JPH11122917A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize the output of a transformer by taking first (the output voltage of a rectifying and smoothing circuit) and second (the terminal voltage of output terminals) voltage detecting means as input, dividing the outputs of the voltage detecting means through a voltage dividing means, taking the output voltage of the rectifying and smoothing circuit as input, obtaining the error output of the divided voltage obtained from the voltage dividing means, relative to a reference voltage, through an error amplifying means, and controlling a switching means according to the output of the error amplifying means. SOLUTION: Two diodes D3, D4 for terminal voltage detection are placed in series between a rectifying and smoothing circuit (a diode D2 and a capacitor C2) and an output switch Q2, and the series circuit of the diodes D3, D4 is connected in series with a voltage dividing resistor R1. Further, a diode D5 is installed so that input is taken between the output switch Q2 and an output terminal V1, and the diodes D3, D4 are inputted between the series circuit and the voltage dividing resistor R1. When the output switch Q2 is on, the output of the rectifying and smoothing circuit is connected to the output terminal V1 and GND through the output switch Q2. When the output switch Q2 is off, detection voltages are obtained through the diodes D3, D4 and voltage dividing resistors R1, R2, and feedback control is exercised on the detection voltages through a controller 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator.

[0002]

2. Description of the Related Art One conventional switching regulator used as a power supply in OA equipment is disclosed in Japanese Unexamined Patent Publication No.
No. 59341, and the switching regulator is configured as shown in FIG. That is, the commercial power supply 1 is full-wave rectified by the full-wave rectifier circuit D1, and is also smoothed by the smoothing capacitor C1, and this DC current is
The voltage is intermittently supplied to the primary winding of the transformer T1 by a switching element Q1 such as ET, and is converted to a required voltage by the transformer T1. Then, the AC output from the secondary winding of the transformer T1 is converted into DC by the rectifier diode D2 and the smoothing capacitor C2, and a required DC current output is obtained at the output terminal V1.

On the output side of the rectifying / smoothing circuit including the diode D2 and the capacitor C2, a shunt regulator IC1 serving as an error amplifying circuit is provided, and connection of voltage dividing resistors R1 and R2 for dividing a voltage between output terminals V1 and GND. The point is connected to the reference terminal of the regulator IC1.

The photodiode PC1 'of the photocoupler connected in series to the regulator IC1 is activated by the current flowing through the regulator IC1, and the phototransistor PC1 of the photocoupler is connected to the switching element Q1.
1 is connected to a controller 2 for controlling a switching frequency. The regulator IC1 is connected to the voltage supplied to the reference terminal and the regulator IC1.
The current flowing through the regulator IC1, that is, the drive current of the photodiode PC1 'is controlled in accordance with the difference voltage from the reference voltage.

In the switching regulator described above, as shown in FIG. 4, it is desirable to provide an output switch Q2 for turning the output on and off at a stage preceding the output terminal V1, which is extremely useful in practical use.

For example, when the output switch Q2 is on,
When the output voltage between the output terminals V1 and GND increases, the regulator IC1 to which the divided voltage is input flows a large current proportional to the difference voltage from the reference voltage to increase the light emission amount of the photo die PC1 '. . In the phototransistor PC1, the amount of light received from the photodiode PC1 'increases, and a current proportional to this amount of light is input to the controller 2. Further, the controller 2 controls the switching element Q1 according to the current value by increasing the current flowing through the phototransistor PC1, reduces the output of the transformer T1, and sets the output terminals V1, G
The voltage between ND is reduced.

Contrary to the above, when the output voltage between the output terminals V1 and GND decreases, the regulator IC1 to which the divided voltage is input flows a current proportional to the difference voltage from the reference voltage, and the photodiode PC1 'Reduce the amount of light emitted. In the phototransistor PC1, the amount of light received from the photodiode PC1 'decreases, and a current proportional to this amount of light is input to the controller 2. And
In the controller 2, the current flowing through the phototransistor PC1 decreases, so that the switching element Q1 is controlled in accordance with the current value, the output of the transformer T1 increases, and the voltage between the output terminals V1 and GND increases.

In this manner, the switching is controlled by feeding back the output voltage, so that a constant output voltage is always supplied stably. Further, the output switch Q
When 2 is off, a divided voltage cannot be obtained by the voltage dividing resistors R1 and R2, and the shunt regulator IC1 does not function normally and cannot be controlled. That is, since the output voltage is not applied to the reference terminal, the regulator IC 1 uses the controller 2 via the photocoupler.
Controls the switching element Q1 so as to increase the output of the transformer T1, and the output of the transformer T1 becomes abnormally high, resulting in trouble.

Therefore, the series circuit of the shunt regulator IC1 and the photodiode PC1 'and the output switch Q
2 and a Zener diode ZD1 for inputting the output voltage of the rectifying and smoothing circuit (diode D2 and capacitor C2) and inputting a constant voltage to the reference terminal of the shunt regulator IC1 when the output switch Q2 is off, instead of the divided voltage. Is provided. The Zener voltage of the Zener diode ZD1 is set higher by 1.5 V due to, for example, the difference between the terminal voltage of the output terminal V1 and the reference voltage of the regulator IC1.

When the output switch Q2 is on,
Since the output of the rectifying / smoothing circuit is output to the output terminal V1 through the output switch Q2, the voltage across the Zener diode ZD1 becomes lower than the Zener voltage, so that no current flows through the Zener diode ZD1 and the state is the same as the open state. Become. For this reason, the detection voltages by the voltage dividing resistors R1 and R2 are input to the regulator IC1, the feedback control is performed by the controller 2 as described above, and the predetermined voltage is stably supplied to the output terminal V1.

When the output switch Q2 is turned off, the detection voltage from the voltage dividing resistors R1 and R2 cannot be obtained, but the output of the rectifying / smoothing circuit is supplied to the Zener diode ZD1. The difference between the Zener voltage of the Zener diode ZD1 and the Zener voltage is input to the regulator IC1, and the regulator IC1 inputs a current corresponding to an error voltage between this voltage and the reference voltage to the controller 2 via a photocoupler. Therefore, the controller 2 controls the switching of the switching element Q1 stably, and
The output side of No. 1 is in a non-control state and does not become abnormally high voltage, and is safe.

[0012]

However, the switching regulator having the above configuration has the following problems. That is, in the switching regulator having the above-described configuration, a zener diode is provided between the rectifying and smoothing circuit and the output switch in order to prevent the output side of the transformer from being in an uncontrolled state and an abnormally high voltage when the output switch is off. , The Zener voltage of the Zener diode only has a specified value (for example, in the related art, it is set to be higher by 1.5 V due to the difference between the terminal voltage of the output terminal and the reference voltage of the regulator). When turned off, the output of the transformer is 1.5V from the terminal voltage of the output terminal.
A high voltage will be output. At this time, in the case of a multi-output switching regulator, the output terminal that does not detect the output voltage, that is, the output whose output voltage is set by the turns ratio of the output winding of the transformer is the set output terminal voltage. A voltage 1.5 V higher than that is output.

Further, even when the output switch is on, if a large output current is required by an OA device or the like connected to the output terminal, a large current flows through the output switch, resulting in a large voltage drop. This tendency increases as inexpensive output switching elements are used. Since the output voltage is detected between the output terminals, the output voltage of the transformer becomes the voltage obtained by adding the voltage drop of the output switch to the terminal voltage of the output terminal to compensate for the voltage drop at the output switch. When the voltage exceeds the Zener voltage of the Zener diode, the Zener diode malfunctions, the terminal voltage of the output terminal drops, and it becomes impossible to stably supply a predetermined voltage to the output terminal.

Furthermore, when the voltage on the output side of the transformer exceeds the Zener voltage of the Zener diode due to the influence of noise or the like, a malfunction of the Zener diode may similarly occur, and a stable output voltage is supplied to the output terminal. You can't do that.

Therefore, the present invention has been made in consideration of the above-mentioned problems of the prior art, and an object thereof is to stably supply a predetermined voltage when an output switch is turned on. The output voltage of the transformer can be stabilized even when the output switch is off,
An object of the present invention is to provide a highly reliable switching regulator.

[0016]

To achieve the above object, a switching regulator of the present invention has the following configuration. That is, in the switching regulator, switching means for interrupting the DC input, a transformer for converting the interrupted DC input to a predetermined voltage, and a rectifying and smoothing circuit for rectifying and smoothing at least one AC output from the transformer and outputting the rectified and smoothed output. An output switch provided between the rectifying / smoothing circuit and an output terminal; first voltage detecting means for detecting an output voltage of the rectifying / smoothing circuit; and second voltage detecting means for detecting a terminal voltage of the output terminal. A voltage dividing means for inputting the first and second voltage detecting means and dividing the voltage of the voltage detecting means, and a voltage dividing means for receiving the output voltage of the rectifying and smoothing circuit as an input and obtaining the divided voltage. Error amplification means for obtaining an error output with respect to the reference voltage.

Alternatively, the first voltage detecting means is composed of two series-connected diodes to which the output of the rectifying / smoothing circuit is inputted, and the second voltage detecting means is a diode to which an output terminal is inputted. There is a feature.

Alternatively, the first voltage detecting means comprises a diode and a resistor connected in series with the output of the rectifying and smoothing circuit as an input, and the second voltage detecting means is a diode with an output terminal as an input. It is characterized by the following.

[0019]

In the switching regulator having the above-described configuration, when the output switch is on, a predetermined voltage can be stably supplied to the output terminal, and when the output switch is off, the detection from the terminal voltage detecting means can be performed. Since a voltage can be obtained, a detection voltage can be input to the error amplifying means. By controlling the switching of the switching means by the control means, the output voltage of the transformer can be stabilized.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a circuit diagram of a switching regulator according to Embodiment 1 of the present invention. FIG.
4, the same reference numerals as those in FIG. 4 denote the same or corresponding elements.

FIG. 1 differs from the prior art in that two diodes D3 and D4 for detecting a terminal voltage are provided in series between a rectifying / smoothing circuit (diode D2 and capacitor C2) and an output switch Q2. D3, D4
Is connected in series to the voltage dividing resistor R1,
The point is that a diode D5 is provided so that the input between the output switch Q2 and the output terminal V1 is input, and the diodes D3 and D4 are input between the series circuit and the voltage dividing resistor R1.

When the output switch Q2 is on,
The output of the rectifying / smoothing circuit is output to the output terminals V1 and GND through the output switch Q2. At this time, the diode D
5 and a voltage dividing resistor R1, R2, a detection circuit can be obtained.
Feedback control is performed, and the output terminals V1, G
A predetermined voltage is stably supplied to ND.

When the output switch Q2 is off,
A detection voltage is obtained by the diodes D3 and D4 and the voltage dividing resistors R1 and R2, and is input to the shunt regulator IC1 so that the controller 2 performs feedback control. At this time, the output voltage of the transformer T1 becomes substantially equal to the terminal voltages of the output terminals V1 and GND when the output switch Q2 is on.

Therefore, the controller 2 controls the switching of the switching element Q1 stably, and
And the terminal voltage between the output terminals V1 and GND can be stabilized, and a highly reliable and safe switching regulator can be provided.

(Embodiment 2) FIG. 2 is a circuit diagram of a switching regulator according to Embodiment 2 of the present invention. Note that FIG.
1, the same reference numerals as those in FIG. 1 indicate the same or corresponding elements.

In FIG. 2, the difference is that a diode D3 for detecting a terminal voltage and a resistor R3 for detecting a terminal voltage are provided in series between the rectifying and smoothing circuit (diode D2 and capacitor C2) and the output switch Q2. And the resistor R3 is connected in series to the voltage dividing resistor R1. That is, a resistor R3 is arranged in place of the diode D4. This circuit performs the same operation as that described in the first embodiment when the output switch Q2 is turned on.

In the case shown in FIG. 2, the stability of the output voltage can be increased with respect to the output load fluctuation of the OA equipment or the like connected to the output terminals V1 and GND by the resistor R3.
It calculates the maximum voltage drop due to the output switch Q2 from the maximum output current required by the OA equipment or the like connected to the output terminal V1, GND. For example, output switch Q2
When a MOS-FET is used for the
The on-resistance between the drain and source of ET is set to 100 mΩ,
Assuming that the maximum output current required by OA equipment is 5 A,
The voltage drop by the MOS-FET is 0.5V. Therefore, the output voltage of the rectifying / smoothing circuit is output to the output terminals V1, GN
It is set to be a voltage obtained by adding 1 V to the terminal voltage between D. This voltage setting is possible by the resistor R3.

Therefore, when the output switch Q2 is on, the stability of the output voltage against output load fluctuations of the OA equipment connected between the output terminals V1 and GND increases, and when the output switch Q2 is off. In this case, the output voltage of the transformer T1 can be stabilized, and a highly reliable and safe switching regulator can be provided.

(Embodiment 3) FIG. 3 is a circuit diagram of a switching regulator according to Embodiment 3 of the present invention. Note that FIG.
, The same reference numerals as those in FIG. 1 or 2 indicate the same or corresponding elements.

In FIG. 3, the difference from the first and second embodiments is that the output is a switching regulator having multiple outputs V1 and V2. For example, the circuits described in the second embodiment are combined. It is a thing. At this time,
An output voltage is obtained at the output terminal V2 according to the turns ratio of the output winding of the transformer T1, and is superimposed on the winding of the output terminal V1, so that a stable output voltage is output to the output terminal V2. The stability of the terminal voltage of the output terminal V1 is important.

Therefore, as shown in FIG. 3, diodes D3 and D3 for detecting the voltage between the input and output terminals of the output switch Q2.
5 and the resistor R3 and the voltage dividing resistors R1 and R2 so that the terminal voltage of the output terminal V1 and the output voltage of the transformer T1 are stably output regardless of whether the output switch Q2 is on or off. Since the feedback control by the controller 2 can be performed and the switching element Q1 can be controlled, a stable output voltage can be output to the output terminal V1 and a stable output voltage can be output to the output terminal V2.

Therefore, when the output switch Q2 is turned on at each of the output terminals V1 and V2, a stable output voltage can be obtained regardless of whether the output switch Q2 is turned off, and the output voltage of the transformer T1 becomes stable. , And a safe switching regulator can be provided.

It should be noted that the present invention is not limited to the above-described embodiment, but can be modified without departing from the scope of the present invention.

[0035]

Since the present invention is configured as described above, it has the following effects.

When a DC input is intermittently switched by a switching means, the voltage is converted into a predetermined voltage by a transformer, and at least one AC output from the transformer is rectified and smoothed by a rectifying and smoothing circuit. A predetermined voltage can be stably supplied to the terminal, and even when the output switch is off, a detection voltage from the terminal voltage detection means can be obtained. Therefore, the detection voltage can be input to the error amplification means. By controlling the switching of the switching means, the output voltage of the transformer can be stabilized, and a highly reliable and safe switching regulator can be obtained.

When the output switch Q2 is turned on, the stability of the output voltage becomes high with respect to the output load fluctuation of the OA equipment connected between the output terminals V1 and GND, and when the output switch Q2 is turned off. In this case, the output voltage of the transformer T1 can be stabilized, and a highly reliable and safe switching regulator can be obtained.

Further, in a multiple output switching regulator having a plurality of outputs, a stable output voltage can be obtained at each of the output terminals V1 and V2 regardless of whether the output switch Q2 is on or off. There is.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switching regulator according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a switching regulator according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a switching regulator according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional switching regulator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Commercial power supply 2 Controller D1 Full-wave rectifier circuit D2, D3, D4, D5 Rectifier diode C1, C2, C3 Smoothing capacitor Q1 Switching element Q2 Output switch T1, T2 Transformer PC1 Photocoupler phototransistor PC1 'Photocoupler photo Diode V1, V2, GND Output terminal R1, R2, R3 Voltage dividing resistor IC1 Shunt regulator ZD1 Zener diode

Claims (3)

[Claims] 1. A switching regulator for intermittently converting a DC input by a switching unit, converting the DC input into a predetermined voltage by a transformer, and rectifying and smoothing at least one AC output from the transformer by a rectifying and smoothing circuit, and outputting the rectified and smoothed circuit. An output switch provided between the rectifying and smoothing circuit; a first voltage detecting means for detecting an output voltage of the rectifying / smoothing circuit; a second voltage detecting means for detecting a terminal voltage of the output terminal; Voltage dividing means for inputting the first and second voltage detecting means and dividing the voltage of the voltage detecting means; and inputting the output voltage of the rectifying and smoothing circuit as an input and obtaining a divided voltage obtained by the voltage dividing means. Error amplifying means for obtaining an error output with respect to a reference voltage, and control means for controlling on / off of the switching means according to the output of the error amplifying means. Switching regulator, characterized in that. 2. The switching regulator according to claim 1, wherein said first voltage detecting means comprises two series-connected diodes to which an output of a rectifying / smoothing circuit is input, and wherein said second voltage detecting means comprises: A switching regulator, wherein the switching terminal is a diode having an output terminal as an input. 3. The switching regulator according to claim 1, wherein said first voltage detecting means comprises a diode and a resistor connected in series with an output of a rectifying / smoothing circuit as an input, and said second voltage detecting means comprises: A switching regulator characterized by a diode whose input is an output terminal.