JP3469128B2 - Switching power supply circuit and power supply device - 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 circuit for supplying a regulated DC voltage to industrial and consumer electronic devices.

[0002]

2. Description of the Related Art In the United States, the standard setting of Energy Star Computer Program was established in 1993 so that the power consumption of a personal computer during standby is 30 W or less. In Japan, the power consumption during standby of a VTR was reduced in 1995. Energy saving of switching power supply circuits used for electronic devices is required against the backdrop of the trend toward lower power consumption worldwide such as regulation to cut 10%.

FIG. 6 shows the configuration of a conventional chopper type switching power supply circuit 50. In the figure, first, the AC voltage stepped down by the insulating transformer T is converted into a full-wave rectifying / smoothing circuit 5.
Input to 1 for rectification and quasi-smoothing. Next, the NPN transistor TR2 as a switching element that repeats ON / OFF of the rectified voltage with a predetermined duty
The DC input voltage is once converted into a high frequency pulse by switching with. Then, the choke coil CH1 for smoothing and the capacitor CO1 convert it again to direct current and stabilize it.

While the transistor TR2 is ON, energy is supplied to the choke coil CH1, the capacitor CO1 and the load. Energy is stored in the choke coil CH1 by the current flowing therethrough. When the transistor TR2 is turned off, the energy stored in the choke coil CH1 is released through the diode D2, and the energy supply to the capacitor CO1 and the load is continued. The ON / OFF cycle and duty of the transistor TR2 are controlled by the controller 52, and the output voltage is stabilized by this.

[0005]

However, in the switching power supply circuit 50, the insulating transformer T is used,
When the transistor TR2 turns ON / OFF during the period when the rectification voltage value obtained by the full-wave rectification smoothing circuit 51 is large,
As shown in FIG. 7, the power consumption of the transistor TR2 is represented by the product of the collector current I _c and the collector-emitter voltage V _CE , so that the switching loss becomes large. Also,
There is also power loss due to the use of the insulation type transformer T,
There has been a limit in reducing the power consumption of the switching power supply circuit 50 during standby.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a switching power supply circuit capable of further reducing power consumption during standby.

[0007]

SUMMARY OF THE INVENTION The switching power supply of the present invention.
In order to solve the above problems, the source circuit has a switching element that switches a rectified voltage, and a control unit that controls the switching cycle and duty .
A switch that supplies power to the load through the switching element.
The switching power supply circuit has a rectified voltage detection means for detecting the rectified voltage, and the control means has the rectified voltage.
The rectified voltage detected by the pressure detection means is above a predetermined value.
The switching element is
The above load that can supply power even when it is in the ON state is connected.
In this state, the switching is controlled so that the switching element is turned on only during the partial period .

When the rectified voltage applied to the switching element changes its magnitude at any time, such as a pulsating current, when the switching element switches at a large voltage value,
Switching loss increases during the ON period. According to the above invention, the control unit controls the switching so that the switching element is in the ON state only during the period when the rectified voltage detected by the rectified voltage detection unit is lower than the predetermined value. Becomes smaller that much. Also, because only the part with low rectified voltage is switched, it is not necessary to step down the voltage from the external power supply using an isolated transformer as in the past, and it is possible to supply power directly from a commercial power supply without using a transformer. There is no power loss as much as possible.

The above can be said both during normal operation and during standby, and is particularly effective during standby, and further lower power consumption can be achieved.

Further, the switching power supply circuit of the present invention is
In order to solve the above problems, the control means is
The switching element is turned on only during the fractional period.
By controlling the switching so that
Characterized by reducing the power consumption of the switching element
There is .

Further, the switching power supply circuit of the present invention is
In order to solve the above problems, the switching element is a depletion type MOSFET.

According to the above invention, the switching element is a depletion type MOSFET and the control means is an MO.
Switching is controlled by applying a voltage of a predetermined level to the gate of the SFET. In this case, MOSFE
Since T is normally on, a MOSFET is
If the channel type is used, ON / OFF can be determined with a threshold value at which the gate voltage seen from the source becomes negative. Therefore, switching can be performed simply by generating a predetermined voltage drop from the output line of the switching element and applying it to the gate, and the switching element can be easily realized.

Further, the switching power supply circuit of the present invention is
In order to solve the above-mentioned problems, a backflow preventing means for preventing a backflow of a current from an output side to an input side is further provided in a preceding stage of the switching element.

According to the above invention, since the switching element is turned on only when the rectified voltage is low, the switching element of the switching element is provided in case the voltage on the output side, for example, the charging voltage of the smoothing capacitor becomes higher. A backflow prevention means such as a diode is provided in the preceding stage. This prevents current from flowing backward from the output side to the input side, and stable operation can be realized.

Further, the switching power supply circuit of the present invention is
In order to solve the above-mentioned problems, it is characterized by further comprising output voltage detection means for detecting an output voltage and feeding back the control to the control of the switching cycle and duty of the control means.

According to the above invention, the output voltage detecting means detects the output voltage of the switching power supply circuit , and the control means controls the switching cycle and duty from the detection result. provide feedback. Therefore, the switching power supply
The voltage of the circuit can be easily stabilized.

Further, in order to solve the above-mentioned problems, the power supply device of the present invention is a switch of the invention described in any one of the above .
The feature is that the switching power supply circuit is integrated into one package.

According to the above invention, since the switching power supply circuit according to any one of the above inventions is provided in one package, it is easy to mount and the electronic equipment using the same can be miniaturized.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a power supply circuit and a power supply device of the present invention will be described below with reference to FIGS.

FIG. 1 shows a chopper type switching power supply circuit 1 of this embodiment. The switching power supply circuit 1 controls to perform switching only during a period when the voltage applied to the switching element is lower than a predetermined value.
The rectifier circuit 2, the rectified voltage detection circuit 3, the backflow prevention circuit 4, the switching element 5, the control circuit 6, the output voltage detection circuit 7, and the smoothing circuit 8.

The rectifier circuit 2 rectifies the commercial AC voltage directly applied to the input terminals P1 and P2 without passing through the insulation type transformer. Rectified voltage detection circuit 3 as rectified voltage detection means
Detects the magnitude of the rectified voltage output from the rectifier circuit 2 and inputs the detection result to the control circuit 6. The backflow prevention circuit 4 as backflow prevention means prevents a current from flowing backward due to the voltage on the output side of the switching power supply circuit 1 becoming higher than that on the input side. The switching element 5 performs switching based on the pulse control signal output from the control circuit 6, generates a high frequency pulse from the rectified voltage, and outputs the high frequency pulse to the output side.

The control circuit 6 as a control means outputs a control signal so as to switch the switching element 5 only during a period when the rectified voltage detected by the rectified voltage detection circuit 3 becomes lower than a predetermined value. The output voltage detection circuit 7 as the output voltage detection means detects the output voltage and inputs the detection result to the control circuit 6. When the detection result is input from the output voltage detection circuit 7, the control circuit 6 detects the amount of deviation of the output voltage from a predetermined value, adjusts the switching cycle and duty, and returns the output voltage to the predetermined value. Change the pulse width and duty of the control signal. Smoothing circuit 8
Smoothes the high-frequency pulse output from the switching element 5 and outputs it as a DC stabilized voltage from the output terminals V1 and V2 to the load.

FIG. 2 shows an example of a more specific structure of the switching power supply circuit 1. In the figure, the rectifier circuit 2
Is composed of a diode bridge full-wave rectifier circuit 2a, and full-wave rectifies the commercial AC voltage applied to the input terminals P1 and P2. The rectified voltage detection circuit 3 is composed of two resistors R1 and R2 for voltage division, which are provided in series immediately after the diode bridge full-wave rectification circuit 2a and between the high-potential-side power source line and the ground-side power source line. A connection point between the resistors R1 and R2 is connected to a PWM comparator 6a described later,
By detecting the rectified voltage by dividing the rectified voltage output from the diode bridge full-wave rectifier circuit 2a, the PW
It is adapted to be input to the M comparator 6a.

The backflow prevention circuit 4 comprises a diode D1, is provided immediately before the MOS transistor TR1, and is connected so as to be in the forward direction from the input side to the output side. This diode D1 is controlled so that the MOS transistor TR1 is turned on only during a period when the rectified voltage is low, as will be described later. In order to prevent the current from flowing backward from the output side to the input side, stable operation of the switching power supply circuit 1 is enabled.

The switching element 5 is composed of an N-channel type and depletion type MOS transistor TR1 and is connected so that the drain is on the input side and the source is on the output side. Further, the output terminal of the control circuit 6 is connected to the gate, and switching is driven according to the voltage of the output terminal. Depletion type M for switching element 5
By using the OS transistor TR1, the rectified voltage on the input side is supplied to the output side because the drain-source is in the ON state, that is, normally-on even when the gate voltage with respect to the source (substrate) is 0V.

Therefore, ON / OFF can be determined with the threshold voltage at which the gate voltage seen from the source becomes negative, and a predetermined voltage drop from the output power line on the high potential side as described later. Switching can be performed simply by generating and applying to the gate. In addition, a parasitic diode D2 exists in the forward direction from the source to the drain between the source and the drain, but the reverse current flowing therethrough is blocked by the diode D1.

The control circuit 6 controls the switching timing of the MOS transistor TR1 and includes a resistor R
3 and a Zener diode ZD1 in series, a PWM comparator 6a, and a Zener diode ZD2 and resistors R4 and R5 in series. A series circuit of the resistor R3 and the Zener diode ZD1 is inserted on the output side of the switching power supply circuit 1 between the power supply line on the high potential side and the power supply line on the ground side. The connection point between the resistor R3 and the Zener diode ZD1 is connected to the non-inverting input terminal of the PWM comparator 6a, whereby a constant voltage is extracted from the output voltage of the switching power supply circuit 1 and PW is set.
It is used as a reference voltage for the M comparator 6a. The inverting input terminal of the PWM comparator 6a has the resistors R1 and R
The rectified voltage detected by the resistors R1 and R2 is compared with the reference voltage to output a predetermined voltage.

Zener diode ZD2 and resistors R4 and R
5 is connected in series with the output side of the power supply line on the high potential side, that is, the source side of the MOS transistor TR1 and the PWM.
It is inserted between the output terminal of the comparator 6a.
Zener diode ZD2 is a MOS transistor TR
It is provided to protect the gate of No. 1. The connection point between the resistor R4 and the resistor R5 is connected to the gate of the MOS transistor TR1 and its potential is MO as described above.
Since the S transistor TR1 is a depletion type, the resistance R4 is larger than the source of the MOS transistor TR1.
It becomes lower by the voltage drop of.

The output voltage detection circuit 7 is composed of a resistor R6 and a resistor R7 connected in series between the high potential side power source line on the output side and the ground side power source line. The connection point between the resistors R6 and R7 is connected to the inverting input terminal of the PWM comparator 6a. That is, the output of the PWM comparator 6a is the rectified voltage detection circuit 3 (resistor R1
R2) and the output side output voltage detection circuit 7 is controlled by the midpoint potential. The smoothing circuit 8 is composed of a smoothing capacitor C1 and is connected between the high-potential-side power source line on the output side and the ground-side power source line to smooth the output voltage of the switching power source circuit 1 and output terminal V.
Output from 1 ・ V2.

In the switching power supply circuit 1 having the above configuration, when a commercial AC voltage is applied between the input terminals P1 and P2, the diode bridge full-wave rectifier circuit 2a is used.
A voltage having a waveform as shown in (a) is obtained. This rectified voltage is detected by resistors R1 and R2 for voltage division, and PWM
It is input to the inverting input terminal of the comparator 6a. The constant voltage value is set so that the voltage input to the inverting input terminal is higher than the constant voltage input to the non-inverting input terminal during the period when the rectified voltage is higher than a predetermined value described later. The PWM comparator 6a includes resistors R4 and R5.
And the voltage is output from the output terminal so that the voltage of the gate with respect to the source of the MOS transistor TR1 becomes a value lower than the threshold value by the voltage division generated by the Zener diode ZD2. Therefore, during this period, the MOS transistor TR1 remains in the OFF state.

On the other hand, while the rectified voltage is lower than the predetermined value, the voltage input to the inverting input terminal of the PWM comparator 6a is lower than the constant voltage input to the non-inverting input terminal. At this time, the PWM comparator 6a is
A voltage that causes the gate of the transistor TR1 to have a voltage higher than the threshold value with respect to the source and a voltage that has a voltage lower than the threshold value based on the potential at the connection point of the resistors R6 and R7 Outputs alternately at a specified duty.
Therefore, the MOS transistor TR1 is turned on during this period.
Switching is repeatedly performed between the state and the OFF state.

The MOS transistor T in the above operation
R1 drain-source voltage V _DS and drain current I _D
FIG. 4 shows an example of a waveform diagram showing the relationship with. Only a predetermined number of times (2 in this case
Since the switching is performed, the drain current I _D flows while the drain-source voltage V _DS is low,
The switching loss represented by the product of current and voltage is extremely small. In addition, since switching is performed only during the period when the rectified voltage is low, it is not necessary to step down the voltage from the external power source using an insulation type transformer as in the past, and the power is directly supplied from the commercial power source without using a transformer. Since the power can be supplied, there is no power loss due to the transformer. The above can be said for both the normal operation and the standby state, and is particularly effective for further reducing the power consumption during the standby state.

The voltage converted to a high frequency by switching as described above is converted by the smoothing capacitor C1 in FIG.
Smoothed to a DC stabilized voltage V _O as shown in (c),
It is output from the output terminals V1 and V2.

In the switching power supply circuit 1, the portion surrounded by the one-dot chain line in FIG. 1 can be sealed in one package. FIG. 5 shows the appearance of an IC (power supply device) 10 which is the package form. There are four lead terminals, which correspond to the input terminals P1 and P2 and the output terminals V1 and V2. The smoothing capacitor C1 is externally attached between the output terminals V1 and V2. The resin portion is provided with a screw fastening hole for attaching to the heat sink. By thus packaging the switching power supply circuit 1 in one package, it becomes easy to mount the switching power supply circuit 1 on the printed circuit board of the electronic device at the same time as other elements, and the size of the electronic device can be reduced.

[0035]

As described above, the power supply circuit of the present invention can be adjusted.
A switching element that switches the current
Control means for controlling the cycle and duty of the itching
And has a power supply to the load through the switching element.
In the switching power supply circuit to be supplied, the rectified voltage
Has a rectified voltage detection means for detecting, the control means,
The rectified voltage detected by the rectified voltage detection means
Switch only during a partial period when
Even if the switching element is in the ON state, the negative power can be supplied.
With the load connected, the switch is only for the partial period.
The above switching so that the switching element is turned on.
Is a configuration for controlling the .

Therefore, since the switching is controlled so that the switching element is turned on only during the period when the rectified voltage is lower than the predetermined value, the power consumption of the switching element is reduced accordingly. Further, it is not necessary to step down the voltage from the external power source by using the insulation type transformer, and the power loss is eliminated by omitting the transformer. The above is
This is true both during normal operation and during standby, and is particularly effective during standby and has the effect of further reducing power consumption.

Further, the switching power supply circuit of the present invention is
As described above, the switching element is a depletion type MOSFET.

Therefore, ON / OFF can be determined with a threshold value at which the gate voltage seen from the source becomes negative, and a predetermined voltage drop is generated from the output line of the switching element and applied to the gate. Switching can be performed simply by Therefore, there is an effect that the switching element can be easily realized.

Further, the switching power supply circuit of the present invention is
As described above, the configuration further includes a backflow preventing unit that prevents a current from flowing back from the output side to the input side before the switching element.

Therefore, even if the voltage on the output side becomes higher than that on the input side, the current can be prevented from flowing backward from the output side to the input side, and stable operation can be realized.

Further, the switching power supply circuit of the present invention is
As described above, the output voltage detecting means for detecting the output voltage and feeding back to the control of the switching cycle and the duty of the control means is further provided.

[0042] Therefore, since the control period and duty of the switching based on the detected output voltage, scan
It is possible to easily stabilize the voltage of the switching power supply circuit .

Further, as described above, the power supply device of the present invention is the switching power supply of the invention described in any of the above.
It is a configuration in which the circuit is packaged.

Therefore, since the switching power supply circuit is provided in one package, it is easy to mount and the electronic device using the switching power supply circuit can be miniaturized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a power supply circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram specifically showing the configuration of the power supply circuit shown in FIG.

3 (a) to 3 (c) are waveform diagrams showing voltage waveforms in the power supply circuit of FIG.

FIG. 4 is a waveform diagram illustrating power loss in a switching element of the power supply circuit of FIG.

FIG. 5 is a plan view showing the outer appearance of the power supply device according to the embodiment of the present invention.

FIG. 6 is a circuit block diagram showing a configuration of a conventional power supply circuit.

7 is a waveform diagram illustrating power loss in a switching element of the power supply circuit in FIG.

[Explanation of symbols]

1 Switching power supply circuit (power supply circuit) 2 rectifier circuit 2a diode bridge full wave rectifier circuit 3 Rectified voltage detection circuit (rectified voltage detection means) 4 Backflow prevention circuit (backflow prevention means) 5 switching elements 6 Control circuit (control means) 6a PWM comparator (control means) 7 Output voltage detection circuit (output voltage detection means) 8 smoothing circuit 10 IC (power supply device) C1 smoothing capacitor D1 diode (backflow prevention means) R1 resistance (rectified voltage detection means) R2 resistance (rectified voltage detection means) R3 resistance (control means) R4 resistance (control means) R5 resistance (control means) TR1 MOS transistor (switching element) ZD1 Zener diode (control means) ZD2 Zener diode (control means)

Continuation of the front page (56) Reference JP-A-11-41825 (JP, A) JP-A-9-261963 (JP, A) JP-A-9-65647 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) H02M 3/155

Claims (6)

(57) [Claims] 1. A switching element for switching a rectified voltage, and a control means for controlling a switching cycle and a duty of the switching element.
In the switching power supply circuit for supplying power to the load, the rectified voltage detection means for detecting the rectified voltage is provided , and the control means is detected by the rectified voltage detection means.
During the partial period when the rectified voltage is lower than the specified value.
Even if the above switching element is in the ON state, power is supplied.
With the load that can be supplied connected, the partial period
A switch characterized by controlling the switching so that the switching element is turned on only during the period
Power supply circuit . 2. The control means is activated only during the partial period.
Switch so that the switching element is turned on.
The power consumption of the switching element is reduced by controlling the switching
The switching power supply circuit according to claim 1 . 3. The depletion type switching element
2. The MOSFET according to claim 1 or 2.
2. The switching power supply circuit described in 2. 4. From the output side to the preceding stage of the switching element
Backflow prevention means to prevent current from flowing back to the input side.
4. The method according to any one of claims 1 to 3, characterized in that
A switching power supply circuit according to any one of the above . 5. An output voltage is detected to detect the output voltage of the control means.
Feed for control of switching period and duty
To further have an output voltage detection means for backing up
The switch according to any one of claims 1 to 4, characterized in that
Power supply circuit . 6. A switch according to any one of claims 1 to 5.
The feature is that the power supply circuit for switching
Power supply device.