An isolated electrolytic capacitor-free constant current charging circuit and switching method thereof

Abstract

The present invention discloses an isolated non-electrolytic capacitor constant current charging circuit, comprising a main circuit and an auxiliary energy storage circuit; an energy supply circuit diode D of the auxiliary energy storage circuit s2 The cathode is connected to the positive terminal of the bridge rectifier circuit and the primary winding N of the flyback converter T p The same-name end of the power supply circuit diode D s2 The anode of is connected to the drain of the energy supply circuit switch tube Q3, and the source of the energy supply circuit switch tube Q3 is connected to the drain of the energy storage circuit switch tube Q2 and the auxiliary energy storage capacitor C b The positive electrode of the energy storage circuit switch Q2 is connected to the auxiliary diode D s1 The cathode of the auxiliary diode D s1 The anode of the auxiliary winding N is connected s2 The other end of the auxiliary winding N s2 The same-name end of the primary winding N p And auxiliary energy storage capacitor C b The invention discloses an isolated electrolytic capacitor-free constant current charging circuit, which has the advantages of long service life and good charging effect.

Description

Technical Field

[0001] The present invention relates to a constant current charging circuit and a switching method, and in particular to an isolated constant current charging circuit based on a non-electrolytic capacitor and a switching method. Background Art

[0002] In recent years, the rapid development of power electronics technology has driven the innovation of various portable electronic products. Portable electronic devices are highly dependent on energy storage batteries. Nowadays, portable devices such as laptops and portable high-power lighting equipment often use lithium batteries for energy storage. In order to extend the service life of lithium batteries, constant current charging mode is often used.

[0003] However, at present, this type of constant current charging charger is large in size, and in order to reduce output ripple, a large number of electrolytic capacitors are used in the circuit. However, electrolytic capacitors have disadvantages such as short life, large size, and sensitivity to temperature, which not only restricts the service life of the charger, but also has poor charging effect. Therefore, a reasonable circuit design is needed to replace the electrolytic capacitors in the conventional constant current charging circuit. Summary of the invention

[0004] The object of the present invention is to overcome the above-mentioned shortcomings and provide an isolated electrolytic capacitor-free constant current charging circuit and a switching method thereof, which have the advantages of long service life and good charging effect.

[0005] The object of the present invention is achieved in that:

[0006] A switching method for an isolated non-electrolytic capacitor constant current charging circuit, characterized in that: the switching method is based on an isolated non-electrolytic capacitor constant current charging circuit, which includes a main circuit and an auxiliary energy storage circuit; the AC input source of the main circuit is connected to a bridge rectifier circuit after passing through an LC filter, and the positive end of the bridge rectifier circuit is connected to the primary winding N of a flyback converter T p The same-name end of the primary winding N p The opposite end of the main switch tube Q 1 The drain of the main switch tube Q 1 The source of the flyback converter is connected to the negative terminal of the bridge rectifier circuit, and the secondary winding N s1 The opposite end is connected to the secondary switch tube Q 4 The drain of the secondary switch tube Q 4 The source is connected to the output filter capacitor C o And lithium battery B T The positive pole of the output filter capacitor is C o The negative electrode of the lithium battery BT is connected to the auxiliary winding N s1 The same-name end of the auxiliary energy storage circuit power supply circuit diode D s2 The cathode is connected to the positive terminal of the bridge rectifier circuit and the primary winding N of the flyback converter Tp The same-name end of the power supply circuit diode D s2 The anode of the power supply circuit is connected to the switch tube Q 3 The drain of the energy supply circuit switch tube Q 3 The source of the energy storage circuit is connected to the switch tube Q 2 The drain and auxiliary energy storage capacitor C b The positive electrode, energy storage circuit switch tube Q 2 The source of the auxiliary diode D s1 The cathode of the auxiliary diode D s1 The anode of the auxiliary winding N is connected s2 The other end of the auxiliary winding N s2 The same-name end of the primary winding N p And auxiliary energy storage capacitor C b The negative electrode;

[0007] When the input power is greater than the output power stage:

[0008] There are four operating modes when the instantaneous input power is greater than the output power:

[0009] Working mode 1 (t 0 -t 1 )

[0010] Energy supply circuit switch tube Q 3 In this power stage, the normally off state is maintained. 0 Previously, the primary inductor current iLm of the flyback converter and the secondary current iD s Both are 0, and the output filter capacitor supplies power to the LED load; t 0 At this moment, the main switch tube Q 1 Conducting, power supply circuit diode D s2 And auxiliary diode D s1 In the main switch tube Q 1 During the on period, the reverse voltage is cut off; the main switch tube Q 1 During the conduction period, the primary inductor current iLm increases linearly; at t 1 At this moment, the main switch tube Q 1 Turn off, the primary inductor current iLm reaches its peak value;

[0011] Working mode 2 (t 1 -t 2 )

[0012] In t 1 Moment Q 1 After shutdown, the energy storage circuit switch tube Q 2 The energy storage circuit starts to work. During this switching cycle, in addition to supplying energy to the output LED load, the excess energy is stored in C bIn this mode, the primary inductor current continues to decrease, and the voltage of the energy storage capacitor increases; the LED load continues to be powered by the output filter capacitor;

[0013] Working mode three (t 2 -t 3 )

[0014] In t 2 At this moment, the energy storage circuit is finished working, and the secondary switch tube Q 4 The remaining energy stored in the transformer is transferred to the secondary switch Q of the flyback converter. 4 , secondary diode D s The local output circuit supplies power to the LED load;

[0015] t 2 At the moment, the secondary current is the peak value in working mode 3, which can be calculated based on the peak current of the auxiliary energy storage circuit in working mode 2; at t 2 to 3 During this period, the secondary current decreases linearly from the peak value to provide energy for the LED load; the current in the secondary loop continues to decrease, and at t 3 At this moment, the energy stored in the transformer is completely released, and the secondary current drops to 0;

[0016] Working mode 4 (t 3 -t 4 )

[0017] After all the energy in the transformer is transferred to the output and the secondary current drops to 0, it enters working mode 4. At this time, the primary inductor current iLm and the secondary current iD s All are 0; the energy required by the LED load is provided by the output filter capacitor;

[0018] When the input power is less than the output power stage:

[0019] Working mode 1 (t 0 -t 1 ):

[0020] Energy storage circuit switch tube Q 2 Keep the normally off state, the energy storage circuit does not work at this stage, C b In this working stage, only energy is supplied, and the voltage of the energy storage capacitor continues to decrease; at t 0 At this moment, the primary inductor current iLm of the flyback converter and the secondary current iD s Both are 0; the main switch tube Q 1 The secondary diode Ds is turned on when the main switch tube Q 1 During the on-time period, the reverse voltage is cut off; the primary inductor current iLm of the flyback converter rises linearly;

[0021] Working mode 2 (t 1 -t 2 ):

[0022] Since the instantaneous input is less than the output power stage, the input power cannot provide enough energy for the output LED load during each on cycle; in this power stage t 1 At this moment, turn off the main switch tube Q 1 And open the power supply circuit diode D s2 , power supply circuit switch tube Q 3 Keep off state; auxiliary energy storage capacitor C b Discharging to the primary inductor of the flyback converter causes the current in the primary inductor to rise and the energy stored in the transformer to increase;

[0023] Working mode three (t 2 -t 3 ):

[0024] In t 2 At this moment, the main switch tube Q 4 The other switch tubes remain disconnected; the secondary diode D s The LED is turned on by the forward voltage. After the energy supply circuit in the second working mode is replenished, the remaining energy in the primary inductor is transferred to the secondary side for output. Due to the continuous energy consumption of the LED load, the secondary current starts to decrease linearly from the maximum value in the second working mode. 3 At this moment, the current in the secondary output circuit drops to 0;

[0025] Working mode 4 (t 3 -t 4 ):

[0026] After the secondary current drops to 0, it enters working mode 4; at this time, the energy required by the LED load is provided by the output filter capacitor, the primary inductor current is 0, and it works in the inductor current discontinuous mode. Compared with the prior art, the beneficial effects of the present invention are:

[0027] The present invention adds an auxiliary winding on the basis of the traditional flyback converter to realize the absorption and release of the energy difference between the instantaneous input power and the output power; by increasing the average voltage and voltage ripple of the energy storage capacitor in the auxiliary energy storage circuit, the capacitance value is reduced, and finally the non-electrolytic capacitor is replaced; the isolated non-electrolytic capacitor constant current charging has the characteristics and advantages of no electrolytic capacitor, high power factor, high integration, high efficiency, long service life, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A topological structure diagram of an isolated constant current charging circuit without electrolytic capacitor of the present invention;

[0029] Figure 2The main working waveform of an isolated electrolytic capacitor-free constant current charging circuit of the present invention within one power frequency cycle.

[0030] Figure 3 and Figure 4 This is the main working waveform of an isolated non-electrolytic capacitor constant current charging circuit in one switching cycle of the present invention ( Figure 3 When the instantaneous input power is greater than the output power, Figure 4 The instantaneous input is less than the output power).

[0031] Figures 5 to 8 ,as well as Figures 9 to 12 The present invention is an isolated type electrolytic capacitor-free constant current charging circuit in a switching cycle. Figures 5 to 8 It is the equivalent circuit diagram of each working mode when the input is greater than the output power stage. Figures 9 to 12 (Equivalent circuit diagram of each mode when the instantaneous input power is less than the output power).

[0032] in:

[0033] Filter capacitor C f 、Filter inductor L f , bridge rectifier circuit, flyback converter T, primary winding N p , secondary winding N s1 , auxiliary winding N s2 , Main switch tube Q 1 , secondary side switch tube Q 4 , secondary diode D s 、Filter capacitor C o 、Lithium battery B T ;

[0034] Auxiliary energy storage capacitor C b , auxiliary diode Ds 1 , Energy storage circuit switch tube Q 2 , power supply circuit diode D s2 , Energy supply circuit switch tube Q 3 . DETAILED DESCRIPTION

[0035] See also Figure 1 , the present invention relates to an isolated electrolytic capacitor-free constant current charging circuit, comprising a main circuit and an auxiliary energy storage circuit;

[0036] The main circuit includes an AC input source, a filter capacitor C f 、Filter inductor L f , bridge rectifier circuit, flyback converter T, primary winding N p , secondary winding N s1 , auxiliary winding N s2 , Main switch tube Q 1, secondary side switch tube Q 4 , secondary diode D s 、Filter capacitor C o And lithium battery B T ;

[0037] The auxiliary energy storage circuit includes an auxiliary energy storage capacitor Cb, an auxiliary diode Ds1, and an energy storage circuit switch tube Q 2 , power supply circuit diode D s2 , Energy supply circuit switch tube Q 3 ;

[0038] The AC input source of the main circuit is connected to the bridge rectifier circuit after passing through the LC filter. The positive end of the bridge rectifier circuit is connected to the primary winding N of the flyback converter T. p The same-name end of the primary winding N p The opposite end of the main switch tube Q 1 The drain of the main switch tube Q 1 The source of the flyback converter is connected to the negative terminal of the bridge rectifier circuit, and the secondary winding N s1 The opposite end is connected to the secondary switch tube Q 4 The drain of the secondary switch tube Q 4 The source is connected to the output filter capacitor C o And lithium battery B T The positive pole of the output filter capacitor is C o And lithium battery B T The negative pole is connected to the auxiliary winding N s1 The eponymous end;

[0039] Auxiliary energy storage circuit power supply circuit diode D s2 The cathode is connected to the positive terminal of the bridge rectifier circuit and the primary winding N of the flyback converter T p The same-name end of the power supply circuit diode D s2 The anode of the power supply circuit is connected to the switch tube Q 3 The drain of the energy supply circuit switch tube Q 3 The source of the energy storage circuit is connected to the switch tube Q 2 The drain and auxiliary energy storage capacitor C b The positive electrode, energy storage circuit switch tube Q 2 The source of the auxiliary diode D s1 The cathode of the auxiliary diode D s1 The anode of the auxiliary winding N is connected s2 The other end of the auxiliary winding N s2 The same-name end of the primary winding N p And auxiliary energy storage capacitor C b of the negative electrode.

[0040] The present invention adopts a method of adding an auxiliary winding in the flyback converter to construct an auxiliary energy storage circuit to realize the storage and release of the instantaneous input pin and output po pulsating power difference. In the design of the auxiliary energy storage circuit, by reasonably increasing the voltage average value of the auxiliary energy storage capacitor and improving the voltage ripple size, it realizes the effective replacement of small-capacitance non-electrolytic capacitors, ensuring that the output current remains constant, and its working mode can be divided into two working stages.

[0041] 1. Working principles of different working stages

[0042] 1.1 Input power is greater than output power stage

[0043] There are four working modes in the stage where the instantaneous input power is greater than the output power. The equivalent circuits corresponding to each working mode are as follows: Figures 5 to 8 shown.

[0044] Working mode 1 (t 0 -t 1 )

[0045] like Figure 5 The equivalent circuit of the working mode is shown in the figure. The switch tube Q of the energy supply circuit 3 In this power stage, the normally off state is maintained. 0 Before, the primary inductor current iLm and the secondary current iDs of the flyback converter are both 0, and the output filter capacitor supplies power to the LED load. 0 At this moment, the main switch tube Q 1 Conducting, power supply circuit diode D s2 And auxiliary diode D s1 In the main switch tube Q 1 During the on period, the main switch tube Q 1 During the conduction period, the primary inductor current iLm increases linearly. 1 At this moment, the main switch tube Q 1 Turn off, the primary inductor current iLm reaches its peak value.

[0046] Working mode 2 (t 1 -t 2 )

[0047] As shown Figure 6 The equivalent circuit of this working mode is shown below. 1 Moment Q 1 After shutdown, the energy storage circuit switch tube Q 2 The energy storage circuit starts to work. During this switching cycle, in addition to the energy supplied to the output LED load, the excess energy is stored in C b In this mode, the primary inductor current continues to decrease and the voltage of the energy storage capacitor increases. The LED load continues to be powered by the output filter capacitor.

[0048] Working mode three (t 2 -t 3 )

[0049] like Figure 7 The equivalent circuit of this working mode is shown below. 2 At this moment, the energy storage circuit is finished working, and the secondary switch tube Q 4 The remaining energy stored in the transformer is transferred to the secondary switch Q of the flyback converter. 4 , secondary diode D s The local output circuit supplies power to the LED load.

[0050] t 2 At the moment, the secondary current is the peak value in working mode 3, which can be calculated based on the peak current of the auxiliary energy storage circuit in working mode 2. 2 to 3 During this period, the secondary current decreases linearly from the peak value to provide energy for the LED load. The current in the secondary loop continues to decrease. 3 At this moment, the energy stored in the transformer is completely released and the secondary current drops to 0.

[0051] Working mode 4 (t 3 -t 4 )

[0052] like Figure 8 The figure shows the equivalent circuit of this mode. After all the energy in the transformer is transferred to the output and the secondary current drops to 0, it enters mode 4. In the working mode 4, the primary inductor current iLm and the secondary current iDs are both 0. The energy required by the LED load is provided by the output filter capacitor.

[0053] 2.2 Input power is less than output power stage

[0054] When the instantaneous input power is greater than the output power, the main waveforms in any switching cycle are as follows: Figure 4 As shown in the figure, the change in the relationship between the instantaneous input power and the output power leads to changes in the topological working mode, working waveform, energy flow direction, and equivalent circuit diagram.

[0055] Figures 9 to 12 Shown is the equivalent circuit diagram of the stage when the instantaneous input is less than the output power.

[0056] Working mode 1 (t 0 -t 1 ):

[0057] like Fig. 9 The figure shows the modal equivalent circuit. The energy storage circuit switch tube Q 2Keep the normally off state, the energy storage circuit does not work at this stage, C b In this working stage, only energy is supplied, and the voltage of the energy storage capacitor continues to drop. 0 At this moment, the primary inductor current iLm of the flyback converter and the secondary current iD s Both are 0. The main switch tube Q 1 Conducting, secondary diode D s In the main switch tube Q 1 During the on period, the reverse voltage is cut off. The primary inductor current iLm of the flyback converter rises linearly.

[0058] Working mode 2 (t 1 -t 2 ):

[0059] like Fig.10 The equivalent circuit of this working mode is shown as follows. Since the instantaneous input is less than the output power stage, the input power cannot provide enough energy for the output LED load during each on cycle. 1 At this moment, turn off the main switch tube Q 1 And open the power supply circuit diode D s2 , power supply circuit switch tube Q 3 Keep the shutdown state. Auxiliary energy storage capacitor C b The primary inductor of the flyback converter is discharged, the primary inductor current increases, and the energy stored in the transformer increases.

[0060] Working mode three (t 2 -t 3 ):

[0061] like Fig.11 The equivalent circuit of this working mode is shown below. 2 At this moment, the main switch tube Q 4 The secondary diode D s The LED is turned on by the forward voltage. After the energy supply circuit in the second working mode is replenished, the remaining energy in the primary inductor is transferred to the secondary side to supply the output. As the LED load continues to consume energy, the secondary current starts to decrease linearly from the maximum value in the second working mode. 3 At this moment, the current in the secondary output loop drops to 0.

[0062] Working mode 4 (t 3 -t 4 ):

[0063] like Fig.12 The equivalent circuit of this working mode is shown in FIG. 1 . After the secondary current drops to 0, the working mode 4 is entered. The energy required by the LED load is provided by the output filter capacitor, the primary inductor current is 0, and the working mode is in the discontinuous inductor current mode.

[0064] The present invention adopts the conventional flyback constant current charging circuit, reasonably adds auxiliary winding, constructs auxiliary energy storage circuit, and realizes high efficiency, high PF and constant current output. Through the auxiliary energy storage circuit, instantaneous input pin and output p are realized. o The storage and release of pulsating power difference reasonably increases the average voltage of the auxiliary energy storage capacitor and increases the voltage ripple size, realizing the effective replacement of small-volume, small-capacitance non-electrolytic capacitors.

[0065] In addition: It should be noted that the above specific implementation is only an optimization scheme of this patent. Any changes or improvements made by technicians in this field based on the above concept are within the scope of protection of this patent.

Claims

1. A switching method for an isolated electrolytic capacitor-free constant current charging circuit, characterized in that: The switching method is based on an isolated non-electrolytic capacitor constant current charging circuit, which includes a main circuit and an auxiliary energy storage circuit; the AC input source of the main circuit is connected to a bridge rectifier circuit after passing through an LC filter, and the positive end of the bridge rectifier circuit is connected to the primary winding N of the flyback converter T. p The same-name end of the primary winding N p The opposite end of the flyback converter T is connected to the drain of the main switch tube Q1, the source of the main switch tube Q1 is connected to the negative end of the bridge rectifier circuit, and the secondary winding N s1 The opposite end is connected to the drain of the secondary switch tube Q4, and the source of the secondary switch tube Q4 is connected to the output filter capacitor C o And lithium battery B T The positive pole of the output filter capacitor is C o The negative electrode of the lithium battery BT is connected to the auxiliary winding N s1 The same-name end of the auxiliary energy storage circuit power supply circuit diode D s2 The cathode is connected to the positive terminal of the bridge rectifier circuit and the primary winding N of the flyback converter T p The same-name end of the power supply circuit diode D s2 The anode of is connected to the drain of the energy supply circuit switch tube Q3, and the source of the energy supply circuit switch tube Q3 is connected to the drain of the energy storage circuit switch tube Q2 and the auxiliary energy storage capacitor C b The positive electrode of the energy storage circuit switch Q2 is connected to the auxiliary diode D s1 The cathode of the auxiliary diode D s1 The anode of the auxiliary winding N is connected s2 The other end of the auxiliary winding N s2 The same-name end of the primary winding N p And auxiliary energy storage capacitor C b The negative electrode; When the input power is greater than the output power stage: There are four operating modes when the instantaneous input power is greater than the output power: Working mode 1 (t0-t1) The energy supply circuit switch Q3 remains in a normally off state in this power stage. Before t0, the primary inductor current iLm of the flyback converter and the secondary current iD s Both are 0, and the output filter capacitor supplies power to the LED load; At t0, the main switch Q1 is turned on, and the diode D s2 And auxiliary diode D s1 During the period when the main switch tube Q1 is turned on, it is cut off due to the reverse voltage; during the period when the main switch tube Q1 is turned on, the primary inductor current iLm rises linearly; at time t1, the main switch tube Q1 is turned off, and the primary inductor current iLm reaches a peak value; Working mode 2 (t1-t2) After Q1 is turned off at time t1, the energy storage circuit switch Q2 is turned on and the energy storage circuit starts to work. During this switching cycle, in addition to supplying energy to the output LED load, the excess energy is stored in C through the energy storage circuit. b In this mode, the primary inductor current continues to decrease, and the voltage of the energy storage capacitor increases; the LED load continues to be powered by the output filter capacitor; Working mode three (t2-t3) At time t2, the energy storage loop is finished, the secondary switch tube Q4 is turned on, and the other switches remain off; the remaining energy stored in the transformer is transferred to the flyback converter through the secondary switch tube Q4 and the secondary diode D s The local output circuit supplies power to the LED load; At t2, the secondary current is the peak value in working mode 3, which can be calculated based on the peak current of the auxiliary energy storage loop in working mode 2. During t2 to t3, the secondary current decreases linearly from the peak value to supply energy to the LED load. The current in the secondary loop continues to decrease. At t3, the energy stored in the transformer is completely released, and the secondary current decreases to 0. Working mode 4 (t3-t4) After all the energy in the transformer is transferred to the output and the secondary current drops to 0, it enters working mode 4. At this time, the primary inductor current iLm and the secondary current iD s All are 0; the energy required by the LED load is provided by the output filter capacitor; When the input power is less than the output power stage: Working mode 1 (t0-t1): The energy storage circuit switch tube Q2 remains in the normally off state. The energy storage circuit does not work at this stage. b In this working stage, only energy is supplied, and the voltage of the energy storage capacitor continues to drop; at time t0, the primary inductor current iLm of the flyback converter and the secondary current iD s are all 0; the main switch tube Q1 is turned on, and the secondary diode Ds is cut off due to the reverse voltage during the period when the main switch tube Q1 is turned on; the primary inductor current iLm of the flyback converter rises linearly; Working mode 2 (t1-t2): Since the instantaneous input is less than the output power stage, the input power cannot provide enough energy for the output LED load during each on cycle. At this power stage t1, the main switch Q1 is turned off and the power supply circuit diode D is turned on. s2 , the energy supply circuit switch tube Q3 remains in the off state; the auxiliary energy storage capacitor C b Discharging to the primary inductor of the flyback converter causes the current in the primary inductor to rise and the energy stored in the transformer to increase; Working mode three (t2-t3): At time t2, the main switch tube Q4 is turned on, and the other switches remain off; the secondary diode D s It is turned on by the forward voltage. After the energy supply circuit in the second working mode is replenished, the remaining energy in the primary inductor is transferred to the secondary side for output. As the LED load continues to consume energy, the secondary current starts to decrease linearly from the maximum value in the second working mode. At t3, the current in the secondary output circuit drops to 0. Working mode 4 (t3-t4): After the secondary current drops to 0, it enters working mode 4; at this time, the energy required by the LED load is provided by the output filter capacitor, the primary inductor current is 0, and it works in the inductor current discontinuous mode.

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