[0095] Figure 10It displays a ripple reduction circuit 720. Figure 7A The circuit waveforms are simulated. The simulation shows the output voltage Vout, load current Iout, control voltage Vc, and the voltage across transistor M1. For the output voltage Vout = 35V, the load current Iout has a peak-to-peak ripple of 30mA. Voltage Vc and voltage V... M1 The same. Therefore, the inter-peak ripple current is reduced by about 80% (30mA vs. 140mA).

[0096] The power converter disclosed herein allows for the suppression of output ripple from a PFC converter. Furthermore, it can be used over a relatively wide output voltage range, thus making it suitable for various load conditions.

[0097] The methods and corresponding power converters disclosed herein can be used in a variety of applications. For example, the power supply circuit of this disclosure can be integrated as part of an LED driver.

[0098] Figure 11 This is a diagram of another ripple reduction circuit. The ripple reduction circuit 1100 is similar to... Figure 7B The ripple reduction circuit is described, and the same reference numerals are used to denote the corresponding components. In this example, the linear regulator has been removed. The current mirror circuit 1124 is similar to the current mirror 724, but without the resistor Rcfg. Instead, the load is placed directly at node E, between Vout and VC. The size ratio of transistors S1 and S2 can be selected such that the load current I through S2... 负载 The constant factor N' is multiplied by the reference current I passing through S1. ref .

[0099] Figure 12 This is an illustration of an LED driver including an AC / DC power supply according to this disclosure. In this example, Figure 7A This circuit is used to power semiconductor light sources (such as LEDs, LED strings, or LED arrays). During operation, the ripple voltage across the LED is minimized, thereby improving light output. The output voltage can be varied to provide the degree of dimming of the light source. The LED current (load current) can be changed by altering the DC voltage applied across the LED.

[0100] Therefore, those skilled in the art will understand that variations in the disclosed arrangement are possible without departing from this disclosure. Thus, the above description of specific embodiments has been made merely by way of example and not for limiting purposes. Those skilled in the art will appreciate that minor modifications can be made to the described operation without significant alterations.

Claims

1. A ripple reduction circuit for use with an AC / DC power supply providing an output voltage to a load, the ripple reduction circuit comprising: an input terminal for receiving the output voltage; a low pass filter adapted to filter AC components of the output voltage to obtain a filtered DC voltage; and a current mirror circuit adapted to generate a reference current based on the filtered DC voltage, wherein the reference current is a sum of a first current component and a second current component, wherein the ripple reduction circuit is adapted to generate a control voltage having AC components in phase with AC components of the output voltage. The load is arranged between a first output terminal and a second output terminal, the ripple reduction circuit comprising a linear regulator adapted to regulate a voltage at the second output terminal based on the control voltage.

2. The ripple reduction circuit of claim 1, wherein, The linear regulator is a low dropout regulator.

3. The ripple reduction circuit of claim 2, wherein, The voltage at the second output terminal is equal to the control voltage.

4. The ripple reduction circuit of claim 2, wherein, The low dropout regulator comprises an operational amplifier coupled to a switch.

5. The ripple reduction circuit of claim 3, wherein, The first current component is fixed and the second current component is variable based on an output of the low pass filter.

6. The ripple reduction circuit of claim 1, wherein, The current mirror circuit comprises a first switch coupled to the low pass filter via a first resistance and a second switch coupled to the input terminal via a second resistance or via the load.

7. The ripple reduction circuit of claim 1, wherein, The current mirror circuit comprises a third resistance coupled to a voltage source configured to provide a reference voltage, wherein the third resistance is coupled to a control terminal of the first switch and a control terminal of the second switch.

8. The ripple reduction circuit of claim 7, wherein, The low pass filter has a time constant greater than a predetermined ripple period of the output voltage.

9. The ripple reduction circuit of claim 1, wherein, 10. An AC / DC power supply comprising a power factor correction converter coupled to the ripple reduction circuit of claim 1. The power factor correction converter comprises a rectifier coupled to a transformer having a primary winding and a secondary winding, a switch coupled to the primary winding, and a power factor controller coupled to the switch, wherein the power factor correction converter is operable in at least one of a constant voltage mode and a constant current mode.

11. The AC / DC power supply of claim 10, wherein, The power factor correction converter is adapted to provide a variable output voltage.

12. The AC / DC power supply of claim 11, wherein, 13. A method for reducing ripple of an AC / DC power supply providing an output voltage to a load, the method comprising: receiving the output voltage from the AC / DC power supply; filtering AC components of the output voltage with a low pass filter to obtain a filtered DC voltage; generating a reference current based on the filtered DC voltage using a current mirror circuit, wherein the reference current is a sum of a first current component and a second current component; and generating a control voltage having AC components in phase with AC components of the output voltage. The load is arranged between a first output terminal and a second output terminal, the method comprising regulating a voltage at the second output terminal based on the control voltage.

14. The method of claim 13, wherein, ​ 15. The method of claim 13, wherein, The output voltage varies over an output range, and wherein a ripple of a load output voltage or a load output current is substantially reduced or eliminated over the output range.

16. The method of claim 13, wherein, The reference current has a first current component and a second current component, wherein the first current component is fixed and the second current component is changeable based on an output of the low pass filter.

17. The method of claim 13, comprising subtracting a DC component of the output voltage to obtain the control voltage.

18. The method of claim 13, comprising generating the control voltage using the reference current and the output voltage.

19. An LED driver comprising an AC / DC power supply, wherein, The AC / DC power supply comprises a power factor correction converter coupled to a ripple reduction circuit, The ripple reduction circuit comprises: an input terminal for receiving an output voltage from the AC / DC power supply; a low pass filter adapted to filter an AC component of the output voltage to obtain a DC voltage; and a current mirror circuit adapted to generate a reference current based on the DC voltage, wherein the reference current is a sum of a first current component and a second current component, wherein the ripple reduction circuit is adapted to provide a control voltage having an AC component that is in phase with the AC component of the output voltage.

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