CN100592611C - Pulse width modulation controller applied to switching type voltage stabilizer - Google Patents

Abstract

The invention discloses a pulse width modulation controller applied to a switching type voltage stabilizer, which comprises an error amplifier, a soft start control circuit, a compensation load and a comparator. The error amplifier receives a reference voltage and a feedback voltage and outputs an error current signal according to the reference voltage and the feedback voltage; the soft start control circuit outputs a compensation current signal according to at least one soft start control signal; the compensating load receives the error current signal and the compensating current signal and outputs a compensating signal; the comparator receives a slope signal and the compensation signal and outputs a pulse width modulation signal; the error amplifier compensates according to the preset soft start compensation current when the power supply voltage rises, and slowly charges the common ground VSS of the circuit, so that the error signal is slowly increased until the soft start control period is finished, and the soft start function when the power supply voltage rises is realized.

Description

A Pulse Width Modulation Controller Applied to Switching Regulator

technical field

The invention relates to a soft start pulse width modulation controller, in particular to a pulse width modulation controller applied to a switching voltage stabilizer.

Background technique

When the initial power supply voltage VDD of the switching regulator rises, because the gain of the error amplifier is too high, the pulse width modulation output has the largest duty cycle (Duty cycle) at the beginning, and the output terminal of the power conversion module is quickly charged by the input power supply , The power conversion system will be damaged by overvoltage and overcurrent, so it is necessary to use the soft start method to protect the power conversion system.

FIG. 1 is a circuit diagram of an existing pulse width modulation controller using a resistor 121 , a capacitor 122 , and Zener diodes 123 and 124 to realize soft start. In this circuit 10, when the power supply voltage VDD is about to rise, the circuit 10 uses the capacitor 122 and the Zener diode 124 to output the error signal ERR from the error amplifier 11 and discharge it to the circuit common ground VSS; and when the power supply voltage VDD rises, the reference voltage REF passes through The resistor 121 begins to charge to the capacitor 122, and the charging time constant is: τ=R1*C1; when the capacitor 122 is fully charged, the Zener diode 124 will be reverse-biased, so that the output of the comparator 13 is isolated from the soft-start circuit 12, No longer affected by the soft start circuit 12, the purpose of soft start of the converter is achieved. Due to the need for a larger charging time constant, a larger value of the resistor 121 and the value of the capacitor 122 is required. Therefore, the capacitor 122 is generally connected externally in existing applications to save chip area, but this also increases external components and packaging. Number of pins.

FIG. 2 is another conventional circuit diagram using a resistor 221 , a capacitor 222 , and an input buffer 223 to realize soft start. The circuit 20 utilizes the characteristic that the resistor 221 and the capacitor 222 are charged by the power supply voltage VDD, and its charging time constant is: τ=R2*C2, so that the voltage VC across the capacitor 222 increases with the rise of the power supply voltage VDD. And the input voltage REF2 of the positive terminal of the error amplifier 21 is referred to the voltage VC of the capacitor 222 when the power supply voltage VDD rises, so that the comparison reference potential for suppressing the input voltage FB2 of the negative terminal of the error amplifier 21 is the voltage VC at both ends of the capacitor 222; when the capacitor 222 is fully charged, That is, the input voltage REF2 of the positive terminal of the error amplifier 21 is no longer affected, so that the output of the comparator 23 is isolated from the soft-start circuit 22 and is no longer affected by the soft-start circuit 22, thereby achieving the purpose of soft-starting the converter. Similarly, due to the need for a larger charging time constant, a larger value of the resistor 221 and capacitor 222 is required. Generally, the capacitor 222 is externally connected in existing applications to save chip area, but this also increases external components. and the number of package pins.

Contents of the invention

In view of the above problems, the purpose of the present invention is to propose a soft start method, which utilizes the control of the output terminal of the error amplifier to realize the function of soft start while achieving the purpose of small area and high integration.

To achieve the above object, the present invention provides a pulse width modulation controller applied to a switching regulator, which includes an error amplifier, a soft-start control circuit, a compensation load and a comparator. Wherein, the error amplifier receives a reference voltage and a feedback voltage, and outputs an error current signal accordingly. The soft start control circuit outputs a compensation current signal according to at least one soft start control signal. The compensation load receives the error current signal and the compensation current signal and outputs a compensation signal. The comparator receives a slope signal and the compensation signal, and outputs a pulse width modulation signal.

In this way, the error amplifier, when the power supply voltage VDD rises, compensates according to the preset soft-start compensation current, and slowly charges the circuit common ground VSS, so that the error signal slowly increases until the soft-start control cycle ends, so as to realize the rise of the power supply voltage VDD when the soft start function.

Description of drawings

FIG. 1 is a circuit diagram of an existing soft start using resistors, capacitors, and Zener diodes.

FIG. 2 is another conventional circuit diagram for implementing soft start by using resistors, capacitors, and input buffers.

FIG. 3 is a schematic circuit diagram of a pulse width modulation controller applied to a switching voltage regulator according to the present invention.

FIG. 4 is a schematic circuit diagram of an embodiment of the error amplifier in FIG. 3 .

FIG. 5 is a schematic circuit diagram of an embodiment of the soft-start control circuit in FIG. 3 .

FIG. 6 is a detailed circuit schematic diagram of the soft start mode applied to the switching regulator according to the present invention.

Figure 7 (1) and (2) are schematic diagrams of the voltage and current waveforms of the switching regulator without soft-start protection respectively.

Fig. 8 (1) and (2) are schematic diagrams of the voltage and current waveforms of the soft start method applied to the switching regulator according to the present invention, respectively.

in:

10, 20, 30...Applied to the soft start mode of switching regulator; 11, 21, 31...Error amplifier; 12, 22, 32...Soft start control circuit; 13, 23, 33. ..Comparator; 121...resistor; 122...capacitor; 123, 124...zener diode; 221...; resistor; 222...capacitor; 223...input buffer; 2231, 2232...bias current; 2233, 2234, 2235...transistor; 34...compensation load; 41...transconductance amplifier; 410, 411, 412, 413, 414, 415, 416, 417, 418 ...transistor; 419...resistor; 420...reference current source; 50, 51, 52, 53, 54, 55, 56, 57, 58...transistor; 59...reference current source

Detailed ways

In order to make the above-mentioned and other objects, features and advantages of the present invention more comprehensible, the preferred embodiments of the present invention will be specifically cited below, together with the accompanying drawings, for detailed description as follows:

The invention adopts the transconductance amplifier as the error amplifier, and controls the output current of the transconductance amplifier at the beginning of the start-up of the switching voltage regulator so that the output current rises slowly, and then slowly charges the compensation load. In this way, the duty cycle of the PWM output signal of the PWM comparator can be increased flexibly, so as to prevent the switching regulator from outputting overvoltage and overcurrent at the beginning of start-up and damaging the switching power components.

The following describes in detail the soft start method of the present invention applied to the switching regulator with reference to the figures.

FIG. 3 is a schematic circuit diagram of a pulse width modulation (PWM, Pulse Width Modulated) controller applied to a switching voltage regulator according to the present invention. As shown in the figure, the soft start method 30 uses an error amplifier 31 to compare the reference voltage REF and the output feedback signal FB of the switching regulator to generate an error signal ERR, wherein the error amplifier 31 is a transconductance amplifier. At the same time, the soft-start control circuit 32 is used to control the output current of the error amplifier 31 to slowly charge the compensation load 34 . Wherein, the compensating load 34 can be realized by the existing resistor 341 connected in series with the capacitor 342 , so that the error signal ERR output by the error amplifier 31 increases slowly. At the same time, a comparator 33 is used to compare the error signal ERR and a ramp signal RAMP to generate a pulse width modulation signal PWM for regulating and controlling the switching regulator. The comparator 33 can be realized by using an existing operational amplifier. Since the error signal ERR is controlled to rise slowly, the pulse width modulation signal PWM output by the comparator 33 has the characteristic of slow opening of the duty cycle, so as to achieve the purpose of soft start.

FIG. 4 is a schematic circuit diagram of an embodiment of the error amplifier 31 in FIG. 3 . A transconductance differential amplifier unit includes transistors 411 and 412 forming a differential amplifier pair and a resistor 419 forming a transconductance source. The reference current source 420, and the transistors 410, 415, 416, 418 constitute a bias current source; the transistors 413, 414 constitute an active load. Among them, the transistor 413 is used to transmit the differential current generated by the differential amplifier pair (transistors 411, 412) through the resistor 419 after comparing the reference voltage REF and the voltage regulator output feedback signal FB, and the transistor 414 is a symmetrical load for To achieve differential amplification symmetry; the transistor 417 and the above-mentioned transistor 413 form a current mirror for current output, and the output current value of the error amplifier 31 is determined according to the bias current source of the transistor 418 .

FIG. 5 is a schematic circuit diagram of an embodiment of the soft-start control circuit 32 of FIG. 3 . The soft-start control circuit 32 uses the reference current source 59 and the transistor 58 to form an input bias current source. Transistors 50, 51, 52, and 53 form bias current sources for four-bit regulation output, each having different regulation capabilities. For example, the transconductances of transistors 50, 51, 52, and 53 are gm=1, gm=2, and gm respectively. =4, gm=8. Transistors 54 , 55 , 56 , and 57 form output current control switches, which are controlled by digital control signals C0 , C1 , C2 , and C3 to control the value of the output current IOUT. The minimum output current IOUT is when transistors 54, 55, 56, and 57 are all off, and there is no output current; the maximum output current IOUT is when transistors 54, 55, 56, and 57 are all on, and the maximum current is the current of transistors 50, 51, 52, and 53 Sum. Digital control signals C0, C1, C2, and C3 control transistors 54, 55, 56, and 57 to be turned on at the beginning of the soft-start control period, and then adjust the turn-on and cut-off of transistors 54, 55, 56, and 57 over time , so as to control the output current IOUT so that it decreases with time, and at the end of the predetermined soft-start control cycle, the transistors 54, 55, 56, and 57 are all turned off so that the output current IOUT is zero.

FIG. 6 is a detailed circuit schematic diagram of the soft start mode applied to the switching regulator according to the present invention. In this embodiment, the soft-start control circuit 32 uses the output current value of the error amplifier 31 as the reference current source 59 . When the power supply voltage VDD rises, the switching regulator outputs a feedback signal FB lower than the reference voltage REF, and the error amplifier 31 outputs an error current to charge the compensation load 34 . At the same time, the soft-start control cycle is turned on, so that the soft-start control circuit 32 discharges the compensation load 34 and fully compensates the error current output by the error amplifier 31, so that the voltage of the output error signal ERR to the circuit common ground VSS is controlled to rise slowly from 0 . The comparator 33 compares the above-mentioned error signal ERR and a ramp signal RAMP to generate a pulse width modulation signal PWM whose duty cycle is slowly turned on, so as to achieve the purpose of soft start. When the soft-start control cycle ends, the soft-start control circuit 32 no longer compensates the output error current of the error amplifier 31, so that the output error signal ERR is properly modulated according to the load condition output by the switching regulator to achieve soft-start and switching regulator. purpose of isolation from normal operation of the transformer.

Figure 7 (1) and (2) are schematic diagrams of the voltage and current waveforms of the switching regulator without soft-start protection respectively. It can be clearly seen from the diagram that if the switching regulator does not have soft-start protection, it will output excessive voltage and current instantaneously when the circuit starts up, and the power conversion system will be damaged by over-voltage and over-current.

Fig. 8 (1) and (2) are schematic diagrams of the voltage and current waveforms of the soft start method applied to the switching regulator according to the present invention, respectively. It can be seen from the figure that after the soft start protection, the duty cycle of the pulse width modulation output gradually increases after the start, so that the output voltage and output current have the characteristics of soft start, and the purpose of overvoltage and overcurrent protection for the power conversion system is achieved. .

Claims (6)

1. A pulse width modulation controller applied to a switching voltage regulator, characterized in that it comprises: an error amplifier, receiving a reference voltage and a feedback voltage, and outputting an error current signal accordingly; A soft start control circuit, outputting a compensation current signal according to at least one soft start control signal; a compensation load, receiving the error current signal and the compensation current signal and outputting a compensation signal accordingly; and a comparator, receiving a ramp signal and the compensation signal, and outputting a pulse width modulation signal, Wherein the soft-start control circuit includes at least one bias current source, and the bias current source generates a corresponding bias current according to the error current signal, The soft-start control circuit further includes at least one control switch corresponding to each of the at least one bias current source, and the control switch controls the output of the bias current according to the at least one soft-start control signal, The sum of the output bias currents forms the compensation current signal. 2. The pulse width modulation controller according to claim 1, wherein said compensating load comprises a resistor. 3. The pulse width modulation controller according to claim 2, wherein said error amplifier is a transconductance amplifier. 4. The pulse width modulation controller according to claim 3, wherein the error amplifier comprises: a reference current source generating a reference current; and A transconductance differential amplification unit generates the error current signal according to the reference voltage and the feedback voltage, and based on the reference current. 5. The pulse width modulation controller according to claim 1, wherein the soft start control circuit outputs the maximum value of the compensation current signal at the beginning of a predetermined soft start control period. 6. The pulse width modulation controller according to claim 1, wherein the soft start control circuit outputs the minimum value of the compensation current signal at the end of a predetermined soft start control period.

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