JP4109502B2 - Step-down chopper regulator circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a step-down chopper regulator circuit, and more particularly to a step-down chopper regulator provided with an overcurrent protection circuit when an output is short-circuited.
[0002]
[Prior art]
FIG. 3 is a circuit diagram of a step-down chopper regulator circuit using a conventional five-terminal step-down switching regulator IC 2 (Sanken SI-8050S; the circuit configuration is shown in FIG. 4). 1) Vin, switching output terminal (2) SWout, ground terminal (3) GND, output detection terminal (4) Vos, soft start terminal (5) S. A five-terminal step-down switching regulator IC 2 having five terminals S is connected between the positive side of the DC power source 1 and the choke coil 7, and the input terminal {circle around (1)} Vin is connected to the positive side of the DC power source 1. (1) The first capacitor 3 is connected between Vin and the negative side of the DC power source, and the switching output terminal (2) The connection point of the SWout / choke coil 7 and the negative side of the DC power source 1 are connected to the first diode. 6, ground terminal (3) GND is connected to the negative side of DC power supply 1, soft start terminal (5) S.M. The second capacitor 4 is connected between S and the negative electrode side of the DC power source 1, and the output detection terminal (4) Vos is connected to the output side of the choke coil 7, and between the output side and the negative electrode side of the DC power source 1. And a third capacitor 5 is connected.
[0003]
In the above circuit, the output detection terminal (4) Vos of the 5-terminal step-down switching regulator IC2 is connected to the connection point between the choke coil 7 and the positive electrode of the third capacitor 5, and the output voltage and the reference voltage in the IC2 are And a feedback signal is given from the output of the error amplifier to the comparator in the IC2. The signal is compared with the signal from the oscillator in the IC2, and H (high) and L (low) signals are given to the base of the NPN transistor at the switching output terminal {circle around (2)} to output a constant output voltage. Such switching duty is determined.
Here, soft start terminal (5) The second capacitor 4 connecting S to the ground terminal (3) GND is used to stop the function of the comparator by dropping the output of the internal power source for driving the comparator in the IC 2 to L (low) at the time of activation. Used for.
When the second capacitor 4 is charged, the function of the comparator operates and a soft start is performed.
[0004]
In the above circuit, when an overcurrent state occurs, the overcurrent protection function operates on the collector side of the NPN transistor in the IC2 connected to the switching output terminal (2) SWout in the 5-terminal step-down switching regulator IC2, The relationship between the oscillator signal applied to the comparator in the IC 2 and the output of the error amplifier is as shown in the timing chart of FIG. 8B, and the duty of H (high) and L (low) is changed. That is, when a normal current of Iout = I ₁ (0 <I ₁ <I ₂ ) flows, as shown in the timing chart of FIG. 8A, a constant output voltage V ₁ is output. While controlling the Duty constant when the overcurrent state of Iout = I _2, as shown in the time chart of FIG. 8 (b), sends a signal pulse width on the above IC2 internal oscillator is reduced, the The voltage supplied to the load 8 starts to decrease by reducing the ON pulse width output from the switching output terminal (2) SWout of the IC2.
However, as shown in the time chart of FIG. 8B, even if the output voltage becomes 0V, the internal power supply in the IC 2 remains on and the comparator is operated, so that the oscillation does not stop and is short-circuited. There is a problem that the current I ₂ continues to flow, the choke coil generates heat, and is in a dangerous state.
[0005]
[Problems to be solved by the invention]
As described above, the conventional step-down chopper regulator circuit is not provided with means for stopping the oscillation of the five-terminal step-down switching regulator IC2 when an overcurrent state occurs, and even when the output voltage becomes 0V. , current shows the drooping characteristic as shown in FIG. 6, because of a problem of short-circuit current I ₂ continues to flow, the circuit configuration capable of stopping the oscillation of the IC2 has been required.
[0006]
[Means for Solving the Problems]
The present invention solves the above-described problems, and includes an input terminal (1) Vin, a switching output terminal (2) SWout, a ground terminal (3) GND, an output detection terminal (4) Vos, and a soft start terminal (5). S. A comparator with 5 terminals of S and an overcurrent protection function , driven by an internal power supply, compares the feedback signal from the output detection terminal (4) Vos with the signal from the oscillator, and the switching output terminal (2) SWout 5 terminal step-down switching regulator IC2 outputs a constant output voltage from the connected between the positive pole and the choke coil 7 of the DC power source 1, an input terminal to the positive side of the DC power source 1 (1) to Vin, the input The first capacitor 3 is connected between the terminal and the negative side of the DC power source, and the connection point of the switching output terminal (2) SWout / choke coil 7 and the negative side of the DC power source 1 are connected by the first diode 6. Connect the ground terminal (3) GND to the negative side of the DC power supply 1 and the soft start terminal (5) S.M. A second capacitor 4 is connected between S and the negative electrode side of the DC power source 1, and the output detection terminal (4) Vos is connected to the output side of the choke coil 7, between the output side and the negative electrode side of the DC power source 1. In the step-down chopper regulator circuit configured by connecting the third capacitor 5 to the
A PNP transistor 9 is connected in parallel with the second capacitor, and a soft start terminal (5) S.P. S is connected to the fourth capacitor 10 between the base and the emitter, the negative electrode side of the DC power supply 1 is connected to the collector, and the base and the output side of the choke coil 7 are connected by the second diode 11 or the resistor 12. The five-terminal step-down switching regulator IC2 detects the overcurrent state from the output detection terminal (4) Vos and operates the overcurrent protection function from the switching output terminal (2) SWout. When the voltage of the third capacitor 5 drops below the anode voltage of the second diode 4, the second diode 4 becomes conductive and the PNP transistor 9 is turned on, whereby the soft start terminal (5) S.M. The step-down chopper regulator circuit is characterized in that S is grounded to the negative electrode side, the internal power supply and the oscillator are stopped, and the output from the switching output terminal (2) SWout is turned off .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, a five-terminal step-down switching regulator IC 2 is connected between the positive electrode side of the DC power source 1 and the choke coil 7, and each terminal, the first capacitor 3, the second capacitor 4, and the first diode. 6, a PNP transistor 9 is connected in parallel with the second capacitor 4, and the soft start terminal {circle over (5)} is connected to the emitter of the PNP transistor 9. S is connected to the fourth capacitor 10 between the base and the emitter, the negative electrode side of the DC power supply 1 is connected to the collector, and the base and the output side of the choke coil 7 are connected by the second diode 11 or the resistor 12. Thus, an overcurrent protection circuit is configured.
In the overcurrent protection circuit, when the voltage of the third capacitor 5 drops below the anode voltage of the second diode 11 in the overcurrent state, the second diode 11 becomes conductive, so that the PNP transistor 9 Is turned on and the soft start terminal (5) S conducts to the ground side. As a result, the output of the five-terminal step-down switching regulator IC2 is turned off, no short-circuit current flows, and the choke coil can be prevented from generating heat. Therefore, the safety of the circuit device can be improved without increasing the rated current value and size specification of the choke coil.
[0008]
【Example】
The step-down chopper regulator circuit according to the embodiment of the present invention is different from the conventional example in that the overcurrent protection circuit is configured. The circuit operation will be described below with reference to the output voltage-output current characteristic diagram of FIG. 5 and the timing chart of FIG.
When the current flowing through the load 8 in FIG. 1 increases and enters an overcurrent state (I = I ₂ ), the current detection function inside the 5-terminal step-down switching regulator IC2 detects the overcurrent as described above. In FIG. 5, when the voltage supplied to the load 8 starts to decrease and decreases to V ₂ , the base current of the PNP transistor 9 flows through the diode 11 of FIG. 1, and the impedance between the emitter and collector of the transistor 9 begins to decrease, Soft start terminal (5) The voltage between S and ground also begins to drop. Soft start terminal (5) As shown in the timing chart of FIG. 7A, S (capacitor 4 connection) maintains a certain voltage V ₁ during normal oscillation, and this voltage V ₁ and the reference voltage inside the IC 2 are compared with each other. Compare by. In the normal state, the output of the comparator remains H (high) without being inverted, but when an overcurrent state occurs, it decreases from V ₁ to V ₂ as shown in the timing chart of FIG. 7B. Since the output of the comparator is inverted and becomes L (low), the internal power supply of the IC2 is turned off, the internal oscillator is also turned off, the oscillation of the IC2 is stopped, and the internal switching output terminal (2) SWout is completely turned off, and the short-circuit current flowing through the load 8 can be reduced to zero.
Here, the fourth capacitor 10 connected between the base and the emitter of the transistor 9 is for preventing the transistor 9 from being turned on at the start-up and malfunctioning.
By configuring the circuit as described above, the short-circuit current flowing through the load 8 can be reduced to 0, and the choke coil 7 can also be rated current: 5 A and size: φ10 × 5 L in the embodiment. Compared with the rated current of the example: 8A, size φ15 × 8L, it was possible to significantly improve.
Further, in FIG. 2 as a second embodiment, a resistor 12 is connected instead of the second diode 11 (the resistance value corresponds to the anode resistance of the second diode 11), but the same effect as described above is obtained. Obtained.
[0009]
【The invention's effect】
In the present invention, when the circuit is configured as described above, since the oscillation of the five-terminal step-down switching regulator IC2 is completely stopped when an overcurrent state occurs, the short-circuit current flowing through the load 8 becomes zero. The safety of the apparatus can be improved, and parts with a small rated current and size specification can be used.
[Brief description of the drawings]
FIG. 1 is a circuit diagram using a diode in a step-down chopper regulator circuit according to an embodiment of the present invention.
FIG. 2 is a circuit diagram using a resistor in a step-down chopper regulator circuit according to another embodiment of the present invention.
FIG. 3 is a circuit diagram of a conventional step-down chopper regulator circuit.
4 is a circuit diagram of the conventional step-down chopper regulator circuit of FIG. 3 describing a circuit configuration of a five-terminal step-down switching regulator IC2. FIG.
FIG. 5 is a characteristic diagram showing a relationship between output voltage and output current in the step-down chopper regulator circuit according to the embodiment of FIG. 1;
6 is a characteristic diagram showing a relationship between output voltage and output current in the step-down chopper regulator circuit according to the conventional example of FIG.
7 is a timing chart of circuit operation in the step-down chopper regulator circuit according to the embodiment of FIG. 1; FIG.
FIG. 8 is a timing chart of circuit operation in the step-down chopper regulator circuit according to the conventional example of FIG. 3;
[Explanation of symbols]
1 DC power supply 2 5-terminal step-down switching regulator IC
3 1st capacitor 4 2nd capacitor 5 3rd capacitor 6 1st diode 7 choke coil 8 load 9 PNP transistor 10 4th capacitor 11 2nd diode 12 resistance

Claims (1)

A comparator with 5 terminals of an input terminal, a switching output terminal, a ground terminal, an output detection terminal, a soft start terminal and an overcurrent protection function , driven by an internal power supply, and a feedback signal from the output detection terminal and an oscillator A five-terminal step-down switching regulator IC that compares a signal and outputs a constant output voltage from the switching output terminal is connected between the positive side of the DC power source and the choke coil, and the input terminal is connected to the positive side of the DC power source. The first capacitor is connected between the input terminal and the negative side of the DC power source, the connection point of the switching output terminal / choke coil and the negative side of the DC power source are connected by the first diode, and the ground terminal is connected. Connect to the negative side of the DC power supply, connect a second capacitor between the soft start terminal and the negative side of the DC power supply, and connect the output detection terminal. The output side of the Yokukoiru, in a third step-down chopper regulator circuit constituted by connecting a capacitor between the negative electrode side of the output-side DC power supply,
A PNP transistor is connected in parallel with the second capacitor, a soft start terminal is connected to the emitter of the PNP transistor, a fourth capacitor is connected between the base and the emitter, a negative side of the DC power supply is connected to the collector, and the base and Connect the output side of the choke coil with a second diode or resistor to form an overcurrent protection circuit ,
When the five-terminal step-down switching regulator IC detects an overcurrent state from the output detection terminal, it operates an overcurrent protection function to reduce the output voltage from the switching output terminal,
When the voltage of the third capacitor drops below the anode voltage of the second diode, the second diode is turned on, and the PNP transistor is turned on, so that the soft start terminal is grounded to the negative side. ,
A step-down chopper regulator circuit, wherein the internal power supply and the oscillator are stopped to turn off the output from the switching output terminal .

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