CN110536516B - Digital control method of LED driving power supply without electrolytic capacitor - Google Patents

Digital control method of LED driving power supply without electrolytic capacitor Download PDF

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CN110536516B
CN110536516B CN201910922367.1A CN201910922367A CN110536516B CN 110536516 B CN110536516 B CN 110536516B CN 201910922367 A CN201910922367 A CN 201910922367A CN 110536516 B CN110536516 B CN 110536516B
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林国庆
陈伟
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Fuzhou University
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Abstract

The invention relates to a digital control method of an electrolytic capacitor-free LED driving power supply. The digital controller acquires PFC circuit output voltage and LED load current and carries out weighting feedback to realize high power factor and constant current output, the time sequence and the duty ratio of a driving signal required by a half-bridge resonant circuit switching tube are determined by acquiring rectification circuit output voltage and LED load power, when the instantaneous value of the PFC output voltage is increased, the working duty ratio of the switching tube is increased, and when the instantaneous value of the PFC circuit output voltage is reduced, the working duty ratio of the switching tube is reduced, so that the working duty ratio of the half-bridge resonant circuit switching tube can automatically follow the instantaneous value change of the PFC output voltage, thereby effectively inhibiting low-frequency ripples of the PFC circuit output voltage, reducing the capacity of an energy storage capacitor at the output end of the PFC circuit, and replacing an electrolytic capacitor with a thin-film capacitor to realize no electrolytic capacitance.

Description

Digital control method of LED driving power supply without electrolytic capacitor
Technical Field
The invention relates to a digital control method of an electrolytic capacitor-free LED driving power supply.
Background
In recent years, the LED technology has been rapidly developed, and is popular among people due to its advantages of energy saving, long service life, high lighting effect, and the like, and thus becomes a new generation of lighting source. Because the LED driving power supply needs the electrolytic capacitor to balance input and output power, and the service life of the electrolytic capacitor is rapidly reduced along with the rise of temperature, the advantage of long service life of the LED lamp cannot be fully exerted. Therefore, it is indispensable to develop an LED driving power source having high reliability, high power factor and long life matched with an LED light source.
Aiming at high-power application occasions, the performance requirement of an LED driving power supply generally adopts a two-stage structure, a first-stage power factor correction circuit generally adopts a Boost circuit, and the LED driving power supply has the advantages of simple driving circuit, high PF value, small total harmonic distortion and high efficiency. The second-stage DC/DC converter usually adopts a half-bridge resonant converter to realize the conversion of electric energy and the control of constant current, can work in a higher frequency range, and can realize soft switching at the same time. For an LED driving power supply with a high power factor, the alternating current input voltage and the current have the same phase, the input instantaneous power contains double power frequency pulsation, and the output power is a constant value and has the same size as the average value of the input power. In order to balance the pulsating power between the ac input power and the dc output power, a large-capacity electrolytic capacitor is usually connected in parallel to the output side of the first-stage pfc circuit, and the electrolytic capacitor is usually used as the capacitor. The service life of the electrolytic capacitor is usually only about 1 ten thousand hours and is not matched with the service life of the LED for 8-10 ten thousand hours, the service life of the electrolytic capacitor is greatly influenced by the ambient temperature, and the service life of the electrolytic capacitor is reduced by about one half when the temperature is increased by 10 ℃, so that the electrolytic capacitor becomes a main factor influencing the service life of the LED driving power supply, and the electrolytic capacitor is large in size and limits the power density of the driving power supply to be further improved.
Disclosure of Invention
The invention aims to provide a digital control method of an LED driving power supply without electrolytic capacitors, which can effectively inhibit low-frequency ripples of the output voltage of a PFC circuit, reduce the capacity of an energy storage capacitor at the output end of the PFC circuit, and can replace the electrolytic capacitors with thin-film capacitors to realize no electrolytic capacitors.
In order to achieve the purpose, the technical scheme of the invention is as follows: a digital control method of an electrolytic capacitor-free LED driving power supply is provided, and the electrolytic capacitor-free LED driving power supply comprises a rectifying circuit, a PFC circuit, a half-bridge resonant circuit, two paths of LED current-sharing circuits and a control circuit; the half-bridge resonant circuit comprises switching tubes S1 and S2, inductors L1 and L2, capacitors C1 and C2 and a transformer T1, and the two-way LED current-sharing circuit comprises a current-sharing capacitor C3, diodes D1 and D2, capacitors C10 and C20, an LED load LED1 and an LED 2; the input end of a rectifying circuit is connected with an alternating current power supply, the output end of the rectifying circuit is connected with the input end of a PFC circuit, the first output end of the PFC circuit is connected with one end of S1, the second output end of the PFC circuit is connected with one end of S2, one end of C2 and one end of the primary side of T1, the other end of S1 is connected with the other end of S2 and is connected with one end of L2 and the other end of C2 through C1 and L1, the other end of L2 is connected with the other end of the primary side of T1, one end of the secondary side of T1 is connected with the anode of D1 and the cathode of D2 through C3, the other end of the secondary side of T1 is connected with one end of C20, the anode of LED2, one end of C10 and the cathode of LED1, the cathode of D1 is connected with the other end of C10 and the anode of LED1, and the anode of D2 is connected with the other end of C20 and the cathode of LED 2; the method is realized in the following way: the control circuit generates a control signal required by the PFC circuit by collecting the output voltage of the rectification circuit, the output voltage of the PFC circuit, the LED load current and the LED load voltage, and enables the working duty ratio of the switching tubes S1 and S2 of the half-bridge resonant circuit to automatically follow the change of the instantaneous value of the output voltage of the PFC circuit, so that the low-frequency ripple of the output voltage of the PFC circuit is suppressed, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
In an embodiment of the present invention, the control circuit includes a digital controller, and a PFC circuit driving circuit and a half-bridge resonant circuit driving circuit connected to the digital controller; the digital controller generates a required PFC circuit driving signal and a required half-bridge resonant circuit driving signal through software programming, wherein the PFC circuit driving signal is generated by collecting output voltage of a PFC circuit and LED load current and carrying out weighted feedback on the output voltage and the LED load current; the half-bridge resonant circuit driving signal is generated by collecting the output voltage of the rectifying circuit and the LED load power and according to the control method, the duty ratio of the driving signal can automatically follow the change of the instantaneous value of the output voltage of the PFC circuit, so that the low-frequency ripple of the output voltage of the PFC circuit is inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
In an embodiment of the present invention, the method utilizes the constant current characteristic of the half-bridge resonant circuit, that is, when the half-bridge resonant circuit operates at the constant current resonant frequency, the output current:
i0＝kc×vPFC×sin(D×π)
wherein v isPFCFor the instantaneous value of the output voltage of the PFC circuit, D is the working duty cycle of S1, kcThe output current is only related to the output voltage of the PFC circuit and the working duty ratio D of a switching tube of the half-bridge resonant circuit when the resonance parameter of the half-bridge resonant circuit is fixed; when PFWhen the instantaneous value of the C output voltage is increased, the working duty ratio of a switching tube on the half-bridge resonant circuit is increased, and the instantaneous value i of the output current is increased0＝kc×vPFCIncrease in xsin (Dxπ); when the instantaneous value of the PFC output voltage is reduced, the working duty ratio of a switching tube of the half-bridge resonant circuit is reduced, and the instantaneous value of the output current is reduced, so that the problem of unbalanced input and output instantaneous power of the LED driving power supply is solved, low-frequency ripples of the output voltage of the PFC circuit are effectively inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
In an embodiment of the invention, the control circuit determines the time sequence and the duty ratio of the driving signals required by S1 and S2 by collecting the output voltage of the rectifying circuit and the LED load power, and controls the duty ratio of the half-bridge resonant circuit to enable the output voltage of the rectifying circuit to pass through a zero-crossing point as a starting point
Figure BDA0002217449750000021
Regularly change, wherein kdIs the duty factor, DminThe minimum working duty cycle of S1 at rated load; when in use
Figure BDA0002217449750000022
When D is equal to kd×Dmin(ii) a When in use
Figure BDA0002217449750000023
When the temperature of the water is higher than the set temperature,
Figure BDA0002217449750000024
when in use
Figure BDA0002217449750000025
When D is 0.5kd(ii) a That is, from the zero crossing point of the output voltage of the rectifying circuit, the working duty ratio of S1 is from D according to the sine ruleminIncreasing to a maximum of 0.5 and decreasing to DminCompleting a working period which is half of the power frequency period of the input alternating current power supply; the switch tubes S2 and S1 are conducting complementarily, and both vary sinusoidally.
In an embodiment of the present invention, k isdIs selected from PFThe C circuit output voltage depends on the load power, and when the load power increases, the duty ratio kdThe larger the voltage is, the voltage of an energy storage capacitor at the output end of the PFC circuit is reduced; the duty factor k is reduced when the load power is reduceddThe smaller the voltage of the energy storage capacitor at the output end of the PFC circuit is, the more the voltage of the energy storage capacitor at the output end of the PFC circuit is increased.
In an embodiment of the present invention, DminThe selection of the PFC circuit is determined by the LED load voltage, the maximum value and the minimum value of the PFC circuit output voltage and the peak-to-average ratio of the LED load current.
Compared with the prior art, the invention has the following beneficial effects: the invention effectively inhibits the low-frequency ripple of the output voltage of the PFC circuit, reduces the capacity of the energy storage capacitor at the output end of the PFC circuit, and can use the thin-film capacitor to replace an electrolytic capacitor to realize non-electrolytic capacitance.
Drawings
FIG. 1 is a schematic diagram of an electrolytic capacitor-free LED driving power supply and control thereof.
Fig. 2 is an equivalent circuit diagram of a half-bridge LCL resonant network of the present invention.
FIG. 3 shows the main operating waveforms of the LED driving power supply without electrolytic capacitor according to the present invention.
FIG. 4 is a duty cycle operating waveform of a driving signal of a switching tube of a half-bridge resonant circuit according to the present invention.
FIG. 5 is Dmin＝0.1，kdWhen the voltage is 1, the LED driving power supply without electrolytic capacitor mainly simulates a waveform.
FIG. 6 is Dmin＝0.2，kdWhen the voltage is 1, the LED driving power supply without electrolytic capacitor mainly simulates a waveform.
FIG. 7 is Dmin＝0.2，kdThe LED driving power supply without electrolytic capacitor is mainly simulated when the voltage is equal to 0.8.
Detailed Description
The technical scheme of the invention is specifically explained below with reference to the accompanying drawings.
The invention provides a digital control method of an electrolytic capacitor-free LED driving power supply, which provides an electrolytic capacitor-free LED driving power supply, and comprises a rectifying circuit, a PFC circuit, a half-bridge resonant circuit, two paths of LED current-sharing circuits and a control circuit; the half-bridge resonant circuit comprises switching tubes S1 and S2, inductors L1 and L2, capacitors C1 and C2 and a transformer T1, and the two-way LED current-sharing circuit comprises a current-sharing capacitor C3, diodes D1 and D2, capacitors C10 and C20, an LED load LED1 and an LED 2; the input end of a rectifying circuit is connected with an alternating current power supply, the output end of the rectifying circuit is connected with the input end of a PFC circuit, the first output end of the PFC circuit is connected with one end of S1, the second output end of the PFC circuit is connected with one end of S2, one end of C2 and one end of the primary side of T1, the other end of S1 is connected with the other end of S2 and is connected with one end of L2 and the other end of C2 through C1 and L1, the other end of L2 is connected with the other end of the primary side of T1, one end of the secondary side of T1 is connected with the anode of D1 and the cathode of D2 through C3, the other end of the secondary side of T1 is connected with one end of C20, the anode of LED2, one end of C10 and the cathode of LED1, the cathode of D1 is connected with the other end of C10 and the anode of LED1, and the anode of D2 is connected with the other end of C20 and the cathode of LED 2; the control circuit generates a control signal required by the PFC circuit by collecting the output voltage of the rectification circuit, the output voltage of the PFC circuit, the LED load current and the LED load voltage, and enables the working duty ratio of the switching tubes S1 and S2 of the half-bridge resonant circuit to automatically follow the change of the instantaneous value of the output voltage of the PFC circuit, so that the low-frequency ripple of the output voltage of the PFC circuit is suppressed, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
The invention relates to a digital control method of an electrolytic capacitor-free LED driving power supply, which utilizes the constant current characteristic of a half-bridge resonant circuit, namely when the half-bridge resonant circuit works at a constant current resonant frequency, the output current is as follows:
i0＝kc×vPFC×sin(D×π)
wherein v isPFCFor the instantaneous value of the output voltage of the PFC circuit, D is the working duty cycle of S1, kcThe output current is only related to the output voltage of the PFC circuit and the working duty ratio D of a switching tube of the half-bridge resonant circuit when the resonance parameter of the half-bridge resonant circuit is fixed; when the instantaneous value of the PFC output voltage is increased, the working duty ratio of a switching tube on the half-bridge resonant circuit is increased, and the instantaneous value i of the output current is increased0＝kc×vPFCIncrease in xsin (Dxπ); when instantaneous value of PFC output voltage is reduced, operation of switching tube of half-bridge resonant circuit is implementedThe duty ratio is reduced, and the instantaneous value of the output current is reduced, so that the problem of unbalanced input and output instantaneous power of the LED driving power supply is solved, low-frequency ripples of the output voltage of the PFC circuit are effectively inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
The following is a specific implementation of the present invention.
Fig. 1 is a two-stage electrolytic capacitor-less LED driving power supply and a control schematic diagram thereof according to an embodiment of the present invention. The PFC circuit adopts a Boost converter; the half-bridge resonant circuit consists of switching tubes S1 and S2, inductors L1 and L2, capacitors C1 and C2 and a transformer T1, and works at the constant-current frequency of the LCL resonant network. The LED load is driven by two paths of current sharing circuits, one path is composed of D1, C10 and LED1, the other path is composed of D2, C20 and LED2, and C3 is a current sharing capacitor of the two paths of LED loads.
FIG. 2 is an equivalent circuit diagram of a half-bridge LCL resonant network, wherein the input voltage is a square wave signal with a duty ratio D and an amplitude VinThe working frequency is f, and Req is an equivalent resistance converted from an LED load to the primary side of the transformer. The transformer magnetizing inductance Lm is assumed to be large enough to neglect its effect on the load current. The fundamental component amplitude of the input voltage obtained by the fundamental analysis method is
Figure BDA0002217449750000041
The following is derived from the AC analysis: when the half-bridge operating frequency is equal to the resonant frequency of the inductors L1 and C2, i.e.
Figure BDA0002217449750000042
Time, load current
Figure BDA0002217449750000043
kcIs a constant related to the parameters of the half-bridge LCL resonant network only, i.e. when the resonant parameters are fixed, the output current is only related to the input voltage V of the half-bridge LCL resonant networkin(i.e., the output voltage v of the PFC circuit)PFC) And is independent of load resistance. Therefore, when the input voltage of the half-bridge LCL resonant network is constant, the half-bridge LCL resonant network can realize constant current output, and the higher the input voltage of the resonant network is, the larger the load current is, and the reverse direction isThe smaller the load current. The invention realizes the balance of input instantaneous power and output power and the constant current control of the LED load by utilizing the characteristic that the output current of the half-bridge LCL resonant network is irrelevant to the load and changes along with the output voltage of the PFC through the weighted feedback of the output current and the output voltage of the PFC.
As can be seen from fig. 3, the input voltage v is acacZero-crossing point is the starting point when
Figure BDA0002217449750000051
When the output voltage of the PFC circuit is at a minimum value, the output voltage of the PFC circuit is at a minimum value
Figure BDA0002217449750000052
At this time, the output voltage of the PFC circuit is at a maximum value. In order to inhibit the ripple of the output voltage of the PFC circuit as much as possible, the larger the instantaneous value of the output voltage of the PFC circuit is, the larger the working duty ratio of a switching tube of the half-bridge resonant circuit is; the smaller the instantaneous value of the output voltage of the PFC circuit is, the smaller the working duty ratio of a switching tube of the half-bridge resonant circuit is. Therefore, the minimum work duty ratio Dmin of the switching tube of the half-bridge resonant circuit is selected after the output voltage of the rectifying circuit is over-zero
Figure BDA0002217449750000053
(i.e. the
Figure BDA0002217449750000054
) Position of (D), maximum duty cyclemaxArranged after zero crossing of the output voltage of the rectifier circuit
Figure BDA0002217449750000055
(i.e. the
Figure BDA0002217449750000056
) The position of (1) is D, because the output power when the working duty ratio of a switching tube of the half-bridge resonant circuit is 0.5 is maximummax0.5. Because the output voltage of the rectifying circuit is in phase with the alternating current input voltage, the duty ratio of the half-bridge constant current resonant circuit is controlled by taking the zero crossing point of the output voltage of the rectifying circuit as a starting point
Figure BDA0002217449750000057
Regularly change, wherein kdIs the duty ratio (k at rated load)d＝1)，DminThe minimum duty cycle of the tube S1 on the half-bridge resonant circuit at nominal load. When in use
Figure BDA0002217449750000058
When D is equal to kd×Dmin(ii) a When in use
Figure BDA0002217449750000059
When the temperature of the water is higher than the set temperature,
Figure BDA00022174497500000510
when in use
Figure BDA00022174497500000511
When D is 0.5kd(ii) a That is, from the zero crossing point of the output voltage of the rectifying circuit, the duty ratio of the upper tube S1 of the half-bridge resonant circuit is from D according to the sine ruleminIncreasing to a maximum of 0.5 and decreasing to DminCompleting a working period which is half of the power frequency period of the input alternating current power supply; the switch tubes S2 and S1 are in complementary conduction, and both change in a sine rule; duty factor kdDepending on the load power and the output voltage of the PFC circuit, the duty factor k increases as the load power increasesdThe larger the voltage is, the voltage of an energy storage capacitor at the output end of the PFC circuit is reduced; the duty factor k is reduced when the load power is reduceddThe smaller the voltage of the energy storage capacitor at the output end of the PFC circuit is, the more the voltage of the energy storage capacitor at the output end of the PFC circuit is increased. Minimum duty cycle DminThe selection of the PFC circuit is determined by the LED load voltage, the maximum value and the minimum value of the PFC circuit output voltage and the peak-to-average ratio of the LED load current;
the control circuit of the electrolytic capacitor-free LED driving power supply adopts digital control. The PFC circuit adopts a constant-frequency DCM working mode to realize a power factor correction function, the digital controller detects PFC output voltage and LED load current and carries out weighted feedback on the PFC output voltage and the LED load current to generate a driving signal of a BOOST converter switching tube, high power factor is realized, and constant current control on an LED load is realized by adjusting the output voltage of the PFC circuit.
The half-bridge resonant circuit is controlled by constant frequency PWM, and the working frequency is set at the constant current resonant frequency. The digital controller determines the time sequence and the duty ratio of driving signals required by switching tubes S1 and S2 of the half-bridge resonant circuit by acquiring the output voltage of the rectifying circuit and the LED load power. As shown in fig. 4, when the PFC output voltage transient increases, the duty cycle of the switching tube increases; when the instantaneous value of the PFC output voltage is reduced, the working duty ratio of the switching tube is reduced, so that the working duty ratio of the switching tube of the half-bridge resonant circuit can automatically follow the instantaneous value of the PFC output voltage, the low-frequency ripple of the PFC circuit output voltage is effectively inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
The invention adopts a closed-loop control method of weighted feedback of PFC output voltage and LED load current to keep the LED load current constant, and has the advantage of high constant current precision. The half-bridge resonant circuit adopts constant frequency control, is simple to control, and is convenient for the optimal design of a transformer, an inductor and the like.
In order to verify the feasibility of the control scheme, the circuit and the control strategy provided by the invention are simulated. The simulation parameters are as follows: the alternating current input voltage is 220V, the load current is 2A, the output voltage is 70V, and the energy storage capacitor at the output end of the PFC circuit adopts a 10uF film capacitor. The simulation results are as follows: FIG. 5 is Dmin＝0.1，kdThe main simulation oscillogram of the LED driving power supply without electrolytic capacitor when the voltage is 1, and FIG. 6 is Dmin＝0.2，kdFIG. 7 is a waveform diagram showing the main simulation of the LED driving power supply without electrolytic capacitor when 1 is the value, and FIG. 7 is a diagram showing the present invention Dmin＝0.2，kdThe LED driving power supply without electrolytic capacitor is 0.8, and mainly simulates a waveform diagram. It can be seen that the energy storage capacitor at the output end of the PFC circuit adopts a 10uF film capacitor, and the LED driving power supply without electrolytic capacitor is in D statemin＝0.1，k d1 and Dmin＝0.2，kdWhen 1, the device can normally work, the output current is constant at about 2A, the alternating current input current can track the change of the alternating current sinusoidal input voltage, the ripple of the output voltage of the PFC circuit can be effectively controlled, and the condition that the output voltage of the PFC circuit is always higher than the alternating current input voltage can be metThe high power factor is realized, and the output voltage peak value of the PFC circuit can be restrained to reduce the voltage stress of the energy storage capacitor and the switching tube. LED driving power supply without electrolytic capacitor at Dmin＝0.2，kdWhen the voltage peak value of the PFC circuit is close to 500V at 0.8, the PFC circuit outputs the voltage at DminA timing, kdThe smaller the power delivered to the load, the larger the PFC output voltage ripple. As can also be seen by comparing FIGS. 5 and 6, at the same kdAt value, minimum duty cycle DminThe smaller the value is, the smaller the output voltage ripple of the PFC circuit is, the larger the output current ripple is, and the current peak-to-average ratio is increased.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.

Claims (4)

1. A digital control method of an electrolytic capacitor-free LED driving power supply is characterized in that the electrolytic capacitor-free LED driving power supply is provided and comprises a rectifying circuit, a PFC circuit, a half-bridge resonant circuit, two paths of LED current-sharing circuits and a control circuit; the half-bridge resonant circuit comprises switching tubes S1 and S2, inductors L1 and L2, capacitors C1 and C2 and a transformer T1, and the two-way LED current-sharing circuit comprises a current-sharing capacitor C3, diodes D1 and D2, capacitors C10 and C20, an LED load LED1 and an LED 2; the input end of a rectifying circuit is connected with an alternating current power supply, the output end of the rectifying circuit is connected with the input end of a PFC circuit, the first output end of the PFC circuit is connected with one end of S1, the second output end of the PFC circuit is connected with one end of S2, one end of C2 and one end of the primary side of T1, the other end of S1 is connected with the other end of S2 and is connected with one end of L2 and the other end of C2 through C1 and L1, the other end of L2 is connected with the other end of the primary side of T1, one end of the secondary side of T1 is connected with the anode of D1 and the cathode of D2 through C3, the other end of the secondary side of T1 is connected with one end of C20, the anode of LED2, one end of C10 and the cathode of LED1, the cathode of D1 is connected with the other end of C10 and the anode of LED1, and the anode of D2 is connected with the other end of C20 and the cathode of LED 2; the method is realized in the following way: the control circuit generates a control signal required by the PFC circuit by collecting the output voltage of the rectification circuit, the output voltage of the PFC circuit, the LED load current and the LED load voltage, and enables the working duty ratio of switching tubes S1 and S2 of the half-bridge resonant circuit to automatically follow the instantaneous value change of the output voltage of the PFC circuit, so that the low-frequency ripple of the output voltage of the PFC circuit is suppressed, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced; the method utilizes the constant current characteristic of the half-bridge resonant circuit, namely when the half-bridge resonant circuit works at the constant current resonant frequency, the output current is as follows:
i0＝kc×vPFC×sin(D×π)
wherein v isPFCFor the instantaneous value of the output voltage of the PFC circuit, D is the working duty cycle of S1, kcThe output current is only related to the output voltage of the PFC circuit and the working duty ratio D of a switching tube of the half-bridge resonant circuit when the resonance parameter of the half-bridge resonant circuit is fixed; when the instantaneous value of the PFC output voltage is increased, the working duty ratio of a switching tube on the half-bridge resonant circuit is increased, and the instantaneous value i of the output current is increased0＝kc×vPFCIncrease in xsin (Dxπ); when the instantaneous value of the PFC output voltage is reduced, the working duty ratio of a switching tube of the half-bridge resonant circuit is reduced, and the instantaneous value of the output current is reduced, so that the problem of unbalanced input and output instantaneous power of the LED driving power supply is solved, low-frequency ripples of the output voltage of the PFC circuit are effectively inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced;
the control circuit determines the time sequence and the duty ratio of the driving signals required by S1 and S2 by collecting the output voltage of the rectifying circuit and the LED load power, takes the zero crossing point of the output voltage of the rectifying circuit as a starting point, and controls the duty ratio of the half-bridge resonant circuit to enable the half-bridge resonant circuit to be in the same order
Figure FDA0003193145250000011
Regularly change, wherein kdIs the duty factor, DminThe minimum working duty cycle of S1 at rated load; when in use
Figure FDA0003193145250000012
When D is equal to kd×Dmin(ii) a When in use
Figure FDA0003193145250000013
When the temperature of the water is higher than the set temperature,
Figure FDA0003193145250000014
when in use
Figure FDA0003193145250000015
When D is 0.5kd(ii) a That is, from the zero crossing point of the output voltage of the rectifying circuit, the working duty ratio of S1 is from D according to the sine ruleminIncreasing to a maximum of 0.5 and decreasing to DminCompleting a working period which is half of the power frequency period of the input alternating current power supply; the switch tubes S2 and S1 are conducting complementarily, and both vary sinusoidally.
2. The digital control method of the LED driving power supply without the electrolytic capacitor as claimed in claim 1, wherein the control circuit comprises a digital controller, and a PFC circuit driving circuit and a half-bridge resonant circuit driving circuit connected with the digital controller; the digital controller generates a required PFC circuit driving signal and a required half-bridge resonant circuit driving signal through software programming, wherein the PFC circuit driving signal is generated by collecting output voltage of a PFC circuit and LED load current and carrying out weighted feedback on the output voltage and the LED load current; the half-bridge resonant circuit driving signal is generated by collecting the output voltage of the rectifying circuit and the LED load power and according to the control method, the duty ratio of the driving signal can automatically follow the change of the instantaneous value of the output voltage of the PFC circuit, so that the low-frequency ripple of the output voltage of the PFC circuit is inhibited, and the capacity of an energy storage capacitor at the output end of the PFC circuit is reduced.
3. The digital control method of the LED driving power supply without the electrolytic capacitor as claimed in claim 1, wherein the k isdThe selection of the duty ratio k depends on the output voltage of the PFC circuit and the load power, and when the load power is increaseddThe larger the voltage is, the voltage of an energy storage capacitor at the output end of the PFC circuit is reduced; the duty factor k is reduced when the load power is reduceddThe smaller the size of the tube is,the voltage of the energy storage capacitor at the output end of the PFC circuit is increased.
4. The digital control method of LED driving power supply without electrolytic capacitor as claimed in claim 1, wherein D isminThe selection of the PFC circuit is determined by the LED load voltage, the maximum value and the minimum value of the PFC circuit output voltage and the peak-to-average ratio of the LED load current.
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