KR101042220B1 - Soft-Start Circuits and DC-DC Converters and Their Driving Methods - Google Patents

Abstract

The present invention relates to a soft start circuit and a DC-DC converter and a method of driving the same.

The soft start circuit of the DC-DC converter according to the present invention includes a drive signal generator for generating a drive signal of the soft start circuit based on the drive start signal of the DC-DC converter, a stepped signal and a soft start signal based on the drive signal. A reference signal generator for generating a signal, a comparator comparing the stepped signal and the current sense voltage of the inductor of the DC-DC converter, and an inductor control signal for controlling the current flowing through the inductor based on the output signal and the soft start signal of the comparator And an inductor control signal generator.

 DC-DC converters, soft start circuits, stepped signals

Description

Soft start circuit and DC-DC converter and its driving method {Soft Start Circuit and DC-DC Converter and Method

The present invention relates to a soft start circuit and a DC-DC converter and a method of driving the same.

The present invention is derived from a study carried out with the support of the Korea Science Foundation as a source of finance. [Task Management Number: ROA-2007-000-20059-0]

With the development of human-friendly electronic products such as mobile phones, MP3 players and PDAs, a battery that can be used for a long time is required. To meet this need, high efficiency voltage conversion of the battery to the voltage required by the electronics is essential. Therefore, the demand for DC-DC converters is expected to increase further in the future.

In order to ensure the operational stability of the DC-DC converter, it is necessary to prevent excessive initial inductor current from damaging the DC-DC converter. To do this, it is necessary to gradually increase the inductor current step by step at the beginning of the DC-DC converter.

In order to solve this problem, in general, the inductor current is stepped by increasing the input value of the correction amplifier in the DC-DC voltage converter stepwise or increasing the output value of the correction amplifier in the DC-DC voltage converter. There is a way.

First, the method of limiting the input value of the correction amplifier in the DC-DC converter gradually increases the reference voltage from zero by comparing the output voltage and the reference voltage, which are the two inputs of the correction amplifier, at the beginning of operation of the DC-DC converter. . By doing so, the output voltage of the DC-DC converter is gradually compared with the reference voltage from zero to reach the preset voltage, thereby preventing excessive inductor current from flowing initially.

Next, the method of limiting the output value of the correction amplifier in the DC-DC voltage converter includes the voltage of detecting the inductor current, which is the two inputs of the comparator in the DC-DC voltage converter, and the output signal of the correction amplifier at the beginning of operation of the DC-DC voltage converter. To compare. The voltage of the inductor current is limited to the output value of the preset compensation amplifier so that the voltage of the inductor current is gradually increased for a period of time.

Currently, soft start circuits are the most basic and effective technique for preventing the initial transient inductor current of current control mode DC-DC voltage converters. The soft start circuit adjusts the duty ratio of the pulse width modulated signal according to the peak value of the inductor current, so it is easy to adjust the magnitude of the inductor current. Accordingly, the soft start circuit can prevent excessive inductor current from flowing in the initial operation of the DC-DC converter, thereby preventing chip breakage.

1 shows a schematic diagram for explaining a conventional soft start circuit. Referring to FIG. 1, the first switch S1 is closed during the soft start period, which is the initial stage of operation of the DC-DC converter. During this period, the current of the current source 101 charges the capacitor 103 so that the voltage gradually rises. The voltage of the capacitor 103 is compared with the output voltage of the DC-DC converter, which is another input of the correction amplifier 107, so that the output voltage is gradually increased. This prevents excessive current flow through the inductor 105 initially. After the soft start period ends, the first switch S1 is opened and the second switch S2 is closed to start the normal operation of the DC-DC converter.

However, the soft start circuit in FIG. 1 is an external soft start circuit, and since the external soft start circuit requires an external capacitor 103, it does not show efficiency in terms of cost and area. Therefore, there is a need for a method of overcoming an increase in cost and area due to the use of an external capacitor, which has been a disadvantage of an external soft start circuit.

Figure 2 shows a schematic diagram for explaining another conventional soft start circuit. The soft start circuit of FIG. 2 is an internal soft start circuit that improves the disadvantages of the external soft start circuit described in FIG. 1.

Referring to Figure 2, the DC-DC converter has two loops. One is a normal operation loop 201 and the other is a soft start loop 203. In this case, the two loops 201 and 203 operate at the same time instead of separately for each section. That is, the normal operation loop 201 operates from the beginning of the operation of the DC-DC voltage converter, and the current of the inductor 207 is gradually limited through the soft start loop 203. However, this case has a disadvantage in that a compensation capacitor and a compensation resistor are required for both loops 201 and 203. That is, the soft start compensation circuit 205 also requires a compensation capacitor and a compensation resistor, thereby increasing the circuit area and increasing the complexity of the circuit.

Accordingly, the present invention is to solve the above-described problems, in implementing a soft start of the DC-DC voltage converter, by eliminating the external capacitor to satisfy the efficiency of the area and cost while reducing the compensation capacitor and compensation resistor in the soft start loop Elimination aims at increasing the simplicity of the circuit and reducing unnecessary area.

In addition, an object of the present invention is to significantly reduce the size of the soft start circuit by allowing the soft start circuit to operate independently of the DC-DC converter circuit in the soft start section.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The soft start circuit of the DC-DC converter according to an embodiment of the present invention for solving the above problems, the drive signal generator for generating a drive signal of the soft start circuit based on the drive start signal of the DC-DC converter, driving A reference signal generator for generating a stepped signal and a soft start signal based on the signal, a comparator for comparing the current sensed voltage of the stepped signal with the inductor of the DC-DC converter, and an inductor based on the output signal and the soft start signal of the comparator And an inductor control signal generator for generating an inductor control signal for controlling a current flowing in the.

The DC-DC converter according to an embodiment of the present invention includes a drive signal generator for generating a drive signal of a soft start circuit based on a drive start signal of a DC-DC converter, a stepped signal and a soft start signal based on a drive signal. A reference signal generator for generating a signal, a comparator for comparing the current sensed voltage of the stepped signal and the inductor of the DC-DC converter, and a first inductor control for controlling the current flowing through the inductor based on the output signal of the comparator and the soft start signal. A soft start circuit comprising a first inductor control signal generator for generating a signal, and a second inductor control signal generator for generating a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal.

According to an embodiment of the present invention, a method of driving a soft start circuit of a DC-DC converter may include generating a driving signal of the soft start circuit based on a driving start signal of the DC-DC converter, and having a stepped shape based on the driving signal. Generating a signal and a soft start signal, comparing a stepped signal with a current sense voltage of the inductor of the DC-DC converter, and controlling the current flowing through the inductor based on the output signal and the soft start signal of the comparison result. Generating an inductor control signal.

According to an embodiment of the present invention, a method of driving a DC-DC converter may include: generating a driving signal of a soft start circuit based on a driving start signal of a DC-DC converter; a stepped signal and a soft start based on the driving signal; Generating a signal, comparing the stepped signal with the current sense voltage of the inductor of the DC-DC converter, the first inductor control signal for controlling the current flowing through the inductor based on the output signal and the soft start signal of the comparison result Generating a second inductor control signal for controlling a current flowing in the inductor based on a soft start signal.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which: There will be. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

According to the present invention, it is possible to prevent excessive inductor current from flowing during the initial operation of the DC-DC converter while satisfying high area efficiency and circuit simplicity. In addition, the use of external capacitors can be used to achieve area efficiency and cost efficiency.

The following merely illustrates the principles of the invention. Therefore, those skilled in the art, although not explicitly described or illustrated herein, can embody the principles of the present invention and invent various devices that fall within the spirit and scope of the present invention. In addition, all conditional terms and embodiments listed herein are in principle clearly intended to be understood solely for the purpose of understanding the concept of the invention and are not to be limited to the specifically listed embodiments and states. do.

It is also to be understood that the detailed description, as well as the principles, aspects and embodiments of the invention, as well as specific embodiments thereof, are intended to cover structural and functional equivalents thereof. In addition, these equivalents should be understood to include not only equivalents now known, but also equivalents to be developed in the future, that is, all devices invented to perform the same function regardless of structure.

Thus, for example, the block diagrams herein should be understood to represent a conceptual aspect of exemplary circuitry embodying the principles of the invention. Similarly, all flowcharts, state transitions, pseudocodes, and the like are understood to represent various processes performed by a computer or processor, whether or not the computer or processor is substantially illustrated on a computer readable medium and whether the computer or processor is clearly shown. Should be.

The functionality of the various elements shown in the figures, including functional blocks represented by a processor or similar concept, can be provided by the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functionality may be provided by a single dedicated processor, by a single shared processor or by a plurality of individual processors, some of which may be shared.

In addition, the explicit use of terms presented in terms of processor, control, or similar concept should not be interpreted exclusively as a citation of hardware capable of executing software, and without limitation, digital signal processor (DSP) hardware, software for storing It should be understood that it implicitly includes ROM, RAM, and non-volatile memory. Other hardware for the governor may also be included.

In the claims of this specification, components expressed as means for performing the functions described in the detailed description include all types of software including, for example, a combination of circuit elements or firmware / microcode, etc. that perform the functions. It is intended to include all methods of performing the function and are combined with appropriate circuitry for executing the software to perform the function. The invention, as defined by these claims, is equivalent to what is understood from this specification, as any means capable of providing such functionality, as the functionality provided by the various enumerated means are combined, and in any manner required by the claims. It should be understood that.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which: There will be. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention discloses a soft start circuit for gradually increasing the upper limit of the inductor current step by step in order to prevent excessive inductor current from flowing suddenly during the initial operation of the DC-DC converter to damage the entire circuit. The soft start circuit according to the present invention may limit the inductor current of the DC-DC converter to be gradually increased during the soft start period, thereby preventing excessive inductor current from flowing during the initial operation of the DC-DC converter. Here, the DC-DC converter according to the present invention may include a current control mode DC-DC voltage converter.

In addition, the soft start circuit according to the present invention enables the soft start circuit to operate independently of the DC-DC converter circuit in the soft start section, thereby satisfying the efficiency of the area and cost, and excessively during initial operation of the DC-DC converter. The inductor current can be prevented from flowing.

Hereinafter, a soft start circuit, a DC-DC converter, and a driving method thereof according to the present invention will be described in detail.

<Soft start circuit and its driving method>

The soft start circuit according to the present invention is a circuit for soft start of a DC-DC converter, a drive signal generator for generating a drive signal of the soft start circuit based on a drive start signal of the DC-DC converter, and a step based on the drive signal. A reference signal generator for generating type and soft start signals, a comparator for comparing the stepped signal and the current sense voltage of the inductor of the DC-DC converter, and controlling the current flowing through the inductor based on the output signal of the comparator and the soft start signal. And an inductor control signal generator for generating an inductor control signal. Here, the DC-DC converter may include a current control mode DC-DC voltage converter. In addition, the soft start signal may be a signal defining a section in which the soft start is driven.

The soft start circuit according to the present invention is driven independently of the DC-DC converter circuit of the DC-DC converter because it generates the drive signal of the soft start circuit based on the drive start signal of the DC-DC converter. Accordingly, the soft start circuit can be driven while the DC-DC converter is driven.

The drive signal generator may include a rising edge detector for detecting a rising edge of the drive start signal of the DC-DC converter. The driving signal generator may further include an input buffer configured to receive a driving start signal of the DC-DC converter, such that the rising edge detector may detect the rising edge of the output signal of the input buffer.

The rising edge detector detects the rising edge of the driving start signal of the DC-DC converter and outputs the rising edge of the driving start signal of the detected DC-DC converter in a short pulse. In this case, the drive signal of the soft start circuit corresponds to a short pulse.

The input buffer is for making the rising edge of the drive start signal of the DC-DC converter closer to vertical. The output signal of the input buffer is input to the rising edge detector so that the rising edge detector raises the drive start signal of the DC-DC converter. Edges can be detected more easily.

The reference signal generator includes a stair control signal generator for generating a stepped signal and a soft start signal based on the drive signal, and a stepped signal generator for generating a stepped signal based on the step control signal. can do.

The staircase control signal generator may be configured such that the staircase control signal and the soft start signal simultaneously generate rising edges and different timings to generate a plurality of falling edges for generating the stepped signal. The number of steps constituting the stepped signal may be determined according to the number of falling edges. For example, when the driving signal of the soft start circuit is applied to the reference signal generator, the step control signal and the soft start signal may simultaneously generate rising edges to 1, and falling edges may sequentially generate different timings. . Here, 1 and 0 may mean true and false values in a logic circuit or a digital circuit.

As an example of such a configuration, the staircase control signal generator has cascaded N (N is a natural number) T flip-flops and M (N is a natural number and smaller than N) input signals of N T flip-flops. It may include a falling edge detector, M D flip-flop receiving the output signal of the M falling edge detector, and M inverter to invert the output signal of the M D flip-flop.

The stepped signal generator is configured to generate a stepwise incremental signal from a low magnitude signal during a period in which the soft start signal is 1 using the output signal of the stepped control signal generator. As an example of the configuration of the stepped signal generator according to the example of the above-described stepped control signal generator, the stepped signal generator may include a transistor bank unit in which M transistor units in which a first transistor and a second transistor are connected in series, and M transistors in parallel. It may include a resistor connected in series with the second transistor.

The comparator compares the stepped signal with the current sense voltage of the inductor of the DC-DC converter. The comparator compares the current sense voltage of the inductor of the DC-DC converter based on the stepped signal, so that the inductor control signal can be generated so that the current sense voltage of the inductor of the DC-DC converter can be limited according to the stepped signal. Do. For example, when the current sense voltage of the inductor of the DC-DC converter is compared with the stepped signal, when the current sense voltage of the inductor of the DC-DC converter is larger than the magnitude of the stepped signal, the pulse width of the DC-DC converter The modulation signal may be controlled to be OFF.

The inductor control signal generator may be configured with a logic circuit that outputs an output signal of the comparator when the soft start signal is one. Here, 1 and 0 may mean true and false values in the logic circuit or the digital circuit, as described above. As an example of the configuration of the logic circuit, the logic circuit may include first and second inverters for inverting the output signal and the soft start signal of the comparator, and a NOR gate for receiving the output signals of the first and second inverters, respectively. Can be.

As a driving method for driving the above-described soft start circuit, the driving method of the soft start circuit of the DC-DC converter generates a driving signal of the soft start circuit based on the driving start signal of the DC-DC converter, Generating a stepped signal and a soft start signal based on the step; comparing the stepped signal with a current sensed voltage of the inductor of the DC-DC converter; and a current flowing through the inductor based on the output signal and the soft start signal of the comparison result. Generating an inductor control signal for controlling the. Since a detailed description of the method for driving the soft start circuit overlaps with the description of the soft start circuit described above, it will be omitted here.

<DC-DC converter and its driving method>

The DC-DC converter according to the present invention includes a drive signal generator for generating a drive signal of a soft start circuit based on a drive start signal of a DC-DC converter, a reference for generating a stepped signal and a soft start signal based on the drive signal. A signal generator, a comparator for comparing the stepped signal and the current sense voltage of the inductor of the DC-DC converter, and a first inductor control signal for controlling the current flowing through the inductor based on the output signal of the comparator and the soft start signal. A soft start circuit comprising a first inductor control signal generator, and a second inductor control signal generator for generating a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal. Here, since the driving signal generator, the reference signal generator, and the comparator are the same as described in the above-described <soft start circuit>, detailed description thereof will be omitted. Also, since the first inductor control signal generator has the same function as the inductor control signal generator described in the above-described <soft start circuit>, a detailed description thereof will be omitted.

The second inductor control signal generator generates a second inductor control signal for controlling a current flowing through the inductor based on the soft start signal, and is configured as a logic circuit that outputs the first inductor control signal when the soft start signal is 1. Can be. For example, when the soft start signal is 1 (soft start interval), the second inductor control signal generator may input the first inductor control signal, which is an output signal of the soft start circuit, to the controller of the pulse width modulation signal of the DC-DC converter. When the soft start signal is 0 (drive section of the DC-DC converter), the output signal of the DC-DC converter can be input to the controller of the pulse width modulation signal of the DC-DC converter. As an example of the configuration of the logic circuit, the logic circuit includes an AND gate to which an output signal of a comparator in a DC-DC converter for comparing an inverted signal of a soft start signal and an inductor current sense voltage is input, and an output signal of an AND gate. And an OR gate through which the first inductor control signal is input.

As a driving method for driving the above-described DC-DC converter, the driving method of the DC-DC converter generates a driving signal of the soft start circuit based on the driving start signal of the DC-DC converter, and the step based on the driving signal. Generating a signal and a soft start signal, comparing a stepped signal with a current sense voltage of the inductor of the DC-DC converter, and controlling the current flowing through the inductor based on the output signal and the soft start signal of the comparison result. Generating a first inductor control signal, and generating a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal. A detailed description of the driving method of the DC-DC converter overlaps with the description of the DC-DC converter described above, and thus the description thereof will be omitted.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a schematic diagram for explaining a soft start circuit according to the present invention, and FIG. 4 is a timing diagram for explaining the operation of the soft start circuit according to the present invention shown in FIG. It demonstrates with reference to FIG. 3 and FIG.

Referring to FIG. 3, the soft start circuit according to the present invention includes a driving signal generator 301, a reference signal generator 303, a comparator 305, and an inductor control signal generator 307. Here, the soft start signal may be a signal defining a section in which the soft start is driven.

The drive signal generator 301 generates a drive signal of the soft start circuit based on the drive start signal of the DC-DC converter. The driving signal generator 301 may include an input buffer 311 receiving a driving start signal and a rising edge detector 309 detecting a rising edge of an output signal of the input buffer. The input buffer 311 makes the rising edge of the drive start signal closer to vertical. The rising edge detector 309 generates a drive signal of the soft start circuit so that the soft start circuit can be driven only at the rising edge of the drive start signal. The rising edge detector 309 may detect the rising edge of the driving start signal and output a short pulse at the rising edge timing.

Referring to the timing diagram of FIG. 4, when a driving start signal is input to the input buffer 311, the input buffer 311 makes the driving start signal more vertical and outputs a signal. The rising edge detector 309 receives a signal (a) and detects a rising edge, and outputs a signal (b) which is a pulse type signal having a short interval.

Referring to FIG. 3, the reference signal generator 303 generates a stepped signal and a soft start signal based on the driving signal. The reference signal generator 303 may include a step control signal generator 313 and a stepped signal generator 315.

The staircase control signal generator 313 generates a staircase control signal and a soft start signal for generating the stepped signal based on the driving signal. To this end, the staircase control signal generator 313 may be configured such that the staircase control signal and the soft start signal simultaneously generate rising edges and different timings to generate a plurality of falling edges for generating the stepped signal. Here, the staircase control signal generator 313 may receive a clock signal for generating the staircase control signal, and the clock signal of the DC-DC converter may be used. As an example of the configuration of the staircase control signal generator 313, the staircase control signal generator 313 is cascaded N (N is a natural number) T flip-flop, M T receiving the output signal of the N T flip-flop (M is a natural number and smaller than N), and may include M falling edge detectors, M D flip-flops that receive the output signals of M falling edge detectors, and M inverters that invert the output signals of M D flip flops. have. Specific examples thereof will be described later with reference to FIG. 5.

The stepped signal generator 315 generates the stepped signal based on the stepped control signal. The stepped signal generator 315 may receive a predetermined bias voltage for generating the stepped signal. As an example of the configuration of the stepped signal generator 315, the stepped signal generator 315 may include a transistor bank unit in which M transistor units in which a first transistor and a second transistor are connected in series, and M second transistors may be connected. It may include a resistor connected in series. Specific examples thereof will be described later with reference to FIG. 6.

Referring to the timing diagram of FIG. 4, the step control signal generator 313 that receives the (B) signal generates the (C), (D), and (E) soft start signals. Here, (C), (D), and (E) are input to the stepped signal generator 315 to generate the stepped signal, and the stepped signal generator 315 outputs the (bar) signal which is the stepped signal. do.

The comparator 305 compares the stepped signal and the current sense voltage of the inductor of the DC-DC converter. Here, the current sensing voltage of the inductor is converted into a voltage by sensing the current flowing through the inductor. For example, the inductor current sensing voltage may mean a voltage signal whose slope is compensated in the slope compensation circuit by sensing the current flowing in the power PMOS transistor in the current sensing circuit, and the current flowing in the inductor rises according to the switching of the power transistor. It may correspond to the rising part when repeating the fall and fall. If the current sensing voltage of the inductor of the DC-DC converter is greater than the stepped signal, 1 may be output. Whenever the current sense voltage of the inductor exceeds the stepped signal using the output signal of the comparator 305, an OFF signal is generated in the pulse width modulation signal controller to turn off the power PMOS transistor and turn on the power NMOS transistor. The magnitude of the current sense voltage of the inductor can be limited to a stepped signal.

Referring to the timing diagram of FIG. 4, the inductor current sensing voltage is compared based on the (bar) signal, which is a stepped signal.

The inductor control signal generator 307 generates an inductor control signal for controlling the current flowing through the inductor based on the output signal of the comparator 305 and the soft start signal. To this end, the inductor control signal generator 307 may be configured as a logic circuit that outputs the output signal of the comparator 305 when the soft start signal is 1. The logic circuit can be configured by various methods. As an example of the configuration of the logic circuit, the logic circuit includes first and second inverters 317 and 319 for inverting the output signal and the soft start signal of the comparator 305, respectively, and the first and second inverters 317, It may include a NOR gate 321 for receiving the output signal of the 319. The logic value of each logic element according to this example is shown in Table 1 below. Referring to Table 1, when the soft start signal is 1, the output signal of the NOR gate 321 (the output signal of the inductor control signal generator) is the same as the output signal of the comparator 305.

Soft start signal Output signal of comparator Inverted
Soft start signal Inverted
Output signal of comparator Output signal of NOR gate (output signal of inductor control signal generator) 0 0 One One 0 0 One One 0 0 One 0 0 One 0 One One 0 0 One

5 is a view for explaining an embodiment of the staircase control signal generator of the soft start circuit according to the present invention. The staircase control signal generator 313 has cascaded N (N is a natural number) T flip-flops, M (M is a natural number, less than N) falling edge detectors receiving the output signals of N T flip-flops, M D flip-flops receiving the output signals of the M falling edge detectors, and M inverters for inverting the output signals of the M D flip-flops. Referring to FIG. 5, the staircase control signal generator 313 includes six T flip-flops 501 to 506, four falling edge detectors 511 to 514, and four D flip-flops (connected in the form of a cascade). 521 to 524 and four inverters 531 to 534. In the example of FIG. 5, N is 6 and M is 4. The D flip-flop can have four inputs: d, clock, set, and reset. The input set is not used and can always be zero.

The first T flip-flop 501 receives a clock signal and a reset signal. Here, the reset signal is an output signal of the drive signal generator 301. More specifically, it is an output signal of the rising edge detector 309 of the drive signal generator 301. When the output signal of the rising edge detector 309 is input to the first T flip-flop 501, the stair control signal generator 313 is initialized. Here, the T flip-flop is operated as a counter. The output signals of the four T flip-flops 503 to 506 at the rear of the six T flip-flops 501 to 506 are input to the four falling edge detectors 511 to 514, respectively. Here, the four T flip-flops 503 to 506 at the rear end repeat the rising edge and the falling edge, and the four falling edge detectors 511 to 514 detect the first falling edge to form a short pulse of four. It is sent as input to the clocks of D flip-flops 521 to 524. As a result, as shown in the timing diagram of FIG. 4, signals suitable for the falling edge timing are output, such as (C), (D), (E), and soft start signals. Here, since the inputs d of the four D flip-flops 521 to 524 are always inputted with 1, (C), (D), (E), and the soft start signals are the driving start signals of the DC-DC converter again at 0. Keep 0 until the next rising edge that changes to 1. The sections in which (C), (D), (E) and the soft start signal are 1 can be adjusted by adjusting the number N of T flip-flops. In addition, the number of steps of the stepped signal can be adjusted by adjusting the number (M) of the falling edge detector, the D flip-flop, the inverter. The output signals of the four falling edge detectors 511 to 514 are input to the four D flip-flops 521 to 524, respectively, and the output signals of the four D flip flops 521 to 524 are four inverters 531 to 534. Is output via). Here, the output signal of the first to third inverters 531 to 533 is a step control signal input to the stepped signal generator 315, and the output signal of the fourth inverter 534 is a soft start signal.

6 is a view for explaining an embodiment of a stepped signal generator of a soft start circuit according to the present invention. As an example of the configuration of the stepped signal generator 315, the stepped signal generator 315 may include a transistor bank unit in which M transistor units in which a first transistor and a second transistor are connected in series, and M second transistors may be connected. It may include a resistor connected in series. Referring to FIG. 6, M is four. As shown in FIG. 6, the first transistor 601 and the second transistor 602 are connected in series, and four pairs of two transistors thus connected (603 and 604, 605 and 606, 607 and 608) are connected in parallel. Connected. Transistors 602, 604, 606, 608 belonging to the second transistor row of the four transistor pairs 601, 602, 603, 604, 605, 606, 607, and 608 are connected in series with a resistor 609. A bias voltage is applied to the transistors 601, 603, 605, and 607 belonging to the first transistor row of the four transistor pairs, and ground is applied to the transistors belonging to the second transistor row of the four transistor pairs, respectively. , (D) and (e) signals are applied.

7 shows a conceptual diagram of a DC-DC converter with a soft start circuit according to the present invention. Referring to FIG. 7, the DC-DC converter according to the present invention includes a DC-DC conversion loop 740 constituting a loop of a DC-DC conversion circuit and a soft start loop 730 constituting a loop of a soft start circuit. Include. The soft start circuit in the DC-DC converter according to the present invention is configured to be driven independently of the DC-DC converter, so that when the operation of the DC-DC converter starts, the soft start loop 730 for a predetermined time. ) Only works and the DC-DC conversion loop 740 does not work. During this time, the inductor current is gradually increased to prevent excessive inductor current from flowing early in the operation of the DC-DC converter. When the soft start operation ends after a certain time, the soft start loop 730 stops the operation and the DC-DC conversion loop 740 operates to start the normal operation of the DC-DC converter.

The DC-DC converter according to the present invention includes a drive signal generator 701 which generates a drive signal of a soft start circuit based on a drive start signal of a DC-DC converter, and generates a stepped signal and a soft start signal based on the drive signal. The reference signal generator 703, the comparator 705 for comparing the stepped signal and the current sense voltage of the inductor of the DC-DC converter, and the current flowing through the inductor based on the output signal of the comparator 705 and the soft start signal. A soft start circuit 730 including a first inductor control signal generator 707 for generating a first inductor control signal for control, and a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal And a second inductor control signal generator 741 to generate a PSI. Since the soft start circuit 730 has been described in detail with reference to FIGS. 3 to 6, detailed description thereof will be omitted.

The second inductor control signal generator 741 generates a second inductor control signal for controlling the current flowing in the inductor based on the soft start signal. In this way, the current flowing through the inductor may be controlled using the first inductor control signal during the soft start period.

The second inductor control signal generator 741 may be configured as a logic circuit that outputs the first inductor control signal when the soft start signal is 1, and as an example of the configuration of the logic circuit, the logic circuit may be inverting the soft start signal. AND gate 743 to which the output signal of the comparator 747 is input in the DC-DC converter comparing the signal and the inductor current sense voltage, and OR to which the output signal of the AND gate 743 and the first inductor control signal are input. It may include a gate 745. Logical values according to this example are shown in [Table 2]. Referring to Table 2, when the soft start signal is 1, the second inductor control signal generator (the output signal of the OR gate 745) outputs the output signal of the comparator 705 of the soft start circuit and the soft start signal. When the start signal is 0, the output signal of the comparator 747 in the DC-DC converter comparing the inductor current sense voltage is output.

Soft start signal Inverted
Soft star
Signal AND gate output signal First inductor control signal Output signal of OR gate 0 One Comparing the inductor current sense voltage
Output signal of comparator in DC-DC converter 0 Comparing the inductor current sense voltage
Output signal of comparator in DC-DC converter 0 One Comparing the inductor current sense voltage
Output signal of comparator in DC-DC converter 0 Comparing the inductor current sense voltage
Output signal of comparator in DC-DC converter One 0 0 Output signal of comparator of soft start circuit Output signal of comparator of soft start circuit One 0 0 Output signal of comparator of soft start circuit Output signal of comparator of soft start circuit

The method of the present invention as described above may be embodied as a program and stored in a computer-readable recording medium (such as a CD-ROM, a RAM, a ROM, a floppy disk, a hard disk, or a magneto-optical disk). Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

The present invention is used in DC-DC converters and the like.

1 shows a schematic diagram for explaining a conventional soft start circuit.

Figure 2 shows a schematic diagram for explaining another conventional soft start circuit.

Figure 3 shows a schematic diagram for explaining the soft start circuit according to the present invention.

4 is a timing diagram for describing an operation of the soft start circuit according to the present invention shown in FIG. 3.

5 is a view for explaining an embodiment of the staircase control signal generator of the soft start circuit according to the present invention.

6 is a view for explaining an embodiment of a stepped signal generator of a soft start circuit according to the present invention.

7 shows a conceptual diagram of a DC-DC converter with a soft start circuit according to the present invention.

Claims (15)

In the soft start circuit of a DC-DC converter, A drive signal generator for generating a drive signal of the soft start circuit based on a drive start signal of the DC-DC converter; A reference signal generator for generating a stepped signal and a soft start signal based on the drive signal; A comparator comparing the stepped signal with a current sensed voltage of the inductor of the DC-DC converter; And And an inductor control signal generator for generating an inductor control signal for controlling a current flowing in the inductor based on the output signal of the comparator and the soft start signal. The method of claim 1, The soft start signal, A soft start circuit, characterized in that the signal defines a section in which the soft start is driven. The method of claim 1, The drive signal generator, And a rising edge detector for detecting a rising edge of the drive start signal. The method of claim 3, The drive signal generator, An input buffer receiving the driving start signal; The rising edge detector detects a rising edge of an output signal of the input buffer. The method of claim 1, The reference signal generator, A step control signal generator configured to generate the step control signal and the soft start signal for generating the stepped signal based on the driving signal; And And a stepped signal generator for generating the stepped signal based on the stepped control signal. The method of claim 5, The staircase control signal generator, And the step control signal and the soft start signal simultaneously generate rising edges for generating the stepped signal, and generate a plurality of falling edges at different timings. The method of claim 6, The staircase control signal generator, Cascaded N flip-flops, N being a natural number; M falling edge detectors (M being a natural number and less than N) receiving the N T flip-flop output signals; M D flip-flops receiving the output signals of the M falling edge detectors; And And M inverters for inverting output signals of the M D flip-flops. The method of claim 7, wherein The stepped signal generator, A transistor bank unit in which M transistor units in which a first transistor and a second transistor are connected in series are connected in parallel; And And a resistor in series with said M second transistors. The method of claim 1, The inductor control signal generator, And a logic circuit for outputting an output signal of the comparator when the soft start signal is one. 10. The method of claim 9, The logic circuit, First and second inverters for inverting the output signal of the comparator and the soft start signal, respectively; And And a NOR gate configured to receive output signals of the first and second inverters. In a DC-DC converter, A drive signal generator for generating a drive signal of a soft start circuit based on the drive start signal of the DC-DC converter; A reference signal generator for generating a stepped signal and a soft start signal based on the drive signal; A comparator comparing the stepped signal with a current sensed voltage of the inductor of the DC-DC converter; And a first inductor control signal generator for generating a first inductor control signal for controlling a current flowing through the inductor based on the output signal of the comparator and the soft start signal; And And a second inductor control signal generator for generating a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal. The method of claim 11, The second inductor control signal generator, And a logic circuit for outputting the first inductor control signal when the soft start signal is one. The method of claim 12, The logic circuit, An AND gate to which an output signal of a comparator in the DC-DC converter for comparing the inverted signal of the soft start signal and the inductor current sense voltage is input; And And an OR gate to which the output signal of the AND gate and the first inductor control signal are input. In the driving method of the soft start circuit of a DC-DC converter, Generating a drive signal of the soft start circuit based on a drive start signal of the DC-DC converter; Generating a stepped signal and a soft start signal based on the drive signal; Comparing the stepped signal with a current sensed voltage of the inductor of the DC-DC converter; And And generating an inductor control signal for controlling a current flowing in the inductor based on the output signal of the comparison result and the soft start signal. In the driving method of the DC-DC converter, Generating a drive signal of a soft start circuit based on the drive start signal of the DC-DC converter; Generating a stepped signal and a soft start signal based on the drive signal; Comparing the stepped signal with a current sensed voltage of the inductor of the DC-DC converter; Generating a first inductor control signal for controlling a current flowing through the inductor based on the output signal of the comparison result and the soft start signal; And Generating a second inductor control signal for controlling a current flowing in the inductor based on the soft start signal.

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