CN103476184A - Power system with multiplexed output - Google Patents
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Abstract
The invention relates to a power system with the multiplexed output. The power system comprises an input circuit, m first output circuits, n second output circuits, m current control circuits, n voltage reduction switch-type adjusters and a voltage control circuit, wherein the n voltage reduction switch-type adjusters and the n second output circuits are correspondingly connected in a one-to-one mode and used for receiving the output voltage of the second output circuits and controlling the output voltage of the voltage reduction switch-type adjusters to be kept constant. Each first output circuit is used for driving an LED load composed of one or more LED lamp strings. The current control circuits are used for controlling the driving current of the LED load according to simulated light dimming signals and/or PWM light dimming signals to obtain the luminance corresponding to the light dimming signals.
Description
Technical Field
The invention relates to the technical field of electronics, in particular to a power supply system with multiple outputs.
Background
With the continuous innovation of liquid crystal display technology and the increase of application products, the LED backlight is rapidly developed due to the advantages of energy saving, environmental protection, light and thin volume, and the like. However, the brightness of the LED lamp is proportional to the driving current and the forward voltage drop, and varies with the temperature. Therefore, the driving of the LED requires a constant current source to achieve a desired light emission intensity. In order to ensure the normal operation of the LED, the driving power supply is required to be capable of providing a corresponding driving voltage and driving current. In the prior art, a driving power supply applied to LED backlight generally has multiple outputs, at least one constant current output provides a driving current for an LED lamp, and at least one constant voltage output provides power for a system or other loads.
Referring to fig. 1, a functional block diagram of an LED backlight driving power supply in the prior art is shown. In the LED backlight driving power supply adopting the implementation scheme, the multipath output is realized through a plurality of secondary side windings of the transformer. For convenience of description, the LED backlight driving power supply having one constant current output and one constant voltage output is taken as an example for description. Specifically, after the rectification processing of the rectifier bridge 101, the external ac power supply VACIs converted into a sine half-wave DC voltage VINDCAnd is inputted to a primary side winding N of the transformerp。
In the constant current output circuit, the secondary side winding Ns1And a primary side winding NpCoupled due to power switching tube QT1Is periodically turned on and off, thereby forming a secondary winding Ns1A square wave voltage is generated at two ends and then passes through a diode D01And a capacitor C01After filtering, at capacitor C01Generating a fluctuating first output voltage V acrossout1. By an inductance L0Power switch tube QT2Diode D02And a capacitor C02The input end of the boost (boost) power stage circuit receives a first output voltage Vout1And the output end is connected with the LED lamp. The constant current control and drive circuit 102 drives the LED lamp according to the current drive current ILEDAnd a desired drive current IREFError between generates a corresponding drive signal VG2To control the power switch tube QT2Thereby controlling the driving current ILEDWith the desired drive current IREFAnd the consistency is maintained.
In the constant voltage output circuit, the secondary winding Ns2And a primary side winding NpCoupled via a diode D03And a capacitor C03After filtering, at capacitor C03Generating a second output voltage V at both endsout2. Second output voltage Vout2Is transmitted to the primary side of the transformer 101 through the opto-coupler circuit (IC 1A and IC 1B). The error amplifier 103 receives a signal representing the second output voltage Vout2Is fed back toFBAnd a desired output voltage VREFTo generate an error signal Verror. The constant voltage control and drive circuit 104 is responsive to the error signal VerrorGenerating a corresponding drive signal VG1To control the power switch tube QT1Thereby controlling the second output voltage Vout2With the desired output voltage VREFAnd the consistency is maintained.
Through the above description of the technical solution of the conventional LED backlight driving power supply in conjunction with fig. 1, it can be seen that, in order to obtain constant voltage and constant current outputs at the same time in different output loops to meet the requirements of different loads, on one hand, a flyback voltage converter is formed by using the primary side and the secondary side of a transformer to control the switching state of a power switching tube located at the primary side according to the requirement of the constant voltage, so as to obtain the constant voltage output at the output end of the flyback converter; on the other hand, in order to obtain the driving current required by the LED lamp and to provide a sufficient driving voltage to the LED lamp, another step-up type power stage regulator is required to step up the received fluctuating first output voltage and perform constant current control on the output current of the output terminal of the step-up type power stage regulator, thereby driving the LED lamp.
However, with the implementation shown in fig. 1, in the constant current output loop, the conversion loss is increased by the conversion of two-stage voltages, and the working efficiency is reduced. Meanwhile, due to the use of the boost power stage circuit, the power switching tube needs to be selected as a power device with larger parameters (withstand voltage and the like), so that the implementation cost is increased, and the integration implementation of a system is not facilitated; on the other hand, since the first output voltage cannot be effectively limited and protected, when the LED lamp is in an abnormal state (for example, short circuit), damage is caused to the LED lamp and the circuit system.
Disclosure of Invention
In view of this, an object of the present invention is to provide a novel power supply system with multiple outputs, so as to solve the problems of the prior art, such as many components, complex circuit structure, large power loss, and low working efficiency.
A power supply system with multiple outputs according to an embodiment of the present invention includes an input circuit, m first output circuits, n second output circuits, m current control circuits, n step-down switching regulators, and a voltage control circuit, n being a natural number not less than 1, m being a natural number not less than 1, wherein,
the input circuit comprises a primary side winding and a first power switch tube;
one end of the primary side winding receives direct-current input voltage, and the other end of the primary side winding is connected with the first power switch tube;
each of the first output circuit and the second output circuit includes a secondary side winding, a rectifying circuit, and a filter circuit connected in series;
the n buck switching regulators are connected with the n second output circuits in a one-to-one correspondence manner and used for receiving the output voltage of the second output circuits and controlling the output voltage of the buck switching regulators to be kept constant;
each first output circuit is used for driving an LED load consisting of one or more paths of LED lamp strings; the current control circuit is used for controlling the driving current of the LED load according to an analog dimming signal and/or a PWM dimming signal to obtain the brightness corresponding to the dimming signal;
the voltage control circuit is used for controlling the switching state of the first power switch tube according to the output voltage of the second output circuit and the voltage of the negative end of the LED load;
when the voltage control circuit is in a first working state, the voltage control circuit controls the switching state of the first power switching tube according to the output voltage of the second output circuit so as to keep the output voltage of the second output circuit constant;
and in a second working state, the voltage control circuit controls the switching state of the first power switch tube according to the voltage of the negative end of the LED load so as to keep the voltage of the negative end of the LED load constant.
According to an embodiment of the present invention, the voltage control circuit includes a first error operation and compensation circuit corresponding to the LED light string and a second error operation and compensation circuit corresponding to the second output circuit; the first error operation and compensation circuit is used for generating a first compensation signal according to the error between the negative terminal voltage of the LED lamp string and the corresponding first expected reference voltage; the second error operation and compensation circuit is used for generating a second compensation signal according to the error between the output voltage of the second output circuit and the corresponding second expected voltage.
According to an embodiment of the present invention, the voltage control circuit includes a first selection circuit configured to receive the first compensation signal and the second compensation signal and use a minimum value or a maximum value of the first compensation signal and the second compensation signal as a feedback signal.
According to the embodiment of the invention, the power supply system with multi-path output also comprises an optical coupling circuit and a primary side control circuit positioned on the primary side;
the optical coupling circuit transmits the feedback signal to the primary side control circuit;
and the primary side control circuit generates a corresponding control signal according to the feedback signal to control the switching state of the first power switching tube.
According to an embodiment of the present invention, the voltage control circuit further includes a reference voltage generating circuit for adjusting the second desired voltage according to the output voltage of the second output circuit;
the reference voltage generating circuit includes a memory circuit, a second selection circuit, and a clamp circuit, wherein,
the storage circuit is used for receiving the output voltage of the second output circuit and storing energy to generate a storage voltage when the PWM dimming signal is at a high level;
the selection circuit receives the storage voltage and a voltage source, and the output signal of the selection circuit is the larger of the storage voltage and the voltage source;
the clamping circuit comprises a clamping voltage, and when the value of the output signal of the selection circuit is smaller than the clamping voltage, the second expected voltage is the output signal of the selection circuit; when the value of the output signal of the selection circuit is greater than the clamping voltage, the second desired voltage is the clamping voltage.
According to an embodiment of the present invention, the storage circuit includes a controllable switch and a capacitor, and the PWM dimming signal is used to control a switching state of the controllable switch.
According to an embodiment of the present invention, the current control circuit includes an analog dimming control circuit and a PWM dimming control circuit.
According to an embodiment of the present invention, the analog dimming control circuit includes a linear adjustment circuit, and the PWM dimming control circuit includes a switching circuit; the analog dimming signal is used for adjusting a reference source of the linear adjusting circuit; the PWM dimming signal is used for controlling the on-off state of the switch circuit so as to periodically turn on and off the LED lamp string.
According to an embodiment of the present invention, the switch circuit is connected in series to a power supply loop formed by the output end of the first output circuit and the LED light string.
According to an embodiment of the invention, the switching circuit is connected in series between the output of the operational amplifier of the linear regulating circuit and the controllable switch of the linear regulating circuit.
According to an embodiment of the invention, the analog dimming control circuit includes a switching type adjusting circuit, and the switching type adjusting circuit receives the analog dimming signal and the current driving current of the LED light string to adjust the output current of the switching type adjusting circuit.
According to an embodiment of the present invention, the PWM dimming control circuit includes a power supply loop connected in series to the output terminal of the first output circuit, the switching type adjustment circuit, and the LED light string, and the PWM dimming signal is used to control the on/off state of the switching circuit, so as to periodically turn on and off the LED light string.
According to an embodiment of the invention, the PWM dimming signal is used to control an enable state of the switching regulator circuit to periodically turn on and off the LED string.
According to the power supply system with the multi-output, the analog dimming and the PWM dimming can be simultaneously realized, or only the analog dimming or only the PWM dimming can be realized. In the voltage feedback control, the output voltage of the second output circuit and the negative terminal voltage of the LED load are both used as controlled signals. On one hand, the output voltage of the first output circuit is maintained to be the value of the minimum driving voltage which can sufficiently drive all the LED lamp strings through controlling the voltage of the negative end of the LED load, and the working efficiency of the circuit is improved. On the other hand, the output voltage of the second output circuit, namely the input voltage of the buck switching regulator, can be maintained to be basically constant by controlling the output voltage of the second output circuit, so that the fluctuation of the input voltage of the buck switching regulator is avoided, and the working stability of the circuit is improved. Furthermore, the output voltage of the second output circuit is used for adaptively adjusting the reference voltage corresponding to the output voltage of the second output circuit in the voltage feedback loop, so that the system can quickly enter a stable state, and the dynamic response of the system is improved.
Drawings
FIG. 1 is a schematic block diagram of an LED backlight driving power supply in the prior art;
FIG. 2 is a schematic block diagram of a power supply system with multiple outputs according to an embodiment of the present invention;
FIG. 3A is a schematic block diagram illustrating a first embodiment of a current control circuit in a power system with multiple outputs, in accordance with an embodiment of the present invention;
fig. 3B is a waveform diagram illustrating the operation of the current control circuit in the power supply system with multiple outputs shown in fig. 3A when the current control circuit simultaneously has the analog dimming signal and the PWM dimming signal;
FIG. 4 is a schematic block diagram illustrating a second embodiment of a current control circuit in a power system with multiple outputs in accordance with an embodiment of the present invention;
FIG. 5 is a schematic block diagram illustrating a third embodiment of a current control circuit in a power system with multiple outputs in accordance with an embodiment of the present invention;
FIG. 6A is a schematic block diagram of a voltage control circuit of a power system with multiple outputs according to an embodiment of the invention;
FIG. 6B is a waveform diagram illustrating the operation of the voltage control circuit in the power system with multiple outputs shown in FIG. 6A during analog dimming;
FIG. 7A is a schematic block diagram of a reference voltage generating circuit in a power system with multiple outputs according to an embodiment of the present invention;
fig. 7B is a waveform diagram showing an operation of the voltage control circuit having the reference voltage generation circuit shown in fig. 7A at the time of PWM dimming.
Detailed Description
Several preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited to only these embodiments. The invention is intended to cover alternatives, modifications, equivalents, and alternatives that may be included within the spirit and scope of the invention. In the following description of the preferred embodiments of the present invention, specific details are set forth in order to provide a thorough understanding of the present invention, and it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
Referring to fig. 2, a schematic block diagram of a power supply system with multiple outputs according to an embodiment of the invention is shown. In this embodiment, the power supply system 200 includes two outputs, wherein one output signal is a voltage-type signal and the other output signal is a current-type signal.
The power supply system 200 includes an input circuit, a first output circuit, a second output circuit, a current control circuit, a buck switching regulator, and a voltage control circuit. Wherein,
Each of the first output circuit and the second output circuit comprises a secondary side winding coupled with the primary side winding, and a rectifier diode and an output capacitor which are sequentially connected in series at two ends of the primary side winding, so that a power stage circuit with a flyback topology is formed by the primary side winding and the first power switch tube in the input circuit.
For example, in this embodiment, the second output circuit includes a primary side winding NpCoupled secondary winding VS2A rectifier diode D2 and an output capacitor C2, thereby generating an output voltage V2 at the output capacitor C2.
The buck switching regulator 201 is connected to the output terminal of the second output circuit to receive the output voltage V2 and is controlled to be turned on and off according to the control voltageOutput voltage V of off regulator 201OUTAnd is maintained constant.
In this embodiment, the first output circuit is used to drive an LED load 204 composed of two LED strings. Similarly, the first output circuit includes a primary side winding NpCoupled secondary winding VS1A rectifier diode D1 and an output capacitor C1, thereby generating an output voltage V1 at the output capacitor C1 to provide a power supply to the LED load.
The current control circuit 202 receives the analog dimming signal and the PWM dimming signal to control the LED load 104 to have a brightness corresponding to the analog dimming signal and the PWM dimming signal. The current through the LED load 204 is controlled according to the analog dimming signal to adjust the brightness of the LED load 204. The ratio of the switching time of the LED load 204 is controlled according to the PWM dimming signal to adjust the brightness of the LED load 204. Therefore, the power supply system with multiple outputs according to the embodiment of the invention can simultaneously support analog dimming and PWM dimming.
The voltage control circuit 203 is based on the output voltage V of the second output circuit2And the negative terminal voltage V of the LED load 204LEDTo generate a corresponding feedback signal VFBAnd according to the feedback signal VFBGenerating a corresponding drive signal VG1To control the first power switch tube QT1The switch state of (1). Then, the feedback signal VFBCan be transmitted to the primary side control circuit 206 through the optical coupler circuit 205 to generate the driving signal VG1。
Specifically, when the output voltage of the second output circuit needs to be adjusted more, the voltage control circuit controls the switching state of the first power switch tube according to the output voltage of the second output circuit, so that the output voltage of the second output circuit is kept constant.
When the output voltage of the second output circuit needs more regulation, the voltage control circuit adjusts the output voltage according to the voltage V at the negative terminal of the LED load 204LEDControlling the switching state of the first power switch tubeTo maintain a constant voltage at the negative terminal of the LED load.
First power switch tube QT1On and off periodically, the output voltage V of the second output circuit being transferred by energy between the primary side winding and the secondary side winding2An input voltage is provided to buck switching regulator 201. At the same time, the output voltage V of the first output circuit1The LED load 204 is provided with a driving voltage.
In this control method, although a stable output voltage can be obtained by the step-down switching regulator, the feedback signal can represent information of both the output voltage of the second output circuit and the negative terminal voltage of the LED load, and therefore, the fluctuation of the output voltage of the second output circuit can be reduced by controlling the output voltage of the second output circuit, and the operation stability thereof can be improved. On the other hand, through the control of the voltage of the negative terminal of the LED load, the output voltage V1 of the first output circuit can be ensured to be maintained at the minimum value required by driving the LED load, and therefore the conversion efficiency of the circuit is greatly improved.
Here, the circuit structure and the control manner of the buck switching regulator 201 may be set in any suitable manner, and the specific implementation and the control principle thereof will not be described in detail herein.
The following describes an implementation of the current control circuit according to the present invention in detail with reference to specific embodiments.
Referring to fig. 3A, a schematic block diagram of a first embodiment of a current control circuit in a power supply system with multiple outputs according to an embodiment of the present invention is shown.
In this embodiment, only one LED string 204-1 is shown, and for an LED load with multiple LED strings, each LED string is controlled in the same manner as the LED string 204-1, and will not be further described herein.
In this embodiment, the current control circuit includes an analog dimming control circuit and a PWM dimming control circuit. Analog dimming control circuitA linear regulation circuit is used. Specifically, the linear regulating circuit comprises a second power switch tube Q connected between the negative end of the LED lamp string and the ground potential in seriesT2And a resistance R1And an operational amplifier 301. The output signal of the output terminal of the operational amplifier 301 is used to control the second power switch tube QT2In a state where the inverting input terminal is connected to the second power switching tube QT2And a resistance R1A non-inverting input terminal receiving a reference voltage V representing the analog dimming signalREF1. Here, the second power switch tube QT2For example, the output terminal of the operational amplifier 301 is connected to the second power switch QT2The drain of the resistor R1 is connected to the negative terminal of the LED string 204-1, and the resistor R1 is connected to the second power switch tube QT2Between the source of (a) and ground potential; the inverting input terminal of the operational amplifier 301 is connected to the resistor R1 and the second power switch QT2Is connected to the source of (1). Due to the virtual short principle of the operational amplifier, the current on the resistor R1 is forced to the reference voltage VREF1And the resistance value of the resistor R1. Thus, the analog dimming signal enables adjustment of the current through the LED light string 204, and thus the brightness of the LED light string.
Wherein, the analog dimming signal can be converted into the reference voltage V in a filtering mannerREF1. The embodiment shown in fig. 3A illustrates one implementation. Analog dimming signal passes through buffers BF connected in series in sequence1Resistance RFAnd a capacitor CFThen in the capacitor CFGenerates a reference voltage V acrossREF1。
The PWM dimming control circuit may be implemented by a switching circuit. The switch circuit is connected with the output voltage V1 of the first output circuit, the LED lamp string 204-1 and the second power switch tube QT2Resistance R1And ground potential. The PWM dimming control signal controls the on-off state of the switch circuit according to the PWM dimming control signal, thereby adjusting the ratio of the switching time of the power supply circuit containing the LED lamp string 204-1, through which current flows, to realize the PWM dimming signalControl of brightness of LED string lights.
In the embodiment shown in fig. 3A, the switching circuit includes a controllable switch S1. Here, the controllable switch S1 is connected between the output voltage V1 of the first output circuit and the positive terminal of the LED string 204-1. The switching state of the controllable switch S1 is controlled by the PWM dimming control signal. When the PWM dimming signal is at a high level, the controllable switch S1 is turned on, the power supply circuit is turned on, and the current flows through the LED string 204-1; when the PWM dimming signal is low, the controllable switch S1 is turned off, the power supply circuit is turned off, and no current flows through the LED string 204-1. Of course, although not shown in the figure, those skilled in the art can understand that the PWM dimming signal can be converted into a driving signal by a certain driving circuit, and then drives the controllable switch S1. The implementation and connection of the switch circuit is not limited to the embodiment shown in fig. 3, for example, the switch circuit may be located at the negative end of the LED string and the second power switch QT2Between the first power switch tube Q and the second power switch tube QT2And a resistance R1Can also be positioned in the resistor R1And ground potential, and can be positioned between the output end of the operational amplifier 301 and the second power switch tube QT2In the meantime.
By the current control circuit according to the embodiment of the present invention shown in fig. 3, both analog dimming and PWM dimming, or only analog dimming, or only PWM dimming, can be realized. When only the analog dimming is performed, the switch circuit is always kept in a closed state. When only PWM dimming is performed, the reference voltage VREF1An appropriate value may be set.
Referring to fig. 3B, an operation waveform diagram of the current control circuit in the power supply system with multiple outputs shown in fig. 3A when the current control circuit has both the analog dimming signal and the PWM dimming signal is shown. Wherein the dimming signal is simulated here as a converted current signal I corresponding theretoREFTo indicate.
From time t0To time t1Since the PWM dimming signal is maintained at a low level, the PWM dimming signal can be combined with the schematic block diagram shown in fig. 3AThe control switch S1 is in the OFF state so that no current flows through the LED string 204-1 and so that the current I flows through the LEDsLEDIs zero.
From time t1To time t2The PWM dimming signal is maintained at a high level, so the controllable switch S1 is always in a closed state, and the current I flowing through the LEDLEDAnd a current signal IREFAnd (5) the consistency is achieved.
From time t2To time t3Current signal IREFThe PWM dimming signal remains high and the controllable switch S1 is therefore in a closed state. Thus, the current I flowing through the LEDLEDThe current value at time t2 is maintained.
From time t3To time t4Current signal IREFThe PWM dimming signal remains low, and the controllable switch S1 is therefore in the off state. Current I through the LEDLEDMaintained at a value of zero.
And adjusting the brightness of the LED load through the current control circuit according to the analog dimming signal and the PWM dimming signal in a circulating way.
Referring to fig. 4, a schematic block diagram of a second embodiment of a current control circuit in a power supply system with multiple outputs according to an embodiment of the present invention is shown.
In this embodiment, the current control circuit includes an analog dimming control circuit and a PWM dimming control circuit. Here, the analog dimming control circuit employs a switching type adjusting circuit. Specifically, the switching regulator circuit 404 includes an error operation and compensation circuit 401, a PWM control circuit 402, and a power stage circuit 403.
The error calculation and compensation circuit 401 receives a reference voltage V representing the analog dimming signalREF1And a detection signal V representing the current LED load drive currentSENSEAnd performing error operation and compensation operation on the two signals to generate a compensation signal V representing error information between the two signalsCOMP。
The PWM control circuit 402 receives the compensation signal VCOMPGenerating a corresponding control signal VCTRL。
The input voltage of the power stage circuit 403 is the output voltage V of the first output circuit1Control signal VCTRLRegulating the output current I at the output terminal by controlling the switching state of the power switch in the power stage circuit 403OUTAnd provides a driving current to the LED string 204-1, so that the LED string has a brightness corresponding to the analog dimming signal.
Similar to the embodiment shown in fig. 3, the analog dimming signal can be converted into the reference voltage V by filteringREF1。
The PWM dimming control circuit may be implemented by a switching circuit. The switching circuit is connected to the output of the switching regulator circuit 404, the LED string and ground potential. The on-off state of the switch circuit is controlled according to the PWM dimming control signal, so that the ratio of the switching time of the power supply circuit containing the LED lamp string 204-1, through which current flows, is adjusted, and the control of the brightness of the LED lamp string by the PWM dimming signal is realized.
In the embodiment shown in fig. 4, the switching circuit comprises a controllable switch S1. Here, the controllable switch S1 is connected between the negative terminal of the LED string 204-1 and the point potential. The switching state of the controllable switch S1 is controlled by the PWM dimming control signal. The operating principle of the switching circuit is similar to the embodiment shown in fig. 3A. The implementation and connection of the switching circuit is not limited to the embodiment shown in fig. 4, for example, the switching circuit may be located between the positive terminal of the LED string and the output terminal of the switching regulator circuit.
Similarly, with the current control circuit according to the embodiment of the present invention shown in fig. 4, both analog dimming and PWM dimming, or only analog dimming, or only PWM dimming, can be implemented. When only the analog dimming is performed, the switch circuit is always kept in a closed state. When only PWM dimming is performed, the reference voltage VREF1An appropriate value may be set.
Referring to fig. 5, a schematic block diagram of a third embodiment of a current control circuit in a power supply system with multiple outputs according to an embodiment of the present invention is shown.
In this embodiment, similar to the embodiment shown in fig. 4, the analog dimming control circuit remains a switching type regulation circuit. In contrast, the PWM dimming control circuit includes an enable circuit 501. The PWM dimming signal is realized by enabling control of the switching type adjustment circuit 404.
The enable circuit 501 receives the PWM dimming signal to generate a corresponding enable signal EN. The enable signal EN is used to control the operating state of the switching regulator circuit 404. For example, when the enable signal EN is at a high level, the switching regulator circuit 404 is in a normal operating state to provide a driving current for the LED string 204-1; when the enable signal EN is low, the switching regulator circuit 404 is not active and no current flows through the LED string 204-1.
The ratio of the time when the current flows through the LED lamp string is controlled by the enabling circuit according to the PWM dimming signal, so that the LED lamp string has the brightness corresponding to the PWM dimming signal.
Here, in the embodiments shown in fig. 4 and fig. 5, the switching regulator circuit may have a power stage topology with any suitable structure, and the control manner may also be any suitable current mode control mode, for example, a peak current control mode or an average current control mode, and will not be described in detail here.
The following describes a specific implementation manner of the voltage control circuit of the power supply system with multiple outputs according to the present invention in detail with reference to specific embodiments.
Referring to fig. 6A, a schematic block diagram of a voltage control circuit of a power supply system with multiple outputs according to an embodiment of the invention is shown.
In this embodiment, the voltage control circuit includes a first error operation and compensation circuit 601, a second error operation and compensation circuit 602, and a selection circuit 603. Wherein,
the first error calculation and compensation circuit 601 is used for calculating the negative end voltage V of the LED loadLEDAnd a corresponding first desired voltage VREF2Generating a first compensation signal VCOMP1。
Selecting the negative end voltage of the LED lamp string with the maximum required driving voltage for the LED load with more than one LED lamp string; then, with the first desired voltage VREF2Performing error operation, and generating a first compensation signal V after the error operation result is compensatedCOMP1Thereby enabling the output voltage V of the first output circuit1And is maintained to satisfy the minimum driving voltage of all the LED lamp strings.
Similarly, for a power system with a plurality of first output circuits, the first compensation signal V can be generated according to the negative terminal voltage of the LED string with the maximum driving voltage required in all LED stringsCOMP1。
The second error operation and compensation circuit 602 is used for calculating the output voltage V according to the second output circuit2And a corresponding second desired voltage VREF3Generating a second compensation signal VCOMP2。
For a power supply system with more than one second output circuit, the output voltage of each second output circuit corresponds to a second expected voltage or power. At this time, the output voltage V of the second output circuit with the highest second desired voltage or power is selected2And a corresponding second desired voltage VREF3Performing an error operation, and performing a compensation operation on the error operation result to obtain a second compensation signal VCOMP2。
The selection circuit 603 is connected to the output terminals of the first error operation and compensation circuit 601 and the second error operation and compensation circuit 602, respectively, to receive the first compensation signal VCOMP1And a second compensation signal VCOMP2To select one of the signals as a feedback signal VFB。
Here, the first error operation and compensation circuit 601 and the second error operation and compensation circuit 602 may be implemented by operational amplifiers, for example, EA1 and EA2, and a compensation circuit, etc. The compensation circuit can be a capacitor, or a resistor and capacitor circuit, etc. Two input ends of the operational amplifier respectively receive the voltage V of the negative endLEDAnd a corresponding first desired voltage VREF2Or the output voltage V of the second output circuit2And a corresponding second desired voltage VREF3. The selection circuit 603 can select the first compensation signal V according to the difference between the signals received at the non-inverting input terminal and the inverting input terminalCOMP1And a second compensation signal VCOMP2The smaller or the larger of the two is used as the feedback signal VFB. For example, when the non-inverting input of the operational amplifier EA1 receives the negative terminal voltage VLEDThe inverting input terminal receives a first expected voltage VREF2And the non-inverting input terminal of the operational amplifier EA2 receives the output voltage V of the second output circuit2The inverting input terminal receives a second expected voltage VREF3When the output signal of the selection circuit 603 is the first compensation signal VCOMP1And a second compensation signal VCOMP2The smaller of the two as the feedback signal VFB。
One specific implementation of the selection circuit 603 is shown in the functional block diagram of the embodiment shown in fig. 6A. The selection circuit 603 includes a diode DL1And a diode DL2. Diode DL1Is connected to the output of the first error calculation and compensation circuit 601 to receive a first compensation signal VCOMP1. Diode DL2Is connected to the output of the second error calculation and compensation circuit 602 to receive a second compensation signal VCOMP2. Diode DL1And a diode DL2Is connected to each other, the output signal of the common connection point of which is taken as the feedback signal VFB. When the first compensation signal VCOMP1Is less than the second compensation signal VCOMP2Time, diode DL1Conducting, diode DL2Turn-off, feedback signal VFBIs a first compensation signal VCOMP1. When first compensationSignal VCOMP1Greater than the second compensation signal VCOMP2Time, diode DL2Conducting, diode DL1Turn-off, feedback signal VFBFor the second compensation signal VCOMP2。
It is known to those skilled in the art that when the input signals of the non-inverting input terminal and the inverting input terminal of the operational amplifier EA1 and the operational amplifier EA2 are replaced, the output signal of the selection circuit 603 is the first compensation signal VCOMP1And a second compensation signal VCOMP2The larger of them.
According to the voltage control circuit of the embodiment of the invention, the output voltage of the second output circuit and the voltage of the negative terminal of the LED load are used as controlled signals. On one hand, the output voltage of the first output circuit is maintained to be the value of the minimum driving voltage which can sufficiently drive all the LED lamp strings through controlling the voltage of the negative end of the LED load, and the working efficiency of the circuit is improved. On the other hand, the output voltage of the second output circuit, namely the input voltage of the buck switching regulator, can be maintained to be basically constant by controlling the output voltage of the second output circuit, so that the fluctuation of the input voltage of the buck switching regulator is avoided, and the working stability of the circuit is improved.
Referring to fig. 6B, a waveform diagram of the operation of the voltage control circuit in the power supply system with multiple outputs shown in fig. 6A during analog dimming is shown. The dimming signal is here simulated as a converted current signal I corresponding theretoREFTo indicate. Waveform ILEDA waveform diagram showing the driving current flowing through the LED load. First compensation signal VCOMP1Is the negative terminal voltage V to the LED loadLEDAnd a corresponding first desired voltage VREF2And (5) carrying out error and compensation operation. Second compensation signal VCOMP2Is the voltage V2 to the second output circuit and the corresponding second desired voltage VREF3And (5) carrying out error and compensation operation.
From time t0To time t1First compensation signal VCOMP1Is less than the second complementCompensated signal VCOMP2During the time interval, the feedback signal VFBAnd a first compensation signal VCOMP1And (5) the consistency is achieved. The primary side control circuit 206 is based on the first compensation signal VCOMP1To generate a corresponding control signal to regulate the negative terminal voltage V of the LED loadLED. At this time, the negative terminal voltage V of the LED loadLEDAnd a first desired voltage VREF2And the consistency is maintained. Although the output voltage V2 of the second output circuit has a small fluctuation, a stable output voltage can be obtained at the output terminal by the regulation of the step-down switching regulator.
From time t1To time t2First compensation signal VCOMP1Greater than the second compensation signal VCOMP2During the time interval, the feedback signal VFBAnd a second compensation signal VCOMP2And (5) the consistency is achieved. The primary side control circuit 206 is based on the second compensation signal VCOMP2To generate a corresponding control signal to regulate the output voltage V2 of the second output circuit. At this time, the output voltage V2 of the second output circuit and the second desired voltage VREF3And the consistency is maintained. Negative terminal voltage V of LED loadLEDThe LED load can still maintain normal operation without bringing large negative influence to the LED load due to small fluctuation.
From time t2Then, the first compensation signal VCOMP1Greater than the second compensation signal VCOMP2Feedback signal VFBAnd a second compensation signal VCOMP2And (5) the consistency is achieved.
In an LED drive circuit with PWM dimming, a primary side winding N is switched to a high level in a small period of time when a PWM dimming signal starts a low level transitionpThe energy stored in the secondary side is mostly transferred to the secondary side winding Ns2Voltage V of the second output loop2A sharp rise, resulting in a negative terminal voltage V of the LED loadLEDThe voltage LED at the negative terminal of the LED load will drop sharply and possibly to zero, and the voltage LED at the negative terminal of the LED load will take a long time to recover to a steady state, and the dynamic response speed of the system is slow.
Therefore, in order to further improve the dynamic response speed and stability of the power system with multiple outputs, the voltage control circuit according to the embodiment of the invention further comprises a reference voltage generating circuit for generating the second expected voltage V according to the output voltage of the second output circuitREF3。
Referring to fig. 7A, a schematic block diagram of a reference voltage generating circuit in a power system with multiple outputs according to an embodiment of the invention is shown.
In this embodiment, the reference voltage generating circuit includes a memory circuit 701, a selection circuit 702, and a clamp circuit 703. The storage circuit 701 is configured to store energy according to the received output voltage V2 of the second output circuit during an active time interval of the PWM dimming signal, for example, during a time interval when the PWM dimming signal is at a high level, so as to generate a storage voltage VCF. The selection circuit 702 is connected to the output terminal of the memory circuit 701 and the voltage source VFTo receive a storage voltage VCFAnd a voltage source VF(ii) a The output signal of the output terminal is a storage voltage VCFAnd a voltage source VFThe larger of the two. The clamp circuit 703 is connected to the output terminal of the selection circuit 702 and has a clamp voltage VCLAMP. When the value of the output signal at the output of the selection circuit 702 exceeds the clamp voltage VCLAMPAt this time, the output signal of the output terminal of the selection circuit 702 is clamped to the clamp voltage VCLAMP. The output signal of the output terminal of the selection circuit 702 is used as the second desired voltage VREF3。
The embodiment shown in fig. 7A exemplifies one implementation of the memory circuit 701, the selection circuit 702, and the clamp circuit 703.
Wherein the memory circuit 701 comprises a series connection of controllable switches SFAnd a storage capacitor CFTo receive the output voltage V2 of the second output circuit. Controllable switch SFIs associated with the PWM dimming signal. Controllable switch SFAnd a storage capacitor CFAs a storage voltage VCF。
The selection circuit 702 includes a diode DH1And a diode DH2. Diode DH1Is connected to an output of the memory circuit 701 to receive a memory voltage VCFThe cathode is connected to a diode DH2A cathode of (a); diode DH2Is connected to a voltage source VF. When storing the voltage VCFGreater than voltage source VFTime, diode DH1Conducting, diode DH2Off, the output signal of the selection circuit 702, i.e. diode DH1And a diode DH2The output signal of the common connection point is a storage voltage VCF. When storing the voltage VCFLess than voltage source VFTime, diode DH2Conducting, diode DH1Is turned off, the output signal of the selection circuit 702 is the voltage source VF。
The clamping circuit 703 includes a voltage regulator tube DCWith its cathode connected to the output of the selection circuit 702 and its anode connected to ground potential. When the value of the output signal of the selection circuit 702 is larger than the voltage regulator tube DCIs clamped to voltage VCLAMPWhen the value of the output signal of the selection circuit 702 is clamped to the clamp voltage VCLAMP。
When the value of the output signal of the output end of the selection circuit is less than the clamping voltage VCLAMPTime, second desired voltage VREF3The value of (a) is the value of the output signal of the output terminal of the current selection circuit; when the value of the output signal of the output end of the selection circuit is larger than the clamping voltage VCLAMPTime, second desired voltage VREF3Is a clamping voltage VCLAMPThe numerical value of (c).
By a second desired voltage V in a feedback loop to the output voltage of the second output circuitREF3Such that the primary side winding N is switched from a low level to a high level during a start period of the PWM dimming signalpThe energy can be evenly transferred to the second output circuit and the first output circuit, and the negative terminal voltage V of the LED load is avoidedLEDIs sharply fluctuated, quickens the voltage controlThe dynamic response of the circuit is controlled.
Referring to fig. 7B, an operation waveform diagram of the voltage control circuit having the reference voltage generation circuit shown in fig. 7A at the time of PWM dimming is shown.
From time t0 to time t1, the PWM dimming signal is maintained at high level, and the switch S is controlledFClosed, voltage V2 vs. capacitance CFCharging is carried out, and the voltage V is storedCFContinuously increasing by a value greater than the voltage source VFThe numerical value of (c). The voltage control circuit is based on the voltage V at the negative terminal of the LED loadLEDAnd a first desired voltage VREF2To generate a control signal by applying a voltage to the first power switch QT1To the negative terminal voltage VLEDMaintained substantially constant.
From time t1 to time t2, the PWM dimming signal changes from high to low, and the switch S is controlledFAnd (6) turning off. Due to the storage voltage VCFIs greater than the voltage source VFAnd is less than the clamping voltage VCLAMPOf the second desired voltage V, and thus the second desired voltage VREF3Is maintained at the storage voltage V at time t2CFThe numerical value of (c). The voltage control circuit is based on the output voltage V2 of the second output circuit and the second expected voltage VREF3To generate a control signal by applying a voltage to the first power switch QT1To maintain the output voltage V2 substantially constant.
By applying a second reference voltage VREF3Adaptive adjustment of the value of (c), it can be seen that the negative terminal voltage V of the LED loadLEDThe fluctuation of the system is gradually reduced, the system can quickly enter a stable state, and the dynamic response of the system is improved.
It should be noted that the devices with the same names in the embodiments of the present invention have the same functions, and the embodiments with improved practicability can be combined with the above related embodiments, but only have been illustrated on the basis of the previous embodiment. The configuration of the circuit and sampling of signals include, but are not limited to, the forms disclosed above as long as the invention can be implementedThe function of the related circuits described in the embodiments is as follows, e.g. voltage V2, voltage VLEDOr the resistance voltage-dividing circuit can be used for sampling and then carrying out subsequent operation. Therefore, the related modifications made by those skilled in the art on the basis of the circuits disclosed in the embodiments of the present invention are also within the scope of the embodiments of the present invention.
While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.
Claims (13)
1. A power supply system with multiple outputs is characterized by comprising an input circuit, m first output circuits, n second output circuits, m current control circuits, n buck switching regulators and a voltage control circuit, wherein n is a natural number not less than 1, m is a natural number not less than 1,
the input circuit comprises a primary side winding and a first power switch tube;
one end of the primary side winding receives direct-current input voltage, and the other end of the primary side winding is connected with the first power switch tube;
each of the first output circuit and the second output circuit includes a secondary side winding, a rectifying circuit, and a filter circuit connected in series;
the n buck switching regulators are connected with the n second output circuits in a one-to-one correspondence manner and used for receiving the output voltage of the second output circuits and controlling the output voltage of the buck switching regulators to be kept constant;
each first output circuit is used for driving an LED load consisting of one or more paths of LED lamp strings; the current control circuit is used for controlling the driving current of the LED load according to an analog dimming signal and/or a PWM dimming signal to obtain the brightness corresponding to the dimming signal;
the voltage control circuit is used for controlling the switching state of the first power switch tube according to the output voltage of the second output circuit and the voltage of the negative end of the LED load;
when the voltage control circuit is in a first working state, the voltage control circuit controls the switching state of the first power switching tube according to the output voltage of the second output circuit so as to keep the output voltage of the second output circuit constant;
and in a second working state, the voltage control circuit controls the switching state of the first power switch tube according to the voltage of the negative end of the LED load so as to keep the voltage of the negative end of the LED load constant.
2. The power supply system with multiple outputs of claim 1, wherein the voltage control circuit comprises a first error operation and compensation circuit corresponding to the LED light string and a second error operation and compensation circuit corresponding to the second output circuit; the first error operation and compensation circuit is used for generating a first compensation signal according to the error between the negative end voltage of the LED lamp string and the corresponding first expected voltage; the second error operation and compensation circuit is used for generating a second compensation signal according to the error between the output voltage of the second output circuit and the corresponding second expected voltage.
3. The power supply system with multiple outputs according to claim 2, wherein the voltage control circuit comprises a first selection circuit for receiving the first compensation signal and the second compensation signal and using a minimum value or a maximum value of the first compensation signal and the second compensation signal as a feedback signal.
4. The power supply system with multiple outputs according to claim 3, further comprising an optocoupler circuit and a primary side control circuit located on the primary side;
the optical coupling circuit transmits the feedback signal to the primary side control circuit;
and the primary side control circuit generates a corresponding control signal according to the feedback signal to control the switching state of the first power switching tube.
5. The power supply system with multiple outputs according to claim 2, wherein the voltage control circuit further comprises a reference voltage generating circuit for adjusting the second desired voltage according to the output voltage of the second output circuit;
the reference voltage generating circuit includes a memory circuit, a second selection circuit, and a clamp circuit, wherein,
the storage circuit is used for receiving the output voltage of the second output circuit and storing energy to generate a storage voltage when the PWM dimming signal is at a high level;
the selection circuit receives the storage voltage and a voltage source, and the output signal of the selection circuit is the larger of the storage voltage and the voltage source;
the clamping circuit comprises a clamping voltage, and when the value of the output signal of the selection circuit is smaller than the clamping voltage, the second expected voltage is the output signal of the selection circuit; when the value of the output signal of the selection circuit is greater than the clamping voltage, the second desired voltage is the clamping voltage.
6. The power supply system with multiple outputs of claim 5, wherein the storage circuit comprises a controllable switch and a capacitor, and the PWM dimming signal is used to control the switching state of the controllable switch.
7. The power supply system with multiple outputs of claim 1, wherein the current control circuit comprises an analog dimming control circuit and a PWM dimming control circuit.
8. The power supply system with multiple outputs of claim 7, wherein the analog dimming control circuit comprises a linear regulation circuit, and the PWM dimming control circuit comprises a switching circuit; the analog dimming signal is used for adjusting a reference source of the linear adjusting circuit; the PWM dimming signal is used for controlling the on-off state of the switch circuit so as to periodically turn on and off the LED lamp string.
9. The multi-output power supply system according to claim 8, wherein the switch circuit is connected in series between the output terminal of the first output circuit and the power supply loop formed by the LED string.
10. The power supply system with multiple outputs according to claim 8, wherein the switching circuit is connected in series between the output of the operational amplifier of the linear regulating circuit and the controllable switch of the linear regulating circuit.
11. The multi-output power supply system according to claim 7, wherein the analog dimming control circuit comprises a switching regulator circuit, and the switching regulator circuit receives the analog dimming signal and the current driving current of the LED light string to regulate the output current of the switching regulator circuit.
12. The multi-output power supply system according to claim 11, wherein the PWM dimming control circuit is connected in series to the output terminal of the first output circuit, the switching regulator circuit and the LED light string to control the on/off state of the switching circuit, so as to periodically turn on and off the LED light string.
13. The multi-output power supply system according to claim 11, wherein the PWM dimming signal is used to control an enable state of the switching regulator circuit to periodically turn on and off the LED light string.
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| CN 201310446759 CN103476184A (en) | 2013-09-26 | 2013-09-26 | Power system with multiplexed output |
| CN201410083882.2A CN103857152B (en) | 2013-09-26 | 2014-03-07 | There is the power-supply system of multiple-channel output |
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| CN 201310446759 CN103476184A (en) | 2013-09-26 | 2013-09-26 | Power system with multiplexed output |
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| CN103857152B (en) | 2016-08-17 |
| CN103857152A (en) | 2014-06-11 |
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Application publication date: 20131225 |