CN209627751U - A kind of linear LED constant-current control circuit of efficient closed loop - Google Patents

Abstract

The utility model discloses a kind of efficient linear LED constant-current control circuits of closed loop, it is characterised in that: including rectifier bridge (100), light emitting diode group (200), current regulator (P1), closed control circuit (P) and line voltage resistance sampling network (300)；The rectifier bridge (100) is internal circuit power supply by light emitting diode group (200) for carrying out full-wave rectification to alternating current；The cathode of input terminal (VIN) connection light emitting diode group (200) of the current regulator (P1)；The line voltage resistance sampling network (300), obtains sampled voltage VBS；The closed control circuit (P) includes reference voltage chip (400), second operational amplifier (Gm), subtracter, loop compensation capacitor (C1) and resistance (RCS).The utility model solves conventional linear LED drive circuit, and modulating voltage range of choice is narrow, inefficiency, the problem of line regulation difference.

Description

A high-efficiency closed-loop linear LED constant current control circuit

technical field

The utility model relates to an LED drive circuit, in particular to a high-efficiency closed-loop linear LED constant current control circuit.

Background technique

It can be seen from the electrical characteristics of LEDs that the average forward current of LEDs increases linearly with the increase of forward voltage, and small changes in the forward voltage of LEDs after forward conduction will cause large changes in LED current. Moreover, the current has a great influence on the junction temperature of the LED. Excessive current can easily cause the junction temperature of the LED lamp bead to rise and be damaged. In addition, it can be seen from the optical characteristics of the LED that as the forward current increases, the luminous flux of the LED increases, that is, the brightness increases. Therefore, in order to keep the LED luminance constant, it is necessary to ensure the stability of the LED forward current. Therefore, it is very important to design a reasonable driving power supply for LED lighting fixtures.

Traditional linear LED drivers mostly use open-loop control. When the LED is turned on, the LED current remains constant. According to the principle of LED turn-on, when the AC sine wave voltage is just greater than the LED lamp voltage, the efficiency is the highest. With the AC The higher the amplitude of the sine wave voltage than the lamp voltage, the greater the loss and the lower the efficiency. For example, for 220V applications, the lamp voltage must be connected in series to about 250V, so that the efficiency can barely reach about 85%. The lower the lamp voltage, the greater the loss.

At the same time, since the current of the LED lamp is controlled in an open loop during the entire AC cycle, when the power grid fluctuates, the conduction angle of the LED will fluctuate with the fluctuation of the power grid, and the current when the LED is turned on is constant, so when the power grid fluctuation direction is As the AC voltage increases, the conduction angle becomes larger, and the average current of the LED will increase. On the contrary, the direction of grid fluctuation is that the AC voltage decreases, and the conduction angle becomes smaller, and the average current of the LED will decrease, resulting in a poor linear adjustment rate. .

As shown in Figure 1, in a traditional linear LED drive circuit, the LED light string is connected to the positive terminal of the input rectifier bridge, and is set by the linear current control loop P1 composed of OP, MOS transistor M1, VREF voltage, and RCS resistance. The current Io flowing through the LED;

According to the principle of LED conduction, the LED light string will be lit only when the input voltage is higher than the LED forward voltage VLED, the effective power of the system PO=VLED*IO, and the system loss PLOSS=(VBUS-VLED)* IO, from the above two formulas and the working principle of the linear circuit, it can be known that the efficiency is the highest when the DCBUS voltage is just greater than the LED voltage. As shown in Figure 2, since the LED current IO remains constant, when the AC sine wave voltage reaches the peak point , the system loss is the largest.

According to the requirements of the US Energy Star standard, the linear efficiency must reach more than 84%, and the PF value must reach more than 0.7. It is difficult for the traditional linear circuit to meet the above efficiency requirements under the 120V power grid.

Utility model content

The purpose of the invention of the present utility model is to provide a high-efficiency closed-loop linear LED constant current control circuit to solve the problems of narrow lamp voltage selection range, low efficiency, and poor linear adjustment rate in traditional linear LED drive circuits; Control the lamp current waveform so that when the AC sine wave voltage is just higher than the lamp voltage, the lamp current is the largest. The higher the AC sine wave voltage, the smaller the lamp current, which greatly improves the efficiency; at the same time, due to the closed-loop control, the average output LED current can be maintained. constant.

The technical scheme that the utility model adopts is as follows:

The utility model is an efficient closed-loop linear LED constant current control circuit, comprising a rectifier bridge 100, a light emitting diode group 200, a current control loop P1, a closed-loop control circuit P and a line voltage resistance sampling network 300; the rectifier bridge 100 is used for Perform full-wave rectification on the alternating current, and generate an output voltage VBUS, which supplies power to the internal circuit through the light-emitting diode group 200; the input terminal VIN of the current control loop P1 is connected to the negative pole of the light-emitting diode group 200; the line voltage resistance sampling network 300, for sampling the line voltage to obtain the sampling voltage VBS;

The closed-loop control circuit P includes a reference voltage chip 400, a second operational amplifier Gm, a subtractor SUB, a loop compensation capacitor C1 and a resistor RCS;

The input terminal of the reference voltage chip 400 is connected to the input terminal VIN of the current control loop P1, and the output terminal of the reference voltage chip 400 is connected to the non-inverting input terminal of the second operational amplifier Gm;

The inverting input terminal of the second operational amplifier (Gm) is connected to the current control loop P1, the output terminal is connected to the A input terminal of the subtractor SUB, and the output voltage is COMP;

The B input terminal of the subtractor SUB is connected to the line voltage resistance sampling network 300, the output terminal is connected to the current control loop P1, and the output voltage SUB_OUT;

One end of the loop compensation capacitor C1 is connected to the output end of the second operational amplifier Gm, and the other end is grounded;

One end of the resistor RCS is connected to the inverting input end of the second operational amplifier Gm, and the other end is grounded.

Preferably, the line voltage resistance sampling network 300 includes resistors RSUB1 and RSUB2 connected in series; one end of the line voltage resistance sampling network 300 is connected to the cathode of the LED group 200 , and the other end is grounded.

Preferably, one end of the line voltage resistance sampling network 300 is connected to the anode of the LED group 200, and the other end is grounded.

Preferably, the current control loop P1 includes a first operational amplifier OP, the non-inverting input terminal of the first operational amplifier OP is connected to the subtractor output voltage SUB_OUT, the inverting input terminal is connected to the resistor RCS, and the output terminal is connected to the gate of the MOS switch M1 pole; the drain of the MOS switch M1 is connected to the input terminal VIN of the current control loop P1, and the source is connected to the output terminal of the current control loop P1.

Preferably, the subtractor SUB receives the output voltage COMP of the second operational amplifier Gm and the sampling voltage VBS of the line voltage sampling network 300, and performs difference processing between the two voltages.

Preferably, the second operational amplifier Gm and the loop compensation capacitor C1 constitute an integrator for integrating the LED current.

In summary, due to the adoption of the above technical solution, the beneficial effects of the utility model are: compared with the prior art, the present invention discloses a high-efficiency closed-loop linear LED constant current control circuit, and by controlling the lamp current waveform, the AC string When the wave voltage is just higher than the lamp voltage, the lamp current is the largest, and the higher the AC sine wave voltage, the lower the lamp current, which greatly improves the efficiency; at the same time, due to the closed-loop control, the average output LED current can be kept constant.

Description of drawings

Figure 1 is a traditional LED linear constant current control circuit diagram.

Figure 2 is a traditional LED linear constant current control waveform diagram.

Fig. 3 is a circuit diagram of a high-efficiency closed-loop linear LED constant current control circuit of the present invention.

Fig. 4 is a timing diagram of each important node of the high-efficiency closed-loop linear constant current control in the embodiment.

Fig. 5 is a waveform diagram of important nodes of the high-efficiency closed-loop linear constant current control circuit with high VBS sampling voltage.

Fig. 6 is another embodiment of a high-efficiency closed-loop linear LED constant current control circuit diagram.

Marks in the figure: 100 is a rectifier bridge, 200 is a light-emitting diode group, 300 is a line voltage resistance sampling network, and 400 is a reference voltage chip.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is described in detail.

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not intended to limit the utility model.

As shown in Figure 3, a high-efficiency closed-loop linear LED constant current control circuit of the present invention includes a rectifier bridge 100, a light emitting diode group 200, a current control loop P1, a closed-loop control circuit P and a line voltage resistance sampling network 300; The rectifier bridge 100 is used to perform full-wave rectification on the alternating current, and generate an output voltage VBUS, which supplies power to the internal circuit through the light emitting diode group 200; the input terminal VIN of the current control loop P1 is connected to the negative pole of the light emitting diode group 200; The line voltage resistance sampling network 300 is used for sampling the line voltage to obtain the sampling voltage VBS; the line voltage resistance sampling network 300 includes a series resistance RSUB1 and a resistance RSUB2;

The closed-loop control circuit P includes a reference voltage chip 400, a second operational amplifier Gm, a subtractor SUB, a loop compensation capacitor C1 and a resistor RCS; the input end of the reference voltage chip 400 is connected to the input end of the current control loop P1 VIN, the output terminal of the reference voltage chip 400 is connected to the non-inverting input terminal of the second operational amplifier Gm; the inverting input terminal of the second operational amplifier Gm is connected to the current control loop P1, and the output terminal is connected to the A input terminal of the subtractor SUB, output voltage COMP; the B input terminal of the subtractor SUB is connected to the line voltage resistance sampling network 300, the output terminal is connected to the current control loop P1, and the output voltage SUB_OUT; one end of the loop compensation capacitor C1 is connected to the second operational amplifier Gm The output end is connected, and the other end is grounded; one end of the resistor RCS is connected to the inverting input end of the second operational amplifier Gm, and the other end is grounded; the closed-loop control circuit P is used to determine the average current of the LED ILEDAVG=VREF/ RCS, where VREF is the reference voltage of the second operational amplifier Gm, and RCS is the resistance value of the resistor RCS.

In one embodiment, one end of the line voltage resistance sampling network 300 is connected to the cathode of the LED group 200 , and the other end is grounded.

In an embodiment, the current control loop P1 includes a first operational amplifier OP, the non-inverting input terminal of the first operational amplifier OP is connected to the subtractor output voltage SUB_OUT, the inverting input terminal is connected to the resistor RCS, and the output terminal is connected to the MOS switch tube M1 The gate of the MOS switch tube M1 is connected to the input terminal VIN, and the source is connected to the output terminal; the current control loop P1 determines the LED current ILEDSINGLE=VSUB_OUT/RCS when the LED is turned on in a single cycle, where VSUB_OUT is a subtractor The output voltage, RCS is the resistance value of the resistor RCS.

In an embodiment, the subtractor SUB receives the output voltage COMP of the second operational amplifier Gm and the sampling voltage VBS of the line voltage resistance sampling network 300, and performs difference processing on the two voltages to obtain VSUB_OUT, which controls when the LED is turned on. transient current waveform.

In an embodiment, the second operational amplifier Gm and the loop compensation capacitor C1 form an integrator; the integrator is used to integrate the LED current.

As shown in Figure 4, when the system is powered on, the rectifier bridge performs full-wave rectification on the AC VAC and generates an output voltage VBUS. When the voltage of VBUS is greater than the forward voltage of the LED group, the IC takes power through the VIN pin and Start to work, the IC quickly precharges VCOMP to obtain the initial voltage of COMP, and subtracts the COMP voltage from the VBS voltage sampled by the VBS pin to obtain VSUB_OUT, which determines the current of the LED conduction: VSUBOUT=K(m *VCOMP-n*VBS);

According to the working principle of the linear circuit, the effective power of the system is PO=VLED*IO, and the system loss is equal to PLOSS=(VBUS-VLED)*IO. When the rectified VBUS voltage is just greater than the LED voltage, the system efficiency is the highest. , when the voltage of VBUS reaches its peak value, the loss of the system is the highest.

When the LED is turned on, that is, during the Ton period, the loop compensation capacitor C1 discharges, causing VCOMP to drop; and at the same time, because the sampling voltage VBS rises with the increase of the input voltage VBUS, according to the calculation formula of the subtractor, the output voltage VSUBOUT of the subtractor decrease; and because the LED current ILEDSINGLE=VSUB_OUT/RCS when the LED is turned on in a single cycle, the LED current Io decreases; so the LED current Io decreases with the increase of VBUS, and increases with the decrease of VBUS.

In the operation of the high-efficiency closed-loop linear LED constant current control circuit, when the VBUS voltage just reaches the LED voltage, the output voltage VCOMP obtained by integrating the CS voltage of the second operational amplifier Gm and the sampling voltage VBS of the line voltage resistance sampling network 300 are combined by the subtractor SUB Perform subtraction processing to amplify the conduction current of the LED; as the sine wave voltage gradually increases, the LED current gradually decreases, and when the VBUS voltage reaches the peak point, the LED current drops to the minimum; as the sine wave voltage further increases When the sine wave voltage drops to near the LED voltage, the LED current reaches the maximum.

When the VBUS voltage just reaches the LED voltage, try to amplify the conduction current of the LED so that the effective power of the LED at this time accounts for the highest proportion in the entire cycle, and as the sine wave voltage gradually increases, the LED current gradually decreases. When the VBUS voltage reaches the peak point, the LED current drops to the minimum. According to the lossy formula, the loss can be minimized, so as to achieve the purpose of improving the system efficiency in the whole cycle.

In an embodiment, the current control loop P1 and the closed-loop control circuit P are packaged on a single chip IC, and VIN, IS, GND, COMP, and VBS represent the pins of the chip IC; the loop compensation capacitor C1 and the resistor Rcs can be packaged in the IC , can also be set off-chip.

As shown in FIG. 5 , in the embodiment, the magnitude of improving efficiency can also be adjusted by adjusting the voltage VBS sampled by the line voltage resistance sampling network, that is, adjusting the ratio of the sampling resistor network RSUB1 to RSUB2; when the voltage sampled by VBS When it is large enough, the output voltage of the subtractor will drop to zero near the peak point, and the LED conduction current is limited to a period of time when the LED is just turned on. At the same time, due to the limitation of the conduction capability of the MOS, the maximum SUB_OUT voltage will be limited inside the circuit. Value; It can be seen from the linear working principle: the higher the VBS sampling voltage, the higher the efficiency of the system.

As shown in FIG. 6 , in another embodiment, one end of the line voltage resistance sampling network 300 is connected to the anode of the LED group 200 , and the other end is grounded.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present utility model shall be included in this utility model. within the scope of protection of utility models.

Claims (6)

1. a kind of linear LED constant-current control circuit of efficient closed loop, it is characterised in that: including rectifier bridge (100), light-emitting diodes nest of tubes Group (200), current regulator (P1), closed control circuit (P) and line voltage resistance sampling network (300)；The rectifier bridge (100), for carrying out full-wave rectification to alternating current, and output voltage VBUS is generated, is interior by light emitting diode group (200) The power supply of portion's circuit；The cathode of input terminal (VIN) connection light emitting diode group (200) of the current regulator (P1)；It is described Line voltage resistance sampling network (300) obtains sampled voltage VBS for sampling line voltage；

The closed control circuit (P) include reference voltage chip (400), second operational amplifier (Gm), subtracter (SUB), Loop compensation capacitor (C1) and resistance (RCS)；

The input terminal (VIN) of input terminal connection current regulator (P1) of the reference voltage chip (400), reference voltage core The non-inverting input terminal of output end connection second operational amplifier (Gm) of piece (400)；

The reverse input end of the second operational amplifier (Gm) connects current regulator (P1), and output end connects subtracter (SUB) A input terminal, output voltage COMP；

The B input terminal connecting line voltage resistance sampling network (300) of the subtracter (SUB), output end connect current regulator (P1), output voltage SUB_OUT；

Described loop compensation capacitor one end (C1) is connect with the output end of the second operational amplifier (Gm), other end ground connection；

One end of the resistance (RCS) is connect with the inverting input terminal of second operational amplifier (Gm), other end ground connection.

2. the efficiently linear LED constant-current control circuit of closed loop as described in claim 1, it is characterised in that: the line voltage resistance Sampling network (300) includes concatenated resistance (RSUB1) and resistance (RSUB2)；The line voltage resistance sampling network (300) one The cathode of end connection light emitting diode group (200), other end ground connection.

3. the efficiently linear LED constant-current control circuit of closed loop as described in claim 1, it is characterised in that: the line voltage resistance Sampling network (300) one end connects the anode of light emitting diode group (200), other end ground connection.

4. the efficiently linear LED constant-current control circuit of closed loop as described in claim 1, it is characterised in that: the current regulator It (P1) include the first operational amplifier (OP) that the noninverting input of the first operational amplifier (OP) connects subtracter output voltage SUB_OUT, inverting input terminal connect resistance (RCS), and output end connects the grid of MOS switch pipe (M1)；MOS switch pipe (M1) Drain electrode connection current regulator (P1) input terminal (VIN), source electrode connect current regulator (P1) output end.

5. the efficiently linear LED constant-current control circuit of closed loop as described in claim 1, it is characterised in that: the subtracter (SUB) Receive the output voltage COMP of second operational amplifier (Gm) and the sampled voltage of line voltage resistance sampling network (300) VBS, and two voltages are made the difference.

6. the efficiently linear LED constant-current control circuit of closed loop as described in claim 1, it is characterised in that: second operation is put Big device (Gm) and loop compensation capacitor (C1) constitute the integrator integrated to LED current.