JP3633891B2 - Power supply dummy circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dummy circuit for a power supply.
[0002]
[Prior art]
Generally, a dummy circuit composed of a resistor or the like is connected to the output of the power supply. This dummy circuit is used for discharging a smoothing capacitor provided in the power supply and for stabilizing the output voltage.
That is, when the current flowing through the load is very small, it is necessary to flow the current through the dummy circuit in order to discharge the charge accumulated in the smoothing capacitor. Further, when the load current is small, the output voltage of the power supply tends to fluctuate with the change of the load current. Therefore, it is necessary to always supply a certain amount of current to the output of the power supply using a dummy circuit.
[0003]
Conventionally, a resistor is used as the dummy circuit, and the resistor is connected to the output terminal of the power supply device as shown in FIG. Therefore, even when the load is not connected, current always flows from the power supply device to the resistor of the dummy circuit.
[0004]
When the dummy circuit is not connected, the output voltage of the power supply changes as shown in FIG. 9, for example. That is, when the output current is reduced as the load changes, the output voltage varies greatly. In particular, the fluctuation becomes significant when the output voltage is low.
Therefore, if a dummy current having a level indicated by a dotted line in FIG. 9 is always passed using a dummy circuit, fluctuations in the output voltage can be suppressed even if the load fluctuates.
[0005]
[Problems to be solved by the invention]
When the conventional dummy circuit is used, the dummy current flowing through the resistor of the dummy circuit and the dummy power consumed by the dummy circuit change as shown in FIG. 10 along with the change of the output voltage of the power supply device.
That is, as the output voltage of the power supply device increases, the dummy power consumed by the dummy circuit increases rapidly. However, since the power consumed by the dummy circuit is wasted, if the dummy power is increased, the loss of the power supply device is increased and the power efficiency is lowered.
[0006]
It is an object of the present invention to provide a power supply dummy circuit that can suppress voltage fluctuation of a power supply device and suppress an increase in loss.
[0007]
[Means for Solving the Problems]
[Claim 1] A power source having a transformer and connected to a power source including a DC voltage generating circuit that generates a DC voltage of a single polarity based on AC power supplied from one secondary winding of the transformer A reverse polarity DC voltage generating means for generating a DC voltage having a polarity opposite to that of the DC voltage output from the DC voltage generating circuit based on the AC power supplied from the secondary winding. And at least one pseudo load connected between the output terminal of the DC voltage generating circuit and the output terminal of the reverse polarity DC voltage generating means .
In Claim 1, the case where this invention is applied to the power supply device which outputs DC voltage of a single polarity is assumed. The reverse polarity direct current voltage generating means generates a direct current voltage having a reverse polarity to the direct current voltage output from the direct current voltage generation circuit. The pseudo load is connected between the output terminal of the DC voltage generation circuit and the output terminal of the reverse polarity DC voltage generation means.
Therefore, a voltage obtained by adding the first voltage appearing at the output terminal of the DC voltage generating circuit and the second voltage appearing at the output terminal of the reverse polarity DC voltage generating means is applied to the pseudo load. (Posted from 0012)
[0011]
請 Motomeko 2 is a dummy circuit of the power source connected to the output of the power supply, the pseudo changing the impedance of the dummy load connected to the output terminal of the power supply in response to the difference of the output voltage of the power supply Load control means is provided, and the pseudo load is composed of a series circuit of a first resistor, a transistor and a second resistor, and the pseudo load control means has a control voltage inversely proportional to the output voltage of the power source and a constant voltage. A differential amplifier that amplifies a difference from a reference voltage output from the constant voltage generation circuit to be generated; and an operational amplifier that amplifies the output of the differential amplifier, and the output of the operational amplifier is a base of the transistor It is characterized by being connected to .
[0013]
In 請 Motomeko 2, the dummy load control means automatically changed corresponding to the difference of the output voltage of the power supply impedance of the dummy load. That is, the impedance of the transistor constituting the pseudo load changes depending on the output of the operational amplifier.
[0014]
As shown in FIG. 9, in order to stabilize the output voltage of the power supply, a larger dummy current is required as the output voltage becomes lower. Therefore, it is necessary to flow a dummy current IL that exceeds a specified value at the lower limit value VL of the variable range of the output voltage. However, the dummy current required when the output voltage is large may be smaller than IL.
Therefore, if the impedance of the pseudo load is changed corresponding to the difference in the output voltage of the power supply, for example, characteristics as shown in FIG. 6 can be obtained. Therefore, an increase in dummy power when the output voltage is large can be suppressed.
[0015]
Further, in the 請 Motomeko 2, so constituting a dummy load using a transistor, it is possible to continuously change the impedance of the dummy load with a change in the output voltage. Further, it required not greens providing a switch for switching impedance.
[0016]
請 Motomeko 2 Oite is that generates a control voltage which varies inversely approximately the level change before SL output voltage.
Therefore, by controlling the impedance of the pseudo load using the control voltage, the magnitude of the dummy current can be changed in inverse proportion to the change in the output voltage.
[0017]
According to the second aspect of the present invention, it is possible to generate a control voltage that changes linearly with respect to a change in the output voltage, decreases as the output voltage increases, and increases as the output voltage decreases. By controlling the impedance of the pseudo load using this control voltage, it becomes possible to change the magnitude of the dummy current corresponding to the change of the output voltage.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
( Dummy circuit of first power source related to the present invention )
The dummy circuit of the first power supply in connection with the present invention, described with reference to FIG.
[0022]
The power supply output circuit shown in FIG. 1 includes a circuit that generates a positive DC voltage and a circuit that generates a negative DC voltage.
That is, the AC voltage appearing at the secondary winding 12 of the transformer 10 is rectified by the rectifier circuit 41, smoothed by the smoothing circuit 42, and output to the output terminal 22 as a positive DC voltage.
[0023]
The AC voltage appearing at the secondary winding 33 of the transformer 31 is rectified by the rectifier circuit 43, smoothed by the smoothing circuit 44, and appears at the output terminal 24 as a negative DC voltage.
The voltage V + of the output terminal 22 has a positive polarity with respect to the output terminal 23 that is a ground, and the voltage V− of the output terminal 24 has a negative polarity with respect to the output terminal 23.
[0024]
By supplying electric power to the primary winding 11 of the transformer 10 via a switching circuit and controlling the switching duty, the voltage V + of the output terminal 22 can be changed similarly to the output voltage shown in FIG.
[0025]
The voltage V− of the output terminal 24 can be similarly changed, but in this example, it is assumed that the voltage V− is fixed to a certain level.
In the case where no dummy current is supplied, as in the example of FIG. 9, when the output current flowing from the output terminal 22 to a load (not shown) decreases, the voltage V− of the output terminal 22 varies greatly with the current variation.
[0026]
Therefore, a pseudo load 26 is provided for flowing a dummy current. In the example of FIG. 1, both ends of the pseudo load 26 are connected to a positive output terminal 22 and a negative output terminal 24. Therefore, a voltage obtained by adding the potential difference of (V +) and the potential difference of (V−) is applied between the terminals of the pseudo load 26.
In this example, it is assumed that a resistor having a fixed impedance is used as the pseudo load 26. Accordingly, the magnitude of the dummy current flowing through the pseudo load 26 changes as shown in FIG. 5 in proportion to the voltage applied thereto.
[0027]
As shown in FIG. 9, in order to stabilize the output voltage, a larger dummy current is required as the output voltage becomes lower. Therefore, it is necessary to flow a dummy current exceeding a specified value at the lower limit value VL of the variable range of the output voltage.
When the impedance of the pseudo load 26 is determined so that the prescribed dummy current IL flows at the lower limit value VL, the change in the dummy current with respect to the change in the output voltage is represented by the characteristic X1 in FIG. The characteristic of the conventional dummy circuit is represented by X2.
[0028]
As shown in FIG. 5, the characteristic X1 has a larger slope than the characteristic X2, and the change in the dummy current with respect to the increase in the output voltage is small. Therefore, the maximum value IH1 of the dummy current in the dummy circuit of FIG. 1 is sufficiently smaller than the conventional maximum value IH2, and the loss in the dummy circuit is greatly reduced.
(First embodiment)
FIG. 2 is an electric circuit diagram showing the first embodiment of the present invention , which will be described with reference to FIG. This form corresponds to claim 1 . FIG. 2 is an electric circuit diagram showing a configuration of a power supply output circuit including the power supply dummy circuit of this embodiment.
[0029]
This embodiment is a modification of the first power supply dummy circuit related to the present invention . 2, elements corresponding to those in FIG. 1 are denoted by the same reference numerals. The following description will be omitted for parts having the same configuration and operation.
In this embodiment, the DC voltage generation circuit, the reverse polarity DC voltage generation means, and the pseudo load according to claim 1 correspond to the rectifier circuit 41, the negative voltage generation circuit 27, and the pseudo load 26, respectively.
[0030]
In this form, as shown in FIG. 2, the case where this invention is applied with respect to the power supply which outputs DC voltage of a single polarity is assumed. That is, the AC voltage appearing at the secondary winding 12 of the transformer 10 is rectified by the rectifier circuit 41, smoothed by the smoothing circuit 42, and output to the output terminal 22 as a positive DC voltage.
Therefore, in order to generate a negative voltage V− applied to one end of the pseudo load 26, a negative voltage generation circuit 27 is provided. The negative voltage generation circuit 27 includes a diode 28 and a capacitor 29.
[0031]
Further, the diode 14 of the rectifier circuit 41 and the diode 28 of the negative voltage generation circuit 27 are connected in common to one end of the secondary winding 12 with opposite polarities.
Accordingly, as in the case of FIG. 1, a voltage corresponding to the potential difference between the voltage V + of the output terminal 22 and the voltage V− output from the negative voltage generation circuit 27 is applied to the pseudo load 26, and the dummy flowing through the pseudo load 26. The current changes like a characteristic X1 shown in FIG.
[0032]
( Dummy circuit of second power source related to the present invention )
A dummy circuit of the second power source related to the present invention will be described with reference to FIG. FIG. 3 is an electric circuit diagram showing the configuration of the dummy circuit of the second power source related to the present invention .
[0033]
For example, when the dummy circuit shown in FIG. 3 is connected instead of the pseudo load 26 of the power source shown in FIG. 1, the terminals 50a and 50b in FIG. 3 are connected to the output terminals 22 and 23 in FIG. 1, respectively.
The dummy circuit shown in FIG. 3 includes a pseudo load 51, an operational amplifier 55, and an arithmetic circuit 56. The pseudo load 51 includes transistor 52 resistors 53 and 54.
[0034]
The impedance of the transistor 52 in the pseudo load 51 is determined according to the magnitude of the control voltage Vy applied to the positive input of the operational amplifier 55.
The arithmetic circuit 56 is a circuit that calculates and outputs the level of the reciprocal of the input. The voltage Vo of the terminal 50a, that is, the output voltage of the power source is applied to the input of the arithmetic circuit 56. That is, when the input voltage of the arithmetic circuit 56 is represented by Vin, the control voltage Vy appearing at the output of the arithmetic circuit 56 is (K / Vin) (K is a constant).
[0035]
Accordingly, when the output voltage of the power supply increases, the level of the control voltage Vy decreases and the impedance of the transistor 52 increases, so that the dummy current flowing through the pseudo load 51 decreases.
On the other hand, when the output voltage of the power supply decreases, the level of the control voltage Vy increases and the impedance of the transistor 52 decreases, so that the dummy current flowing through the pseudo load 51 increases.
[0036]
That is, the dummy current flowing through the pseudo load 51 changes according to the characteristics shown in FIG. As shown in FIG. 6, a sufficiently large dummy current flows when the output voltage is low. However, since the dummy current decreases as the output voltage increases, an increase in dummy power can be suppressed.
(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. This form corresponds to claim 2 . FIG. 4 is an electric circuit diagram showing the configuration of the dummy circuit of the power supply of this embodiment.
[0037]
This form is a modification of the dummy circuit of the second power source related to the present invention . 4, elements corresponding to those in FIG. 3 are denoted by the same reference numerals. The following description will be omitted for parts having the same configuration and operation.
In this embodiment, the pseudo load of claim 2 corresponds to the resistor 53, the transistor 52, and the resistor 54, the differential amplifier of claim 2 corresponds to the operational amplifier 65, and the operational amplifier of claim 2 corresponds to the operational amplifier 55. To do.
[0038]
For example, when the dummy circuit shown in FIG. 4 is connected instead of the pseudo load 26 of the power source shown in FIG. 1, the terminals 50a and 50b in FIG. 4 are connected to the output terminals 22 and 23 in FIG.
The dummy circuit shown in FIG. 4 includes a pseudo load 51, an operational amplifier 55, a Zener diode 62, an operational amplifier 65, and resistors 61, 63, and 64. The pseudo load 51 includes transistor 52 resistors 53 and 54.
[0039]
The impedance of the transistor 52 in the pseudo load 51 is determined according to the magnitude of the control voltage Vy applied to the positive input of the operational amplifier 55.
The operational amplifier 65 constitutes a differential amplifier circuit. A constant DC voltage Vref generated by the Zener diode 62 is applied to the positive input of the differential amplifier circuit. The voltage Vo of the terminal 50a, that is, the output voltage of the power supply is applied to the negative input of the differential amplifier circuit.
[0040]
The control voltage Vy appearing at the output of the operational amplifier 65 changes as shown in FIG. 7 according to the output voltage Vo.
Therefore, when the output voltage of the power supply increases, the level of the control voltage Vy decreases and the impedance of the transistor 52 increases, so that the dummy current flowing through the pseudo load 51 decreases.
[0041]
On the other hand, when the output voltage of the power supply decreases, the level of the control voltage Vy increases and the impedance of the transistor 52 decreases, so that the dummy current flowing through the pseudo load 51 increases.
That is, the dummy current flowing through the pseudo load 51 changes according to the characteristics shown by the dotted line in FIG. As shown by the dotted line in FIG. 6, a sufficiently large dummy current flows when the output voltage is low. However, since the dummy current decreases as the output voltage increases, an increase in dummy power can be suppressed.
[0042]
In addition, the dummy load 51 of the dummy circuit shown in FIGS. 3 and 4 is an output terminal 22 where a positive voltage appears and an output terminal 24 where a negative voltage appears instead of the pseudo load 26 shown in FIGS. It can also be used by connecting to.
[0043]
【The invention's effect】
According to the present invention, the dummy current when the output voltage of the power supply is high can be suppressed as compared with the conventional case. Therefore, an increase in dummy power can be suppressed, which is effective in improving the power supply efficiency. Further, the pseudo load can be reduced, and the space necessary for cooling the pseudo load can be eliminated.
[Brief description of the drawings]
FIG. 1 is an electric circuit diagram showing a configuration of a power supply output circuit including a first power supply dummy circuit related to the present invention .
FIG. 2 is an electric circuit diagram showing a configuration of a power supply output circuit including a power supply dummy circuit according to the first embodiment;
FIG. 3 is an electric circuit diagram showing a configuration of a dummy circuit of a second power source related to the present invention .
FIG. 4 is an electric circuit diagram showing a configuration of a dummy circuit of a power supply according to the second embodiment.
FIG. 5 is a graph showing a relationship between an output voltage of a power supply and a dummy current.
FIG. 6 is a graph showing a relationship between an output voltage of a power supply and a dummy current.
FIG. 7 is a graph showing the relationship between the output voltage Vo of the power supply and the control voltage Vy.
FIG. 8 is a block diagram showing a conventional dummy circuit.
FIG. 9 is a graph showing the relationship between the output voltage of the power supply and the output current.
FIG. 10 is a graph showing a relationship between an output voltage of a power supply, a dummy current, and dummy power.
[Explanation of symbols]
10, 31 Transformer 11, 32 Primary winding 12, 33 Secondary winding 14, 15, 18, 19 Diode 16, 20 Choke coil 17, 21 Capacitor 22, 23, 24 Output terminal 26 Pseudo load 27 Negative voltage generation Circuit 28 Diode 29 Capacitor 41, 43 Rectifier circuit 42, 44 Smoothing circuit 50a, 50b Terminal 51 Pseudo load 52 Transistor 53, 54, 61, 63 Resistor 55, 65 Operational amplifier 56 Operation circuit 62 Zener diode

Claims (2)

A dummy circuit of a power source having a transformer and connected to a power source including a DC voltage generation circuit that generates a DC voltage with a single polarity based on AC power supplied from one secondary winding of the transformer. And
Based on the AC power supplied from the secondary winding, reverse polarity DC voltage generation means for generating a DC voltage having a polarity opposite to the DC voltage output by the DC voltage generation circuit;
A power supply dummy circuit comprising: at least one pseudo load connected between an output terminal of the DC voltage generation circuit and an output terminal of the reverse polarity DC voltage generation means . A dummy circuit of the power source connected to the output of the power supply,
Providing a pseudo load control means for changing the impedance of the pseudo load connected to the output terminal of the power source in accordance with the difference in the output voltage of the power source;
The pseudo load is
It consists of a series circuit of a first resistor, a transistor and a second resistor,
The pseudo load control means includes
A differential amplifier that amplifies a difference between a control voltage inversely proportional to the output voltage of the power source and a reference voltage output from a constant voltage generation circuit that generates a constant voltage;
An operational amplifier for amplifying the output of the differential amplifier;
The power supply dummy circuit , wherein an output of the operational amplifier is connected to a base of the transistor .

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