JP2001209441A - Circuit for constant-voltage power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit for constant-voltage power supply that can fall a power rapidly even though it has a ripple absorption condenser. SOLUTION: When switches of S1 and S2 are 'on' in the direct current circuit 1, a npn transistor Q1 becomes 'on' and a pnp transistor Q3 becomes 'off', the lower constant-voltage-that a power supply voltage V2 is outputted from line L2. A condenser C2 installed between a line L2 and the earth eliminates output voltage ripples on the direct current circuit 1. When both switches S1 and S2 are 'off', a bias capacitor C1 discharges electricity, a transistor Q4 becomes 'on'. The npn transistor Q1 becomes 'off', at the same time, the pnp transistor Q3 becomes 'on', then the capacitor C2 discharges electric charge. These make the output voltage to fall rapidly. The continuity start time of the transistor Q4 can be decided aribitrarily by the setting of the resistance value of resister R9 and R10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a constant voltage power supply circuit, and more particularly to a technique for improving a fall characteristic of an output voltage of a constant voltage power supply circuit when stopping output from a DC power supply circuit. is there.

[0002]

2. Description of the Related Art Various electronic devices are used in electronic equipment, and as a result, a constant voltage power supply circuit that outputs various DC voltages is required. In this type of constant voltage power supply circuit, the output direct current often includes a ripple, and a large-capacity ripple absorbing capacitor is used to eliminate the ripple.

[0003]

As described above, in a constant voltage power supply circuit that generates a constant voltage using a voltage supplied from a DC power supply circuit, a constant voltage power supply is used to remove ripples from the DC power supply circuit. A ripple absorbing capacitor is provided between the output terminal and the ground to suppress fluctuations in the output voltage. However, when stopping the output of the DC power supply circuit with such a constant voltage power supply circuit, it takes time until the electric charge accumulated in the capacitor for removing the ripple is discharged, so that the delay of the output fall is delayed. There are problems that arise. In addition, when a plurality of types of DC voltages fall with a time difference provided therebetween, the above-mentioned delay in the fall of the output often becomes a problem.

An object of the present invention is to provide a constant-voltage power supply circuit having a fast output fall even when a ripple absorbing capacitor is provided.

Another object of the present invention is to synchronize the discharge of a bias capacitor included in a bias circuit of a voltage adjustment transistor included in a voltage adjustment circuit and the discharge of a ripple absorption capacitor included in a voltage adjustment circuit, thereby rapidly discharging both of them. It is an object of the present invention to provide a constant-voltage power supply circuit that can be performed at a constant voltage.

It is another object of the present invention to provide a constant voltage power supply circuit capable of reliably performing constant voltage control and discharging a capacitor with a small number of transistors.

It is still another object of the present invention to provide a constant voltage power supply circuit capable of stopping output earlier than other DC voltage output stops.

[0008]

A constant voltage power supply circuit according to the present invention comprises a DC power supply circuit, a voltage adjustment circuit, a ripple absorbing capacitor, and a ripple absorbing capacitor discharging circuit. The DC power supply circuit outputs a predetermined DC voltage. The voltage adjusting circuit adjusts the DC voltage to a desired lower constant voltage and outputs the adjusted voltage. The ripple absorbing capacitor is disposed between the output terminal of the voltage adjustment circuit and the ground, and removes a ripple included in the voltage output from the DC power supply circuit. The ripple absorbing capacitor discharging circuit discharges the electric charge accumulated in the ripple absorbing capacitor when stopping the output of the DC power supply circuit. When such a configuration is adopted, the ripple absorbing capacitor can be quickly discharged when the DC power supply is stopped, so that the output can fall quickly.

Another constant voltage power supply circuit of the present invention comprises a DC power supply circuit, a bias circuit, a voltage adjusting circuit, a bias capacitor discharging circuit, a ripple absorbing capacitor,
And a ripple absorbing capacitor discharging circuit. The DC power supply circuit outputs a predetermined DC voltage. The bias circuit is arranged between the output terminal of the DC power supply circuit and ground,
It is composed of a series circuit of a resistor and a bias capacitor.

The voltage adjusting circuit includes a DC power supply circuit, a collector / emitter circuit connected in series, a base having a resistor for forming a bias circuit, and a voltage adjusting transistor connected to a connection point of a bias capacitor. Is output as a lower desired constant voltage. The ripple absorbing capacitor is arranged between the output terminal of the voltage adjusting circuit and the ground, and absorbs the ripple of the output voltage.

When stopping the output of the DC power supply circuit,
A bias capacitor discharge circuit short-circuits the bias capacitor, discharges the charge stored in the bias capacitor, turns off the voltage adjustment transistor,
The discharge circuit of the ripple absorbing capacitor discharges the electric charge accumulated in the ripple absorbing capacitor, thereby making the output fall fast. When the DC power supply circuit is configured to output a plurality of types of voltages, the discharge start time of the bias capacitor discharge circuit is determined by stopping the output of the other DC voltage output from the DC power supply circuit as the timing. Is also good. In particular, when the bias capacitor discharge circuit starts the discharge operation after the output of the other DC voltage has decreased to the predetermined potential, a difference can be provided between the fall times of the outputs of the two types of DC voltages. .

The ripple absorbing capacitor discharging circuit can be constituted by, for example, a series circuit of a discharging transistor and a current limiting element connected in parallel to the ripple absorbing capacitor. In this case, the base of the discharge transistor is connected to the output terminal of the bias circuit (connection point between the resistor and the bias capacitor) directly or via a current limiting element. With this configuration, when the output voltage of the DC power supply is stopped, the bias capacitor is first discharged by the bias capacitor discharging circuit, and then the ripple absorbing capacitor discharging transistor is turned on.
The ripple absorbing capacitor starts discharging. As described above, the ripple absorbing capacitor discharge circuit operates in synchronization with the bias capacitor discharge circuit, so that the fall of the output can be reliably accelerated.

More specifically, the voltage adjusting circuit is composed of a plurality of resistors and divides the voltage between both ends of the ripple absorbing capacitor. A base is connected to a voltage dividing point of the voltage dividing circuit. Current emitter connected to the base of the transistor for controlling the base current of the transistor for voltage adjustment by connecting the collector-emitter circuit to the base of the transistor, and the anode is arranged between the collector-emitter circuit of the transistor for base current control and the ground and the anode is grounded And a current limiting element arranged between the cathode of the Zener diode and the output of the voltage adjustment circuit. In such a voltage adjustment circuit, when the base current control transistor is turned on, the cathode potential of the Zener diode is fixed at a constant value. As a result, the base potential of the base current control transistor is fixed to a constant value obtained by adding the cathode voltage of the Zener diode to the emitter-base voltage of the base current control transistor. Then, a constant current flows through the current limiting element connected between the base potential of the current controlling transistor and the ground, and the constant current is applied between the base of the current controlling transistor and the output of the voltage regulating circuit. A constant voltage is generated by flowing between the elements, and a voltage obtained by adding the constant voltage and the base potential of the voltage adjusting transistor is output as a constant voltage output of the voltage adjusting circuit.

The voltage adjusting transistor and the base current controlling transistor are each composed of an npn transistor, and the discharging transistor is composed of a pnp transistor. When such a transistor is used, the discharge transistor is always off when the voltage adjustment transistor is on, and the discharge transistor is always on when the voltage adjustment transistor is off. Can be easily realized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a constant voltage power supply circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a DC power supply circuit that outputs a predetermined plurality of types of DC voltages (V0 <V1 <V2).
3 is a bias capacitor C1 of a bias circuit described later.
Is a bias capacitor discharging circuit that discharges the voltage. The bias capacitor discharging circuit 3 discharges the charge stored in the bias capacitor C1 when the output of the DC power supply circuit 1 is stopped. Reference numeral 5 denotes a base of the transistor Q1 of the voltage adjustment circuit 7 and a capacitor discharge circuit 9 for ripple absorption.
Is a bias circuit for generating a bias voltage to the base of the transistor Q3. The voltage adjustment circuit 7 is a circuit that adjusts the DC voltage V2 output from the DC power supply circuit 1 to a desired constant voltage lower than the DC voltage V2 and outputs the adjusted voltage. The ripple absorbing capacitor C2 is arranged between the output terminal of the voltage adjusting circuit 7 and the ground. The ripple absorbing capacitor discharging circuit 9 discharges the ripple absorbing capacitor C2 while the output of the DC voltage V1 output from the DC power supply circuit 1 is stopped.

The internal configuration of each block will be described below.
The DC power supply circuit 1 has V0, V1, V2 (where V0 <V1 <
V2) is a known circuit configured to output three types of DC voltages. The circuit that outputs the voltage V2 is connected to the line L1 of the voltage adjustment circuit 7 via the switch S1. The voltage adjustment circuit 7 converts the voltage V2 into a voltage V smaller than the voltage V2 and outputs the voltage V to an output line L2.
The circuit that generates the voltage V1 is connected to the line L3 of the bias capacitor discharge circuit 3 via the switch S2.
The circuit for generating the reference power supply voltage V0 is connected to the line L4 of the bias capacitor discharging circuit 3.

The bias capacitor discharge circuit 3 comprises transistors Q4 and Q5 and resistors R8, R9, R10. From the DC power supply circuit 1, the voltage V1 is applied to the resistors R9 and R10 via the line L3 via the switch S2.
And are applied. The connection point of the resistors R10 and R11 between the line L3 and the ground is connected to the base of the transistor Q5. The emitter of the transistor Q5 is grounded. The collector of the transistor Q5 is connected to the line L4 via the resistor R8 and to the base of the transistor Q4. The emitter of the transistor Q4 is grounded.

The bias circuit 5 comprises a resistor R1 and a capacitor C1, and a connection point of these elements is connected to the collector of the transistor Q4 of the bias capacitor discharge circuit 3. The connection point between the resistor R1 and the capacitor C1 is connected to the voltage adjusting transistor Q1 and the discharging pnp transistor Q3 of the ripple absorbing capacitor discharging circuit 9.
Connected to the base.

The voltage adjusting circuit 7 comprises a voltage adjusting transistor Q1 and a base current controlling npn transistor Q2.
And resistors R2, R3, R4, R5 and a Zener diode ZD. The collector of the voltage controlling transistor Q1 is connected to the line L1 and the emitter is connected to the line L2.
The bases are connected to the collectors of the base current control transistors Q2, respectively. The base of the voltage control transistor Q1 is connected to the resistors R1 and C1 of the bias circuit 5.
The collector of the transistor Q4 of the bias capacitor discharge circuit 3 is connected to this connection point. The emitter of the base current control transistor Q2 is connected to the cathode of the Zener diode ZD,
Also, it is connected to the line L2 via the resistor R2.
The anode terminal of the Zener diode ZD is grounded.

The voltage dividing circuit 7a includes resistors R3, R4 and R5.
It is composed of At the connection point between the resistors R4 and R5,
A voltage obtained by dividing the voltage between the line L2 and the ground appears, and the divided voltage is applied to the base of the base current control transistor Q2. In other words, the voltage dividing circuit 7a forms a voltage detecting circuit for detecting the voltage of the line L2.

The ripple absorbing capacitor discharging circuit 9
It comprises a pnp transistor Q3 and resistors R6 and R7. The emitter of the discharging pnp transistor Q3 is connected to the line L2, and the collector is grounded via the resistor R6. The base of the pnp transistor Q3 is connected to the voltage adjusting transistor Q1 via the resistor R7.
And the connection point between the resistor R1 and the capacitor C1 of the bias circuit 5 and the collector of the transistor Q4 of the bias capacitor discharge circuit 3. The ripple absorbing capacitor circuit 11 includes a ripple absorbing capacitor C2 connecting between the line L2 and the ground.

The switches S1 and S2 of the DC power supply circuit 1 are both ON, and the DC power supply circuit 1
The potential of each part of the circuit in the steady state where V1 and V2 are output will be described. The bases of the voltage adjusting npn transistor Q1 and the discharging pnp transistor Q3 are at substantially the same potential. The emitters of these two transistors are connected to the line L2, and the potential of the line L2 is set to V. Here, the common base potential VB
However, when the voltage adjusting npn transistor Q1 is higher than the potential V of the line L2 and the voltage adjusting npn transistor Q1 is in the on state (conductive state), the discharging pnp transistor Q3 is in the off state. When the transistor Q1 is turned off (disconnected), the discharging pnp transistor Q3 is turned on.

When the switch S2 is turned on and the voltage V1
Is applied to the series circuit of the resistor R9 and the resistor R10, the transistor Q4 of the bias capacitor discharge circuit 3 is in the off state, so that the base potential of the transistor Q1 is controlled by the base current control from the resistor R1 of the bias circuit 4. At the potential determined by the current path of the transistor Q2, and at a level obtained by subtracting the voltage drop of the resistor R1. At this time, the npn transistor Q1 is on, and the transistor Q1 functions to amplify current from the line L1 to L2. Power on moment (moment of switch S2 turning on)
, The potential V of the line L2 is a potential obtained by subtracting the voltage drop between the emitter and the base from the base potential of the npn transistor Q1 for voltage adjustment.

However, the potential V of the line L2, which is temporarily increased at the moment when the switch S2 is turned on, is turned on by the base current supplied from the voltage dividing point of the voltage dividing circuit 7a functioning as a voltage detecting circuit, so that the transistor Q2 becomes conductive. When the Zener diode ZD conducts, the voltage is adjusted to a constant voltage lower than the voltage V2. The voltage dividing point of the voltage dividing circuit 7a is determined by the Zener voltage VZD of the Zener diode ZD and the transistor Q
2 is constant with the sum of the base-emitter voltage VEB2 and the current I flowing through the resistor R5 becomes a constant current. Since this current flows from the resistors R3 and R4 of the voltage dividing circuit 7a, the current flowing through the resistors R3 and R4 is almost equal to the current I flowing through the resistor R5, and the potential V of the line L2 is (VZD + VEB2) + I (R3 + R4). ) And becomes a constant value.

At this time, the base potential (assumed to be equal to VB) of the discharging pnp transistor Q3 for discharging the ripple absorbing capacitor C2 is higher than the potential V of the line L2, and the discharging pnp transistor Q3 is It is off.

In the above-described state, even if a time-varying ripple is applied to the output voltage V2 from the DC power supply circuit 1, the ripple absorbing capacitor C2 performs flattening or rectification, and a ripple appears in the output. Disappears.

Next, a case where the outputs V1 and V2 of the DC power supply circuit 1 are stopped will be described. A discharge process until the potentials of the lines L1 and L2 become 0 after the switches S1 and S2 are simultaneously turned off will be described. First, when the switch S2 is turned off, the transistor Q5 is turned off and the transistor Q4 is turned on, and its collector potential, that is, the potential V at the base of the transistor Q1 is turned on.
When B approaches 0, the voltage adjusting transistor Q1 is turned off. In such a state, the pnp transistor Q
3 turns on, the ripple absorbing capacitor C2 discharges, and the potential V of the line L2 approaches the zero potential in a short time.

The above timing sequence will be described in more detail. When the switches S1 and S2 of the DC power supply circuit 1 are turned off at the same time, the base potential of the transistor Q5 of the bias capacitor discharging circuit 3 approaches 0, and the collector of the transistor Q5 becomes high level.
4 is turned on. As a result, the electric charge of the capacitor C1 is discharged through the collector-emitter circuit of the transistor Q4, and the collector potential of the transistor Q4 finally becomes 0.
become. And an npn transistor Q1 and a pn for discharging
The base potential VB of the p transistor Q3 drops to 0,
The n transistor Q1 is turned off and the pnp transistor Q3 is turned on. When the npn transistor Q1 is turned off, the line L2 is cut off from the line L1. The electric charge accumulated in the large ripple absorbing capacitor C2 is discharged in a short time through the collector-emitter circuit of the discharging pnp transistor Q3 and the resistor R6. There are three discharge paths for the ripple absorbing capacitor C2. That is, the path between the resistor R2 and the Zener diode ZD, the path passing through the resistors R3, R4, and R5, the discharge p
This is a path between the np transistor Q3 and the resistor R6. If there is no path for the discharging pnp transistor Q3, that is, the capacitor discharging circuit 9 for ripple absorption, the resistor R3
Only the path including R4 and R5 becomes a discharge circuit. However, the voltage dividing circuit 7a including the resistors R3, R4, and R5 is
Since this constitutes a voltage detection circuit, the impedance of the circuit is large. Therefore, when the ripple absorbing capacitor C2 is discharged by the voltage dividing circuit 7a, the transistor Q4 is turned on and the capacitor C1 starts discharging, and even if the discharging is completed, the ripple absorbing capacitor C2 is discharged. Since the discharge is not completed, the fall of the output potential V is delayed. However, in this example, since the impedance of the discharge circuit 9 including the pnp transistor Q3 and the resistor R6 is sufficiently smaller than the impedance of the other paths, most of the charge of the capacitor C2 is
The turned-on pnp transistor Q3 and the resistor R6
And is discharged in a short time. Therefore, the output falls faster.

The output voltage of the bias capacitor discharge circuit 3 is
Can fall faster than the other output voltage V1 of the DC power supply circuit 1. That is, the bias capacitor discharge circuit 3 determines the discharge start timing of the ripple absorbing capacitor C2. The resistance values of the resistors R9 and R10 are set so that the transistor Q5 is turned on when the switches S1 and S2 are on. Switch S
2 is turned off, the potential of the line L3 decreases, and the resistor R
When the potential at the voltage dividing point between the resistor 9 and the resistor R10 drops below 0.8 V, the transistor Q5 is immediately turned off. Then, the base potential of transistor Q4 immediately becomes 5V
And the transistor Q4 is turned on, discharging of the capacitor C1 is started, and the collector potential of the transistor Q4 approaches 0. As a result, transistors Q1,
The base potential of Q3 drops, transistor Q3 is turned on, and capacitor C2 is discharged. In this way, by setting the resistance value of the resistor R9 and the resistor R10 to determine the timing of turning off or turning off the transistor Q4, the switch S2 is turned off (the output of the DC voltage V2 is stopped). Later), the potential of the line L3 becomes 0.
It is possible to determine the start time of the conduction of the transistor Q3 within an arbitrary time until the time becomes. As a result, the fall of the output potential V can be made faster than the fall of the voltage V1.

Next, switches S1, S2 of DC power supply circuit 1
Is switched on, and the line L1 and the line L2
A description will be given of the progress from when the voltage reaches 0 to a predetermined potential. When the switch S2 is turned on, the transistor Q5 is turned on and the transistor Q4 is turned off. The potential VL1 of the line L1 immediately rises to the power supply voltage V2. However, the potential at the junction between the bias capacitor C1 of the bias circuit and the resistor R1 is equal to the potential of the capacitor C1.
And rises toward the potential VL1 (V2) of the line L1 with a time constant determined by the resistor R1. As a result, the base potentials of the voltage adjusting npn transistor Q1 and the discharging pnp transistor Q3 increase, the voltage adjusting npn transistor Q1 turns on, and the discharging pnp transistor Q1 turns on.
3 turns off. As a result, the potential V appears on the line L2. The operation of adjusting the potential V to a constant voltage is as described above. As described above, in this circuit, the rise of the potential V is delayed due to the presence of the bias capacitor C1, but there is no particular problem.

[0031]

According to the present invention, even if there is a ripple absorbing capacitor for removing the ripple of the output voltage,
By providing a capacitor discharge circuit for ripple absorption and discharging the electric charge stored in this capacitor in a short time, the fall of the output can be accelerated. Also, since the ripple absorbing capacitor discharging circuit is operated in synchronization with the bias capacitor discharging circuit, the fall of the output can be surely advanced. Further, when the output is stopped with the stop of the output of the other DC voltage as a timing, the fall of the output can be made faster than the fall of the output of the other DC voltage.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an example of an embodiment of a constant voltage power supply circuit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply circuit 3 Bias capacitor discharge circuit 5 Bias circuit 7 Voltage adjustment circuit 7a Voltage divider circuit 9 Ripple absorption capacitor discharge circuit 11 Ripple absorption capacitor circuit

Claims (6)

[Claims] 1. A DC power supply circuit that outputs a predetermined DC voltage, a voltage adjustment circuit that outputs the DC voltage at a desired constant voltage lower than the DC voltage, and an output terminal of the voltage adjustment circuit and a ground. A constant voltage power supply circuit comprising: a ripple absorption capacitor disposed between the DC voltage supply circuit and the ripple absorption capacitor that discharges a charge accumulated in the ripple absorption capacitor when the output of the DC power supply circuit is stopped. A constant voltage power supply circuit comprising a discharge circuit. 2. A DC power supply circuit for outputting a predetermined DC voltage, a resistor having one end connected to the output of the DC power supply circuit, and a bias capacitor having a non-ground terminal connected to the other end of the resistor. A bias circuit, a base is connected to a connection point between the resistor and the capacitor, and a collector-emitter circuit is connected in series to the DC power supply circuit, and a voltage adjustment transistor is included, and a conduction angle of the voltage adjustment transistor is controlled. A voltage adjusting circuit for setting the DC voltage to a desired constant voltage lower than the DC voltage and outputting the same; and when the output of the DC power supply circuit is stopped, the bias capacitor is short-circuited. A capacitor discharging circuit for discharging the electric charge accumulated in the voltage adjusting circuit, and disposed between an output terminal of the voltage adjusting circuit and ground. A constant voltage power supply circuit comprising a ripple absorbing capacitor, and a ripple absorbing capacitor discharging circuit for discharging electric charges accumulated in the ripple absorbing capacitor when the output of the DC power supply circuit is stopped. A constant voltage power supply circuit. 3. The discharging circuit for a ripple absorbing capacitor includes a discharging transistor having a collector-emitter circuit connected in parallel to the ripple absorbing capacitor directly or via a current limiting element, and a base of the discharging transistor. 3. The constant voltage power supply circuit according to claim 2, wherein the constant voltage power supply circuit is connected to the connection point between the resistor and the capacitor directly or via a current limiting element. 4. The voltage adjusting circuit comprises a plurality of resistors, a voltage dividing circuit for dividing a voltage between both ends of the ripple absorbing capacitor, and a base connected to a voltage dividing point of the voltage dividing circuit. A collector / emitter circuit connected to the base of the adjusting transistor to control a base current of the voltage adjusting transistor; and a base current controlling transistor disposed between the collector / emitter circuit of the base current controlling transistor and ground. 4. The constant voltage power supply circuit according to claim 2, comprising a Zener diode having an anode directed to the ground side, and a current limiting element disposed between a cathode of the Zener diode and an output of the voltage adjustment circuit. 5. The constant voltage power supply circuit according to claim 4, wherein each of said voltage adjusting transistor and said base current controlling transistor comprises an npn transistor, and said discharging transistor comprises a pnp transistor. 6. The discharging circuit for a bias capacitor,
6. The constant voltage according to claim 5, further comprising a transistor circuit connected in parallel to the bias capacitor, wherein the transistor circuit becomes conductive when another DC output voltage output from the DC power supply decreases toward zero. Power circuit.