JPH05236642A - Overcurrent protecting circuit for switching regulator - Google Patents

Abstract

PURPOSE:To enhance an efficiency of a switching regulator by suppressing a power loss due to a resistor for detecting an overcurrent to a minimum limit. CONSTITUTION:In a switching regulator, an overcurrent detecting resistor 7 is inserted into a secondary side AC current line of a transformer 4 connected to a switching circuit 3, a voltage across the resistor 7 is amplified by an amplifier 12, and input to a control circuit 13 for controlling the circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection circuit in a switching regulator.

[0002]

2. Description of the Related Art In most cases, switching regulators are provided with an overcurrent protection circuit. Figure 5
An example of a conventional switching regulator and its overcurrent protection circuit is shown.

The switching regulator shown in FIG.
The switching circuit 3 is connected to the input terminals 1 and 2, and the primary winding of the transformer 4 is connected to the switching circuit 3. The anode of the diode 5 is connected to one end of the secondary winding of the transformer 4, and the cathode of the diode 5 is connected to the output terminal 10 via the coil 8. The other end of the secondary winding of the transformer 4 is connected to the output terminal 11 via the overcurrent detection resistor 7. Also,
The other end of the secondary winding of the transformer 4 is connected to the anode of the diode 6, and the cathode of the diode 6 is connected to the cathode of the diode 5. Further, capacitors 9 and 14 are provided between both ends of the resistor 7 and the output terminal 10, respectively.
Is installed. Both ends of the overcurrent detection resistor 7 are connected to the amplifier 12, and the output end of the amplifier 12 is connected to the input end of the control circuit 13 that controls the switching circuit 3. The control circuit 13 is supplied with electric power from the input terminal 1 and monitors the voltage of the output terminal 10 to control the switching duty ratio in the switching circuit 3.

In this switching regulator, the output of the switching circuit 3 is converted into a voltage by a transformer 4, and the AC power thereof is converted into a direct current through a rectifying / smoothing circuit composed of diodes 5, 6, a coil 8 and a capacitor 9. .. Further, the voltage across the resistor 7 for detecting overcurrent is amplified by the amplifier 12 and input to the control circuit 13. When an abnormality occurs in the load and an excessive current flows through the overcurrent detection resistor 7, the voltage drop of the resistor 7 is amplified by the amplifier 12.
By inputting the amplified signal to the control circuit 13,
The control circuit 13 controls the duty ratio of switching by the switching transistor in the switching circuit 3 or protects the power supply by means such as turning off the switching transistor.

[0005]

However, in this conventional overcurrent protection circuit, the overcurrent is detected by the overcurrent detection resistor 7 in the DC line, so that the power loss is large and the efficiency of the switching regulator is low. There was a problem. Further, the control system (control circuit 13) controls the duty ratio of the switching circuit 3 in accordance with the output voltage. However, when the overcurrent detection resistor 7 is provided in the DC line, the output impedance becomes high, and the output impedance becomes high. In order to secure the output stability of the above, the control system (control circuit 13) needs a sufficient dynamic range (controllable range). Therefore, in the case of multiple outputs, if the load current is changed due to the effect of the voltage drop of the resistor 7,
There is also a problem that the cross regulation in which one output fluctuates due to stabilization of one output becomes large. Further, since the resistor 7 needs to have a large power capacity, it has been an obstacle to lowering the price.

Therefore, an object of the present invention is to improve the efficiency of the switching regulator by minimizing the power loss due to the resistor for overcurrent detection, improve the cross regulation in the case of multiple outputs, and reduce the power capacity. An object of the present invention is to provide an overcurrent protection circuit for a switching regulator that can use a resistor.

[0007]

According to a first aspect of the present invention, there is provided an overcurrent protection circuit for a switching regulator, which includes an overcurrent detection resistor inserted in an alternating current line on an output side of the switching circuit of the switching regulator.
And a control circuit for controlling the switching circuit according to the voltage across the resistor.

In this overcurrent protection circuit, the current flowing through the alternating current line on the output side of the switching circuit of the switching regulator is detected by the voltage across the resistor. The control circuit detects the overcurrent from the voltage across the resistor and controls the switching circuit.

An overcurrent protection circuit for a switching regulator according to a second aspect of the present invention is the overcurrent protection circuit according to the first aspect of the invention, in which when the control circuit detects an overcurrent from the voltage across the resistor, switching of the switching circuit is prevented. The duty ratio is controlled or the switching element is turned off.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a first embodiment of the present invention. The switching regulator according to this embodiment includes a switching circuit 3 connected to the input terminals 1 and 2.
The primary winding of the transformer 4 is connected to the switching circuit 3. The anode of the diode 5 is connected to one end of the secondary winding of the transformer 4, and the cathode of the diode 5 is connected to the output terminal 10 via the coil 8. The other end of the secondary winding of the transformer 4 has an output terminal 11
It is connected to the. The anode of the diode 6 is connected to the other end of the secondary winding of the transformer 4, and the cathode of the diode 6 is connected to the cathode of the diode 5. Further, a capacitor 9 is provided between the output terminals 10 and 11.
Is installed.

In the overcurrent protection circuit of this embodiment, the overcurrent detection resistor 7 is inserted in the alternating current line between the other end of the secondary winding of the transformer 4 and the anode of the diode 6. Both ends of the resistor 7 are connected to an amplifier 12, and an output end of the amplifier 12 is connected to an input end of a control circuit 13 that controls the switching circuit 3. The voltage across the resistor 7 is amplified by the amplifier 12, and the control circuit 13
Entered in. The control circuit 13 is supplied with electric power from the input terminal 1 and monitors the voltage of the output terminal 10 to control the switching duty ratio in the switching circuit 3.

In the switching regulator of the present embodiment, the output of the switching circuit 3 is converted into a voltage by the transformer 4, and the AC power thereof is passed through the rectifying / smoothing circuit composed of the diodes 5, 6, the coil 8 and the capacitor 9. Convert to DC.

In this embodiment, when an abnormality occurs in the load and an excessive alternating current flows through the resistor 7, the overcurrent is detected by the voltage across the resistor 7. The amplifier 12 is a resistor 7
Amplifies the voltage across both terminals and sends it to the control circuit 13 as an overcurrent detection signal. When an overcurrent is detected, the control circuit 13 controls the switching duty ratio of the switching transistor of the switching circuit 3 or turns off the switching transistor to protect the power board using the switching regulator from an excessive current. To do.

As described above, according to this embodiment, since the overcurrent detecting resistor 7 is inserted in the alternating current line on the output side of the switching circuit 3, only the duty ratio of the alternating current flowing through the resistor 7 is the power. It becomes a loss, and the power supply can be made highly efficient. Further, when it is attempted to secure the same stability as that of the conventional circuit system, the impedance of the output circuit can be lowered, so that the dynamic range in the control system is less than that of the conventional one. In addition, since it is not necessary to increase the gain more than necessary, it is possible to improve the cross regulation in the case of multiple outputs. Moreover, since the power loss of the resistor 7 is reduced, a small power capacity is sufficient and the cost of the switching regulator can be reduced.

FIG. 2 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a second embodiment of the present invention. In the present embodiment, a resistor 7 is inserted between the output negative side AC line and the anode of the diode 6 to detect an overcurrent. Other configurations, actions and effects are the same as those of the first embodiment. It is similar to the embodiment.

FIG. 3 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a third embodiment of the present invention. The present embodiment is an example of an overcurrent protection circuit in a ringing choke converter type or buck-boost type switching regulator. In the switching regulator of this embodiment, two primary windings of the transformer 4 are connected to the switching circuit 3 based on the above method. Further, the diode 6 and the coil 8 on the secondary side are not provided. Other configurations, operations and effects are similar to those of the first embodiment.

FIG. 4 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a fourth embodiment of the present invention. This embodiment is an example of an overcurrent protection circuit in a switching regulator of a two-stone type such as a push-pull type. In this embodiment, the anode of the diode 5 is connected to one end of the secondary winding of the transformer 4 and the anode of the diode 6 is connected to the other end of the secondary winding.
The cathode of is connected to the output terminal 10 via the coil 8. Further, the center tap of the secondary winding of the transformer 4 is connected to the output terminal 11 via the overcurrent detection resistor 7, and the capacitor 9 is interposed between the output terminals 10 and 11. Other configurations, operations and effects are similar to those of the first embodiment.

[0019]

As described above, according to the present invention, since the resistor for detecting the overcurrent is inserted in the alternating current line on the output side of the switching circuit, only the duty ratio of the alternating current flowing through this resistor is provided. This results in power loss, and the effect of being able to improve the efficiency of the switching regulator by minimizing the power loss due to the resistor.
Also, since the output can be made low impedance, when trying to secure the same stability as the conventional one, the dynamic range is less than the conventional one and it is not necessary to increase the gain more than necessary, so multiple outputs were used. In this case, there is an effect that the cross regulation can be improved.
Further, since the power loss of the resistor is reduced, a small power capacity is sufficient, and the cost of the switching regulator can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a switching regulator and an overcurrent protection circuit thereof in a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a switching regulator and its overcurrent protection circuit in a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a switching regulator and an overcurrent protection circuit thereof in a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional switching regulator and its overcurrent protection circuit.

[Explanation of symbols]

 3 Switching circuit 4 Transformer 5, 6 Diode 7 Overcurrent detection resistor 8 Coil 9 Capacitor 12 Amplifier 13 Control circuit

Claims (2)

[Claims] 1. A resistor for overcurrent detection inserted in an alternating current line on an output side of a switching circuit of a switching regulator, and a control circuit for controlling the switching circuit according to a voltage across the resistor. An overcurrent protection circuit for a switching regulator. 2. The control circuit controls a switching duty ratio of the switching circuit or turns off a switching element when an overcurrent is detected from a voltage across the resistor. Overcurrent protection circuit for switching regulator.