JP2010226820A - Input current limiting circuit and power unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an input current limiting circuit which can limit an input current properly with a simple configuration, and a power unit using the circuit. <P>SOLUTION: A voltage transducer 1, which converts an input voltage Vin from a power source into a desired output voltage Vout, is a step-up type switching DC/DC converter comprising a semiconductor device 10, an output circuit 20, and a phase compensating circuit 30. The input current limiting circuit 2 limits an input current Iin from the power source of the voltage transducer 1 so that it may not exceed a predetermined upper limit value. It has a current detector 40 which generates a detected voltage Vb whose value fluctuates according to the current value of the input current Iin, and a feedback current generator 50 which generates a feedback current Ifb whose value fluctuates according to the voltage value of the detected voltage Vb, and extracts the feedback current Ifb from the output end of an error amplifier 11 that forms the output feedback loop of the voltage transformer 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an input current limiting circuit and a power supply device using the same.

  When using a power supply whose upper limit of current that can be output is severely limited, such as a USB [Universal Serial Bus] power supply, a voltage converter that converts an input voltage from the power supply into a desired output voltage and supplies it to a load is used. The ability to limit the input current from the power supply so as not to exceed a predetermined upper limit while maintaining high conversion efficiency is required.

  Therefore, the conventional voltage converter suppresses the output current to the load by lowering the output voltage to the load when the input current from the power source increases to the vicinity of a predetermined upper limit value. The input current limiting circuit is configured to limit the input current from the input current so as not to exceed a predetermined upper limit value.

  As an example of the related art related to the input current limiting circuit, Patent Document 1 discloses an RC time constant circuit including a first resistor and a capacitor connected between input terminals, and a base inserted into a main circuit. The first transistor to which the terminal voltage of the capacitor is applied, a second resistor connected in series with the first transistor in the main circuit, and a voltage drop across the second resistor are driven by the first transistor. An input current limiting circuit including a second transistor for controlling the first transistor is disclosed and proposed.

Japanese Utility Model Publication No. 63-135411

  However, there are many standards for power supplies, and the upper limit value of the current that can be output for each standard is various. Therefore, in order to limit the input current appropriately for each of these standards, Dedicated ICs (for example, DC / DC converter ICs dedicated to USB power supplies) have to be prepared, and problems such as increased costs and inadequate response to model changes have occurred.

  In view of the above problems, the present invention provides an input current limiting circuit capable of performing appropriate input current limiting with a simple configuration without requiring a dedicated IC, and a power supply device using the same. With the goal.

  In order to achieve the above object, an input current limiting circuit according to the present invention is applied to a voltage converter that converts an input voltage from a power source into a desired output voltage, and the input current from the power source has a predetermined upper limit value. A current detection unit that generates a detection voltage whose voltage value varies according to the current value of the input current, and feedback whose current value varies according to the voltage value of the detection voltage. A feedback current generation unit that generates current and draws out the feedback current from the output terminal of the error amplifier that forms the output feedback loop of the voltage converter (first configuration). Yes.

  In the input current limiting circuit having the first configuration, the current detection unit generates a switch voltage in which the voltage value varies in a pulse shape according to the current value of the switch current flowing in the output transistor of the voltage converter. It is preferable to have a configuration (second configuration) including a sense resistor that performs smoothing of the switch voltage to generate the detection voltage.

  In the input current limiting circuit having the first or second configuration, the feedback current generator includes a resistor and a detection voltage application circuit that generates the feedback current by applying the detection voltage to one end of the resistor. And (3rd configuration).

  A power supply device according to the present invention includes a semiconductor device in which at least a part of the voltage conversion device is integrated, and an input current limiting circuit including any one of the first to third configurations externally attached to the semiconductor device. And a configuration (fourth configuration).

  With the input current limiting circuit according to the present invention and a power supply device using the same, it is possible to perform appropriate input current limiting with a simple configuration without requiring a dedicated IC.

1 is a circuit diagram showing a configuration example of a power supply device using an input current limiting circuit according to the present invention. Schematic diagram for explaining the input current limiting operation The circuit diagram which shows another structural example of the power supply device using the input current limiting circuit which concerns on this invention

  FIG. 1 is a circuit diagram showing a configuration example of a power supply device using an input current limiting circuit according to the present invention. The power supply device of this configuration example includes a voltage conversion device 1 that converts an input voltage Vin from a power supply (such as a USB power supply) whose upper limit value of current that can be output is strictly limited to a desired output voltage Vout, and a voltage conversion device. And an input current limiting circuit 2 that limits the input current Iin from the power source so as not to exceed a predetermined upper limit value. The voltage conversion device 1 is a step-up switching regulator (step-up chopper regulator) including a semiconductor device 10, an output circuit 20, and a phase compensation circuit 30. The input current limiting circuit 2 includes a current detection unit 40 and a feedback current generation unit 50.

  The semiconductor device 10 includes an error amplifier 11, a controller 12, and a driver 13 as circuit blocks integrated therein, and external terminals T1 to T3 as electrical connection means to the outside. Is a general-purpose DC / DC converter IC.

  The error amplifier 11 has a predetermined reference voltage Vref (a constant voltage for setting a target value of the output voltage Vout) input to the non-inverting input terminal (+) and the inverting input terminal (−) via the external terminal T2. An error voltage Verr is generated by amplifying the difference from the feedback voltage Vfb (divided voltage of the output voltage Vout) input to the output voltage Vr. That is, the voltage level of the error voltage Verr becomes higher as the output voltage Vout is lower than the target set value. Thus, the error amplifier 11 is one of the circuit elements that form the output feedback loop of the voltage conversion device 1.

  The controller 12 generates a pulse width modulation signal S <b> 1 (hereinafter referred to as a PWM [Pulse Width Modulation] signal S <b> 1) so that the error voltage Verr input from the error amplifier 11 becomes small, and supplies this to the driver 13. . More specifically, the controller 12 increases the on-duty of the transistor N1 as the error voltage Verr increases. Conversely, the controller 12 decreases the on-duty of the transistor N1 as the error voltage Verr decreases. The duty control of the PWM signal S1 is performed.

  The driver 13 generates a gate drive signal S2 based on the PWM signal S1 input from the controller 12, and supplies this to the output circuit 20.

  In addition to the circuit blocks described above, other circuit blocks (for example, protection circuit blocks such as a low-input malfunction prevention circuit and a temperature protection circuit) may be appropriately incorporated in the semiconductor device 10.

  The output circuit 20 includes, as elements connected to the outside of the semiconductor device 10, an N-channel MOS [Metal Oxide Semiconductor] field effect transistor N1, a coil L1, a diode D1, a capacitor C1, a resistor R1, and a resistor R2. , Comprising. One end of the coil L1 is connected to the input end of the input voltage Vin. The other end of the coil L1 is connected to the drain of the transistor N1 and the anode of the diode D1. The gate of the transistor N1 is connected to the output terminal of the driver 13 (the output terminal of the gate signal S2) via the external terminal T1 of the semiconductor device 10. The source and back gate of the transistor N1 are connected to the ground terminal via the sense resistor 41 that forms the input current limiting circuit 2. The cathode of the diode D1 is connected to the output terminal of the output voltage Vout. Note that the output terminal of the output voltage Vout is grounded via the capacitor C1. The output terminal of the output voltage Vout is grounded via a resistance voltage dividing circuit including a resistor R1 and a resistor R2. A connection node (output terminal of the feedback voltage Vfb) between the resistor R1 and the resistor R2 is connected to the inverting input terminal (−) of the error amplifier 11 via the external terminal T2 of the semiconductor device 10.

  The phase compensation circuit 30 includes a resistor Rx and a capacitor Cx. One end of the resistor Rx is connected to the output terminal of the error amplifier 11 via the external terminal T3 of the semiconductor device 10. The other end of the resistor Rx is connected to one end of the capacitor Cx. The other end of the capacitor Cx is grounded.

  The current detection unit 40 is a means for generating a detection voltage Vb whose voltage value varies according to the current value of the switch current Isw flowing through the transistor N1 (and hence the current value of the input current Iin). , A resistor 42 and a capacitor 43. One end of the sense resistor 41 is connected to the source of the transistor N1. The other end of the sense resistor 41 is grounded. One end of the resistor 42 is connected to one end of the sense resistor 41. The other end of the resistor 42 is grounded via the capacitor 43, and is also connected to the non-inverting input terminal (+) of the operational amplifier 52 forming the feedback current generating unit 50 as the output terminal of the detection voltage Vb.

  That is, the sense resistor 41 functions as a current / voltage conversion element that generates a switch voltage Va whose voltage value varies in a pulse shape according to the current value of the switch current Isw flowing through the output transistor N1, and the resistor 42 and the capacitor 43 are , And functions as a smoothing circuit that smoothes (integrates) the switch voltage Va to generate the detection voltage Vb. Note that the resistance value of the sense resistor 41 is desirably set to a minute value so as not to impair the conversion efficiency of the voltage conversion device 1.

  The feedback current generation unit 50 generates a feedback current Ifb whose current value varies according to the voltage value of the detection voltage Vb, and returns the feedback current from the output terminal of the error amplifier 11 forming the output feedback loop of the voltage conversion device 1. A means for extracting Ifb, which comprises a resistor 51, an operational amplifier 52, and an npn bipolar transistor 53. As described above, the detection voltage Vb is input from the current detection unit 40 to the non-inverting input terminal (+) of the operational amplifier 52. The inverting input terminal (−) of the operational amplifier 52 is connected to the emitter of the transistor 53. The output terminal of the operational amplifier 52 is connected to the base of the transistor 53. The collector of the transistor 53 is connected to the output terminal of the error amplifier 11 via the external terminal T3 of the semiconductor device 10. The emitter of the transistor 53 is grounded via the resistor 51.

  Note that the operational amplifier 52 sets the conductivity of the transistor 53 so that the detection voltage Vb input to the non-inverting input terminal (+) matches the one-end voltage of the resistor 51 input to the inverting input terminal (−). Control. Therefore, when the resistance value of the resistor 51 is R, the current value of the feedback current Ifb is calculated according to the mathematical formula Vb / R. Thus, in the feedback current generator 50, the operational amplifier 52 and the transistor 53 function as a detection voltage application circuit that generates the feedback current Ifb by applying the detection voltage Vb to one end of the resistor 51.

  Next, the basic operation (DC / DC conversion operation of the voltage conversion device 1) of the power supply device having the above configuration will be described in detail.

  When the transistor N1 is turned on, a switch current Isw directed to the ground terminal flows through the coil L1 via the transistor N1 and the sense resistor 41, and the electrical energy is stored. Note that, when charge is already accumulated in the capacitor C1 during the ON period of the transistor N1, the output current Iout from the capacitor C1 flows through a load (not shown). Further, at this time, the anode potential of the diode D1 is lowered to almost the ground potential via the transistor N1 and the sense resistor 41, so that the diode D1 is in a reverse bias state and current flows from the capacitor C1 toward the transistor N1. There is no.

  On the other hand, when the transistor N1 is turned off, the electric energy accumulated in the coil L1 is released by the counter electromotive voltage generated in the coil L1. At this time, since the diode D1 is in a forward bias state, the current flowing through the diode D1 flows into a load (not shown) and also flows into the ground terminal through the capacitor C1, thereby charging the capacitor C1. By repeating the above operation, a DC output boosted and smoothed by the capacitor C1 is supplied to a load (not shown).

  In this way, the semiconductor device 10 drives the coil L1 that is an energy storage element by on / off control of the transistor N1, thereby boosting the input voltage Vin and generating the output voltage Vout (boost switching). Regulator).

  Next, the input current limiting operation of the power supply device configured as described above will be described in detail with reference to FIG. 2 together with FIG. FIG. 2 is a schematic diagram for explaining the input current limiting operation. 2 represents the output current Iout, and the vertical axis in FIG. 2 represents the output voltage Vout or the input current.

  As described above, the current detection unit 40 receives the switch current Isw flowing through the transistor N1 by the sense resistor 41, generates the pulsed switch voltage Va, and smoothes the switch voltage Isw ( As a result, the detection voltage Vb whose voltage value fluctuates according to the integrated current value of the input current Iin) is generated. Note that the voltage value of the detection voltage Vb increases as the input current Iin increases, and decreases as the input current Iin decreases.

  On the other hand, the feedback current generator 50 applies the detection voltage Vb to one end of the resistor 51 to generate a feedback current Ifb whose current value varies according to the voltage value of the detection voltage Vb. Pull out from the output end. Note that the higher the voltage value of the detection voltage Vb, the larger the current value of the feedback current Ifb drawn from the output terminal of the error amplifier 11. In other words, the current value of the feedback current Ifb drawn from the output terminal of the error amplifier 11 increases as the current value of the input current In increases.

  While the feedback current Ifb is drawn from the output terminal of the error amplifier 11 within the range of the current output capability of the error amplifier 11, the voltage value of the error voltage Verr output from the error amplifier 11 does not vary greatly, and the output voltage Vout is output as usual, and the voltage value is maintained at a predetermined target value.

  On the other hand, when the current value of the input current Iin increases and the current value of the feedback current Ifb drawn from the output terminal of the error amplifier 11 exceeds the current output capability of the error amplifier 11 (for example, 30 μA), it is output from the error amplifier 11. The voltage value of the error voltage Vfb decreases, the on-duty of the transistor N1 based on the PWM signal S1 decreases, and the output voltage Vout starts to decrease. As a result, the output current Iout to the load decreases, and as a result, the input current Iin from the power source decreases.

  When the input current Iin is reduced by such an input current limiting operation, the current value of the feedback current Ifb is also reduced. Therefore, the voltage value of the error voltage Vfb output from the error amplifier 11 is recovered, and the transistor N1 based on the PWM signal S1 is recovered. , The output voltage Vout starts to rise.

  Thereafter, by repeating the same operation as described above, the voltage value of the error voltage Verr output from the error amplifier 11 is limited according to the current value of the input current Iin, and the input current Iin is maintained at a predetermined upper limit value. As a result, the output voltage Vout decreases.

  As described above, in the voltage conversion device 1 to which the input current limiting circuit 2 is applied, when the input current Iin reaches a predetermined upper limit value, the input current Iin can no longer be drawn from the power source, and the input current Iin current Feedback is applied so that the value stabilizes at a predetermined upper limit.

  That is, in the voltage conversion device 1 to which the input current limiting circuit 2 is applied, only a few general-purpose semiconductor devices 10 are provided without preparing a dedicated IC for each power source (for example, a DC / DC converter IC dedicated to a USB power source). By connecting only one external element, the input current limiting characteristics required for various power supply standards can be easily and inexpensively realized, so the design can be simplified when developing a new set. Is possible.

  The upper limit value of the input current Iin corresponds to a current value at which the feedback current Ifb drawn from the output terminal of the error amplifier 11 becomes equal to the current output capability of the error amplifier 11. That is, the upper limit value of the input current Iin can be arbitrarily adjusted by adjusting the resistance value of the resistor 51.

  Further, if the feedback current Ifb is extracted from the output terminal of the error amplifier 11, the external terminal T3 for connecting the existing phase compensation circuit 30 can be used as an external terminal for extracting the feedback current Ifb. Therefore, it is reasonable that the number of pins of the semiconductor device 10 is not increased unnecessarily.

  In the above embodiment, the input current limiting circuit according to the present invention is used as means for limiting the input current Iin of the voltage converter 1 (step-up switching regulator) that boosts the input voltage Vin to generate the output voltage Vout. However, the application target of the input current limiting circuit 2 according to the present invention is not limited to this. For example, a step-up / down regulator (so-called SEPIC [Single-Ended Primary Inductance] shown in FIG. It can be widely applied to other types of voltage conversion devices such as a converter circuit).

  The configuration of the present invention can be variously modified within the scope of the present invention in addition to the above embodiment.

  The present invention is, for example, a technique that can be suitably used as an input current limiting circuit applied to a voltage conversion device that converts an input voltage from a power supply whose upper limit of outputable current is strictly limited to a desired output voltage. It is.

DESCRIPTION OF SYMBOLS 1 Voltage converter 2 Input current limiting circuit 10 Semiconductor device (general-purpose DC / DC converter IC)
DESCRIPTION OF SYMBOLS 11 Error amplifier 12 Controller 13 Driver 20 Output circuit 30 Phase compensation circuit 40 Current detection part 41 Sense resistance 42 Resistance 43 Capacitor 50 Feedback current generation part 51 Resistance 52 Operational amplifier 53 npn type bipolar transistor N1 N channel type MOS field effect transistor (output transistor) )
L1, L2 Coil D1 Diode C1, C2 Capacitor R1, R2 Resistor T1-T3 External terminal Rx Resistor Cx Capacitor

Claims (4)

An input current limiting circuit that is applied to a voltage conversion device that converts an input voltage from a power source into a desired output voltage and limits an input current from the power source so as not to exceed a predetermined upper limit value,
A current detection unit that generates a detection voltage whose voltage value varies according to the current value of the input current;
A feedback current generator that generates a feedback current whose current value varies according to the voltage value of the detection voltage, and draws the feedback current from an output terminal of an error amplifier that forms an output feedback loop of the voltage converter;
An input current limiting circuit comprising:   The current detection unit includes a sense resistor that generates a switch voltage in which a voltage value varies in a pulse shape according to a current value of a switch current that flows through an output transistor of the voltage converter, and the detection voltage by smoothing the switch voltage. The input current limiting circuit according to claim 1, further comprising: a smoothing circuit that generates   2. The feedback current generation unit includes a resistor and a detection voltage application circuit that generates the feedback current by applying the detection voltage to one end of the resistor. 3. The input current limiting circuit according to 2.   A semiconductor device in which at least a part of the voltage conversion device is integrated, and an input current limiting circuit according to any one of claims 1 to 3 externally attached to the semiconductor device. A featured power supply.

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