CN114710856B - Switch circuit and LED driving circuit - Google Patents
Switch circuit and LED driving circuit Download PDFInfo
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- CN114710856B CN114710856B CN202111404169.XA CN202111404169A CN114710856B CN 114710856 B CN114710856 B CN 114710856B CN 202111404169 A CN202111404169 A CN 202111404169A CN 114710856 B CN114710856 B CN 114710856B
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- 238000005070 sampling Methods 0.000 claims abstract description 133
- 238000001914 filtration Methods 0.000 claims abstract description 27
- 239000003990 capacitor Substances 0.000 claims description 27
- 230000003321 amplification Effects 0.000 claims description 12
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 12
- 238000001514 detection method Methods 0.000 claims description 10
- 238000010586 diagram Methods 0.000 description 7
- 230000001939 inductive effect Effects 0.000 description 6
- 238000000034 method Methods 0.000 description 4
- 230000010354 integration Effects 0.000 description 2
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- 230000009286 beneficial effect Effects 0.000 description 1
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- 238000006243 chemical reaction Methods 0.000 description 1
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B45/00—Circuit arrangements for operating light-emitting diodes [LED]
- H05B45/30—Driver circuits
- H05B45/37—Converter circuits
- H05B45/3725—Switched mode power supply [SMPS]
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Abstract
The invention discloses a switch circuit and an LED driving circuit, wherein the switch circuit comprises: the power switch tube and the inductor are connected; the sampling resistor is used for sampling the instantaneous current flowing through the inductor to obtain a first sampling signal; the filtering unit is connected in parallel with the two ends of the sampling resistor and is used for outputting a second sampling signal after carrying out low-pass filtering on the first sampling signal so as to realize sampling of average current flowing through the inductor; and the control unit is used for generating a control signal for controlling the on/off of the power switch tube according to the first sampling signal and the second sampling signal so as to drive the LED. The invention can improve the control precision and linearity of the output current.
Description
Technical Field
The invention relates to the technical field of power electronics, in particular to a switching circuit and an LED driving circuit.
Background
The LED has the advantages of small volume, high brightness, low power consumption, less heat generation, long service life, rich and colorful color types and the like, and is widely applied to a plurality of fields of illumination, display and the like. In current LED driving, a switching power supply with a low power factor (for example, a power factor smaller than 0.7) is often used to drive the LED to work, wherein, a power switching tube is periodically turned on/off, so that stable output can be obtained on a load. In LED applications, there are occasions when it is necessary to adjust and control the brightness of the LED lamp, i.e. to achieve dimming by adjusting the output average current of the LED load. The brightness of the LED load can be adjusted by controlling the on/off state of the power switch tube through a dimming control circuit.
The control scheme of the switching circuit comprises a constant on-time control mode and a constant off-time control mode. Referring to the constant on-time control circuit shown in fig. 1 and the constant off-time control circuit shown in fig. 2, the two existing control modes are mainly that a sampling resistor Rs is arranged in a switch circuit, a voltage signal V1 at two ends of the sampling resistor Rs is directly sampled to serve as an output voltage feedback signal, the output voltage feedback signal and a reference voltage signal Vref are subjected to operation amplifier U1 and compensation unit 1 to obtain a current reference signal, the current reference signal is compared with a sampling signal representing an inductance current (marked as I L) in a comparator U2, and then the control signal vgs_q1 for controlling the power switching tube Q1 to be turned off is generated after the conversion of a logic circuit. The magnitude of the reference voltage signal Vref is adjusted by the dimming signal to adjust the magnitude of the output current, thereby realizing the dimming function.
However, the existing dimming scheme cannot sample the negative value of the inductor current I L, but in the discontinuous mode (DCM) of the inductor current of the switching circuit, the inductor current I L in the circuit resonates to the negative value, referring to fig. 3, when the on time of the power switching transistor Q1 in the next period occurs at a different position after the resonance (for example, corresponds to a different time within the period of t1-t5 in fig. 3), if the negative value is not sampled into the closed-loop current loop, the control error of the output current, that is, the output current deviates from the set value, and in addition, the case of non-linearity of the average current of the output current may also occur. For this case. In the prior art, no countermeasure is generally taken or simple processing is to forcedly control the power switch tube Q1 to conduct at the valley position of the waveform of the drain-source voltage Vds_Q1 (forcedly conducting at the valley for short), the forceful conducting at the valley does not consider the continuous change of the inductive current I L, so that the problem of nonlinearity of the output current can be avoided, but the forceful conducting at the valley possibly brings low-frequency jitter of the output current, so that a forceful jitter frequency mechanism is needed to be added in a circuit for preventing the low-frequency jitter, the condition of low-frequency jitter is ensured not to occur, the control mode is complex, and the cost is high.
Accordingly, there is a need to provide an improved solution to overcome the above technical problems in the prior art.
Disclosure of Invention
In order to solve the technical problems, the invention provides the switch circuit and the LED driving circuit, which can eliminate the influence of negative pressure sampling on sampling precision, improve the control precision and linearity of output current output by the circuit, and simultaneously can not influence instantaneous control of inductance current, and the method is simple and easy to realize.
According to a first aspect of the present invention, there is provided a switching circuit comprising: the power switch tube and the inductor are connected;
The sampling resistor is used for sampling the instantaneous current flowing through the inductor to obtain a first sampling signal;
the filtering unit is used for outputting a second sampling signal after carrying out low-pass filtering on the first sampling signal so as to realize sampling of average current flowing through the inductor;
And the control unit is used for generating a control signal for controlling the on/off of the power switch tube according to the first sampling signal and the second sampling signal.
Optionally, the filtering unit is an RC filtering unit, and includes a first resistor and a first capacitor;
the first resistor and the first capacitor are connected in series and then connected with the sampling resistor in parallel, and a connecting node of the first resistor and the first capacitor outputs the second sampling signal.
Optionally, the control unit includes:
and the reference current generation circuit is used for converting the second sampling signal into a current signal and integrating the converted current signal to generate a current reference signal for controlling the inductance current.
Optionally, the reference current generating circuit includes:
the input end of the transconductance amplifier receives the second sampling signal, and the output end of the transconductance amplifier outputs a converted current signal;
and the second resistor and the second capacitor are sequentially connected in series between the output end of the transconductance amplifier and the reference ground, and integrate the converted current signal to generate the current reference signal.
Optionally, the control unit includes:
An operational amplification circuit configured to perform differential operation on the second sampling signal and a reference voltage signal;
And the compensation unit is configured to compensate the operation result of the operational amplification circuit so as to generate a current reference signal for controlling the inductance current.
Optionally, the control unit further includes:
and the comparison circuit is configured to compare the current reference signal with the first sampling signal or compare the current reference signal with a preset triangular wave signal and generate a turn-off trigger signal of the power switch tube according to a comparison result.
Optionally, the control unit further includes a zero-crossing detection unit, where the zero-crossing detection unit is configured to obtain a zero-crossing time of the current on the inductor according to the first sampling signal, and generate a conduction trigger signal of the power switching tube after the zero-crossing time or a preset time from the zero-crossing time.
Optionally, the triangular wave signal is provided by a signal generator, and the signal generator is configured to start providing the triangular wave signal after a zero crossing time of the current on the inductor is detected by the zero crossing detection unit.
Optionally, the control unit further includes a constant off-time control unit configured to generate the on-trigger signal of the power switching tube after receiving the fixed time of the off-trigger signal.
The invention also provides an LED driving circuit, which comprises a power switch tube and an inductor which are connected;
The sampling resistor is used for sampling the instantaneous current flowing through the inductor to obtain a first sampling signal;
the filtering unit is used for outputting a second sampling signal after carrying out low-pass filtering on the first sampling signal so as to realize sampling of average current flowing through the inductor;
and the control unit is used for generating a control signal for controlling the on/off of the power switch tube according to the first sampling signal and the second sampling signal so as to drive the LED.
Optionally, the filtering unit is an RC filtering unit, and includes a first resistor and a first capacitor;
the first resistor and the first capacitor are connected in series and then connected with the sampling resistor in parallel, and a connecting node of the first resistor and the first capacitor outputs the second sampling signal.
Optionally, the control unit includes:
and the reference current generation circuit is used for converting the second sampling signal into a current signal and integrating the converted current signal to generate a current reference signal for controlling the inductance current.
Optionally, the reference current generating circuit includes:
the input end of the transconductance amplifier receives the second sampling signal, and the output end of the transconductance amplifier outputs a converted current signal;
and the second resistor and the second capacitor are sequentially connected in series between the output end of the transconductance amplifier and the reference ground, and integrate the converted current signal to generate the current reference signal.
Optionally, the control unit includes:
An operational amplification circuit configured to perform differential operation on the second sampling signal and a reference voltage signal;
And the compensation unit is configured to compensate the operation result of the operational amplification circuit so as to generate a current reference signal for controlling the inductance current.
Optionally, the control unit further includes:
and the comparison circuit is configured to compare the current reference signal with the first sampling signal or compare the current reference signal with a preset triangular wave signal and generate a turn-off trigger signal of the power switch tube according to a comparison result.
The beneficial effects of the invention at least comprise: according to the switch circuit and the LED driving circuit, the sampling resistor is arranged in the switch circuit or the LED driving circuit, the instantaneous value of the inductance current can be sampled, meanwhile, the filtering units are connected in parallel at the two ends of the sampling resistor, the negative value part of the inductance current in the DCM working mode can be smoothed and even filtered through the filtering of the sampling signal of the sampling resistor, the sampling of the average current of the inductance is realized, the influence of negative pressure sampling on the sampling precision is overcome, the problem that the output current of the circuit is nonlinear is avoided without forced valley conduction setting, the control precision and the linearity of the output current of the circuit are improved, the instantaneous control of the inductance current cannot be influenced, and the method is simple and easy to realize.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Drawings
FIG. 1 is a schematic diagram showing the structure of a switch circuit in a conventional constant on-time control mode;
FIG. 2 is a schematic diagram showing the structure of a switch circuit in a constant off-time control mode according to the prior art;
FIG. 3 shows a schematic diagram of a timing waveform of a portion of signals in a switching circuit;
Fig. 4 is a schematic diagram showing the structure of a switching circuit in a constant off-time control mode according to a first embodiment of the present invention;
fig. 5 is a schematic diagram showing the structure of a switching circuit in a constant on-time control mode according to a first embodiment of the present invention;
fig. 6 is a schematic diagram showing the structure of a switching circuit in a constant off-time control mode according to a second embodiment of the present invention;
fig. 7 is a schematic diagram showing a configuration of a switching circuit in a constant on-time control mode according to a second embodiment of the present invention.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. The invention may, however, be embodied in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
As shown in fig. 4 and 5, a switching circuit according to a first embodiment of the present invention includes, as an example, a step-down circuit including: input capacitance Ci, output capacitance Co, power switch Q1, inductance L, diode D1, sampling resistor Rs, filter unit 10, and control unit 20.
The drain of the power switch tube Q1 is connected with the input end of the circuit to receive the input voltage Vin, the gate of the power switch tube Q1 is connected with the control unit 20, the source of the power switch tube Q1 is connected with the first output end of the circuit via the inductor L, the power switch tube Q1 receives the input voltage Vin and is turned on/off based on the control signal provided by the control unit 20, and then an output voltage Vo is generated between the first output end and the second output end of the circuit to provide an output current for a load. In one possible embodiment, the power switch Q1 is an NMOS field effect transistor.
The diode D1 is a freewheeling diode, the cathode of which is connected to the source of the power switch Q1, and the anode of which is connected to the ground.
The input capacitor Ci is connected between the drain of the power switch Q1 and the reference ground, and is used for filtering the input voltage Vin. The output capacitor Co is connected between the first output terminal and the second output terminal of the switching circuit.
The sampling resistor Rs is connected in series in the output loop of the switching circuit, and specifically, the sampling resistor Rs is connected between the second output end of the switching circuit and the reference ground, and is used for sampling the instantaneous current flowing through the inductor L to obtain a first sampling signal V1.
The filtering unit 10 is connected in parallel to two ends of the sampling resistor Rs, and is configured to receive the first sampling signal V1, and output a second sampling signal V2 after performing low-pass filtering on the first sampling signal V1, so as to sample an average current flowing through the inductor L (i.e. an average value of output currents of the circuit).
Illustratively, the filtering unit 10 disclosed in the embodiment of the present invention includes at least one stage of RC filtering unit, where each stage of RC filtering unit includes a first resistor R1 and a first capacitor C1. For example, taking a one-stage RC filter unit as an example, the first resistor R1 and the first capacitor C1 are connected in series and then connected in parallel to the sampling resistor Rs, and the filter unit 10 receives the first sampling signal V1 at a connection node between the first resistor R1 and the sampling resistor Rs, and outputs the second sampling signal V2 at a connection node between the first resistor R1 and the first capacitor C1. Based on the working principle of the RC filter unit, the negative part of the inductance current I L can be smoothed or even filtered by reasonably setting the resistance value of the first resistor R1 and the capacitance value of the first capacitor C1 in the RC filter unit, so that the average current of the inductance L can be sampled. When the resistance value of the first resistor R1 and the capacitance value of the first capacitor C1 are set, a larger value is not required to be selected, and only the negative value of the inductor current I L is required to be filtered out, so that the circuit cost is reduced.
The invention is based on the sampling resistor Rs and the filtering unit 10, and can simultaneously realize the sampling of the instantaneous value and the average value of the inductive current I L in each switching period, wherein the first sampling signal V1 which is obtained based on the sampling resistor Rs and characterizes the instantaneous value of the inductive current I L can be used for realizing the control of the instantaneous value of the inductive current I L which is the instantaneous current of the inductance L, such as the zero-crossing detection of the inductive current, the peak value control of the inductive current and the like; the second sampling signal V2, which is obtained based on the filtering unit 10 and represents the average value of the inductor current I L, can overcome the problem of sampling the negative value of the inductor current I L in the switching circuit because the average current of the inductor L is insensitive to time, thereby eliminating the influence of negative pressure sampling on the sampling precision, so that the invention does not need to perform forced valley conduction control on the power switching tube Q1, can also avoid the problem of nonlinear output current of the circuit, and improves the control precision and linearity of the output current of the circuit.
The control unit 20 is configured to generate a control signal vgs_q1 for controlling the on/off of the power switching transistor Q1 according to the first sampling signal V1, the second sampling signal V2 and the reference voltage signal Vref.
Alternatively, referring to fig. 4, the control unit 20 may be configured to implement on and off control of the power switching transistor Q1 in a constant off-time control manner. At this time, the control unit 20 further includes: an operational amplification circuit U1, a compensation unit 1, a comparison circuit U2, and a constant off-time control unit 6. The operational amplifier circuit U1 is configured to receive the second sampling signal V2 and the reference voltage signal Vref, and perform differential operation on the second sampling signal V2 and the reference voltage signal Vref; the compensation unit 1 is configured to compensate the operation result of the operational amplification circuit U2 to generate a current reference signal; the comparison circuit U2 is configured to compare the current reference signal with the first sampling signal V1, or compare the current reference signal with a preset triangular wave signal, and generate a turn-off trigger signal of the power switching tube Q1 according to a comparison result. The constant off-time control unit 6 is configured to generate an on-trigger signal of the power switching tube Q1 after a fixed time of receiving the off-trigger signal. The constant off-time control unit 6 is, for example, a delay unit or a timer unit.
Optionally, referring to fig. 5, the control unit 20 may be further configured to implement on and off control of the power switch Q1 in a constant on-time control manner. At this time, the control unit 20 further includes: an operational amplification circuit U1, a compensation unit 1, a comparison circuit U2 and a zero-crossing detection unit 3. The operational amplifier circuit U1 is configured to receive the second sampling signal V2 and the reference voltage signal Vref, and perform differential operation on the second sampling signal V2 and the reference voltage signal Vref; the compensation unit 1 is configured to compensate the operation result of the operational amplification circuit U2 to generate a current reference signal; the comparison circuit U2 is configured to compare the current reference signal with the first sampling signal V1, or compare the current reference signal with a preset triangular wave signal, and generate a turn-off trigger signal of the power switching tube Q1 according to a comparison result. The zero-crossing detection unit 3 is configured to obtain a zero-crossing time of the current on the inductor L according to the first sampling signal V1, and generate a conduction trigger signal of the power switching tube Q1 after the zero-crossing time or a preset time from the zero-crossing time. It should be noted that, the specific principle of the zero-crossing detection unit 3 for obtaining the zero-crossing time of the current on the inductor L can be understood with reference to the prior art, and the present invention will not be described in detail.
For example, when the comparison circuit U2 generates the off trigger signal of the power switching tube Q1 by comparing the current reference signal with a preset triangular wave signal, the triangular wave signal received by it may be provided by the signal generator 2. And further the signal generator 2 is configured to start providing the triangular wave signal after the zero crossing moment of the current on the inductance L is detected by the zero crossing detection unit 3 to reduce the power consumption.
The reference voltage signal Vref received by the operational amplifier circuit U1 is supplied from the reference voltage generating circuit. Alternatively, the reference voltage generating circuit may be a subunit disposed in the control unit 20, or may be a separate module disposed outside the control unit 20. When the switch circuit is applied to a lighting system, the switch circuit can provide reference voltage signals Vref with different voltage values under the control of an analog dimming signal or a digital dimming signal so as to realize the adjustment of the driving current for driving the LEDs.
Further, on the basis of the foregoing embodiment, the present invention may further provide the RS flip-flop 4 and the driver 5 in the control unit 20 to logically convert the generated on trigger signal and off trigger signal. The reset end of the RS flip-flop 4 receives the off trigger signal, the set end of the RS flip-flop 4 receives the on trigger signal, and the output end of the RS flip-flop 4 is connected with the gate of the power switch tube Q1 after passing through the driver 5, so as to provide the control signal vgs_q1 for the gate of the power switch tube Q1.
Further, as shown in fig. 6 and 7, a switching circuit according to a second embodiment of the present invention includes, as an example, a step-down circuit including: input capacitance Ci, output capacitance Co, power switch Q1, inductance L, diode D1, sampling resistor Rs, filter unit 10, and control unit 30. The circuit structure of the switch circuit disclosed in the second embodiment of the present invention is substantially the same as that of the switch circuit disclosed in the first embodiment, and the same points of the switch circuit can be understood with reference to the foregoing description of the first embodiment, and will not be repeated here.
The difference is that: the control unit 30 in the present embodiment is configured to generate a control signal for controlling the on/off of the power switch Q1 according to the first sampling signal V1 and the second sampling signal V2.
Alternatively, referring to fig. 6, the control unit 30 may be configured to implement on and off control of the power switching transistor Q1 in a constant off-time control manner. At this time, the control unit 30 further includes: a reference current generating circuit 7, a comparing circuit U2, and a constant off-time control unit 6. The reference current generating circuit 7 is configured to convert the second sampling signal V2 into a current signal, and integrate the converted current signal to generate a current reference signal; the comparison circuit U2 is configured to compare the current reference signal with the first sampling signal V1, or compare the current reference signal with a preset triangular wave signal, and generate a turn-off trigger signal of the power switching tube Q1 according to a comparison result. The constant off-time control unit 6 is configured to generate an on-trigger signal of the power switching tube Q1 after a fixed time of receiving the off-trigger signal. The constant off-time control unit 6 is, for example, a delay unit or a timer unit.
Alternatively, referring to fig. 7, the control unit 30 may be further configured to implement on and off control of the power switching transistor Q1 in a constant on-time control manner. At this time, the control unit 30 further includes: a reference current generating circuit 7, a comparing circuit U2 and a zero-crossing detecting unit 3. The reference current generating circuit 7 is configured to convert the second sampling signal V2 into a current signal, and integrate the converted current signal to generate a current reference signal; the comparison circuit U2 is configured to compare the current reference signal with the first sampling signal V1, or compare the current reference signal with a preset triangular wave signal, and generate a turn-off trigger signal of the power switching tube Q1 according to a comparison result. The zero-crossing detection unit 3 is configured to obtain a zero-crossing time of the current on the inductor L according to the first sampling signal V1, and generate a conduction trigger signal of the power switching tube Q1 after the zero-crossing time or a preset time from the zero-crossing time.
In the present embodiment, the reference current generating circuit 7 includes: the transconductance amplifier U3, the second capacitor C2 and the second resistor R2. The input end of the transconductance amplifier U3 receives the second sampling signal V2, and the output end of the transconductance amplifier U3 outputs the converted current signal. The second capacitor C2 and the second resistor R2 form a series circuit, the first end of which is connected to the output of the transconductance amplifier U3 and the second end is connected to the reference ground. In this embodiment, the voltage signals at two ends of the series circuit are current reference signals generated by integrating the converted current signals. It can be understood that the resistance value of the second resistor R2 and the capacitance value of the second capacitor C2 in the reference current generating circuit 7 should be reasonably set according to the rule of the integrating circuit and the actual integration requirement, and the second resistor R2 is used for adjusting the gain after current integration.
In the present embodiment, in the reference current generating circuit 7 provided in the control unit 30, the transconductance amplifier U3 can be utilized to convert the voltage type second sampling signal V2 into the current signal, and the second capacitor C2 is utilized to integrate the current signal to generate the current reference signal, so that the problem of output signal loss caused by rapid saturation of the operational amplifier U1 in the process of generating the current reference signal by error comparison (for example, the scheme of generating the current reference signal based on the operational amplifier U1 in the first embodiment of the present invention) can be avoided.
Further, on the basis of the foregoing embodiment, the present invention may further provide the RS flip-flop 4 and the driver 5 in the control unit 30 to logically convert the generated on trigger signal and off trigger signal. The reset end of the RS flip-flop 4 receives the off trigger signal, the set end of the RS flip-flop 4 receives the on trigger signal, and the output end of the RS flip-flop 4 is connected with the gate of the power switch tube Q1 after passing through the driver 5, so as to provide the control signal vgs_q1 for the gate of the power switch tube Q1.
Taking the switching circuit shown in fig. 4,5, 6 and 7 as an example, the control unit 20 or the control unit 30 samples the obtained first sampling signal V1 representing the instantaneous value of the inductor current I L (i.e. the output current) and the second sampling signal V2 representing the average value of the inductor current I L (i.e. the output current) output by the filtering unit 10 based on the sampling resistor RS, so as to realize accurate control of on and off of the power switching tube Q1, and further realize step-down output of the switching circuit on the input voltage Vin, that is, fig. 4,5, 6 and 7 show examples of applying the technical scheme disclosed in the application to the step-down circuit topology. It should be understood that the disclosed solution is equally applicable to boost circuit topologies. The application is not limited in this regard.
It should be noted that the switching circuit disclosed in each embodiment of the present invention may be applied to the topology field of the switching power supply, to implement a step-up or step-down topology for the switching power supply. Meanwhile, the switch circuit can be equally applied to the field of lighting systems such as LED dimming, and the switch circuit can be equivalently regarded as an LED driving circuit for driving LEDs.
In summary, the sampling resistor is arranged in the switch circuit, the sampling of the instantaneous value of the inductance current can be realized, meanwhile, the filtering units are connected in parallel at the two ends of the sampling resistor, the sampling signal of the sampling resistor is filtered, the negative value part of the inductance current can be smoothed and even filtered, the sampling of the average current of the inductance is realized, the influence of negative pressure sampling on the sampling precision is overcome, the problem of nonlinearity of the output current of the circuit can be avoided without forced valley conduction setting, the control precision and linearity of the output current of the circuit are improved, the instantaneous control of the inductance current can not be influenced, and the method is simple and easy to realize. The invention does not sample the output current but obtains the average inductor current by filtering the inductor current, and only one sampling node is needed.
Finally, it should be noted that: it is apparent that the above examples are only illustrative of the present invention and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (15)
1. A switching circuit, comprising:
the power switch tube and the inductor are connected;
The sampling resistor is used for sampling the instantaneous current flowing through the inductor to obtain a first sampling signal;
the filtering unit is used for outputting a second sampling signal after carrying out low-pass filtering on the first sampling signal so as to realize sampling of average current flowing through the inductor;
A control unit for generating a control signal for controlling the power switch tube to be turned on/off according to the first sampling signal and the second sampling signal,
Wherein the control unit includes:
an operational amplification circuit configured to perform differential operation on the second sampling signal and a reference voltage signal to generate a current reference signal;
And the comparison circuit is configured to compare the current reference signal with the first sampling signal and generate a turn-off trigger signal of the power switch tube according to a comparison result.
2. The switching circuit of claim 1, wherein the filter unit is an RC filter unit comprising a first resistor and a first capacitor;
the first resistor and the first capacitor are connected in series and then connected with the sampling resistor in parallel, and a connecting node of the first resistor and the first capacitor outputs the second sampling signal.
3. The switching circuit according to claim 1, wherein the operational amplifier circuit is replaced with a reference current generating circuit,
The reference current generation circuit is used for converting the second sampling signal into a current signal and integrating the converted current signal to generate a current reference signal for controlling the inductance current.
4. The switching circuit of claim 3, wherein the reference current generation circuit comprises:
the input end of the transconductance amplifier receives the second sampling signal, and the output end of the transconductance amplifier outputs a converted current signal;
and the second resistor and the second capacitor are sequentially connected in series between the output end of the transconductance amplifier and the reference ground, and integrate the converted current signal to generate the current reference signal.
5. The switching circuit of claim 1, wherein the control unit further comprises:
And the compensation unit is configured to compensate the operation result of the operational amplification circuit and then generate the current reference signal for controlling the inductance current.
6. The switching circuit of any of claims 3-5, wherein the comparison circuit is replaced with: comparing the current reference signal with a preset triangular wave signal, and generating a turn-off trigger signal of the power switch tube according to a comparison result;
The triangular wave signal starts to be provided after the zero crossing instant of the current on the inductor, and the zero crossing instant of the current on the inductor is obtained from the first sampling signal.
7. The switching circuit of claim 6, wherein the control unit further comprises a zero crossing detection unit configured to obtain a zero crossing time of the current on the inductor from the first sampling signal and generate the turn-on trigger signal of the power switching tube after the zero crossing time or a preset time from the zero crossing time.
8. The switching circuit of claim 7, wherein the triangular wave signal is provided by a signal generator.
9. The switching circuit of claim 6, wherein the control unit further comprises a constant off-time control unit configured to generate the on-trigger signal of the power switching tube after a fixed time of receipt of the off-trigger signal.
10. An LED driving circuit, comprising,
The power switch tube and the inductor are connected;
The sampling resistor is used for sampling the instantaneous current flowing through the inductor to obtain a first sampling signal;
the filtering unit is used for outputting a second sampling signal after carrying out low-pass filtering on the first sampling signal so as to realize sampling of average current flowing through the inductor;
a control unit for generating a control signal for controlling the power switch tube to be turned on/off according to the first sampling signal and the second sampling signal so as to drive the LED,
Wherein the control unit includes:
an operational amplification circuit configured to perform differential operation on the second sampling signal and a reference voltage signal to generate a current reference signal;
And the comparison circuit is configured to compare the current reference signal with the first sampling signal and generate a turn-off trigger signal of the power switch tube according to a comparison result.
11. The LED driving circuit of claim 10, wherein the filter unit is an RC filter unit comprising a first resistor and a first capacitor;
the first resistor and the first capacitor are connected in series and then connected with the sampling resistor in parallel, and a connecting node of the first resistor and the first capacitor outputs the second sampling signal.
12. The LED driving circuit according to claim 10, wherein the operational amplifier circuit is replaced with a reference current generating circuit,
The reference current generation circuit is used for converting the second sampling signal into a current signal and integrating the converted current signal to generate a current reference signal for controlling the inductance current.
13. The LED driving circuit of claim 12, wherein the reference current generating circuit comprises:
the input end of the transconductance amplifier receives the second sampling signal, and the output end of the transconductance amplifier outputs a converted current signal;
and the second resistor and the second capacitor are sequentially connected in series between the output end of the transconductance amplifier and the reference ground, and integrate the converted current signal to generate the current reference signal.
14. The LED driving circuit of claim 10, wherein the control unit further comprises:
And the compensation unit is configured to compensate the operation result of the operational amplification circuit and then generate the current reference signal for controlling the inductance current.
15. The LED driving circuit according to any one of claims 12-14, wherein the comparison circuit is replaced with: comparing the current reference signal with a preset triangular wave signal, and generating a turn-off trigger signal of the power switch tube according to a comparison result;
The triangular wave signal starts to be provided after the zero crossing instant of the current on the inductor, and the zero crossing instant of the current on the inductor is obtained from the first sampling signal.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105636303A (en) * | 2014-11-03 | 2016-06-01 | 华润矽威科技（上海）有限公司 | Constant-current control circuit and method |
| CN111432529A (en) * | 2020-03-17 | 2020-07-17 | 成都芯源系统有限公司 | Control circuit and control method of true zero current dimming circuit |
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| CN103580456B (en) * | 2013-11-26 | 2016-04-20 | 矽力杰半导体技术(杭州)有限公司 | Switching Power Supply control method and control circuit and the Switching Power Supply with this control circuit |
| CN104407659B (en) * | 2014-10-20 | 2016-04-27 | 矽力杰半导体技术(杭州)有限公司 | The output current sample circuit of supply convertor and output voltage compensating circuit |
| CN104486891B (en) * | 2014-12-30 | 2018-02-27 | 杭州士兰微电子股份有限公司 | LED drive circuit and constant-current driver |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105636303A (en) * | 2014-11-03 | 2016-06-01 | 华润矽威科技（上海）有限公司 | Constant-current control circuit and method |
| CN111432529A (en) * | 2020-03-17 | 2020-07-17 | 成都芯源系统有限公司 | Control circuit and control method of true zero current dimming circuit |
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