JPH0524973Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field This invention is a stabilized power supply integrated circuit used on the main power supply side in a system that supplies power from an auxiliary power supply to a load when the main power supply is cut off. Regarding.

(b) Conventional technology In recent years, many electronic devices using microcomputers, memories, etc. have been developed, and as such electronic devices become more complex and sophisticated,
Safety, reliability, etc. of power supplies are becoming important. In particular, in devices that use memory, backup is performed using an auxiliary power source so that the contents of the memory will not be erased even if the main power source is cut off due to a power outage or the like.

Conventionally, a power supply device using an auxiliary power supply applies voltage from the main power supply to the load (for example, memory) through a diode, and when the main power supply is cut off, the voltage is applied from the auxiliary power supply such as a battery to the load through the diode. is configured to apply. Here, the diode inserted between the main power supply and the load is to prevent reverse current from the auxiliary power supply,
Due to the presence of this diode, the voltage from the main power supply is reduced by the diode's forward voltage (e.g.
Moreover, even if the main power supply is stabilized, the voltage will change due to the temperature and current characteristics of the diode when the temperature or load current changes.

Therefore, as shown in Japanese Utility Model Publication No. 58-31213, a transistor is inserted between the output of the stabilized main power supply and the load, and when the main power supply is energized, the transistor is turned on to output the main power supply. A method has been proposed in which the difference between the voltage and the voltage applied to the load is set to the collector-emitter saturation voltage, that is, about several tens of mV.

(c) Problems to be solved by the invention In either the power supply device with a diode inserted between the main power supply and the load, or the power supply device with a transistor inserted between the main power supply and the load, as mentioned above, the diode or transistor A power supply device needs to have a capacity corresponding to the load current, and the larger the load current, the larger the power supply device becomes, increasing the mounting area of the power supply device and increasing the cost.

Therefore, we will explain why it is necessary to insert a diode or transistor for backflow prevention into the output path of the main power supply even though a stabilized power supply integrated circuit is used for the main power supply. As shown in FIG. 2, the conventional integrated circuit for a stabilized power supply divides the stabilized output voltage Vout by feedback resistors 1 and 2, and uses the divided voltage and the reference voltage Vref as an error detector. 3 and by controlling the transistor 4 with its detection output, the unregulated voltage Vin becomes the regulated voltage Vout.
This is what is output as. Furthermore, in FIG. 2, the Zener diode 5 and resistors 6 and 7 are a safe area protection circuit for the transistor 4, the transistor 8 is a current limiting transistor for the transistor 4, and 9 is a current source for driving the transistor 4. It is.

According to the stabilized power supply integrated circuit shown in FIG.
A current path to ground is formed through the stabilized voltage output terminal 10, the resistors 11, 7, 6, and the Zener diode 5, and between the resistors 11, 7, and the base-collector of the transistor 8.
A current path is formed to reach the unregulated voltage input terminal 12 via the forward direction of the PN junction between the base and collector of the transistor 4. Therefore, unless a backflow prevention diode is connected to the stabilized voltage output terminal 10, current will flow from the auxiliary power source, increasing power consumption, and especially if the auxiliary power source is a battery, its life will be shortened. be.

(d) Means for solving the problems The present invention has been made in view of the above points, and includes an error detection circuit that detects fluctuations in the output voltage of the output terminal that supplies voltage to the load, and It is equipped with an output voltage control circuit that works to cancel fluctuations in the output voltage using the output of the detection circuit, and when the main power is cut off, the output voltage is output in the current path of the protection circuit and bias circuit built into the output voltage control circuit. By providing a reverse current prevention diode that is reverse biased from the terminal to the ground direction, the conventional drawbacks are eliminated.

(E) Effect As mentioned above, by providing a backflow prevention diode in the current path of the protection circuit and bias circuit built into the output voltage control circuit, when the main power supply is energized, the unregulated voltage input terminal can be Normal operation is performed in the forward direction with respect to the grounding or the output terminal direction of the stabilized voltage.On the other hand, when the main power is cut off, the direction is reversed with respect to the grounding direction from the output terminal and the grounding direction via the input terminal. It acts as a bias and prevents current from flowing due to the voltage applied to the output terminal from the auxiliary power supply.

(f) Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 13 is an output voltage control circuit, 14 is a voltage follower circuit, and 15 is an error detection circuit. The output voltage control circuit 13 stabilizes the unregulated voltage Vin applied to the input terminal 16 and outputs a constant voltage Vout from the output terminal 17.
Due to fluctuations in the load connected to the output voltage Vout
When the voltage changes, the voltage follower circuit 14 and the error detection circuit 15 detect the change, and the output of the error detection circuit 15 operates to cancel the change.

Here, the voltage follower circuit 14 is a well-known differential amplifier circuit, and the output terminal 17 is connected to the base of one transistor 18 that is differentially connected.
The base of the other transistor 19 is directly connected to the emitter of the output transistor 20. That is, the voltage follower circuit 14 is an amplifier circuit with a voltage gain of 1 with 100% feedback, and the output terminal 17
A voltage equal to the voltage Vout outputted at the output transistor 20 is generated at the emitter of the output transistor 20. The error detection circuit 15 to which the output voltage of the voltage follower circuit 14 is applied includes feedback resistors 21 and 22 connected between the output of the voltage follower circuit 14 and ground;
a reference voltage circuit 23, a feedback resistor 21,
22 is applied to the (-) input terminal, and a reference voltage Vref is applied to the (+) input terminal. Therefore, when the main power supply is energized, the output terminal 17
When the voltage Vout output from the circuit changes due to the influence of the load, the output of the voltage follower circuit 14 changes similarly, and the voltage divided by the feedback resistors 21 and 22 changes. For example, the voltage Vout at the output terminal 17 decreases and the divided voltage becomes the reference voltage.
When it becomes smaller than Vref, the output voltage of the amplifier circuit 24 increases, and the output voltage of the transistor 25 and the diode 2 increases.
The current flowing from the current source 6 to the transistors 27 and 28 of the output voltage control circuit 13 increases.
As a result, the collector current of the output transistor 29 increases, and is corrected by being raised by the voltage drop of the output voltage Vout. Conversely, when the output voltage Vout increases, the amplifier circuit 24
9, the output voltage Vout decreases. In this way, the voltage Vout output from the output terminal 17 is stabilized.

Since the transistor 18 of the voltage follower circuit 14 described above is of the PNP type, it is a diode in the opposite direction from the base to the emitter direction and from the base to the collector direction. Therefore,
If the main power supply is interrupted, the current path from the base to ground and input terminal 16 is blocked.

On the other hand, the output voltage control circuit 13
NPN for outputting stabilized voltage Vout from Vin
type output transistor 29, a driver transistor 27 for driving the output transistor 29,
28, transistors 30 and 31 for current limiting of the output transistor 29, and a Zener diode 3.
2 and a safe area protection circuit consisting of resistors 33, 34, and 35, and the output voltage is adjusted by controlling the current flowing to the bases of driver transistors 27, 28. In addition, between the Zener diode 32 and the resistor 33 in the safety area protection circuit, there is a connection between the input terminal 16 and the output terminal 17.
A diode 36 which is in the forward direction with respect to the direction
Furthermore, a diode 3 which is also in the forward direction is connected via a resistor 37 between the bases of the transistors 27 and 28 and the collector of the transistor 30.
8 are connected. This diode 36, 38
This is to cut off the current path from the output terminal 17 to the input terminal 16 when the main power supply is cut off. That is, when the voltage applied to the input terminal 16 disappears, a voltage is applied to the output terminal 17 from the auxiliary power supply, but in the current path via the resistors 39, 35, 34, 33 and the Zener diode 32, the diode 36 is reversed. biased and also resistors 39, 35,
34, since the diode 38 is reverse biased in the current path via the base collector of the transistor 30, the resistor 37, and the base collectors of the transistors 27 and 28, the current path is reverse biased from the output terminal 17 to the input terminal 16.
The current flow to is blocked.

(G) Effects of the invention As described above, according to the invention, since the stabilized voltage output terminal of the stabilized power supply integrated circuit itself has a backflow prevention function, it is possible to prevent backflow in a power supply device equipped with an auxiliary power supply. This eliminates the need to externally connect diodes, transistors, etc., which reduces the mounting area and has the advantage of reducing costs. In addition, since the reverse current prevention diode according to the present invention is not included in the output circuit of the stabilized voltage, there is no need to increase the size even when extracting a large current, reducing the chip size and improving the performance of integrated circuits for stabilized power supplies. It contributes to

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional example. Explanation of main figure numbers, 13...Output voltage control circuit,
14... Voltage follower circuit, 15... Error detection circuit, 16... Input terminal, 17... Output terminal.

Claims (1)

[Scope of utility model registration request] In a stabilized power supply integrated circuit used for the main power supply of a system that supplies voltage from an auxiliary power supply to a load when the main power supply is cut off, detecting fluctuations in the voltage output from an output terminal that supplies power to the load. an error detection circuit; and an output voltage control circuit that operates to cancel fluctuations in the voltage by the output of the error detection circuit; a voltage follower circuit is provided between the output terminal and the error detection circuit; By providing a diode that is reverse biased from the output terminal to the grounding direction in the current path of the protection circuit and bias circuit built into the output voltage control circuit, reverse current flow can be prevented when the main power supply is cut off. An integrated circuit for a stabilized power supply characterized by preventing