JPH0560180U - Switching regulator - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the power loss caused by the detection of load current. [Structure] A flywheel current due to the magnetic action of the choke coil 8 flows through the resistor 7, and thus the diode 6, as a load current only while the switch circuit 3 is off. Then, the voltage representing the magnitude of the load current is input to the amplifier circuit 10. The amplifier circuit 10 smoothes the input voltage, amplifies it to a predetermined level, and compares the voltage value with a predetermined reference voltage to generate a control signal for the electronic dummy 9. Based on the control signal, the electronic dummy 9 turns on when the load current falls below a certain value, and prevents the output voltage from rising abnormally. In this circuit, the resistor 7 has a switch circuit 3
Since the current flows only during the period when the switch is off, the power loss occurs only during that period, and as a result, the power loss becomes about half of the conventional value.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a power supply device, and more particularly to a switching regulator.

[0002]

[Prior 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, smoothed by the choke coil 34 and the capacitor 36, and output. The stabilizing circuit 31 is a circuit for stabilizing the output voltage, and outputs a control signal based on the regulator output voltage divided by the resistors 38 and 39 to control ON / OFF of the switch circuit 30. Therefore, the output voltage is stabilized.

The resistor 40 is for detecting the load current I, and FIG. 6 shows changes in the load current detected by the resistor 40. During the period of TON, the switch circuit 30 is on, and the transformer 29 is excited during that period, so that the value of the current I rises with the passage of time as shown in the figure. At that time, the load current flows to the load side through the diode 32. On the other hand, during the period of TOFF, the switch circuit 30 is off, and during that time, a flywheel current flows as a load current through the diode 33 by the magnetic action of the choke coil 34. Its value decreases with 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 becomes less than the minimum current value determined by the inductance of the choke coil 34 and the discontinuous mode operation state occurs, the output voltage becomes abnormal due to the uncontrollable state. Rise to. The electronic dam 35 and the amplifier circuit 37 connected between the output terminals 27 are provided to prevent such an abnormal rise in the output voltage.

That is, the voltage across the resistor 40 representing the value of the load current I is amplified by the amplifier circuit 37 and supplied to the electronic dummy 35 as a control signal. Then, when the value of the load current I 2 becomes equal to or less than the minimum current value, the output voltage of the amplifier circuit 37 also decreases accordingly, and at that time, the electronic dummy is turned on to prevent the output voltage from rising.

[0006]

[Problems to be solved by the device]

However, in such a conventional switching regulator, the value of the load current is detected by inserting the resistor 40 in the output line, which causes power loss. That is, assuming that the value of the load current is I and the value of the resistor 40 is R, the power of I ² R (W) is consumed by the resistor 40, and as a result, the power that can be supplied to the load decreases. That is, the resistance 40 for current detection is one of the factors that hinder the efficiency improvement of the power supply.

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

[0008]

[Means for Solving the Problems]

 The present invention includes a transformer, a first diode whose anode is connected to one end of a secondary winding of the transformer, a second diode whose cathode is connected to the cathode of the diode, and a choke coil. A smoothing circuit for smoothing the voltage generated between the cathodes of the first and second diodes and the other end of the secondary winding of the transformer, and the voltage applied to the primary winding of the transformer A switch circuit for switching, a stabilizing circuit for controlling the switch circuit based on the regulator output voltage, and the output terminal of the smoothing circuit are connected, and when a predetermined control signal is input, the regulator output voltage is reduced. And a control circuit that outputs the control signal to the electronic dummy based on the voltage corresponding to the magnitude of the load current. In the ching regulator, a voltage, which is connected between the anode of the second diode and the other end of the secondary winding of the transformer and represents the current flowing through the second diode, is expressed as the magnitude of the load current. Is provided with current detection means for outputting to the control circuit a voltage corresponding to the above.

[0009]

【Example】

 Next, an embodiment of the present invention will be described 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 the current detecting resistor 7 is connected between the anode of the diode 6 and the terminal 17. The smoothing choke coil 8 is connected between the cathodes of the diodes 5 and 6 and the output terminal 16, and the smoothing capacitor 11 is also connected between the output terminals 16 and 17. The resistors 12 and 13 for detecting the output voltage 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 to stabilize the output voltage. An electronic dummy 9 for preventing the output voltage from rising abnormally is connected between the output terminals 16 and 17, and a control signal thereof is supplied from an amplifier circuit 10. The amplifier circuit 10 amplifies the voltage across the resistor 7 and supplies the electronic dam 9 with the control signal.

The amplifier circuit 10 has a configuration as shown in FIG. 2 in detail. The operational amplifier 42, the resistors 41 and 43, and the capacitor 45 form a widening 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 A resistor 41 is connected between the non-inverting input terminal and the inverting input terminal, and a resistor 43 and a capacitor 45 are connected in parallel between the inverting input terminal and the output terminal. The operational amplifier 48, the resistors 46 and 49, and the reference voltage source 47 form a comparator, and the resistor 49 is connected between the non-inverting input terminal and the output terminal of the amplifier 48, and between the non-inverting input terminal and the ground. A resistor 46 and a power supply 47 are connected in series with the. 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 the present embodiment configured as described above, the resistance 7, and hence the diode 6, are provided only in the period of TO FF in which the switch circuit 3 is off, as shown in FIG. A flywheel current due to the magnetic action of the choke coil 8 flows as a load current.

Therefore, a voltage representing the magnitude of the load current Id and having the same waveform as that of FIG. 3 is input to the amplifier circuit 10. Then, in the amplifier circuit 10, the amplifier circuit including the operational amplifier 42 smoothes the input voltage and amplifies the voltage to a predetermined level, and the comparator including the operational amplifier 48 outputs the amplified voltage to the power supply 47 and an amplifier. The output voltage of the pump 48 is divided by the resistors 46 and 49 and compared with the determined voltage. If the former exceeds the latter, the load current has fallen below the minimum current value described above, a low-level voltage is output, the electronic dummy 9 is turned on, and the rise in output voltage is suppressed. ..

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 switch circuit 3 is turned off in the resistor 7. The current flows only during the period, so that the power loss due to the current flowing through the resistor 7 occurs only during that period. Therefore, assuming that the period in which the switch circuit 3 is on is equal to the period in which the switch circuit 3 is off, the power loss is about half that of the conventional case. Further, since the voltage detected by the resistor 7 is an AC voltage, amplification in the amplifier circuit 10 is easy, and as a result, the electronic dummy 9 can be operated sufficiently even if the value of the resistor 7 is reduced. 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 switching regulator differs from the switching regulator of FIG. 1 in that a current transformer 26 is used instead of the resistor 7. That is, the primary winding of the current transformer 26 is inserted between the anode of the diode 6 and the terminal 17, the resistor 27 is connected between both terminals of the secondary winding, and the amplifier circuit 10 has both ends of the resistor 27. The voltage is taken in 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 value of which is much smaller than that of the resistor 7, and the power loss becomes extremely small.

[0015]

[Effect of the device]

 As described above, the present invention includes a transformer, a first diode whose anode is connected to one end of a secondary winding of the transformer, and a second diode whose cathode is connected to a cathode. A smoothing circuit that includes a choke coil and smoothes the voltage generated between the cathodes of the first and second diodes and the other end of the secondary winding of the transformer, and is applied to the primary winding of the transformer. A switch circuit that switches the voltage, a stabilization circuit that controls the switch circuit based on the regulator output voltage, and a regulator output voltage that is connected to the output terminal of the smoothing circuit and receives a predetermined control signal. Switch that includes an electronic dummy that lowers the load and a control circuit that outputs a control signal to the electronic dummy based on the voltage corresponding to the magnitude of the load current. In the regulator, the voltage that is connected between the anode of the second diode and the other end of the secondary winding of the transformer and that represents the current flowing through the second diode is the voltage that corresponds to the magnitude of the load current. Is provided with a current detection means for outputting to the control circuit.

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 the period when the switch circuit is off, so the current flows through the resistor. The power loss caused by this is about half that of the conventional one. Further, since the detection voltage by the resistance is AC, it is easy to amplify the detection voltage in the control circuit, and as a result, the electronic dummy can be operated sufficiently even if the resistance value is reduced. Therefore, the power loss due to the resistance can be further reduced.

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

[Brief description of 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 that constitutes the switching regulator of FIG.

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

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.

[Explanation of symbols]

 2 transformer 3 switch circuit 4 stabilizing 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)

[Scope of utility model registration request] 1. 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 the cathode of the diode, and a choke coil, The first and second
A smoothing circuit for smoothing the voltage generated between the cathode of the diode and the other end of the secondary winding of the transformer, and a switch circuit for switching the voltage applied to the primary winding of the transformer, A stabilizing circuit that controls the switch circuit based on the regulator output voltage; an electronic dummy that is connected to the output terminal of the smoothing circuit and reduces the regulator output voltage when a predetermined control signal is input; A switching regulator including a control circuit that outputs the control signal to the electronic dummy based on a voltage corresponding to a magnitude, wherein an anode of the second diode and a transformer of the transformer are provided.
A current detection unit is provided that is connected between the other end of the next winding and outputs 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 in that