JP3403606B2 - Stabilized power supply circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilized power supply circuit which is applied to, for example, a small power device such as a mobile phone and stabilizes the voltage of an input power supply such as a rechargeable battery.

[0002]

2. Description of the Related Art FIG. 5 shows an example of a stabilized power supply circuit conventionally used in a series regulator or the like, which is a low saturation type circuit using PNP transistors as power transistors. According to the figure, the power transistor Tr is connected to the input terminal connected to the rechargeable battery as the input power source V _0.
The emitter terminal of No. 1 is connected, and the collector terminal is connected to the output terminal to which the load is connected. The base terminal of the power transistor Tr1 has a power transistor Tr
A transistor Tr2 for driving 1 is connected.

The base terminal of the transistor Tr2 has 2
The output terminal of an operational amplifier Amp that inverts and amplifies the difference value between two input signals and outputs the inverted value is connected. This operational amplifier A
The mp inputs a voltage (comparison voltage) obtained by dividing the voltage on the load output side by the voltage dividing resistors R1 and R2 and the reference voltage Vref, and outputs a difference value thereof. A transistor Tr3 is connected to the base terminal of the transistor Tr2, and a control signal for turning on / off the power output to the load side of the stabilized power supply circuit is input to the base terminal of the transistor Tr3. It is connected to the ON / OFF pin.

An output capacitor C composed of an electrolytic capacitor or the like and functioning as a filter is connected in parallel to the external output of the stabilized power supply circuit composed of the above components.

The operation of this stabilized power supply circuit will be described below.
The operational amplifier Amp inputs and compares the output voltage divided by the resistors R1 and R2 with the reference voltage Vref. Then, the difference value is inverted and amplified and given to the transistor Tr2 as a base current. The transistor Tr2 is controlled by this base current, and thereby controls the current flowing to the base terminal of the power transistor Tr1. By this control, the collector of the power transistor Tr1
The emitter voltage Vce is adjusted and the output voltage is stabilized.

The power output to the load side is turned on / off by controlling the base terminal of the transistor Tr2 which drives the power transistor Tr1 by the transistor Tr3. That is, to turn on the output, set the ON / OFF pin to Low. As a result, the transistor Tr3 does not operate, and the output of the operational amplifier Amp is the transistor Tr3.
2 is applied to the base terminal of the power transistor Tr1.
Operates and the output turns on.

On the other hand, in order to turn off the output, the ON / OFF terminal is set to High. As a result, the transistor Tr3 operates and the transistor Tr2 turns off. Therefore, the power transistor Tr1 also does not operate, and the output is turned off. In this way, when the ON / OFF pin is low, the output is on, and when the ON / OFF pin is high, the output is off. In this case, the transistor Tr3 functions as output control means.

By the way, when such a stabilized power supply circuit is used, in order to prevent the oscillation of the output to the load side and stabilize the output, an output capacitor C is output as shown in FIG. Connect in parallel to the terminals. The capacity of this output capacitor C is actually several μF to several hundreds μF,
The larger the load current, or the larger the fluctuation of the load current, the larger it must be. .

When the ON / OFF terminal is set to High and the output is turned off, the power transistor Tr1 is turned off. Therefore, the charge stored in the output capacitor C is divided through the load or in the regulated power supply circuit. It is discharged through the resistors R1 and R2 (see the arrow in FIG. 5). In particular, in the state of no load (the output side is open), all the charges of the output capacitor C are discharged through the voltage dividing resistors R1 and R2 in the stabilized power supply circuit.

In small power devices such as mobile phones and electronic notebooks, a rechargeable battery is often used as an input power source.
In order to extend the operating time of these devices, it is necessary to reduce the operating current of the stabilized power supply circuit as much as possible to suppress the power consumption. Therefore, in the stabilized power supply circuit, the voltage dividing resistors R1 and R2 must be set to values as large as possible. Specifically, the value of the resistor R1 is usually set to about several kΩ, but in the case where the operating current of the circuit is suppressed,
The value of the resistor R1 is set to about several tens kΩ to several hundreds kΩ.

[0011]

However, the voltage dividing resistor R
When the values of 1 and R2 are increased, the discharge time of the output capacitor C becomes longer when the output is turned off in the no-load state or the light load state. Therefore, the off response deteriorates for the discharging time of the output capacitor C, which may cause malfunction of the device connected to the load side.

By the way, P is connected to the power transistor Tr1.
In the stabilized power supply circuit using the NP transistor, as shown in FIG. 6, when the input side is momentarily short-circuited due to a contact failure or the like, the charge of the output capacitor C flows to the input side through the power transistor Tr1 and the power is reduced. There is a risk that the transistor Tr1 and the circuit elements around it may be destroyed.

Therefore, in order to protect the above circuit elements,
As shown in FIG. 7, a diode D is connected to both ends of the power transistor Tr1 so that the charge on the output side is forced to flow to the input side. However, since the diode D for protecting the circuit element is connected to both ends of the power transistor Tr1, it is necessary to use a diode having a large capacity. Therefore, the size of the diode D becomes large, and the diode must be mounted outside the stabilized power supply circuit, resulting in an increase in component cost and an enlargement of the device.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a stabilized power supply circuit which shortens the discharge time of an output capacitor and eliminates a malfunction of a connected device caused by a long discharge time.

Another object of the present invention is to provide a stabilized power supply circuit capable of protecting circuit elements with a simple structure when the input side is short-circuited.

[0016]

According to the means for solving the problems according to the present invention, a capacitor for stabilizing the output is connected to the output side, an output control element for controlling the output, and an on / off switch for the output control element. A stabilized power supply circuit provided with an output control means is provided with a discharging means for instantaneously discharging electric charges accumulated in a capacitor when an output is turned off.

Specifically, the discharging means is composed of a switching transistor connected in parallel to the downstream side of the output control element, and when the output is turned off, the switching transistor operates to instantly form a capacitor through the switching transistor. Since the accumulated charges are discharged, it is possible to prevent the malfunction of the connected device due to the long discharge time.

Further, the discharge means may be connected with a delay means for delaying the start of discharge by the discharge means when the output is turned off. According to this, it is possible to prevent a short circuit on the input side caused by the discharge time starting too early when the output is turned off.

Another means for solving the problem according to the present invention is to provide a stabilized power supply circuit having an output control element for controlling an output, wherein a capacitor for stabilizing output is connected to an output side,
It is provided with a protection means for preventing a reverse current flowing when the input side is short-circuited, and a discharge means for instantaneously discharging the electric charge accumulated in the capacitor by the activation of the protection means.

Specifically, the protection means is composed of a protection switching transistor connected in parallel on the upstream side of the output control element, and the discharge means is a discharge switching transistor connected in parallel on the downstream side of the output control element. Composed of.

According to the above configuration, for example, when the input side is short-circuited due to a contact failure or the like, the discharge switching transistor operates due to the operation of the protection switching transistor, and the discharge is performed through the discharge switching transistor. A reverse current does not flow in the circuit element directly connected between the two. Therefore, these circuit elements can be protected.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a diagram of a stabilized power supply circuit according to a first embodiment of the present invention. This stabilized power supply circuit is applied to, for example, a small power device such as a mobile phone, and is a circuit for suppressing fluctuation of the input voltage supplied from a rechargeable battery or the like and supplying a stable voltage to a load. In addition,
The basic part of the circuit shown in FIG. 1 is the same as that of FIG. 5 described in the “Prior Art”, and therefore the description thereof is omitted, and the characteristic part will be mainly described below. Further, the same reference numerals are used for the same functional parts as in FIG.

According to FIG. 1, the power transistor Tr1
A switching transistor Tr4 as a discharging means is connected in parallel via a current limiting resistor R3 to the downstream side of the voltage dividing resistor R1 and the base terminal of the switching transistor Tr4 is turned ON / OFF. It is connected to the OFF pin.

With this configuration, a High signal is input from the ON / OFF terminal, the transistor Tr3 operates to turn off the load side output, and at the same time, the switching transistor Tr4 operates. This allows the output capacitor C
The electric charge stored in the capacitor flows through the resistor R3 and the switching transistor Tr4 to GND and is discharged instantaneously (see the arrow in FIG. 1).

That is, as in the conventional case, the voltage dividing resistors R1,
Although the discharge time of the output capacitor C was lengthened by increasing the resistance value of R2, the output side of the output capacitor C is short-circuited to GND via the switching transistor Tr4 when the output is turned off. The discharge time can be significantly shortened, and the response when the output is off can be improved. Therefore, it is possible to prevent the malfunction of the device connected to the output side, which has occurred due to the long discharge time of the output capacitor C.

The connection of the switching transistor Tr4 in this circuit is at a position closest to the output terminal to the output capacitor C in consideration of discharge of the charge accumulated in the output capacitor C, as shown in FIG. Most preferably it is connected.

FIG. 2 is a diagram showing a modified example of the stabilized power supply circuit. As shown in the figure, the base terminal of the transistor Tr3 is connected to the power supply voltage Vcc and the base terminal of the switching transistor Tr4, the transistor Tr5 is inserted between the base terminal of the transistor Tr3 and GND, and the base terminal of the transistor Tr5 is connected. May be connected to the ON / OFF terminal.

Thus, when the ON / OFF terminal is set to Low, the transistor Tr5 does not operate, but the transistor Tr3 operates by the power supply voltage Vcc, so the output is turned off. At this time, the switching transistor Tr4 is turned on. On the other hand, if the ON / OFF pin is set to High,
The transistor Tr5 operates, the base terminal of the transistor Tr3 becomes Low, and the transistor Tr3 does not operate.
Therefore, the output is turned on. At this time, the switching transistor Tr4 is not turned on.

That is, when the ON / OFF terminal is High, the output is off, and when the ON / OFF terminal is Low, the output is on. However, with the configuration shown in FIG. 2, the ON / OFF terminal is High.
When is ON, the output is on, and when the ON / OFF pin is Low, the output is off. That is, the logic of the control signal at the ON / OFF terminal can be inverted. Therefore, when you want to invert the logic of the control signal at the ON / OFF terminal,
The stabilized power supply circuit having the configuration shown in FIG. As a result, the versatility of this stabilized power supply circuit can be expanded. In the figure, R4 is a current limiting resistor.

By the way, in the stabilized power supply circuit shown in FIG. 1 or FIG. 2, the switching transistor Tr4 discharges at the same time when the output is turned off.
There are cases where the power transistor Tr1 is turned off later than the discharge by the switching transistor Tr4 due to the responsiveness of the circuit elements. When the turning off of the power transistor Tr1 is delayed, a current may flow from the input side through the power transistor Tr1 and the switching transistor Tr4, and the input side may be short-circuited with GND.

Therefore, as shown in FIG. 3, delay means may be provided so as to delay the control signal input from the ON / OFF terminal to the switching transistor Tr4. In this way, the power transistor Tr1
Is not discharged earlier than the switching transistor Tr4 is turned off, and the input side is not short-circuited with GND.

Specifically, transistors Tr6 and Tr7 as delay means are connected in series between the base terminal of the switching transistor Tr4 and GND. Accordingly, the control signal input from the ON / OFF terminal is given to the switching transistor Tr4 with a delay due to the on / off response time of the transistors Tr6 and Tr7, and the timing at which the switching transistor Tr4 operates can be delayed. it can. Therefore, the output capacitor C
It is possible to delay the start of discharge of the electric charge stored in
The problem that the input side is short-circuited with GND as described above can be solved. In the figure, R5 and R6 are current limiting resistors.

<Second Embodiment> FIG. 4 is a diagram of a stabilized power supply circuit according to a second embodiment of the present invention. The feature of this second embodiment is that a protection means for preventing a reverse current flowing due to a short-circuit on the input side is provided on the upstream side of the power transistor Tr1, and the charge stored in the output capacitor C is activated by the operation of the protection means. The point is that a discharge means for discharging the is provided.

For example, if the electric charge of the output capacitor C is not immediately discharged when the input side is momentarily short-circuited due to a contact failure or the like, the voltage on the output side becomes higher than the voltage on the input side, and the voltage is input from the output side. Reverse current may flow to the side.
More specifically, the current due to the charge of the output capacitor C may flow backward to the input side through the power transistor Tr1 and destroy the power transistor Tr1 and the circuit elements around it.

Therefore, the switching transistor T as a protection means is provided on the upstream side of the power transistor Tr1.
r8 is connected in parallel, and the collector terminal of the switching transistor Tr8 is connected to the base terminal of the switching transistor Tr4 as the discharging means. Other configurations are similar to those of the first embodiment.

With this configuration, when the input side is short-circuited, the switching transistor Tr8 operates, and accordingly the switching transistor Tr4 also operates.
Therefore, the electric charge stored in the output capacitor C is discharged through the switching transistor Tr4 (see the arrow in FIG. 4). Therefore, since a reverse current does not flow in the power transistor Tr1 and the circuit elements in the vicinity thereof, these circuit elements can be protected even if the input side is short-circuited.

Moreover, it is not necessary to attach a large diode for protecting the circuit element to the stabilized power supply circuit as in the conventional case, and the protection circuit can be easily constructed by using the small switching transistors Tr4 and Tr8. it can. Therefore, the circuit configuration can be simplified and downsized, and the cost can be reduced.

Further, according to FIG. 4, the base terminal of the switching transistor Tr4 is connected to the ON / OFF terminal. Therefore, as described in the first embodiment, the switching transistor Tr4 has the output OFF state. It will also function as a discharge transistor. Therefore, the switching transistor Tr4 has both the discharge function when the output is off and the discharge function when the input is short-circuited, and the circuit can be further simplified.

The present invention is not limited to the above embodiment, and many modifications and changes can be added to the above embodiment within the scope of the present invention. For example, this stabilized power supply circuit is not limited to small power equipment,
The present invention may be applied to the power supply unit of any electric equipment other than office equipment such as a facsimile or a copying machine.

Further, in FIG. 1, the power transistor Tr
Although the low-saturation type series regulator using the PNP transistor has been described in No. 1, the above circuit may be applied to a general-purpose series regulator using the NPN transistor as the power transistor Tr1 and a switching type regulator.

A general-purpose relay may be used instead of the switching transistor. Further, an RC delay circuit composed of a resistor and a capacitor may be provided instead of the delay transistors Tr6 and Tr7 shown in FIG.

[0043]

As described above, according to the present invention, when the power supply output to the load side is turned off, the switching transistor operates and the electric charge accumulated in the capacitor can be instantly discharged. The responsiveness at the time of off can be improved, and, for example, the malfunction of the connected device due to the long discharge time of the capacitor can be prevented.
Therefore, a highly reliable stabilized power supply circuit can be provided.

Further, by providing the delay means for delaying the start of the discharge when the output is turned off, it is possible to prevent a short circuit on the input side caused by the start of the discharge time being too early.

Further, by providing the protection means, for example, when the input side is short-circuited due to a contact failure or the like, the discharge switching transistor operates due to the operation of the protection switching transistor, and the electric charge stored in the capacitor through the discharge switching transistor operates. Is discharged, a reverse current does not flow in the circuit element directly connected between the input terminal and the output terminal. Therefore, it is possible to provide a stabilized power supply circuit capable of protecting those circuit elements even if the input side is short-circuited.

In addition, since the protection circuit can be formed by a small switching transistor without using a large diode for protecting the circuit element as in the conventional case, the circuit structure can be simplified and downsized, and the cost can be reduced. Can be reduced.

[Brief description of drawings]

FIG. 1 is a stabilized power supply circuit diagram according to a first embodiment of the present invention.

FIG. 2 is a stabilized power supply circuit diagram showing a modified example of the first embodiment.

FIG. 3 is a stabilized power supply circuit diagram showing another modification of the first embodiment.

FIG. 4 is a stabilized power supply circuit diagram according to a second embodiment.

FIG. 5: Conventional stabilized power supply circuit diagram

[Fig. 6] Similarly, a stabilized power supply circuit diagram when the input side is short-circuited.

[Figure 7] Similarly, a stabilized power supply circuit diagram with an external diode.

[Explanation of symbols]

C output capacitor Tr1 power transistor Tr3, Tr6, Tr7 transistor Tr4 switching transistor (discharge transistor) Tr8 switching transistor (protection transistor)

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Claims (3)

(57) [Claims] 1. An output stabilizing capacitor is connected to the output side, and is connected to an output control element including a PNP transistor for controlling the output and a terminal to which a control signal for turning the output on / off is input. An output control means for turning on / off the output control element according to the control signal, and an electric charge stored in the capacitor which is connected to the terminal and operates by input of the control signal for turning off the output. comprising a discharging means for discharging, and protection means for operating said discharging means in order to prevent the reverse current flowing through the output control device when the voltage of the input side is higher than the voltage of the output side, the protective means The input voltage is higher than the output voltage.
By operating the discharge means when the temperature becomes higher
To discharge the electric charge stored in the capacitor,
A stabilized power supply circuit characterized by preventing a reverse current flowing through an output control element . 2. The protection means is composed of a protection switching transistor connected in parallel to the upstream side of the output control element, and the discharge means is a discharge switching connected in parallel to the downstream side of the output control element. The protection switching transistor
Is the base of the switching transistor for discharge.
The discharge switching transistor operates and discharges by operating the protection switching transistor when the input side is short-circuited and the output side voltage becomes higher than the input side voltage. The stabilized power supply circuit according to claim 1, wherein: 3. The stabilized power supply circuit according to claim 1, wherein the discharging means is connected to a delay means for delaying the start of discharging by the discharging means when the output is turned off.