TWI674037B - LED driver circuit supporting low voltage input and its control chip - Google Patents

Abstract

An LED driving circuit supporting low voltage input has: a power conversion unit for converting an input voltage into an output current under the control of a switching channel; and a control unit having: a logic control unit for generating A switching signal; a driving circuit having the switching channel to be coupled with the power conversion unit, and the switching channel is controlled by the switching signal; an overvoltage protection module for a shutdown period and a preset A comparison result of time generates an overvoltage signal; and a mask logic circuit for determining whether a conduction period exceeds a maximum conduction period and determining a potential of a mask signal according to a judgment result, and using the mask signal to mask Cover the overvoltage signal to avoid flickering of an LED module.

Description

LED driving circuit and control chip supporting low voltage input

This case relates to an LED driving circuit, and more particularly to an LED driving circuit supporting low voltage input.

Please refer to FIG. 1, which is a circuit diagram of a conventional switch-type LED driving circuit. As shown in FIG. 1, the conventional switch-type LED driving circuit has a bridge rectifier unit 11, a capacitor 12, a resistor 13, a capacitor 14, a capacitor 15, an LED module 16, a diode 17, a The inductor 18, a control chip 19, a resistor 20 and a resistor 21.

During operation, an AC alternating current is rectified and filtered by the bridge rectifier unit 11 and the capacitor 12 to generate a bus voltage V _IN . The bus voltage V _IN generates a power supply voltage after low-pass filtering of the resistor 13 and the capacitor 14. Control chip 19; control chip 19 controls a power conversion operation through a 500V switching transistor (not shown in the figure) provided between the DRAIN pin and the CS pin internally; the resistor 20 determines an overvoltage protection unit. The required reference voltage value; resistor 21 provides a current sampling signal V _CS ; capacitor 15 provides the effect of reducing the current ripple of LED module 16; diode 17 provides an inductor current release path; inductor 18 provides a cumulative current iL; and the control chip 19 determines the duty cycle of the power conversion operation according to the current sampling signal V _CS and determines whether to enter an over-voltage protection mode according to the reference voltage value.

Please refer to FIG. 2, which illustrates an inductor current waveform diagram of the conventional switching LED driving circuit of FIG. 1. As shown in FIG. 2, it is a waveform of the inductor current iL in a critical conduction mode, which is mainly divided into an on-phase and an off-phase.

In the conducting phase, the control chip 19 turns on the internal switching transistor to store energy in the inductor 18. At this time, the inductor current iL will always rise, and the voltage of the current sampling signal V _CS provided by the resistor 21 is also Rise with it. When the voltage of the current sampling signal V _CS is greater than an internal reference voltage V _REF (not shown in the figure), the control chip 19 turns off the switching transistor, and at this time, the inductor current iL rises to the maximum value I _PK . The time T _ON during the conduction phase can be expressed as follows: Where L is the inductance value of the inductor 18, V _IN is the bus voltage, V _LED is the load voltage, I _PK = V _REF / R _CS , and R _CS is the resistance value of the resistor 21.

In the cut-off phase, the control chip 19 turns off the internal switching transistor, the inductor 18 releases energy through the diode 17, and the inductor current iL decreases from the peak value _IPK . When the inductor current iL drops to zero, a current zero-crossing detection module (not shown in the figure) inside the control chip 19 will turn on the switching transistor again, and the off time T _OFF can be expressed as follows:

Since there is no auxiliary winding, can not directly detect the voltage across the LED module 16, therefore, the current common practice is detected by comparing the phase of the off time T _OFF, and an internal reference time T _OVP, the size of the time of T _OVP It can be determined by the resistance value of the resistor 20. If T _OFF > T _OVF , the voltage across the LED module 16 is low, and the circuit can work normally; If T _OFF <T _OVP , it indicates that the voltage across the LED module 16 is high, the circuit needs to enter the overvoltage protection mode to prevent The LED module 16 is burned out.

However, after the input AC voltage AC passes through the bridge rectifier unit 11 and the capacitor 12, ripples are still generally generated in the bus voltage V _IN . Especially when V _{IN is} small and the voltage of LED module 16 is large, and the minimum value of V _IN is close to the voltage of LED module 16, Ton will be very large at this time, which may cause the switching frequency of the circuit to fall into In the frequency range of the sound (20 ~ 20KHz) that human ears can hear, this phenomenon is generally called inductance howling. The general solution to the inductor howling is to add a maximum on-time module inside the control chip 19, which is when the required T _ON exceeds a maximum on-time, even if the positive peak value of the inductor current does not reach I _PK Turn off the switching transistor. However, since the peak value of the inductor current iL is low at this time, the T _OFF time will be correspondingly reduced, so it is likely that T _OFF <T _OVP will cause the circuit to enter the overvoltage protection mode, which will cause the LED module 16 Flicker occurs.

To solve the above problems, a new LED driving circuit is urgently needed in the art.

It is an object of the present invention to provide an LED driving circuit supporting low voltage input, which can prevent an LED driving circuit by a mask mechanism in the case of a low voltage difference between an input voltage and the cross-voltage of an LED module. Enter the over-voltage protection mode to avoid flickering of the LED module.

Another object of the present invention is to provide an LED driving circuit supporting low voltage input, which can prevent the LED driving circuit from entering through a mask mechanism when one of the LED driving circuits exceeds a preset maximum on time. Over-voltage protection mode to avoid flickering of an LED module.

In order to achieve the above purpose, an LED driving circuit supporting low voltage input is proposed, which has: a power conversion unit including an inductor, a capacitor, and a diode, which is used to control a The input voltage is converted into an output current to drive an LED module; and a control unit having: a logic control unit for generating a switching signal, the switching signal has an on period and an off period; a driving circuit With the switch channel, one end of the switch channel is coupled to the power conversion unit, and the other end of the switch channel is coupled to a ground potential via a resistor to generate a current sensing signal at the resistor, and the switch The channel is controlled by the switching signal; an overvoltage protection module is used to generate an overvoltage signal according to a comparison result between the off period and a preset time, when the off period is less than the preset time , The overvoltage signal presents a first applied potential, and when the off period is not less than the preset time, the overvoltage signal presents a first inactive potential, the first applied potential and the An inactive potential is two complementary logic potentials; and a mask logic circuit for determining whether the conduction period exceeds a maximum conduction period and determining a potential of a mask signal according to a determination result, and using the mask signal The over-voltage signal is masked to generate an over-voltage protection signal, wherein when the conduction period exceeds the maximum conduction period, the mask signal presents a second action potential, and when the conduction period does not exceed the maximum conduction period When the mask signal presents a second inactive potential, the second applied potential and the second inactive potential are two complementary logic potentials; and when the mask signal exhibits the second applied potential, the transition Voltage protection signal It is in an inactive state to prevent the logic control unit from entering an overvoltage protection mode. When the mask signal represents the second inactive potential and the overvoltage signal represents the first active potential, the overvoltage The protection signal is in an active state to drive the logic control unit into the over-voltage protection mode.

In one embodiment, the control unit has a current zero-crossing detection module to enable the switching signal to start a conducting period when the current of the inductor drops to zero.

In one embodiment, the mask logic circuit includes a latch unit having a first input terminal, a second input terminal, and an output terminal. The first input terminal is used to communicate with a maximum on-time state signal. Coupled, and the second input terminal is coupled to a current peak signal; an inverter having an input terminal to be coupled to the output terminal of the latch unit, and an output terminal to provide the A mask signal; and an inverse gate, having two input terminals to be coupled to the mask signal and the overvoltage signal, respectively, and an output terminal to provide the overvoltage protection signal.

In one embodiment, the mask logic circuit has a maximum on-time module for generating the maximum on-time status signal, and the maximum-on-time state signal is used to make the maximum on-time when the on-time exceeds the maximum on-time. The on-time state signal exhibits an active state; and a peak current detection module for generating the current peak signal, and the peak current signal exhibits an effect when the current of the inductor reaches a peak status.

In one embodiment, the latch unit includes a reverse or gate latch.

In one embodiment, the latch unit includes a reverse latch latch.

In one embodiment, the mask logic circuit has a latch unit having a first input terminal, a second input terminal, and an output terminal. The first input terminal is used for coupling with a leading edge blanking signal. Connected, and the second input terminal is coupled with a current comparison signal; an inverter having an input terminal to be coupled to the output terminal of the latch unit, and an output terminal to provide the shielding Shroud signal; a reverse sum brake having two input terminals to be coupled to the mask signal and the overvoltage signal, and an output terminal to provide the overvoltage protection signal; A leading-edge blanking signal generating module for generating the leading-edge blanking signal, which is in an active state during an initial period of the conducting period; and a comparator for sensing the signal according to the current Perform a comparison operation with a reference voltage to generate the current comparison signal.

In one embodiment, the latch unit includes a reverse or gate latch.

In one embodiment, the latch unit includes a reverse latch latch.

In addition, the present invention also provides a control chip including the control unit of the LED driving circuit supporting the low voltage input as described above.

In order to allow your reviewers to further understand the structure, characteristics and purpose of this creation, drawings and detailed descriptions of the preferred embodiments are attached below.

11‧‧‧Bridge rectifier unit

12, 14, 15‧‧‧ capacitors

13, 20, 21‧‧‧ resistance

16, 300‧‧‧LED module

17‧‧‧diode

18‧‧‧Inductance

19‧‧‧control chip

100‧‧‧ Power Conversion Unit

200‧‧‧Control unit

201‧‧‧Logic Control Unit

202‧‧‧Drive circuit

203‧‧‧Current zero-crossing detection module

204‧‧‧Overvoltage protection module

205‧‧‧Mask logic circuit

2051‧‧‧Latch unit

2051a, 2051b ‧‧‧ reverse OR gate

2052‧‧‧Inverter

2053‧‧‧Reverse Gate

2054‧‧‧Maximum On-Time Module

2055‧‧‧Peak current detection module

2056‧‧‧ Leading-Edge Blanking Signal Generation Module

2057‧‧‧ Comparator

FIG. 1 is a circuit diagram of a conventional switch-type LED driving circuit.

FIG. 2 is a waveform diagram of an inductor current of the conventional switching LED driving circuit of FIG. 1.

FIG. 3 is a block diagram of an LED driving circuit supporting low voltage input according to an embodiment of the present invention.

FIG. 4 is a block diagram of an embodiment of a mask logic circuit in a control unit shown in FIG. 3.

FIG. 5 is a block diagram of another embodiment of a mask logic circuit in a control unit shown in FIG. 3.

Please refer to FIG. 3, which is a block diagram illustrating an embodiment of an LED driving circuit supporting low voltage input according to the present invention. As shown in FIG. 3, the LED driving circuit has a power conversion unit 100 and a control unit 200 to drive an LED module 300.

The power conversion unit 100 includes an inductor, a capacitor, and a diode, and is used to control a switching channel (the switching channel is provided by a switching transistor (not shown) inside the control unit 200). An input voltage V _{IN is} converted into an output current I _OUT to drive the LED module 300, wherein the LED module 300 has a cross-voltage V _LED .

The control unit 200 may be implemented by a control chip, and has a logic control unit 201, a driving circuit 202, a current zero crossing detection module 203, an overvoltage protection module 204, and a mask logic circuit 205.

The logic control unit 201 is used to generate a switching signal V _PWM . The switching signal V _PWM has a turn-on period and a turn-off period, and is triggered by a current zero-crossing signal ZCD to start a turn-on period.

The driving circuit 202 has the switching channel. One end D of the switching channel is coupled to the power conversion unit 100, and the other end CS is coupled to a ground voltage via a resistor 210 to generate a current sensing signal V _{CS of} the inductor. , And the switching channel is controlled by the switching signal V _PWM .

The current zero-crossing detection module 203 is used to make the switching signal start a conducting period when the current of the inductor drops to zero.

The over-voltage protection module 204 is configured to generate an over-voltage signal OVP according to a comparison result between a representative signal T _OFF and a preset time during the shutdown period. When the shutdown period is shorter than the preset time, The overvoltage signal OVP presents a first applied potential, and when the off period is not less than the preset time, the overvoltage signal OVP presents a first inactive potential, and the first applied potential and the first applied potential The inactive potential is two complementary logic potentials (eg, a high logic potential and a low logic potential, or a low logic potential and a high logic potential, respectively).

The mask logic circuit 205 is used to determine whether the conduction period exceeds a maximum conduction period and determine the potential of a mask signal according to a judgment result, and use the mask signal to mask the overvoltage signal OVP to generate an overvoltage. The protection signal OVPOUT, wherein when the conducting period exceeds the maximum conducting period, the mask signal presents a second applied potential, and when the conducting period does not exceed the maximum conducting period, the mask signal presents a first Two inactive potentials, the second inactive potential and the second inactive potential are two complementary logic potentials (eg, a high logic potential and a low logic potential, or a low logic potential and a high logic potential, respectively) ; And when the mask signal presents the second applied potential, the overvoltage protection signal OVPOUT assumes an inactive state to prevent the logic control unit 201 from entering an overvoltage protection mode, and when the mask signal presents When the second inactive potential is described and the overvoltage signal OVP presents the first applied potential, the overvoltage protection signal OVPOUT presents an active state to drive the logic control Overvoltage protection means 201 enters the mode.

Please refer to FIG. 4, which is a block diagram of an embodiment of a mask logic circuit 205 of the control unit 200 of FIG. 3. As shown in FIG. 4, the mask logic circuit 205 has a latch unit 2051, an inverter 2052, a reverse AND gate 2053, a maximum on-time module 2054, and a peak current detection module 2055.

The latch unit 2051 has a first input terminal, a second input terminal, and an output terminal. The first input terminal is used for coupling with a maximum on-time state signal TON_MAX, and the second input terminal is connected with a current. The peak signal CS_OUT is coupled. In this embodiment, although the latch unit 2051 is implemented by a reverse OR gate latch (consisting of reverse OR gate 2051a and reverse OR gate 2051b), it can also be implemented by a reverse OR gate latch.

The inverter 2052 has an input terminal to be coupled to the output terminal of the latch unit 2051, and an output terminal to provide a mask signal MSK.

The inverting gate 2053 has two input terminals to be respectively coupled to the mask signal MSK and the overvoltage signal OVP, and an output terminal to provide the overvoltage protection signal OVPOUT.

The maximum on-time module 2054 is used to generate a maximum on-time status signal TON_MAX, and it causes the maximum on-time status signal TON_MAX to assume an active state when the on-period exceeds the maximum on-period (implemented here) In the example, the action state is a high logic potential).

The peak current detection module 2055 is used to generate a current peak signal CS_OUT, and it makes the current peak signal CS_OUT present an active state when the current of the inductor reaches a peak value, so as to provide The mask logic circuit 205 is reset.

Please refer to FIG. 5, which is a block diagram of another embodiment of the mask logic circuit 205 of the control unit 200 of FIG. 3. As shown in FIG. 5, the mask logic circuit 205 has a latch unit 2051, an inverter 2052, an inverse AND gate 2053, a leading-edge blanking signal generation module 2056, and a comparator 2057.

The latch unit 2051 has a first input terminal, a second input terminal and an output terminal. The first input terminal is used for coupling with a leading edge blanking signal CS_LEB, and the second input terminal is compared with a current. The signal CMP is coupled. In this embodiment, although the latch unit 2051 is implemented by a reverse OR gate latch (consisting of reverse OR gate 2051a and reverse OR gate 2051b), it can also be implemented by a reverse OR gate latch.

The inverter 2052 has an input terminal to be coupled to the output terminal of the latch unit 2051, and an output terminal to provide a mask signal MSK.

Reverse gate 2053 has two input terminals to be coupled to the mask signal MSK and the overvoltage signal OVP, respectively, and an output terminal to provide the overvoltage protection signal OVPOUT.

The leading-edge blanking signal generation module 2056 is used to generate the leading-edge blanking signal CS_LEB, and it shows an active state during an initial period of the on period (in this embodiment, the active state is a High logic potential pulse) to reset the mask logic circuit 205 in each switching cycle.

The comparator 2057 is configured to perform a comparison operation according to the current sensing signal V _{CS of} the inductor and a reference voltage V _REF to generate the current comparison signal CMP. The waveform of the current sensing signal V _{CS is shown} in the waveform of the inductor current iL in FIG. 2. During the conducting phase, the control unit 200 turns on the internal switching transistor to store energy in the inductor. At this time, the current of the inductor iL will keep rising, and the voltage of the current sensing signal V _CS provided by the resistor 210 will also rise accordingly; in the cut-off phase, the control unit 200 turns off the internal switching transistor, and the inductance is released through the diode Energy, the current iL of the inductor decreases from the peak value I _PK , and the voltage of the current sensing signal V _CS also decreases accordingly. When the peak voltage of the current sensing signal V _CS is greater than the reference voltage V _REF , it means that the on-period exceeds the maximum on-period.

According to the above technical solution, the present invention can prevent the LED driving circuit from entering the over-voltage protection mode by a mask mechanism in the case where there is a low voltage difference between the voltage of V _IN and the across-voltage V _{LED of the} LED module 300. As a result, flickering of the LED module 300 is prevented. In addition, the present invention resets the mask logic circuit 205 during the on period of each switching cycle, and detects the voltage difference between V _IN and V _LED during the off period to determine whether the mask signal MSK needs to be generated. Therefore, when the V _IN voltage rises from low to high, the mask signal MSK will not always mask the over-voltage signal OVP because it always presents the operating state, so that the LED module 300 has a risk of burning. In other words, the present invention can prevent the LED module 300 from flickering, and can also avoid the risk of burning the LED module 300.

In addition, since the global civil alternating current standard mainly has two alternating current standards of 220V area and 110V area, the present invention provides different corresponding embodiments for the two alternating current standards:

(1) The 220V area (220V ~ 240V) is mainly used in 140 countries including China, Europe, and India.

When driving an 18W system, the typical LED output is 150V / 110mA, and the capacitor C1 generally uses 4.7uF. If the input voltage of the AC power is as low as 176VAC (less than 20% of the typical value of 220VAC), the bus voltage V _IN will be close to the output voltage of the LED module and the on-time will exceed the maximum on-time, which may be premature. Switch off the channel. At this time, using the technical solution of the present invention can avoid prematurely closing the switch channel and preventing the LED module from flickering.

(2) 110V area (100V ~ 130V), mainly used in the United States, Japan, Canada and other countries.

When driving an 18W system with a typical LED output of 72V / 240mA, the capacitor C1 generally uses 6.8uF. If the input voltage of the AC power is as low as 88VAC (less than 20% of the typical value of 220VAC), the bus voltage V _IN will be close to the output voltage of the LED module and the on-time will exceed the maximum on-time, which may be premature. Switch off the channel. At this time, using the technical solution of the present invention can avoid prematurely closing the switch channel and preventing the LED module from flickering.

With the design disclosed above, the present invention has the following advantages:

1. The LED driving circuit supporting low voltage input of the present invention can prevent an LED driving circuit from entering overvoltage protection by a mask mechanism in the case of a low voltage difference between an input voltage and the cross-voltage of an LED module. Mode to avoid flickering of the LED module.

2. The LED driving circuit supporting low voltage input of the present invention can prevent the LED driving circuit from entering the overvoltage protection mode by a mask mechanism when one of the LED driving circuits is turned on during a preset maximum on time. To avoid flickering of an LED module.

The one disclosed in this case is one of the preferred embodiments, and any change or modification that originates from the technical ideas of this case and is easily inferred by those who are familiar with the technology, does not depart from the scope of patent rights in this case.

Claims (9)

An LED driving circuit supporting low-voltage input has a power conversion unit including an inductor, a capacitor and a diode, which is used to convert an input voltage into an output current under the control of a switching channel Driving an LED module; and a control unit having: a logic control unit for generating a switching signal having a turn-on period and a turn-off period; a driving circuit having the switch channel and the switch One end of the channel is coupled to the power conversion unit, the other end of the switch channel is coupled to a ground potential through a resistor to generate a current sensing signal at the resistor, and the switch channel is controlled by the switch signal; An overvoltage protection module is used to generate an overvoltage signal according to a comparison result between the off period and a preset time. When the off period is less than the preset time, the over voltage signal presents a first An active potential, when the off period is not less than the preset time, the overvoltage signal exhibits a first non-active potential, the first active potential and the first non-active potential are two complementary Logic potential; and a mask logic circuit to determine whether the conduction period exceeds a maximum conduction period and determine the potential of a mask signal according to a judgment result, and use the mask signal to mask the overvoltage signal to generate An overvoltage protection signal, wherein when the conduction period exceeds the maximum conduction period, the mask signal exhibits a second action potential, and when the conduction period does not exceed the maximum conduction period, the mask signal exhibits a A second inactive potential, the second inactive potential and the second inactive potential are two complementary logic potentials; and when the mask signal assumes the second inactive potential, the overvoltage protection signal assumes an inactive State to prevent the logic control unit from entering an overvoltage protection mode, when the mask signal exhibits the second inactive potential and the overvoltage signal exhibits the first active potential, the overvoltage protection signal exhibits a Active state to drive the logic control unit into the overvoltage protection mode; wherein the mask logic circuit has: a latch unit with a first input Terminal, a second input terminal and an output terminal, the first input terminal is used for coupling with a maximum on-time state signal, and the second input terminal is coupled with a current peak signal; an inverter, It has an input terminal to couple with the output terminal of the latch unit, and an output terminal to provide the mask signal; and an inverting gate, with two input terminals to respectively connect with the mask signal And the overvoltage signal is coupled, and an output terminal is provided to provide the overvoltage protection signal. The LED driving circuit supporting low voltage input as described in item 1 of the patent application scope, wherein the control unit further has a current zero-crossing detection module to start the switching signal when the current of the inductor falls to zero One of the on periods. The LED driving circuit supporting low voltage input as described in item 1 of the patent application scope, wherein the mask logic circuit has: a maximum on-time module for generating the maximum on-time status signal, and it is in When the conduction period exceeds the maximum conduction period, the maximum conduction time state signal assumes an active state; and a peak current detection module is used to generate the current peak signal, which is located in the inductance When the current reaches a peak value, the current peak signal assumes an active state. The LED driving circuit supporting low voltage input as described in item 1 of the patent application scope, wherein the latch unit includes an inverter or a latch. The LED driving circuit supporting low voltage input as described in item 1 of the patent application scope, wherein the latch unit includes an inverter and a gate latch. An LED driving circuit supporting low-voltage input has a power conversion unit including an inductor, a capacitor and a diode, which is used to convert an input voltage into an output current under the control of a switching channel Driving an LED module; and a control unit having: a logic control unit for generating a switching signal having a turn-on period and a turn-off period; a driving circuit having the switch channel and the switch One end of the channel is coupled to the power conversion unit, the other end of the switch channel is coupled to a ground potential through a resistor to generate a current sensing signal at the resistor, and the switch channel is controlled by the switch signal; An overvoltage protection module is used to generate an overvoltage signal according to a comparison result between the off period and a preset time. When the off period is less than the preset time, the over voltage signal presents a first An active potential, when the off period is not less than the preset time, the overvoltage signal exhibits a first non-active potential, the first active potential and the first non-active potential are two complementary Logic potential; and a mask logic circuit to determine whether the conduction period exceeds a maximum conduction period and determine the potential of a mask signal according to a judgment result, and use the mask signal to mask the overvoltage signal to generate An overvoltage protection signal, wherein when the conduction period exceeds the maximum conduction period, the mask signal exhibits a second action potential, and when the conduction period does not exceed the maximum conduction period, the mask signal exhibits a A second inactive potential, the second inactive potential and the second inactive potential are two complementary logic potentials; and when the mask signal assumes the second inactive potential, the overvoltage protection signal assumes an inactive State to prevent the logic control unit from entering an overvoltage protection mode, when the mask signal exhibits the second inactive potential and the overvoltage signal exhibits the first active potential, the overvoltage protection signal exhibits a Active state to drive the logic control unit into the overvoltage protection mode; wherein the mask logic circuit has: a latch unit with a first input Terminal, a second input terminal and an output terminal, the first input terminal is used for coupling with a leading-edge blanking signal, and the second input terminal is coupled with a current comparison signal; an inverter has An input terminal is coupled to the output terminal of the latch unit, and an output terminal is used to provide the mask signal; an inverting gate has two input terminals to respectively connect with the mask signal and the signal The overvoltage signal is coupled, and an output terminal is provided to provide the overvoltage protection signal; a leading-edge blanking signal generating module is used to generate the leading-edge blanking signal, and it is during the conduction period In an initial period of, an active state is shown; and a comparator, used to perform a comparison operation based on the current sensing signal and a reference voltage to generate the current comparison signal. The LED driving circuit supporting low voltage input as described in Item 6 of the patent application scope, wherein the latch unit includes an inverter or a latch. The LED drive circuit supporting low voltage input as described in item 6 of the patent application scope, wherein the latch unit includes an inverter and a gate latch. A control chip comprising the control unit of the LED driving circuit supporting low voltage input as described in any one of the patent application items 1 to 8.