TWI480715B - A control apparatus for reducing total current harmonic distortion and output current by primary-side control of power factor corrector in led power driver - Google Patents

Description

LED power drive power factor corrector with primary side feedback to reduce current distortion while controlling output current control device

The invention relates to a power factor corrector structure, which can be used for LED driving, which can have extremely high power and very low current harmonic distortion at low power, especially in the average current mode control in a multiplier circuit. The control method and device for controlling the output current by controlling the power supply to achieve a full-voltage input and having a stable output current to reduce the input current harmonic distortion and controlling the output of the multiplier by the magnitude of the output reflected voltage.

Switched power supplies are often used in the industry because they provide a reliable and stable power supply. For example: financial system operation (ATM), communication network system, medical service system, various household appliances, general computers and liquid crystal equipment, but such power supply will generate harmonic pollution and noise interference, especially the higher output power The impact on other devices is also greater. So the input part of the power supply is a very important part. Since the traditional PFC mainly focuses on the correction of the power factor, as long as the current harmonic distortion caused by the control can meet the requirements of the regulations, LED lighting has become more and more important in energy saving in recent years, and since the regulations have not regulated the LED lighting, Therefore, many current LED power drivers do not pay much attention to the power factor, most of them can reach 0.9~0.95, but there is no requirement for current harmonic distortion. More than 90% of the products in the market have ATHP of more than 25%, even the traditional Requires less than 15% can not be achieved, the main reason is that there are three parts of the cost and power supply architecture and LED power is small, because the traditional LED power driver is mostly controlled by constant current output, because the different input is the city voltage The period of the PWM will be very different, causing the output current to be affected by the continuous wave. Generally, there will be about 5%~10% variation. If the DCM or CRM control mode is adopted, the input and output are The currents in the switching cycle are all triangles, and the relative current ripple is also the largest. Because the DCM/CRM current and large EMI filter capacitors are relatively large, both the power factor and the current harmonics are It will be worse, so for the traditional way to add the LED power under the cost requirement, it is difficult to reduce the interference to the mains and improve the electricity consumption of the mains. It is also difficult to improve the current THD, so it will affect the cost. Low cost THD Good PF value LED POWER DRIVER requirements will be higher and more difficult to design.

In Europe, the United States, Japan and other countries have regulations to limit the harmonics of electronic equipment, such as the IEC 61000-3-2 standard regulations published by the International Electro-technical Commission (IEC). The use of Active Power Factor Correction (PFC) is a solution. PFC converters are actually combined in series with a DC/DC converter. At present, there are two kinds of PFCs commonly used in the industry, one is CRM PFC (CRM is the boundary operation mode), and the other is CCM PFC (CCM is continuous conduction operation mode), although both methods can complete the operation function of PFC. Single-stage design such as FLYBACK or SEPIC is used on the LED power supply driver, but in order to avoid input current distortion, the bandwidth of the secondary side constant current loop is designed to be small. This method will cause the system to have an impact on the LED input current. Current, in general, the LED's withstand current is very low. If you want to speed up the current loop, this will seriously distort the waveform of the input current. So the two can't take care of both. The conventional techniques used in current PFC phase-locked controllers are described below.

Figures 1 and 2 show the critical mode CRM PFC and controller of the prior art, and Fig. 3 shows the current waveform of the reverse-chirping critical mode. It can be clearly understood from the control block diagram that the CRM PFC circuit mainly has two internal feedback loops and an external feedback loop. The inner loop is the current control loop (dashed line on the right). The main control command is determined by the line voltage MULT of the rectified feedforward forward loop, so that the input impedance of the converter can be made resistive. However, because the current waveform of CRM/DCM applied to the reverse sampling is not the input current of the mains, the peak value of the current waveform in Figure 3, when filtered by the EMI filter, produces severe current harmonic distortion, which is Because the peak current is filtered, the average of Figure 3 The value is different from the sine wave. This is the sampling method of the CRM/DCM current loop.

The outer loop is the voltage control loop (the dotted line on the right). It is mainly based on the internal reference command of the IC and the voltage division value INV of the output terminal. The output voltage is adjusted by comparing the results. Since the output voltage contains twice the chopping component of the mains frequency, this chopping voltage is connected back to the input COMP of the multiplier circuit via the error amplifier inside the IC, which will cause the second and third harmonics of the input current to be distorted. Therefore, in order to avoid input current distortion, the conventional method is to design the bandwidth of the voltage loop to be about 1/10 of the line frequency. This method will cause the transient response of the system to load fluctuation to be slow.

The above-mentioned CRM PFC works in a limited manner by its control mode. Therefore, in order to suppress the harmonic distortion of the input current, the speed of the transient response must be sacrificed. This kind of control method is more difficult to apply to LED power supply. The main reason is that LED power supply is mostly under 30W. When the power of application is smaller, the PF value and current harmonic distortion are more difficult to control. Especially LED is mostly used in single stage. Flyback type, because EMI is mainly regulated by EN55015 from 9kHz to 30MHz, the reverse hopping current is large, and usually uses a large EMI capacitor to meet the requirements of the regulations, thus causing the PF value to be worse than ATHD. At the same time, a constant current loop is used on the secondary side. In order to design the bandwidth of the current loop to be small for the PF value and the ATHD, this method will cause the system to have an inrush current to the LED. Generally, the LED has a low withstand current. In order to speed up the current loop, this will seriously distort the waveform of the input current. In addition, by controlling the use of DCM/CRM, the PF value and ATHD and output constant current will be more difficult to process, so the transient response is improved and reduced. Input current harmonics are very difficult without increasing cost.

Therefore, the present invention is directed to the shortcomings of the prior art, and proposes a control device that is simple and reasonable in design, does not affect the stability of the original control method, and effectively improves the above-mentioned deficiency.

The object of the present invention is to provide a power factor corrector for an LED power driver to perform primary side power control using average current mode control, to improve power factor, reduce input current harmonic distortion, reduce input current harmonics, and stabilize LED voltage variation. The nature of the current.

A second object of the present invention is to provide a control method suitable for any architecture (for example, a boost architecture, a flyback architecture, or a SEPIC architecture), which can stabilize the LED current according to the LED voltage without The secondary measurement plus constant voltage and constant current control circuit, the output current is constant at the input of the full voltage range.

In order to achieve the above and other objects, the characteristics of two CCM (Climate Conduction Mode, CCM)/CRM (CRM) PFC control methods commonly used in the industry are improved. The present invention uses an average current mode by an internal multiplier. The input current control of the primary side power is performed. The multiplier has three inputs, and the output of the Imul of the multiplier is controlled by the B input as the voltage feedback, and the input A of the multiplier is the Iac current control command, the multiplier The input C is the Vrms feedforward voltage command. This method has a slow start function and does not need to be added to the slow-up circuit because the voltage at the input C of the initial multiplier that is started is 1.57 times the normal value because this input is in the multiplier. It will multiply by a square, so the output Imul of the multiplier will drop to 40% of normal, so the power will be 40% normal at startup.

Since the PFC is controlled by a dual loop, the current control loop is used to make the input impedance of the converter resistive, and the voltage control loop is mainly used to regulate the output voltage. The PFC of the present invention reduces the input current harmonics in the LED power drive application while changing the output Imul of the multiplier by changing the B input of the multiplier by changing the reflected voltage of the forward voltage of the LED in Fig. 6.

The first aspect of the present invention teaches a control device for a power factor corrector that can operate in a CCM or CRM control mode. The power factor modifier circuit has a voltage loop buffer whose output Connected to a multiplier input B; the multiplier output Imul is connected to the positive terminal of a current loop error amplifier. After the multiplier feed voltage signal is processed via voltage division, its output is connected to the multiplier input C. The multiplier output is connected to the positive input of a comparator; a current detection signal is connected to the negative terminal of the current loop error amplifier via a resistor; the output of the current loop error amplifier is connected to the R input of the flip-flop, the pulse generator The output is connected to the S input of the flip-flop; the final flip-flop output is the switch drive signal of the power factor corrector; it is characterized by the configuration of the external circuit: the voltage buffer is on the voltage loop, and the output is connected to the power factor controller. The input terminal B is used as an average value of the output voltage to control the power.

A second aspect of the present invention teaches a control device for a power factor corrector that utilizes a multiplier to obtain a voltage loop signal having a value connected to a multiplier input B. This point has a maximum clamp limit when the forward voltage of the LED is The normal value is even higher. The voltage loop is the maximum limit. When the LED forward voltage is lower than the normal value, the voltage value of the voltage loop is lower, so the multiplier input B goes low and the multiplier output Imul also goes low. When the other inputs of the multiplier are not changed, the power output of the PFC is determined by the voltage loop value, so the output power is also controlled to stabilize the LED current, and the current will become larger because the LED voltage becomes lower under the primary side power control. problem.

A third aspect of the present invention teaches a control device for a power factor corrector that can be a CCM and CRM and a hybrid control mode controller. The power factor corrector circuit adopts an average current mode, and the fourth sampled current waveform is compared with a multiplier RC filter (the architecture of FIG. 7 is consistent with the mains current) connected to the multiplier Imul at the current feedback input. This power factor corrector circuit is different from the conventional CRM and DCM peak current sampling, so the current harmonic distortion can be reduced to less than 10%.

A fourth aspect of the present invention teaches a control device for a power factor corrector that controls the output of an Imul of a multiplier whose voltage is fed back as a constant value, and the input A of the multiplier is an Iac current control command, multiplication Input C is the Vrms feedforward voltage command. This method has a slow start function and does not need to be added to the slow-up circuit because the voltage of the input C of the multiplier at the initial start is 1.57 times the normal value (5 pictures Vrms) because this input In the multiplier, the square is multiplied, so the output Imul of the multiplier will drop to 40% of normal, so the power will start at 40% of normal, which will limit the starting current of the LED, and there will be no LED current. cut back.

A fifth aspect of the present invention teaches a control device for a power factor corrector that utilizes the output of Imul of the three input relationships of the multiplier (AXB/C ² ), the input A of the multiplier is an Iac current control command, the multiplier The input C is the Vrms feedforward voltage command. This method can change the Imul output value when different input voltage sources are used, and then change the input current so that the input power (VinXIin) is a fixed value, so the output voltage and current can be eliminated. The loop reduces the cost and achieves a stable current output.

The above and other objects and advantages of the present invention will be more fully understood from the description and appended claims appended claims.

In Figure 4, the current peak is the current waveform of Rsense in Figure 7. After an RC low-pass filter, it is the average current in Figure 4. This current waveform signal is connected to one of the current error amplifiers as a feedback signal.

Please refer to FIG. 5, which is a timing diagram of the mains input current when starting according to an embodiment of the present invention. The Vrms in Fig. 5 will reach 1.57 times the normal value before starting. This is because the voltage after Vac via the bridge rectifier 608 starts to be the peak waveform of the full wave, which starts after the mains Vac passes the voltage after the bridge rectifier 608. It becomes a full-wave waveform, and the Vrms in Fig. 5 turns on and drops to the normal value. Therefore, Vrms is used to start the slow start at the start, which is used to limit the starting power and thus limit the starting current of the LED, and avoid the damage of the impact current to the LED.

Please refer to FIG. 6. FIG. 6 is a diagram showing a voltage feedback buffer and a multiplier architecture according to an embodiment of the present invention. The power factor corrector control device utilizes a multiplier, The obtained voltage loop signal is connected to the multiplier input B. This point has the highest clamp limit. When the forward voltage of the LED is normal or even higher, the voltage loop is the maximum limit value, when the LED forward voltage is normal. The value is low, the voltage value of this voltage loop is lower, so the multiplier input B goes low, the multiplier output Imul also goes low, and when the other inputs of the multiplier are not changed, the power output of the PFC is determined by the voltage loop value. Therefore, the output power is also controlled so that the LED current is stabilized, and the problem that the current becomes large due to the lowering of the LED voltage under the primary side power control is not caused.

The circuit architecture of the embodiment of the present invention is shown in FIG. The mode of the present invention is different from the conventional PFC control method for LED driving. The current signal at the input of the current feedback is the RC filtered signal (average of Figure 4). Like the signal waveform of the mains, the current to be controlled by the controller will be consistent with the mains current and thus reduce the current harmonics.

Fig. 8 shows a control method and apparatus of the power factor corrector of the present invention. After the mains V _ac passes through the bridge rectifier 608, the output is connected to the PFC structure circuit 609 (this structure can be a boost converter or a flyback converter or SEPIC). The PFC controller has a voltage buffer 601 whose output is coupled to a multiplier 602; the output of the multiplier 602 is coupled to a current loop error amplifier 603, and the output of the current loop error amplifier 603 is coupled to a R of a flip flop 605 Input; a pulse generator 604 whose output is also connected to the input of the flip-flop 605; a gate 606, the Q output of the flip-flop 605 is connected to an input of the gate 606; and an inverter 607, pulse wave The output of generator 604 is also coupled to the input of inverter 605, the output of inverter 607 is coupled to the other input of AND gate 606, and the output of gate 606 is the body motion signal of the power factor corrector.

The features and spirit of the present invention are more clearly described in the detailed description of the preferred embodiments of the present invention, and are not intended to limit the scope of the invention. On the contrary, the intention is to cover various modifications and equivalent arrangements within the scope of the invention as claimed.

601‧‧‧Voltage buffer

602‧‧‧Multiplier

603‧‧‧ Current loop error amplifier

604‧‧‧ Pulse generator

605‧‧‧Factor

606‧‧‧ and gate

607‧‧‧ reverser

608‧‧‧Bridge rectifier

609‧‧‧PFC structure circuit

Figure 1 is a schematic diagram of a conventional circuit architecture.

Figure 2 is a control block diagram of a critical mode CRM PFC of the prior art.

Figure 3 is a diagram of the critical mode current waveform of the prior art.

Figure 4 is a continuous current waveform in accordance with an embodiment of the present invention.

Figure 5 is a timing diagram of the mains input current at startup in accordance with an embodiment of the present invention.

Figure 6 is a diagram of a voltage feedback buffer and multiplier architecture in accordance with an embodiment of the present invention.

Figure 7 is a circuit diagram of an embodiment of the present invention.

Figure 8 is a diagram of a controller in accordance with an embodiment of the present invention.

601‧‧‧Voltage buffer

602‧‧‧Multiplier

603‧‧‧ Current loop error amplifier

604‧‧‧ Pulse generator

605‧‧‧Factor

606‧‧‧ and gate

607‧‧‧ reverser

608‧‧‧Bridge rectifier

609‧‧‧PFC structure circuit

Claims (1)

A control device for an LED driving power factor corrector, comprising: an LED driving power factor corrector, which is a continuous conduction mode (CCM); the power factor corrector circuit has a voltage buffer, and the output thereof is connected to a multiplier; the output of the multiplier is coupled to a current loop error amplifier, the multiplier output is coupled to a positive input of a comparator; a current sense signal is coupled to the negative input of the comparator; a flip flop, the The output of the current loop error amplifier is connected to the R input of the flip flop; the output of a pulse generator is connected to the S input of the flip flop; the output of the flip flop is a switch drive signal of the power factor corrector; At least: the configuration of the external circuit: a set of voltage buffers is located on the voltage loop, and the output of the voltage buffer is connected to the multiplier input of the power factor controller as an average value of the output voltage as an output current control signal Control the output power to control the output current; a set of RC filters filter the Rsense current detection signal to match the mains current. The current feedback signal is connected to a current loop error amplifier to control the current waveform.