JP2004229407A - Power supply circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a power supply circuit in which a load is protected surely by performing load protection control quickly. <P>SOLUTION: A circuit for monitoring the output voltage and performing overcurrent protection is formed independently from a switching element for interruption and a feedback line to that circuit is provided between the switching element for interruption and the load. Consequently, load protection control is performed quickly and the load is protected surely. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit, and more particularly to a power supply circuit that performs output voltage control.
[0002]
[Prior art]
In a power supply circuit that controls output voltage, for example, a boost type power supply circuit, there is known an example in which a switching element for blocking is provided between an input and an output in order to prevent a short-circuit current from flowing when a load is short-circuited (for example, And Patent Document 1).
[0003]
In this power supply circuit, as shown in FIG. 2, an output voltage is detected using a resistor R100 and a resistor R200 at a connection point S on the input side of the switching element Q200, and the switching element Q100 is changed based on the detection result. The output voltage is controlled to a constant value (boost control) by turning on / off.
[0004]
In the power supply circuit, the detection result of the output voltage at the connection point S is also input to the abnormality detection unit 130, and when the abnormality detection unit 130 detects an abnormality due to a load short circuit, the switching element Q200 is connected via the switch control unit 120. It is turned off and the input side and the output side are shut off so that no short-circuit current flows.
[0005]
[Patent Document 1]
JP 2001-327067 A (FIG. 2)
[0006]
[Problems to be solved by the invention]
However, in the conventional power supply circuit as shown in the above-described example, when a voltage drop due to a load short-circuit occurs, the boosting coil L100 and the switching element Q100 perform a boosting control and continue to pass a current. Since the element Q2 acts as a delay element, the voltage at the detection point S does not drop immediately even if a load voltage drop occurs. Therefore, there is a possibility that a time delay occurs between the time when the load short circuit occurs and the time when the abnormality detection circuit detects the abnormality and the switching element Q200 is turned off, and an overcurrent due to the short circuit flows to the load and damages the load.
[0007]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power supply circuit that quickly controls load protection and reliably protects a load.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a power supply circuit according to the present invention described in claim 1 includes a boost control unit that boosts an input DC voltage to a predetermined voltage and supplies the boosted voltage to a load, the boost control unit, A switch unit that is provided in series with a load and is in a conductive state or a non-conductive state, and in the conductive state, supplies the output voltage of the boost control unit to the load, and in a non-conductive state A voltage at a connection point between the switch unit and the load, a switch unit that does not supply the output voltage of the boost control unit to the load, a switch control unit that controls the switch unit to a conductive state or a non-conductive state And when the voltage does not exceed a predetermined threshold value, the switch unit is held in a conductive state via the switch control unit, and when the voltage exceeds a predetermined threshold value, Above Via the switch control unit is characterized by and a monitor protection controller for stopping the operation of the boosting control unit controls the switching unit in a non-conductive state.
[0009]
In the first aspect of the present invention, the boost control unit boosts the input DC voltage to a predetermined voltage and supplies the boosted voltage to the load. The monitoring protection control unit detects a voltage at a connection point between the switch unit and the load, and compares the voltage with a predetermined threshold value. One or more threshold values can be set as the threshold value.
[0010]
The monitoring protection control unit holds the switch unit in a conductive state via the switch control unit when the voltage does not exceed a predetermined threshold value, and the voltage exceeds the predetermined threshold value. When this occurs, the switch unit is controlled to be in a non-conductive state via the switch control unit and the operation of the boost control unit is stopped. Here, since the voltage at the connection point used for the comparison by the monitoring control unit is between the switch unit and the load, the voltage at the connection point immediately drops when the voltage drop of the load occurs.
[0011]
For this reason, when a voltage fluctuation exceeding the threshold occurs, such as a voltage drop due to a short circuit of the load, the operation of the boost control unit is immediately stopped, and the switch unit is immediately controlled to be in a non-conducting state so that the input side and the output Since the side is cut off, overcurrent can be prevented from flowing to the load.
[0012]
In this way, the load protection can be controlled quickly and the load can be reliably protected.
[0013]
According to a second aspect of the present invention, in the first aspect of the invention, the monitoring protection control unit includes a threshold setting unit that sets the threshold, and the threshold is the load It is characterized by being set to a predetermined value for monitoring an abnormal change in the voltage supplied to.
[0014]
In the invention according to claim 2, the threshold value setting unit sets the threshold value to a predetermined value for monitoring an abnormal change in the voltage supplied to the load. That is, it is possible to set a threshold value in consideration of the assumed voltage fluctuation range of the load and the magnitude of the voltage drop.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a power supply circuit according to the present invention will be described in detail with reference to the accompanying drawings.
[0016]
FIG. 1 shows a configuration of a step-up power supply circuit 10 to which the present exemplary embodiment is applied. The step-up power supply circuit 10 includes an input terminal Tin, an output terminal Tout, a coil L1, a diode D, a capacitor C, a resistor R1, a resistor R2, a switching transistor Q1, a coil L2, a switching transistor Q2, an operational amplifier 12, and a reference power supply 14. , A drive circuit 16, a switch control unit 18, and a monitoring protection circuit control unit 20.
[0017]
The DC voltage input from the input terminal Tin is supplied to the load via the coil L1, the diode D, the coil L2, the transistor Q2, and the output terminal Tout.
[0018]
One end of the capacitor C is connected to the diode D and the coil L2, and the other end is grounded. The other end of the coil L2 is connected to the switching transistor Q2.
[0019]
The resistor R1 and the resistor R2 are connected in series, the other end of the resistor R1 is connected to the capacitor C and the coil L2, and the other end of the resistor R2 is grounded.
[0020]
One input terminal of the operational amplifier 12 is supplied with a voltage at a connection point A between the resistors R1 and R2 (hereinafter referred to as a detection voltage), and the other input terminal is supplied with a voltage (reference voltage 14). (Hereinafter referred to as a reference voltage). The operational amplifier 12 amplifies the difference between the detection voltage and the reference voltage and outputs it to the drive circuit 16.
[0021]
The reference voltage may be set according to the voltage supplied to the load.
[0022]
The drive circuit 16 continuously generates a pulse wave having a duty (= pulse on time / pulse period) according to the output of the operational amplifier 12 at a constant period. When this pulse is on, the switching circuit Q1 is turned on. When the pulse is off, the switching transistor Q1 is turned off.
[0023]
The monitoring protection circuit control unit 20 is configured to be able to set one or more threshold values. As this threshold value, one value may be set, or a plurality of values such as an upper limit value and a lower limit value in consideration of the voltage fluctuation range of the load may be set.
[0024]
The monitoring protection circuit control unit 20 is supplied with a voltage at a connection point P between the switching transistor Q2 and the load (hereinafter referred to as a connection point voltage). The monitoring protection circuit control unit 20 compares the connection point voltage with the above-described threshold value, and when the connection point voltage does not exceed the threshold value, holds the switching transistor Q2 on via the switch control unit 18 to connect When the point voltage exceeds the threshold value, the switching transistor Q2 is turned off via the switch control unit 18.
[0025]
Next, the operation of the above embodiment will be described.
[0026]
When the switching transistor Q1 is turned on by the output of the drive circuit 16, a current flows through the coil L1. When a predetermined time (on time of the pulse wave generated by the drive circuit 16) elapses, the drive circuit 16 turns off the switching transistor Q1. As a result, the current flowing through the coil L1 changes to generate an electromotive force, and a voltage corresponding to the sum of the input voltage and the electromotive force of the coil L1 is supplied to the load side.
[0027]
When the switching transistor Q1 is turned off, the output voltage decreases with time, but when the predetermined time (pulse off time) elapses, the pulse is turned on again, and the above operation is repeated to boost the input voltage. Is done.
[0028]
The step-up power supply circuit 10 can step up the voltage thus input to a predetermined value and hold it.
[0029]
In addition, current flows through the diode D to the load side, and charges are accumulated in the capacitor C. When a large current flows through the load, the current supplied to the input terminal Tin may be insufficient. However, at this time, the charge accumulated in the capacitor C is discharged, so that the insufficient current can be compensated. . The step-up power supply circuit 10 smoothes the output current by the capacitor C and the coil L2.
[0030]
When the connection point voltage does not exceed the threshold value, the monitoring protection circuit control unit 20 holds the switching transistor Q2 on via the switch control unit 18. As a result, the voltage boosted to the predetermined value is supplied to the load, and a current flows to the load.
[0031]
Further, with respect to the boosted voltage, a voltage is detected at the connection point A by the resistors R1 and R2, and the voltage is input to the operational amplifier 12 as a detected voltage. The operational amplifier 12 compares the detected voltage with the reference voltage, amplifies the difference between the detected voltage and the reference voltage, and outputs the amplified voltage to the drive circuit 16.
[0032]
When the detected voltage falls below the reference voltage, the drive circuit 16 determines the duty of the on / off operation of the switching transistor Q1 (= on time ÷ operation) according to the output of the operational amplifier 12, that is, the difference between the detected voltage and the reference voltage. (Period). For example, when the detection voltage is larger than the reference voltage, the duty of the on / off operation of the switching transistor Q1 is lowered so that the output voltage becomes smaller. Conversely, when the detection voltage is smaller than the reference voltage, the switching transistor Q1 The duty of ON / OFF operation is increased to increase the output voltage.
[0033]
As described above, the step-up power supply circuit 10 can supply the necessary voltage to the load even when the voltage fluctuates by changing the duty of the on / off operation of the switching transistor Q1.
[0034]
The output voltage (connection point voltage) is also detected at the connection point P between the switching transistor Q2 and the load, and is input to the monitoring protection circuit control unit 20. The monitoring protection circuit control unit compares the input connection point voltage with the above-described threshold value, and controls the switching transistor Q2 and the drive circuit 16 as shown below based on the comparison result. Although there is a time lag from when the voltage of the load fluctuates until the voltage at the connection point S fluctuates, the voltage at the connection point P fluctuates immediately.
[0035]
When the connection point voltage does not exceed the threshold value, the monitoring protection circuit control unit 20 holds the switching transistor Q2 on via the switch control unit 18, and the voltage fluctuates beyond the expected range due to a short circuit of the load or the like. When the connection point voltage exceeds a threshold value, the monitoring protection circuit control unit 20 stops the operation of the drive circuit 16 and turns off the switching transistor Q2 via the switch control unit 20 to thereby turn off the power supply circuit. Between the load and the load so that no overcurrent flows through the load.
[0036]
As described above, since the boosting power supply circuit 10 performs control based on the connection point voltage, it is possible to quickly control load protection and to reliably protect the load.
[0037]
As described above, the step-up power supply circuit 10 to which the present exemplary embodiment is applied boosts the input voltage to a predetermined voltage, holds it, supplies it to the load, and causes a voltage fluctuation of the load. But the necessary voltage can be supplied to the load.
[0038]
Further, the boost type power supply circuit 10 can quickly control the load protection even when a large voltage fluctuation occurs due to a load short circuit or the like, and can reliably protect the load.
[0039]
The power supply circuit according to the present invention is not based on the connection of a specific load, and can be applied to a load in general that requires boosting of the input voltage. However, a small input voltage is required for the load. Since the voltage is boosted and output, it is particularly effective for handy devices, such as mobile phones, compact cameras, digital cameras, video cameras, etc., that receive a small voltage equivalent to about one to two dry batteries.
[0040]
When the power supply circuit of the present invention is used for such a device, the input voltage is about 1.5 to 3.6 V, and the input voltage is boosted to about 5 V and output. If the voltage fluctuation range assumed by the device, for example ± 0.1 V, is used as a threshold for this output voltage, the monitoring protection control unit will immediately start if the voltage fluctuates beyond this range due to a short circuit or the like. The boost control unit is stopped and the switch unit is turned off (off) to shut off the input and output, thereby protecting the device.
[0041]
【The invention's effect】
As described above, according to the power supply circuit of the present invention, the load protection can be quickly controlled and the load can be reliably protected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a boost type power supply circuit according to an embodiment of the present invention.
FIG. 2 is a configuration diagram showing an example of a conventional boost type power supply circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Boost type power supply circuit, 12 ... Operational amplifier, 14 ... Reference power supply, 16 ... Drive circuit, 18 ... Switch control part, 20 ... Monitoring protection circuit control part, Tin * ..Input terminal, Tout ... output terminal, L1 and L2 ... coil, Q1 and Q2 ... switching transistor, D ... diode, C ... capacitor, R1 and R2 ... resistor, P and A ... Connection point

Claims (2)

A boost control unit that boosts an input DC voltage to a predetermined voltage and supplies the boosted voltage to a load;
A switch unit that is provided in series between the boost control unit and the load and is in a conductive state or a non-conductive state, and supplies the output voltage of the boost control unit to the load in the conductive state And a switch unit that does not supply the output voltage of the boost control unit to the load in a non-conductive state;
A switch control unit for controlling the switch unit to a conductive state or a non-conductive state;
Detecting a voltage at a connection point between the switch unit and the load, and when the voltage does not exceed a predetermined threshold, holding the switch unit in a conductive state via the switch control unit, A monitoring protection control unit for controlling the switch unit to be in a non-conductive state via the switch control unit and stopping the operation of the boost control unit when the voltage exceeds a predetermined threshold;
A power supply circuit comprising: The monitoring protection control unit includes a threshold value setting unit that sets the threshold value, and the threshold value is set to a predetermined value for monitoring an abnormal change in voltage supplied to the load. The power supply circuit according to claim 1.

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