WO2015024224A1

WO2015024224A1 - Led constant-current circuit and led lamp

Info

Publication number: WO2015024224A1
Application number: PCT/CN2013/082026
Authority: WO
Inventors: 刘晓峰
Original assignee: Liu Xiaofeng
Priority date: 2013-08-22
Filing date: 2013-08-22
Publication date: 2015-02-26
Also published as: CN104813745A; CN104813745B

Abstract

An LED constant-current circuit and an LED lamp, which are used for improving the stability of a circuit when an electronic transformer supplies power. The LED constant-current circuit comprises a bridge rectifier circuit (DB), a sampling circuit (46) and a buck constant-current circuit (2), and further comprises: a first capacitor (C1), a first charging circuit (42) used for charging the first capacitor (C1) when the voltage of the first capacitor (C1) is lower than the output voltage of the bridge rectifier circuit (DB), wherein the first charging circuit (42) is connected to the bridge rectifier circuit (DB) and the first capacitor (C1), respectively; and a second charging circuit (44) used for charging the first capacitor (C1) when the output voltage of the bridge rectifier circuit (DB) is higher than the voltage of the first capacitor (C1), wherein the second charging circuit (44) is connected to the bridge rectifier circuit (DB) and the first capacitor (C1), respectively. The LED lamp comprises an LED constant-current circuit, prevents the overcurrent protection of an electronic transformer triggered at the moment of power-on, and improves the reliability of a circuit, so that the whole lamp has no flicker when the electronic transformer supplies power.

Description

LED constant current circuit and LED lamp

The present invention relates to the field of LED lighting, and more particularly to an LED constant current circuit and an LED lamp. Background technique

As an alternative light source for traditional luminaires, LED luminaires will not be replaced in the original lighting and electronic transformers for replacement and cost savings. The original electronic transformer is designed for halogen lamps. The electronic transformer is designed with under-power protection and over-power protection. When the load power is too low and enters its protection range, the electronic transformer will be in intermittent output state. When the power is too high, the electronic transformer will also turn off the output. Only when the load power is kept within a certain range, the electronic transformer can work normally and output.

Figure 1 shows a common LED step-down constant current drive circuit. When connected to the AC (DC) power supply, it is rectified by the bridge rectifier circuit DB, capacitor C1 is filtered, and then the buck constant current control chip provides a constant operating current to the LED. The biggest disadvantage of Figure 1 is that if the input voltage is rectified and filtered, if the voltage on C1 is lower than Vled+Vmos+Vic+VRs, the LED brightness is lower than the normal value, or even not at all. Where Vied is the forward voltage drop of the LED string; Vmos is the MOSFET tube voltage drop; Vic is the IC constant current threshold voltage; VRs is the sense resistor voltage drop.

When the above circuit electronic transformer charges C1 to the output voltage of the electronic transformer, the output current of the electronic transformer is reduced to 4, so that the under-power protection is performed, and the output voltage is stopped. However, after the load works for a certain period of time, Va starts to drop, and the electronic transformer can be charged again. After C1 is full, the electronic transformer stops working again. In this way, in addition to the 100Hz power frequency ripple on C1, a low frequency ripple is superimposed. A single 100Hz ripple is difficult to recognize by the human eye, but after superimposing another low frequency ripple. , a new 4 艮 low frequency ripple will be generated, so that the human eye can feel the LED light flashing.

Figure 2 is also an LED boost constant current drive circuit with more applications. When connected to the AC/DC power supply, it is rectified by the bridge rectifier circuit DB, filtered by the capacitor C1, and boosted by the constant current. The control chip provides the rated operating current for the LED. The disadvantages are: If the load LED has a small number of series connections (requires a low output voltage), the boost controller will not be able to pass the voltage on C1 higher than the output LED voltage. Stabilizes the output current, causing abnormal brightness and even damaging the LED.

When the input voltage is lower than the output voltage, the circuit can work normally when the input voltage is lower than the output voltage. However, if the input voltage is higher or equal to the output voltage, it will not work normally. If the input is an electronic transformer, because the output of the electronic transformer oscillates a high-frequency intermittent pulse voltage of different amplitudes, and the frequency and amplitude of the voltage pulse voltage of the output of different electronic transformers will be different. If C1 is charged and discharged, This causes C1 to reduce the service life due to the equivalent series resistance heating, and also has the problem described above in Figure 1 causing the LED to flicker.

Of course, because each electronic transformer's under-power protection point, over-power protection point, and detection delay time are different, this will cause the LEDs of the above circuit to match different types of electronic transformers, and some will flash. Some will not flash; some will be noticeable, and some will not be noticeable. Because of the piecemeal error of the components, even the same batch of electronic transformers, the same batch of LED lights will have different results.

Figure 3 is a relatively good LED driver circuit. Due to the use of the buck-boost structure, the deficiencies in Figure 1 and Figure 2 can be solved to a certain extent. However, due to the existence of C1, the driver may still be connected. When entering the electronic transformer, especially when protecting the electronic transformer with low current point, the electronic transformer enters the overcurrent protection state without output due to the charging of C1, and the operating voltage of the boost controller in Fig. 3 (Vin ) is obtained from the previous C1, which will cause the voltage at the C1 terminal to be lower than the normal operating voltage of the chip during operation, resulting in the voltage of the latter stage (both ends of C2) being too low, so that the step-down constant current circuit cannot work. Under normal circumstances, the LED flashes, but the probability of flicker is much smaller than that of Figures 1 and 2. It is compatible with some electronic transformers.

However, the control ICs in the circuits of Figures 2 and 3 are all taken from the C1 terminal. When using the electronic transformer, the voltage across C1 cannot be guaranteed to be higher than the startup voltage of the control IC. The control IC will work in the interval. In the state, the voltage across C2 in Figure 3 will appear lower than the operating voltage of the subsequent step-down constant current circuit, and is also in intermittent operation. Table Now the human eye can recognize that the LED light flashes.

In addition, when the control IC stops working, the current of the inductor L1 decreases, and it is easy to trigger the under-power protection of the electronic transformer.

Therefore, in the prior art, there is a problem of circuit instability caused by the power supply of the electronic transformer to the LED lamp. Summary of the invention

The invention provides an LED constant current circuit and an LED lamp, which are used for solving the circuit instability problem caused by the electronic transformer of the prior art for powering the LED lamp.

In order to achieve the above object, according to an aspect of the present invention, an LED constant current circuit is provided, and the following technical solutions are adopted:

LED constant current circuit, including bridge rectifier circuit, sampling circuit and step-down constant current circuit, also includes:

a first capacitor; a first charging circuit for charging the first capacitor when a voltage of the first capacitor is lower than an output voltage of the bridge rectifier circuit, wherein the first charging circuit is respectively connected to the a bridge rectifier circuit and the first capacitor; a second charging circuit for charging the first capacitor when an output voltage of the bridge rectifier circuit is higher than a voltage of the first capacitor Two charging circuits respectively connect the bridge rectifier circuit and the first capacitor.

Further, the first charging circuit includes: a second capacitor, the first end is connected to the bridge rectifier circuit; the first resistor is connected to the second end of the second capacitor, and the second end is connected to the second end The positive pole of the first capacitor.

Further, the second charging circuit includes: an inductor, the first end is connected to the bridge rectifier circuit;

a diode, a first end connected to the second end of the first inductor, and a second end connected to the anode of the first capacitor;

a boost control chip, the first end is connected to the anode of the first capacitor, the second end is connected to the cathode of the first capacitor; the MOS transistor is connected to the second end of the inductor, and the gate is connected to the boost The third end of the control chip has a drain connected to the negative terminal of the first capacitor. Further, the sampling circuit includes: a second resistor, the first end is connected to the anode of the first capacitor; the third resistor is connected to the second end of the second resistor, and the second end is connected to the second end The negative pole of a capacitor.

Further, the first end of the step-down constant current circuit is connected to the third resistor, and the second end is connected to the second resistor through a target LED lamp.

According to a second aspect of the present invention, an LED luminaire is provided, and the following technical solution is adopted:

LED luminaires, including the above-mentioned LED constant current circuit.

Further, the LED lamp further includes an electronic transformer, and the electronic transformer is connected to the LED constant current circuit through a bridge rectifier circuit of the LED lamp.

Compared with the prior art, the present invention avoids causing over-power protection of the electronic transformer by removing the filter capacitor after the bridge rectifier circuit DB. By adopting the technical scheme of the invention, the overcurrent protection of the electronic transformer is triggered at the moment of power-on, and the reliability of the circuit is greatly improved. After the output of the electronic transformer is passed through the bridge rectifier circuit, the first capacitor is supplied through two channels. Since the capacitor voltage cannot be abruptly changed, the inductor current cannot be abruptly changed, so the two sets of currents charged for the first capacitor have a phase difference, and the first capacitor has two The voltage at the terminal is also more stable. After the change control IC outputs power from the booster circuit, since the voltage across the first capacitor can be kept higher than the startup voltage of the control IC, even if the input voltage is low, the boost control IC or the boost constant current control IC can be guaranteed. Is working. In addition, when the output of the electronic transformer is lower than the operating voltage of the control IC, the current of the inductor L1 rises, effectively preventing the electronic transformer from entering the under-power protection state. Therefore, the LED constant current circuit provided by the invention can realize the whole lamp without flicker when being powered by the electronic transformer, and can be compatible with various electronic transformers. DRAWINGS

The drawings are intended to provide a further understanding of the present invention, and are intended to be a part of the invention. In the drawing:

1 is a schematic structural view of a conventional LED buck constant current driving circuit according to the background art of the present invention; 2 is a schematic structural diagram of an LED boost constant current driving circuit with more applications as described in the background art of the present invention;

3 is a schematic structural view of an LED driving circuit according to the background art of the present invention; FIG. 4 is a schematic structural view of an LED constant current circuit according to Embodiment 1 of the present invention; and FIG. 5 is a diagram showing a constant current of the LED according to Embodiment 2 of the present invention; Schematic diagram of the structure of the circuit. detailed description

The embodiments of the present invention are described in detail below with reference to the drawings, but the invention may be embodied in many different ways as defined and covered by the claims.

4 is a schematic structural view of an LED constant current circuit according to Embodiment 1 of the present invention. Referring to FIG. 4, the LED constant current circuit includes a bridge rectifier circuit 40, a sampling circuit 46 and a step-down constant current circuit 48, and specifically includes: a first capacitor C1; and a low voltage at the first capacitor C1 a first charging circuit 42 for charging the first capacitor C1 when the output voltage of the bridge rectifier circuit 40 is received, the first charging circuit 42 is respectively connected to the bridge rectifier circuit 40 and the first capacitor a second charging circuit 44 for charging the first capacitor C1 when the output voltage of the bridge rectifier circuit 40 is higher than the voltage of the first capacitor C1, the second charging circuit 44 respectively The bridge rectifier circuit 40 is connected to the first capacitor C1.

In the above technical solution of the embodiment, the first charging circuit 42 and the second charging circuit 44 are respectively used to charge the first capacitor C1. The structure adopting the dual channel charging avoids triggering the electronic transformer overcurrent protection at the moment of power-on. Greatly improve the reliability of the circuit. At the same time, it is also guaranteed that the boost control IC or the boost constant current control IC is always in operation when the input voltage is low.

FIG. 5 is a schematic structural view of an LED constant current circuit according to Embodiment 2 of the present invention. Referring to Fig. 5, Fig. 5 shows a preferred circuit configuration of the first charging circuit 42 and the second charging circuit 44.

First, the first charging circuit 42 may specifically include: a second capacitor C2, the first end of the second capacitor C2 is connected to the bridge rectifier circuit 40, that is, DB in FIG. 5; the first resistor R1, the first a first end of the resistor R1 is connected to the second end of the second capacitor C2, The second end of the first resistor R1 is connected to the anode of the first capacitor CI.

The above is the priority circuit configuration of the first charging circuit 42, but the configuration of the first charging circuit 42 is not limited thereto, and any of the first capacitors C1 can be used when the voltage of the first capacitor C1 is lower than the output voltage of the bridge rectifier circuit 40. The circuits for charging are all within the scope of the present invention.

Preferably, the second charging circuit 44 may specifically include: an inductor L1, the first end of the inductor L1 is connected to the bridge rectifier circuit 40, that is, DB in FIG. 5; the diode D1, the first end of the diode D1 is connected a second end of the first inductor L1, a second end of the diode D1 is connected to the positive electrode C1 of the first capacitor; a boost control chip IC, a first end of the boost control chip IC is connected to the positive electrode of the first capacitor C1 The second end of the boost control chip IC is connected to the negative pole of the first capacitor C1; the MOSFET Q1, the source of the MOS transistor Q1 is connected to the second end of the inductor L1, and the gate of the MOS transistor Q1 is connected to the rise The third end of the voltage control chip IC, the drain of the MOS transistor Q1 is connected to the cathode of the first capacitor C1.

The above is the priority circuit configuration of the second charging circuit 44, but the configuration of the second charging circuit 44 is not limited thereto, and any when the output voltage of the bridge rectifier circuit 40 is higher than the voltage of the first capacitor C1 The circuit for charging the first capacitor C1 is within the protection scope of the present invention.

Optionally, the sampling circuit 46 includes: a second resistor R2, a first end of the second resistor R2 is connected to the anode of the first capacitor C1; and a third resistor R3 is connected to the first end of the third resistor R3. The second end of the second resistor R2, the second end of the third resistor R3 is connected to the cathode of the first capacitor C1.

Optionally, the first end of the step-down constant current circuit 48 is connected to the third resistor R3, and the second end of the step-down constant current circuit 48 is connected to the second resistor R2 through a target LED lamp.

By adopting the technical scheme of the invention, the overcurrent protection of the electronic transformer is triggered at the moment of power-on, which greatly improves the reliability of the circuit. After the output of the electronic transformer is passed through the bridge rectifier circuit, the first capacitor is supplied through two channels. Since the capacitor voltage cannot be abruptly changed, the inductor current cannot be abruptly changed, so the two sets of currents charged for the first capacitor have a phase difference, and the first capacitor has two The voltage at the terminal is also more stable. After the change control IC outputs power from the booster circuit, since the voltage across the first capacitor can always be higher than the startup voltage of the control IC, even if the input The lower voltage also ensures that the boost control IC or boost constant current control IC is always active. In addition, when the output of the electronic transformer is lower than the operating voltage of the control IC, the current of the inductor L1 rises, effectively preventing the electronic transformer from entering the underpower protection state. Therefore, the LED constant current circuit provided by the invention can realize the whole lamp without flicker when being powered by the electronic transformer, and can be compatible with various electronic transformers.

The present invention provides an LED lamp comprising the above-described LED constant current circuit.

Optionally, the LED luminaire further includes an electronic transformer, and the electronic transformer is connected to the LED constant current circuit through a bridge rectifier circuit of the LED luminaire.

Compared with the prior art, the LED lamp of the invention avoids the over-power protection of the electronic transformer by removing the filter capacitor after the bridge rectifier circuit DB, and realizes stable power supply of the LED lamp.

Claims

Claim

An LED constant current circuit comprising a bridge rectifier circuit, a sampling circuit and a step-down constant current circuit, characterized in that:

First capacitor

a first charging circuit for charging the first capacitor when a voltage of the first capacitor is lower than an output voltage of the bridge rectifier circuit, the first charging circuit is respectively connected to the bridge rectifier circuit And the first capacitor;

a second charging circuit for charging the first capacitor when an output voltage of the bridge rectifier circuit is higher than a voltage of the first capacitor, the second charging circuit being respectively connected to the bridge rectifier circuit And the first capacitor.

The LED constant current circuit according to claim 1, wherein the first charging circuit comprises:

a second capacitor, the first end is connected to the bridge rectifier circuit;

The first resistor is connected to the second end of the second capacitor, and the second end is connected to the anode of the first capacitor.

3. The LED constant current circuit according to claim 1, wherein the second charging circuit comprises:

An inductor, the first end is connected to the bridge rectifier circuit;

a diode, the first end is connected to the second end of the first inductor, and the second end is connected to the anode of the first capacitor;

a boosting control chip, the first end is connected to the anode of the first capacitor, and the second end is connected to the cathode of the first capacitor;

a MOS transistor, a source connected to the second end of the inductor, a gate connected to the third end of the boost control chip, and a drain connected to the negative terminal of the first capacitor.

The LED constant current circuit according to any one of claims 1 to 3, wherein the sampling circuit comprises:

a second resistor, the first end is connected to the anode of the first capacitor;

The third resistor has a first end connected to the second end of the second resistor, and a second end connected to the negative pole of the first capacitor.

The LED constant current circuit according to claim 4, wherein the first end of the step-down constant current circuit is connected to the third resistor, and the second end is connected to the second resistor through a target LED lamp.

An LED lamp comprising the LED constant current circuit according to any one of claims 1 to 5.

The LED lamp of claim 6, further comprising: an electronic transformer, wherein the electronic transformer is connected to the LED constant current circuit through a bridge rectifier circuit of the LED lamp.