CN114585128A

CN114585128A - Load open circuit detection circuit and LED driver with same

Info

Publication number: CN114585128A
Application number: CN202011390858.5A
Authority: CN
Inventors: 胡敏强
Original assignee: MEAN WELL (GUANGZHOU) ELECTRONICS CO Ltd
Current assignee: MEAN WELL (GUANGZHOU) ELECTRONICS CO Ltd
Priority date: 2020-12-02
Filing date: 2020-12-02
Publication date: 2022-06-03
Anticipated expiration: 2040-12-02
Also published as: CN114585128B

Abstract

The invention mainly provides a load open circuit detection circuit which is applied to executing load open circuit detection on a constant voltage LED driver, wherein the constant voltage LED driver comprises a power type MOS transistor and is coupled with an LED lamp. The basic components of the load open circuit detection circuit of the invention comprise: a microcontroller and a detection circuit unit. The detection circuit unit is coupled to a drain terminal of the power type MOS transistor and the microcontroller. Under the condition that the brightness of the LED lamp is more than 0% and less than 100%, the detection circuit unit receives a detection signal transmitted by the microcontroller and simultaneously receives a component output signal transmitted by the drain terminal of the power type MOS transistor, so that a sampling signal is generated according to the detection signal and the component output signal. After receiving the sampling signal, the microcontroller performs at least one signal process on the sampling signal, thereby determining whether the constant voltage LED driver is in an open load state according to the result of the signal process.

Description

Load open circuit detection circuit and LED driver with same

Technical Field

The present invention relates to the field of electronic circuits, and more particularly, to an open load detection circuit for an LED driver with PWM dimming function.

Background

As is well known, a Light-Emitting Diode (LED) is a solid-state Light-Emitting device that is widely used at present, and has advantages of small size, energy saving, and long service life, so it has been widely used in the manufacture of various lighting devices in people's daily life. With the rapid development and application of LED lighting devices, commercially available LED lighting devices further have a dimmable function.

DALI, the full name of English is Digital Addressable Lighting Interface, the full name of Chinese is Digital Addressable Lighting Interface, for being applied to LED Lighting device's an international general dimming signal protocol, have energy-efficient, the structure is nimble, easy to maintain, powerful advantage such as powerful. Therefore, the LED lighting device using DALI protocol for dimming control has good expandability. In order for a dimming controller to be compatible with the various LED drivers of an LED lighting fixture, the standards-making organization for the DALI protocol requires that the LED drivers that are dimming controlled using the DALI protocol all comply with the test standards of the DALI specification. To date, the specification standard for DALI has evolved from version 1.0 to version 2.0, with the test specification also increasing the load open detection of LED drivers.

When designing an LED lighting device or system, it is necessary to select a suitable LED driver in consideration of the connection manner of the LED assembly as a load, so as to ensure stable operation of the LED lighting device or system. Therefore, engineers familiar with the design and fabrication of LED drivers know that LED drivers are classified into Constant Current (CC) LED drivers and Constant Voltage (CV) LED drivers. It should be noted that the constant current LED driver is easy to perform the load open circuit detection, because the output voltage of the LED driver becomes large when the load is open, and the load open circuit detection can be completed by detecting the large output voltage.

On the other hand, fig. 1 shows a block diagram of a conventional constant voltage LED driver. As shown in fig. 1, a conventional constant voltage LED driver 1a is coupled to an LED lamp 2a (i.e., a load unit), and further includes a dimming signal conversion unit 11a, a current sampling resistor 12a, a current detection unit 13a, and a power switch element 14 a. Fig. 2 shows a graph of load factor versus output voltage. In an ideal case, the constant voltage LED driver 1a can maintain a constant output voltage regardless of a variation in the load ratio of the output terminal thereof (i.e., the luminance of the LED lamp 2 a). To describe in more detail, for the constant voltage LED driver 1a to perform dimming control on the LED lamp 2a by using the DALI signal, the dimming signal conversion unit 11a must convert the input DALI signal into a PWM signal. Fig. 3 shows the operation timing diagram of the PWM signal. Further, after the PWM signal is transmitted to a control terminal of the power switch component 14a (i.e., the gate terminal of the power MOS transistor, the PWM signal is used to control the power switch component 14a to be turned on and off periodically, so as to switch the current (i.e., the output current) flowing through the LED lamp 2a into the current in the PWM form, therefore, the brightness of the LED lamp 2a can be controlled by modulating the Duty cycle of the PWM signal, and fig. 3 shows the operation timing chart of the output current.

Practical experience shows that the load open circuit detection scheme suitable for the constant current LED driver is not suitable for the constant voltage LED driver 1 a. The main reason is that, for the constant current LED driver, the output voltage of the no-load operation is necessarily higher than the output voltage of the on-load operation, so that the detection of the open circuit of the load (i.e., no-load detection) of the constant current LED driver can be easily completed by using the output voltage detection and comparison method. However, as can be seen from fig. 2, the output voltage of the constant voltage LED driver 1a when it is operated at no load is almost the same as the output voltage when it is operated at load (even when it is fully loaded), and even if there is a difference due to the up-down variation error, the difference is very small. For this reason, the load open circuit detection scheme suitable for the constant current LED driver is not suitable for application to the constant voltage LED driver 1 a.

Practical experience has also shown that the method of determining whether the load is open by detecting the output current is not suitable for the constant voltage LED driver 1 a. As shown in fig. 3 and 4, when the PWM signal controls the power switch element 14a to be turned on and off periodically, the current (i.e., the output current) flowing through the LED lamp 2a is switched to the PWM type current. Therefore, for the constant voltage LED driver 1a with an output voltage of 24V and an output power of 120 w, if the load is evaluated to be open by means of average current, the detected output current is only 50mA when the brightness of the LED lamp 2a is regulated to be 1% (close to no load) by the PWM signal (i.e., the LED lamp 2a operates in the low brightness mode). In contrast, in the case where the brightness of the LED lamp 2a is regulated by the PWM signal to be 100% (full load) (i.e., the LED lamp 2a operates in the high brightness mode), the detected output current is 500 mA. Fig. 5 is a graph showing the load factor versus the average current.

As described above, if the resistance value of the current sampling resistor 12a shown in fig. 1 is 50m Ω, the output voltages detected at the time of full load and near no load are 250mV and 2.5mV, respectively. In other words, the difference between the full load output voltage and the near no load output voltage is only 247.5 mV. To achieve accurate detection and comparison of such a low voltage difference, the chip cost of the comparator and/or microcontroller at the back end is high. Fig. 6 is a graph showing the load factor versus the detected output voltage.

If only the output current when the PWM signal is ON is detected, the measurement curve is recorded in fig. 7. As shown in fig. 7, under the same load condition, for example, 100% luminance or 5% luminance, the values of the sampled output currents are the same. Therefore, when the brightness of the LED lamp 2a is controlled by the PWM signal having the duty ratio of 10%, the average current flowing through the LED lamp 2a is 10A × 10% to 1A, but in practice, the current of 10A is switched to a form in which the maximum value is still 10A but the duty ratio is 10% (i.e., a current in the PWM form). Therefore, when dimming the same load unit (i.e., the LED lamp 2a), the output current when the PWM signal detected by the current detection unit 13a is ON is the same regardless of the load condition of the load unit. For this reason, the method of taking only the output current at the time when the PWM signal is ON is still not suitable for load open detection as the constant voltage LED driver 1 a.

It should be noted that the aforementioned method of only taking the output current when the PWM signal is ON also has a problem that the power consumption of the current sampling resistor 12a is too large. In the constant-voltage LED driver 1a having an output voltage of 12V and an output power of 120 w, when the resistance value of the current sampling resistor 12a is 50m Ω, the power consumed by the load unit (i.e., the LED lamp 2a) is 120 w, and the output current when the PWM signal is ON is 10A, the voltage drop across the current sampling resistor 12a is 500mV, resulting in that the current sampling resistor 12a consumes 5 w of power. ON the other hand, in the case where the power consumed by the load unit (i.e., the LED lamp 2a) is 12 watts and the output current when the PWM signal is ON is taken as 1A, the voltage drop across the current sampling resistor 12a is only 50mV, resulting in 50 milliwatts of power being consumed by the current sampling resistor 12 a. As can be seen from the foregoing description, in consideration of the power consumption problem of the current sampling resistor 12a, the selection of the resistance value of the current sampling resistor 12a cannot make the constant voltage LED driver 1a of a single model specification take into account both the large wattage load and the small wattage load, otherwise the load detection misjudgment may be caused by the power consumption of the current sampling resistor 12 a.

As can be seen from the above description, at present, a load open circuit detection scheme suitable for the constant voltage LED driver is still lacking. Accordingly, the present invention is directed to a load open circuit detection circuit and an LED driver having the same.

Disclosure of Invention

The present invention provides a load open circuit detection circuit for performing a load open circuit detection on a constant voltage LED driver, wherein the constant voltage LED driver includes a power MOS transistor and is coupled to an LED lamp. The basic components of the load open circuit detection circuit of the invention comprise: a microcontroller and a detection circuit unit. The detection circuit unit is coupled to a drain terminal of the power type MOS transistor and the microcontroller. Under the condition that the brightness of the LED lamp is more than 0% and less than 100%, the detection circuit unit receives a detection signal transmitted by the microcontroller and simultaneously receives a component output signal transmitted by the drain terminal of the power type MOS transistor, so that a sampling signal is generated according to the detection signal and the component output signal. After receiving the sampling signal, the microcontroller performs at least one signal process on the sampling signal, thereby determining whether the constant voltage LED driver is in an open load according to the result of the signal process.

To achieve the above object, the present invention provides an embodiment of the load open circuit detection circuit for performing a load open circuit detection on a constant voltage LED driver including a first MOS transistor and a coupled LED lamp, and the load open circuit detection circuit includes:

a microcontroller coupled to a DALI signal for generating a first PWM signal according to the DALI signal, so as to transmit the first PWM signal to a gate terminal of the first MOS transistor; and

a detection circuit unit having a first electrical terminal coupled to the microcontroller, a second electrical terminal coupled to a drain terminal of the first MOS transistor, and a third electrical terminal coupled to the microcontroller;

wherein, under the condition that the first MOS transistor drives the LED lamp to make the brightness thereof more than 0% and less than 100% according to the control of the first PWM signal, the detection circuit unit receives a detection signal transmitted by the microcontroller and simultaneously receives a component output signal transmitted by the drain terminal of the first MOS transistor, thereby generating a sampling signal according to the detection signal and the component output signal;

after receiving the sampling signal transmitted by the detection circuit unit, the microcontroller performs at least one signal process on the sampling signal, so as to determine whether the constant voltage LED driver is in an open load according to the result of the signal process.

In an embodiment, when the first MOS transistor drives the LED lamp to have a brightness greater than 0% and less than 100% according to the control of the first PWM signal, the sampling signal is a sampling PWM signal, and a phase of the sampling PWM signal is the same as a phase of the first PWM signal.

In one embodiment, the microcontroller has a dimming signal conversion unit for converting the DALI signal into the first PWM signal, such that the first PWM signal has a duty ratio ranging from 0% to 100%.

In one embodiment, the detection circuit unit includes:

a diode having an anode terminal coupled to the drain terminal of the first MOS transistor;

a first resistor having a first end coupled to a cathode end of the diode;

a second MOS transistor, a gate terminal of which is coupled to a second terminal of the first resistor;

a second resistor having a first terminal coupled to a common node between the gate terminal of the second MOS transistor and the second terminal of the first resistor, and a second terminal coupled to a source terminal of the second MOS transistor;

a third resistor having a first end coupled to a drain of the second MOS transistor and a second end coupled to a working voltage;

a third MOS transistor, a drain terminal of which is coupled to a common node between the source terminal of the second MOS transistor and the second terminal of the second resistor, and a source terminal of which is coupled to a ground terminal;

a fourth resistor having a first end coupled to a gate terminal of the third MOS transistor and a second end coupled to the ground terminal;

a fifth resistor having a first terminal coupled to a common node between the gate terminal of the third MOS transistor and the first terminal of the fourth resistor, and a second terminal coupled to the microcontroller;

the second end of the fifth resistor is used as the first electrical end of the detection circuit unit to receive the detection signal, the anode end of the diode is used as the second electrical end of the detection circuit unit to receive the component output signal, and the drain end of the second MOS transistor is used as the third electrical end of the detection circuit unit to output the sampling signal.

In another embodiment, the third MOS transistor is turned off according to the control of the detection signal in a case where the first MOS transistor drives the LED lamp to have a brightness equal to 0% according to the control of the first PWM signal.

In another embodiment, in a case that the first MOS transistor drives the LED lamp to have a brightness equal to 100% according to the control of the first PWM signal, the microcontroller replaces the first PWM signal with a second PWM signal at intervals, thereby facilitating the detection circuit unit to complete the acquisition and output of the sampling signal. Wherein a Duty cycle (Duty cycle) of the second PWM signal is 99%.

Drawings

Fig. 1 is a block diagram of a conventional constant voltage LED driver;

FIG. 2 is a graph of load factor versus output voltage;

FIG. 3 is a timing diagram of the PWM dimming signal;

FIG. 4 is a timing diagram of the operation of the output current;

FIG. 5 is a graph of load rate versus average current;

FIG. 6 is a graph of load factor versus detected output voltage;

FIG. 7 is a graph of duty cycle versus output current at which the PWM signal is ON;

FIG. 8 is a block diagram of an open load detection circuit according to the present invention;

fig. 9 is a timing diagram illustrating operation of the PWM dimming signal;

fig. 10 is an operation timing diagram of the PWM dimming signal, the component output signal, and the sampling signal; and

FIG. 11 is a circuit topology structure diagram of the load open circuit detection circuit of the present invention.

The main symbols in the figures illustrate:

1: load open circuit detection circuit

11 microcontroller

12 detection circuit unit

2: constant voltage LED driver

3: LED lamp

Q1 first MOS transistor

Q2 second MOS transistor

Q3 third MOS transistor

D1 diode

R1 first resistor

R2 second resistor

R3 third resistor

R4 fourth resistor

R5 fifth resistor

R6 sixth resistor

R7 seventh resistor

1a constant voltage LED driver

11a dimming signal conversion unit

12a current sampling resistor

13a current detection unit

14a power switch assembly

2a LED Lamp

Detailed Description

In order to more clearly describe the open load detection circuit and the LED driver having the open load detection circuit of the present invention, the following description will be made in detail with reference to the accompanying drawings.

Fig. 8 is a block diagram of a load open circuit detection circuit according to the present invention. As shown in fig. 8, the present invention provides a load open circuit detection circuit 1, which is applied to perform a load open circuit detection on a constant voltage LED driver 2 including a first MOS transistor Q1 and a coupling to an LED lamp 3, and the basic components thereof include: a microcontroller 11 and a detection circuit unit 12, wherein the microcontroller 11 is coupled to a DALI signal for generating a first PWM signal according to the DALI signal. Please refer to fig. 9, which shows a timing chart of the PWM dimming signal. According to the design of the present invention, the microcontroller 11 has a dimming signal conversion unit for converting DALI signal into the first PWM signal, so as to transmit the first PWM signal as a PWM dimming signal to a gate terminal of the first MOS transistor Q1. It is inevitable for electronic engineers involved in the design and manufacture of LED drivers to know that, as the duty ratio of the PWM dimming signal is modulated between 0% and 100%, the first MOS transistor Q1 correspondingly drives the LED lamp 3 to adjust the brightness between 0% and 100%.

More specifically, the detection circuit unit 12 has a first electrical terminal coupled to the microcontroller 11, a second electrical terminal coupled to a drain terminal of the first MOS transistor Q1, and a third electrical terminal coupled to the microcontroller 11. So configured, in the case that the first MOS transistor Q1 drives the LED lamp 3 to have the brightness greater than 0% and less than 100% according to the control of the first PWM signal (i.e., PWM dimming signal), the microcontroller 11 sends a detection signal to the detection circuit unit 12, so as to detect whether the constant voltage LED driver 2 is in an open load state. Meanwhile, the detection circuit unit 12 also receives a component output signal transmitted from the drain terminal of the first MOS transistor Q1, so as to generate a sampling signal according to the detection signal and the component output signal.

Fig. 10 shows operation timing diagrams of the PWM dimming signal, the component output signal, and the sampling signal. In one embodiment, as shown in fig. 10, the sampling signal output by the detection circuit unit 12 is a sampling PWM signal, and the phase of the sampling PWM signal is the same as the phase of the first PWM signal (i.e., PWM dimming signal). Therefore, after receiving the sampling signal transmitted by the detection circuit unit 12, the microcontroller 11 then performs at least one signal processing on the sampling signal, including: a counting process is performed on the sampling signal to obtain a counting value. Then, the microcontroller 11 can determine that the constant voltage LED driver 2 does not have the load open circuit phenomenon as long as the comparison result shows that a difference between the count value and the reference count value is within a reasonable range by comparing the count value with the reference count value. Conversely, when the difference is out of a reasonable range, it indicates that the constant voltage LED driver 2 has a load open.

Fig. 11 is a circuit topology structure diagram of the load open circuit detection circuit of the present invention. As shown in fig. 8 and 11, the detection circuit unit 12 includes: a diode D1, a first resistor R1, a second MOS transistor Q2, a second resistor R2, a third resistor R3, a third MOS transistor Q3, a fourth resistor R4, and a fifth resistor R5. An anode terminal of the diode D1 is coupled to a drain terminal of the first MOS transistor Q1, a first terminal of the first resistor R1 is coupled to a cathode terminal of the diode D1, and a gate terminal of the second MOS transistor Q2 is coupled to a second terminal of the first resistor R1. More specifically, the second resistor R2 has a first terminal coupled to a common node between the gate terminal of the second MOS transistor Q2 and the second terminal of the first resistor R1, and a second terminal coupled to the source terminal of the second MOS transistor Q2.

As described above, the first terminal of the third resistor R3 is coupled to the drain terminal of the second MOS transistor Q2, and the second terminal thereof is coupled to an operating voltage VCC. Also, the drain terminal of the third MOS transistor Q3 is coupled to a common node between the source terminal of the second MOS transistor Q2 and the second terminal of the second resistor R1, and the source terminal thereof is coupled to a ground terminal. Two ends of the fourth resistor R4 are respectively coupled to a gate terminal of the third MOS transistor Q3 and the ground terminal. Furthermore, a ground terminal of the fifth resistor R5 is coupled to a common node between the gate terminal of the third MOS transistor Q3 and the first terminal of the fourth resistor R4, and a second terminal thereof is coupled to the microcontroller 11.

According to the design of the present invention, as shown in fig. 8 and 11, the second terminal of the fifth resistor R5 is used as the first electrical terminal of the detection circuit unit 12 for receiving the detection signal, the anode terminal of the diode D1 is used as the second electrical terminal of the detection circuit unit 12 for receiving the device output signal, and the drain terminal of the second MOS transistor Q2 is used as the third electrical terminal of the detection circuit unit 12 for outputting the sampling signal.

To describe in more detail, as shown in fig. 10 and 11, when the first MOS transistor Q1 drives the LED lamp 3 to have a brightness greater than 0% and less than 100% according to the control of the PWM dimming signal (i.e., the first PWM signal), the microcontroller 11 outputs a high-level detection signal to the gate terminal of the third MOS transistor Q3, thereby controlling the third MOS transistor Q3 to be turned on. At this time, since the gate terminal of the first MOS transistor Q1 is controlled by the PWM dimming signal, the first MOS transistor Q1 is turned ON and the second MOS transistor Q2 is turned off during the PWM-ON period of the PWM dimming signal. Conversely, during the PWM-OFF period of the PWM dimming signal, the first MOS transistor Q1 is turned OFF and the second MOS transistor Q2 is turned on. Therefore, as shown in fig. 10 and 11, the phase of the device output signal outputted from the drain of the first MOS transistor Q1 is 90 ° different from the phase of the PWM dimming signal, and the phase of the sampling signal outputted from the drain of the second MOS transistor Q2 is the same as the phase of the PWM dimming signal. Therefore, after receiving the sampling signal transmitted by the detection circuit unit 12, the microcontroller 11 then performs at least one signal processing on the sampling signal, including: a counting process is performed on the sampling signal to obtain a counting value. Then, the microcontroller 11 can determine that the constant voltage LED driver 2 does not have the load open circuit phenomenon as long as the comparison result shows that a difference between the count value and the reference count value is within a reasonable range by comparing the count value with the reference count value. Conversely, when the difference is out of a reasonable range, it indicates that the constant voltage LED driver 2 has a load open.

It should be noted that, when the first MOS transistor Q1 drives the LED lamp 3 to have a brightness equal to 0% according to the control of the first PWM signal, the microcontroller 11 outputs a low-level detection signal to the gate terminal of the third MOS transistor Q3, thereby controlling the third MOS transistor Q3 to turn off. As can be seen from fig. 9, making the first PWM signal (i.e., PWM dimming signal) a low level signal can make the brightness of the LED lamp 3 be 0%. In this case, the second MOS transistor Q2 and the third MOS transistor Q3 are in the off state at the same time, so that no leakage current flows through the LED lamp 3, and it is ensured that the LED lamp 3 does not emit weak light. Strictly speaking, in the case where the luminance of the LED lamp 3 is 0%, it does not make sense to perform the load open detection for the constant voltage LED driver 2.

It should be further noted that, when the first MOS transistor Q1 drives the LED lamp 3 to have a brightness equal to 100% according to the control of the first PWM signal, as can be seen from fig. 8, the PWM dimming signal is a high level signal, so that the first MOS transistor Q1 is maintained in an on state, and the second MOS transistor Q2 is maintained in an off state. It should be understood that, at this time, the sampling signal outputted from the drain terminal of the second MOS transistor Q2 continues to be at a high level, so that the microcontroller 11 cannot perform the so-called counting process on the sampling signal at the high level, and naturally cannot complete the load open circuit detection of the constant voltage LED driver 2. For the foregoing reasons, the present invention specifically designs the microcontroller 11 to replace the first PWM signal with a second PWM signal at intervals as the PWM dimming signal, so that the sampling signal outputted from the drain of the second MOS transistor Q2 has the same waveform and the same phase as the second PWM signal, thereby facilitating the microcontroller 11 to complete the load open circuit detection of the constant voltage LED driver 2. In one embodiment, the second PWM signal has a duty ratio of 99%, and if the constant voltage LED driver 2 is in the load open state, the drain of the second MOS transistor Q2 does not output the sampled PWM signal having a duty ratio of 99%.

It should be noted that fig. 11 also shows that the load open circuit detection circuit 1 of the present invention further includes a sixth resistor R6 and a seventh resistor R7. The sixth resistor R6 has a first terminal coupled to a common node between a source terminal of the first MOS transistor Q1 and the ground terminal, and a second terminal coupled to the gate terminal of the first MOS transistor Q1. Moreover, a first terminal of the seventh resistor R7 is coupled to a common node between a gate terminal of the first MOS transistor Q1 and the second terminal of the sixth resistor R6, and a second terminal thereof is coupled to the microcontroller 11.

Thus, the above description has been provided for a complete and clear description of the load open circuit detection circuit 1 provided by the present invention. In particular, the open load detection circuit 1 of the present invention has the following features and advantages:

(1) compared with the prior art (as shown in fig. 1), the load open circuit detection circuit 1 of the present invention only has a microcontroller 11 (having a dimming signal conversion function) and a detection circuit unit 12, and does not include a current sampling resistor that would generate significant power consumption. Therefore, in the process of performing load open circuit detection on the constant voltage LED driver 2, no current sampling resistor generates significant power consumption to affect the detection and judgment of the load open circuit.

(2) The load open circuit detection circuit 1 of the present invention only has a microcontroller 11 and a detection circuit unit 12, wherein the microcontroller 11 has the function of dimming signal conversion at the same time, so the load open circuit detection circuit 1 of the present invention can be directly applied to the existing constant voltage LED driver 2 without generating additional chip acquisition cost.

(3) As shown in fig. 9 and 11, when the first MOS transistor Q1 drives the LED lamp 3 to have a brightness equal to 0% according to the control of the PWM dimming signal, the invention utilizes the microcontroller 11 to output a low-level detection signal to the gate terminal of the third MOS transistor Q3, thereby controlling the third MOS transistor Q3 to turn off. In this case, since the second MOS transistor Q2 and the third MOS transistor Q3 are in the off state at the same time, no leakage current flows through the LED lamp 3, and it is ensured that the LED lamp 3 does not emit weak light.

(4) As shown in fig. 9 and 11, when the first MOS transistor Q1 drives the LED lamp 3 to have a brightness equal to 100% according to the control of the PWM dimming signal, since the first MOS transistor Q1 is maintained in the on state and the second MOS transistor Q2 is maintained in the off state, the sampling signal output from the drain terminal of the second MOS transistor Q2 is a low level signal, and thus the microcontroller 11 cannot complete the load open circuit detection of the constant voltage LED driver 2 according to the low level signal. In this case, the present invention is specifically designed to make the microcontroller 11 send out a second PWM signal with a duty ratio of 99% at intervals as the PWM dimming signal, so that the sampling signal output from the drain terminal of the second MOS transistor Q2 has the same waveform and the same phase as the second PWM signal, thereby facilitating the microcontroller 11 to complete the load open circuit detection of the constant voltage LED driver 2.

It should be emphasized that the above detailed description is specific to possible embodiments of the invention, but this is not intended to limit the scope of the invention, and equivalents and modifications, which do not depart from the technical spirit of the invention, are intended to be included within the scope of the invention.

Claims

1. An open load detection circuit for performing an open load detection on a constant voltage LED driver including a first MOS transistor and a constant voltage LED lamp coupled thereto, comprising:

a microcontroller coupled to a DALI signal for generating a first PWM signal according to the DALI signal, so as to transmit the first PWM signal to a gate terminal of the first MOS transistor Q1; and

2. The circuit of claim 1, wherein the sampling signal is a sampling PWM signal, and the phase of the sampling PWM signal is the same as the phase of the first PWM signal when the first MOS transistor drives the LED lamp to have a brightness greater than 0% and less than 100% according to the control of the first PWM signal.

3. The circuit of claim 1, wherein the microcontroller comprises a dimming signal conversion unit for converting the DALI signal into the first PWM signal, such that the first PWM signal has a duty cycle ranging from 0% to 100%.

4. The load open circuit detection circuit according to claim 1, wherein the detection circuit unit comprises:

a diode, an anode terminal of which is coupled to the drain terminal of the first MOS transistor;

a first resistor having a first end coupled to a cathode end of the diode;

a fourth resistor having a first end coupled to a gate terminal of the third MOS transistor and a second end coupled to the ground terminal; and

5. The load open circuit detection circuit according to claim 4, wherein the third MOS transistor is turned off according to the control of the detection signal in a case where the first MOS transistor drives the LED lamp to have a brightness equal to 0% according to the control of the first PWM signal.

6. The load open circuit detection circuit according to claim 4, wherein the microcontroller replaces the first PWM signal with a second PWM signal at intervals when the first MOS transistor drives the LED lamp to have a brightness equal to 100% according to the control of the first PWM signal, so as to facilitate the detection circuit unit to complete the collection and output of the sampling signal.

7. The load open circuit detection circuit according to claim 5, further comprising:

a sixth resistor having a first terminal coupled to a common node between a source terminal of the first MOS transistor and the ground terminal, and a second terminal coupled to the gate terminal of the first MOS transistor; and

a seventh resistor, a first terminal of which is coupled to a common node between a gate terminal of the first MOS transistor and the second terminal of the sixth resistor, and a second terminal of which is coupled to the microcontroller.

8. The load open-circuit detection circuit according to claim 5, wherein a duty cycle of the second PWM signal is 99%.

9. The load open circuit detection circuit according to claim 6, wherein the signal processing comprises: a counting process is performed on the sampling signal to obtain a counting value.

10. A constant voltage LED driver characterized by having the load open circuit detection circuit according to any one of claims 1 to 9.