CN109168219B

CN109168219B - Damping circuit and LED drive circuit with same

Info

Publication number: CN109168219B
Application number: CN201811115055.1A
Authority: CN
Inventors: 张军明; 季悦; 黄必亮; 任远程; 周逊伟
Original assignee: Joulwatt Technology Hangzhou Co Ltd
Current assignee: Joulwatt Technology Co Ltd
Priority date: 2015-04-30
Filing date: 2015-04-30
Publication date: 2020-12-01
Anticipated expiration: 2035-04-30
Also published as: CN109168219A; CN104797058B; CN104797058A

Abstract

The invention provides a damping circuit and an LED drive circuit with the same. The damping circuit comprises a damping element, a control circuit and a control switch. The damping element is electrically connected with the direct current bus. The control circuit obtains a power supply voltage from the direct current bus and compares the power supply voltage with a threshold voltage, and when the direct current bus voltage is higher than the threshold voltage, the control circuit outputs a first control signal. The control switch is respectively electrically connected with the damping element and the control circuit, and the control switch switches the damping element into the circuit based on a first control signal output by the control circuit. By arranging the damping circuit in the LED driving circuit, the damping circuit can effectively inhibit the voltage on the direct current bus from continuously rising in the starting stage, and effectively reduce the voltage-resistant grade of the next-stage circuit, so that the LED driving is compatible with the electronic ballast.

Description

Damping circuit and LED drive circuit with same

The present application is a divisional application of application No. 201510220932.1, application date 2015, 4/30, entitled "damping circuit and LED driving circuit having damping circuit".

Technical Field

The invention relates to the field of LED driving, in particular to a damping circuit and an LED driving circuit with the same.

Background

The traditional electronic ballast is connected with a fluorescent lamp load, and certain environmental pollution exists because the luminous efficiency of the fluorescent lamp is lower. Today, energy conservation and emission reduction are becoming a trend to replace fluorescent lamps with LED lamps. In order to realize direct replacement, the LED lamp needs to be capable of receiving common commercial power to supply power to the LED lamp, and needs to be capable of being directly connected, namely, an electronic ballast of a fluorescent lamp is used as power supply of the LED lamp. However, the output of the electronic ballast is a high-frequency ac signal, and the LED lamp requires dc power supply, which cannot be directly matched. Therefore, it is usually necessary to rectify the output of the electronic ballast into direct current through a rectifier bridge and then convert it into direct current required by the LED load using the LED driver.

However, since the electronic ballast is designed specifically for fluorescent lamps, its operation includes a start-up phase and a steady-state phase. During the starting phase, the electronic ballast outputs a high voltage to break down the tube of the fluorescent lamp, so as to realize the glow discharge of the fluorescent lamp, and the output voltage of the electronic ballast is usually between hundreds of volts and one thousand volts and is far higher than the voltage in the steady state phase (usually below 200V). If such an electronic ballast suitable for a conventional fluorescent lamp is directly connected to an LED driver, the high voltage generated in the start-up stage will pose a great challenge to the design of the LED driver in the subsequent stage.

Disclosure of Invention

The invention provides a damping circuit and an LED driving circuit comprising the same, aiming at solving the problem that when an electronic ballast supplies power to an LED lamp, the high voltage output in the starting stage of the electronic ballast brings difficulty to the design of a rear-stage LED driver.

In order to achieve the above object, the present invention provides a damping circuit including a damping element, a control circuit, and a control switch. The damping element is electrically connected with the direct current bus. The control circuit obtains a power supply voltage from the direct current bus and compares the power supply voltage with a threshold voltage, and when the power supply voltage is higher than the threshold voltage, the control circuit outputs a first control signal. The control switch is respectively electrically connected with the damping element and the control circuit, and the control switch switches the damping element into the circuit based on a first control signal output by the control circuit.

In an embodiment of the invention, the control circuit includes a comparator and a controller, one input terminal of the comparator inputs the supply voltage, the other input terminal inputs the voltage threshold, the output terminal outputs the comparison signal to the controller, and the controller outputs the first control signal to the control switch according to the comparison signal.

In an embodiment of the invention, the control circuit further includes a timer, the timer starts timing when the controller outputs the first control signal, the controller outputs the second control signal when the timing time reaches the time threshold, and the control switch switches the damping element out of the circuit based on the second control signal output by the control circuit.

In an embodiment of the invention, the damping circuit further includes a voltage-stabilizing power supply circuit, and the voltage-stabilizing power supply circuit performs voltage stabilization on the power supply voltage and outputs the voltage-stabilizing power supply voltage to the control circuit.

In an embodiment of the invention, the voltage-stabilizing power supply circuit includes a diode and a charging capacitor, an anode of the diode is electrically connected to the output end of the damping element, a cathode of the diode is respectively connected to the charging capacitor and the control circuit, the dc bus voltage charges the charging capacitor through the damping element and the diode, and voltages at two ends of the charging capacitor are output to the control circuit.

In an embodiment of the invention, the damping element is a power resistor.

In an embodiment of the present invention, the control switch is an NMOS transistor or an NPN transistor, and when the control switch is an NMOS transistor, the drain of the NMOS transistor is electrically connected to the output terminal of the damping element, the gate of the NMOS transistor is electrically connected to the control circuit, and the source of the NMOS transistor is grounded; when the control switch is an NPN triode, the collector of the NPN triode is electrically connected with the output end of the damping element, the base of the NPN triode is electrically connected with the control circuit, and the emitter of the NPN triode is grounded.

In an embodiment of the present invention, the control switch is a PMOS transistor or a PNP triode, and when the control switch is the PMOS transistor, the drain of the PMOS transistor is electrically connected to the damping element, the gate of the PMOS transistor is electrically connected to the control circuit, and the source of the PMOS transistor is connected to the dc bus; when the control switch is a PNP triode, the collector of the PNP triode is electrically connected with the output end of the damping element, the base of the PNP triode is electrically connected with the control circuit, and the emitter of the PNP triode is connected with the direct current bus.

According to another aspect of the present invention, there is also provided an LED driving circuit having a damping circuit, the LED driving circuit including an electronic ballast, a rectifying circuit, a capacitor connected in parallel to an output terminal of the rectifying circuit, and the damping circuit described above.

In an embodiment of the present invention, the rectifying circuit may be a full-bridge rectifying circuit or a half-bridge rectifying circuit.

According to the damping circuit and the LED driving circuit with the damping circuit, when the direct current bus outputs high voltage (such as the starting stage of an electronic ballast), the damping element is switched into the circuit through the control switch, so that the high voltage output by the direct current bus is restrained, the voltage withstanding grade of a post-stage circuit is reduced, and the damage or the incapability of working caused by the high voltage is effectively avoided. The specific implementation mode is as follows: the control circuit obtains a power supply voltage from the direct current bus, and when the power supply voltage is higher than a set voltage threshold value, the control circuit outputs a first control signal to close the control switch. When the control switch is closed, the damping element connected with the direct current bus is switched into the circuit, and the damping element effectively inhibits the continuous rising of the bus voltage, so that the rear-stage circuit is protected and enters a normal working state.

In practical use, when the load is connected to the dc bus and has an output current, the voltage on the dc bus will gradually decrease. Therefore, to improve the efficiency of the circuit, the damping element must be switched out of the circuit in time after the load is switched on. In this embodiment, by setting a time threshold, when the first control signal closes the control switch, the timer starts timing, and after the time threshold is reached, the control circuit outputs the second control signal to close the control switch, so as to switch the damping element out of the circuit in time, thereby eliminating power consumption on the damping element and increasing output power of the circuit.

In order to make the aforementioned and other objects, features and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below.

Drawings

Fig. 1 is a schematic diagram of a conventional LED driving circuit having an electronic rectifier as an input.

Fig. 2 is a schematic diagram of a damping circuit according to an embodiment of the present invention.

Fig. 3 is a schematic diagram of an LED driver circuit having the damping circuit shown in fig. 2.

Fig. 4 shows the output voltage of the electronic ballast of fig. 1 at various stages.

Fig. 5 shows the output voltage of the electronic ballast of fig. 3 at different stages.

Fig. 6 is a schematic diagram of an LED driving circuit with a damping circuit according to another embodiment of the present invention.

Fig. 7 is a timing chart showing the voltage between the two terminals of the charging capacitor and the voltage of the control terminal of the control switch in fig. 3.

Detailed Description

Fig. 1 shows a conventional LED driving circuit, in which an ac high-frequency signal output from an electronic ballast is rectified and then directly output to an LED driver. However, since the electronic ballast is designed specifically for the fluorescent lamp, the fluorescent lamp needs to perform a glow discharge in the lighting phase, and the glow discharge needs a very high voltage. Therefore, the output of the electronic ballast includes two phases, one of which is a start phase, in which the electronic ballast outputs a high voltage to glow the fluorescent lamp, and when the fluorescent lamp is lit, the electronic ballast enters a steady-state phase to output a normal operating voltage of about 200V.

In fig. 1, the electronic ballast is directly connected to the LED driver, and during the start-up phase of the electronic ballast, since the LED load is not turned on, the load has no output current, and at this time, the output of the electronic ballast is rectified and then charges the capacitor connected in parallel to the output terminal of the rectifying circuit, so that the voltage across the capacitor is rapidly increased and reaches the start-up voltage of the electronic ballast. This requires that the LED driver have an extremely high voltage withstand level that can withstand the high voltage of approximately one thousand volts output by the electronic ballast during the startup phase. This poses a great challenge to the design of LED drivers, and further, the compatible design of LED drivers for electronic ballasts is difficult due to the different voltages output by different electronic ballasts.

To solve the above problem, the present invention provides a damping circuit 300 suitable for an electronic ballast as an input to drive an LED. Correspondingly, the present embodiment also provides an LED driving circuit including the damping circuit 300. The operation of the damping circuit 300 will be described in detail below in conjunction with an LED driving circuit. However, the present invention does not limit the application of the damping circuit 300 to the LED driving circuit. In other embodiments, the damping circuit 300 can be applied to other circuits that need to suppress the bus voltage rise in a short time.

As shown in fig. 3, the LED driving circuit with the damping circuit provided in this embodiment includes an electronic ballast 100, a rectifying circuit 200, a capacitor 400 connected in parallel to an output terminal of the rectifying circuit 200, and a damping circuit 300. Since the LED lamp needs to be driven by a dc signal, the high frequency ac signal output by the electronic ballast 100 is rectified by the rectifier circuit 200 to form a dc signal output. In the present embodiment, the rectifying circuit 200 is a full bridge rectifier composed of four diodes. However, the present invention is not limited thereto. In other embodiments, the rectifying circuit 200 may be a half-bridge rectifying circuit.

As shown in fig. 2, the damping circuit 300 includes a damping element 1, a control circuit 2, and a control switch 3. The damping element 1 is electrically connected to the dc bus. The control circuit 2 obtains a supply voltage from the dc bus and compares the supply voltage with a threshold voltage, and when the supply voltage is higher than the threshold voltage, the control circuit 2 outputs a first control signal. In the present embodiment, the control circuit 2 obtains the supply voltage from the dc bus through the damping element 1. However, the present invention is not limited thereto. In other embodiments, the control circuit 2 may be connected to the dc bus via a resistor R to obtain the supply voltage (as shown in fig. 6). The control switch 3 is electrically connected to the damping element 1 and the control circuit 2, respectively, and the control switch 3 switches the damping element 1 into a circuit based on a first control signal output by the control circuit 2.

As shown in fig. 3, when the control switch 3 is closed, the damping element 1 is switched into a circuit, a loop is formed among the capacitor 400, the damping element 1 and the control switch 3, and the voltage across the capacitor 400 does not continuously rise, thereby achieving the effect of suppressing the rise of the dc bus voltage. Fig. 4 shows the output voltage of the electronic ballast in different stages in the conventional LED driver. Fig. 5 shows the output voltage of the electronic ballast 100 at different stages after adding the damping circuit 300 provided by the present invention. Comparing fig. 4 and fig. 5, it is obvious that, after the damping circuit 300 is added, the output voltage of the electronic ballast 100 in the starting stage is well suppressed, and correspondingly, the rectified dc bus voltage is also well suppressed.

In the present embodiment, the damping element 1 is a power resistor. However, the present invention is not limited thereto.

In the present embodiment, the control circuit 2 includes a comparator 21 and a controller 22, one input terminal of the comparator 21 inputs the supply voltage obtained from the dc bus, the other input terminal inputs the voltage threshold, the output terminal outputs the comparison signal to the controller 22, and the controller 22 outputs the first control signal to the control switch 3 according to the comparison signal. In this embodiment, the controller 22 is also used for driving the LED load of the subsequent stage. However, the present invention is not limited thereto. In other embodiments, the controller 22 and the LED driver may be separately and independently disposed.

In this embodiment, the control switch 3 is an NMOS transistor and is independent from the control circuit 2. However, the present invention is not limited thereto. In order to reduce the area occupied by the circuit board components, in other embodiments, the control switch 3 and the control circuit 2 may be integrated.

The drain electrode of the NMOS tube is electrically connected with the output end of the damping element 1, the grid electrode of the NMOS tube is electrically connected with the control circuit 2, and the source electrode of the NMOS tube is grounded. When the supply voltage input by the comparator 21 is greater than the voltage threshold, the comparator 21 outputs a first control signal to the controller 22, the controller 22 outputs a high level to the gate of the NMOS transistor, and the NMOS transistor is turned on to switch the damping element 1 into a circuit. However, the present invention does not set any limit to the specific type of the control switch 3. In other embodiments, the control switch 3 may be an NPN transistor or other P-type switch (such as a PMOS transistor or a PNP transistor). When the control switch 3 is an NPN transistor, the circuit form is the same as that of the present embodiment, the position of the NMOS transistor is directly replaced by the NPN transistor, the base of the NPN transistor is electrically connected to the controller 22, the collector of the NPN transistor is electrically connected to the output end of the damping element 1, and the emitter of the NPN transistor is grounded.

However, when the control switch 3 is a P-type switching tube, as shown in fig. 6, the damping element 1 and the control switch 3 exchange positions. Specifically, at this time, the drain (collector) of the P-type switching tube is electrically connected to the damping element 1, the gate (base) of the P-type switching tube is connected to the controller 22, and the source (emitter) of the P-type switching tube is connected to the dc bus.

After the control switch 3 switches the damping element 1 into the circuit, the control circuit 2 controls a switch to connect the LED load to the dc bus, and the electronic ballast 100 can continuously supply power to the LED load. When the LED load is turned on to generate an output current, the voltage across the capacitor 400 is gradually stabilized after charging and discharging, and the dc bus voltage is gradually decreased and falls back to the voltage value at the steady-state stage. In this case, in order to improve the efficiency of the circuit, i.e., to improve the ratio between the input power and the output power, it is desirable to reduce unnecessary consumption in the circuit as much as possible, and therefore, the damping element 1 is switched out of the circuit after the load is turned on to generate the output current.

In this embodiment, the control circuit 2 further includes a timer 23, when the controller 22 outputs the first control signal, the timer 23 starts to count time, and when the counted time reaches the time threshold, the controller 22 outputs the second control signal. The control switch 3 switches the damping element 1 out of the circuit based on the second control signal output by the controller 22, and power consumption does not occur on the damping element 1 any more, thereby greatly improving efficiency. In fig. 7, when the controller 22 outputs the first control signal at time t0, and when the LED load is connected to the dc bus to generate the output current at time t1, the time threshold is t1-t 0.

In practical use, under the influence of external interference, the voltage of the dc bus may change, and the change may cause the malfunction of the comparator 21, thereby affecting the switching of the control switch 3 and the normal operation of the whole damping circuit 300. In order to prevent the comparator 21 from misoperation caused by the voltage fluctuation of the direct current bus, the damping circuit 300 provided by the invention further comprises a voltage stabilizing power supply circuit 4. The voltage stabilizing power supply circuit 4 performs voltage stabilizing processing on the acquired power supply voltage and outputs the processed power supply voltage to the control circuit 2.

The regulated power supply circuit 4 includes a diode 41 and a charging capacitor 42. The anode of the diode 41 is connected to the output of the damping element 1, and the cathode of the diode 41 is connected to the charging capacitor 42 and one of the inputs of the comparator 21. In the starting stage of the electronic ballast, the dc bus voltage charges the charging capacitor 42 through the damping element 1 and the diode 41, the voltage Vcc across the charging capacitor 42 quickly reaches the starting voltage of the control circuit 2, and the control circuit 2 starts and starts to operate. In some embodiments, the start-up voltage of the control circuit may coincide with the threshold set by the comparator 21, i.e. when the voltage Vcc across the charging capacitor 42 reaches the threshold voltage set by the comparator 21, the control circuit 2 switches the damping circuit on (i.e. the switch 3 is turned on). Meanwhile, the threshold set by the comparator 21 may be higher than the starting voltage of the control circuit, that is, when the voltage Vcc across the charging capacitor 42 continues to increase with the increase of the bus voltage, the control circuit 2 switches the damping circuit on when the threshold set by the comparator 21 is reached. This arrangement can greatly simplify circuit design. However, the present invention is not limited thereto. In other embodiments, a separate power supply circuit may be used to activate the control circuit 2.

When the damping circuit is switched on (i.e. the switch tube 3 is turned on), the voltage Vcc across the charging capacitor 42 will not discharge through the diode 41 due to the diode 41, and the voltage at the Vcc point is kept stable. The voltage of the Vcc point ensures the normal operation of the comparator 21, and effectively avoids the misoperation of the comparator 21. As shown in fig. 7, the stable Vcc voltage makes the voltage Vg output to the gate of the control switch 3 stable for a period of time, and the control switch 3 switches stably.

In summary, according to the damping circuit 300 and the LED driving circuit with the damping circuit provided by the present invention, when the dc bus outputs a high voltage (e.g. at the start-up stage of the electronic ballast), the damping element 1 is switched into the circuit by the control switch 3, so as to suppress the high voltage output by the dc bus, reduce the voltage withstanding level of the subsequent circuit, and effectively avoid the damage or the inoperability caused by the high voltage. The specific implementation mode is as follows: the control circuit 2 obtains a supply voltage from the direct current bus, and when the supply voltage is higher than a set voltage threshold value, the control circuit 2 outputs a first control signal to close the control switch 3. When the control switch 3 is closed, the damping element 1 connected with the direct current bus is switched into a circuit, and the damping element 1 effectively inhibits the continuous rising of the bus voltage, so that the rear-stage circuit is protected and enters a normal working state.

In practical use, when the load is connected to the dc bus and has an output current, the voltage on the dc bus will gradually decrease. Therefore, to improve the efficiency of the circuit, the damping element 1 needs to be switched out of the circuit in time after the load is switched on. In this embodiment, when the first control signal closes the control switch 3, the timer 23 starts to count time, and after the time threshold is reached, the control circuit 2 outputs the second control signal to close the control switch 3, so as to switch the damping element 1 out of the circuit in time, thereby eliminating the power consumption on the damping element 1 and increasing the output power of the circuit.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A damping circuit for use in a circuit with an electronic ballast, comprising:

the damping element is electrically connected with the direct current bus;

the control circuit acquires power supply voltage from the direct current bus and compares the power supply voltage with threshold voltage, when the power supply voltage is higher than the threshold voltage, the control circuit outputs a first control signal, the control circuit comprises a comparator and a controller, one input end of the comparator inputs the power supply voltage, the other input end of the comparator inputs a voltage threshold, the output end of the comparator outputs a comparison signal to the controller, and the controller outputs the first control signal to the control switch according to the comparison signal;

the control switch is respectively and electrically connected with the damping element and the control circuit, and the control switch switches the damping element into the circuit based on a first control signal output by the control circuit;

the damping element and the control switch are connected in series to form a series circuit, and the series circuit is connected to two ends of a direct current bus.

2. The damping circuit of claim 1, wherein the control circuit further comprises a timer, wherein the timer starts counting when the controller outputs the first control signal, wherein the controller outputs the second control signal when the counted time reaches the time threshold, and wherein the control switch switches the damping element out of the circuit based on the second control signal output by the control circuit.

3. The damping circuit of claim 1, further comprising a regulated power supply circuit, wherein the regulated power supply circuit regulates the power supply voltage and outputs the regulated power supply voltage to the control circuit.

4. The damping circuit of claim 3, wherein the voltage-stabilizing power supply circuit comprises a diode and a charging capacitor, an anode of the diode is electrically connected to the output terminal of the damping element, a cathode of the diode is respectively connected to the charging capacitor and the control circuit, the dc bus voltage charges the charging capacitor through the damping element and the diode, and the voltage across the charging capacitor is output to the control circuit.

5. The damping circuit of claim 1, wherein the damping element is a power resistor.

6. The damping circuit of claim 1, wherein the control switch is an NMOS transistor or an NPN transistor, and when the control switch is an NMOS transistor, a drain of the NMOS transistor is electrically connected to the output terminal of the damping element, a gate of the NMOS transistor is electrically connected to the control circuit, and a source of the NMOS transistor is grounded; when the control switch is an NPN triode, the collector of the NPN triode is electrically connected with the output end of the damping element, the base of the NPN triode is electrically connected with the control circuit, and the emitter of the NPN triode is grounded.

7. The damping circuit of claim 1, wherein the control switch is a PMOS transistor or a PNP triode, and when the control switch is a PMOS transistor, the drain of the PMOS transistor is electrically connected to the damping element, the gate of the PMOS transistor is electrically connected to the control circuit, and the source of the PMOS transistor is connected to the dc bus; when the control switch is a PNP triode, the collector of the PNP triode is electrically connected with the output end of the damping element, the base of the PNP triode is electrically connected with the control circuit, and the emitter of the PNP triode is connected with the direct current bus.

8. An LED driving circuit with a damping circuit, which is characterized by comprising an electronic ballast, a rectifying circuit, a capacitor connected in parallel with the output end of the rectifying circuit and the damping circuit as claimed in any one of claims 1 to 7.

9. The LED driving circuit with the damping circuit according to claim 8, wherein the rectifying circuit is a full-bridge rectifier or a half-bridge rectifier.