JPH11341800A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit which is able to return the output voltage to a set value quickly while avoiding wasteful power waste when the output voltage exceeds a specified value. SOLUTION: This power unit is equipped with an output circuit which receives an output voltage, by rectifying and smoothing the induced voltage of a transformer T based on the supply of a switching voltage, and a resistor against the discharging of a smoothing capacitor C1 which is connected to this output circuit, and moreover this has an output voltage control circuit 11 which monitors the output voltage, using an output control element IC2 for performing the linear action in the vicinity of the set value of output voltage and the turning on action or off action in the state that it is higher or lower than the set value of the output voltage, and a discharge circuit 1, which detects the turning operation off condition that it is higher than the set value of the output voltage in the control element IC2 and discharges the charge of the smoothing capacitor C1 and also detects the return condition to a linear operation by the drop in the output voltage in the output control element IC2 and breaks the discharge path of the charge of the smoothing capacitor C1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Generally, a discharge resistor is connected to an output circuit for supplying a predetermined output voltage to a load in a power supply device.

When the output voltage is of a variable type, there is no problem in increasing the output voltage. However, when the output voltage is decreased, the output voltage drops to a set value due to a load current and a discharge resistor provided in the power supply unit. Try to be.

When a load of a power supply device operates with a pulse current, a smoothing capacitor (electrolytic capacitor) having a large capacitance value is selected as a smoothing capacitor (electrolytic capacitor) provided in an output circuit in order to smooth the pulse current.

In the case of such a power supply, it takes a considerable time to lower the output voltage to a set value.

An example of a conventional power supply will be described with reference to FIG.

The conventional power supply shown in FIG. 3 converts a DC voltage from a power supply E into a switching voltage based on the switching operation of a switching transistor Q1, supplies the switching voltage to a primary winding of a transformer T, An output circuit for obtaining an output voltage V to be supplied to a load by rectifying and smoothing the induced voltage of the line by a diode D1 as a rectifying element and a smoothing capacitor C1, and a connection between the positive electrode of the smoothing capacitor C1 and ground in this output circuit. And a discharge resistor R6 for discharging the charge of the smoothing capacitor C1.

The switching transistor Q1 performs a switching operation with a variable voltage width under the control of the switching controller IC1.

The output circuit of the power supply device performs a linear operation near the set value Vo of the output voltage V and an ON operation or an OFF operation in a state higher or lower than the set value of the output voltage V, thereby performing switching control. An output voltage control circuit 11 using an output control element IC2 for controlling the unit IC1 is connected to a discharge circuit 12 for discharging the charge of the smoothing capacitor C1 via the discharge resistor R6.

The output voltage control circuit 11 includes a photocoupler PC1 combining a light emitting diode D2 connected to the positive pole of the smoothing capacitor C1 and a phototransistor QP.
And a resistor R connected between the photocoupler PC1 and ground.
3 and an output control element IC2.

The output voltage control circuit 11 has an output control element driving circuit for varying the ON width of the switching transistor Q1 by the switching control section IC1 by controlling the output current of the photocoupler PC1 by the output control element IC2. doing.

The output control element driving circuit includes a photocoupler P
A series circuit of resistors R1 and R2 connected in series between the anode of the light emitting diode D2 in C1 and ground, and a resistor R connected in parallel to the series circuit of the resistors R1 and R2.
4, a series circuit of a voltage drop switch SW10, a resistor R5, and a voltage rise switch SW2 in a double configuration including a switch SW11 and a switch SW12, a connection point of a resistor R1, a resistor R2, and a connection point of a resistor R3, an output control element IC2 And a coupling capacitor C2 connected between them.

The connection point between the resistors R1 and R2 and the connection point between the voltage drop switch SW10 and the resistor R5 are both connected to the gate of the output control element IC2.

The discharge circuit 12 includes a first transistor Q2 having a collector and an emitter connected between the discharge resistor R6 and ground, a terminal of the discharge resistor R6 on the smoothing capacitor C1 side, and the voltage drop switch SW10. , A resistor R9 connected between the other terminal of the switch SW12 and the ground, a resistor R9 connected between the other terminal of the switch SW12 and the ground, and a ground between the base of the first transistor Q2 and the ground. It comprises a connected resistor R7, a capacitor C3 connected between the other terminal of the switch SW12 and the base of the first transistor Q2, and a series circuit of a resistor R8.

[0015]

By the way, the discharge time t of the output voltage V in the above-described power supply device is determined by setting the capacitance value of the smoothing capacitor C1 to C10, the resistance value of the discharge resistor R6 to R60, and the initial value of the output voltage V. When the output voltage at time t after the value Vout and the rectified output of the diode D1 is turned off is Vt,
It is determined by t = -C10.R60.ln (Vout / Vt).

However, the above-described power supply has the following problems.

That is, in the power supply device shown in FIG. 3, the output voltage V is not always applied to the discharge resistor R6, and the diode D1
A voltage based on the discharge of the capacitor C1 is applied only when the rectified output of the capacitor C1 is turned off, thereby allowing the electric charge of the capacitor C1 to be discharged for a short time.

However, in order to make the operation effective, FIG.
As shown in (1), it is necessary to provide a double voltage drop switch SW10 for generating a signal for turning on the first transistor Q2 in the output control element drive circuit, and there is a problem that the circuit configuration becomes complicated.

In the power supply device shown in FIG. 3, when the output voltage V rises above a set value (set voltage) Vo, the switches SW11 and SW12 of the dual voltage drop switch SW10 are turned on to turn on the output voltage. Is lowered, the first transistor Q2 is turned on for a fixed time t2 determined by the time constant determined by the capacitance value of the capacitor C3 and the resistance value of the resistor R8, and the voltage applied to the discharge resistor R6 Has a waveform shown in the lower section of FIG. 3, and as a result, as shown in the upper section of FIG. 3, the output voltage V once drops to 0 (V) lower than the set value Vo during a certain time t2. This causes an undershoot state, which causes troubles such as malfunctioning of the load.

The present invention solves the above problem easily, and when the output voltage rises above a set value (set voltage), the output voltage V can be quickly set to the set value while avoiding wasteful power consumption by the discharge resistor. It is an object of the present invention to provide a power supply device that can be returned to a power supply.

[0021]

According to the first aspect of the present invention,
A power supply comprising: an output circuit for obtaining an output voltage to be supplied to a load by rectifying and smoothing an induced voltage of a transformer based on a supply of a switching voltage by a rectifying element and a smoothing capacitor; and a discharge resistor of the smoothing capacitor connected to the output circuit. In the device, the output voltage is monitored using a linear operation near the set value of the output voltage and an output control element that performs an on operation or an off operation in a state higher or lower than the set value of the output voltage, and the level of the output voltage is monitored. An output voltage control circuit that controls the output voltage to a set value by changing the voltage width of the switching voltage in accordance with the above, and detects an off operation in a state higher than the set value of the output voltage in the output control element, and The charge of the smoothing capacitor is discharged through the discharge resistor, and the linearity of the output control element caused by the drop of the output voltage is reduced. It is characterized in that it has a discharge circuit sever charge discharge path of the smoothing capacitor by detecting the return state of the operation.

According to the present invention, when the output voltage rises above the set value, the discharge circuit detects an off operation in a state higher than the set value of the output voltage in the output control element, and charges the smoothing capacitor. The output voltage is dropped by discharging through the discharge resistor, and the return state of the output control element to the linear operation due to the drop of the output voltage is detected to cut off the discharge path of the charge of the smoothing capacitor and to reduce the output voltage. Since the further drop is prevented, when the output voltage rises above the set value, it is possible to quickly return the output voltage to the set value while avoiding wasteful power consumption due to the discharge resistor.

According to a second aspect of the present invention, there is provided an output circuit for obtaining an output voltage to be supplied to a load by rectifying and smoothing an induced voltage of a transformer based on a supply of a switching voltage by a diode and a smoothing capacitor, and a smoothing circuit connected to the output circuit. A power supply device having a discharge resistance of a capacitor, wherein the output is controlled by using an output control element that performs a linear operation near a set value of an output voltage and an ON operation or an OFF operation in a state higher or lower than the set value of the output voltage. A voltage control circuit that monitors the voltage and controls the output voltage to a set value by changing the voltage width of the switching voltage according to the level of the output voltage; and a second output voltage control circuit connected between the discharge resistor and ground. 1
And the transistor is turned on by an off operation in a state higher than a set value of the output voltage of the output control element to turn on the first transistor to discharge the charge of the smoothing capacitor through the discharge resistor, and to perform output control. A discharge circuit including a second transistor that detects a state of return to linear operation due to a drop in the output voltage of the element, turns off the first transistor, and disconnects a circuit from the discharge resistor to ground. It is characterized by the following.

According to the present invention, when the output voltage rises above the set value, the second transistor of the discharge circuit detects an off operation in a state higher than the set value of the output voltage in the output control element. By turning on one transistor, the charge of the smoothing capacitor is discharged through the discharge resistor to lower the output voltage.

Further, the second transistor detects a return state of the output control element to the linear operation due to the drop of the output voltage, turns off the first transistor, and cuts off a circuit from the discharge resistor to the ground. As a result, since the discharge of the charge of the smoothing capacitor is stopped to prevent the output voltage from dropping further, when the output voltage rises above the set value, it is possible to avoid wasteful power consumption by the discharge resistor. It is possible to quickly return the output voltage to the set value.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a power supply unit according to the present invention will be described below in detail with reference to FIGS.
In the power supply device of the present embodiment shown in FIG.
Elements having the same functions as those of the conventional power supply shown in FIG.

The power supply device shown in FIG.
The DC voltage from the power supply E is applied to the switching transistor Q1
Switching voltage based on the switching operation of
This switching voltage is supplied to the primary winding of the transformer T, and the induced voltage of the secondary winding is converted to a diode D as a rectifying element.
1 and an output circuit for obtaining an output voltage V to be supplied to a load after rectifying and smoothing the output voltage by a smoothing capacitor C1, and discharging the smoothing capacitor C1 connected between the positive electrode of the smoothing capacitor C1 and the ground in this output circuit. A discharge resistor R6.

The switching transistor Q1 performs a switching operation with a variable voltage width under the control of the switching controller IC1.

The output circuit of the power supply device performs a linear operation near the set value Vo of the output voltage V and an ON operation or an OFF operation in a state higher or lower than the set value of the output voltage V, and performs switching control. An output voltage control circuit 11 using an output control element IC2 for controlling the unit IC1 is connected to a discharge circuit 1 for discharging the charge of the smoothing capacitor C1 via the discharge resistor R6.

The output voltage control circuit 11 includes a photocoupler PC1 combining a light emitting diode D2 connected to the positive pole of the smoothing capacitor C1 and a phototransistor QP.
And a resistor R connected between the photocoupler PC1 and ground.
3 and an output control element IC2.

The output voltage control circuit 11 has an output control element drive circuit for varying the ON width of the switching transistor Q1 by the switching control section IC1 by controlling the output current of the photocoupler PC1 by the output control element IC2. doing.

The output control element driving circuit includes a photocoupler P
A series circuit of resistors R1 and R2 connected in series between the anode of the light emitting diode D2 at C1 and the ground, a resistor R4 connected in parallel to the series circuit of the resistors R1 and R2, a voltage drop switch SW1 and a resistor It comprises a series circuit of R5 and a voltage raising switch SW2, and a coupling capacitor C2 connected between a connection point of the resistors R1 and R2 and a connection point of the resistor R3 and the output control element IC2.

The connection point between the resistors R1 and R2 and the connection point between the voltage drop switch SW1 and the resistor R5 are both connected to the gate of the output control element IC2.

The discharge circuit 1 comprises a first transistor Q2 having a collector and an emitter connected between the discharge resistor R6 and ground, a discharge resistor R6, a first transistor Q2
And a series circuit of a second transistor Q3, a resistor R11 and a resistor R12 connected in parallel to the series circuit of FIG. 1, and a connection between the connection point of the resistor R3 and the output control element IC2 and the base of the second transistor Q3. It comprises a resistor R14 and a resistor R13 connected between the emitter and the base of the second transistor Q3. Further, the connection point of the resistors R11 and R12 is connected to the base of the first transistor Q2.

That is, in the power supply device of the present embodiment, the voltage drop switch SW1 of the output control element driving circuit in the output voltage control circuit 11 is simplified as compared with the conventional device, and the output voltage V of the output control element IC2 is reduced. Set value Vo
The linear operation in the vicinity and the ON operation or the OFF operation in a state higher or lower than the set value of the output voltage V are performed by the resistor R
It is characterized in that the second transistor Q3 of the discharge circuit 1 is monitored via the circuit 14 and the first transistor Q2 is turned on and off.

Next, the operation of the power supply according to the present embodiment will be described with reference to FIG.

In this power supply device, the switching transistor Q1 controlled by the switching control unit IC1 performs a switching operation with a variable ON width based on the output signal of the photocoupler PC1 of the output voltage control circuit 11, whereby the switching operation is performed. The output voltage V induced in the secondary winding of the transformer T and rectified and smoothed by the diode D1 and the capacitor C1 is kept constant.

Here, the description of the operation of the voltage raising switch SW2 for increasing the output voltage V is omitted.

When the voltage drop switch SW1 is turned on when the output voltage V rises above the set value Vo, the output voltage control of the output voltage control circuit 11 causes the ON width of the switching transistor Q1 to be reduced as much as possible. V tries to fall.

Here, since the output voltage V is higher than the set value Vo, the operation of the output control element IC2 is not a linear operation but an on / off operation and a complete off state. When the output control element IC2 is turned off, the second transistor Q3 connected to the resistor R14 of the discharge circuit 1 is turned on, and the first transistor Q2 is turned on via the resistor R11. As a result, the charge of the smoothing capacitor C1 is discharged via the discharge resistor R6, and the waveform of the voltage applied to the discharge resistor R6 drops as shown in the lower column of FIG.
Therefore, the output voltage V is set to the set value V as shown in the upper section of FIG.
o can be reached quickly.

Next, when the output voltage V reaches the set value Vo, the output control element IC2 returns from the on / off operation to the control operation of the linear operation, and the second transistor Q3 and the first transistor Q2 are turned off. Off, the discharge path of the smoothing capacitor C1 is cut off, the discharge is completed, and the output voltage V
No descent.

With the above operation, the first transistor Q2 is turned on only when the output voltage V is higher than the set value Vo, thereby setting the output voltage V while minimizing the resistance loss of the discharge resistor R6. The value Vo can be quickly reached.

Further, in the power supply device of the present embodiment, since the discharging time of the smoothing capacitor C1 is not fixed at a fixed value unlike the conventional device, the undershoot in which the output voltage V drops below the set value Vo is not obtained. It is possible to avoid a malfunction of the load without any phenomenon.

[0044]

According to the present invention, when the output voltage rises above a set value, this state is detected, and the output of the smoothing capacitor is discharged through a discharge resistor to lower the output voltage. Since the discharge of the charge of the smoothing capacitor is stopped by detecting the state in which the voltage has reached the set value, it is possible to quickly return the output voltage to the set value while avoiding wasteful power consumption by the discharge resistor. A power supply can be provided.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram showing changes in an output voltage and a voltage applied to a discharge resistor when the output voltage is reduced in the power supply device according to the embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional power supply device.

FIG. 4 is a waveform diagram showing a change in an output voltage and a voltage applied to a discharge resistor when the output voltage is reduced in a conventional power supply device.

[Explanation of symbols]

 Reference Signs List 1 discharge circuit 11 output voltage control circuit C smoothing capacitor D1 rectifier diode E power supply IC1 switching control unit IC2 output control element PC1 photocoupler Q1 switching transistor Q2 first transistor Q3 second transistor R6 discharge resistance SW1 voltage drop switch SW2 voltage rise Switch T Transformer V Output voltage Vo Set value

Claims (2)

[Claims] An output circuit for obtaining an output voltage to be supplied to a load by rectifying and smoothing an induced voltage of a transformer based on a supply of a switching voltage by a rectifying element and a smoothing capacitor, and a discharge resistance of the smoothing capacitor connected to the output circuit Monitoring the output voltage using an output control element that performs a linear operation near the set value of the output voltage and an on operation or an off operation in a state higher or lower than the set value of the output voltage. ,
An output voltage control circuit that controls the output voltage to a set value by changing the voltage width of the switching voltage according to the level of the output voltage, and an off operation in a state higher than the set value of the output voltage in the output control element. Detects and discharges the charge of the smoothing capacitor through the discharge resistor, and detects a return state to the linear operation due to the drop of the output voltage in the output control element, and disconnects the discharge path of the charge of the smoothing capacitor. A power supply device comprising: a circuit; 2. An output circuit for rectifying and smoothing an induced voltage of a transformer based on a supply of a switching voltage by a diode and a smoothing capacitor to obtain an output voltage to be supplied to a load.
In a power supply device having a discharge resistance of the smoothing capacitor connected to the output circuit, a linear operation near a set value of the output voltage and an ON operation or an OFF operation in a state higher or lower than the set value of the output voltage are performed. Monitoring the output voltage using an output control element,
An output voltage control circuit that controls the output voltage to a set value by changing a voltage width of the switching voltage according to the level of the output voltage; a first transistor connected between the discharge resistor and ground; The output control element is turned on by an off operation in a state higher than a set value of the output voltage to turn on the first transistor to discharge the charge of the smoothing capacitor through the discharge resistor; A discharge circuit comprising a second transistor for detecting a state of return to linear operation due to a voltage drop, turning off the first transistor, and cutting off a circuit from the discharge resistor to ground. And power supply.