Linear constant current switching power supply

Abstract

A linear constant current switching power supply is provided that includes a first capacitor, a second capacitor, and an output capacitor configured to: when a rectified system input voltage is lower than a system output voltage but higher than a voltage on at least one of the first capacitor and the second capacitor, the first capacitor and the second capacitor are parallel to each other, the first capacitor and the second capacitor are charged by the rectified system input voltage via different current paths, and an output capacitor provides current to flow through a load.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to a linear constant current switching power supply. Background Technology

[0002] A switching power supply, also known as a switching converter or switching power supply, is a type of power supply. The function of a switching power supply is to convert a voltage level from one voltage level to the voltage or current required by the user through different architectures (e.g., flyback, buck, or boost architectures). Summary of the Invention

[0003] According to an embodiment of the present invention, a linear constant current switching power supply includes a first capacitor, a second capacitor, and an output capacitor, configured such that: when the rectified system input voltage is lower than the system output voltage but higher than the voltage on at least one of the first and second capacitors, the first and second capacitors are connected in parallel, the rectified system input voltage charges the first and second capacitors respectively through different current paths, and the output capacitor provides the current flowing through the load. Attached Figure Description

[0004] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0005] Figure 1 A schematic diagram of a traditional linear constant current switching power supply topology is shown.

[0006] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals in a linear constant current switching power supply.

[0007] Figure 3 A schematic diagram of the topology of a linear constant current switching power supply according to an embodiment of the present invention is shown.

[0008] Figure 4 It shows Figure 3 The diagram shows the division of the operating region of a linear constant current switching power supply within one power frequency cycle.

[0009] Figure 5 It shows Figure 3 The diagram shows the equivalent circuit of a linear constant current switching power supply when the rectified system input voltage Vin is higher than the system output voltage Vo across the load LED.

[0010] Figure 6 It shows Figure 3The diagram shows the equivalent circuit of a linear constant current switching power supply when the rectified system input voltage Vin is slightly lower than the system output voltage Vo across the load LED, but higher than the voltage across capacitors C1 and C2.

[0011] Figure 7 It shows Figure 3 The diagram shows the equivalent circuit of a linear constant current switching power supply when the rectified system input voltage Vin is significantly lower than the system output voltage Vo across the load LED, but higher than the voltage across capacitors C1 and C2.

[0012] Figure 8 It shows Figure 3 The diagram shows the equivalent circuit of a linear constant current switching power supply when the rectified system input voltage Vin is lower than the voltage across capacitors C1 and C2.

[0013] Figure 9A It shows Figure 3 The diagram shows the waveforms of multiple signals when the linear constant current switching power supply is in operation, including the operating state of region 2.

[0014] Figure 9B It shows Figure 3 The waveform diagrams shown for multiple signals in the operating state of the linear constant current switching power supply do not include the operating state in region 2.

[0015] Figure 10 A schematic diagram of another linear constant current switching power supply topology according to an embodiment of the present invention is shown.

[0016] Figure 11 It shows Figure 10 The diagram shows the waveforms of multiple signals from the linear constant current switching power supply. Detailed Implementation

[0017] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a comprehensive understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configuration and algorithm presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. In the accompanying drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the invention. Furthermore, it should be noted that the term "A connected to B" as used herein can mean "A and B are directly connected" or "A and B are indirectly connected via one or more other elements."

[0018] Figure 1 A schematic diagram of a traditional linear constant current switching power supply topology is shown. Figure 1 In the linear constant current switching power supply 100 shown, the current flowing through the switch S1 can be sampled by the current sampling resistor Rcs to generate the load current sampling voltage Vcs (since the average current flowing through the output capacitor Co is 0 in steady state, the average current flowing through the switch S1 is equal to the current flowing through the load light-emitting diode (LED)). The switch S1 can be controlled to operate in the saturation region based on the load current sampling voltage Vcs to ensure that the current flowing through the load LED is constant. Since the system input current Iin only flows through switch S1 when the rectified system input voltage Vin is higher than the system output voltage Vo across the load LED (in which case the conduction phase angle of the system input current Iin is small), in order to achieve a high power factor (PF), a bleeder switch S2 and a bleeder resistor Rb need to be added. When the rectified system input voltage Vin is lower than the system output voltage Vo across the load LED (i.e., no current flows through switch S1), the bleeder switch S2 is in the conducting state, so that the system input current Iin forms a bleeder current through the bleeder switch S2 and the bleeder resistor Rb and changes with the rectified system input voltage Vin.

[0019] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals in a linear constant current switching power supply. Vo represents the system output voltage across the load LED, Vin represents the rectified system input voltage, Vcs represents the load current sampling voltage, and Iin represents the system input current. Combined with... Figure 1 and Figure 2 It can be seen that when the rectified system input voltage Vin is less than the system output voltage Vo across the load LED, the system input current Iin is discharged through the branch composed of the bleeder switch S2 and the bleeder resistor Rb. This part of the energy is completely lost in the bleeder resistor Rb and cannot be transferred to the load LED, thus seriously affecting the system efficiency of the linear constant current switching power supply.

[0020] In view of the above, a linear constant current switching power supply according to an embodiment of the present invention is proposed, which can meet certain power factor (PF) requirements without affecting system efficiency. For example, it can simultaneously achieve PF > 0.9 and system efficiency > 82%.

[0021] Figure 3 A schematic diagram of the topology of a linear constant current switching power supply according to an embodiment of the present invention is shown. Figure 3In the linear constant current switching power supply 300 shown, S1, Sa, Sb, Sc, and Sd are semiconductor switching devices. The conduction phase angle of the system input current Iin is increased by charging capacitors C1 and C2 in parallel, thereby improving PF (for example, achieving PF>0.9).

[0022] Figure 4 It shows Figure 3 The diagram shows the division of the operating region of a linear constant current switching power supply within one power frequency cycle. (Combined with...) Figure 3 and Figure 4 It can be seen that, based on the magnitude of the rectified system input voltage Vin, the operating state of the linear constant current switching power supply 300 can be divided into four operating regions (i.e., Figure 4 Areas 1 to 4 shown) or three work areas (i.e., Figure 4 The regions shown are 1, 3, and 4; region 2 is not included.

[0023] Figure 5 It shows Figure 3 The diagram shows the equivalent circuit of the linear constant current switching power supply 300 when the rectified system input voltage Vin is higher than the system output voltage Vo across the load LED. Figure 5 As shown, when the rectified system input voltage Vin is higher than the system output voltage Vo across the load LED, switch S1 operates in the saturation region, and switches Sa, Sb, Sc, and Sd are in the off state. The current flowing through the load LED is provided by the rectified system input voltage Vin, and the current flowing through switch S1 is equal to the system input current Iin (current flow direction is shown by the arrow). During this stage, the linear constant current switching power supply 300 operates in region 1. That is, when the rectified system input voltage Vin is higher than the system output voltage Vo across the load LED, capacitors C1 and C2 neither charge nor discharge. The rectified system input voltage Vin provides the current flowing through the load LED while simultaneously charging the output capacitor Co. Here, the system input current Iin flows to ground through switch S1 and the current sampling resistor Rcs. The magnitude of the current flowing through switch S1 can be controlled based on the load current sampling voltage Vcs on the current sampling resistor Rcs, thereby controlling the magnitude of the current flowing through the load LED.

[0024] Figure 6 It shows Figure 3 The diagram shows the equivalent circuit of the linear constant current switching power supply 300 when the rectified system input voltage Vin is slightly lower than the system output voltage Vo across the load LED, but higher than the voltage across capacitors C1 and C2. Figure 6As shown, when the rectified system input voltage Vin is slightly lower than the system output voltage Vo across the load LED but higher than the voltage across each of capacitors C1 and C2, switches S1, Sa, Sb, Sc, and Sd are all off, the system input current Iin is 0, and the current flowing through the load LED is provided by the output capacitor Co (current flow direction is shown by the arrow). During this stage, the linear constant current switching power supply 300 operates in region 2. That is, when the rectified system input voltage Vin is slightly lower than the system output voltage Vo across the load LED but higher than the voltage across each of capacitors C1 and C2 (for example, the difference between the rectified system input voltage Vin and the voltage across at least one of capacitors C1 and C2 is greater than a predetermined threshold), capacitors C1 and C2 neither charge nor discharge, and the current flowing through the load LED is provided by the output capacitor Co.

[0025] It should be noted that if the linear constant current switching power supply 300 has high requirements for system efficiency, then the operating states of the linear constant current switching power supply 300 can be divided into... Figure 4 The four operating regions are shown; if the linear constant current switching power supply 300 has high requirements for power factor (PF) or total harmonic distortion (THD), the operating states of the linear constant current switching power supply 300 can be divided into four categories. Figure 4 The three work areas other than area 2 shown (i.e., area 1, area 3, and area 4).

[0026] Figure 7 It shows Figure 3 The diagram shows the equivalent circuit of the linear constant current switching power supply 300 when the rectified system input voltage Vin is significantly lower than the system output voltage Vo across the load LED, but higher than the voltage across capacitors C1 and C2. Figure 7As shown, when the rectified system input voltage Vin is significantly lower than the system output voltage Vo across the load LED but still higher than the voltage across at least one of capacitors C1 and C2, switches S1 and Sc are off, switches Sa and Sb operate in the saturation region, and switch Sd is on. The rectified system input voltage Vin charges capacitor C1 via switch Sa and capacitor C2 via switches Sb and Sd. The current flowing through the load LED is provided by the output capacitor Co (current flow direction is shown by the arrow). During this stage, the linear constant current switching power supply 300 operates in region 3. That is, when the rectified system input voltage Vin is significantly lower than the system output voltage Vo across the load LED but still higher than the voltage across at least one of capacitors C1 and C2 (for example, the difference between the rectified system input voltage Vin and the voltage across at least one of capacitors C1 and C2 is less than a predetermined threshold), capacitors C1 and C2 are connected in parallel. The rectified system input voltage Vin charges capacitors C1 and C2 respectively through different current paths, and the current flowing through the load LED is provided by the output capacitor Co. Specifically, the rectified system input voltage Vin charges capacitor C1 via switch Sa. Resistor Rc1 detects the charging current of capacitor C1 and converts it into a voltage. The current flowing through switch Sa can be controlled based on the voltage across resistor Rc1, thereby controlling the charging current of capacitor C1. Simultaneously, the rectified system input voltage Vin charges capacitor C2 via switches Sb and Sd. Resistor Rc2 detects the charging current of capacitor C2 and converts it into a voltage. The current flowing through switch Sb can be controlled based on the voltage across resistor Rc2, thereby controlling the charging current of capacitor C2.

[0027] Figure 8 It shows Figure 3 The diagram shows the equivalent circuit of the linear constant current switching power supply 300 when the rectified system input voltage Vin is lower than the voltage across capacitors C1 and C2. Figure 8As shown, when the rectified system input voltage Vin is lower than the voltage across each of capacitors C1 and C2, switches Sb and Sc are in the on state, and switch S1 operates in the saturation region. The rectified system input voltage Vin cannot provide current to the load LED, nor can it charge capacitors C1 and C2. The system input current Iin is zero. Capacitors C1 and C2 discharge in series through switches Sb and Sc to provide current to the load LED (current flow direction is shown by the arrow). During this stage, the linear constant current switching power supply 300 operates in region 4. In other words, when the rectified system input voltage Vin is lower than the voltage across each of capacitors C1 and C2, capacitors C1 and C2 are connected in series, and the discharge of capacitors C1 and C2 provides the current flowing through the load LED. Meanwhile, the current sampling resistor Rcs detects the magnitude of the current flowing through the load LED (i.e., the discharge current of capacitors C1 and C2) and converts it into a load current sampling voltage. The magnitude of the current flowing through the switch S1 can be controlled based on the load current sampling voltage on the current sampling resistor Rcs, thereby controlling the magnitude of the discharge current of capacitors C1 and C2 (i.e., the magnitude of the current flowing through the load LED).

[0028] exist Figure 3 In the linear constant current switching power supply 300 shown, the series and parallel connections of capacitors C1 and C2 are controlled by switches Sc and Sd. When switch Sd is in the on state and switch Sc is in the off state, capacitors C1 and C2 are connected in parallel. When switch Sd is in the off state and switch Sc is in the on state, capacitors C1 and C2 are connected in series.

[0029] Figure 9A It shows Figure 3 The diagram shows the waveforms of multiple signals during the operation of the linear constant current switching power supply 300 in region 2. Here, Vo represents the system output voltage across the load LED, Vin represents the rectified system input voltage, Vcs represents the load current sampling voltage, and Iin represents the system input current. Figure 9A As shown, the period from t0 to t1 corresponds to the operating state of region 1. During this time, the rectified system input voltage Vin provides current to the load LED and simultaneously charges the output capacitor Co. The period from t1 to t2 corresponds to the operating state of region 2, where the output capacitor Co provides current to the load LED. The period from t2 to t3 corresponds to the operating state of region 3, where the output capacitor Co still provides current to the load LED, and the rectified system input voltage Vin charges capacitors C1 and C2. The period from t3 to t4 corresponds to the operating state of region 4, where capacitors C1 and C2, connected in series, discharge to the load LED. It should be noted that the operating states are the same at symmetrical points on both sides of the power frequency cycle.

[0030] Figure 9B It shows Figure 3The operating states of the linear constant current switching power supply 300 shown do not include the operating states in region 2. In these waveforms, Vo represents the system output voltage across the load LED, Vin represents the rectified system input voltage, Vcs represents the load current sampling voltage, and Iin represents the system input current. Figure 9B As shown, the period from t5 to t6 corresponds to the operating state of region 1. During this time, the rectified system input voltage Vin provides current to the load LED and simultaneously charges the output capacitor Co. The period from t6 to t7 corresponds to the operating state of region 3. During this time, the output capacitor Co provides current to the load LED, and the rectified system input voltage Vin charges capacitors C1 and C2. The period from t7 to t8 corresponds to the operating state of region 4. During this time, capacitors C1 and C2 are connected in series and discharge to the load LED. It should be noted that the operating states are the same at symmetrical points on both sides of the power frequency cycle.

[0031] Figure 10 A schematic diagram of the topology of another linear constant current switching power supply 1000 according to an embodiment of the present invention is shown. To achieve a THD of less than 20%, Figure 10 The operating states of the linear constant current switching power supply 1000 shown do not include the operating state in region 2. In the operating state in region 4 (i.e., during the series discharge of capacitors C1 and C2), the system input current Iin forms a discharge current via switch Se and resistor Rb and varies with the rectified system input voltage Vin. That is, when capacitors C1 and C2 discharge to provide current flowing through the load LED, resistor Rb acts as a discharge resistor, switch Se acts as a discharge switch, and the system input current Iin forms a discharge current via resistor Rb and switch Se, varying with the rectified system input voltage Vin. Figure 10 Other details and combinations of the linear constant current switching power supply 1000 shown Figures 3 to 9B The linear constant current switching power supply 300 is described in the same way, so it will not be repeated here.

[0032] Figure 11 It shows Figure 10 The diagram shows the operating waveforms of multiple signals from the linear constant current switching power supply 1000. In this waveform, Vo represents the system output voltage across the load LED, Vin represents the rectified system input voltage, Vcs represents the load current sampling voltage, and Iin represents the system input current. Figure 11As shown, the period from t0 to t1 corresponds to the operating state of region 1. During this time, the rectified system input voltage Vin provides current to the load LED and simultaneously charges the output capacitor Co. The period from t1 to t2 corresponds to the operating state of region 3. During this time, the output capacitor Co provides current to the load LED, and the rectified system input voltage Vin charges capacitors C1 and C2. The period from t2 to t3 corresponds to the operating state of region 4. During this time, capacitors C1 and C2, connected in series, discharge to the load LED. The system input current Iin, through switch Se and resistor Rb, forms a discharge current that changes with the rectified system input voltage Vin. It should be noted that the operating states are the same at symmetrical points on both sides of the power frequency cycle.

[0033] This invention increases the conduction phase angle of the system input current Iin by charging capacitors C1 and C2 in parallel, thereby improving the power factor (PF) of the linear constant current switching power supply. Then, when the rectified system input voltage Vin is so low that it can neither provide current to the load LED nor charge capacitors C1 and C2, the load LED is discharged through capacitors C1 and C2 in series, discharging the previously charged energy to the load LED. This achieves both high PF and high system efficiency, thus realizing a linear constant current switching power supply with high PF and high system efficiency.

[0034] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A linear constant current switching power supply, comprising a first capacitor, a second capacitor, and an output capacitor, configured as follows: When the rectified system input voltage is lower than the system output voltage but higher than the voltage on at least one of the first and second capacitors, the first and second capacitors are connected in parallel. The rectified system input voltage charges the first and second capacitors respectively through different current paths, and the output capacitor provides the current flowing through the load. When the difference between the rectified system input voltage and the voltage on at least one of the first and second capacitors is less than a predetermined threshold, the first and second capacitors are connected in parallel, and the rectified system input voltage charges the first and second capacitors respectively through different current paths, and the output capacitor provides the current flowing through the load.

2. The linear constant current switching power supply according to claim 1 is further configured as follows: When the rectified system input voltage is lower than the voltage on each of the first and second capacitors, the first and second capacitors are connected in series, and the discharge of the first and second capacitors provides the current flowing through the load.

3. The linear constant current switching power supply according to claim 1 is further configured as follows: When the rectified system input voltage is higher than the system output voltage, the first capacitor and the second capacitor neither charge nor discharge, and the current flowing through the load is provided by the rectified system input voltage, which simultaneously charges the output capacitor.

4. The linear constant current switching power supply according to claim 1 is further configured as follows: When the difference between the rectified system input voltage and the voltage on at least one of the first and second capacitors is greater than the predetermined threshold, the first and second capacitors neither charge nor discharge, and the output capacitor provides the current flowing through the load.

5. The linear constant current switching power supply according to claim 2 further includes a bleed resistor and a bleed switch, wherein, When the current flowing through the load is provided by the discharge of the first capacitor and the second capacitor, the system input current forms a discharge current via the discharge resistor and the discharge switch and varies with the rectified system input voltage.

6. The linear constant current switching power supply according to claim 1 is further configured as follows: The rectified system input voltage charges the first capacitor via a first switch, and the charging current of the first capacitor is detected by a first resistor, wherein... The magnitude of the current flowing through the first switch is controlled based on the voltage across the first resistor.

7. The linear constant current switching power supply according to claim 1 is further configured as follows: The rectified system input voltage charges the second capacitor via a second switch, and the charging current of the second capacitor is detected by a second resistor, wherein... The magnitude of the current flowing through the second switch is controlled based on the voltage across the second resistor.

8. The linear constant current switching power supply according to claim 7 is further configured to: The first capacitor and the second capacitor are connected in series and in parallel by the third switch and the fourth switch, wherein: When the third switch is in the ON state and the fourth switch is in the OFF state, the first capacitor and the second capacitor are connected in parallel. When the third switch is in the off state and the fourth switch is in the on state, the first capacitor and the second capacitor are connected in series.

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