CN104797058B - Damping circuit and LED drive circuit with damping circuit - Google Patents

Abstract

The invention provides a damping circuit and an L ED driving circuit with the damping circuit, wherein the damping circuit comprises a damping element, a control circuit and a control switch, the damping element is electrically connected with a direct current bus, the control circuit acquires a power supply voltage from the direct current bus and compares the power supply voltage with a threshold voltage, when the voltage of the direct current bus 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, the control switch switches the damping element into a circuit based on the first control signal output by the control circuit, and by arranging the damping circuit in the L ED driving circuit, the damping circuit can effectively inhibit the voltage on the direct current bus from continuously increasing in a starting stage, effectively reduce the voltage-withstanding grade of a next stage circuit, and enable L ED driving to be compatible with an electronic ballast.

Description

Damping circuit and LED drive circuit with damping circuit

technical field

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

Background technique

The traditional electronic ballast is connected to the load of the fluorescent lamp, because the luminous efficiency of the fluorescent lamp is relatively low, there is a certain degree of environmental pollution. In today's energy saving and emission reduction, replacing fluorescent lamps with LED lamps has become a trend. In order to achieve direct replacement, LED lamps not only need to be able to accept ordinary mains electricity for their power supply, but also need to be able to be directly connected, that is, the electronic ballast of fluorescent lamps as their power supply. However, the output of the electronic ballast is a high-frequency AC signal, while the LED lamp needs a DC power supply, and the two cannot be directly matched. Therefore, it is usually necessary to rectify the output of the electronic ballast into a DC through a rectifier bridge, and then use the LED driver to convert it into the DC required by the LED load.

However, since electronic ballasts are specially designed for fluorescent lamps, their working process includes start-up phase and steady-state phase. In the start-up phase, the electronic ballast outputs a high voltage to break down the tube of the fluorescent lamp and realize the glow discharge of the fluorescent lamp. Its output voltage is usually between hundreds of volts and one thousand volts, which is much higher than the voltage in the steady state stage. (Usually below 200V). If the electronic ballast suitable for traditional fluorescent lamps is directly connected to the LED driver, the high voltage generated during the start-up phase will bring great challenges to the design of the subsequent LED driver.

Contents of the invention

The present invention provides a damping circuit and an LED with a damping circuit in order to solve the problem that the high voltage output by the electronic ballast during the start-up stage brings difficulties to the design of the subsequent LED driver when the electronic ballast is used as power supply for the LED lamp. Drive circuit.

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

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

In one embodiment of the present invention, the control circuit further includes a timer. When the controller outputs the first control signal, the timer starts counting. When the counted time reaches the time threshold, the controller outputs the second control signal. The control switch is based on the control circuit The output second control signal switches the damping element out of circuit.

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

In one embodiment of the present invention, the voltage stabilizing power supply circuit includes a diode and a charging capacitor. The anode of the diode is electrically connected to the output terminal of the damping element, and the cathode of the diode is respectively connected to the charging capacitor and the control circuit. The DC bus voltage passes through the damping element and the control circuit. The diode charges the charging capacitor, and the voltage across the charging capacitor is output to the control circuit.

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

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

In one embodiment of the present invention, the control switch is a PMOS transistor or a PNP transistor. When the control switch is a PMOS transistor, the drain of the PMOS transistor is electrically connected to the damping element, and the gate of the PMOS transistor is electrically connected to the control circuit. The source of the tube is connected to the DC bus; when the control switch is a PNP transistor, the collector of the PNP transistor is electrically connected to the output end of the damping element, the base of the PNP transistor is electrically connected to the control circuit, and the emitter of the PNP transistor is connected to the DC busbar.

According to another aspect of the present invention, there is also provided an LED driving circuit with a damping circuit, the LED driving circuit includes an electronic ballast, a rectifying circuit, a capacitor connected in parallel at the output end of the rectifying circuit, and the above-described damping circuit.

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

According to the damping circuit and the LED drive circuit with the damping circuit of the present invention, when the DC bus outputs high voltage (such as the start-up stage of the electronic ballast), the damping element is cut into the circuit by controlling the switch, so as to realize the high voltage output from the DC bus. Inhibit and reduce the withstand voltage level of the subsequent stage circuit, effectively avoiding damage or inoperability caused by high voltage. The specific implementation method is: the control circuit obtains the power supply voltage from the DC bus, and when the power supply voltage is higher than the set voltage threshold, the control circuit outputs a first control signal to close the control switch. When the control switch is closed, the damping element connected to the DC bus will be cut into the circuit, and the damping element can effectively restrain the bus voltage from continuing to rise, so as to protect the subsequent circuit and make it enter the normal working state.

In actual 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, in order to improve the efficiency of the circuit, it is necessary to cut the damping element out of the circuit in time after the load is connected. In this embodiment, by setting the time threshold, when the first control signal closes the control switch, the timer starts counting, and when the time threshold is reached, the control circuit outputs the second control signal to close the control switch, and the damping element is cut out of the circuit in time. Eliminate the power consumption on the damping element and increase the output power of the circuit.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments are described below in detail with accompanying drawings.

Description of drawings

Figure 1 shows the schematic diagram of an existing LED drive circuit with an electronic rectifier as input.

FIG. 2 is a schematic diagram of a damping circuit provided by an embodiment of the present invention.

FIG. 3 is a schematic diagram of an LED driving circuit with the damping circuit shown in FIG. 2 .

Figure 4 shows the output voltage of the electronic ballast in Figure 1 at different stages.

Figure 5 shows the output voltage of the electronic ballast in Figure 3 at different stages.

FIG. 6 is a schematic diagram of an LED driving circuit with a damping circuit provided by another embodiment of the present invention.

FIG. 7 is a time sequence diagram between the voltage at both ends of the charging capacitor in FIG. 3 and the voltage at the control terminal of the control switch.

Detailed ways

Figure 1 shows the existing LED drive circuit, in which the AC high-frequency signal output by the electronic ballast is directly output to the LED driver after being rectified. However, since electronic ballasts are specially designed for fluorescent lamps, fluorescent lamps need to perform glow discharge during the lighting stage, and glow discharge requires a very high voltage. Therefore, the output of the electronic ballast includes two stages, one of which is the start-up stage, in which the electronic ballast outputs high voltage to make the fluorescent lamp glow, and when the fluorescent lamp is lit, the electronic ballast enters the steady-state stage, Output a normal working voltage of about 200V.

In Figure 1, the electronic ballast is directly connected to the LED driver. During the start-up phase of the electronic ballast, since the LED load is not connected, the load has no output current. At this time, the output of the electronic ballast is rectified. The capacitor connected in parallel at the output end of the rectifier circuit is charged, so that the voltage at both ends of the capacitor rises rapidly and reaches the starting voltage of the electronic ballast. This requires the LED driver to have a very high withstand voltage level, which can withstand the high voltage of nearly one thousand volts output by the electronic ballast during the start-up phase. This will bring a huge challenge to the design of the LED driver, and further, different electronic ballasts output different voltages, and it is also very difficult to design the compatibility of the LED driver with the electronic ballast.

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

As shown in FIG. 3 , the LED driving circuit with a damping circuit provided in this embodiment includes an electronic ballast 100 , a rectification circuit 200 , a capacitor 400 connected in parallel at the output end of the rectification 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 this embodiment, the rectifier circuit 200 is a full-bridge rectifier composed of four diodes. However, the present invention does not make any limitation thereto. In other embodiments, the rectification circuit 200 can be half-bridge rectification.

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 power supply voltage from the DC bus and compares the power supply voltage with a threshold voltage. When the power supply voltage is higher than the threshold voltage, the control circuit 2 outputs a first control signal. In this embodiment, the control circuit 2 obtains the power supply voltage from the DC bus through the damping element 1 . However, the present invention does not make any limitation thereto. In other embodiments, the control circuit 2 can be connected to the DC bus through a resistor R, so as 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 cuts the damping element 1 into the circuit based on the first control signal output by the control circuit 2 .

As shown in Figure 3, when the control switch 3 is closed, the damping element 1 is cut into the circuit, and a loop is formed between the capacitor 400, the damping element 1 and the control switch 3, and the voltage at both ends of the capacitor 400 will not continue to rise, thereby suppressing the DC bus voltage Elevated effect. Fig. 4 shows the output voltage of the electronic ballast in different stages in the existing 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 can be clearly seen that after the damping circuit 300 is added, the output voltage of the electronic ballast 100 in the start-up phase is well suppressed, and correspondingly, the rectified DC bus voltage will also be greatly suppressed. Good restraint.

In this embodiment, the damping element 1 is a power resistor. However, the present invention does not make any limitation thereto.

In this embodiment, the control circuit 2 includes a comparator 21 and a controller 22, one of the input terminals of the comparator 21 inputs the supply voltage obtained from the DC bus, the other input terminal inputs a voltage threshold, and the output terminal outputs a comparison signal to The controller 22, 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 to drive the subsequent LED load. However, the present invention does not make any limitation thereto. In other embodiments, the controller 22 and the LED driver can be set independently.

In this embodiment, the control switch 3 is an NMOS transistor and is set independently from the control circuit 2 . However, the present invention does not make any limitation thereto. In order to reduce the area occupied by circuit board components, in other embodiments, the control switch 3 and the control circuit 2 can be integrated together.

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

However, when the control switch 3 is a P-type switch 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 switch is electrically connected to the damping element 1, the grid (base) of the P-type switch is connected to the controller 22, and the source of the P-type switch The pole (emitter) is connected to the DC bus.

After the control switch 3 cuts 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 output current, the voltage at both ends of the capacitor 400 is gradually stabilized after charging and discharging, and the DC bus voltage gradually decreases and falls back to the voltage value in the steady state stage. At this time, in order to improve the efficiency of the circuit, that is, to increase the ratio between the output power and the input power, it is hoped to reduce unnecessary consumption in the circuit as much as possible. Therefore, when the load is connected to generate output current, the damping element 1 is cut out. circuit.

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 counting. When the counted time reaches the time threshold, the controller 22 outputs the second control signal. The control switch 3 cuts the damping element 1 out of the circuit based on the second control signal output by the controller 22 , so that no power consumption occurs on the damping element 1 and the efficiency is greatly improved. In FIG. 7 , time t0 is when the controller 22 outputs the first control signal, and time t1 is when the LED load is connected to the DC bus to generate output current, and the time threshold is t1-t0.

In actual use, affected by external disturbances, the voltage of the DC bus will change, which may cause misoperation of the comparator 21 , thereby affecting the switching of the control switch 3 and further affecting the normal operation of the entire damping circuit 300 . In order to prevent the misoperation of the comparator 21 caused by the fluctuation of the DC bus voltage, the damping circuit 300 provided by the present invention further includes 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 then outputs it to the control circuit 2 .

The voltage stabilizing power supply circuit 4 includes a diode 41 and a charging capacitor 42 . The anode of the diode 41 is connected to the output end of the damping element 1 , and the cathode of the diode 41 is respectively connected to the charging capacitor 42 and one of the input ends of the comparator 21 . In the starting phase of the electronic ballast, the DC bus voltage charges the charging capacitor 42 through the damping element 1 and the diode 41, and 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 working. In some embodiments, the start-up voltage of the control circuit can be consistent with the threshold set by the comparator 21, that is, when the voltage Vcc across the charging capacitor 42 reaches the threshold voltage set by the comparator 21, the control circuit 2 will damp The circuit cuts in (that is, switch 3 is turned on). At the same time, the threshold set by the comparator 21 can also be higher than the start-up voltage of the control circuit, that is, when the voltage Vcc across the charge point capacitor 42 continues to rise with the increase of the bus voltage, when it reaches the threshold set by the comparator 21 After the threshold value, the control circuit 2 cuts in the damping circuit. This setup greatly simplifies circuit design. However, the present invention does not make any limitation thereto. In other embodiments, an independent power supply circuit can be used to activate the control circuit 2 .

When the damping circuit is cut in (that is, the switch tube 3 is turned on), due to the presence of the diode 41, the voltage Vcc across the charging capacitor 42 will not be discharged through the diode 41, and the voltage at the Vcc point remains stable at this time. The voltage at the Vcc point ensures the normal operation of the comparator 21 and effectively avoids misoperation of the comparator 21 . As shown in FIG. 7 , the stable Vcc voltage keeps 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, the damping circuit 300 provided by the present invention and the LED drive circuit with the damping circuit, when the DC bus output high voltage (such as the start-up phase of the electronic ballast), the damping element 1 is cut into the circuit by controlling the switch 3 to realize Suppress the high voltage output by the DC bus, reduce the withstand voltage level of the subsequent circuit, and effectively avoid damage or inoperability caused by high voltage. The specific implementation method is: the control circuit 2 obtains the power supply voltage from the DC bus, and when the power supply voltage is higher than the set voltage threshold, 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 to the DC bus will be cut into the circuit, and the damping element 1 can effectively suppress the continuous rise of the bus voltage to protect the subsequent circuit and make it enter a normal working state.

In actual 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, in order to improve the efficiency of the circuit, it is necessary to cut the damping element 1 out of the circuit in time after the load is connected. In this embodiment, when the first control signal closes the control switch 3, the timer 23 starts timing, and when the time threshold is reached, the control circuit 2 outputs the second control signal to close the control switch 3, and the damping element 1 is cut out of the circuit in time, The power consumption on the damping element 1 is eliminated, and the output power of the circuit is improved.

Although the present invention has been disclosed above by preferred embodiments, it is not intended to limit the present invention. Any skilled person can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the present invention The scope of protection should be subject to the scope of protection required by the claims.

Claims (8)

1. a kind of antihunt circuit characterized by comprising

Damping element is electrically connected DC bus；

Control circuit obtains supply voltage and by supply voltage compared with threshold voltage, when supply voltage height from DC bus When threshold voltage, the control circuit exports first control signal, and the control circuit includes comparator and controller, described One of input terminal of comparator inputs supply voltage, another input terminal input voltage threshold value, and letter is compared in output end output Number to controller, controller exports first control signal to control switch according to comparison signal；

Control switch, is electrically connected the damping element and control circuit, and the control switch is based on the control circuit The damping element is cut circuit by the first control signal of output；

The damping element and the control switch connect to form series circuit, and the series circuit is connected to the two of DC bus End；

The control circuit further includes timer, and when the controller exports first control signal, timer starts timing, when Timing time arrival time threshold value, the controller export second control signal, control switch exported based on control circuit the Damping element is cut out circuit by two control signals.

2. antihunt circuit according to claim 1, which is characterized in that the antihunt circuit further includes voltage stabilizing power supplying circuit, The voltage stabilizing power supplying circuit exports after carrying out steady pressure treatment to supply voltage to control circuit.

3. antihunt circuit according to claim 2, which is characterized in that the voltage stabilizing power supplying circuit includes diode and charging Capacitor, the diode anode be electrically connected damping element output end, the cathode of diode respectively with charging capacitor and control Circuit processed is connected, and DC bus-bar voltage is charged by damping element and diode pair charging capacitor, the electricity at charging capacitor both ends Pressure is exported to control circuit.

4. antihunt circuit according to claim 1, which is characterized in that the damping element is power resistor.

5. antihunt circuit according to claim 1, which is characterized in that the control switch be NMOS tube or NPN triode, When control switch is NMOS tube, the drain electrode of NMOS tube and the output end of damping element are electrically connected, the grid of NMOS tube and control Circuit processed is electrically connected, the source electrode ground connection of NMOS tube；When control switch is NPN triode, the collector of NPN triode and resistance The output end of Buddhist nun's element is electrically connected, and the base stage and control circuit of NPN triode are electrically connected, and the emitter of NPN triode connects Ground.

6. antihunt circuit according to claim 1, which is characterized in that the control switch be PMOS tube or PNP triode, When control switch is PMOS tube, the drain electrode of PMOS tube and damping element are electrically connected, grid and the control circuit electricity of PMOS tube Property connection, the source electrode of PMOS tube connects DC bus；When control switch is PNP triode, the collector of PNP triode and resistance The output end of Buddhist nun's element is electrically connected, and the base stage and control circuit of PNP triode are electrically connected, and the emitter of PNP triode connects Connect DC bus.

7. a kind of LED drive circuit with antihunt circuit, which is characterized in that including electric ballast, rectification circuit, be connected in parallel on The capacitor of rectification circuit output end and antihunt circuit as described in any one of claims 1 to 6.

8. the LED drive circuit according to claim 7 with antihunt circuit, which is characterized in that the rectification circuit is Full-bridge rectification or Half bridge rectifier.