JP2005210845A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply circuit with a short determining mechanism effective in the integration and improvement of determination accuracy. <P>SOLUTION: The power supply circuit 10 converts power by controlling a switching element SW disposed between a power supply source 100 and a load 102, and is provided: with a clock generating circuit 19 for generating a clock signal as the control timing of the switching element, a PWM circuit 14 for controlling the switching element based on the clock signal; an OCP circuit 16 for detecting the value of a current flowing from the power supply source to the load, and generating an overcurrent pulse in synchronization with the clock signal when the current value is a predetermined value or larger; and a short determining circuit 18 for determining the short circuit of the load by counting the number of the overcurrent pulses generated by the OCP circuit. The PWM circuit controls the switching element based on the overcurrent pulses generated from the OCP circuit and the determined result from the short determining circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power supply circuit that performs power conversion by switching control, and more particularly, to a power supply circuit that determines an output short circuit using an overcurrent detection mechanism.

  In a power supply circuit that converts the output of the power source into power by switching control and supplies it to the load, if a short circuit occurs on the load side due to a failure or other cause, the voltage drops all at once and overcurrent flows, causing damage to the power supply circuit itself Or load damage.

For this reason, it is desired to detect a short circuit on the load side at an early stage and to protect it. In order to meet this requirement, a conventional power supply circuit has proposed a method of determining a short-circuit state by monitoring the output voltage of the power supply circuit and verifying an abnormal drop in the output voltage. In this method, the time when the output voltage drops below a predetermined voltage is measured, and when this measurement result exceeds a certain reference, it is assumed that a short circuit has occurred and protection is applied. The following Patent Document 1 discloses specific means for measuring time used in the above method.
However, the short-circuit phenomenon that actually occurs on the load side may be a complete short-circuit and the resistance value may be 0Ω, but it may be an incomplete short-circuit that maintains a short-circuit impedance of several Ω. In some cases, it may be difficult to determine a short circuit using the conventional method described above.

  That is, when an incomplete short circuit occurs, it is difficult to determine how many volts or less the voltage drop is abnormal, and it is also difficult to determine the strictness as a criterion for the voltage drop time. . On the other hand, if the reference voltage value is set high or the drop time reference value is set short in order to improve the accuracy of incomplete short-circuit detection, the overcurrent and load generated when the power supply circuit starts up It cannot be distinguished from a voltage drop due to fluctuations, which causes the protection mechanism to malfunction.

  Further, in the above conventional method, it is necessary to measure time of several ms to several tens of ms in order to detect a short circuit state, and in order to realize this, a time constant circuit having a capacity of several thousand pF is necessary. . It is very difficult to make an IC including such a large-capacity time constant circuit, and even if it can be integrated, an undesirable result may be obtained in terms of size and cost.

  A method of measuring time with a digital counter circuit without using such a time constant circuit is also conceivable, but the clock frequency of the switching power supply circuit is increasing year by year, and in a power supply circuit that operates with an MHz class clock, Since a counter circuit with 10 or more stages is required, such a method is difficult to meet the demand for miniaturization.

On the other hand, as a means for determining an output short circuit, as shown in Patent Documents 2 and 3 shown below, a technique for counting the number of overcurrent detections and determining a short circuit state based on the result is known. ing.
Japanese Patent Laid-Open No. 11-262270 However, these documents do not propose a specific configuration of how to handle an overcurrent signal in relation to the switching control of the power supply circuit, and are more integrated. In order to establish all of 1) switching control, 2) overcurrent protection, and 3) short-circuit determination with the above structure, it is necessary to make it more concrete in relation to the PWM circuit that is the basis of switching control.

  The means described in Patent Documents 2 and 3 only count the number of overcurrent detections, and a configuration for actually realizing this counting and a configuration with improved accuracy are desired.

  Therefore, an object of the present invention is to provide a short circuit determination technique effective for integration and improvement of determination accuracy.

  In order to achieve the above object, the invention according to claim 1 is the control timing of the switching element in the power supply circuit that performs power conversion by controlling the switching element arranged between the power supply source and the load. A clock generation circuit that generates a clock signal; a PWM circuit that controls the switching element based on the clock signal; and a value of a current that flows from the power supply source toward the load, the current value being a predetermined reference When the value exceeds the value, the OCP circuit that generates an overcurrent pulse at a timing synchronized with the clock signal and the number of overcurrent pulses generated by the OCP circuit are counted to determine the short-circuit state of the load. A short circuit determination circuit, wherein the PWM circuit is based on an overcurrent pulse generated by the OCP circuit and a determination result of the short circuit determination circuit. There are, and controlling the switching element.

  Here, the power supply source corresponds to a target for supplying power to the power supply circuit, such as an output of a battery or another power conversion circuit, and the load includes an active circuit such as an IC or a resistive load such as a lamp. In addition, a motor for driving electric power, various devices, and the like are applicable, and a single connection or a plurality of connections are within the scope of the present invention.

  As a switching element, it is generally desirable to configure with a power FET, and as a clock generation circuit, it can be configured with a commonly used oscillation circuit, and the switching element is driven at a MHz class frequency. Is desirable.

  The PWM circuit uses the clock signal to generate a pulse signal in which the duty of the ON / OFF interval is controlled, outputs the pulse signal to the switching element, and outputs the regulated voltage to the load.

  The OCP circuit detects the value of the current flowing from the power supply source toward the load, and this detection point may be any of the preceding stage, the rear stage, and immediately before the load of the switching element, from the power supply source. It may be detected at an arbitrary point between the loads.

  The OCP circuit determines the occurrence of overcurrent at a timing synchronized with the clock signal, and when the occurrence of overcurrent is confirmed, outputs an overcurrent pulse of a predetermined length to both the PWM circuit and the short circuit determination circuit. The length of the overcurrent pulse may be the same as the period in which the overcurrent is generated or may be an impulse signal. If the overcurrent generation state can be confirmed for each clock cycle, the effect of the present invention can be obtained. Can do.

  The short circuit determination circuit counts the number of overcurrent pulses generated by the OCP circuit, determines that the short circuit state is reached when the count result reaches a predetermined number, and outputs a short circuit determination signal to the PWM circuit.

  The PWM circuit controls the switching element using both the overcurrent pulse generated by the OCP circuit and the determination result of the short circuit determination circuit. That is, when an overcurrent pulse occurs, the PWM circuit stops the power supply to the load until the overcurrent state is resolved by fixing the switching element to the OFF state for a certain period of time. After the cancellation, normal switching control is resumed. Regardless of this, when the short circuit determination circuit detects a short circuit state, the switching element is forcibly fixed to the OFF state.

  Thus, by effectively utilizing the overcurrent pulse generated by the OCP circuit for both overcurrent protection and short circuit determination, it is possible to realize both overcurrent protection and short circuit protection with a circuit configuration suitable for integration. It becomes possible.

  In addition, in the present invention, it is possible to incorporate a short circuit protection function with a minimum configuration because PWM control, overcurrent pulse generation, and overcurrent pulse counting can be performed using a clock signal that is a reference for switching control. At the same time, it is possible to make a highly accurate short-circuit determination with a resolution comparable to the period of the clock signal.

  Note that the power supply circuit according to the present invention can be applied to any of a step-up type, a step-down type, a step-up / down type, and an inversion type.

  According to a second aspect of the present invention, in a power supply circuit that performs power conversion by controlling a switching element disposed between a power supply source and a load, a clock signal serving as a control timing of the switching element is generated. A clock generation circuit, a PWM circuit that controls the switching element based on the clock signal, and a value of a current flowing from the power supply source toward the load are detected, and the current value is equal to or greater than a predetermined reference value. An OCP circuit that generates an overcurrent pulse at a timing synchronized with the clock signal, and a short-circuit determination circuit that determines a short-circuit state of the load by detecting continuity of the overcurrent pulse generated by the OCP circuit; It is characterized by comprising.

  Here, each component of the invention according to the present invention can be configured in the same manner as in the first invention. However, the present invention has a configuration for detecting the continuity of the overcurrent pulse, thereby further enhancing the configuration. Accurate short-circuit determination is possible.

  The continuity of the overcurrent pulse can be detected and evaluated by, for example, the method described in claim 3. By evaluating this continuity, whether the occurrence of overcurrent is caused by a complete short circuit, It is possible to distinguish whether it is caused by an incomplete short circuit, caused by load fluctuation, or caused by a start-up period.

  For example, in the case of a complete short circuit, the impedance on the load side is as close to 0Ω as possible, so an overcurrent pulse is continuously generated and continuously output until either the power supply source or the load is disconnected. In the case of load fluctuation, continuous / discontinuous appears irregularly according to the change of the operating current on the load side. In the case of incomplete short-circuiting, if the short-circuit impedance is low, it continues for a long period of time, but if the short-circuit impedance is relatively high, discontinuous points may appear.

  Therefore, in the present invention, the accuracy of short circuit determination is improved by evaluating the continuity of the overcurrent pulse as well as simply counting as in the prior art. The definition of continuity is not limited to the case where an overcurrent pulse continues to be generated simultaneously with a clock signal, as will be described in the later-described embodiment. It is also possible to adopt a configuration in which it is determined that the data is continuous.

  According to a third aspect of the present invention, in the second aspect of the present invention, the short circuit determination circuit outputs a mask pulse longer than a period of the clock signal using the overcurrent pulse as a trigger, and a level of the mask pulse. The continuity of the overcurrent pulse is detected by observing the change.

  Thus, by using a mask pulse longer than the period of the clock signal, it is possible to detect the continuity of the overcurrent pulse output in synchronization with the clock signal. Here, in order to increase the redundancy of continuity, a mask pulse having a length corresponding to two cycles of the clock signal may be used.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, the short circuit determination circuit includes a counter that counts the number of the overcurrent pulses, and calculates a logical product of the mask pulse and the clock signal. By taking the counter, a reset signal of the counter is generated.

  In this way, by counting overcurrent pulses with a counter and controlling the reset of the counter with a mask pulse, the continuous time of the overcurrent pulse can be detected, and preparation for the next continuity evaluation by counter reset is performed. be able to.

  According to a fifth aspect of the present invention, in the second aspect of the invention, the short circuit determination circuit detects the continuity of the overcurrent pulse during a period other than a start-up period until the output voltage to the load is stabilized. It is characterized by doing.

  By configuring in this way, confusion with the overcurrent generated during the startup period is prevented, and more accurate short-circuit determination can be realized.

  According to a sixth aspect of the present invention, in a power supply circuit that performs power conversion by controlling a switching element disposed between a power supply source and a load, a clock signal serving as a control timing of the switching element is generated. A clock generation circuit, a PWM circuit that controls the switching element based on the clock signal, and a value of a current flowing from the power supply source toward the load are detected, and the current value is equal to or greater than a predetermined reference value. An OCP circuit that generates an overcurrent pulse at a timing synchronized with the clock signal, and a short-circuit determination circuit that determines a short-circuit state of the load by detecting a discontinuous point of the overcurrent pulse generated by the OCP circuit It is characterized by comprising.

  Here, each component of the invention according to the present invention can be configured in the same manner as in the first invention. However, in the present invention, a configuration for detecting a discontinuous point of an overcurrent pulse is provided. High-precision short-circuit determination is possible. In the invention according to claim 2, the continuity of the overcurrent pulse is evaluated. However, the invention according to this claim is characterized in that a discontinuous point is detected, and even if the overcurrent pulse train of a predetermined cycle is one pulse. This includes the case where it is missing and the case where the overcurrent pulse generation period changes. When it is desired to provide redundancy for detection of discontinuous points, a case where several pulses are continuously missing may be defined as discontinuous.

  According to a seventh aspect of the invention, in the sixth aspect of the invention, the short circuit determination circuit outputs a mask pulse longer than the period of the clock signal using the overcurrent pulse as a trigger, and the level of the mask pulse. A discontinuous point of the overcurrent pulse is detected by observing the change.

  The invention according to claim 8 is the invention according to claim 7, wherein the short-circuit determination circuit includes a counter that counts the number of the overcurrent pulses, and calculates a logical product of the mask pulse and the clock signal. By taking the counter, a reset signal of the counter is generated.

  According to a ninth aspect of the present invention, in the sixth aspect of the invention, the short circuit determination circuit detects the discontinuity point of the overcurrent pulse during a period other than the start-up period until the output voltage to the load is stabilized. It is characterized by detecting.

  As described above, according to the present invention, the PWM circuit performs switching control based on the overcurrent pulse generated by the OCP circuit and the determination result of the short circuit determination circuit. Short circuit determination is possible.

  In the present invention, the continuity and discontinuity of the overcurrent pulse are detected, and the short-circuit state is determined based on the result, so that the short-circuit determination can be performed with higher accuracy.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a power supply circuit according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the configuration of the embodiment described below, and can be modified as appropriate.

  FIG. 1 is a circuit block diagram showing an embodiment of a power supply circuit according to the present invention. As shown in the figure, the power supply circuit 10 according to the present embodiment is used as a power conversion circuit that steps down the input voltage Vin of the battery 100 connected to the input side to a predetermined output voltage Vout and outputs it to the load 102. The

  The power supply circuit 10 includes a switching element SW, a control unit 12 that controls the switching element, a diode D1 that functions as a rectifying element, an inductor L and a capacitor C that smooth the output of the switching element SW, The voltage dividing resistors R1 and R2 for feeding back the output voltage Vout to the control unit 12 and a clock generation unit 19 for generating a basic clock of the control unit 12 are configured.

  The control unit 12 detects a current value flowing through the switching element SW, a PWM circuit 14 that performs PWM (Pulse Width Modulation) control based on the feedback voltage FB obtained from the voltage dividing resistors R1 and R2, and detects OCP (Over Current). An OCP circuit 16 that performs (Protection) control and a short-circuit determination circuit 18 that determines an output short-circuit of the power supply circuit 10 based on an overcurrent pulse generated by the OCP circuit.

  FIG. 2 is a circuit block diagram showing an embodiment of the OCP circuit shown in FIG. As shown in the figure, the OCP circuit 16 compares a resistor R3 and a transistor Tr that detect a high-side current I-H flowing through the switching element SW, and the detected high-side current I-H with a predetermined reference level V1. Thus, the OCP level comparator 20 that determines whether or not an overcurrent has occurred and a mono-multi circuit 22 that generates an overcurrent pulse when it is determined that an overcurrent has occurred.

  Here, the switching element SW and the transistor Tr constitute a current mirror, and a current (IH) / n of 1 / n of the high side current IH flows through the resistor R3. The OCP level comparator 20 compares the detection voltage VId generated by the 1 / n current (I−H) / n with the difference Vin−V1 between the input voltage Vin and the reference voltage V1. At this time, when the detection voltage VId becomes smaller than the differential voltage Vin−V1, that is, when the high side current I−H becomes larger than a predetermined value, an overcurrent detection signal is output from the OCP level comparator 20 to the mono-multi circuit 22. Thus, an overcurrent pulse OCP is generated.

  FIG. 3 is a circuit block diagram showing an embodiment of the short circuit determination circuit shown in FIG. As shown in the figure, the short circuit determination circuit 18 includes a counter 34 that counts the number of overcurrent pulses OCP generated by the OCP circuit 16, and a decoder that detects that the count result of the counter 34 has reached a predetermined reference value. 36, an RS Philip flop 38 that is set by the output of the decoder 36 and reset by an external start signal Power on, and a mono length that extends the pulse length of the overcurrent pulse OCP to a length determined by the time constant C2 · R4. 1 and an AND element 32 that generates a reset signal of the counter 34 by ANDing the mask signal Mask output from the mono-multi circuit 30 and the clock signal CLK generated by the clock generator 19 shown in FIG. Consists of

  FIG. 4 is a circuit block diagram showing an embodiment of the PWM circuit shown in FIG. As shown in the figure, the PWM circuit 14 includes a waveform generation circuit 46 that generates a PWM waveform that becomes an ON / OFF control signal for the switching element SW, an overcurrent pulse OCP generated by the OCP circuit 16, and a short-circuit determination circuit 18. Based on the output signal, the output of the waveform generation circuit 46 is masked, and an AND element 42 and a NOT element 44 that generate a gate signal to the switching element SW are configured. That is, the AND element 42 masks the PWM waveform generated by the waveform generation circuit 46 when either the overcurrent pulse OCP generated by the OCP circuit 16 or the determination signal generated by the short circuit determination circuit 18 is input. Thus, the switching element SW is maintained in the OFF state until both the overcurrent state and the output short circuit are resolved, and the power supply circuit 10 is protected.

  FIG. 5 is a timing chart showing the basic operation of the power supply circuit shown in FIG. As shown in the figure, the clock generator 19 shown in FIG. 1 generates a clock signal CLK having a predetermined frequency, for example, 1 MHz, and outputs it to the controller 12. The control unit 12 generates a gate signal synchronized with the clock signal and controls the switching element SW. When the overcurrent pulse OCP is at the Hi level, this gate signal is masked by the AND element 42 in FIG. 4 to maintain the Low level, and when the overcurrent state is eliminated, the output of the waveform generation circuit 46 becomes the gate signal. It becomes.

  The OCP circuit 16 detects the high-side current I-H flowing through the switching element SW, and generates an overcurrent pulse OCP that becomes Hi level during a period when this value exceeds Vocp. The short circuit determination circuit 18 uses the counter 34 shown in FIG. 3 to count the number of overcurrent pulses OCP, and uses the mono-multi circuit 30 to mask the overcurrent pulse OCP extended to the period T1. Generate a pulse.

  Each time the overcurrent pulse OCP is input to the mono-multi circuit 30, this mask pulse is continuously generated as Shot1, Shot2,... As shown in FIG. The mask pulse Mask output from the output terminal maintains a low level output during a period in which the overcurrent pulse OCP is continuously output, that is, while the generation period of the overcurrent pulse is shorter than the extension period T1 of the mono-multi circuit 30. Then, after the generation of the overcurrent pulse OCP is stopped, the level returns to the Hi level.

  The AND element 32 of FIG. 3 uses this mask pulse Mask to mask the clock signal CLK while the overcurrent pulse OCP is continuously generated, and when the generation of the overcurrent pulse OCP is stopped, the clock signal CLK Is used to reset the counter 34.

  FIG. 6 is a timing chart showing a first operation example of the power supply circuit shown in FIG. The example shown in the figure shows an operation example when it is determined that a short circuit has occurred in the power supply circuit or on the load side, and the power supply to the load is stopped.

  As shown in the figure, when a short circuit occurs in the power supply circuit or on the load side, the overcurrent pulse OCP is continuously output. When the overcurrent pulse OCP is continuously output in this way, the power supply circuit 10 in FIG. 1 considers that an output short circuit has occurred when the count result of the overcurrent pulse OCP reaches a predetermined reference number, for example, 13 times. A determination signal is output, the output of the PWM circuit 14 is masked, and the gate signal to the switching element SW is stopped. As a result, the switching element SW is turned off, the load 102 is disconnected from the battery 100, and the power supply from the battery to the load is stopped until the reset signal to the RS flip-flop 38 by the activation signal shown in FIG. 3 is input. To do.

  FIG. 7 is a timing chart showing a second operation example of the power supply circuit shown in FIG. The example shown in the figure shows an operation example in the case where an overcurrent pulse is generated but it is not determined that the output is short-circuited, for example, when an overcurrent occurs due to a sudden load change, for example.

  As shown in the figure, the overcurrent pulse OCP when a sudden load change occurs is not a long-term continuous output, but a pulse train in which discontinuous points are formed everywhere in the overcurrent pulse train output at a constant period. . Since this discontinuous point occurs at the time when the load side enters a stable state and the sudden change is completed, if there is such a discontinuous point, it can be regarded as an overcurrent occurrence due to a sudden load change rather than a short circuit.

  When this discontinuity occurs, the counter 34 is reset by the action of the mono-multi circuit 30 and the discrimination signal is not output, so the output PWM of the waveform generation circuit 46 becomes the gate signal. Here, although it is difficult to discriminate from FIG. 7, as described above, when the overcurrent pulse is at the Hi level, the gate signal is masked by the AND element 42 in FIG. When it is eliminated, the output PWM of the waveform generation circuit 46 becomes a gate signal. That is, in the example shown in FIG. 7, the protection by the overcurrent pulse is performed, but the short circuit protection is not performed.

  FIG. 8 is a timing chart showing a modified setting example of the power supply circuit shown in FIG. In the example shown in the figure, the time constants C2 and R4 of the mono-multi circuit 30 shown in FIG. 3 are set to T2 that is slightly longer than two periods of the clock signal CLK, thereby making it redundant for determining the continuity of overcurrent pulses. It is an example of an operation when giving. As shown in the figure, when the output pulse length of the mono-multi circuit 30 is set to T2, if an overcurrent pulse occurs during the period of two clock signals, the output pulse of the mono-multi circuit 30 is The mask signal Mask is kept at the low level in succession to Shot1, Shot2,.

  FIG. 9 is a timing chart illustrating an operation example of the power supply circuit illustrated in FIG. 1 in the modification setting example illustrated in FIG. As shown in the figure, when the time constant of the mono-multi circuit is set to T2, even if a discontinuous point for one pulse occurs when the count value of the overcurrent pulse OCP reaches n = 6. Since the discontinuous point within two cycles of the clock signal does not affect the mask pulse having the length of T2, the counter is not reset and the counting of the overcurrent pulse is continued, and the discrimination signal is reached when n = 13. Is output.

  FIG. 10 is a circuit block diagram showing another configuration example of the short circuit determination circuit shown in FIG. The example shown in the figure is a configuration example that is effective when it is desired to improve the discrimination accuracy between overcurrent generation at startup and overcurrent generation at short circuit. One cause of malfunction of the short-circuit determination circuit is when the power supply is started. When the power supply is started, the output terminal starts from OV in the same manner as the output short circuit. If the set value of the decoder is small, it may be determined that the short circuit occurs at the start time. In this configuration example, in order to prevent such a malfunction, a timer for defining the activation time is provided and ORed to the reset signal of the counter.

  In addition to the components of the short circuit determination circuit 18 shown in FIG. 3, the short circuit determination circuit 18 shown in FIG. And an OR element 50 to be added as a reset signal.

  The start-up timer 52 measures the time from when the power supply to the power supply circuit 10 is turned on until the output voltage Vout reaches a predetermined reference level and stabilizes, and outputs the Hi level during the period when the output voltage Vout is unstable. After the voltage Vout is stabilized, the Low level is output. As a result, since the counter 34 is always reset during the transition period immediately after the power supply circuit 10 is activated, the short circuit determination circuit 18 detects the overcurrent pulse OCP during a period other than the activation period until the output voltage Vout to the load is stabilized. Will be detected. With such a configuration, a malfunction of the short circuit determination at the time of startup is prevented.

  Such a start-up timer 52 can be configured by using the output of the soft start timer of the power supply circuit 10, and is replaced with a configuration for measuring the time until the output voltage Vout is stabilized as described above. Thus, a configuration may be adopted in which the elapsed time from immediately after startup is measured, and the Low level is output when the measurement result reaches a standard time required to reach a stable state.

  Furthermore, when it is desired to more strictly prevent the malfunction of the short circuit determination due to various factors, the count number that can distinguish the load fluctuation and the short circuit from the operation mode specification of the load connected to the power supply circuit 10 and the actual operation test result ( In the above-described example, it is desirable to obtain (strictly n = 13) and set it to the value of the decoder 36. For example, in order to prevent malfunction due to sudden load change, repeat the actual machine test multiple times to determine the maximum time for sudden load change, and set a value greater than the number of clocks corresponding to this maximum time in the decoder. A malfunction due to a sudden change is preferably prevented.

  In addition, in order to further increase the determination accuracy, it is possible to use a combination of the malfunction prevention mechanism with the load fluctuation shown in FIG. 8 and the malfunction prevention mechanism at the time of startup shown in FIG. If allowed, the technique described in the above-mentioned Patent Document 1, that is, the output voltage Vout of the power supply circuit 10 is monitored, and the time when the detected output voltage Vout drops below a predetermined voltage is measured. When the measurement result becomes equal to or higher than a certain standard, a configuration may be combined in which protection is performed assuming that a short circuit has occurred.

  FIG. 11 is a circuit block diagram showing a second embodiment of the OCP circuit shown in FIG. The OCP circuit shown in the figure is a configuration example in which malfunctions at the start-up are prevented by providing two large and small OCP levels serving as a reference for overcurrent determination.

  In the OCP circuit shown in the figure, the reference voltage Vref is connected to the non-inverting terminal of the OCP level comparator 20, and the output of the current mirror composed of the switching element SW and the transistor Tr is passed through the OCP level changeover switch 21 to the OCP level. It is connected to the inverting terminal of the comparator 20.

  Here, the OCP level changeover switch 21 is switched according to the count time of the activation timer 52, and during the period when the activation timer 52 is counting the activation time, the “1” side of the OCP level changeover switch 21 is selected, After the voltage VI1 is input to the inverting terminal of the OCP level comparator 20 and the start-up time has elapsed, the “0” side of the OCP level selector switch 21 is selected, and the voltage VI2 is input to the inverting terminal of the OCP level comparator 20 Is done.

  Since there is a relationship of “voltage VI1 <voltage VI2” between the voltage VI1 selected at the start-up time and the voltage VI2 selected after the start-up time has elapsed, the start-up time is determined to be an overcurrent as a result. The standard becomes higher, and malfunctions with output short circuits are less likely to occur. The switch element SW2 in the figure is a rectifying element that functions in the same manner as the diode D1 in FIG. 1, and any of these may be used.

  FIG. 12 is a circuit block diagram showing a third embodiment of the OCP circuit shown in FIG. The example shown in the figure is a configuration example when the connection form of the reference voltage to the OCP level comparator 20 is reversed from the example of FIG. In the example shown in the figure, two large and small reference values VI1 and VI2 are connected to the non-inverting terminal of the OCP level comparator 20 via the OCP level changeover switch 21, and the current mirror is connected to the inverting input terminal of the OCP level comparator 20. The output is connected. Even with such a configuration, similarly to FIG. 11, by setting the reference level VI1 of the startup time to be lower than the reference level VI2 after the startup time has elapsed, erroneous determination between startup and short-circuit can be suitably prevented. The

  According to the present invention, output short-circuit determination accuracy can be improved with a configuration suitable for integration, and therefore, application to a power supply circuit that requires smaller and more accurate control is expected.

1 is a circuit block diagram showing an embodiment of a power supply circuit according to the present invention. FIG. 2 is a circuit block diagram showing an embodiment of the OCP circuit shown in FIG. 1. FIG. 2 is a circuit block diagram illustrating an embodiment of a short circuit determination circuit illustrated in FIG. 1. FIG. 2 is a circuit block circuit diagram showing an embodiment of a PWM circuit shown in FIG. 1. 2 is a timing chart showing a basic operation of the power supply circuit shown in FIG. 1. 3 is a timing chart illustrating a first operation example of the power supply circuit illustrated in FIG. 1. 6 is a timing chart illustrating a second operation example of the power supply circuit illustrated in FIG. 1. 3 is a timing chart illustrating a modification setting example of the power supply circuit illustrated in FIG. 1. FIG. 9 is a timing chart illustrating an operation example of the power supply circuit illustrated in FIG. 1 in the modification setting example illustrated in FIG. 8. FIG. 5 is a circuit block diagram illustrating another configuration example of the short circuit determination circuit illustrated in FIG. 1. FIG. 3 is a circuit block diagram showing a second embodiment of the OCP circuit shown in FIG. 1. FIG. 4 is a circuit block diagram showing a third embodiment of the OCP circuit shown in FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Power supply circuit, 12 ... Control part, 14 ... PWM circuit, 16 ... OCP circuit, 18 ... Short circuit determination circuit, 19 ... Clock generation part, 20 ... OCP level comparator, 21 ... OCP level changeover switch, 22, 30 ... Mono-multi circuit, 32, 42 ... AND element, 34 ... counter, 36 ... decoder, 38 ... RS flip-flop, 44 ... NOT element, 46 ... waveform generation circuit, 50 ... OR element, 52 ... start-up timer, 100 ... battery, 102 ... Load

Claims (9)

In a power supply circuit that performs power conversion by controlling a switching element disposed between a power supply source and a load,
A clock generation circuit for generating a clock signal to be a control timing of the switching element;
A PWM circuit for controlling the switching element based on the clock signal;
An OCP circuit that detects a value of a current flowing from the power supply source toward the load, and generates an overcurrent pulse at a timing synchronized with the clock signal when the current value exceeds a predetermined reference value; ,
A short-circuit determination circuit that determines the short-circuit state of the load by counting the number of overcurrent pulses generated by the OCP circuit;
The PWM circuit controls the switching element based on an overcurrent pulse generated by the OCP circuit and a determination result of the short circuit determination circuit. In a power supply circuit that performs power conversion by controlling a switching element disposed between a power supply source and a load,
A clock generation circuit for generating a clock signal to be a control timing of the switching element;
A PWM circuit for controlling the switching element based on the clock signal;
An OCP circuit that detects a value of a current flowing from the power supply source toward the load, and generates an overcurrent pulse at a timing synchronized with the clock signal when the current value exceeds a predetermined reference value; ,
A power supply circuit comprising: a short circuit determination circuit that determines a short circuit state of the load by detecting continuity of an overcurrent pulse generated by the OCP circuit.   The short circuit determination circuit outputs a mask pulse longer than the cycle of the clock signal using the overcurrent pulse as a trigger, and detects the continuity of the overcurrent pulse by observing a level change of the mask pulse. The power supply circuit according to claim 2.   The short circuit determination circuit includes a counter that counts the number of the overcurrent pulses, and generates a reset signal of the counter by calculating a logical product of the mask pulse and the clock signal. Item 4. The power supply circuit according to Item 3.   The power supply circuit according to claim 2, wherein the short circuit determination circuit detects the continuity of the overcurrent pulse in a period other than a start-up period until the output voltage to the load is stabilized. In a power supply circuit that performs power conversion by controlling a switching element disposed between a power supply source and a load,
A clock generation circuit for generating a clock signal to be a control timing of the switching element;
A PWM circuit for controlling the switching element based on the clock signal;
An OCP circuit that detects a value of a current flowing from the power supply source toward the load, and generates an overcurrent pulse at a timing synchronized with the clock signal when the current value exceeds a predetermined reference value; ,
A power supply circuit comprising: a short circuit determination circuit that determines a short circuit state of the load by detecting a discontinuous point of an overcurrent pulse generated by the OCP circuit.   The short circuit determination circuit outputs a mask pulse longer than the cycle of the clock signal using the overcurrent pulse as a trigger, and detects a discontinuous point of the overcurrent pulse by observing a level change of the mask pulse. The power supply circuit according to claim 6.   The short circuit determination circuit includes a counter that counts the number of the overcurrent pulses, and generates a reset signal of the counter by calculating a logical product of the mask pulse and the clock signal. Item 8. The power supply circuit according to Item 7.   The power supply circuit according to claim 6, wherein the short circuit determination circuit detects a discontinuous point of the overcurrent pulse in a period other than a start-up period until an output voltage to the load is stabilized.

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