JP2013192329A - Switching power supply device - Google Patents

Abstract

In a switching power supply device, the degree of freedom in setting power consumption when it is determined that an overcurrent state is raised.
A switching power supply device that converts a DC voltage applied to an input terminal to an alternating current using a switching element and applies the DC voltage to a primary side of a transformer, has a current detection terminal, and the voltage value of the current detection terminal is A controller for determining an overcurrent state when a predetermined threshold is reached, a first resistor and a second resistor connected in series between the input terminal and the current detection terminal, and between the current detection terminal and the ground terminal A third resistor connected, a current detection resistor for detecting a primary current of the transformer, a fourth resistor for dividing a voltage generated in the current detection resistor by the third resistor, and a first resistor and a second resistor. A Zener diode connected in a reverse bias direction between the connection point and the ground terminal.
[Selection] Figure 1

Description

  The present invention relates to a switching power supply device, and more particularly to a technique for increasing the degree of freedom of power consumption setting when it is determined that an overcurrent state occurs.

  The switching power supply device converts DC power into AC power using a switching element and supplies it to the primary side of the transformer. Then, predetermined DC power is obtained by rectifying and smoothing AC power transmitted to the secondary side of the transformer.

  FIG. 6 is a diagram showing a conventional schematic circuit example of a typical flyback switching power supply device as a switching power supply device. In this figure, a switching power supply device 300 receives an AC voltage Vin, converts it to a predetermined DC voltage Vo, and supplies it to a load RL.

  The input voltage Vin is rectified and smoothed by the diode bridge DB and the capacitor Cb, and becomes a DC voltage Vp having a value corresponding to the input voltage Vin. In general, a commercial power supply is used as the input voltage Vin. However, since the voltage varies from country to country and the usage environment also varies, in order to obtain a general-purpose power supply device, the input voltage Vin should be compatible with a range of about 90V to 264V. It is necessary to keep.

  The switching power supply apparatus 300 includes a control IC 310. The control IC 310 switches the switching element Q to convert the DC voltage Vp into high-frequency AC and applies it to the primary side of the transformer Tr. Since this energy is transmitted to the secondary side of the transformer Tr, the DC voltage Vo is output by rectifying by the diode Dr and smoothing by the capacitor Cr.

  The value of the DC voltage Vo is fed back to the control IC 310 by an output voltage monitoring circuit (not shown), and the control IC 310 adjusts the switching operation of the switching element Q so that the DC voltage Vo becomes a predetermined value. At startup, the control IC 310 receives the initial drive power via the startup resistor R4, and continues the control operation by receiving the operating power from an auxiliary winding (not shown) of the transformer Tr after starting the switching operation. To do.

  The switching power supply device 300 includes a current detection resistor R5 for detecting the current Ip flowing through the primary winding of the transformer Tr. A value obtained by dividing the voltage drop generated in the current detection resistor R5 by the resistor R6 and the resistor R3 (R3, R6 >> R5) is input to the current detection terminal IS of the control IC 310. When the voltage at the current detection terminal IS reaches a predetermined threshold value, the control IC 310 determines that an overcurrent state occurs, and temporarily stops the switching element Q switching operation to protect the component from a temperature rise or the like.

  As described above, the general-purpose power supply device needs to support a wide range of input voltage Vin, but even when the same power is output, as shown in FIG. The current Ip becomes smaller than that at the time of low voltage input. When the current Ip is small, the voltage drop of the current detection resistor R5 is also small. Therefore, when a high voltage is input, the power consumption when the voltage of the current detection terminal IS reaches the threshold value and the overcurrent state is determined is low. It will be much larger than the input.

  Therefore, in the switching power supply device 300, the DC voltage Vp obtained by rectifying and smoothing the input voltage Vin is divided using the input correction resistors R1 and R3 (R1 >> R5), and is shown in FIG. 7B. As described above, a bias voltage proportional to the input voltage is applied to the current detection terminal IS of the control IC 310.

  As a result, as shown in FIG. 7C, the voltage of the current detection terminal IS of the control IC 310 has a waveform in which a bias voltage and a voltage proportional to the current Ip are superimposed, and an overcurrent state is determined when a high voltage is input. The power consumption when it is done is designed to be suppressed.

JP 2009-268227 A

  By using the input correction resistors R1 and R3 to apply a bias voltage to the current detection terminal IS, power consumption when an overcurrent state is determined when a high voltage is input can be suppressed. FIG. 8 shows a state in which the voltage of the current detection terminal IS reaches a threshold value and is determined to be in an overcurrent state for each DC voltage Vp obtained by rectifying and smoothing the input voltage Vin in the conventional switching power supply apparatus 300. It is a figure which shows power consumption Pin. The broken line in the figure indicates the characteristic when there is no input correction resistor. By using the input correction resistor, the power consumption Pin when the overcurrent state is determined at the time of high voltage input is suppressed. I understand that.

  However, by providing an input correction resistor, the power consumption characteristics become convex as shown in this figure, and the overcurrent at a moderate voltage input is higher than the power consumption in the overcurrent state at the time of high voltage input. Power consumption in the state increases.

  The power consumption characteristic can be raised or lowered by changing the ratio of the input correction resistors R1 and R3, but the fluctuation tends to be the same in the entire input voltage range. For example, by setting the ratio of the resistor R3 to be large, it is possible to reduce the power consumption that causes an overcurrent state when a medium voltage is input. However, since the characteristics at the time of high voltage input change in the same way, the power consumption that becomes the overcurrent state at the time of high voltage input becomes too small, and the overcurrent state occurs at the start-up when the power consumption is large, so that it starts normally There is a risk that it will not be possible.

  On the other hand, if the input correction resistor is set so that the power consumption that becomes the overcurrent state at the time of high voltage input becomes large in order to avoid the starting failure at the time of high voltage input, the overcurrent state at the time of moderate voltage input The power consumption becomes larger. In this case, the size of the core must be increased in order to avoid magnetization saturation of the transformer Tr, or the wire diameter must be increased in order to reduce heat generation, leading to an increase in the size of the switching power supply device.

  Therefore, an object of the present invention is to increase the degree of freedom in setting power consumption when it is determined that the switching power supply apparatus is in an overcurrent state.

In order to solve the above problems, a switching power supply device according to the present invention is a switching power supply device that converts a DC voltage applied to an input terminal into an alternating current using a switching element and applies the AC voltage to a primary side of a transformer, and includes a current detection terminal. A control unit for determining an overcurrent state when the voltage value of the current detection terminal reaches a predetermined threshold; a first resistor connected in series between the input terminal and the current detection terminal; Two resistors, a third resistor connected between the current detection terminal and the ground terminal, a current detection resistor for detecting a primary side current of the transformer, and a voltage generated in the current detection resistor with the third resistor And a Zener diode connected in a reverse bias direction between a connection point between the first resistor and the second resistor and the ground terminal.
For example, the first resistor corresponds to the resistor R1 of the embodiment, the second resistor corresponds to the resistor R2 of the embodiment, the third resistor corresponds to the resistor R3 of the embodiment, and the fourth resistor This corresponds to the resistor R6 in the example, and the current detection resistor corresponds to the resistor R5 in the embodiment.
In order to suppress the influence of characteristic variation due to the temperature of the Zener diode, a diode in the forward bias direction may be connected in series with the Zener diode.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device can raise the freedom degree of power consumption setting when it determines with an overcurrent state.

It is a block diagram which shows the structure of the switching power supply device which concerns on this embodiment. It is a figure which shows the bias voltage applied to current detection terminal IS of control IC. It is a figure which shows the power consumption characteristic when it determines with the overcurrent state in the switching power supply device of this embodiment. It is a block diagram which shows the switching power supply device at the time of using DC power supply. It is a block diagram which shows the switching power supply device which connected the diode for temperature compensation. It is a figure which shows the example of the conventional schematic circuit of the switching power supply of a typical flyback system as a switching power supply. It is a figure which shows the waveform of each part at the time of high voltage input and low voltage input. It is a figure which shows the power consumption characteristic when it determines with the overcurrent state in the conventional switching power supply device.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the switching power supply device according to the present embodiment. As shown in this figure, the switching power supply apparatus 100 according to the present embodiment receives an AC voltage Vin, converts it to a predetermined DC voltage Vo, and supplies it to a load RL.

  The input voltage Vin is rectified and smoothed by the diode bridge DB and the capacitor Cb, and becomes a DC voltage Vp having a value corresponding to the input voltage Vin. A portion to which the DC voltage Vp is applied is referred to as an input end, and a primary ground portion of the transformer Tr is referred to as a ground end.

  The switching power supply device 100 includes a control IC 110. The control IC 110 switches the switching element Q to convert the DC voltage Vp into high-frequency AC and applies it to the primary side of the transformer Tr. Since this energy is transmitted to the secondary side of the transformer Tr, the DC voltage Vo is output by rectifying by the diode Dr and smoothing by the capacitor Cr.

  The value of the DC voltage Vo is fed back to the control IC 110 by an output voltage monitoring circuit (not shown), and the control IC 110 adjusts the switching operation of the switching element Q so that the DC voltage Vo becomes a predetermined value. At startup, the control IC 110 receives supply of initial drive power via the startup resistor R4. After starting the switching operation, the control IC 110 continues operation by receiving operation power from an auxiliary winding (not shown) of the transformer Tr. To do.

  The switching power supply device 100 includes a current detection resistor R5 for detecting the current Ip flowing through the primary winding of the transformer Tr. A value obtained by dividing the voltage drop generated in the current detection resistor R5 by the resistor R6 and the resistor R3 (R3, R6 >> R5) is input to the current detection terminal IS of the control IC 110. At this time, the resistor R3 is connected to the ground terminal and the current detection terminal IS of the control IC 110. When the voltage at the current detection terminal IS reaches a predetermined threshold value, the control IC 110 determines that an overcurrent state occurs, and temporarily stops the switching element Q switching operation to protect the component from a temperature rise or the like.

  The above configuration is the same as that of the conventional switching power supply apparatus 300. However, in the switching power supply apparatus 100 of the present embodiment, the conventional input correction resistor R1 that connects the input terminal and the current detection terminal IS of the control IC 110 is provided. The resistor R1 and the resistor R2 are connected in series. The connection point between the resistor R1 and the resistor R2 and the ground terminal are connected by a Zener diode Dz.

  The Zener diode Dz is connected in the reverse bias direction. When the voltage Vp at the input terminal becomes equal to or higher than Vpz, the voltage applied to the resistors R2 and R3 is equal to the Zener voltage Vz regardless of the value of the voltage Vp at the input terminal. To do. Here, Vpz is a voltage value at the input terminal when the voltage applied to the resistors R2 and R3 is the same as the Zener voltage Vz.

  On the other hand, when the voltage at the input terminal is equal to or lower than Vpz, no current flows through the Zener diode Dz. For this reason, as shown in FIG. 2, the bias voltage applied to the current detection terminal IS of the control IC 110 is proportional to the input terminal voltage Vp when the input terminal voltage Vp is equal to or lower than Vpz, and when the input terminal voltage Vp is equal to or higher than Vpz. It becomes almost constant.

  In the range where the voltage at the input terminal is equal to or lower than Vpz, the bias voltage applied to the current detection terminal IS of the control IC 110 is proportional to the input terminal voltage Vp. A convex shape is formed as in the conventional case using a resistor. Since the bias voltage applied to the current detection terminal IS of the control IC 110 is constant in the range where the voltage at the input terminal is equal to or higher than Vpz, the power consumption characteristic when it is determined as an overcurrent state has conventionally been an auxiliary input resistance. As in the case of not using it, it increases as the input terminal voltage Vp increases.

  For this reason, the power consumption characteristics when the switching power supply device 100 according to the present embodiment is determined to be in the overcurrent state have a convex shape and a right-upward shape with the input terminal voltage Vpz as a boundary, as shown in FIG. It becomes a connected shape.

  At this time, the convex shape below the input terminal voltage Vpz can be set by the values of the resistors R1, R2, R3, R5, and R6, and the upward shape above the input terminal voltage Vpz is the Zener voltage. It can be set by the values of Vz, resistor R2, resistor R3, resistor R5, and resistor R6.

  Therefore, the power consumption Pin when the overcurrent state is determined at an intermediate input voltage is not too large, and the power consumption Pin when the overcurrent state is determined at a high input voltage. It can be set individually so that it is not too small. That is, the degree of freedom in setting the power consumption when it is determined as an overcurrent state is increased.

  For example, the value of the resistor R3 is relatively increased to increase the bias voltage at a medium input voltage, to reduce power consumption when it is determined as an overcurrent state, and to bias by the effect of the Zener diode Dz. An increase in voltage can be suppressed, and power consumption can be increased when it is determined as an overcurrent state at a high input voltage.

  As a result, it is possible to prevent an increase in the size of the transformer due to large power consumption when it is determined as an overcurrent state at a moderate input voltage, and an overcurrent state occurs normally when starting up at a high voltage input. It becomes possible to prevent the failure to start.

  In addition, as shown in FIG. 4, the switching power supply apparatus 100 may be configured to connect the DC power supply E having the voltage Vp to the input end. In this case, the diode bridge DB is not necessary.

  Further, a diode Dc having a temperature characteristic opposite to that of the Zener diode Dz may be connected in series with the Zener diode Dz in the forward bias direction. Thereby, the influence of the characteristic fluctuation | variation by the temperature of Zener diode Dz can be suppressed. A diode-connected transistor may be used instead of the diode Dc.

DESCRIPTION OF SYMBOLS 100 ... Switching power supply device 300 ... Switching power supply device 110 ... Control IC
310 ... Control IC

Claims (2)

A switching power supply device that converts a DC voltage applied to an input terminal into an alternating current using a switching element, and applies it to a primary side of a transformer,
A control unit having a current detection terminal and determining an overcurrent state when a voltage value of the current detection terminal reaches a predetermined threshold;
A first resistor and a second resistor connected in series between the input terminal and the current detection terminal;
A third resistor connected between the current detection terminal and the ground terminal;
A current detection resistor for detecting a primary side current of the transformer;
A fourth resistor for dividing a voltage generated in the current detection resistor by the third resistor;
A switching power supply device comprising: a Zener diode connected in a reverse bias direction between a connection point between the first resistor and the second resistor and the ground terminal.   2. The switching power supply device according to claim 1, wherein a diode in a forward bias direction is connected in series with the Zener diode.