An LED driver power supply using an overvoltage protection circuit

Abstract

The present invention discloses an LED driver power supply using an overvoltage protection circuit, comprising: a rectifier bridge, an input capacitor, a rectifier diode, an inductor, an output capacitor, a dummy load, an output LED load, a current sampling resistor, an OVP setting resistor, a power tube, and a control chip; the main control chip includes an error amplifier, a compensation capacitor, a first comparator, a shutdown logic module, a first control logic module, a drive circuit, a demagnetization detection circuit, and an overvoltage protection circuit. The present invention eliminates the auxiliary winding and the sampling circuit connected thereto in the prior art, and also eliminates the sampling circuit for the CS pin in the prior art. In the application of a dimming LED power supply system, when the peak current of the inductor changes, it can detect whether the output voltage is overvoltage, and promptly shut down the system's switching action to achieve the purpose of overvoltage protection.

Description

Technical Field

[0001] The present invention relates to the technical field of LED driving power supplies, and in particular to an LED driving power supply applying an overvoltage protection circuit. Background Art

[0002] LED lighting has achieved significant development due to its advantages such as high brightness, high efficiency, and long life. There are many different LED driver power supply topologies, with the non-isolated Buck topology being widely used due to its simple structure, low cost, and high efficiency. If the output of an LED driver power supply is open-circuited or overvoltage occurs, the LED driver chip must trigger output overvoltage protection to control the output voltage from rising further, preventing damage to the output capacitor and other connected devices. Common overvoltage protection methods include the following:

[0003] The first one is Figure 1 As shown, the output voltage is monitored by sampling the auxiliary winding. The sampled signal is compared with an internal reference voltage. When the sampled voltage exceeds the reference voltage, the output is considered overvoltage, and the switch is shut off to implement the protection function. The disadvantages of this method are the large number of peripheral components, high cost, and high power consumption.

[0004] The second type Figure 2 As shown in the figure, this method utilizes the volt-second balance principle of the inductor and sets a fixed reference time. This is compared with the system's demagnetization time to monitor the output voltage and implement protection. However, this method is not applicable when the inductor peak current varies, such as in dimming systems.

[0005] The third type Figure 3 As shown in the figure, by sampling the peak voltage of the CS pin, setting a reference time that follows the CS peak voltage and comparing it with the system's demagnetization time to monitor the output voltage, the protection function is achieved. The disadvantages of this method are that the circuit is complex and the sampling accuracy is high, which is not conducive to reducing costs and the protection voltage consistency is not high. Summary of the Invention

[0006] The purpose of the present invention is to provide an LED driver power supply using an overvoltage protection circuit. The protection circuit is suitable for use in a dimming LED driver power supply system with a varying inductor current peak value, and can achieve the goals of low cost, high consistency, continuous adjustability, and high reliability.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] An LED driver power supply using an overvoltage protection circuit includes: a rectifier bridge, an input capacitor, a rectifier diode, an inductor, an output capacitor, a dummy load, an output LED load, a current sampling resistor, an OVP setting resistor, a power tube, and a control chip;

[0009] One end of the rectifier bridge is respectively connected to one end of the input capacitor, the cathode of the rectifier diode, one end of the output capacitor, one end of the dummy load, and one end of the output LED load, and the other end of the rectifier bridge is respectively connected to the other end of the input capacitor, the other end of the OVP setting resistor, the other end of the current sampling resistor, and the ground; the anode of the rectifier diode is respectively connected to the drain of the power tube and one end of the inductor, the gate of the power tube is connected to the output end of the main control chip, the input end of the main control chip is connected to one end of the OVP setting resistor, and the source of the power tube is connected to one end of the current sampling resistor; the other end of the inductor is respectively connected to the other end of the output capacitor, the other end of the dummy load, and the other end of the output LED load;

[0010] The main control chip includes an error amplifier, a compensation capacitor, a first comparator, a shutdown logic module, a first control logic module, a drive circuit, a demagnetization detection circuit and an overvoltage protection circuit;

[0011] The output end of the error amplifier is respectively connected to one end of the compensation capacitor, the inverting input end of the first comparator, and the input end of the overvoltage protection circuit. The non-inverting input end of the error amplifier is input with a reference voltage signal, and the inverting input end of the error amplifier is input with an output current signal. The other end of the compensation capacitor is grounded. The non-inverting input end of the first comparator is connected to one end of the current sampling resistor, and the output end of the first comparator is connected to the second input end of the shutdown logic module. The first input end of the shutdown logic module is connected to the output end of the overvoltage protection circuit, and the output end of the shutdown logic module is respectively connected to the first input end of the first control logic module and the input end of the overvoltage protection circuit. The second input end of the shutdown logic module is connected to the output end of the demagnetization detection circuit, and the output end of the shutdown logic module is connected to the input end of the drive circuit. The output end of the drive circuit is respectively connected to the gate of the power transistor and the input end of the demagnetization detection circuit. The output end of the demagnetization detection circuit is also connected to the input end of the overvoltage protection circuit.

[0012] Optionally, the overvoltage protection circuit includes: a second comparator, a timing capacitor, a switch, a voltage-current conversion circuit, a second control logic module, a third control logic module and an OVP control logic module;

[0013] The input end of the voltage-current conversion circuit is connected to one end of the OVP setting resistor, the output end of the voltage-current conversion circuit is respectively connected to one end of the switch and one end of the timing capacitor, and the other end of the switch and the other end of the timing capacitor are both grounded; the non-inverting input end of the second comparator is connected to one end of the timing capacitor, the inverting input end of the second comparator is connected to the output end of the error amplifier, the output end of the second comparator is connected to the second input end of the OVP control logic module, and the output signal of the second comparator controls the output current of the voltage-current conversion circuit; the first input end of the OVP control logic module is connected to the output end of the second control logic module, the third input end of the OVP control logic module is connected to the output end of the third control logic module, and the output end of the OVP control logic module is connected to the first input end of the shutdown logic module; the input of the second control logic module is the maximum on-time signal of the main control chip, and the input end of the third control logic module is connected to the output end of the demagnetization detection circuit.

[0014] Optionally, the shutdown logic module is an OR gate.

[0015] Optionally, the first control logic module is an RS trigger; the first input end of the first control logic module is the R end, and the second input end of the first control logic module is the S end.

[0016] Optionally, the OVP control logic module is a three-input AND gate.

[0017] Optionally, the second control logic module and the third control logic module are both inverters.

[0018] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0019] This invention eliminates the auxiliary winding and its connected sampling circuitry, as well as the sampling circuitry for the CS pin, as is commonly found in prior art. In dimming LED power supply systems, when the inductor peak current changes, the system can detect whether the output voltage is overvoltage and promptly shut down the system's switching operation, achieving overvoltage protection.

[0020] The circuit of the present invention generates a reference current I0 through an OVP setting resistor. The timing capacitor and reference current I0 jointly generate a reference time T0. Overvoltage is determined by comparing T0 with the demagnetization time Tdem output by the demagnetization detection circuit. The output voltage of the error amplifier controls both the inductor peak current and the reference time T0. Therefore, the circuit of the present invention is suitable for LED driver power supplies with variable inductor peak current. It eliminates the need for an inductor current peak sampling circuit, saving costs and improving the consistency of the protection voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 This is a schematic diagram of the structure of a driving power supply that monitors the output voltage through an auxiliary winding.

[0023] Figure 2 A schematic diagram of an existing drive power supply structure that is not suitable for changes in inductor current peak value;

[0024] Figure 3 The figure is a schematic diagram of the structure of a driving power supply for sampling the peak value of the inductor current.

[0025] Figure 4 A schematic diagram of the circuit structure of an LED driving power supply with an overvoltage protection circuit provided by the present invention;

[0026] Figure 5 A schematic diagram of an overvoltage protection circuit provided by the present invention;

[0027] Figure 6 A working principle diagram of the overvoltage protection circuit provided by the present invention;

[0028] Figure 7 Another working principle diagram of the overvoltage protection circuit provided by the present invention;

[0029] Figure 8 This is a schematic diagram of the principle of shielding the overvoltage protection function when the input voltage decreases in the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] The purpose of the present invention is to provide an LED driver power supply using an overvoltage protection circuit. The protection circuit is suitable for use in a dimming LED driver power supply system with a varying inductor current peak value, and can achieve the goals of low cost, high consistency, continuous adjustability, and high reliability.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 4 As shown, the LED driver power supply with an overvoltage protection circuit provided by the present invention includes: a rectifier bridge composed of diodes D1-D4, an input capacitor C1, a rectifier diode D5, an inductor Lm, an output capacitor Cout, a dummy load Rout, an output LED load Dload, a current sampling resistor Rcs, an OVP setting resistor R3, a power tube Q1 and a control chip 100.

[0034] One end of the rectifier bridge is respectively connected to one end of the input capacitor C1, the cathode of the rectifier diode D5, one end of the output capacitor Cout, one end of the dummy load Rout, and one end of the output LED load Dload. The other end of the rectifier bridge is respectively connected to the other end of the input capacitor C1, the other end of the OVP setting resistor R3, the other end of the current sampling resistor Rcs, and ground; the anode of the rectifier diode D5 is respectively connected to the drain of the power tube Q1 and one end of the inductor Lm; the gate of the power tube Q1 is connected to the output end of the main control chip 100, the input end of the main control chip 100 is connected to one end of the OVP setting resistor R3, and the source of the power tube Q1 is connected to one end of the current sampling resistor Rcs; the other end of the inductor Lm is respectively connected to the other end of the output capacitor Cout, the other end of the dummy load Dload, and the other end of the output LED load Dload.

[0035] The main control chip 100 includes an error amplifier 101 , a compensation capacitor 102 , a first comparator 103 , a shutdown logic module 104 , a first control logic module 105 , a driving circuit 106 , a demagnetization detection circuit 107 and an overvoltage protection circuit 108 .

[0036] The output end of the error amplifier 101 is respectively connected to one end of the compensation capacitor 102, the inverting input end of the first comparator 103, and the input end of the overvoltage protection circuit 108. The input of the non-inverting input end of the error amplifier 101 is the reference voltage signal Vref, the input of the inverting input end of the error amplifier 101 is the output current signal Ioutsp, and the other end of the compensation capacitor 102 is grounded; the non-inverting input end of the first comparator 103 is connected to one end of the current sampling resistor, and the input is the current sampling signal CS. The output end of the first comparator 103 is connected to the second input end of the shutdown logic module 104, the first input end of the shutdown logic module 104 is connected to the output end of the overvoltage protection circuit 108, and the output end of the shutdown logic module 104 is connected to the first input end of the first control logic module 105; the output signal Tonmax of the shutdown logic module 104 is also connected to the input end of the overvoltage protection circuit 108. A second input terminal of the shutdown logic module 104 is connected to an output terminal of the demagnetization detection circuit 107. The output terminal of the shutdown logic module 104 is connected to an input terminal of the drive circuit 106. The output terminal of the drive circuit 106 is respectively connected to the gate of the power tube and the input terminal of the demagnetization detection circuit 107. The output terminal of the demagnetization detection circuit 107 is also connected to an input terminal of the overvoltage protection circuit 108.

[0037] like Figure 5 As shown, the overvoltage protection circuit includes: a second comparator comp1, a timing capacitor C0, a switch K1, a voltage-current conversion circuit 109, a second control logic module 112, a third control logic module 113 and an OVP control logic module 111;

[0038] The input of the voltage-to-current conversion circuit 109 is connected to one end of the OVP setting resistor, and the output of the voltage-to-current conversion circuit is connected to one end of the switch K1 and one end of the timing capacitor C0, respectively. The other ends of the switch K1 and the other ends of the timing capacitor C0 are both grounded. The non-inverting input of the second comparator comp1 is connected to one end of the timing capacitor C0, the inverting input of the second comparator comp1 is connected to the output of the error amplifier, and the output of the second comparator comp1 is connected to the second input of the OVP control logic module 111. The output signal of the second comparator comp1 controls the output current of the voltage-to-current conversion circuit 109. The first input of the OVP control logic module 111 is connected to the output of the second control logic module 112, the third input of the OVP control logic module 111 is connected to the output of the third control logic module 113, and the output of the OVP control logic module 111 is connected to the first input of the shutdown logic module. The input of the second control logic module 112 is the maximum on-time signal of the main control chip 100, and the input of the third control logic module 113 is connected to the output of the demagnetization detection circuit.

[0039] The voltage-to-current conversion circuit 109 outputs a timing current, I0, which varies with the OVP setting resistor R3. I0 is controlled by the output signal 110 of the second comparator comp1 and flows into the top plate of the timing capacitor C0. Switch K1 is controlled by the on-state signal TON from the main control chip 100. When TON is logic high, switch K1 is closed; when TON is logic low, switch K1 is open.

[0040] In this embodiment, the shutdown logic module is an OR gate; the first control logic module is an RS trigger, the first input end of the first control logic module is the R end, and the second input end of the first control logic module is the S end; the OVP control logic module is a three-input AND gate; the second control logic module and the third control logic module are both inverters.

[0041] The basic principle of the circuit of the present invention is to use the output voltage of the internal error amplifier 101 to set a reference time T0. By comparing T0 with the demagnetization time Tdem, the output overvoltage protection function is implemented under different peak currents of the inductor Lm. Through closed-loop control within the main control chip 100, the output voltage ea_out of the error amplifier 101 is set to the threshold voltage of the inductor current sampling terminal CS. Therefore, the peak current Ipk of the inductor Lm is modulated by ea_out. According to the volt-second balance principle, it can be seen that:

[0042]

[0043] Where Vcs is the current sense pin voltage, Ipk is the inductor's peak current, Vout is the output voltage, Lm is the inductance, and Tdem is the inductor's demagnetization time, which refers to the time it takes for the inductor's current to drop from its peak value to zero. ea_out is the output voltage of the error amplifier 101, which is also the threshold voltage of the inductor's current sampling terminal, CS. The current sampling resistor, Rcs, is the current sampling resistor from the inductor's current sampling terminal, CS, to ground.

[0044] The main control chip 100 sets a reference time T0, which is as follows:

[0045]

[0046] I0 is the reference charging current generated by the OVP setting resistor R3 through the voltage-to-current conversion circuit 109, and C0 is the timing capacitor.

[0047] Combining equations (1) and (2), we have the following expression:

[0048]

[0049] According to formula (3), by comparing the durations of T0 and Tdem, it is possible to determine whether the output voltage is overvoltage. When the system is operating normally, the duration of T0 is less than Tdem. As the output voltage gradually increases, according to formula (3), the duration of Tdem gradually decreases, but the duration of T0 does not change. When the duration of Tdem is less than T0, the output voltage is judged to be overvoltage, the response signal ovp is output, and the main control chip 100 shuts down the switch.

[0050] It should be noted that when the input voltage decreases, the voltage difference across the inductor Lm decreases, resulting in a decrease in the inductor current slope and a longer conduction time. At this time, the system operates in the maximum conduction time Tonmax state set by the main control chip 100. The present invention will shield the overvoltage protection circuit 108 to avoid erroneous judgment.

[0051] The overvoltage protection circuit 108 of the present invention uses closed-loop control, and the ea_out voltage is related to the system's constant current reference voltage. This voltage also has the same effect on T0 and Tdem. As shown in equation (3), C0 is a fixed capacitor, and I0 is set by the OVP setting resistor R3. Therefore, the resulting output voltage is only dependent on the OVP setting resistor R3, the inductor Lm, and the current sampling resistor Rcs.

[0052] like Figure 6 As shown, when the power tube Q1 starts to turn on, TON is at high logic. The current of the inductor Lm rises linearly. It turns off Q1 after reaching the ea_out voltage. Due to the presence of the compensation capacitor 102, the ea_out signal is maintained. When Q1 is turned off, the current of the inductor Lm starts to decrease linearly. The time it takes for the current of the inductor Lm to drop from the peak to 0 is the demagnetization time Tdem. At the same time, the timing capacitor C0 is charged by I0, and the voltage waveform of the timing capacitor C0 is ramp1. When ramp1 reaches the ea_out voltage, the I0 current is turned off. The time it takes for ramp1 to rise from 0 to ea_out is T0. This time is compared with the demagnetization time Tdem. When the T0 time is less than the Tdem time, the ovp output signal is always at low logic, and the system is in normal working state; when the T0 time is greater than the Tdem time, the ovp output signal is at high logic, and the control logic 105 turns off the TON signal of the next cycle, turns off Q1, and output overvoltage protection occurs.

[0053] like Figure 7 As shown, it should be noted that when the negative input voltage of the error amplifier 101 changes (for example, during dimming), the ea_out voltage decreases, and the peak voltage of CS decreases accordingly, and T0 also decreases accordingly. According to formulas (1), (2), and (3), it can be determined that the OVP voltage does not change at this time.

[0054] like Figure 8As shown, when the input voltage decreases, ea_out remains at a fixed value. However, due to the maximum on-time limit, the peak voltage of CS decreases, and the demagnetization time is also shortened. The circuit of the present invention uses the maximum on-time signal Tonmax to mask the output signal 110 of the second comparator comp1. When the main control chip 100 operates in the maximum on-time state, the Tonmax signal flips to a high logic level after TON is turned off, and ovp is locked at a low logic level to prevent false triggering.

[0055] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0056] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. An LED driver power supply using an overvoltage protection circuit, characterized in that: include: Rectifier bridge, input capacitor, rectifier diode, inductor, output capacitor, dummy load, output LED load, current sampling resistor, OVP setting resistor, power tube and main control chip; One end of the rectifier bridge is respectively connected to one end of the input capacitor, the cathode of the rectifier diode, one end of the output capacitor, one end of the dummy load, and one end of the output LED load, and the other end of the rectifier bridge is respectively connected to the other end of the input capacitor, the other end of the OVP setting resistor, the other end of the current sampling resistor, and the ground; the anode of the rectifier diode is respectively connected to the drain of the power tube and one end of the inductor, the gate of the power tube is connected to the output end of the main control chip, the input end of the main control chip is connected to one end of the OVP setting resistor, and the source of the power tube is connected to one end of the current sampling resistor; the other end of the inductor is respectively connected to the other end of the output capacitor, the other end of the dummy load, and the other end of the output LED load; The main control chip includes an error amplifier, a compensation capacitor, a first comparator, a shutdown logic module, a first control logic module, a drive circuit, a demagnetization detection circuit and an overvoltage protection circuit; The output end of the error amplifier is respectively connected to one end of the compensation capacitor, the inverting input end of the first comparator, and the input end of the overvoltage protection circuit; the input of the non-inverting input end of the error amplifier is a reference voltage signal, the input of the inverting input end of the error amplifier is an output current signal, and the other end of the compensation capacitor is grounded; the non-inverting input end of the first comparator is connected to one end of the current sampling resistor, the output end of the first comparator is connected to the second input end of the shutdown logic module, the first input end of the shutdown logic module is connected to the output end of the overvoltage protection circuit, and the output end of the shutdown logic module is respectively connected to the first input end of the first control logic module and the input end of the overvoltage protection circuit; The second input end of the shutdown logic module is connected to the output end of the demagnetization detection circuit, the output end of the shutdown logic module is connected to the input end of the drive circuit, and the output end of the drive circuit is respectively connected to the gate of the power tube and the input end of the demagnetization detection circuit; The output end of the demagnetization detection circuit is also connected to the input end of the overvoltage protection circuit; The overvoltage protection circuit includes: a second comparator, a timing capacitor, a switch, a voltage-current conversion circuit, a second control logic module, a third control logic module and an OVP control logic module; The input end of the voltage-current conversion circuit is connected to one end of the OVP setting resistor, the output end of the voltage-current conversion circuit is respectively connected to one end of the switch and one end of the timing capacitor, and the other end of the switch and the other end of the timing capacitor are both grounded; the non-inverting input end of the second comparator is connected to one end of the timing capacitor, the inverting input end of the second comparator is connected to the output end of the error amplifier, the output end of the second comparator is connected to the second input end of the OVP control logic module, and the output signal of the second comparator controls the output current of the voltage-current conversion circuit; the first input end of the OVP control logic module is connected to the output end of the second control logic module, the third input end of the OVP control logic module is connected to the output end of the third control logic module, and the output end of the OVP control logic module is connected to the first input end of the shutdown logic module; the input of the second control logic module is the maximum on-time signal of the main control chip, and the input end of the third control logic module is connected to the output end of the demagnetization detection circuit.

2. The LED driving power supply using an overvoltage protection circuit according to claim 1, characterized in that: The shutdown logic module is an OR gate.

3. The LED driving power supply using an overvoltage protection circuit according to claim 1, characterized in that: The first control logic module is an RS trigger; the first input end of the first control logic module is the R end, and the second input end of the first control logic module is the S end.

4. The LED driving power supply using an overvoltage protection circuit according to claim 1, characterized in that: The OVP control logic module is a three-input AND gate.

5. The LED driving power supply using an overvoltage protection circuit according to claim 1, characterized in that: The second control logic module and the third control logic module are both inverters.

Images