JP3490327B2 - Switching power supply - Google Patents

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 for obtaining a plurality of output voltages, and an output voltage whose voltage is not directly stabilized by a feedback control operation of a control system including a main switching element. It relates to a technique for stabilizing.

[0002]

2. Description of the Related Art In recent years, electronic devices are equipped with a large number of functional circuits and devices therein, and as a matter of course, the driving voltage to be supplied to these functional circuits and devices is of two or more types (voltage values). became. For example, in order to obtain a plurality of voltages having different voltage values, it is conceivable to use a power supply device provided with the necessary number of power supply circuits of the voltage. However, as the number of power supply circuits increases, the cost increases and the shape also increases.Therefore, a power supply device built into an electronic device can obtain multiple output voltages with different voltage values from one power supply circuit. In many cases, a multi-output type switching power supply device is required. As an example of such a multi-output type switching power supply device, there has conventionally been a switching power supply device having a configuration as shown in FIG.

In the circuit shown in FIG. 3, first, the primary winding N1 of the transformer T1 and the main current path of the main switching transistor Q1 are connected in series between the input terminal 1 on the high potential side and the ground to perform main switching. The control circuit 4 is connected to the base of the transistor Q1. It should be noted that the ground is a reference potential point of the circuit shown in FIG. 3, and the input terminal on the low potential side and each output terminal on the low potential side are connected to the ground although they are not shown. One end a of the secondary winding N2 of the transformer T1
Is the first output terminal 2 on the high potential side through the diode D1
The capacitor C2 is connected between the output terminal 2 and the ground, and the diode D1 and the output capacitor C are connected.
2 forms the first output circuit 5b of the power supply device.

The tap CT of the secondary winding N2 is connected to the second output terminal 3 on the high potential side via the diode D3, and the capacitor C5 is connected between the output terminal 3 and the ground. The diode D3 and the capacitor C5 form a second output circuit 6b of the power supply device. The other end b of the secondary winding N2 is connected to the ground. And input terminal 1
A capacitor C1 for filtering is connected between the output terminal 2 and the ground, and a series circuit of a resistor R1 and a resistor R2 for detecting the output voltage is connected between the output terminal 2 and the ground, and the resistors R1 and R2 are connected.
The circuit configuration is such that the voltage appearing at the connection point is input to the control circuit 4.

In the circuit of FIG. 3 having such a configuration, the switching transistor Q1 repeatedly turns on and off in accordance with the drive signal output from the control circuit 4, and the alternating voltage is applied to the secondary winding N2 of the transformer T1 accordingly. Occurs.
Here, the alternating voltage appearing between one end a and the other end b of the secondary winding N2 is rectified and smoothed in the first output circuit 5b,
As a result, the first output voltage V _O1 appears at the position of the first output terminal 2. Further, the alternating voltage appearing between the tap CT of the secondary winding N2 and the other end b is rectified and smoothed in the second output circuit 6b, whereby the second output is provided at the position of the second output terminal 3. The voltage V _O2 appears.

By the way, the voltage signal appearing at the connection point of the resistors R1 and R2 has a magnitude corresponding to the voltage value of the first output voltage V _O1 appearing at the first output terminal 2. When the first output voltage V _O1 fluctuates from a predetermined value for some reason, the control circuit 4 changes the pulse width of the drive signal according to the voltage signal appearing at the connection point of the resistors R1 and R2, and the switching transistor Q1. The ratio of ON and OFF periods, that is, the on-dity is changed. When the on-duty of the switching transistor Q1 changes, the primary winding N1
The flow rate of the current passing through the unit per unit time changes, and the amount of energy transmitted from the primary side to the secondary side of the transformer T1 changes. Then, the first output voltage V _{O 1} has an effect of restoring its voltage value to the original predetermined voltage value according to the changed amount of transmitted energy.

The first output voltage V _O1 of the circuit shown in FIG. 3 is stabilized at a predetermined value by the control of the switching operation based on the magnitude of the output voltage as described above, so-called feedback control. Regarding the second output voltage V _O2 , if the voltage value of the first output voltage V _O1 is stable at a substantially constant value, an external factor, that is, the state of the external load connected to each output terminal, is obtained. As long as the input voltage V _IN and the input voltage V _IN do not change, the voltage value becomes stable at a substantially constant value.

[0008]

In the circuit shown in FIG. 3, when the state of the external load connected to the output terminal 2 or 3 or the input voltage V _IN changes, the first output voltage V
_{Since O1} is stabilized by the above feedback control operation, the voltage value hardly changes. However, regarding the second output voltage V _O2 , even if the voltage value of the first output voltage V _O1 is tentatively stable, the voltage value fluctuates due to changes in various external factors. This is because the magnetic coupling between the windings of the transformer T1 constituting the power supply circuit is not perfect (coupling coefficient is 1.0), and a voltage drop occurs due to the electric resistance existing in each winding and the current flowing therethrough. It is thought that the cause is.

[0009] Accordingly, switching power supply and the circuit configuration shown in FIG. 3, when the input voltage V _{I N} and as the state of the external load varies greatly, high voltage value of the second output voltage V _O2 stability However, in other words, there is a problem that only one of the first output voltages V _O1 on which the feedback control acts can obtain a voltage with high stability. Therefore, an object of the present invention is to obtain a switching power supply device that can obtain a plurality of output voltages with high stability against changes in external factors.

[0010]

A switching power supply device according to the present invention is configured so that a main switching element and a winding of an inductance component are connected in series to turn on the main switching element.
In a switching power supply device that obtains an output voltage from a voltage appearing at a predetermined winding end of an inductance component with an off operation, one end of the switching power supply is connected to a predetermined winding end of the inductance component through a rectifying element. , Is connected with a smoothing circuit between one end of the output capacitor and the output terminal, and its control terminal is supplied with a synchronous drive signal by a voltage appearing at a predetermined winding position of the inductance component,
Further, it is characterized by including an auxiliary switching element which is in an ON state when the main switching element is in an ON state and which is in an OFF state when the main switching element is in an OFF state.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A main switching element, an inductance component, a diode and an output capacitor are mutually connected to form a power supply circuit, and a control circuit and the like are further incorporated in the power supply circuit to stabilize the terminal voltage of the output capacitor. To this end, a feedback control system is formed. An auxiliary switching element and a smoothing circuit are connected between this output capacitor and the output terminal of the power supply device. A synchronous drive signal based on a voltage generated at a predetermined winding position of the inductance component is input to the control terminal of the auxiliary switching element so that the auxiliary switching element is also turned on when the main switching element is on. Further, a control transistor that operates according to the output voltage is connected to the control terminal of the auxiliary switching element, and if the output voltage is higher than a predetermined value, the auxiliary switching element is turned off by the control transistor.

[0012]

FIG. 1 shows a circuit of a switching power supply device according to a first embodiment of the present invention, which can obtain a plurality of output voltages having high stability against changes in external factors. The circuit shown in FIG. 1 has the following circuit configuration. The choke coil L1 and the main switching transistor Q1 are connected in series between the input terminal 1 and the ground, and the control circuit 4 is connected to the base of the main switching transistor Q1. A filter capacitor C1 is connected between the input terminal 1 and ground. One end of the choke coil L1 on the main switching transistor Q1 side is connected to one end of the output capacitor C2 via the diode D1, and the other end of the output capacitor C2 is connected to ground. One end of the output capacitor C2 is the first
The output terminal 2 is connected to the diode D1 and the output capacitor C2 to form a first output circuit 5a.

The emitter of the auxiliary switching transistor Q2 is connected to one end of the output capacitor C2, and the collector of the auxiliary switching transistor Q2 is connected to the choke coil L.
It is connected to the second output terminal 3 via 2. A commutation diode D2, the other end of which is connected to the ground, and a capacitor C3 are connected to both ends of the choke coil L2 to form a smoothing circuit. The base of the auxiliary switching transistor Q2 is connected to one end of the choke coil L1 on the main switching transistor Q1 side through a parallel circuit of a resistor R5 and a capacitor C4, and the main control transistor Q3 is connected between the base and the emitter of the auxiliary switching transistor Q2. Connect the current path.

A resistor R3 is connected between the base and emitter of the first control transistor Q3, and the first control transistor Q3 is connected.
Of the second control transistor Q4 through the resistor R4
Connect to the collector. The emitter of the second control transistor Q4 is connected to ground, and the base is a constant voltage diode D.
It is connected to the second output terminal 3 via Z1. This auxiliary switching transistor Q2, first and second control transistors Q3, Q4, resistors R3, R4, R5, capacitor C
The second output circuit 6a includes the third and the third C4, the choke coil L2, the commutation diode D2, and the constant voltage diode DZ1.
Make up. Then, the resistors R1 and R2 are connected in series between the first output terminal 2 and the ground, and the resistors R1 and R2 are connected.
The voltage signal appearing at the connection point is input to the control circuit 4.

The schematic operation of the circuit of FIG. 1 having such a configuration is as follows. When the main switching transistor Q1 is turned on and off according to the signal supplied from the control circuit 4, a voltage having a waveform as shown in the uppermost stage of FIG. 2 appears at one end of the choke coil L1 and the collector of the main switching transistor Q1. First, when the main switching transistor Q1 is turned on, the collector voltage V _C1 of the main switching transistor Q1 becomes substantially zero, and a current flows from the input terminal 1 to the choke coil L1. During this time, energy is accumulated in the choke coil L1.

Next, when the main switching transistor Q1 is turned off, a flyback voltage is generated in the choke coil L1 and a combined voltage of the input voltage _VIN and the flyback voltage appears at the collector of the main switching transistor Q1. This combined voltage is supplied to the output capacitor C2 via the diode D1, and the output capacitor C2 is charged. At this time, the voltage appearing between the terminals of the output capacitor C2 is supplied to the external load from the first output terminal 2 as the first output voltage V _O1 . In the steady operation state, the first output voltage V _O1 performs control operation such as changing the ON period of the main switching transistor Q1 according to the voltage value, and the resistors R1 and R2.
And the control circuit 4, and the main switching transistor Q1
Is stabilized by a feedback control system composed of

On the other hand, when the main switching transistor Q1 is turned on, the collector voltage V _C1 of the main switching transistor Q1 decreases and the resistor R5 and the capacitor C4 move from the base of the auxiliary switching transistor Q2.
Current begins to flow through the parallel circuit of. Then, the auxiliary switching transistor Q2 is forward biased and is turned on. When the auxiliary switching transistor Q2 is turned on, a voltage whose magnitude is substantially equal to the first output voltage V _O1 appears in the collector of the auxiliary switching transistor Q2, as shown in the third stage of FIG. While the auxiliary switching transistor Q2 is in the ON state, the choke coil L2 and the capacitor C3 are connected to the auxiliary switching transistor Q2 from the output capacitor C2.
Energy is supplied via the. As a result, the second output voltage V _O2 appears at the second output terminal 3, and its voltage value increases while the auxiliary switching transistor Q2 is in the ON state.

Immediately after the circuit shown in FIG. 1 is activated and the second output voltage V _O2 is low, the auxiliary switching transistor Q2 maintains the ON state while the main switching transistor Q1 is in the ON state. Eventually, when the main switching transistor Q1 is turned off, a combined voltage of the input voltage V _IN and the flyback voltage appears at the collector of the main switching transistor Q1. Then, the auxiliary switching transistor Q2 receives the same combined voltage at its emitter via the diode D1 and at its base via the parallel circuit of the resistor R5 and the capacitor C4. As a result, no forward bias is supplied between the base and emitter of the auxiliary switching transistor Q2, and the auxiliary switching transistor Q2 shifts to the off state. At this time, the diode D1 supplies a reverse bias to the auxiliary switching transistor Q2 by its forward voltage drop, and the auxiliary switching transistor Q2
It plays a role in improving the turn-off speed of 2.

Then, when the circuit shown in FIG. 1 is already in the steady operation state, when the voltage value of the second output voltage V _O2 becomes slightly higher than the Zener voltage of the constant voltage diode DZ1, the second control transistor is generated. Q4 is turned on,
Along with this, the first control transistor Q3 is also turned on. When the first control transistor Q3 is turned on, the base and emitter of the auxiliary switching transistor Q2 are short-circuited, and the auxiliary switching transistor Q2 is turned off. When the auxiliary switching transistor Q2 is turned off, the energy supply to the choke coil L2 and the capacitor C3 is cut off, and the output of the second output voltage V _O2 is maintained by the energy accumulated up to that time in the choke coil L2 and the capacitor C3. . After that, the second output voltage V _O2 gradually decreases due to energy consumption in the load connected to the second output terminal 3.

When the second output voltage V _O2 becomes slightly lower than the Zener voltage of the constant voltage diode DZ1, eventually,
The second control transistor Q4 and the first control transistor Q3 are turned off, and the short-circuit state between the base and the emitter of the auxiliary switching transistor Q2 is released. Here, if the main switching transistor Q1 is already in the off state, the combined voltage of the input voltage V _IN and the flyback voltage appears at the collector of the main switching transistor Q1. Then, the auxiliary switching transistor Q2 is not supplied with the forward bias and remains in the off state. The second output voltage V _O2 continues to decrease while the auxiliary switching transistor Q2 is in the off state. However, substantially, the main switching transistor Q1 is turned on immediately after the second output voltage V _O2 becomes slightly lower than the Zener voltage of the constant voltage diode DZ1.
Then, the auxiliary switching transistor Q2 is also turned on, and the second output voltage V _O2 increases again. This state is as shown in each voltage waveform of FIG.

By performing the above operation,
Even if the provisional state, the load state, or the input voltage V _IN changes, the second output voltage V _O2 is stabilized near the voltage value determined by the Zener voltage of the constant voltage diode ZD1. When the switching power supply device is configured by the circuit shown in FIG. 1, although some ripple appears due to the switching operation, it is highly stable against changes in external factors such as the state of the external load and the input voltage V _IN. Multiple output voltages (2
One) You will get it.

One feature of the switching power supply device of the present invention is that the operation timings of the main switching transistor Q1 and the auxiliary switching transistor Q2 are "on-on". That is, in the step-up type switching power supply device as shown in FIG. 1, the ON period of the main switching element is longer than the OFF period, and the OFF period becomes longer as the input voltage and the value of the output voltage of the feedback control become more distant from each other. Will be a short time. In the same technology as the present invention,
There is a method to stabilize the output voltage by adjusting the ON period of the synchronous rectifying element, but the operating timing of the synchronous rectifying element is "ON".
-Off 'relationship.

Then, in the technology using the synchronous rectification element,
When the switching power supply device is a step-up type, since the off period of the switching element is short, the time during which the synchronous rectifying element can be in the on state is shortened. Therefore, especially when the voltage difference between the input voltage and the output voltage is large, a situation occurs in which the expected output voltage cannot be obtained. However, if “on-on” as in the present invention, in the case where the switching power supply device is a step-up type, the time that can be the on period of the auxiliary switching transistor can be lengthened rather,
The expected voltage can be easily obtained.

In the embodiment of the present invention shown in FIG. 1, the present invention is applied to the power supply device for obtaining the first and second output voltages, but three or more output voltages are obtained. The present invention may be applied to a power supply device having a configuration. Further, in the circuit of the embodiment, the choke coil L1, the main switching transistor Q1, and the first output circuit 5a have a circuit configuration of a boost chopper converter, but a configuration using a transformer may be used as shown in FIG. . Further, in the embodiment, the present invention is applied to the step-up type switching power supply device, but the present invention may be applied to the step-up / down type switching power supply device, and the second switching device includes the auxiliary switching element. The circuit portion of the output circuit may have a polarity inversion circuit configuration instead of the step-down chopper circuit configuration.

[0025]

The switching power supply device according to the present invention is
The auxiliary switching element and the smoothing circuit are connected to the output capacitor whose terminal voltage is stabilized by the control operation of the feedback control system including the main switching element. Then, while using the output capacitor as the voltage supply source,
It is characterized in that the auxiliary switching element is driven so as to be in the ON state when the switching element is in the ON state, and the output voltage is obtained. According to the present invention as described above, it is possible to configure a multi-output type switching power supply device capable of obtaining a plurality of output voltages having high stability with respect to changes in external factors such as an external load state and an input voltage V _IN. Will be able to.

[Brief description of drawings]

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

FIG. 2 is a diagram showing voltage waveforms of respective parts of the circuit shown in FIG. 1 and operation timings of two switching elements.

FIG. 3 is a circuit diagram of an example of a conventional multi-output type switching power supply device.

[Explanation of symbols]

1: input terminal 2: first output terminal 3: second
Output terminal 4: Control circuit 5a, 5b: First
Output circuit 6a, 6b: second output circuit C2: output capacitor C3: capacitor D
1: diode D2: commutation diode DZ1: constant voltage diode L1, L2: choke coil Q1: main switching transistor (main switching element) Q2: auxiliary switching transistor (auxiliary switching element) Q3, Q4: control transistor V
_IN : Input voltage V _O1 : First output voltage V
_O2 : second output voltage

Claims (5)

(57) [Claims] 1. A main switching element and a winding of an inductance component are connected in series, and an output voltage is obtained from a voltage appearing at a predetermined winding end of the inductance component when the main switching element is turned on and off. In a switching power supply device, one end of which is connected to a predetermined winding end of the inductance component via a rectifying element, and a smoothing circuit is connected between one end of the output capacitor and an output terminal and the control thereof is performed. The terminal is supplied with a synchronous drive signal by the voltage appearing at a predetermined winding position of the inductance component, and there is a period in which the main switching element is in the on state when the main switching element is in the on state, and the main switching element is in the off state. A switching power supply device comprising: an auxiliary switching element that is turned off when in a state. 2. The main current path is connected to the control terminal of the auxiliary switching element, operates according to the output voltage appearing at the output terminal, and the auxiliary switching is performed when the output voltage is higher than a predetermined voltage value. The switching power supply device according to claim 1, further comprising a control transistor that shifts the element to an off state. 3. The switching according to claim 1, wherein the voltage appearing across the output capacitor is stabilized by a feedback control operation of a control system including the main switching element. Power supply. 4. The multi-output type wherein the voltage appearing across the output capacitor is the first output voltage and the voltage appearing at the output terminal is the second output voltage. The switching power supply device according to any one of claims 1 to 3. 5. The switching power supply device according to claim 4, wherein the input voltage supplied is lower than the first output voltage, and the power supply device is a step-up type power supply device.