CN103166434A

CN103166434A - Multi-mode pulse-width modulation (PWM) control circuit

Info

Publication number: CN103166434A
Application number: CN2011104176220A
Authority: CN
Inventors: 杨丰; 李高林; 程玉华
Original assignee: SHANGHAI RESEARCH CENTER OF ENGINEERING AND TECHNOLOGY FOR SOLID-STATE LIGHTING; Shanghai Research Institute of Microelectronics of Peking University
Current assignee: SHANGHAI RESEARCH CENTER OF ENGINEERING AND TECHNOLOGY FOR SOLID-STATE LIGHTING; Shanghai Research Institute of Microelectronics of Peking University
Priority date: 2011-12-14
Filing date: 2011-12-14
Publication date: 2013-06-19

Abstract

The invention discloses a multi-mode pulse-width modulation (PWM) control circuit. Compared with a traditional PWM control circuit, the multi-mode PWM control circuit is characterized in that a multi-channel and multi-voltage PWM comparator is used, and the reference voltage of the PWM comparator is changed according to different feedback voltages of a switch power system. The method is used, the demand that currents which flow through a light emitting diode (LED) are dynamically controlled under different loads can be satisfied, and then, a chip is controlled to work in different modes, and high efficiency in a full load range is achieved. The circuit structure can not only satisfy a multi-mode control demand, but also soft start peak value current control is added, system starting overswing is avoided, and system functions are further completed. Leading edge blanking control is added, and mistake judgment caused by overswing of a voltage detecting end is avoided.

Description

The multi-mode pwm control circuit

Technical field

The present invention relates to integrated circuit fields, field of power electronics, especially LED switch power supply system field.

Background technology

The peak current comparison circuit is that most switch power supply systems are necessary, and along with the current loop control model is occupied an leading position day by day, the peak current comparison circuit is more and more extensive in the application of electronic system.Be accompanied by the continuous lifting that various standards require switch power efficiency, the Switching Power Supply design faces huge challenge.In order to realize system high efficiency rate in full-load range, up-to-date high power switching power supply adopts the multi-mode control program more, utilizes the efficiency advantage of different modulating mode to realize high efficiency in full-load range.Meanwhile, chip design is had higher requirement, the different mode control mode needs different peak currents, and traditional single peak value current control circuit no longer can satisfy new demand.Traditional peak current comparison circuit as shown in Figure 1.Fig. 1 is typical peak current comparison circuit, and wherein, R1, R2 are bleeder circuits.System feedback voltage FB is sampled and delivers to the peak current comparison circuit, advances R1, R2 electric resistance partial pressure, directly delivers to PWM comparator negative terminal.This moment, the negative terminal voltage of PWM comparator was For a desirable comparator, when positive input was identical with the negative input current potential, comparator reversed.Therefore, the power tube source voltage terminal when comparator negative terminal CS sampling rises to

The time, comparator reverses, and output is reversed to high level by low level.This output signal is delivered to power tube drive circuit and is closed power tube, stops to the load transfer energy.Traditional peak current circuit relatively has obvious shortcoming, and its negative input reference voltage is invariable, can only complete the constant peak Current Control, if when being in low load in system, the operating frequency of system can sharply increase, and the switching tube loss will increase, and system effectiveness descends.Can not adapt to people to the new demand of Switching Power Supply.

The present invention namely improves traditional current peak comparator, has namely solved low efficiency problem when hanging down load of bringing due to fixed reference potential, satisfies up-to-date multi-mode demand for control.Multichannel peak current comparison circuit principle as shown in Figure 2.Compare with typical peak current comparison circuit, increasing by three multi-strobe circuit MUX1, MUX2, MUX3 and a comparator C omp, also increased simultaneously another comparator, be used for the restriction to peak current, also comprised a LEB unit, be used for lead-edge-blanking, the false judgment that causes when preventing the overshoot of voltage detecting end.Adopt multichannel mode to solve the weakness of the single reference voltage of conventional peak comparison circuit, satisfied the different operating status requirements and then realized the system high efficiency rate.

Summary of the invention

The present invention has successfully solved the problem relatively of peak current in multi-mode PWM control system, and system is the decrease in efficiency along with the load reduction no longer, satisfies high efficiency requirement in full-load range.In the present invention, relative traditional circuit has increased by three multi-strobe circuits and a comparator, forms three different branch roads.Different branch roads will be sent into PWM comparator negative input to the different reference voltages of system requirements according to feedback voltage, satisfy different working modes to the demand of peak current.

Description of drawings

Fig. 1 is the schematic diagram of traditional peak current comparison circuit;

Fig. 2 is peak current comparison circuit schematic diagram of the present invention;

Fig. 3 is the circuit diagram of LEB of the present invention.

Embodiment

Fig. 2 is peak current comparison circuit of the present invention, wherein, R1, R2 are divider resistances, MUX1, MUX2, MUX3 are multi-strobe circuits, Comp and PWM are comparators, LEB is the lead-edge-blanking circuit, and LEB enters and door with OUT1 and OUT2 respectively through after reverser, and two Output rusults process or doors with door produce the power tube cut-off signals afterwards.

System feedback voltage FB is sampled and delivers to the peak current comparison circuit, through R1, R2 electric resistance partial pressure, directly delivers to the MUX1 end.This moment, this terminal voltage was

When system load is heavier, need peak current to follow the load positive change.The direct reflected load situation of voltage that adopts the electric resistance partial pressure mode to obtain can directly be controlled peak current.The dividing potential drop ratio of resistance is mainly according to the loop gain Demand Design of system.When system load began to drop to a certain degree, system need to switch to frequency modulation(FM) or across under the recurrent pulse pattern, these two kinds of mode of operations all need the constant peak electric current, and the system peak electric current no longer is subject to the feedback voltage impact.Realize that by MUX1 and control signal CTRL1 peak current switches between FB dividing potential drop and fixed reference in circuit.When CTRL1 was high level, multi-strobe circuit MUX1 delivered to PWM comparator negative terminal with the FB voltage division signal, satisfied heavy duty peak working load electric current needs; When CTRL1 was low level, multi-strobe circuit MUX1 delivered to PWM comparator negative terminal with fixed voltage V1, satisfied than underload peak working load electric current needs.

This circuit has also comprised soft start peak current path.In system's soft start-up process, because output voltage is not also set up, FB feedback voltage value is very high.Can not directly control peak current this moment with FB voltage.If with FB voltage control peak current, can't avoid surge, output voltage meeting overshoot, the stability of a system descends.Therefore adopt the soft start SS signal controlling peak current of rising.Only have when the FB voltage drop to a certain extent the time, just recover to adopt FB voltage control peak current.In order to realize above-mentioned functions, circuit adopts CTRL2 signal controlling FB signal and SS signal, when CTRL2 is high electricity, and MUX2 gating FB signal branch peak value reference voltage; But when CTRL2 is low level, MUX2 gating SS signal branch peak value reference voltage.System avoids starting the too high and surge problem that produces of peak current like this.Slow for avoiding starting simultaneously, circuit limitations the SS minimum voltage, SS and voltage V1 compare, and get both higher values.Physical circuit implementation: SS and V1 voltage compare by comparator C omp, and comparator is output as low level before the SS terminal voltage rises to V1, control MUX3 gating V1 branch road reference voltage; Comparator is output as high level after the SS terminal voltage rises to V1, controls MUX3 gating SS branch road reference voltage.Not only realize steady soft start but also avoid toggle speed excessively slow by foregoing circuit.

The electric current that also has a comparator to be used for convection current overpower pipe in the present invention carries out current limliting, and CS signal and fixed voltage V2 are compared, and when CS terminal voltage value reached V2, output OUT2 became high level, thereby made OUT become high level, and power tube is turn-offed.

In current controlled circuit, when switch conduction moment has pulse peak current, this peak current derives from the inductance burr.If this moment, the sample rate current value, can produce erroneous trigger, lead-edge-blanking is used for eliminating this erroneous trigger.After switch conduction, the output of PWM comparator will could be controlled output through a lead-edge-blanking time.So just can prevent false triggering.Through lead-edge-blanking (LEB) time, the PWM comparator could affect output after power MOSFET is opened.Do not occur under other abnormal conditions, in a single day circuit is opened, and just has the output pulse width of a minimum, and this width is exactly lead-edge-blanking (LEB) time.Fig. 3 is the circuit diagram of LEB of the present invention.

Obviously, those skilled in the art can carry out various changes and modification and not break away from the spirit and scope of the present invention the present invention.Like this, if within of the present invention these are revised and modification belongs to the scope of claim of the present invention and equivalent technologies thereof, the present invention also is intended to comprise these changes and modification interior.

Claims

1. New Multi-mode pwm control circuit ,This circuit is sampled from output voltage, changes to determine PWM comparator reference voltage by monitoring load; Control needs switch peak value electric current according to multi-mode and satisfy system's needs; This circuit output signal is sent in power tube drive circuit as the power tube cut-off signals.

2. multi-mode pwm control circuit as claimed in claim 1, it is characterized in that, adopt a comparator, three multi-strobe circuits and a PWM comparator, realized the selection of multichannel reference voltage, satisfy simultaneously the demand of system's startup and steady switch operating state.

3. multi-mode pwm control circuit as claimed in claim 1, is characterized in that, adopts three control signal gating different branch, switches fast reference voltage level, also can adopt other logical operation mode, reaches same purpose.

4. multi-mode pwm control circuit as claimed in claim 1, is characterized in that, it has also comprised the Current-Limiting Comparator of convection current overpower tube current.

5. multi-mode pwm control circuit as claimed in claim 1, is characterized in that, it has also comprised lead-edge-blanking control, the false judgment that causes when preventing the overshoot of voltage detecting end.