JP2010226821A - Output current limiting circuit and power unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an output current limiting circuit which applies to a voltage transducer which converts an input voltage into a desired output voltage for supply to the load, and limits an output current to a load so that it may not exceed a predetermined upper limit value. <P>SOLUTION: Provided are a current detector Rs which generates a detected voltage Va whose value fluctuates according to the value of an output current Iout, a switch P1 which is inserted onto a current path from a voltage transducer 1 to a load Z, and a switch control unit which turns on a switch P1 when determined that the output voltage Iout does not reach a predetermined upper limit value based on the detected voltage Va, and turns off the switch P1 when determined that the output current Iout has reached the predetermined upper limit value. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

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

  In order to enhance not only high conversion efficiency but also device safety, power supply devices that operate with power supplied from a USB [Universal Serial Bus] power supply or a power supply device for a mobile phone are excessive. There is a need for a drooping overcurrent protection function capable of setting a current protection value with high accuracy and flexibility.

  As an example of the related art related to the above, Patent Document 1 can be cited.

JP 2002-169618 A

  However, the overcurrent protection function provided in a general DC / DC converter IC is not highly accurate, and the overcurrent protection value is fixed and the protection characteristic (overcurrent protection curve) is also 6 is not a drooping type but a foldback type (operation stop type that shuts down the operation of the IC when an overcurrent is detected) as shown in FIG. 6, and thus is not necessarily suitable for a charger of a mobile phone.

  In particular, many of the conventional power supply devices generate a detection voltage corresponding to an output current using an on-resistance of an output transistor built in the semiconductor device, and a predetermined threshold voltage generated inside the semiconductor device. Thus, overcurrent detection is performed, and variations in the on-resistance of the output transistor have a great influence on the accuracy of the overcurrent protection function. Therefore, in order to make the conventional overcurrent protection function highly accurate, it is necessary to correct the on-resistance variation of the output transistor to each individual by integrating a laser trimming resistance element in the semiconductor device.

  As described above, the conventional power supply apparatus has various problems to be solved when applied to a charger for a mobile phone. In order to solve these problems one by one, a dedicated IC (for each application) ( For example, it is necessary to prepare a DC / DC converter IC dedicated to a USB power supply or a DC / DC converter IC dedicated to a charger for a mobile phone. It was.

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

  In order to achieve the above object, an output current limiting circuit according to the present invention is applied to a voltage converter that converts an input voltage into a desired output voltage and supplies the output voltage to a load, and the output current to the load has a predetermined upper limit. A current detection unit for generating a detection voltage whose voltage value varies according to the current value of the output current; and on a current path from the voltage converter to the load An inserted switch; based on the detected voltage, when it is determined that the output current has not reached a predetermined upper limit value, the switch is turned on, and it is determined that the output current has reached a predetermined upper limit value And a switch control unit that turns off the switch when the operation is performed (first configuration).

  In the output current limiting circuit having the first configuration, the current detection unit includes a sense resistor having one end connected to the output end of the voltage converter and the detection voltage drawn from the other end. A configuration (second configuration) is preferable.

  In the output current limiting circuit having the second configuration, the switch control unit includes a detection voltage amplification unit that amplifies the detection voltage to generate an amplification detection voltage; and the amplification detection voltage is set to a predetermined threshold voltage. A voltage comparison unit that turns on the switch when not reached and turns off the switch when the amplified detection voltage reaches a predetermined threshold voltage (third configuration). .

  In the output current limiting circuit having the third configuration, the detection voltage amplifying unit includes an operational amplifier; one end is connected to one end of the sense resistor, and the other end is connected to a non-inverting input terminal of the operational amplifier. A first resistor; one end connected to the non-inverting input terminal of the operational amplifier and the other end connected to the ground terminal; one end connected to the other end of the sense resistor and the other end of the operational amplifier A third resistor connected to the inverting input terminal; and a fourth resistor having one end connected to the inverting input terminal of the operational amplifier and the other end connected to the output terminal of the operational amplifier (fourth) (Configuration).

  In the output current limiting circuit having the third or fourth configuration, the voltage comparison unit includes a threshold voltage generation unit that generates the threshold voltage; a base is connected to an application terminal of the threshold voltage, and a collector is A pnp bipolar transistor connected to the ground terminal and having an emitter connected to a predetermined potential terminal via a resistor; a base connected to the emitter of the pnp bipolar transistor, and an emitter connected to the application terminal of the amplified detection voltage And a npn-type bipolar transistor whose collector is connected to the control terminal of the switch (a fifth configuration).

  In the output current limiting circuit having the second configuration, the switch control unit includes a threshold voltage generating unit that generates a predetermined threshold voltage; a first input terminal is connected to an application terminal of the detection voltage; And a comparator having a second input terminal connected to the threshold voltage application terminal and an output terminal connected to the control terminal of the switch (sixth structure).

  In the output current limiting circuit having the sixth configuration, the switch control unit may have a configuration (seventh configuration) including a phase compensation unit connected to the output terminal of the comparator.

  In the output current limiting circuit having the sixth configuration, the switch control unit divides the detection voltage to generate a divided detection voltage, and outputs the divided detection voltage to the first input terminal of the comparator. A configuration including the voltage dividing section (eighth configuration) is preferable.

  A power supply device according to the present invention includes a semiconductor device in which at least a part of the voltage converter is integrated, and an output current limiting circuit comprising any one of the first to eighth configurations externally attached to the semiconductor device. And (9th configuration).

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

A circuit diagram showing an example of composition of a power unit using an output current limiting circuit of a 1st embodiment Schematic diagram for explaining the output current limiting operation (descent type) according to the present invention The circuit diagram which shows the example of 1 structure of the power supply device using the output current limiting circuit of 2nd Embodiment The circuit diagram which shows the example of 1 structure of the power supply device using the output current limiting circuit of 3rd Embodiment The circuit diagram which shows another structural example of the power supply device using the output current limiting circuit based on this invention Schematic diagram for explaining the conventional output current limiting operation (foldback type)

  FIG. 1 is a circuit diagram showing a configuration example of a power supply device using the output current limiting circuit of the first embodiment. The power supply device of this configuration example includes a voltage converter 1 that converts an input voltage Vin into a desired output voltage Vout and supplies the output voltage Vout to the load Z, and an output current Iout to the load Z that is applied to the voltage converter 1 is a predetermined value. And an output current limiting circuit 2 for limiting so as not to exceed an upper limit value (overcurrent protection value). The voltage conversion device 1 is a step-up switching regulator (step-up chopper regulator) having a semiconductor device 10, an output circuit 20, and a phase compensation circuit 30.

  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. The cathode of the diode D1 is connected to one end of a sense resistor Rs that forms the output current limiting circuit 2 as an output end of the output voltage Vout (that is, an output end of the voltage converter 1). 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.

  As described above, the output current limiting circuit 2 limits the output current Iout to the load Z so as not to exceed a predetermined upper limit value. The output current limiting circuit 2 includes a sense resistor Rs and a P-channel MOS field effect transistor. P1, resistors R11 to R18, an operational amplifier AMP, a pnp bipolar transistor Q1, and an npn bipolar transistor Q2.

  One end of the sense resistor Rs is connected to the output terminal of the voltage conversion device 1 (the output terminal of the output voltage Vout). The other end of the sense resistor Rs is connected to the source of the transistor P1. A detection voltage Va whose voltage value varies according to the current value of the output current Iout is drawn from the other end of the sense resistor Rs. That is, the sense resistor Rs functions as a current / voltage conversion element of a current detection unit that generates the detection voltage Va whose voltage value varies according to the current value of the output current Iout. The resistance value of the sense resistor Rs is desirably set to a very small value so as not to impair the conversion efficiency of the voltage conversion device 1.

  The source and back gate of the transistor P1 are connected to the other end of the sense resistor Rs. The drain of the transistor P1 is connected to the load Z. That is, the transistor P1 is inserted in the current path from the voltage conversion device 1 to the load Z, and functions as a switch that is turned on / off according to the control voltage input to the gate thereof.

  One end of the resistor R11 is connected to one end (high potential end) of the sense resistor Rs. The other end of the resistor R11 is connected to the non-inverting input terminal (+) of the operational amplifier AMP. One end of the resistor R12 is connected to the non-inverting input terminal (+) of the operational amplifier AMP. The other end of the resistor R12 is connected to the ground terminal. One end of the resistor R13 is connected to the other end (low potential end) of the sense resistor Rs. The other end of the resistor R13 is connected to the inverting input terminal (−) of the operational amplifier AMP. One end of the resistor R14 is connected to the inverting input terminal (−) of the operational amplifier AMP. The other end of the resistor R14 is connected to the output end of the operational amplifier AMP. That is, the operational amplifier AMP and the resistors R11 to R14 function as a detection voltage amplification unit that inverts and amplifies the detection voltage Va drawn from the other end of the sense resistor Rs to generate the amplified detection voltage Vx.

  The voltage value of the amplification detection voltage Vx can be calculated by the following equation (1). In equation (1), “Vx” is the voltage value of the amplified detection voltage Vx, “Va” is the voltage value of the detection voltage Va, and “Vb” is the reference voltage drawn from the connection node between the resistor R11 and the resistor R12. The voltage value of Vb, “Vout” indicates the voltage value of the output voltage Vout, and “R11” to “R14” indicate the resistance values of the resistors R11 to R14, respectively.

  As can be seen from the above equation (1), the gain and offset amount of the detection voltage amplification unit can be arbitrarily set by appropriately setting the resistance ratio between the resistor R11 and the resistor R12 and the resistance ratio between the resistor R13 and the resistor R14. It is possible to adjust.

  One end of the resistor R16 is connected to the application end of the output voltage Vout. The other end of the resistor R16 is connected to the base of the transistor Q2. One end of the resistor R17 is connected to the base of the transistor Q2. The other end of the resistor R17 is connected to the ground terminal. A predetermined threshold voltage Vy is drawn from a connection node between the resistor R16 and the resistor R17. That is, the resistor R16 and the resistor R17 function as a threshold voltage generation unit that divides the output voltage Vout to generate a predetermined threshold voltage Vy. The threshold voltage Vy can be arbitrarily adjusted by appropriately setting the resistance ratio of the resistors R16 and R17.

  As described above, the base of the transistor Q1 is connected to the application terminal of the threshold voltage Vy (a connection node between the resistor R16 and the resistor R17). The collector of the transistor Q1 is connected to the ground terminal. The emitter of the transistor Q1 is connected to the application terminal of the output voltage Vout via the resistor R15. The base of the transistor Q2 is connected to the emitter of the transistor Q1. The emitter of the transistor Q2 is connected to the application end of the amplification detection voltage Vx (the output end of the operational amplifier AMP). The collector of the transistor Q2 is directly connected to the gate (switch control terminal) of the transistor P1, and is also connected to the source of the transistor Q2 via the resistor R18. That is, the transistor Q1 and the transistor Q2 function as a voltage comparison unit that performs on / off control of the transistor P1 depending on whether or not the amplified detection voltage Vx reaches a predetermined threshold voltage Vy.

  To summarize the above configuration, in the output current limiting circuit 2 of the first embodiment, the detection voltage amplification unit (the operational amplifier AMP and the resistors R11 to R14), the threshold voltage generation unit (the resistors R16 and R17), and the voltage comparison The part (transistors Q1, Q2) turns on the transistor P1 when it is determined that the output current Iout has not reached the predetermined upper limit value based on the detection voltage Va, and the output current Iout has reached the predetermined upper limit value. When it is determined that the transistor P1 is present, it functions as a switch controller that turns off the transistor P1.

  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 through the transistor N1, and the electric energy is stored. Note that if the charge has already been accumulated in the capacitor C1 during the ON period of the transistor N1, the output current Iout flows from the capacitor C1 through the output current limiting circuit 2 to the load Z. At this time, since the anode potential of the diode D1 is lowered to almost the ground potential via the transistor N1, the diode D1 is in a reverse bias state, and no current flows from the capacitor C1 toward the transistor N1.

  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 the forward bias state, the current flowing through the diode D1 flows into the load Z through the output current limiting circuit 2, and also flows into the ground terminal through the capacitor C1. Will charge. By repeating the above operation, the load Z is supplied with the DC output boosted and smoothed by the capacitor C1.

  As described above, 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 to generate the output voltage Vout and supplying the output voltage Vout to the load Z. Functions as a component of the voltage converter 1 (step-up switching regulator).

  Next, the output 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 an output current limiting operation (descent type) according to the present invention. The horizontal axis in FIG. 2 indicates the output current Iout, and the vertical axis in FIG. 2 indicates the output voltage Vout.

  The amount of voltage drop at the sense resistor Rs increases in proportion to the current value of the output current Iout. Therefore, as the output current Iout increases, the voltage value of the detection voltage Va decreases, and the voltage value of the amplified detection voltage Vx obtained by inverting and amplifying the detection voltage Va increases. Here, since the transistor Q2 can be turned on while the amplification detection voltage Vx is lower than the threshold voltage Vy, the transistor P1 is also turned on, and the current path of the output current Iout is in a conductive state. On the other hand, when the output current Iout reaches a predetermined overcurrent protection value and the amplified detection voltage Vx becomes higher than the threshold voltage Vy, the transistor Q2 cannot be turned on, so that the transistor P1 is also turned off, and the output current Iout The current path is cut off.

  When the output current Iout is reduced by such an output current limiting operation, the amount of voltage drop at the sense resistor Rs is also reduced, so that the amplified detection voltage Vx falls below the threshold voltage Vy, and the transistor P1 returns to the on state again.

  Thereafter, by repeating the same operation as described above, in the voltage conversion device 1 to which the output current limiting circuit 2 is applied, when the output current Iin reaches a predetermined upper limit value, the output current Iout beyond the load Z is reached. Cannot be supplied, and feedback is applied so that the current value of the output current Iout is stabilized at a predetermined upper limit value. That is, the output current limiting circuit 2 functions as a constant current source that outputs a constant output current Iout to the load Z.

  As described above, with the output current limiting circuit 2 of the present embodiment, the output voltage Vout decreases while maintaining the current value of the output current Iout at a predetermined upper limit without shutting down the operation of the voltage conversion device 1. Thus, it becomes possible to realize a drooping output current limiting characteristic (overcurrent protection curve).

  That is, if it is the voltage converter 1 to which the output current limiting circuit 2 is applied, a dedicated IC for each application (for example, a DC / DC converter IC dedicated to a USB power supply or a DC / DC converter IC dedicated to a charger of a mobile phone) ), A drooping-type overcurrent protection function that can set the overcurrent protection value with high accuracy and flexibility simply by connecting only a few external elements to the general-purpose semiconductor device 10 Since it can be realized at a low cost, it is possible to simplify the design when developing a new set.

  FIG. 3 is a circuit diagram showing a configuration example of a power supply device using the output current limiting circuit of the second embodiment. The output current limiting circuit 2 of the present embodiment includes the above-described sense resistor Rs and transistor P1, and as a circuit element of a switch control unit for turning on / off the transistor P1, a comparator CMP, resistors R21 to R23, And a capacitor C21.

  One end of the resistor R21 is connected to one end (high potential end) of the sense resistor Rs. The other end of the resistor R21 is connected to the non-inverting input terminal (+) of the comparator CMP. One end of the resistor R22 is connected to the non-inverting input terminal (+) of the comparator CMP. The other end of the resistor R22 is connected to the ground terminal. That is, the resistor R21 and the resistor R22 function as a threshold voltage generation unit that divides the output voltage Vout and generates a predetermined threshold voltage Vc. The threshold voltage Vc can be arbitrarily adjusted by appropriately setting the resistance ratio between the resistors R21 and R22.

  As described above, the non-inverting input terminal (+) of the comparator CMP is connected to the threshold voltage Vc application terminal (a connection node between the resistor R21 and the resistor R22). The inverting input terminal (−) of the comparator CMP is connected to the other end (low potential terminal) of the sense resistor Rs. The output end of the comparator CMP is connected to one end of the resistor R23. The other end of the resistor R23 is connected to the gate of the transistor P1. One end of the capacitor C21 is output to the gate of the transistor P1. The other end of the capacitor C21 is connected to the drain of the transistor P1. That is, a phase compensation unit including a resistor R23 and a capacitor C21 is connected to the output terminal of the comparator CMP. With such a configuration, it is possible to avoid a situation in which the ON / OFF operation of the transistor P1 is frequently repeated (oscillation state) and to perform stable feedback control.

  In the output current limiting circuit 2 configured as described above, the voltage value of the detection voltage Va decreases as the output current Iout increases. Here, when the detection voltage Va is higher than the threshold voltage Vc, the output logic of the comparator CMP is at a low level, and the transistor P1 can be turned on, so that the current path of the output current Iout becomes conductive. On the other hand, when the output current Iout reaches a predetermined overcurrent protection value and the detection voltage Va becomes lower than the threshold voltage Vc, the output logic of the comparator CMP becomes high level, and the transistor P1 cannot be turned on. The current path of the current Iout is cut off.

  When the output current Iout is reduced by such an output current limiting operation, the amount of voltage drop at the sense resistor Rs is also reduced, so that the detection voltage Va exceeds the threshold voltage Vc, and the transistor P1 returns to the on state again.

  Thereafter, by repeating the same operation as described above, in the voltage conversion device 1 to which the output current limiting circuit 2 is applied, when the output current Iin reaches a predetermined upper limit value, the output current Iout beyond the load Z is reached. Cannot be supplied, and feedback is applied so that the current value of the output current Iout is stabilized at a predetermined upper limit value. That is, the output current limiting circuit 2 functions as a constant current source that outputs a constant output current Iout to the load Z.

  Thus, in the case of the output current limiting circuit 2 of the present embodiment, the current value of the output current Iout is set to a predetermined upper limit without shutting down the operation of the voltage converter 1 as in the first embodiment described above. A drooping output current limiting characteristic (overcurrent protection curve) in which the output voltage Vout decreases while maintaining the value can be realized.

  FIG. 4 is a circuit diagram showing a configuration example of a power supply device using the output current limiting circuit of the third embodiment. The output current limiting circuit 2 of the present embodiment includes the above-described sense resistor Rs and transistor P1, and as a circuit element of a switch control unit that turns on and off the transistor P1, a comparator CMP, resistors R31 to R34, It has.

  One end of the resistor R31 is connected to one end (high potential end) of the sense resistor Rs. The other end of the resistor R31 is connected to the non-inverting input terminal (+) of the comparator CMP. One end of the resistor R32 is connected to the non-inverting input terminal (+) of the comparator CMP. The other end of the resistor R32 is connected to the ground terminal. That is, the resistor R31 and the resistor R32 function as a threshold voltage generation unit that divides the output voltage Vout and generates a predetermined threshold voltage Vc. The threshold voltage Vc can be arbitrarily adjusted by appropriately setting the resistance ratio between the resistors R31 and R32.

  One end of the resistor R33 is connected to the other end (low potential end) of the sense resistor Rs. The other end of the resistor R33 is connected to the inverting input terminal (−) of the comparator CMP. One end of the resistor R34 is connected to the inverting input terminal (−) of the comparator CMP. The other end of the resistor R34 is connected to the ground terminal. That is, the resistor R33 and the resistor R34 function as a detection voltage dividing unit that divides the detection voltage Va to generate a predetermined divided detection voltage Vd. The divided voltage detection voltage Vd can be arbitrarily adjusted by appropriately setting the resistance ratio of the resistors R33 and R34.

  As described above, the non-inverting input terminal (+) of the comparator CMP is connected to the threshold voltage Vc application terminal (a connection node between the resistor R31 and the resistor R32). The inverting input terminal (−) of the comparator CMP is connected to the application terminal (connection node between the resistor R33 and the resistor R34) of the divided voltage detection voltage Vd as described above. The output terminal of the comparator CMP is connected to the gate of the transistor P1.

  In the output current limiting circuit 2 configured as described above, the voltage value of the divided detection voltage Vd decreases as the output current Iout increases. Here, when the divided voltage detection voltage Vd is higher than the threshold voltage Vc, the output logic of the comparator CMP is at a low level, and the transistor P1 can be turned on, so that the current path of the output current Iout becomes conductive. On the other hand, when the output current Iout reaches a predetermined overcurrent protection value and the divided voltage detection voltage Vd becomes lower than the threshold voltage Vc, the output logic of the comparator CMP becomes high level and the transistor P1 cannot be turned on. The current path of the output current Iout is cut off.

  When the output current Iout is reduced by such an output current limiting operation, the amount of voltage drop at the sense resistor Rs is also reduced, so that the divided voltage detection voltage Vd exceeds the threshold voltage Vc, and the transistor P1 returns to the ON state again.

  Thereafter, by repeating the same operation as described above, in the voltage conversion device 1 to which the output current limiting circuit 2 is applied, when the output current Iin reaches a predetermined upper limit value, the output current Iout beyond the load Z is reached. Cannot be supplied, and feedback is applied so that the current value of the output current Iout is stabilized at a predetermined upper limit value. That is, the output current limiting circuit 2 functions as a constant current source that outputs a constant output current Iout to the load Z.

  Thus, in the case of the output current limiting circuit 2 of the present embodiment, the current of the output current Iout can be obtained without shutting down the operation of the voltage conversion device 1 as in the first and second embodiments described above. A drooping output current limiting characteristic (overcurrent protection curve) in which the output voltage Vout decreases while maintaining the value at a predetermined upper limit value can be realized.

  Further, in the case of the output current limiting circuit 2 of the present embodiment, unlike the second embodiment, a configuration for comparing the divided detection voltage Vd obtained by dividing the detection voltage Va with a predetermined threshold voltage Vc. Therefore, the upper limit value (overcurrent protection value) of the output current Iout can be adjusted more arbitrarily.

  In the above embodiment, the input current limiting circuit according to the present invention is used as means for limiting the output current Iout of the voltage converter 1 (boost switching regulator) that boosts the input voltage Vin to generate the output voltage Vout. However, the application target of the output 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 Converter] shown in FIG. ] Can be widely applied to other types of voltage converters.

  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 a technique that can be suitably used as, for example, an output current limiting circuit applied to a voltage converter that converts an input voltage into a desired output voltage and supplies the output voltage to a load.

DESCRIPTION OF SYMBOLS 1 Voltage converter 2 Output current limiting circuit 10 Semiconductor device (general-purpose DC / DC converter IC)
11 Error Amplifier 12 Controller 13 Driver 20 Output Circuit 30 Phase Compensation Circuit N1 N-channel 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 Rs Sense Resistor R11-R18, R21-R23, R31-R34 Resistor P1 P-channel MOS Field Effect Transistor Q1 Pnp Bipolar Transistor Q2 npn type bipolar transistor AMP operational amplifier CMP comparator C21 capacitor Z load

Claims (9)

An output current limiting circuit that is applied to a voltage conversion device that converts an input voltage into a desired output voltage and supplies the load to a load, and limits the output current to the load 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 output current;
A switch inserted on a current path from the voltage converter to the load;
Based on the detected voltage, the switch is turned on when it is determined that the output current has not reached the predetermined upper limit value, and the switch is turned on when it is determined that the output current has reached the predetermined upper limit value. A switch controller to turn off;
An output current limiting circuit comprising:   2. The output current limiting circuit according to claim 1, wherein one end of the current detection unit is connected to an output end of the voltage converter, and a sense resistor from which the detection voltage is drawn is connected from the other end. .   The switch control unit amplifies the detection voltage to generate an amplification detection voltage; and turns on the switch when the amplification detection voltage does not reach a predetermined threshold voltage, and the amplification detection voltage is The output current limiting circuit according to claim 2, further comprising: a voltage comparing unit that turns off the switch when a predetermined threshold voltage is reached.   The detection voltage amplification unit includes an operational amplifier; one end connected to one end of the sense resistor and the other end connected to a non-inverting input terminal of the operational amplifier; one end connected to a non-inverting input terminal of the operational amplifier A second resistor connected at the other end to the ground terminal; a third resistor connected at one end to the other end of the sense resistor and connected at the other end to the inverting input terminal of the operational amplifier; 4. The output current limiting circuit according to claim 3, further comprising: a fourth resistor connected to the inverting input terminal of the operational amplifier and having the other end connected to the output terminal of the operational amplifier.   The voltage comparison unit includes a threshold voltage generation unit that generates the threshold voltage; a base is connected to an application terminal of the threshold voltage, a collector is connected to a ground terminal, and an emitter is connected to a predetermined potential terminal via a resistor An pnp bipolar transistor having a base connected to an emitter of the pnp bipolar transistor, an emitter connected to an application terminal of the amplified detection voltage, and a collector connected to a control terminal of the switch; The output current limiting circuit according to claim 3 or 4, characterized by comprising:   The switch control unit includes a threshold voltage generation unit that generates a predetermined threshold voltage; a first input terminal is connected to the detection voltage application terminal, a second input terminal is connected to the threshold voltage application terminal, and an output 3. The output current limiting circuit according to claim 2, further comprising: a comparator having an end connected to a control end of the switch.   The output current limiting circuit according to claim 6, wherein the switch control unit includes a phase compensation unit connected to an output terminal of the comparator.   The switch control unit includes a detection voltage dividing unit that divides the detection voltage to generate a divided detection voltage and outputs the divided detection voltage to a first input terminal of the comparator. 6. The output current limiting circuit according to 6.   A semiconductor device in which at least a part of the voltage conversion device is integrated, and an output current limiting circuit according to any one of claims 1 to 8, which is externally attached to the semiconductor device. A featured power supply.

Images