JPH07143739A - Switching power supply device - Google Patents

Abstract

PURPOSE:To obtain a switching power supply device having a high power conversion efficiency by further reducing loss generated in a transistor rectifying device. CONSTITUTION:A driving transistor Q3 is mounted between the base and the ground of a transistor Q2 as a rectifying device. A driving signal is inputted to the base of the driving transistor Q3 from the node of the transistor Q2 and a choke coil L1 generating flyback voltage, and the transistor Q2 is turned on-off in conformity with the on-off operation of the switching transistor Q1. Accordingly, when the transistor Q2 keeps an off state, the leakage of currents in the base direction from its collector can be prevented, and the loss of the transistor rectifying device is reduced, thus improving the power conversion efficiency of a switching power supply device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device in which the loss during conduction of a rectifying element is reduced and power conversion efficiency is improved.

[0002]

2. Description of the Related Art A diode is exclusively used as a rectifying element for converting alternating current and voltage into direct current. When rectifying with a diode, a forward voltage V _F and current existing in the diode are used. It must be borne in mind that the diode will have a loss corresponding to the product of If the purpose of which minimize the loss of the rectifying element hand, the collector of the transistor in the on state, the saturation voltage between the emitter is smaller than the forward voltage V _F of the diode, little loss generated It is known to be completed. Therefore, as one means for improving the power conversion efficiency of the switching power supply device, it has been considered to use a transistor instead of a diode for the rectifying element. As a switching power supply device using such a transistor rectifying element, the present inventor has proposed a switching power supply device as shown in FIG. 4 in Japanese Patent Application No. 4-105807.

Although a detailed description of the configuration and operation of the circuit shown in FIG. 4 is omitted, the operation of the transistor Q2 as a transistor rectifying element is as follows. That is,
When the switching transistor Q1 is turned off, the current flowing through the input terminal 1, the choke coil L1, the collector and the emitter of the switching transistor Q1 is cut off. As a result, a flyback voltage is generated in the choke coil L1, and the voltage of the collector of the switching transistor Q1 rises to the voltage obtained by adding the flyback voltage to the input voltage V _IN . When a voltage obtained by combining the flyback voltage and the input voltage V _IN is applied to the emitter of the transistor Q2, the transistor Q2 is forward-biased between the emitter and the base and is turned on. Transistor Q
When 2 is turned on, a high voltage obtained by combining the flyback voltage and the input voltage V _IN described above is supplied to the load RL via the output terminal 2.

On the contrary, when the switching transistor Q1 is turned on, the voltage of the collector of the switching transistor Q1 and the voltage of the emitter of the transistor Q2 are lowered, and the forward bias between the emitter and the base of the transistor Q2 is released and the transistor Q2 is turned off. As described above, the transistor Q2 is turned on when the switching transistor Q1 is turned off and the output voltage of the collector is increased, and is turned off when the voltage is lowered. That is, in the circuit shown in FIG. 4, the output of the switching transistor Q1 is a signal for turning on and off the transistor Q2.

[0005]

By using a transistor instead of a diode as a rectifying element, it is possible to improve the power conversion efficiency of a switching power supply device. However, unlike a diode, a transistor is turned on.
It is necessary to perform off control. If a PNP type transistor is used for the transistor rectifying element, it is possible to provide a special driving circuit at the base of the transistor rectifying element.
Only by securing a current path between the base and the ground, it is possible to perform on / off operation according to the operation of the switching transistor. Therefore, the circuit configuration is simple, and it is possible to realize a highly efficient switching power supply device while suppressing an increase in cost.

However, the PNP type transistor is
Due to the N-junction structure, it can be considered that diodes are formed in the direction from the emitter to the base and in the direction from the collector to the base. Therefore, even if the switching transistor turns on and the emitter rectifier element voltage drops and the transistor rectifier element turns off, a simple circuit configuration that only secures a current path between the base and ground When the collector voltage of the rectifying element becomes higher than the base voltage, a current leaking from the collector toward the base is generated. The leakage current increases the loss of the transistor rectifying element, and results in lowering the power conversion efficiency of the switching power supply device even though the power conversion efficiency is higher than that of the switching power supply using the diode as the rectifying element. Therefore, it is an object of the present invention to provide a switching power supply device using a PNP-type transistor rectifying device, which further realizes high power conversion efficiency by further reducing the loss generated in the transistor rectifying device. .

[0007]

DISCLOSURE OF THE INVENTION The present invention is a switching power supply device for obtaining a desired DC power by generating a flyback voltage in an inductance element when a switching element is turned off and rectifying and smoothing energy by the flyback voltage. In, a PNP type bipolar transistor is used as a rectifying element, a driving transistor of an NPN type bipolar transistor for operating the transistor rectifying element is provided at the base of the transistor rectifying element, and a base of the driving transistor is provided. On the other hand, an on / off control signal is supplied from a connection point between the transistor rectifying element and the inductance element.

[0008]

FIG. 1 is a circuit diagram of a switching power supply device according to the present invention, which realizes high power conversion efficiency by reducing the loss generated by a transistor rectifying element.
The same components as those in FIG. 4 in FIG. 1 are designated by the same reference numerals. In FIG. 1, reference numerals 1 and 2 respectively indicate an input terminal and an output terminal on the high potential side, and the input and output terminals on the low potential side are common to the ground. The input terminal 1 is connected to the collector of the NPN type switching transistor Q1 via the choke coil L1, and the emitter of the switching transistor Q1 is connected to the ground. The collector of the switching transistor Q1 is connected to the emitter of a PNP type transistor Q2 as a transistor rectifying element, and the collector of the transistor Q2 is connected to the output terminal 2. A capacitor C1 and a capacitor C2 are respectively connected between the input terminal 1 and the output terminal 2 and the ground, and a resistor R for dividing the output voltage is further connected between the output terminal 2 and the ground.
1 and the series circuit of the resistor R2 are connected.

The connection point between the resistors R1 and R2 is connected to the control circuit 3
Of the control circuit 3 and the pulse output terminal (PO) of the control circuit 3 are connected to the base of the switching transistor Q1. A diode D1 is provided between the emitter and collector of the transistor Q2 so as to connect the anode to the emitter and the cathode to the collector. The base of the transistor Q2 is connected to the collector of the driving transistor Q3, which is an NPN transistor, through the parallel circuit of the resistor R3 and the capacitor C3, and the emitter of the driving transistor Q3 is connected to the ground. The base of the transistor Q2 is further connected to the cathode of the diode D2, and the anode of the diode D2 is connected to ground. Transistor Q
A resistor R4 is connected between the emitter of 2 and the base of the driving transistor Q3, and a resistor R5 is connected between the base and the emitter of the driving transistor Q3.

The circuit configured as described above forms a so-called chop-up type switching power supply device,
The operation of this circuit is as follows. Control circuit 3
When the switching transistor Q1 is turned off by the signal from, the flyback voltage is generated in the choke coil L1 by the energy stored when the switching transistor Q1 is in the on state. Therefore, a high voltage in which the flyback voltage generated in the choke coil L1 is superimposed on the input voltage V _IN is applied to the collector of the switching transistor Q1 and the emitter of the transistor Q2 as a rectifying element. The high voltage obtained by combining the input voltage V _IN applied to the emitter of the transistor Q2 and the flyback voltage is also input to the base of the driving transistor Q3 via the resistor R4, whereby the driving transistor Q3 is positive between the base and the emitter. Biased and turned on. Driving transistor Q
3 is turned on, the emitter and the base of the transistor Q2 are positively biased and the transistor Q2 is turned on.
Is turned on.

When the transistor Q2 is turned on, a high voltage obtained by combining the input voltage V _IN and the flyback voltage is supplied to the load RL. Next, when the switching transistor Q1 is turned on, the collector of the switching transistor Q1 and the transistor Q1.
The voltage of the emitter of 2 decreases, and at the same time, the voltage of the base of the driving transistor Q3 also decreases. As a result, the driving transistor Q3 is turned off, and the transistor Q2 is turned off by releasing the driving transistor Q3 from the positive bias state between the emitter and the base. In the above operation, the transistor Q2
The on / off operation of is controlled by the driving transistor Q3. Therefore, even if the voltage of the emitter of the transistor Q2 drops and the transistor Q2 is turned off, the collector side has a high potential and the base side has a low potential. It will be blocked by transistor Q3.
Therefore, the loss generated in the transistor Q2 is reduced, and a switching power supply device with high power conversion efficiency can be obtained.

Here, the parallel circuit of the resistor R3 and the capacitor C3 connected to the base of the transistor Q2 has a function of limiting the base current of the transistor Q2, and if it exists between the base of the transistor Q2 and the ground, it is driven. The transistor Q3 may be provided on the emitter side instead of the collector side. Further, the diode D2 forms a discharge path of the charge accumulated in the base region when the transistor Q2 is turned off. In the circuit shown in FIG. 1, the cathode of the diode D2 is the transistor Q.
Drive transistor Q directly connected to base 2
Even if it is connected to the collector of No. 3, the effect is the same, and it may be provided so as to form a parallel current path between the collector and the emitter of the driving transistor Q3. However, this diode D2 may be removed from the circuit in some cases. Furthermore, the diode D1 becomes conductive only for a short period of time after the switching transistor Q1 is turned off until the transistor Q2 is turned on.
Only during this period, a high voltage obtained by combining the input voltage V _IN and the flyback voltage is supplied to the load RL, and the switching transistor Q1 and the transistor Q2 function to be protected from the high voltage. However, it may be excluded depending on the specifications of the switching power supply device.

FIG. 2 shows a circuit of another embodiment of the present invention. 2 is different from the embodiment of FIG. 1 in that an RC series circuit in which a capacitor C4 is added to a resistor R4 is connected between the emitter of the transistor Q2 and the base of the driving transistor Q3, and Three points: diode D3 is connected between the base and emitter of Q3 so that the base and cathode are connected instead of resistor R5, and diode D1 connected between the collector and emitter of transistor Q2 is removed. Is. The other circuit configurations are the same. With such a circuit configuration, the switching power supply device functions as a buck-boost converter.

First, the operation of the circuit when the input voltage V _IN is lower than the required output voltage V _O is as follows. When the switching transistor Q1 is turned off by the signal from the control circuit 3, the choke coil L1
A flyback voltage is generated at. This flyback voltage is superimposed on the input voltage V _IN, and the high voltage resulting from the superposition is the collector of the switching transistor Q1, the emitter of the transistor Q2, the resistor R4 and the capacitor C.
It will be added to the base of the driving transistor Q3 through the series circuit of 3. As a result, the driving transistor Q
In No. 3, the base and the emitter are positively biased and turned on.

When the driving transistor Q3 is turned on, the transistor Q2 is also positively biased between the emitter and the base to be turned on, and a high voltage obtained by combining the input voltage V _IN and the flyback voltage is supplied to the load RL. Will be done. When the switching transistor Q1 turns on, the switching transistor Q1
The voltage of the collector of 1 and the voltage of the emitter of the transistor Q2 decrease, and at the same time, the voltage of the base of the driving transistor Q3 also decreases. As a result, the driving transistor Q3 is turned off, and the transistor Q2 is turned off by releasing the driving transistor Q3 from the positive bias state between the emitter and the base. In this way, the operation when the input voltage V _IN is lower than the required output voltage V _O is the same as the operation of the circuit shown in FIG. 1, and the circuit operates as a boost converter.

The operation when the input voltage V _IN is higher than the output voltage V _O required next is as follows. When the output voltage V _O increases, the control circuit 3 shortens the ON period of the switching transistor Q1 but does not stop the switching operation. Therefore, when the input voltage V _IN is higher than the output voltage V _O , the switching transistor Q1 continues the switching operation with a very short ON period. Here, the presence of the capacitor C4 prevents the voltage of the DC component from being applied to the base of the driving transistor Q3, and only the pulsating component due to the ON / OFF operation of the switching transistor Q1 is applied to the base of the driving transistor Q3. Will be done. Therefore, the driving transistor Q3 controls the base current of the transistor Q2 according to the switching operation of the switching transistor Q1. This causes the transistor Q2 to operate like a series regulator.

Therefore, the required output voltage V_OAgainst
Input voltage V_INFunctions as a step-down converter when the voltage is high
However, it is a step-up / down type switching power supply as a whole.
From the above, the embodiment of the present invention shown in FIG.
Required output voltage V _OInput voltage V_INWhere is low
In this case, as in the embodiment shown in FIG.
It is possible to reduce the loss of the transistor Q2, which is high.
Can be a switching power supply with power conversion efficiency
It In addition, it is a boost type by exchanging some circuit components.
Buck-boost type switching power supply
It can be a device and can easily handle a wide input voltage.
Can be a switching power supply.

FIG. 3 shows another embodiment of the present invention. The circuit of FIG. 3 corresponds to the diode D in the circuit of FIG.
Instead of 2, a series circuit of a capacitor C5 and a resistor R6 is provided between the base of the transistor Q2 and the ground. The other circuit configuration is the same as the circuit of FIG. As is well known, there is a slight delay time in turning on a transistor element. Similarly, since there is a delay time in turning on the driving transistor Q3, the time difference from the turning off of the switching transistor Q1 to the turning on of the transistor Q2 becomes large. When this time difference becomes large, a high voltage, which is the sum of the input voltage V _IN and the flyback voltage, is applied between the collector and the emitter of the switching transistor Q1, and the loss and voltage load of the switching transistor Q1 increase.

Therefore, in the circuit shown in FIG. 3, a series circuit of a capacitor C5 and a resistor R6 is provided at the base of the transistor Q2. By doing so, when the voltage of the emitter of the transistor Q2 rises, the base of the transistor Q2 is positively biased even if the driving transistor Q3 is in the off state. Therefore, the time difference from the turning-off of the switching transistor Q1 to the turning-on of the transistor Q2 is reduced, and the switching transistor Q1
It is possible to improve the power conversion efficiency of the switching power supply device by reducing the power loss. In the embodiment shown in FIG. 3, one end of the series circuit of the capacitor C5 and the resistor R6 is connected to the base of the transistor Q2, but it may be connected to the collector of the driving transistor Q3. Further, in the embodiment shown in FIG. 1, as in the circuit shown in FIG. 3, instead of the diode D2, a capacitor C5 and a resistor R5 are provided.
It goes without saying that the same effect can be obtained by connecting the series circuits of No. 6 together.

[0020]

As described above, the switching power supply device according to the present invention uses a PNP type transistor for the rectifying element, and the transistor rectifying element receives the control signal from the connection point of the transistor rectifying element and the choke coil. It is characterized by being turned on and off by a driving transistor. Thereby, the loss of the transistor as the rectifying element can be reduced, and the switching power supply device with high power conversion efficiency can be obtained.
Further, by changing a part of the circuit, a highly efficient step-up / down type switching power supply device can be easily obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a switching power supply device according to the present invention.

FIG. 2 is a circuit diagram of another embodiment of the switching power supply device according to the present invention.

FIG. 3 is a circuit diagram of still another embodiment of the switching power supply device according to the present invention.

FIG. 4 is a circuit diagram of a switching power supply device proposed in Japanese Patent Application No. 4-105807.

[Explanation of symbols]

 1 Input Terminal 2 Output Terminal 3 Control Circuit Q1 Switching Transistor Q2 Transistor as Rectifier Q3 Driving Transistor

Claims (3)

[Claims] 1. A switching power supply device for generating a desired DC power by generating a flyback voltage in an inductance element when a switching element is turned off and rectifying and smoothing energy due to the flyback voltage. A bipolar transistor is used, a driving transistor of an NPN type bipolar transistor for operating the transistor rectifying element is connected to the base of the transistor rectifying element, and the transistor rectifying element is connected to the base of the driving transistor. A switching power supply device, wherein an on / off control signal is supplied from a connection point of the inductance element. 2. A diode element whose forward direction is from the emitter to the base is provided between the base and the emitter of the driving transistor, and the on / off signals are supplied to the base of the driving transistor through a capacitive element. The switching power supply device according to claim 1, wherein the switching power supply device is provided. 3. The base of the transistor rectifying element,
The switching power supply device according to claim 1 or 2, wherein a current path parallel to the main current path of the driving transistor is provided by a series circuit of a resistor and a capacitor or a capacitor.