CN110868054B - Soft start device and method for DC-DC converter - Google Patents

Soft start device and method for DC-DC converter Download PDF

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Publication number
CN110868054B
CN110868054B CN201910217978.6A CN201910217978A CN110868054B CN 110868054 B CN110868054 B CN 110868054B CN 201910217978 A CN201910217978 A CN 201910217978A CN 110868054 B CN110868054 B CN 110868054B
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converter
signal
output
output voltage
pwm
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CN110868054A (en
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尹秉勋
金庚焕
梁大成
郑遂暋
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Shenzhen Zhuoyun Semiconductor Co ltd
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Shenzhen Zhuoyun Semiconductor Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • H02M1/0058—Transistor switching losses by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K7/00—Modulating pulses with a continuously-variable modulating signal
    • H03K7/08—Duration or width modulation ; Duty cycle modulation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

The invention relates to a soft start device and a method for a direct current-direct current converter, wherein the method comprises the following steps: supplying a current in a linear charging mode such that an output voltage of the dc-dc converter rises linearly from an initial level; driving and controlling a plurality of the power switching elements connected in parallel in an asynchronous manner at an initial stage of entering a switching mode, thereby increasing an output voltage while preventing an inrush current from occurring; after the asynchronous drive control, the plurality of power switching elements connected in parallel are synchronously driven and controlled, so that the output voltage of the dc-dc converter is rapidly raised to a target level.

Description

Soft start device and method for DC-DC converter
Technical Field
The present invention relates to a power supply device, and more particularly, to a soft start device and method for a dc-dc converter.
Background
A power supply device for stably supplying power in an electronic communication apparatus belongs to the most basic part of a speech system, and as such a power supply device, a switching mode power supply device such as a dc-dc converter is under study.
In the dc-dc converter performing the boosting operation, an excessive inrush current (inrush current) may occur at the time of starting (startup), and in order to prevent such a phenomenon, it is necessary to apply a soft start method.
Typical soft-start systems include a linear charging (linear charging) system in which a limited current is supplied to an output capacitor to boost an output voltage of a dc-dc converter, a switching (switching) system in which an output voltage of a dc-dc converter is boosted by changing a PWM (pulse width modulation) duty ratio, and the like.
In addition, a soft start method has recently appeared in which the above-described linear charging method and switching method are combined to convert the linear charging mode to the switching mode.
However, in a mode conversion section from the linear charging mode to the switching mode, a current flowing through an inductor of the dc-dc converter is instantaneously and sharply increased, so that an excessive inrush current occurs. This transient inrush current can cause degradation of the inductor or damage to the circuit, transient response of the output voltage, and the like.
As a solution to the above problems, there is a soft start device and method for a dc-dc converter proposed and granted by the present inventors (korean patent laid-open No. 10-1642761). The device supplies current in a linear charging mode to linearly increase the output voltage of a DC-DC converter, performs switching operation according to a PWM duty ratio in a switching mode to increase the output voltage to a target level, determines whether to enter the switching mode from the linear charging mode, and controls the PWM duty ratio in the switching mode based on a control signal. In addition, the inventive apparatus generates a control signal having an initial slope in response to the initial slope of the switching mode during the switching mode interval to increase the PWM duty ratio step by step, and controls the PWM duty ratio with reference to the current limit value during the switching mode to limit the current of the dc-dc converter. The phenomenon of instantaneous inrush current when the linear charging mode is converted into the switching mode is effectively prevented through the mode.
However, in order to realize linear control at the time of mode switching, the above-described apparatus generates a control signal (E/a OUT) having an initial slope to gradually increase the PWM duty in response to the slope of the control signal at the initial stage of the switching mode. That is, since there is a slope limit on the control signal (E/a OUT) in the mode transition section, it is difficult to rapidly raise the output voltage to the target level.
[ Prior art documents ]
Patent documents: korean granted patent No. 10-1642761
Disclosure of Invention
The present invention has been made to solve the above problems, and an object of the present invention is to provide a soft start device and method for a dc-dc converter, which can prevent a phenomenon of instantaneous inrush current occurring when switching from a linear charge mode to a switching mode, can realize a stable mode switching, and can rapidly increase an output voltage of the dc-dc converter to a target level.
Another object of the present invention is to provide a soft start device for a dc-dc converter and a method thereof, which can prevent an instantaneous inrush current from occurring without adjusting a slope of a control signal when an inrush current occurs when a linear charging mode is switched to a switching mode.
In order to solve the above-mentioned technical problem, a soft-start device for a dc-dc converter according to an embodiment of the present invention includes:
a gate controller for supplying a current in a linear charging mode to linearly increase an output voltage of the DC-DC converter from an initial level;
a PWM driver performing a switching action according to a PWM duty ratio in a switching mode to raise the output voltage to a target level;
an overcurrent prevention unit that controls the PWM duty based on a current limit value to limit a current of the dc-dc converter during a switching mode; and
a PWM signal generating section for outputting a PWM signal for controlling the PWM duty based on a control signal in a switching mode,
the gate controller compares an input voltage and an output voltage of the dc-dc converter to determine whether to enter a linear charge mode and a switching mode, and generates and outputs a signal for driving and controlling a plurality of power switching elements connected in parallel to an inductor of the dc-dc converter in a synchronous manner after driving and controlling the plurality of power switching elements in an asynchronous manner at an initial stage of the switching mode.
In addition, in the soft start device for the dc-dc converter, the gate controller includes:
a plurality of comparators comparing an input voltage and an output voltage of the dc-dc converter at different paths, respectively, to generate an output selection signal, wherein input detuning amounts of the plurality of comparators are different from each other;
a signal selection output unit that applies one of a second PWM signal input from the PWM driver, the output voltage, and a power switching element driving signal for linearly increasing an output voltage of the dc-dc converter in a linear charging mode to one of the plurality of power switching elements, in accordance with a combination of the output selection signals output from the comparators, respectively,
one of the output selection signals respectively output from the comparators is output as a drive control signal of the PWM driver.
Further, an input misadjustment amount of one of the comparators is adjusted to output a first output selection signal required for logic level conversion when a difference between the output voltage and the input voltage decreases to a predetermined misadjustment amount (offset), and an input misadjustment amount of the other of the comparators is adjusted to output a second output selection signal required for logic level conversion when a difference between the output voltage and the input voltage exceeds the predetermined misadjustment amount.
In addition, the PWM signal generation unit includes:
an error amplifier that generates an error signal required for conversion into a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the dc-dc converter;
and a comparator that generates a PWM signal for controlling a PWM duty based on a signal obtained by adding a current detection signal of the DC-DC converter to a ramp signal and the error signal in a switching mode.
The soft start timer is used for setting a current limiting value of the overcurrent prevention part to determine soft start time, and when a current detection signal fed back by the DC-DC converter reaches the current limiting value, the overcurrent prevention part generates a current limiting signal to control the PWM duty ratio.
In addition, another embodiment of the present invention relates to a soft-start method for a dc-dc converter for controlling driving of a power switching element connected in parallel with an inductor of the dc-dc converter, including the steps of:
supplying a current in a linear charging mode such that an output voltage of the dc-dc converter rises linearly from an initial level;
driving and controlling a plurality of the power switching elements connected in parallel in an asynchronous manner at an initial stage of entering a switching mode, thereby increasing an output voltage while preventing an inrush current from occurring;
after the asynchronous drive control, the plurality of power switching elements connected in parallel are synchronously driven and controlled, so that the output voltage of the dc-dc converter is rapidly raised to a target level.
According to the method, an input voltage and an output voltage of the dc-dc converter are compared at different paths, respectively, to determine whether to enter the linear charging mode and the switching mode, whether to drive in the asynchronous manner, and whether to drive in the synchronous manner, respectively.
According to the above-described aspect, the present invention drives the power switching element in an asynchronous manner at the initial stage of the switching mode from the linear charge mode, can prevent the occurrence of an instantaneous inrush current, and can obtain a stable inductor waveform by negative feedback, and can raise the output voltage of the dc-dc converter to a target level more quickly by adopting the asynchronous manner at the initial stage of the switching mode.
Drawings
Fig. 1 is a schematic structural diagram of a soft start device for a dc-dc converter according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of the gater 12 in fig. 1.
Fig. 3 is a timing chart for explaining the operation of the soft start device for the dc-dc converter according to the embodiment of the present invention.
Fig. 4 is a timing chart for explaining the effect of the soft start device for the dc-dc converter in the embodiment of the present invention.
Detailed Description
Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In describing the present invention, a detailed description of a known function or structure, for example, a specific structure of a dc-dc converter will not be described. The switching mode, which is classified into the asynchronous drive mode and the synchronous drive mode in the following terms, may be defined as a gate control mode.
First, fig. 1 is a schematic structural diagram of a soft start device for a dc-dc converter according to an embodiment of the present invention, and fig. 2 is a schematic structural diagram of a gate controller 12 in fig. 1.
The soft start device for a dc-dc converter according to an embodiment of the present invention uses a linear charge mode and a switching mode together to realize soft start, and uses an asynchronous driving method and a synchronous driving method together in the switching mode, thereby preventing inrush current from occurring at an initial stage of switching of the switching mode and rapidly increasing an output voltage of the dc-dc converter to a target level.
In order to achieve the above-described features, in the soft start device for a dc-dc converter according to the embodiment of the present invention, an inductor L is connected to an input Voltage (VIN), and power semiconductor transistors N1 and P1 as power switching elements are connected in parallel to the inductor L. The power semiconductor transistor may use a MOS (metal-oxide-semiconductor) transistor. The power switching element P1 is connected to an output Voltage (VOUT) terminal of the dc-dc converter, and feedback resistors R1 and R2, an output capacitor C, and a load R3 are connected to one end of the power switching element P1.
The gate of the other power switching element N1 is connected to a PWM driver 11 (described later) that performs a switching operation based on a drive signal (PWM _ N) input in the switching mode.
In addition, gate controller 12 compares an input Voltage (VIN) and an output Voltage (VOUT) of the dc-dc converter to determine whether to enter a linear charging mode in which a current is supplied to linearly increase the output Voltage (VOUT) of the dc-dc converter from an initial level and a switching mode. In addition, the gate controller 12 generates and outputs signals (SEL, PWM _ P) for driving and controlling the power switching elements N1, P1 connected in parallel to the inductor L of the dc-dc converter in an asynchronous manner at the initial stage of the switching mode, and then driving and controlling the power switching elements N1, P1 in a synchronous manner.
Hereinafter, the specific mechanism and operation of the gate 12 will be described in detail with reference to fig. 2.
The gate controller 12 includes:
a plurality of comparators C0, C1 comparing an input Voltage (VIN) and an output Voltage (VOUT) of the dc-dc converter at different paths, respectively, to generate output selection signals S0, S1, input detuning amounts of the plurality of comparators C0, C1 being different from each other;
the signal selection output unit M applies one of a PWM1 signal D2 input from a PWM driver 11 described later, the output Voltage (VOUT) D1, and a power switching element driving signal D0 for linearly increasing the output voltage of the dc-dc converter in the linear charging mode to the power switching element P1 according to a combination of the output selection signals S0 and S1 output from the comparators C0 and C1, respectively, and outputs one of output selection signals S0 and S1 output from the comparators C0 and C1, respectively, as the driving control signal SEL of the PWM driver 11.
As shown in fig. 2, the power switching element driving signal may be a signal that mirrors the high-side SWTR of the boost chopper circuit and the reference current. In the linear charging, when the voltage of the output capacitor C rises, Vds of the high-side SWTR decreases, resulting in a decrease in the current copy value. Therefore, in a section where the output voltage is almost close to the input voltage, the linear charging section is changed to the switching mode.
Further, one of the comparators C0, C1, for example, the comparator C0, is adjusted to output a first output selection signal S0 required for logic level conversion at a time point TD0 when the difference between the output Voltage (VOUT) and the input Voltage (VIN) decreases to a predetermined amount of detuning, as shown in S0 in the signal timing chart of fig. 3, and the other comparator C1 of the comparators outputs a second output selection signal S1 required for logic level conversion at a time point TD1 when the difference between the output Voltage (VOUT) and the input Voltage (VIN) exceeds the predetermined amount of detuning.
When the comparators C0 and C1 having the input detuning amount adjustment value are used, the output selection signals S0 and S1 applied to the signal selection output unit M may have logic levels of "0, 0", "1, 0", "1, 1", respectively, and the logic level "0, 0" may be defined to indicate a linear charging mode, "1, 0" may be defined to indicate an asynchronous operation mode in a switching mode, and "1, 1" may be defined to indicate a synchronous operation mode in the switching mode.
That is, the gate controller 12 generates the PWM _ P signal necessary for controlling the power switching element P1 and the signal SEL necessary for driving the PWM driver 11 based on the input Voltage (VIN) and the output Voltage (VOUT), and controls the switching operation of the power switching elements N1 and P1 in the linear charge mode and the switching mode section by the asynchronous driving method and the synchronous driving method. This gate 12 mirrors the current flowing through the inductor L in the linear charging mode, and charges the output capacitor C with the mirrored current, so that the output Voltage (VOUT) of the converter rises linearly from the initial level almost up to the input Voltage (VIN) level.
As shown in fig. 1, the soft start apparatus for a dc-dc converter according to the embodiment of the present invention further includes a PWM driver 11, where the PWM driver 11 performs a switching operation according to a PWM duty ratio in a switching mode to raise an output Voltage (VOUT) to a target level.
In the switching mode, the PWM driver 11 performs a switching operation of the inductor L power switching elements N1, P1 connected in parallel to the dc-dc converter in a non-synchronous or synchronous driving manner according to the PWM duty ratio, thereby increasing the output Voltage (VOUT). IN the switching section, the PWM duty of the PWM driver 11 is controlled by a PWM signal (PWM _ IN) output from PWM signal generation units 13, 16, and 17, which will be described later.
Also, the soft start apparatus for the dc-dc converter in the embodiment of the present invention further includes an overcurrent preventing part 14, and when the current detection signal (I _ sense) corresponding to the current flowing through the inductor L reaches the current Limit value Limit _ ref, the overcurrent preventing part 14 outputs a current Limit signal (I _ Limit) to control the PWM duty, thereby limiting the current of the inductor L. Overcurrent prevention unit 14 controls the PWM duty based on the current limit value in the switching mode to limit the current flowing through inductor L of the inverter, thereby protecting the circuit. As shown in the drawing, the overcurrent prevention unit 14 may be formed of a comparator.
In addition, the soft start device for the dc-dc converter in the embodiment of the present invention may further include a soft start timer 15. The soft start timer 15 may decide the current amount control time (SS _ T) based on the current Limit value (Limit _ ref) of the overcurrent prevention part 14.
IN addition, the soft-start device for a dc-dc converter according to the embodiment of the present invention further includes PWM signal generating units 13, 16, and 17, and the PWM signal generating units 13, 16, and 17 output a PWM signal (PWM _ IN) required to control the PWM duty based on a control signal (E/a OUT) IN a switching mode.
An error amplifier (E/a)17 constituting the PWM signal generating section is configured to compare the feedback Voltage (VFB) and the reference voltage (Vref) at a point of time when the linear charging mode is deviated, to enter a switching mode, to receive the feedback voltage obtained from the output voltage of the dc-dc converter through the inverting terminal and the reference voltage through the non-inverting terminal, and to generate a control signal (E/a OUT) based on a difference between the two voltages to switch to the switching mode.
The adder 13 adds the current detection signal (i _ sense) fed back from the dc-dc converter and the Ramp signal (Ramp), and inputs the added signal to the comparator 16 through a non-inverting terminal.
The comparator 16 receives a signal obtained by adding a current detection signal (i _ sense) of the dc-dc converter and a Ramp signal (Ramp) and a control signal (E/a OUT) during the switching mode, compares the two signals, and generates a PWM signal (PWM _ IN) to control the PWM duty ratio according to the comparison result.
Hereinafter, the operation of the soft start device for a dc-dc converter having the above-described configuration will be described with reference to fig. 3 and 4.
Fig. 3 is a timing chart for explaining the operation of the soft-start device for the dc-dc converter in the embodiment of the present invention, and fig. 4 is a timing chart for explaining the effect of the soft-start device for the dc-dc converter in the embodiment of the present invention.
First, the gate controller 12 compares the values of the input Voltage (VIN) and the output Voltage (VOUT) to determine whether to enter the linear charging mode and the switching mode. When the outputs of the two comparators C0 and C1 of the gate controller 12, that is, the logic levels of the output selection signals S0 and S1 are "0, 0", the operation mode is set to the linear charging mode, and in the linear charging mode, the signal from the drive signal generator is applied to the power switching element P1 as the PWM _ P signal through the output terminal OUT of the signal selection output unit M, and the output selection signal S0 is applied to the PWM driver 11 as the output selection signal SEL to stop the operation.
In the linear charging mode, the PWM _ P signal and the PWM _ N signal as shown in fig. 3 are applied to the power switching elements N1, P1, respectively, so that the output Voltage (VOUT) rises linearly from the initial level.
That is, in the linear charging mode, when the input Voltage (VIN) is higher than the output Voltage (VOUT), the PWM _ P signal is driven through a current mirror (current mirror) to perform linear charging.
When the output Voltage (VOUT) gradually rises to time TD0 shown in fig. 3 and decreases to a predetermined amount of mismatch from the input Voltage (VIN), the output of the comparator C0 in the gate controller 12, i.e., the output selection signal S0, becomes "1" level, and the switching mode is entered, and in the initial stage of the entry of the switching mode, the output Voltage (VOUT) is applied to the power switching element P1 as a PWM _ P signal via the signal selection output unit M, and the output selection signal S0 of logic "1" level is applied to the PWM driver 11 as the output selection signal SEL.
By the output Voltage (VOUT) being applied to the power switching element P1, the power switching element P1 is in an OFF state, and during a non-operation (OFF DUTY), as shown in fig. 1, driving is performed in a diode manner, and the PWM _ N signal outputted by the normal driving of the PWM driver 11 is applied to the power switching element N1, so that the power switching elements constituting the dc-dc converter are driven in a non-synchronous manner. In the asynchronous drive mode, as shown in fig. 3, the PWM _ N signal is driven in an operating (ON DUTY) D1 mode and a non-operating (OFF DUTY) D1' mode.
For reference, when the power switching elements N1, P1 are driven in a synchronous manner at the beginning of the switching mode from the linear charging mode, the slope of the current (IIND) flowing through the inductor L has a rising slope according to VIN/L in the operating section, and has a falling slope according to (VIN-VOUT)/L in the non-operating section but has a rising slope in a certain section. As a result, an inrush current occurs in the SS2 section as shown in IIND1 of fig. 4.
In contrast, in the present invention, the power switching devices N1 and P1 are driven in a non-synchronous manner at the beginning of the switching mode from the linear charge mode, and as shown in fig. 3, the slope of the current IIND flowing through the inductor L has a rising slope in the operating interval, i.e., S1, according to VIN/L and a falling slope in the non-operating interval, i.e., S7, according to (VIN-VD (diode voltage) -VOUT)/L, thereby preventing an instantaneous inrush current from occurring when the switching devices are driven in a synchronous manner immediately after the linear charge mode.
When the output Voltage (VOUT) further increases after the switching operation in the asynchronous drive mode, the output selection signal S1, which is the output of the comparator C1 in the gate controller 12, is inverted to the "1" level (at time TD1 in fig. 3), and the synchronous drive mode is switched.
In the synchronous drive mode, the PWM1 signal output from the PWM driver 11 is applied to the power switching element P1 as a PWM _ P signal. In the synchronous driving mode, as shown in fig. 3, driving is performed in an active D2 and a non-active D2' manner of the PWM _ P signal and the PWM _ N signal. The current (IIND) flowing through the inductor L has a rising slope according to VIN/L in the S8 section and a falling slope according to (VIN-VOUT)/L in the S9 section, and then the output voltage is generated by a stable PWM driving through negative feedback.
In the current limiting mode in the soft start interval, the PWM duty is increased with the passage of time, and normal control is performed by PWM duty control with negative feedback at a point in time when the feedback voltage and the reference voltage (Vref) exceed the PWM duty.
For reference, when it is designed to make the current Limit value (Limit _ ref) of overcurrent prevention unit 14 lower than the normal operation interval after the soft start to suppress the rapid current supply, the soft start interval in which the PWM duty is normally controlled by negative feedback is set after the switching mode. The current Limit value (Limit _ ref) is determined by the output (SS _ T) of the soft start timer, and after the designed soft start time, the current Limit value (Limit _ ref) is changed to a larger value so as to avoid influencing the current driving capability in the normal operation interval. The current Limit value (Limit _ ref) is preferably set to be lower than the normal operation interval after the soft start to suppress abrupt current supply.
The technical effect of the gate controller 12 of the present invention that executes the above-described operation will be specifically described below with reference to fig. 4.
First, LIMIT _ REF in fig. 4 indicates the above-described current LIMIT value, E/a OUT indicates a control signal, IIND1, IIND2, and IIND3 respectively indicate currents flowing through the inductor L, where IIND1 indicates a waveform diagram of the related art in which only the linear charging mode LCM and the synchronous driving mode Sync (the output voltage at this time is VOUT1) are used, IIND2 indicates a waveform diagram of the related art in which the synchronous driving mode Sync (the output voltage at this time is VOUT2) is used after the PWM duty is increased stepwise in response to a fixed initial slope at the initial stage of the switching mode entry, and IIND3 indicates a current flowing through the inductor L according to the present invention (the output voltage at this time is VOUT 3).
As shown in IIND1 in fig. 4, when the power switching elements are driven in a synchronous manner immediately after the SS1 section indicating the linear charge mode (switching mode section) in the SS2 section, an inrush current occurs.
As can be seen from IIND2, the use of a control signal (E/a OUT) having a constant slope in the initial section of SS2 suppresses the occurrence of an inrush current indicated by IIND1, but has a disadvantage in that it takes a long time for the output voltage VOUT2 to reach the target level.
In contrast, in the current IIND3 flowing through the inductor L by the control of the gate controller 12 of the present invention, the power switching elements N1 and P1 are driven asynchronously in the SS2 interval following the SS1 interval which is the linear charge mode interval, thereby preventing the occurrence of an instantaneous inrush current, and the output voltage VOUT3 is driven at the current-limiting duty ratio to rise to a high voltage in a more block time than VOUT 2. In the SS3 section following the SS2 section, the power switching elements N1 and P1 are driven in a synchronized manner, and thus have stable driving based on negative feedback.
That is, the present invention drives the power switching element in an asynchronous manner at the initial stage of entering the switching mode from the linear charging mode, thereby preventing the instantaneous inrush current, and at the same time, a stable inductor waveform can be obtained based on the negative feedback.
The embodiments described above are merely examples and various modifications and equivalents may be made to the embodiments of the present invention by those skilled in the art. The scope of the invention should be determined with reference to the appended claims.

Claims (6)

1. A soft-start apparatus for a dc-dc converter, comprising:
a gate controller for supplying a current in a linear charging mode to linearly increase an output voltage of the DC-DC converter from an initial level;
a PWM driver for performing a switching operation according to a PWM duty ratio in a switching mode to raise the output voltage to a target level;
an overcurrent prevention unit that controls the PWM duty based on a current limit value to limit a current of the dc-dc converter during a switching mode; and
a PWM signal generating section for outputting a PWM signal for controlling the PWM duty based on a control signal in a switching mode,
the gate controller compares an input voltage and an output voltage of the DC-DC converter to determine whether to enter a linear charging mode and a switching mode, and generates and outputs a signal for driving and controlling a plurality of power switching elements connected in parallel to an inductor of the DC-DC converter in a synchronous manner after driving and controlling the plurality of power switching elements in an asynchronous manner at an initial stage of the switching mode,
the gate controller includes:
a plurality of comparators comparing an input voltage and an output voltage of the dc-dc converter at different paths, respectively, to generate an output selection signal, wherein input detuning amounts of the plurality of comparators are different from each other;
a signal selection output unit that applies one of a second PWM signal input from the PWM driver, the output voltage, and a power switching element driving signal for linearly increasing an output voltage of the dc-dc converter in a linear charging mode to one of the plurality of power switching elements, in accordance with a combination of the output selection signals output from the comparators, respectively,
one of the output selection signals respectively output from the comparators is output as a drive control signal of the PWM driver.
2. The soft-start apparatus for a DC-DC converter according to claim 1,
an input misadjustment amount of one of the plurality of comparators is adjusted to output a first output selection signal required for logic level conversion when a difference between the output voltage and the input voltage decreases to a prescribed misadjustment amount, and an input misadjustment amount of another one of the plurality of comparators is adjusted to output a second output selection signal required for logic level conversion when a difference between the output voltage and the input voltage exceeds the prescribed misadjustment amount.
3. The soft-start apparatus for a DC-DC converter according to claim 1,
the PWM signal generation section includes:
an error amplifier that generates an error signal required for conversion into a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the dc-dc converter;
and a comparator that generates a PWM signal for controlling a PWM duty based on a signal obtained by adding a current detection signal of the DC-DC converter to a ramp signal and the error signal in a switching mode.
4. The soft-start apparatus for a DC-DC converter according to claim 1,
further comprising a soft start timer that sets a current limit value of the overcurrent prevention section to thereby determine a soft start time,
the overcurrent prevention part generates a current limit signal to control the PWM duty when a current detection signal fed back from the dc-dc converter reaches a current limit value.
5. A soft start method for a dc-dc converter having an inductor with a power switching element connected in parallel thereto, comprising the steps of:
supplying a current in a linear charging mode such that an output voltage of the dc-dc converter rises linearly from an initial level;
driving and controlling a plurality of the power switching elements connected in parallel in an asynchronous manner at an initial stage of entering a switching mode, thereby increasing an output voltage while preventing an inrush current from occurring; and
driving and controlling a plurality of the power switching elements connected in parallel in a synchronous manner after the asynchronous manner driving control, thereby rapidly raising an output voltage of the dc-dc converter to a target level,
wherein an input voltage and an output voltage of the DC-DC converter are respectively compared at different paths by a plurality of comparators having input detuning amounts different from each other to generate an output selection signal,
applying one of a second PWM signal input from a PWM driver, the output voltage, and a power switching element driving signal for linearly increasing an output voltage of a DC-DC converter in a linear charging mode to one of the plurality of power switching elements according to a combination of the output selection signals respectively output from the comparators,
one of the output selection signals respectively output from the comparators is output as a drive control signal of the PWM driver.
6. The soft-start method for a DC-DC converter according to claim 5,
in the switching mode, at a point in time when the output voltage of the dc-dc converter is higher than the input voltage, switching is made to the synchronous mode driving.
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