JP2577315Y2 - Switching regulator - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to a switching regulator.

[0002]

2. Description of the Related Art An example of a conventional switching regulator of this type is shown in FIG. The voltage applied to the input terminal 28 is switched by the switch circuit 30, and as a result, an AC voltage is applied to the primary winding of the transistor 29. Then, the secondary winding of the transistor 29 outputs an AC voltage having a value corresponding to the winding ratio. The AC voltage is rectified by the diodes 32 and 33 and further smoothed by the choke coil 34 and the capacitor 36 to be output. The stabilizing circuit 31 is a circuit for stabilizing the output voltage. The stabilizing circuit 31 outputs a control signal based on the regulator output voltage divided by the resistors 38 and 39, and controls on / off of the switch circuit 30. Stabilize the output voltage.

The resistance 40 is for detecting the load current I, and the change in the load current detected by the resistance 40 is shown in FIG. During the TON period, the switch circuit 30 is on, and during that time, the transformer 29 is excited.
The value of the current I increases as time passes as shown in the figure. At this time, the load current flows to the load side through the diode 32. On the other hand, during the TOFF period, the switch circuit 3
0 is off. During this time, a flywheel current flows as a load current through the diode 33 due to the magnetic action of the choke coil 34. Its value decreases over time as shown in the figure. In the figure, I0 represents the average value of the load current I.

By the way, when the value of the load current falls below the minimum current value defined by the inductance of the choke coil 34 and the operation mode becomes the discontinuous mode, the control becomes impossible and the output voltage rises abnormally. I do. The electronic dummy 35 and the amplifier circuit 37 connected between the output terminals 27 are provided to prevent such an abnormal increase in the output voltage.

That is, a resistor 40 representing the value of the load current I
Are amplified by an amplifier circuit 37 and supplied to an electronic dummy 35 as a control signal. When the value of the load current I becomes equal to or less than the minimum current value, the amplification circuit 37
The output voltage of the electronic dummy also decreases accordingly, at which time the electronic dummy is turned on to prevent the output voltage from rising.

[0006]

However, in such a conventional switching regulator, the value of the load current is
Since the detection is performed by inserting the resistor 40 into the output line, power loss is caused. That is, the value of the load current is I, the resistance 4
Assuming that the value of 0 is R, the power of I ² R (W) is consumed by the resistor 40, and the power that can be supplied to the load is reduced accordingly. In other words, the current detection resistor 40 is one of the hindrance factors for increasing the efficiency of the power supply.

An object of the present invention is to solve such a problem and to provide a switching regulator in which a power loss caused by current detection is reduced.

[0008]

Means for Solving the Problems The present invention provides a transformer and
A first diode having an anode connected to one end of a secondary winding of the transformer, a second diode having a cathode connected to a cathode of the diode, and a choke coil, wherein the first and second diodes include Circuit for smoothing a voltage generated between the cathode of the transformer and the other end of the secondary winding of the transformer, a switch circuit for switching a voltage applied to a primary winding of the transformer, and the switch circuit A stabilizing circuit that controls the regulator output voltage based on the regulator output voltage, an electronic dummy that is connected to an output terminal of the smoothing circuit and reduces the regulator output voltage when a predetermined control signal is input, and a magnitude of a load current. And a control circuit that outputs the control signal to the electronic dummy based on a voltage corresponding to The anode of said second diode is connected between the other end of the secondary winding of the transformer, a voltage representative of the current flowing through the second diode,
Current control means for outputting a voltage corresponding to the magnitude of the load current to the control circuit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a switching regulator according to the present invention. One end of the primary winding of the transformer 2 is connected to one input terminal 14, and the other end is connected to the other input terminal 15 through the switch circuit 3. One end of the secondary winding of the transistor 2 electromagnetically coupled to the primary winding of the transistor 2 is connected to the anode of the diode 5, and the other end is connected to one output terminal 17. The cathode of the diode 6 is connected to the cathode of the diode 5, and a current detecting resistor 7 is connected between the anode of the diode 6 and the terminal 17. Choke coil 8 for smoothing
Is connected between the cathodes of the diodes 5 and 6 and the output terminal 16. Similarly, the smoothing capacitor 11 is connected to the output terminal 1.
It is connected between 6 and 17. Output voltage detection resistor 1
2 and 13 are connected in series between the terminals 16 and 17, and the connection point of both resistors is connected to the input terminal of the stabilizing circuit 4. The stabilizing circuit 4 controls on / off of the switch circuit 3 based on the input voltage, and stabilizes the output voltage. An electronic dummy 9 for preventing an output voltage from rising abnormally is connected between the output terminals 16 and 17, and its control signal is supplied from an amplifier circuit 10. The amplification circuit 10 amplifies the voltage between both ends of the resistor 7 and
Is supplied with the control signal.

The amplifier circuit 10 has a configuration as shown in FIG. Operational amplifier 42, resistors 41 and 4
3. The capacitor 45 forms an amplifier circuit having the function of a low-pass filter. The non-inverting input terminal of the amplifier 42 is connected to the connection point between the resistor 7 and the diode 6, and the non-inverting input terminal and the inverting input terminal. Resistor 41 between terminals
Is connected between the inverting input terminal and the output terminal.
3 and the capacitor 45 are connected in parallel. The operational amplifier 48, the resistors 46 and 49, and the reference voltage source 47 constitute a comparator. A resistor 49 is connected between the non-inverting input terminal and the output terminal of the amplifier 48, and is connected between the non-inverting input terminal and the ground. , A resistor 46 and a power supply 47 are connected in series. The inverting input terminal of the amplifier 48 is connected to the output terminal of the operational amplifier 42, and the output terminal of the amplifier 48 is connected to the electronic dummy 9.

In the switching regulator of this embodiment having the above-described configuration, the resistor 7 and therefore the diode 6, as shown in FIG. 3, supply the load current only during the TOFF period when the switch circuit 3 is off. , A flywheel current flows due to the magnetic action of the choke coil 8.

Therefore, the amplifier circuit 10 has a load current Id
, And a voltage having the same waveform as the waveform of FIG. 3 is input. In the amplifier circuit 10, the operational amplifier 42
Amplifying circuit composed of an amplifier amplifies the input voltage and amplifies it to a predetermined level, and a comparator comprising an operational amplifier 48 converts the amplified voltage into a power supply 47 and an output voltage of the amplifier 48 by resistors 46 and 49. And the voltage is compared with the determined voltage. If the former exceeds the latter, the load current falls below the minimum current value described above, and a low-level voltage is output to turn on the electronic dummy 9, thereby suppressing an increase in the output voltage.

As described above, in the switching regulator of this embodiment, since the resistor 7 for detecting the load current is connected in series with the diode 6, the resistor 7 is connected to the resistor 7 during the period when the switch circuit 3 is off. The current flows only in
Therefore, power loss due to the current flowing through the resistor 7 occurs only during that period. Therefore, assuming that the period during which the switch circuit 3 is on is equal to the period during which the switch circuit 3 is off, the power loss is approximately half that in the related art. Further, since the voltage detected by the resistor 7 is an AC voltage, amplification in the amplifier circuit 10 is easy. As a result, even if the value of the resistor 7 is reduced, the electronic dummy 9 can be operated sufficiently.
Therefore, the power loss due to the resistor 7 can be further reduced.

Next, another embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. This switching regulator is different from the switching regulator of FIG.
Is that a current transformer 26 is used instead of the current transformer 26. That is, the primary winding of the current transformer 26 is inserted between the anode of the diode 6 and the terminal 17, and
A resistor 27 is connected between both terminals of the next winding, and the amplifier circuit 1
0 is designed to take in the voltage across the resistor 27 as a voltage representing the load current. In this case, what is connected in series with the diode 6 is the primary winding of the transformer 26, the resistance of which is much smaller than the resistance 7, and the power loss is extremely small.

[0015]

As described above, the present invention provides a transformer, a first diode having an anode connected to one end of a secondary winding of the transformer, and a second diode having a cathode connected to a cathode of the diode. And a smoothing circuit including a choke coil, for smoothing a voltage generated between the cathodes of the first and second diodes and the other end of the secondary winding of the transformer, and a primary winding of the transformer. A switch circuit for switching an applied voltage, a stabilizing circuit for controlling the switch circuit based on a regulator output voltage, and a regulator circuit connected to an output terminal of the smoothing circuit and receiving a predetermined control signal. An electronic dummy for reducing the voltage; and a control circuit for outputting a control signal to the electronic dummy based on a voltage corresponding to the magnitude of the load current. In the switching regulator, a voltage that is connected between the anode of the second diode and the other end of the secondary winding of the transformer and represents a current flowing through the second diode corresponds to a magnitude of the load current. A current detection means for outputting a voltage to the control circuit is provided.

Therefore, in the switching regulator of the present invention, when a resistor is used as the current detecting means, the current flows through the resistor only during a period in which the switch circuit is off. The power loss caused by this is about half that of the conventional case. Further, since the detection voltage by the resistor is an alternating current, it is easy to amplify the detection voltage in the control circuit. As a result, even if the resistance value is reduced, the electronic dummy can be operated sufficiently. Therefore, the power loss due to the resistance can be further reduced.

Further, when a current transformer is used in place of the resistor as the current detecting means, what is connected in series with the second diode is a primary winding of the current transformer, and the resistance value is smaller than that of the resistor. Since it is much smaller, the power loss is very small.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a switching regulator according to the present invention.

FIG. 2 is a circuit diagram showing in detail an amplifier circuit constituting the switching regulator of FIG. 1;

FIG. 3 is a graph showing a current flowing through a resistor for detecting a load current in the switching regulator of FIG. 1;

FIG. 4 is a circuit diagram showing another example of the switching regulator according to the present invention.

FIG. 5 is a circuit diagram showing an example of a conventional switching regulator.

FIG. 6 is a graph showing a current flowing through a resistor for detecting a load current in the switching regulator of FIG. 5;

[Explanation of symbols]

 2 Transformer 3 Switch circuit 4 Stabilization circuit 5, 6 Diode 7, 12, 13, 41, 43, 46, 49 Resistance 8 Choke coil 9 Electronic dummy 10 Amplification circuit 11 Capacitor 14, 15 Input terminal 16, 17 Output terminal 42, 48 Operational amplifier 47 Reference voltage source

Claims (1)

(57) [Scope of request for utility model registration] A transformer, a first diode having an anode connected to one end of a secondary winding of the transformer, a second diode having a cathode connected to a cathode of the diode, and a choke coil. The first and second
A smoothing circuit for smoothing a voltage generated between the cathode of the diode and the other end of the secondary winding of the transformer; a switch circuit for switching a voltage applied to a primary winding of the transformer; A stabilizing circuit that controls the switch circuit based on a regulator output voltage, an electronic dummy connected to an output terminal of the smoothing circuit, and configured to reduce the regulator output voltage when a predetermined control signal is input; A switching regulator comprising: a control circuit that outputs the control signal to the electronic dummy based on a voltage corresponding to a magnitude; an anode of the second diode;
Current detecting means connected to the other end of the next winding and outputting a voltage representing a current flowing through the second diode to the control circuit as a voltage corresponding to the magnitude of the load current; A switching regulator characterized by the above-mentioned.