Patent Description:
Currently, in an LED dimming circuit, a constant current source output current is typically maintained stable by quickly charging and discharging an inductor through a switch of a MOSFET (metal oxide semiconductor field effect transistor), in which the constant current source regulates an output current through pulse-width modulation (PWM). The PWM can output a higher frequency and perform several periodic regulations in a certain period of time. Currently, two methods are often used in order to improve resolution of LED dimming. One method is connecting an electronic switch in parallel at both ends of an LED. The electronic switch is typically a MOSFET, and a flow direction of the current is quickly controlled by MOSFET conduction, so that the LED can be turned off quickly over a plurality of cycles to achieve a smooth dimming effect. Another method is connecting a MOSFET at the negative electrode of the LED to increase the resolution of LED dimming by quickly turning off the MOSFET.

However, the above two methods often lead to a problem of non-smooth LED dimming. When the MOSFET is turned on, internal resistance thereof is typically as low as a mΩ level, and thus energy of the inductor is difficult to be consumed by the MOSFET connected in parallel or in series at both ends of the LED before the MOSFET of the constant current source in a next cycle is turned on. If the energy of the inductor in a previous cycle has insufficient time to be consumed, an inductor current of the previous cycle may act on the charging and discharging of the inductor in the next cycle since the current at both ends of the inductor cannot be mutated. Therefore, in such case, when the MOSFET in the next cycle is turned on, the inductor current increases, which affects the stability of the constant current source output current and leads to nonlinear and non-smooth LED dimming effect.

<CIT> discloses a converter circuit for matrix beam dimming, which includes a constant current source circuit having an inductor element and an LED dimming circuit that are sequentially connected in series, wherein the LED dimming circuit includes an LED and an electronic switch, a positive electrode of the LED being connected to an output end of the constant current source circuit, and the first electronic switch being connected in parallel with the LED, the LED is controlled by a PWM signal. Such circuit results in unsmooth and ununiform dimming effect.

The present invention aims thus provides an LED dimming device with energy quick release of an inductor in a constant current source to solve the problem of non-smooth LED dimming.

It is accomplished for the device by the features of claim <NUM>.

The dependent claims relate to advantageous further embodiments of the invention.

According to the present invention, an LED dimming device with energy quick release of an inductor in a constant current source includes a constant current source circuit having an inductor element and an LED dimming circuit, the constant current source and the LED dimming circuit being sequentially connected in series. The LED dimming circuit includes an LED and a first electronic switch. A positive electrode of the LED is connected to an output end of the constant current source circuit, and the first electronic switch is connected in parallel with the LED. The LED dimming device further comprises an energy quick release circuit and a first control circuit. The energy quick release circuit is connected in series with the first electronic switch to accelerate releasing the excess energy in the constant current source circuit. The first control circuit is connected to the first electronic switch to control turning on or off of the first electronic switch.

In order to improve the stability and uniformity of variation of the output current of the constant current source, the energy quick release circuit is designed as a resistor having a resistance value greater than or equal to <NUM> ohms and smaller than or equal to a resistance value of the LED to effectively consume the excess energy in a previous dimming cycle.

The LED dimming device in the present invention is a modification based on existing LED dimming circuits by adding an energy quick release circuit and a first control circuit to quickly release the excess energy generated in the constant current source circuit in each cycle. An entire circuit in the present invention comprises two parts: a constant current source circuit and an LED dimming circuit, in which the constant current source circuit can provide a constant current, and the LED dimming circuit can adjust luminous flux and illumination level of the LED to uniformize brightness of a light source and comprises the LED and the first electronic switch. Based on the LED dimming circuit, a preferred embodiment of the present invention adds the energy quick release circuit and the first control circuit, and specific connection relationships in the LED dimming device include: an output end of the constant current source circuit is connected to the positive electrode of the LED, a negative electrode of the LED is connected to the ground, the first electronic switch can be connected in parallel at both ends of the LED or can be connected in series to the negative electrode of the LED, the energy quick release circuit is connected to a positive or a negative electrode of the first electronic switch, and the first control circuit is connected to the first electronic switch to control turning on or off of the first electronic switch. According to the present invention, the first electronic switch is controlled to be turned on or off quickly by the first control circuit, thereby enabling the energy quick release circuit connected in series with the first electronic switch to release the excess energy generated by an inductor element in the constant current source in each cycle more quickly, avoiding unreleased energy to influence charging and discharging of the inductor element in a subsequent cycle, allowing the constant current source to output a current with stable and uniform variation, and achieving a smooth and uniform dimming effect.

According to a preferred embodiment of the present invention, the constant current source circuit can be a DC-DC converter circuit.

The DC-DC converter circuit is a voltage converter circuit that effectively outputs a fixed voltage after changing an input voltage, having three types: a boost DC-DC converter circuit, a buck DC-DC converter circuit, and a buck-boost DC-DC converter circuit. Embodiments of the present invention can adopt any DC-DC converter circuit as a constant current source circuit.

According to a preferred embodiment of the present invention, the constant current source circuit can include a second electronic switch, a second control circuit and a freewheeling semiconductor component. The second electronic switch is connected in series at one end of the inductor element, the other end of the inductor element is connected to the positive electrode of the LED, the second control circuit is connected to the second electronic switch to control turning on or off of the second electronic switch, and the freewheeling semiconductor component is connected between the positive electrode of the inductor element and the ground.

The constant current source circuit adopted in a preferred embodiment of the present invention is a buck DC-DC converter circuit with an output voltage smaller than or equal to an input voltage, and wide load range. The buck DC-DC converter circuit according to the present invention comprises a second electronic switch, an inductor element, a second control circuit and a freewheeling semiconductor component, and specific circuit connection relationships include: the second electronic switch is connected in series at one end of the inductor element, the other end of the inductor element is connected to the positive electrode of the LED, the second control circuit is connected to the second electronic switch to control turning on or off of the second electronic switch, the positive electrode of the freewheeling semiconductor component is connected to one end of the inductor element while the other end is connected to the ground. The freewheeling semiconductor component in the present invention can be a diode or a MOSFET capable of maintaining continuous output current of the constant current source. The operating principle of the freewheeling semiconductor component is that a diode or a MOSFET is connected in parallel at both ends of the inductor element, when a current flows through the inductor element, an induced electromotive force is generated at both ends thereof, and when the current vanishes, the induced electromotive force thereof generates an inverse voltage to the elements in the circuit. What's more, with the configuration of the diode or the MOSFET being connected in parallel at both ends of the inductor element, when the current flowing through the inductor vanishes, the induced electromotive force generated by the inductor element is consumed through work done by a circuit formed by the diode and a coil, thereby safely protecting other elements in the circuit.

According to a preferred embodiment of the present invention, the first control circuit is configured to control the turning on or off of the first electronic switch by controlling a pulse width of the PWM.

Additionally, the second control circuit may also control the turning on or off of the second electronic switch by controlling the pulse width of the PWM.

The constant current source circuit adopted in a preferred embodiment of the present invention is a DC-DC converter circuit and can use three types of control circuit according to requirements of the converter circuit, including PWM control circuit, PFM control circuit, and PWM/PFM convert control circuit. The present invention adopts a PWM control circuit, in which both the first control circuit and the second control circuit control the turning on or off of the first electronic switch and the second electronic switch through PWM, a cycle of a control signal is maintained unchanged when an input voltage is changed, and the on-time of the electronic switch is changed by changing a pulse output width, so that the output voltage is stable with high efficiency and has good output voltage ripple and noise.

According to a preferred embodiment of the present invention,, when the first electronic switch is connected in parallel at both ends of the LED, a turn-on signal for controlling the first electronic switch and a PWM signal for controlling the second electronic switch are in reverse phase.

According to the connection relationship between the first electronic switch and the LED, a corresponding control signal is selected for the purposes of the present invention. When the first electronic switch is connected in parallel at both ends of the LED, the turn-on signal for controlling the first electronic switch and the PWM signal for controlling the second electronic switch are in reverse phase, so that the first electronic switch can be turned on quickly when the second electronic switch is turned off in each dimming cycle, therefore the energy of the inductor element in the previous dimming cycle can rapidly flow to a resistor, and the resistor can quickly consume the excess energy of the inductor element in the previous dimming cycle. The above design of circuit connections guarantees that the energy of the inductor element in the previous dimming cycle can quickly flow to the energy quick release circuit and quickly release the excess energy of the inductor element in the previous dimming cycle in order to avoid affecting the stability of the output current of the constant current source in the next dimming cycle.

According to a preferred embodiment of the present invention,, the LED dimming circuit can further include a third electronic switch connected in series with the LED.

The third electronic switch connected in series with the LED can control quick on-off of the circuit where the LED is located, thereby increasing LED frequency and improving the dimming effect.

According to a preferred embodiment of the present invention, the first electronic switch can be an N-channel MOSFET.

A MOSFET including a P-type substrate and two high concentration N diffusion regions is referred to as an N-channel MOSFET. When the tube is conducted, an N-type conduction channel is formed between the two high concentration N diffusion regions. An N-channel enhanced MOSFET refers to an N-channel MOSFET in which a forward bias must be applied on a gate and only a conduction channel is generated when a gate-source voltage is greater than a threshold voltage. An N-channel depletion MOSFET refers to an N-channel MOSFET in which a conduction channel is generated when no gate voltage is applied (the gate-source voltage is zero). A preferred embodiment of the present invention adopts a circuit formed of N-channel MOSFETs, which has high input impedance, substantially does not need absorption current, and thus a current load problem does not have to be considered when a CMOS integrated circuit is connected to an NMOS integrated circuit.

According to a preferred embodiment of the present invention, the second electronic switch is a MOSFET.

The second electronic switch in a preferred embodiment of the present invention adopts a MOSFET, and both P-channel MOSFET and N-channel MOSFET can be adopted. A P-channel MOSFET has two P+ regions on an N-type silicon substrate, referred to as a source electrode and a drain electrode respectively with no conduction therebetween, a sufficient positive voltage (the source electrode connects the ground) is applied to the gate, and an N-type silicon surface under the gate presents a P-type inversion layer as a channel connecting the source electrode and the drain electrode. Changing the gate voltage can change electron density in the channel, thereby changing the channel resistance. PMOS circuit control is simple, and a PMOS circuit technology can be adopted for a digital control circuit of a preferred embodiment of the present invention.

In a comparative example which is not part of the claimed invention, in addition to a resistor, the energy quick release circuit may be other working elements or an energy storage circuit capable of collecting excess energy to provide power for an appliance. The energy quick release circuit in the present invention is a resistor, the number of which may be one or more, the resistance value is greater than or equal to <NUM> ohms to effectively consume the excess energy in the previous dimming cycle while the resistance value is smaller than or equal to the resistance value of the LED itself. If the resistance value is greater than the LED resistance value, when the resistor is connected in parallel with the LED, the current flowing through the LED may be greater than the current flowing through the resistor, thereby affecting a quick turning off of the LED.

Compared with the prior art, the present invention can obtain some beneficial effects. The present invention comprises the energy quick release circuit and the first control circuit in the LED dimming circuit, the first electronic switch is controlled to be turned on or off quickly by the first control circuit, thereby enabling the energy quick release circuit connected in series with the first electronic switch to release the excess energy generated by the inductor element in the constant current source circuit in each cycle more quickly, avoiding unreleased energy to influence charging and discharging of the inductor element in a subsequent cycle, allowing the constant current source to output a current with stable and uniform variation, and achieving a smooth and uniform dimming effect.

Additional advantages, features and possible applications of the present invention will be apparent from the description which follows, in which reference is made to the embodiments illustrated in the drawings.

The drawings are for illustrative purposes only and are not to be construed as limiting the present invention. For better explanation of the following embodiments, some components in the drawings may be omitted, enlarged, or reduced, and sizes of these components do not represent sizes of actual products. For those skilled in the art, it will be understood that some known structures and descriptions thereof in the drawings may be omitted.

The DC-DC converter circuit is a voltage converter circuit that effectively outputs a fixed voltage after changing an input voltage, and can be divided into three types: a boost DC-DC converter circuit, a buck DC-DC converter circuit, and a buck-boost DC-DC converter circuit. The constant current source circuit in a preferred embodiment of the present invention is a buck DC-DC converter circuit, which features in that an output voltage is smaller than or equal to an input voltage, and a load range is wide. However, the constant current source in the present invention is not limited to a buck DC-DC converter circuit, the actual circuit design can be changed in combination with the type of selected DC-DC converter circuit.

<FIG> shows a logic circuit diagram of an LED dimming device with energy quick release of an inductor in a constant current source according to one embodiment. According to this embodiment, the constant current source circuit <NUM> is connected in series with an LED dimming circuit <NUM>. The LED dimming circuit <NUM> comprises an LED <NUM> and a first electronic switch <NUM>. A positive electrode of the LED <NUM> is connected to an output end of the constant current source circuit <NUM>, while a negative electrode of the LED <NUM> is connected to the ground, and the first electronic switch <NUM> is connected in parallel at both ends of the LED <NUM>. The LED dimming device <NUM> further comprises an energy quick release circuit <NUM> and a first control circuit <NUM>, in which the energy quick release circuit <NUM> is connected in series with the first electronic switch <NUM> to accelerate releasing the excess energy in the constant current source circuit <NUM>. The first control circuit <NUM> is connected to the first electronic switch <NUM> to control turning on or off of the first electronic switch <NUM>.

Specifically, the energy quick release circuit <NUM> can adopt working elements or an energy storage circuit. The present embodiment uses a resistor, the number of which in actual application is not limited to only one. A resistance value of the resistor is greater than or equal to <NUM> ohms in order to consume excess energy and is smaller than or equal to a resistance value of the LED <NUM> to avoid affecting turning off the LED <NUM>.

According to some embodiments the LED dimming circuit can further include a third electronic switch <NUM> connected in series with the LED <NUM> to control quick on-off of the circuit where the LED <NUM> is located, thus increasing the LED frequency and improving the dimming effect.

<FIG> is a logic circuit diagram showing a constant current source circuit uses a buck DC-DC converter circuit according to some embodiments. The constant current source circuit <NUM> comprises a second electronic switch <NUM>, an inductor element <NUM>, a second control circuit <NUM>, and a freewheeling semiconductor component <NUM>. Specific connection relationships include: an output end of the second electronic switch <NUM> is connected in series with one end of the inductor element <NUM>, the other end of the inductor element <NUM> is connected to the positive electrode of the LED <NUM>, the second control circuit <NUM> is connected to the second electronic switch <NUM> to control turning on or off of the second electronic switch <NUM>, a positive electrode of the freewheeling semiconductor component <NUM> is connected to the inductor element <NUM>, and a negative electrode of the freewheeling semiconductor component <NUM> is connected to the ground.

<FIG> shows an application circuit diagram according to one embodiment. The constant current source circuit <NUM> mainly comprises a second electronic switch <NUM>, which is a P-channel MOSFET Q1, a diode D1 as the freewheeling semiconductor component <NUM>, an inductor L1 as the inductor element <NUM>, and a second control circuit <NUM>. The second control circuit <NUM> is a peripheral circuit including a constant current driving chip U1, a plurality of resistors (R2, R3, R4, R6, R7, R10), and a plurality of capacitors (C1, C3, and C5). The LED dimming circuit <NUM> mainly comprises an LED, a first electronic switch <NUM>, which is an N-channel MOSFET Q2, a resistor R1 as the energy quick release circuit <NUM>, and a first control circuit <NUM> controlling the N-channel MOSFET Q2 to be turned on or off. The first control circuit <NUM> is a peripheral circuit including a gate driver U2, resistors R8 and R9, and a capacitor C6.

Specifically, circuit connection relationships in the embodiment include: a gate and a source electrode of the P-channel MOSFET Q1 are connected with the constant current driving chip U1, the drain electrode of the P-channel MOSFET Q1 is connected to one end of the inductor L1, the diode D1 is connected between the inductor L1 and the ground, the positive electrode of the LED is connected to one end of the inductor L1, the negative electrode of the LED is connected with the ground, the N-channel MOSFET Q2 is connected in parallel at both ends of the LED, the first control circuit is connected to the gate of the N-channel MOSFET Q2 to control turning on or off of the N-channel MOSFET Q2, and the resistor R1 is connected in series with a source electrode or a drain electrode of the N-channel MOSFET Q2.

As <FIG> and <FIG> shown, the second control circuit <NUM> according to some embodiments controls the turning on or off of the P-channel MOSFET by controlling the pulse width of the PWM, and the first control circuit <NUM> controls the turning on or off of the N-channel MOSFET by controlling the pulse width of the PWM.

Preferably, when the N-channel MOSFET is connected in parallel with the LED, the channel number of the N-channel MOSFET is controlled and the PWM signal controlling the P-channel MOSFET are in reverse phase.

Specifically, a control method according to some embodiments is as follows. As shown in <FIG>, the second control circuit <NUM> regulates the turning on or off of the P-channel MOSFET Q1 in the constant current source circuit by controlling the pulse-width of the PWM. When the P-channel MOSFET Q1 is turned on or off quickly enough, the constant current source can output a current with adjustable magnitude, while the first control circuit controls a negative signal input end of the gate driver U2 of the N-channel MOSFET Q2 by PWM, so that the gate driver U2 outputs a signal inverted to the PWM, which ensures that the N-channel MOSFET Q2 can be turned on quickly when the P-channel MOSFET Q1 of the constant current source is turned off in each dimming cycle, allows the energy of the inductor element in the previous dimming cycle to flow quickly to the resistor R1 and quickly consume energy through the resistor R1, avoids affecting the stability of the current output by the constant current source, and achieving a smooth and uniform effect of LED dimming.

Claim 1:
An LED dimming device with energy quick release of an inductor in a constant current source, comprising: the constant current source circuit (<NUM>) having an inductor element (<NUM>); and
an LED dimming circuit (<NUM>), the constant current source (<NUM>) and the LED dimming circuit (<NUM>) being sequentially connected in series,
wherein the LED dimming circuit (<NUM>) comprises
an LED (<NUM>);
a first electronic switch (<NUM>), a positive electrode of the LED (<NUM>) being connected to an output end of the constant current source circuit (<NUM>), and the first electronic switch (<NUM>)being connected in parallel with the LED (<NUM>);
a first control circuit (<NUM>), which is connected to the first electronic switch (<NUM>) to control turning on or off of the first electronic switch (<NUM>), and
characterized by an energy quick release circuit (<NUM>), which is connected in series with the first electronic switch (<NUM>) to accelerate releasing excess energy in the constant current source circuit (<NUM>), wherein the energy quick release circuit (<NUM>) is a resistor having a resistance value greater than or equal to <NUM> ohms and smaller than or equal to a resistance value of the LED (<NUM>) to consume the excess energy in a previous dimming cycle.