CN205430699U - Two -stage formula LED drive power supply with PFC function - Google Patents

Abstract

The utility model discloses a two -stage formula LED drive power supply with PFC function comprises preceding, back two -stage circuit and control chip, and the preceding stage circuit be the PFC circuit based on the BOOST chopper, and the back level is the anti - sharp formula DCDC transfer circuit of quasi -resonance, control chip control main switch pipe Q2's break -make, control chip is equipped with eight pins, and pin 1 is the system output, mainly provides the gate pole drive for the MOSFET switch, pin 2 is voltage detecting, pin 3 detects for rectification input voltage, pin 4 is the restriction of outside power and turn -offs the control end, pin 5 is the earthing terminal, pin 6 is the primary current sense terminal, pin 7 is the drive of the outside MOSFET switch tube of output, pin 8 is the chip power supply end. Because the system has adopted two -stage formula structure, has simplified circuit structure greatly, can realize LED's constant current steady voltage control to higher power factor has.

Description

A two-stage LED drive power supply with PFC function

technical field

The invention relates to the field of power supply technology, in particular to power supply design based on power electronics technology, and is mainly applied to LED driving.

Background technique

Saving energy, protecting the environment, and developing green lighting products are key tasks that my country's lighting industry has been actively carrying out since the early 1990s. LED has the advantages of energy saving, long life, environmental protection, small size, flexible control, fast response, etc., so it has been popularized to thousands of households. However, the power factor of traditional LED driving power is low, and the input current has serious harmonics, resulting in poor power quality and serious pollution to the power grid, which also limits the widespread use of LED lights to a certain extent. The traditional single-stage LED drive power supply integrates PFC correction and DC/DC conversion. It uses few devices and low cost, but a large electrolytic capacitor needs to be added to the secondary side to overcome ripple and low-frequency voltage flicker. The input current peak is large, which seriously affects the service life of the LED. The traditional two-stage LED drive power supply sets the PFC and DC/DC converter independently. Although the mutual independence is good and the load capacity is strong, but there are many devices used, the reliability is poor, the efficiency is low, and the control circuit is relatively complicated, resulting in high cost. , also limits the application in low power occasions. In view of this, this patent proposes a two-stage LED drive power supply with PFC function, aiming to solve the above problems, thereby accelerating the use of LED light sources.

Contents of the invention

The purpose of the utility model is to provide a new two-stage LED drive power supply with PFC function.

In order to achieve the above purpose, the utility model adopts the following technical scheme: a two-stage LED drive power supply with PFC function, which is composed of front and rear two-stage circuits and a control chip, and the front-stage circuit is based on BOOST The PFC circuit of the oscillator, the latter stage is a quasi-resonant flyback DC/DC conversion circuit;

The control chip controls the on-off of the main switch tube Q2, and the control chip is provided with eight pins, the pin 1 is the system output, which mainly provides the gate drive for the MOSFET switch; the pin 2 is the voltage detection, mainly from The input signal of the auxiliary winding, thus providing secondary voltage feedback output regulation; pin 3 is rectified input voltage detection, used for input undervoltage and overvoltage protection, and this pin provides current for chip startup; pin 4 is external power Limit and shutdown control terminal; pin 5 is the ground terminal; pin 6 is the primary current detection terminal; it is mainly used for cycle peak current detection; pin 7 is the output external MOSFET switch tube drive; pin 8 is the chip power supply terminal .

Preferably, in the two-stage LED drive power supply with PFC function, the control chip uses the control chip iw3614 as the main control element of the system to control the on-off of the main switch tube.

Preferably, the two-stage LED drive power supply with PFC function includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, The eighth resistor, the ninth resistor, the first capacitor, the second capacitor, the third capacitor, the fourth capacitor, the fifth capacitor, the sixth capacitor, the first diode, the second diode, the third diode, The fourth diode, the first switching tube and the second switching tube, the fourth resistor is connected in series with the fifth resistor, the fourth diode is connected in series with the seventh resistor, the pin 8 of the control chip is connected with the first The four diodes are connected, the pin 7 of the control chip is connected to the second switch tube through the eighth resistor, the pin 1 of the control chip is connected to the second resistor, the third resistor and the first switch tube respectively, and the pin 7 of the control chip is connected to the second resistor, the third resistor and the first switch tube respectively, A switch tube is connected with the first resistor.

Preferably, in the two-stage LED drive power supply with PFC function, the front-stage circuit includes a PFC correction circuit, a rectification and filtering output circuit, and a rectification and filtering output circuit between the PFC correction circuit and the rectification and filtering output circuit. Between the feedback control unit, the PFC correction circuit includes a PFC power correction chip and a flyback output voltage circuit and a PWM boost topology circuit respectively connected to the PFC power correction chip; the flyback output voltage circuit includes a Demagnetization time and valley voltage sampling circuit, a flyback input control circuit; the feedback control unit includes an isolated optocoupler feedback circuit, first and second operational amplifier units, and is used to give the isolated optocoupler feedback unit, the second 1. An auxiliary power supply circuit powered by the second operational amplifier unit; a PWM constant current topology unit connected to the feedback control unit.

Compared with the prior art, the beneficial effect is that, by adopting the above scheme, the system adopts a two-stage structure, and the PFC and the DC/DC conversion circuit share one control chip, which greatly simplifies the circuit structure and can realize the constant current and voltage regulation control of the LED. And has a high power factor.

Description of drawings

Fig. 1 is a circuit structure diagram of the utility model.

detailed description

In order to enable those engaged in the related fields of LED driving power supply technology to better understand the solution of the present invention, specific circuit design steps are given below.

As shown in Figure 1, a two-stage LED drive power supply with PFC function is composed of front and rear two-stage circuits and a control chip. The front stage circuit is a PFC circuit based on BOOST chopper, and the rear stage is quasi-resonant. Flyback DC/DC conversion circuit;

The control chip controls the on-off of the main switch tube Q2, and the control chip is provided with eight pins, the pin 1 is the system output, which mainly provides the gate drive for the MOSFET switch; the pin 2 is the voltage detection, mainly from The input signal of the auxiliary winding, thus providing secondary voltage feedback output regulation; pin 3 is rectified input voltage detection, used for input undervoltage and overvoltage protection, and this pin provides current for chip startup; pin 4 is external power Limit and shutdown control terminal; pin 5 is the ground terminal; pin 6 is the primary current detection terminal; it is mainly used for cycle peak current detection; pin 7 is the output external MOSFET switch tube drive; pin 8 is the chip power supply terminal .

Preferably, in the two-stage LED drive power supply with PFC function, the control chip uses the control chip iw3614 as the main control element of the system to control the on-off of the main switch tube.

Preferably, the two-stage LED drive power supply with PFC function includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, The eighth resistor, the ninth resistor, the first capacitor, the second capacitor, the third capacitor, the fourth capacitor, the fifth capacitor, the sixth capacitor, the first diode, the second diode, the third diode, The fourth diode, the first switching tube and the second switching tube, the fourth resistor is connected in series with the fifth resistor, the fourth diode is connected in series with the seventh resistor, the pin 8 of the control chip is connected with the first The four diodes are connected, the pin 7 of the control chip is connected to the second switch tube through the eighth resistor, the pin 1 of the control chip is connected to the second resistor, the third resistor and the first switch tube respectively, and the pin 7 of the control chip is connected to the second resistor, the third resistor and the first switch tube respectively, A switch tube is connected with the first resistor.

Preferably, in the two-stage LED drive power supply with PFC function, the front-stage circuit includes a PFC correction circuit, a rectification and filtering output circuit, and a rectification and filtering output circuit between the PFC correction circuit and the rectification and filtering output circuit. Between the feedback control unit, the PFC correction circuit includes a PFC power correction chip and a flyback output voltage circuit and a PWM boost topology circuit respectively connected to the PFC power correction chip; the flyback output voltage circuit includes a Demagnetization time and valley voltage sampling circuit, a flyback input control circuit; the feedback control unit includes an isolated optocoupler feedback circuit, first and second operational amplifier units, and is used to give the isolated optocoupler feedback unit, the second 1. An auxiliary power supply circuit powered by the second operational amplifier unit; a PWM constant current topology unit connected to the feedback control unit.

First, according to the input voltage, select the resistance value of R _st of the acceleration start circuit, which will affect the conduction time and cycle of the switch tube Q2, thereby affecting the effect of PFC. Since the resistor is connected to pin 3 of the chip, the internal voltage division coefficient is set to 0.0043. Taking the input voltage as 230V as an example, the internal resistance of the pin is _Rvin = 2.5kΩ, and the starting resistor can be selected as:

${\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; v</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 580</span>}\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; \&Omega;</span>}$

Second, choose the BLEEDER resistor. When the chip is started, there will be three half-cycle conduction times, about 30ms, to initialize the state of the dimmer, select the BLEEDER resistor, can provide a fixed maintenance current, and limit the peak value of the input circuit at the same time, according to experience, when the 47Ω resistor is selected, the current is less than 148mA.

Third, design the inductance of the PFC, and the conduction time of the chopper circuit is:

T _on ＝4μs-2.2μs/v×V _{in_a}

T＝12.2μs+8.8μs/v×V _{in_a}

Adjusting the inductance can make the chopper work in continuous current and saturation state. Taking 230V as an example, for a 18-20W LED power supply, the inductance can be selected as 3.2mH, and the power factor can reach more than 90%.

Fourth, design the transformer and select the MOSFET and rectifier. Transformer design can be selected directly according to the data page of iw3614, and the rectifier and MOSFET can be selected according to the data page.

Fifth, in order to improve the anti-electromagnetic interference capability of the system, carry out anti-electromagnetic interference EMI design, in the case of high-power design, I-shaped magnetic core coils can be used, and two-stage LC filter design can be carried out at the same time.

Because the system adopts a two-stage structure, PFC and DC/DC conversion circuit share one control chip, which greatly simplifies the circuit structure, can realize constant current and voltage regulation control of LED, and has a high power factor.

The above content is a detailed description of the present invention in conjunction with the preferred technical solutions. It cannot be determined that the specific implementation of the invention is limited to these. Simple deduction and replacement made without departing from the idea of the present invention should be regarded as protection of the present invention. scope.

Claims (4)

1. A two-stage LED drive power supply with PFC function, characterized in that: it is composed of front and rear two-stage circuits and a control chip, the front stage circuit is a PFC circuit based on BOOST chopper, and the rear stage is quasi-resonant Flyback DC/DC conversion circuit; The control chip controls the on-off of the main switch tube Q2, and the control chip is provided with eight pins, the pin 1 is the system output, which mainly provides the gate drive for the MOSFET switch; the pin 2 is the voltage detection, mainly from The input signal of the auxiliary winding, thus providing secondary voltage feedback output regulation; pin 3 is rectified input voltage detection, used for input undervoltage and overvoltage protection, and this pin provides current for chip startup; pin 4 is external power Limit and shutdown control terminal; pin 5 is the ground terminal; pin 6 is the primary current detection terminal; it is mainly used for cycle peak current detection; pin 7 is the output external MOSFET switch tube drive; pin 8 is the chip power supply terminal . 2. A two-stage LED drive power supply with PFC function according to claim 1, characterized in that the control chip uses the control chip iw3614 as the main control element of the system to control the on-off of the main switch tube. 3. A two-stage LED drive power supply with PFC function according to claim 1, characterized in that it comprises a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor Resistor, seventh resistor, eighth resistor, ninth resistor, first capacitor, second capacitor, third capacitor, fourth capacitor, fifth capacitor, sixth capacitor, first diode, second diode, The third diode, the fourth diode, the first switch tube and the second switch tube, the fourth resistor is connected in series with the fifth resistor, the fourth diode is connected in series with the seventh resistor, and the control chip The pin 8 of the control chip is connected with the fourth diode, the pin 7 of the control chip is connected with the second switch tube through the eighth resistor, and the pin 1 of the control chip is connected with the second resistor, the third resistor and the second resistor respectively. A switch tube is connected, and the first switch tube is connected with the first resistor. 4. A two-stage LED drive power supply with PFC function according to claim 1, characterized in that, said pre-stage circuit includes a PFC correction circuit, a rectification and filtering output circuit, and a A feedback control unit between the circuit and the rectification and filtering output circuit, the PFC correction circuit includes a PFC power correction chip and a flyback output voltage circuit and a PWM boost topology circuit respectively connected to the PFC power correction chip; The excitation output voltage circuit includes a demagnetization time and valley voltage sampling circuit, a flyback input control circuit; the feedback control unit includes an isolated optocoupler feedback circuit, first and second operational amplifier units, and is used to give the isolated An optocoupler feedback unit, an auxiliary power supply circuit powered by the first and second operational amplifier units; a PWM constant current topology unit connected to the feedback control unit.