CN102570805A - Buck converter - Google Patents

Abstract

The invention relates to a buck converter for converting input voltage into output voltage and providing the output voltage to a load. The buck converter comprises a PWM (pulse-width modulation) controller and a voltage converting circuit, wherein the PWM controller is electrically connected with the voltage converting circuit. The PWM controller comprises a triangular wave power supply. The buck converter further comprises a regulating circuit and a detecting circuit, wherein the regulating circuit is electrically connected with the detecting circuit. The regulating circuit comprises a pull-up power supply connected with the triangular wave power supply. When the detecting circuit detects that the load is changed from a light load into a heavy load, the pull-up power supply is connected with the triangular wave power supply in series by the regulating circuit, so as to increase the PWM signal duty ratio output by the PWM controller.

Description

buck converter

technical field

The invention relates to a buck converter.

Background technique

During the working process of electronic products, they are usually powered by only one main power supply (such as a commonly used 5V power supply). Since various integrated circuits with different functions in electronic products often need to use different operating voltages, it is necessary to set a step-down converter to convert the power supply voltage into other required voltages.

Please refer to Fig. 1, which is a circuit diagram of a known buck converter. The buck converter is used to convert the input voltage V1 into an output voltage V2. The step-down converter includes a pulse-width modulation (Pulse-Width Modulation, PWM) controller 1, a voltage conversion circuit 2 connected to the PWM controller 1, and an output terminal connected to the voltage conversion circuit 2 and the PWM controller. Feedback circuit 3 between input terminals.

The PWM controller 1 includes a triangular wave power supply 4, a comparator 5 and an N-channel Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) Q1. The triangular wave power supply 4 outputs the triangular wave V3 to the non-inverting input terminal of the comparator 5, the output terminal of the feedback circuit 3 is connected to the inverting input terminal of the comparator 5, and the output terminal of the comparator 5 outputs the PWM signal Vp to the gate of Q1 ; The drain of Q1 is connected to the power supply through the resistor R1, and the source is grounded.

The voltage conversion circuit 2 includes an N-channel MOSFET Q2, an N-channel MOSFET Q3, an inductor L1 and a filter capacitor C1. The drain of Q2 is connected to the input voltage V1, the gate is connected to the output terminal of comparator 5, and the source is connected to the drain of Q3; the gate of Q3 is connected to the drain of Q1, and the source is grounded; both ends of the inductor L1 respectively connected to the source of Q2 and the drain of Q3; the other end of the filter capacitor C1 is grounded, and the output voltage V2 is output between the inductor L1 and the filter capacitor C1; the feedback circuit 3 is used to convert the output voltage into feedback The voltage V4 is fed back to the comparator 5 for comparison with the triangular wave V3 to output the PWM signal Vp (as shown in FIG. 2 ). When the output terminal signal of the comparator 5 and the PWM signal Vp are at a high level, Q2 is turned on and Q3 is cut off, the inductance L1 stores electric energy, and the output voltage V2 gradually increases; when the output terminal signal of the comparator 5 and the PWM signal When Vp is at a low level, Q2 is turned off and Q3 is turned on, the inductor L1 releases electric energy, and the output voltage V2 gradually decreases.

In the prior art, the relationship between the average value of the output voltage V2 and the input voltage V1 is: V2/V1=D, where D is the duty cycle of the PWM signal Vp generated by the PWM controller, that is, the positive pulse of the PWM signal Vp The ratio of time to the duty cycle of the PWM signal Vp. Therefore, different output voltages V2 can be generated by adjusting the duty cycle of the PWM signal Vp.

During actual use of the step-down converter, the load connected to it is often switched as required. When the load changes from a light load with a small resistance value to a heavy load with a large resistance value, the output current of the buck converter will decrease, and the output voltage V2 may be pulled down by the heavy load, so that it is much lower than expected value. The above situation may affect the stability of the output voltage V2, and further affect the stability of the whole circuit using the step-down converter.

Contents of the invention

In view of this, it is necessary to provide a step-down converter capable of adjusting the output voltage according to the connected load.

A step-down converter, which is used to convert an input voltage into an output voltage and provide it to a load. The step-down converter includes a pulse width modulation controller, a voltage conversion circuit and a feedback circuit electrically connected in sequence. The pulse width The modulation controller includes a triangular wave power supply and a comparator, the anode of the triangular wave power supply is connected to the non-inverting input terminal of the comparator; the voltage conversion circuit is connected to the input voltage, and outputs an output voltage; the feedback circuit is electrically connected to the pulse A width modulation controller, the feedback circuit generates a feedback voltage according to the output voltage and inputs it to the inverting input terminal of the comparator, and the output terminal of the comparator outputs a pulse width modulation signal, and the output voltage is related to the duty ratio of the pulse width modulation signal proportional to, the buck converter also includes:

The regulating circuit includes a first electronic switch, a second electronic switch and a pull-up power supply. One end of the first electronic switch is connected to the pull-up power supply, and the other end is connected to the negative pole of the triangular wave power supply; one end of the second electronic switch is grounded, and the other end one end connected to the negative pole of the triangular wave power supply; and

A detection circuit electrically connected to the first electronic switch and the second electronic switch, when the detection circuit detects that the current value of the output terminal of the step-down converter is lower than the preset reference current value of the detection circuit , the detection circuit controls the first electronic switch to be turned on, and at the same time, the second electronic switch is turned off, and the triangular wave power supply is connected in series to the pull-up power supply through the first electronic switch to increase the duty cycle of the pulse width modulation signal.

The step-down converter detects the change of the load by setting the detection circuit, and controls the regulation circuit according to the change of the load. When the load changes from a light load to a heavy load, the regulation circuit is now On the basis of a triangular wave power supply, a pull-up power supply is connected in series to increase the minimum potential amplitude of the triangular wave, thereby increasing the duty cycle of the pulse width modulation signal, and finally increasing the output voltage, effectively preventing the output voltage from being overloaded Pulling low will affect the stable operation of the circuit.

Description of drawings

Figure 1 is a simplified circuit diagram of a known buck converter.

Fig. 2 is a PWM signal waveform diagram when the load connected to the step-down converter shown in Fig. 1 is a standard value.

FIG. 3 is a circuit diagram of a buck converter according to a preferred embodiment of the present invention.

Fig. 4 is a PWM signal waveform diagram when the load connected to the step-down converter shown in Fig. 3 is a standard value.

FIG. 5 is a PWM signal waveform diagram when the load connected to the step-down converter shown in FIG. 3 is heavy.

Description of main component symbols

Buck Converter 100

PWM controller 1, 10

Triangular wave power supply 4, 11

Comparator 5, 13

Voltage conversion circuit 2, 20

Feedback circuit 3, 30

Regulating circuit 40

The first electronic switch 41

Second electronic switch 43

D/A Converter 45

Inductance L1

Filter capacitor C1

Detection circuit 50

Power management chip 51

Load 200

N-channel MOSFET Q1, Q2, Q3, Q11, Q43

P-channel MOSFET Q41

Resistors R1, R11

Pull-up resistor R41

Detection resistor R51

Input voltage V1, Vin

Output voltage V2, Vout

Feedback voltage Vf, V4

Triangular wave V3, Vt

Digital output value Vd

Switch signal Vs

PWM signal Vp

Pull-up voltage Vh

Detailed ways

Please refer to FIG. 3 , the step-down converter 100 of the present invention is used to convert the input voltage Vin into a lower output voltage Vout for the load 200 . The buck converter 100 includes a PWM controller 10 , a voltage conversion circuit 20 , a feedback circuit 30 , a regulation circuit 40 and a detection circuit 50 . The voltage conversion circuit 20 is connected to the input voltage Vin, and outputs the converted output voltage Vout; the feedback circuit 30 is electrically connected between the output terminal of the voltage conversion circuit 20 and the PWM controller 10, and according to the output The voltage Vout generates a feedback voltage Vf and inputs it to the PWM controller 10; the PWM controller 10 outputs a PWM signal Vp according to the feedback voltage Vf, and controls the operation of the voltage conversion circuit 20 according to the PWM signal Vp, that is, the output voltage Vout and The duty ratio of the PWM signal Vp is proportional; the detection circuit 50 is electrically connected to the load 200 for detecting the change of the load 200 to control the adjustment circuit 40 to adjust the output of the PWM controller 10, and finally The magnitude of the output voltage Vout is adjusted.

The PWM controller 10 includes a triangular wave power supply 11, a comparator 13 and an N-channel MOSFET Q11. The positive pole of the triangular wave power supply 11 is connected to the positive input terminal of the comparator 13 , and the negative pole is connected to the regulating circuit 40 . The triangular wave power supply 11 outputs the triangular wave Vt to the comparator 13 . The non-inverting input of the comparator 13 is connected to the output of the feedback circuit 30, that is, the feedback voltage Vf output by the feedback circuit 30 is input to the comparator 13 through the inverting input of the comparator 13 for comparison with the triangular wave Vt. , the comparison result is the PWM signal Vp, and the PWM signal Vp is output to the gate of Q11 through the output terminal of the comparator 13 . The source of Q11 is grounded, the drain is connected to a +5V power supply (not shown) through the resistor R11 , and the drain of Q11 is connected to the voltage converting circuit 20 . The PWM signal Vp and the output of Q11 are inverted, that is, when the PWM signal Vp is at a high level, Q11 outputs a low level; when the PWM signal Vp is at a low level, it outputs a high level. Both the PWM signal Vp and the output of the PWM signal Vp are input to the voltage conversion circuit 20 to jointly control the voltage conversion circuit 20 to convert the input voltage Vin into an output voltage Vout.

The regulating circuit 40 includes a first electronic switch 41 , a second electronic switch 43 and a pull-up power supply (not shown). In this preferred implementation manner, the pull-up power supply is a digital/analog (D/A) converter 45 . One end of the first electronic switch 41 is connected to the D/A converter 45 , and the other end is connected to the negative pole of the triangular wave power supply 11 ; one end of the second electronic switch 43 is grounded, and the other end is connected to the negative pole of the triangular wave power supply 11 . Both the first electronic switch 41 and the second electronic switch 43 are electrically connected to the detection circuit 50 . The first electronic switch 41 and the second electronic switch 43 are turned on or off under the control of the detection circuit 50, and the switching states of the first electronic switch 41 and the second electronic switch 43 are opposite, that is, when the first electronic switch When the switch 41 is turned on, the second electronic switch 43 is turned off; when the first electronic switch 41 is turned off, the second electronic switch 43 is turned on. In this way, the negative pole of the triangular wave power supply 11 can be grounded or connected in series with the D/A converter 45 respectively.

In this preferred implementation manner, the first electronic switch 41 is a P-channel MOSFET Q41, and the second electronic switch 43 is an N-channel MOSFET Q43. The gate of Q41 is connected to the power supply providing +5V voltage through the pull-up resistor R41 , the source is connected to the negative pole of the triangular wave power supply 11 , and the drain is connected to the D/A converter 45 . In this preferred embodiment, the output voltage of the D/A converter 45 is adjustable, that is, the D/A converter 45 can output pull-up voltage Vh of different voltage values under the control of the detection circuit 50 . The gate of Q43 is connected to the power supply providing +5V voltage through the pull-up resistor R41 , the source is grounded, and the drain is connected to the negative pole of the triangular wave power supply 11 . It can be understood that the first electronic switch 41 may also be a PNP transistor, and its base, emitter and collector correspond to the gate, source and drain of Q41 respectively. The second electronic switch 43 can also be an NPN transistor, and its base, emitter and collector correspond to the gate, source and drain of Q43 respectively.

In this preferred embodiment, the detection circuit 50 includes a power management chip 51 and a detection resistor R51 electrically connected. The power management chip 51 is electrically connected to the gate of Q41 and the gate of Q43 , and the power management chip 51 is electrically connected to the D/A converter 45 . The detection resistor R51 is connected in series between the voltage conversion circuit 20 and the load 200 , and both ends of the detection resistor R51 are electrically connected to the power management chip 51 . The power management chip 51 pre-stores a reference current value, a plurality of current variation intervals and a plurality of digital output values Vd, and each current variation interval corresponds to a digital output value Vd. The D/A converter is preset with a plurality of pull-up voltages Vh, and each pull-up voltage Vh corresponds to one of the digital output values Vd. When the resistance value of the load 200 changes, the power management chip 51 detects the voltage across the detection resistor R51 to obtain the current value across the detection resistor R51, and compares the current value with the reference current value In comparison, when the current value at both ends of the detection resistor R51 is less than the reference current value, a current difference is obtained, and the power management chip 51 outputs the digital output value Vd to The D/A converter, the D/A converter outputs the pull-up voltage Vh corresponding to the digital output value Vd; at the same time, the power management chip 51 outputs the switching signal Vs to the first electronic switch 41 and the second electronic switch 41. The switch 43 is used to control whether the first electronic switch 41 and the second electronic switch 43 are turned on or off.

Please refer to FIG. 4 . FIG. 4 is a waveform diagram when the load connected to the step-down converter 100 is a standard value, that is, the current flowing through the detection resistor R51 is a reference value. At this time, the power management chip 51 outputs a low-level switching signal Vs to the gates of Q41 and Q43, so that Q41 is turned off, Q43 is turned on, and the negative electrode of the triangular wave power supply 11 is grounded through Q43. At this time, the lowest potential value of the triangular wave Vt is 0V.

Please refer to FIG. 5 , when the load is switched from light load to heavy load, the current flowing through the detection resistor R51 decreases relative to the reference current, and the power management chip 51 detects the voltage across the detection resistor R51 to Obtain the current value at both ends of the detection resistor R51, compare the current value with the reference current value, and obtain a current difference, and the power management chip 51 outputs the corresponding digital value of the current variation range where the current difference is located. The output value Vd is sent to the D/A converter, and the D/A converter outputs a pull-up voltage Vh corresponding to the digital output value Vd. In this preferred embodiment, the pull-up voltage Vh is 0.5V. At the same time, the power management chip 51 outputs a high-level switching signal Vs to the gate of Q41 and the gate of Q43, so that Q41 is turned on, and the Q43 is cut off. The triangular wave power supply 11 and the pull-up provided by the D/A converter 45 The voltage Vh is superimposed in series, so that the lowest potential value of the triangular wave Vt input to the comparator 13 is 0.5V, and after it is compared with the feedback voltage Vf by the comparator 13, the positive pulse time of the output PWM signal Vp is relative to the triangular wave When the lowest potential value of Vt is 0V, it increases, that is, the duty cycle of the PWM signal Vp is increased, thereby increasing the output voltage Vout of the voltage conversion circuit 20, thereby preventing the output voltage Vout from being pulled by a heavy load too low.

It can be understood that the pull-up power supply can also be a voltage source with a single output voltage value. For example, it is a 0.5V power supply. At this time, the power management chip 51 does not need to control the output of the 0.5V power supply. As long as the power management chip 51 controls Q41 to be turned on and Q43 to be turned off, the triangular wave power supply 11 is connected in series with the 0.5V power supply. plus, so that the lowest potential value of the triangular wave Vt input to the comparator 13 is 0.5V.

Compared with the prior art, the step-down converter 100 detects the change of the load by setting the detection circuit 50, and controls the regulation circuit 40 according to the change of the load. When the load changes from light load to When overloaded, the regulating circuit 40 is to connect the pull-up power supply in series on the basis of the existing triangular wave power supply 11 to increase the lowest potential amplitude of the triangular wave Vt, thereby increasing the duty cycle of the PWM signal Vp, and finally increasing the output The size of the voltage Vout effectively prevents the output voltage Vout from being pulled down by heavy loads and affecting the stable operation of the circuit.

Claims (9)

1. step-down controller; Provide to load after being used for converting input voltage to output voltage; Said step-down controller comprises Pwm controller, voltage conversion circuit and the feedback circuit that electrically connects successively; Said Pwm controller comprises triangular wave power supply and comparator, and the positive pole of this triangular wave power supply is connected to the normal phase input end of this comparator; This voltage conversion circuit is connected to input voltage, and the output output voltage; Said feedback circuit is electrically connected to this Pwm controller; Feedback circuit produces the reverse input end that feedback voltage inputs to this comparator according to this output voltage; The output output pulse width modulation signal of this comparator is characterized in that said step-down controller also comprises:

Regulating circuit comprises that first electronic switch, second electronic switch draw power supply on reaching, and this first electronic switch, one end is connected to and draws power supply on this, and the other end is connected to the negative pole of this triangular wave power supply; This second electronic switch, one end ground connection, the other end is connected to the negative pole of this triangular wave power supply; And

Circuit for detecting; Be electrically connected to this first electronic switch and second electronic switch; When the output end current value that detects this step-down controller when this circuit for detecting is lower than the preset reference current value of this circuit for detecting; This this first electronic switch conducting of circuit for detecting control makes this second electronic switch end simultaneously, and this triangular wave power supply is connected serially to through this first electronic switch and draws power supply to increase the duty ratio of this pulse width modulating signal on this.

2. step-down controller as claimed in claim 1; It is characterized in that: said circuit for detecting detecting resistance and power management chip; This detecting resistance string is connected between this voltage conversion circuit and the load; This power management chip is judged the change in current that flows through on this detecting resistance through the change in voltage of detecting these detecting resistance two ends, to control the on off state of first electronic switch and second electronic switch through this power management chip, controls the output of drawing power supply on this simultaneously.

3. step-down controller as claimed in claim 2 is characterized in that: the said reference current value that prestores in this power management chip, a plurality of electric current constant interval and a plurality of digital output value, the corresponding digital output value of each electric current constant interval; Drawing power supply on being somebody's turn to do is D/A converter; Be preset with in the said D/A converter and draw voltage on a plurality of; Draw the corresponding described digital output value of voltage on each, this detects the current value at resistance two ends this power management chip detecting, and this current value is compared with reference current value; When the current value at these detecting resistance two ends during less than this reference current value; Promptly obtain an electric current difference, this power management chip is promptly exported the corresponding digital output value of the electric current constant interval at this electric current difference place to this D/A converter, and this D/A converter is promptly exported and drawn voltage to connect with said triangular wave power supply on this digital output value is corresponding.

4. step-down controller as claimed in claim 1 is characterized in that: drawing power supply on wherein said is the voltage source with single output voltage values.

5. like each described step-down controller of claim 1 to 4, it is characterized in that: said first electronic switch is a P channel metal layer semiconductcor field effect transistor, and said second electronic switch is the metal oxide layer semiconductor field-effect transistor.

6. step-down controller as claimed in claim 5 is characterized in that: the grid of this P channel metal layer semiconductcor field effect transistor is connected to circuit for detecting, and source electrode is connected to the negative pole of this triangular wave power supply, and drain electrode is connected to draws power supply on this; The grid of this N channel metal layer semiconductcor field effect transistor is connected to circuit for detecting, source ground, and drain electrode is connected to the negative pole of this triangular wave power supply.

7. step-down controller as claimed in claim 6 is characterized in that: the grid of this P channel metal layer semiconductcor field effect transistor is connected to power supply through pull-up resistor; The grid of this N channel metal layer semiconductcor field effect transistor is connected to said power supply through said pull-up resistor.

8. like each described step-down controller of claim 1 to 4, it is characterized in that: said first electronic switch is the positive-negative-positive triode, and said second electronic switch is a NPN type triode.

9. step-down controller as claimed in claim 8 is characterized in that: the base stage of this positive-negative-positive triode is connected to circuit for detecting, and emitter is connected to the negative pole of this triangular wave power supply, and collector electrode is connected to and draws power supply on this; The base stage of this NPN type triode is connected to circuit for detecting, grounded emitter, and collector electrode is connected to the negative pole of this triangular wave power supply.

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