Dimming circuit
地域：
Shanghai
摘要
A dimming control method and a dimming circuit are used to control the brightness of a LED. The dimming circuit includes a power conversion unit having an input end, an output end, an inductor, and a switch. When the dimming current signal is higher than or equal to a first current threshold, the switch is controlled such that the power conversion unit operates in a continuous Conduction mode or a boundary Conduction mode; when the dimming current signal is lower than the first current threshold, the switch is controlled such that the power conversion unit operates in a discontinuous Conduction mode; and when the dimming current signal is lower than a second current threshold, the switch is controlled such that the power conversion unit operates in a chopping control mode.
說明書
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The present application is a divisional application divided from U.S. patent application Ser. No. 17/322,935 filed on May 18, 2021, which claims priority of patent application No. 202010455009.7 filed in P.R. China on May 26, 2020 under 35 U.S.C. § 119(a), the entire contents of which are hereby incorporated by reference.
Some references, if any, which may include patents, patent applications and various publications, may be cited and discussed in the description of this invention. The citation and/or discussion of such references, if any, is provided merely to clarify the description of the present invention and is not an admission that any such reference is “Prior Art” to the present invention described herein. All references listed, cited and/or discussed in this specification are incorporated herein by reference in their entireties and to the same extent as if each reference was individually incorporated by reference.
The invention relates to the field of lighting, and particularly to a dimming circuit.
權(quán)利要求
What is claimed is:1. A dimming circuit for controlling the brightness of a light emitting diode, comprising:a power conversion unit having an input end, an output end, an inductor and a switch, the power conversion unit configured to receive an input voltage from the input end, and convert the input voltage into an output voltage output from the output end by operation of the switch; an input voltage sampling circuit configured to generate an input voltage sampling signal by detecting the input voltage; an output voltage sampling circuit configured to generate an output voltage sampling signal by detecting the output voltage; a current sampling circuit configured to generate a current sampling signal by detecting a current flowing through the switch; a dimming signal sampling circuit configured to receive a dimming signal to calculate and generate a dimming current signal; a driving circuit connected to the switch for driving the switch to turn on or turn off; and a control unit configured to receive the input voltage sampling signal, the output voltage sampling signal, the current sampling signal and the dimming current signal, and output a control signal to the driving circuit to control the switch; wherein,the control unit compares the dimming current signal with a first current threshold and a second current threshold, when the dimming current signal is higher than or equal to the first current threshold, the control unit controls the switch such that the power conversion unit operates in a continuous conduction mode or a boundary conduction mode; when the dimming current signal is lower than the first current threshold, the control unit controls the switch such that the power conversion unit operates in a discontinuous conduction mode; and in the discontinuous conduction mode, when the dimming current signal is lower than the second current threshold, the control unit controls the switch such that the power conversion unit operates in a chopping control mode. 2. The dimming circuit according to claim 1 , wherein the control unit comprises:a dimming processing module configured to set a peak current reference according to the dimming current signal; a comparator module configured to compare the current sampling signal with the peak current reference, and output a corresponding compared output signal according to a comparing result; a switching time calculation module configured to calculate a switching period or an on time or an off time of the switch; and a timer module configured to receive the compared output signal and the switching period or the on time or the off time of the switch, and output the control signal formed of a plurality of pulses. 3. The dimming circuit according to claim 2 , wherein when the dimming current signal is higher than or equal to the first current threshold, the control unit controls the switch such that the power conversion unit operates in a continuous conduction mode; wherein,the switching time calculation module calculates the off time of the switch according to the output voltage sampling signal, a set ripple current reference, and an inductance of the inductor. 4. The dimming circuit according to claim 3 , wherein,when the current sampling signal is equal to the peak current reference, the comparator module outputs a reset signal, and the timer module clears counting and output a low level when detecting the reset signal; when the timer module starts counting from zero, and a counter value increases to a first compare value, an output of the timer module is flipped over to a high level, thereby outputting the control signal formed of a plurality of pulses, such that the power conversion unit operates in the continuous conduction mode; wherein the first compare value corresponds to the off time of the switch. 5. The dimming circuit according to claim 4 , wherein the off time of the switch is calculated by the following formula: wherein Toff is the off time of the switch, Vout is the output voltage, Ipp is the ripple current reference, and L is the inductance of the inductor. 6. The dimming circuit according to claim 4 , wherein when the dimming current signal is higher than or equal to the second current threshold and lower than the first current threshold, the switching time calculation module sets a fixed switching period and calculates the on time of the switch according to the input voltage sampling signal, the output voltage sampling signal and the dimming current signal, and the control unit controls the power conversion unit to operate in a constant frequency discontinuous conduction mode by altering a duty cycle of the control signal. 7. The dimming circuit according to claim 4 , wherein,when the dimming current signal is higher than or equal to a third current threshold and lower than the first current threshold, the switching time calculation module calculates the switching period of the switch according to the input voltage sampling signal, the output voltage sampling signal, the dimming current signal, and the ripple current reference; and the switching time calculation module calculates the on time of the switch according to the input voltage sampling signal, the output voltage sampling signal, and the ripple current reference, and the control unit controls the power conversion unit to operate in a variable frequency discontinuous conduction mode. 8. The dimming circuit according to claim 7 , wherein,the switching period of the switch is calculated by the following formula: wherein Ts is the switching period of the switch, Ipp is the ripple current reference, L is the inductance of the inductor, Vin is the input voltage, Idim is the dimming current signal, and Vout is the output voltage; and the on time of the switch is calculated by the following formula: wherein Ton is the on time of the switch, Ipp is the ripple current reference, and L is the inductance of the inductor. 9. The dimming circuit according to claim 7 , wherein,when the dimming current signal is higher than or equal to the second current threshold and lower than the third current threshold, the switching time calculation module sets a fixed switching period and calculates the on time of the switch according to the input voltage sampling signal, the output voltage sampling signal, and the dimming current signal, and the control unit controls the power conversion unit to operate in a constant frequency discontinuous conduction mode. 10. The dimming circuit according to claim 7 , wherein,the timer module sets a maximum counter reference value according to the switching period; wherein, when a counter value of the timer module increases to the maximum counter reference value, counting is cleared, and an output is a low level; when the counter value increases from zero to a second compare value, an output is flipped over to a high level, thereby outputting the control signal formed of a plurality of pulses; wherein the second compare value is set by subtracting the on time of the switch from the switching period. 11. The dimming circuit according to claim 10 , wherein,in the discontinuous conduction mode, the peak current reference is fixed to a corresponding peak current reference when the dimming current signal is equal to the first current threshold, and the comparator module always outputs the low level. 12. The dimming circuit according to claim 11 , wherein the control unit further comprises: a chopping processing module connected to the timer module and the dimming processing module; wherein,when the dimming current signal is lower than the second current threshold, the timer module fixes the duty cycle of the control signal, and the chopping processing module adjusts the number of pulses of the control signal to adjust the output current by chopping, thereby controlling the switch to make the power conversion unit to operate in the chopping control mode. 13. The dimming circuit according to claim 12 , wherein the timer module fixes the duty cycle of the control signal to a corresponding duty cycle when the dimming current signal is equal to the second current threshold. 14. The dimming circuit according to claim 4 , wherein,the on time of the switch is calculated by the following formula: wherein Ton is the on time of the switch, L is the inductance of the inductor, Vin is the input voltage, Vout is the output voltage, Idim is the dimming current signal, and fg is a switching frequency of the switch. 15. The dimming circuit according to claim 1 , further comprising a zero-crossing detection circuit configured to generate a zero-crossing detecting signal by detecting a zero-crossing point of a current on the inductor of the power conversion unit. 16. The dimming circuit according to claim 15 , wherein,when the current sampling signal is equal to the peak current reference, the comparator module outputs a reset signal, and the timer module clears counting and output a low level when detecting the reset signal; when the zero-crossing detection circuit detects the zero-crossing point of the current, an output of the timer module is flipped over to a high level, thereby outputting the control signal formed of a plurality of pulses, such that the power conversion unit operates in the boundary conduction mode. 17. The dimming circuit according to claim 16 , wherein,when the dimming current signal is higher than the second current threshold and lower than the first current threshold, a switching period of the switch is fixed; and an on time of the switch is calculated according to the input voltage, the output voltage, the dimming current signal, and an inductance of the inductor, and an output current is adjusted by adjusting a duty cycle of the control signal, thereby controlling the switch to make the power conversion unit to operate in the discontinuous conduction mode. 18. The dimming circuit according to claim 17 , wherein,the on time of the switch is calculated by the following formula: wherein Ton is the on time of the switch, L is the inductance of the inductor, Vin is the input voltage, Vout is the output voltage, Idim is the dimming current signal, and fg is a switching frequency of the switch. 19. The dimming circuit according to claim 17 , wherein,the timer module sets a maximum counter reference value according to the switching period; wherein, when a counter value of the timer module increases to the maximum counter reference value, counting is cleared, and an output is a low level; when the counter value increases from zero to a second compare value, an output is flipped over to a high level, thereby outputting the control signal formed of a plurality of pulses; wherein the second compare value is set by subtracting the on time of the switch from the switching period. 20. The dimming circuit according to claim 19 , wherein,in the discontinuous conduction mode, the peak current reference is fixed to a corresponding peak current reference when the dimming current signal is equal to the first current threshold, and the comparator module always outputs the low level. 21. The dimming circuit according to claim 20 , wherein the control unit further comprises: a chopping processing module connected to the timer module and the dimming processing module; wherein,when the dimming current signal is lower than the second current threshold, the timer module fixes the duty cycle of the control signal, and the chopping processing module adjusts the number of pulses of the control signal to adjust the output current by chopping, thereby controlling the switch to make the power conversion unit to operate in the chopping control mode. 22. The dimming circuit according to claim 21 , wherein the timer module fixes the duty cycle of the control signal to a corresponding duty cycle when the dimming current signal is equal to the second current threshold.
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