Patent Description:
In the field of lighting technology, it is often needed to configure a driving current, which is used to drive a lighting device. The lighting device is LED (Light Emitting Diode) for example.

The lighting device is driven by a driver, which outputs direct current to the lighting device. For most of low cost drivers, output current has high ripple coefficient, e.g. ±<NUM>% or even higher. High ripple coefficient may make the lighting device to flicker.

Low ripple current is now mandatory to meet regulatory requirements for suppressing low-frequency ripple (<NUM> to <NUM>) in LED lighting applications for numerous markets.

Single stage convert is general used as the cost effective solution of LED drivers, which always keep high power factor but also high ripple current. It's low acceptance on the market for these high ripple current devices. Ripple suppression circuit is developed to keep low cost and provide high levels of ripple suppression while maintaining a high power factor.

<FIG> is a diagram of a ripple suppression circuit according to an existing solution. As shown in <FIG>, a ripple suppression circuit <NUM> comprises a capacitor C65 and a transistor Q61, C65 provides filtering that is equal to a capacitor of (B+<NUM>)*C<NUM>, where B equals to DC (direct current) current gain of Q61, C<NUM> is capacitance of C65. Therefore, the ripple suppression circuit <NUM> can work as a capacitance multiplier. Output voltage of the ripple suppression circuit <NUM> can be provided for driving LED. Besides, the ripple suppression circuit <NUM> further comprises C63, D63, D64, D65, D69, R63, R64, R66, R67, DR66 and L61; their working principle can be referred to related art, such as <CIT>. As another example, document <CIT> discloses an active filter circuit for power supply smoothing.

<FIG> is a diagram of input voltage and output voltage of the ripple suppression circuit <NUM>. As shown in <FIG>, a ripple voltage with amplitude of 6V is added on a DC voltage of 50V. There is a voltage drop V_drop on Q61, V_drop results in a difference between the output voltage and minimum value of the input voltage.

Inventor of this disclosure found the following limitation in the ripple suppression circuit <NUM> shown in <FIG>: value of DR66 needs to be tuned to cover worst case; voltage drop on Q61 is related with output voltage and input voltage; voltage drop on Q61 might be pretty high at the worst case and causes low efficiency and potential thermal issues.

The invention is defined by a ripple suppression circuit, in accordance with claims <NUM> and <NUM>, and by a controlling method of a ripple suppression circuit, in accordance with claims <NUM> and <NUM>. In general, embodiments of the present disclosure provide ripple suppression circuits, controlling methods and a driving equipment. In the embodiments, a voltage control circuit is used to make output voltage to equal to the minimum value, therefore, the difference between the output voltage and minimum value of the input voltage can be reduced.

According to various embodiments of the present disclosure, the difference between the output voltage and minimum value of the input voltage can be reduced; therefore, power dissipation is reduced, and higher efficiency can be obtained in the ripple suppression circuit.

The above and other aspects, features, and benefits of various embodiments of the disclosure will become more fully apparent, by way of example, from the following detailed description with reference to the accompanying drawings, in which like reference numerals or letters are used to designate like or equivalent elements.

The present disclosure will now be discussed with reference to several example embodiments.

As used herein, the terms "first" and "second" refer to different elements. The terms "comprises," "comprising," "has," "having," "includes" and/or "including" as used herein, specify the presence of stated features, elements, and/or components and the like, but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. The term "based on" is to be read as "based at least in part on. " The term "one embodiment" and "an embodiment" are to be read as "at least one embodiment. " The term "another embodiment" is to be read as "at least one other embodiment. " Other definitions, explicit and implicit, may be included below.

A ripple suppression circuit is provided in a first embodiment.

<FIG> is a diagram of a ripple suppression circuit in accordance with an example not forming part of the present disclosure. As shown in <FIG>, a ripple suppression circuit <NUM> includes a first input port X1-a, a first output port X2-a, a first capacitor C2, a first transistor Q1, a second diode D4, second capacitor C1, a second transistor Q2, a third capacitor C3, and a voltage control circuit <NUM>.

In the example, the first input port X1-a is configured to receive an input voltage via a first diode D2, the input voltage is denoted as Vin. The first output port X2-a is configured to output an output voltage, the output voltage is denoted as Vout.

In the example, the first capacitor C2 is configured to be connected between the first input port X1-a and a ground port. The first transistor Q1 is configured to be connected between the first input port X1-a and the first output port X2-a. The second diode D4 and the second capacitor C1 are configured to be connected in series between the first input port X1-a and the ground port.

The second transistor Q2 is configured to be coupled between a base of the first transistor Q1 and a connecting node A of the second diode D4 and the second capacitor C1. The third capacitor C3 is configured to be connected between a base of the second transistor Q2 and the ground port.

As shown in <FIG>, the first transistor Q1 is a bipolar transistor, for example an NPN bipolar transistor. The second transistor Q2 is a bipolar transistor, for example an NPN bipolar transistor. An emitter of Q1 is connected to the first output port X2-a, a collector of Q1 is connected to the first input port X1-a, a base of Q1 is connected to an emitter of Q2 via a resistor R3. The collector of the second transistor Q2 is connected to the node A. The embodiment will not be limited thereto, the first transistor Q1 and second transistor Q1 can be of other type, for example a MOS FET (Metal-Oxide-Semiconductor Field-Effect Transistor).

The voltage control circuit <NUM> is configured to be connected to the base of the second transistor Q2. When the input voltage drops to a minimum value, the voltage control circuit <NUM> makes voltage of the base of the second transistor Q2 to be higher than the minimum value, and makes the output voltage to equal to the minimum value.

The difference between the output voltage and minimum value of the input voltage can be reduced; therefore, power dissipation of Q1 is reduced, and higher efficiency can be obtained in the ripple suppression circuit <NUM>.

It should be noted that the working principle of the ripple suppression circuit <NUM> is described from the view point of voltage, that is, the ripple suppression circuit <NUM> can suppress voltage ripple on the output voltage, however the ripple suppression circuit <NUM> can also suppress current ripple on output current, it depends on a V-I characteristic of a load of the ripple suppression circuit <NUM>. For example, when a load of the ripple suppression circuit <NUM> is an LED or other electrical element having a similar V-I characteristic with an LED, low ripple on the output voltage will result in low ripple on the output current which drives the LED, therefore the ripple suppression circuit <NUM> is used for suppressing current ripple on output current. For another example, when a load of the ripple suppression circuit <NUM> is a resistor or other electrical element having a similar V-I characteristic with a resistor, the output voltage with low ripple is used to drive the resistor, therefore the ripple suppression circuit <NUM> can suppress voltage ripple on output voltage.

As shown in <FIG>, the voltage control circuit <NUM> includes: a first resistor R2, a third diode D1 and a fourth diode D5.

The first resistor R2 is configured to be connected between the collector of the second transistor Q2 and the base of the second transistor Q2. A current may flow from the collector of Q2 to the base of Q2 via the first resistor R2 to charge the third capacitor C3.

The third diode D1 and the fourth diode D5 are configured to be reversely coupled in serial between the first input port X1-a and the base of the second transistor Q2. A cathode of the third diode D1 is connected to the first input port X1-a, an anode of the fourth diode D5 is coupled to the base of the second transistor Q2. For example, the anode of the fourth diode D5 is connected to the base of the second transistor Q2 via a resistor R4.

As shown in <FIG>, V1 denotes a DC voltage, V2 denotes a ripple voltage, V2 is added on V1 so as to simulate the DC voltage with ripple. For example, V1 is 50V, V2 is sine signal with amplitude of 6V and frequency of <NUM>.

The DC voltage with ripple is rectified by a diode D2. At the output side, a resistor R1 is connected between the output port X2-a and the ground port.

As shown in <FIG>, when the input voltage drops to the minimum value Vin_min, voltage of the base of Q2 and the output voltage satisfies the following conditions:
<MAT>
<MAT>
<MAT>.

In (<NUM>), (<NUM>) and (<NUM>), Vo denotes the output voltage, Vb denotes the voltage of the base of Q2, Vf2 denotes a turn-on voltage of D1 or D5, Vf1 denotes a voltage drop between the base of Q2 and the emitter of Q2 or a voltage drop between the base of Q1 and the emitter of Q1. Vf1 is equal to Vf2.

According to (<NUM>), Vo is equal to Vin_min, thus difference between the output voltage and the minimum of the input voltage can be reduced. The power dissipation of the ripple suppression circuit <NUM> is reduced, and the risk of thermal issue is reduced.

<FIG> is a diagram of input voltage and output voltage of the ripple suppression circuit <NUM>. As shown in <FIG>, a ripple voltage with an amplitude of 6V is added on a DC voltage of 50V. <NUM> denotes the input voltage, <NUM> denotes the output voltage. The output voltage <NUM> is equals to the minimum of the input voltage <NUM>. Therefore, the difference between the output voltage <NUM> and the minimum of the input voltage <NUM> is getting smaller.

<FIG> is a diagram of a ripple suppression circuit in accordance with another embodiment of the present disclosure. As shown in <FIG>, a ripple suppression circuit 30a is a variation of the ripple suppression circuit <NUM>, their differences will be described as follows Description for common elements in <FIG> and <FIG> is omitted.

As shown in <FIG>, the ripple suppression circuit 30a includes a voltage control circuit 100a. The voltage control circuit 100a includes: a fourth capacitor C4, a fifth diode D11, a sixth diode D51, a comparator X1 and an optical coupler U1.

As shown in <FIG>, the fourth capacitor C4 is configured to be coupled between the ground port and the connecting node A of the second diode D4 and the second capacitor C1.

The fifth diode D11 and the sixth diode D51 are configured to be reversely coupled in series between the first input port X1-a and the fourth capacitor C4. A cathode of the sixth diode D51 is connected to the first port X1-a, an anode of the fifth diode D11 is connected to the fourth capacitor C4. Besides, a resistor R2 is connected between the anode (connecting node A) of D11 and the collector (connecting node B) of Q2. The resistor R2 has a large resistance (e.g. <NUM> Ω), and is used for charging the fourth capacitor C4.

The comparator X1 is configured to compare the voltage at the base of the second transistor Q2 with the voltage of anode of the fifth diode D11, and output a comparison result. For example, a resistor R6 is connected between the anode of D11 and "+" input port of the comparator X1, so as to detect the voltage of the anode (i.e. the voltage of connecting node A) of D11; a resistor R9 is connected between the base of Q2 and "-" input port of the comparator X1, so as to detect the voltage of the base (i.e. Vb) of Q2; a resistor R7 is connected between the "+" input port of X1 and the ground port; a resistor R8 is connected between the "-" input port of X1 and the ground port, resistance of R7 is equal to resistance of R8; a voltage V3 is applied to a "+" power input port of X1, a "-" power input port of X1 is connected to the ground port; a resistor R5 is connected to an output port of X1. When the voltage of anode of D11 is higher than the voltage of base of Q2, the output port of X1 outputs a signal with high voltage as a comparison result.

The optical coupler U1 is configured to be controlled by the comparison result, when the voltage of the anode of the fifth diode D11 is higher than the voltage at the base of the second transistor Q2, the optical coupler U1 couples the base of the second transistor Q2 to the anode of the fifth diode D11.

For example, an input port of the optical coupler U1 receives the comparison result, two output ports of the optical coupler U1 are connected to the base of the second transistor Q2 and the connecting node A (the collector of Q2) of the second diode D4 and the second capacitor C1, respectively. When the comparison result is with high voltage, a transistor in U1 is conducted, and C3 is discharged by the transistor in U1, R4 and R9, until the voltage of the base of Q2 is equal to the voltage of connecting node A.

As shown in <FIG>, when the input voltage drops to the minimum value Vin_min, the voltage of connecting node A is (Vin_min+<NUM>*Vf21). The voltage of the base of Q2 and the output voltage (Vo) satisfies the following conditions:
<MAT>
<MAT>
<MAT>.

In (<NUM>), (<NUM>) and (<NUM>), Vo denotes the output voltage, Vb denotes the voltage of the base of Q2, Vf21 denotes a turn-on voltage of D11 or D51, Vf1 denotes a voltage drop between the base of Q2 and the emitter of Q2 or a voltage drop between the base of Q1 and the emitter of Q1. Vf1 is equal to Vf21.

According to (<NUM>), in the embodiment of <FIG>, Vo is equal to Vin_min, thus difference between the output voltage and the minimum of the input voltage can be reduced. The power dissipation of the ripple suppression circuit 30a is reduced, and the risk of thermal issue is reduced.

<FIG> is a diagram of a ripple suppression circuit in accordance with another embodiment of the present disclosure. As shown in <FIG>, a ripple suppression circuit 30b is variation of the ripple suppression circuit <NUM>; their differences will be described as follows. Description for common elements in <FIG> and <FIG> is omitted.

As shown in <FIG>, the ripple suppression circuit 30b includes a voltage control circuit 100b. The voltage control circuit 100b includes: a controller M1, a fifth diode D11, and an optical coupler U1. The voltage control circuit 100b further includes a resistor R9, which is used to feedback a base voltage of Q2 to the controller M1.

The controller M1 is configured to detect the input voltage Vin, and output a controlling signal. When the input voltage drops to the minimum value (i.e. Vin_min), the controller M1 compares (Vin_min+2Vf1) with the base voltage (Vb) of Q2. If (Vin_min+2Vf1) is higher than Vb, the controller M1 outputs a first controlling signal. When the base voltage (Vb) of Q2 is equal to (Vin_min+2Vfl), the controller M1 stops outputting the first controlling signal. For example, the controller M1 is MCU (Microcontroller Unit).

The optical coupler U1 is configured to be controlled by the controlling signal, when the first controlling signal is received, the optical coupler U1 connects the base of the second transistor Q2 to the collector of the second transistor Q2.

For example, an input port of the optical coupler U1 receives the controlling signal, two output ports of the optical coupler U1 are coupled to the base of the second transistor Q2 and the collector of the second transistor Q2, respectively. For example, when U1 receives the first controlling signal, a transistor in U1 is conducted, and the capacitor C3 is discharged by the transistor in U1 and the resistor R9, until the base voltage (Vb) of Q2 is equal to (Vin_min+2Vf1). As shown in <FIG>, the resistor R9 is used for two purposes: one is to sample the base voltage (Vb) for M1, and the other one is to discharge C3.

As shown in <FIG>, when the input voltage drops to the minimum value Vin_min, the controller M1 controls the base voltage (Vb) of Q2 to become Vb=Vin_min+<NUM>*Vf1,and output voltage Vo becomes Vo=Vb- <NUM>*Vf1=Vin_min. Vf1 denotes a voltage drop between the base of Q2 and the emitter of Q2 or a voltage drop between the base of Q1 and the emitter of Q1.

According to the embodiment of <FIG>, Vo is equal to Vin_min, thus difference between the output voltage and the minimum of the input voltage can be reduced. The power dissipation of the ripple suppression circuit 30b is reduced, and the risk of thermal issue is reduced.

In <FIG>, <FIG> and <FIG>, the ripple suppression circuit 100a, 100b further includes a Zener diode D3. An anode of the Zener diode D3 is connected to the base of the second transistor Q2, a cathode of the Zener diode D3 is connected to the collector of the second transistor Q2. The Zener diode D3 can keep the voltage drop between the collector and base of Q2 from getting too high.

A controlling method of a ripple suppression circuit. The ripple suppression circuit of the first aspect of embodiments is provided in an embodiment. The same contents as those in the first aspect of embodiments are omitted.

<FIG> shows a flowchart of a controlling method <NUM> of the ripple suppression circuit.

As shown in <FIG>, the method <NUM> includes:
Block <NUM>: when the input voltage drops to a minimum value, the voltage control circuit (100a, 100b) makes voltage of the base of the second transistor (Q2) to be higher than the input voltage, and the output voltage to equal to the minimum value.

According to the second aspect of embodiments, the difference between the output voltage and minimum value of the input voltage can be reduced; therefore, power dissipation of Q1 and the ripple suppression circuit is reduced, and higher efficiency can be obtained in the ripple suppression circuit.

A driving equipment is provided in an embodiment. The driving equipment includes a driving circuit and the ripple suppression circuit according to the first aspect of embodiments.

In the embodiment, the ripple suppression circuit receives the input voltage provided by the driving circuit, and outputs signal with low ripple coefficient. The signal with low ripple coefficient may be provided to a lighting device, so that flicker of the lighting device can be reduced.

The driving circuit may be formed by a flyback converter or resonant halfbridge converter or LLC converter including a transformer. Instead of the transformer there might from an inductor a part of a switched converter e.g. a buck converter or boost converter which forms the driving circuit. The clocking of the driving circuit and especially the transformer by at least one controllable switch which is clocked at high frequency may depend on a controlling signal inputted to a control input of the driving circuit. For instance the frequency and / or the duty cycle of the controllable switch of the driving circuit may be adjusted in dependency on the controlling signal inputted to an input of the driving circuit.

The driving circuit may generate a driving current or driving voltage for the lighting device. The driving circuit may output the driving current or driving voltage for the lighting device at the first input port X1-a in order to output the input voltage to the ripple suppression circuit <NUM> (or 30a, 30b).

Claim 1:
A ripple suppression circuit, comprising:
a first diode (D2);
a first input port, configured to receive an input voltage via the first diode (D2);
a first output port, configured to output an output voltage;
a first capacitor (C2), configured to be connected between the first input port and a ground port;
a first transistor (Q1), configured to be connected between the first input port and the first output port;
a second diode (D4) and a second capacitor (C1), configured to be connected in series between the first input port and the ground port;
a second transistor (Q2), configured to be coupled between a base of the first transistor and a connecting node of the second diode (D4) and the second capacitor (C1);
a third capacitor (C3), configured to be connected between a base of the second transistor and the ground port; and
a voltage control circuit (100a) configured to be connected to the base of the second transistor (Q2), wherein when the input voltage drops to a minimum value, the voltage control circuit (<NUM>) is configured to make a voltage of the base of the second transistor (Q2) to be higher than the input voltage, and the output voltage to be equal to the minimum value,
characterized in that the voltage control circuit (100a) comprises:
a fourth capacitor (C4), configured to be coupled between the ground port and the connecting node of the second diode (D4) and the second capacitor (C1);
a fifth diode (D11) and a sixth diode (D51), configured to be reversely coupled in series between the first input port and the fourth capacitor (C4), a cathode of the sixth diode (D51) is connected to the first port, an anode of the fifth diode (D11) is coupled to the fourth capacitor (C4);
a comparator (X1), configured to compare the voltage at the base of the second transistor (Q2) with the voltage of the anode of the fifth diode (D11), and output a comparison result; and
an optical coupler (U1), configured to be controlled by the comparison result, wherein when the voltage at the base of the second transistor (Q2) is lower than the voltage of the anode of the fifth diode (D11), the optical coupler is configured to couple the base of the second transistor (Q2) to the anode of the fifth diode (D11).