JP4728360B2 - Power circuit - Google Patents

Description

  The present invention relates to a DC-DC conversion power supply circuit, for example, a DC-DC conversion power supply circuit having two operation modes of a normal operation mode and an operation standby mode.

In recent years, electrical appliances that are always energized, such as televisions and video tape recorders, are used in the standby mode for most of the time, and are rapidly consumed in these standby modes. The ratio of electric power to the total power consumption is increasing year by year. Thus, how to reduce the power consumption in the operation standby mode is a major technical problem.
A DC-DC conversion power supply circuit having a conventional operation standby mode will be described below with reference to FIG.
The input voltage Vin supplied from the primary side is converted into high-frequency alternating current by the switch 22, the PWM control element 36, and the transformer 24. After voltage conversion by the transformer 24, the input voltage Vin is rectified to direct current by the secondary-side smoothing circuit 25, and Vout1 and Vout2 Is output. The PWM control element 16 is supplied with a voltage from the smoothing circuit 23 connected to the primary auxiliary winding of the transformer 24, and performs PWM control of the input by turning on and off the switch 22. Vout1 and Vout2 are connected to the secondary side smoothing circuit 25 in parallel. The switch 26 is turned on / off by a control signal from the control circuit 37, and the output of Vout2 is turned on in the normal operation mode and turned off in the operation standby mode. The output voltage detection circuit 28 includes a light emitting portion 34 of a photocoupler, a shunt regulator 31, a resistor 38 and a resistor 39.

  When the reference voltage determined by the shunt regulator 31 is Vref, and the resistance values of the resistor 38 and the resistor 39 are R1 and R2, respectively.

(Equation 1)
Vout1 = Vref × (1 + R1 / R2)

It becomes. The light emitting unit 34 of the photocoupler detects a change in Vout1, converts the current, and transmits this to the light receiving unit 35 of the photocoupler. The PWM control element 36 performs PWM control of Vin by turning on and off the switch 22 so that Vout1 becomes a predetermined value based on a signal received from the light receiving unit 35.
In the normal operation mode, the switch 26 is turned on by a signal from the control circuit 37, and both Vout1 and Vout2 are output. Since Vout1 and Vout2 are connected in parallel, Vout1 should be Vout2. However, in actuality, the switch 26 has a voltage drop corresponding to the ON resistance value of the switch 26 × the output current, so Vout2 is slightly smaller than Vout1. Become.
In the operation standby mode, the switch 26 is turned off by a signal from the control circuit 37, the output of Vout2 is stopped, and Vout1 is output at the same voltage as in the normal operation. In this conventional example, Vout1 becomes the same voltage in the normal operation mode and the standby mode. However, in this other example, the DC-DC conversion for reducing the standby voltage in the operation standby mode described in JP-A-7-170730 is described. There is a power circuit. This is to reduce the output voltage in the operation standby mode by changing the division resistance ratio of the output voltage detection circuit for controlling the PWM control element according to the operation mode.

However, in the conventional configuration shown above, Vout1 cannot be changed even when the normal operation mode is shifted to the operation standby mode, and the voltage is applied to the load in the operation standby mode under the same conditions as in the normal operation. I was supplying. For this reason, there existed a problem from a viewpoint of power consumption reduction.
Further, when the system-side capacitance 30 of Vout2 is large, an inrush current flows to charge the capacitance 30 when the operation standby mode is canceled, and Vout1 may temporarily drop. In this case, although Vout1 is restored immediately, there is a risk of causing a logic reset (about 4.7 [V] or less) on the system side.
Further, in the circuit described in Japanese Patent Laid-Open No. 7-170730, a similar phenomenon in which the voltage drops temporarily was also observed.
Further, in the normal operation mode, since the switch 26 has an on-resistance value, Vout2 slightly decreases due to a voltage drop at the switch 26.

Accordingly, a first object of the present invention is to provide a power supply circuit that can reduce Vout1 in the operation standby mode, prevent a drop in the voltage of Vout1 when the operation standby mode is canceled, and supply a stable voltage. That is.
A second object of the present invention is to provide a power supply circuit in which a voltage drop at the switch is reduced by using a switch element having a small on-resistance value when turning on / off Vout2. .

In the first aspect of the present invention, a secondary side voltage converted by a transformer and rectified to a direct current through a secondary side smoothing circuit, and a first voltage output means to which the secondary side voltage is connected; Second voltage output means, and an output voltage detection circuit for detecting a voltage change of the second voltage output means by resistance division in order to set the secondary side voltage to a predetermined voltage and transmitting the change to the primary side of the transformer A first switch connected in series to the first voltage output means; a second switch for detecting an output voltage downstream of the first switch and changing a voltage dividing resistance ratio of the output voltage detection circuit; A normal operation mode in which a voltage is output from the first voltage output means with the first switch turned on, and an operation standby in which no voltage is output to the first voltage output means with the first switch turned off. Mode, and When the first switch is turned from on to off to enter the operation standby mode, the second switch detects the output stop of the first voltage output means and changes the voltage dividing resistance ratio of the output voltage detection circuit. Then, the primary side of the transformer is controlled so that the secondary side voltage is lower than the normal operation mode. When the first switch is turned on from the off state to the normal operation mode, the second switch is By detecting the output voltage of the first voltage output means and changing the voltage dividing resistance ratio of the output voltage detection circuit, the primary side of the transformer is adjusted so that the secondary side voltage becomes the voltage of the normal operation mode. The first object is achieved by a DC-DC conversion power supply circuit that is controlled.
According to a second aspect of the present invention, in the first aspect of the present invention, the first switch is an N-type MOSFET or a relay to achieve the second object.

In the first aspect of the invention, in the operation standby mode, the output of Vout2 is stopped and detected to reduce the output voltage of Vout1, and in the normal mode, Vout2 is output and detected to detect the output voltage of Vout1. By increasing the power consumption, power consumption in the standby mode can be reduced, and a drop in the voltage of Vout1 at the time of switching from the operation standby mode to the normal mode can be prevented.
According to the second aspect of the present invention, the voltage drop at the switch can be reduced by turning on and off Vout2 with the switch having a small on-resistance value.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG. 1 and FIG.
FIG. 1 shows a power supply circuit for DC-DC conversion according to an embodiment of the present invention.
The input voltage Vin supplied from the primary side is converted into high-frequency alternating current by the switch 2, the PWM control element 16 and the transformer 4, and after voltage conversion by the transformer 4, it is rectified to direct current by the secondary-side smoothing circuit 5, and Vout1 and Vout2 Is output.

The PWM control element 16 is supplied with a voltage from the smoothing circuit 3 connected to the primary auxiliary winding of the transformer 4 and turns the switch 2 on and off to modulate the pulse width of the input. Vout1 and Vout2 are connected to the secondary side smoothing circuit 5 in parallel. The switch 6 is turned on / off by a control signal from the control circuit 19, and the output of Vout2 is turned on in the normal operation mode and turned off in the operation standby mode. The output voltage detection circuit 8 includes a photocoupler light emitting unit 17, a shunt regulator 11, a resistor 13, and a resistor 12. The light emitting unit 17 of the photocoupler detects a change in Vout1, converts the current, and transmits this to the light receiving unit 18 of the photocoupler. The PWM control element 16 performs PWM control of Vin by turning on and off the switch 2 so that Vout1 becomes a predetermined value based on a signal received by the light receiving unit 18. An output voltage detection circuit 8 is connected to Vout1 and Vout2.
The output voltage detection circuit 8 includes a switch 15 made of a transistor having a base connected to Vout2 and a resistor 14 that can be turned on / off by the switch 15. The resistor 14 is connected in parallel to the resistor 13 via the switch 15.

With the above configuration, in the normal operation mode, the switch 6 is turned on by the signal from the control circuit 19, and Vout2 is output. Although Vout1 and Vout2 are connected in parallel, as described above, since there is a voltage drop at the switch 6, Vout2 is slightly smaller than Vout1. While Vout2 is being output, the switch 15 is off and the resistor 14 does not function, so Vout1 and Vout2 are determined by the divided resistance ratio of the resistor 13 and the resistor 12.
When the reference voltage determined by the shunt regulator 11 is Vref, and the resistance values of the resistor 13 and the resistor 12 are R1 and R2, respectively.

(Equation 2)
Vout1 = Vref × (1 + R1 / R2)

It becomes.
In the operation standby mode, the signal from the control circuit 19 turns off the switch 6 and stops the output to Vout2. When the output to Vout2 is stopped, the switch 15 is turned on, and the resistor 13 and the resistor 14 are connected in parallel. The output of Vout1 is determined by the combined resistance in which the resistor 13 and the resistor 14 are connected in parallel, and the voltage dividing resistance ratio between the resistor 13 and the resistor 12. At this time, if the value of the resistor 14 is R3,

(Equation 3)
Vout1 = Vref × ((R1 × R3) / (R1 + R3) + R2) / R2

Thus, when the resistor is appropriately selected so that R1 >> R3, Vout1 in the operation standby mode can be reduced to a predetermined value.
As an example, if R1 = 560 [Ω], R2 = 510 [Ω], R3 = 10 [kΩ] Vref = 2.5 [V],
Normal operation mode Vout2 = 5.245 [V]
Operation standby mode Vout2 = 5.0995 [V]
Thus, the output voltage in the operation standby mode can be reduced.
Here, assuming that a current of 1 [A] always flows on the system side of Vout1,
The power consumption in the normal operation mode is

(Equation 4)
5.245 [V] × 1 [A] = 5.245 [W]

The power consumption in the standby mode is

(Equation 5)
5.0995 [V] × 1 [A] = 5.099 [W]

Thus, power saving of 0.1455 [W] is achieved.
Further, as described above, in the conventional circuit shown in FIG. 3, when the capacitance 30 of the system on the Vout2 side is large, the capacitance 30 is charged when the operation standby mode is switched to the normal mode. In addition, a large inrush current flows, and as a result, a temporary voltage drop 53 of Vout1 shown in FIG. 5 may occur.
Usually, in order to prevent this voltage drop, it is necessary to increase the capacitance of the secondary side smoothing circuit 25. In this embodiment, switching from the operation standby mode to the normal operation mode is performed by turning on the switch 6 based on a signal from the control circuit 19, detecting Vout2 output as a result, turning off the switch 15, and turning off the output voltage detection circuit 8. Therefore, the switching from the operation standby mode of the Vout1 to the normal operation mode is slightly delayed with respect to the release of the operation standby mode signal, so that the Vout1 does not drop. A voltage can be supplied stably.
In the DC-DC conversion power supply circuit according to this embodiment, it is desirable to use an element having a small on-resistance value in order to minimize the voltage drop due to the on-resistance value of the switch 6. Normally, a P-type MOS-FET is used as the switch 6, but the loss due to the switch 6 can be reduced by using an N-type MOS-FET or a relay.

FIG. 2 is a diagram illustrating the operation of the power supply circuit for DC-DC conversion according to the second embodiment as time on the horizontal axis and voltage on the vertical axis. While the operation standby mode signal 41 is output by the control circuit 19, Vout1 is 5 [V] and Vout2 is 0 [V].
When the operation standby mode signal 41 is canceled and the normal operation mode is entered, the switch 6 is turned on and Vout2 is output. By detecting this turned-on Vout2 and turning off the switch 15, the voltage-dividing resistance ratio with respect to the shunt regulator 11 changes, and Vout2 rises to 5.2 [V]. Since Vout1 rises with the switch 15 turned off after detecting that Vout2 is turned on, the rise of Vout2 causes a delay 44 with respect to the release of the operation standby mode 41, and then becomes 5.2 [V]. Become.

FIG. 4 is a diagram showing the operation of the conventional DC-DC conversion power supply circuit of FIG. 3 as time on the horizontal axis and voltage on the vertical axis. Vout1 is always 5.2 [V] regardless of the presence or absence of the operation standby mode signal 46. When the operation standby signal 46 is released and the operation mode is shifted to the normal operation mode, Vout2 increases from 0 [V] to 5.2 [V].
FIG. 5 is a diagram showing the operation of a conventional DC-DC conversion power supply circuit when the electrostatic capacity 30 of the system on the Vout2 side is large, with time on the horizontal axis and voltage on the vertical axis. When the operation standby mode signal 50 is canceled and the normal operation mode is entered, Vout2 is output. At this time, since the electrostatic capacitance 30 on the system side is charged, an inrush current flows, and a temporary voltage drop 53 occurs in Vout1. Although this drop in Vout1 recovers immediately, in some cases, it may cause a logic reset on the system side.

It is a circuit diagram of the power supply circuit for DC-DC conversion based on the Example of this invention. It is a wave form diagram of the power supply circuit for DC-DC conversion conversion based on the Example of this invention. It is a circuit diagram of the power supply circuit for the conventional DC-DC conversion. It is a wave form diagram of the power supply circuit for the conventional DC-DC conversion. It is a wave form diagram of the power supply circuit for the conventional DC-DC conversion in case an inrush current is large.

Explanation of symbols

2 switch 6 switch 7 operation standby mode voltage reduction circuit 8 output voltage detection circuit 11 shunt regulator 12 resistor 13 resistor 14 resistor 15 switch 16 PWM control element 17 light emitting unit 18 light receiving unit

Claims (2)

A secondary side voltage converted by a transformer and rectified to a direct current through a secondary side smoothing circuit;
First voltage output means to which the secondary side voltage is connected; second voltage output means;
An output voltage detection circuit for detecting a voltage change of the second voltage output means by resistance division in order to set the secondary side voltage to a predetermined voltage and transmitting it to the primary side of the transformer;
A first switch connected in series to the first voltage output means;
A second switch that detects an output voltage downstream of the first switch and changes a voltage dividing resistance ratio of the output voltage detection circuit;
A normal operation mode in which the first switch is turned on to output a voltage from the first voltage output means;
An operation standby mode in which the first switch is turned off and no voltage is output to the first voltage output means, and
When the first switch is turned from on to off to enter the operation standby mode, the second switch detects the output stop of the first voltage output means and changes the voltage dividing resistance ratio of the output voltage detection circuit. And the primary side of the transformer is controlled so that the secondary side voltage is lower than the normal operation mode.
When the first switch is turned on from the off state to the normal operation mode, the second switch detects the output voltage of the first voltage output means and changes the voltage dividing resistance ratio of the output voltage detection circuit. The power source circuit for DC-DC conversion is characterized in that the primary side of the transformer is controlled so that the secondary side voltage becomes a voltage in a normal operation mode.   The power supply circuit according to claim 1, wherein the first switch includes an N-type MOSFET or a relay.

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