JP2011101506A - Power circuit and method of controlling output from the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve more preferable output control in a power circuit. <P>SOLUTION: The power circuit includes a power-supply main circuit (1) for generating a DC output voltage by transforming a DC input voltage, an output short-circuit protective circuit (5) for activating an output when the output voltage is lower than a first voltage, and a differential voltage detecting circuit (6) for activating the output when a differential voltage of the input voltage and the output voltage is lower than a second voltage. The power circuit further includes a control circuit (7) for bringing the power-supply main circuit (1) to a shutdown state requiring a restart when the output from the output short-circuit protective circuit (5) is active and the output from the differential voltage detecting circuit (6) is inactive, and a reset circuit (4) for releasing the shutdown state when the input voltage is lower than a third voltage. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a power supply circuit, and more particularly to a technique for protecting a power supply circuit from a low voltage input and an output short circuit.

  A power supply circuit that converts a DC voltage supplied from a battery, an AC adapter, or the like into a desired voltage and outputs the voltage is used in many electronic devices. In general, when an output short circuit occurs, the power supply circuit includes an output short circuit protection circuit that stops the output in order to avoid destruction of components due to overcurrent. Further, there is an input voltage detection circuit that operates an output short-circuit protection circuit to stop output when it is detected that the input voltage has dropped too much (see, for example, Patent Document 1).

JP 2004-282964 A

  The conventional power supply circuit treats the input voltage drop and output short circuit in the same row for output stop, so even if the output voltage drops due to the input voltage drop, it must be restarted assuming that the output short circuit has occurred. Will be shut down. However, when the cause of the output stop is on the input side, that is, when the output stops due to a decrease in the input voltage, it is preferable that the output automatically recovers when the input voltage is restored.

  In view of this point, an object of the present invention is to realize more preferable output control of a power supply circuit.

  In order to solve the above problems, the present invention has taken the following solutions. That is, a power supply main circuit that transforms a DC input voltage to generate a DC output voltage, an output short circuit protection circuit that activates an output when the output voltage is lower than the first voltage, an input voltage and an output The differential voltage detection circuit that activates the output when the difference voltage from the voltage is lower than the second voltage, and the power supply when the output of the output short-circuit protection circuit is active and the output of the differential voltage detection circuit is inactive. It is assumed that the main circuit includes a control circuit that puts the main circuit into a shutdown state that needs to be restarted, and a reset circuit that releases the shutdown state when the input voltage is lower than the third voltage.

  According to this, when only the output voltage drops too much while maintaining the input voltage, the power supply main circuit is shut down, and the shutdown state is released by temporarily shutting off the input voltage. In other words, even if the output voltage is lowered due to a drop in the input voltage, the power supply main circuit is not shut down, and thus there is no need to restart.

  Preferably, when the output of the output short circuit protection circuit is active and the output of the differential voltage detection circuit is active, the control circuit puts the power supply main circuit into an output stop state that does not require restart.

  According to this, when the output voltage decreases too much as the input voltage decreases, the power supply main circuit enters an output stop state that does not require restart, and automatically returns to the normal state when the input voltage is restored.

  According to the present invention, it is possible to prevent the power supply circuit from frequently shutting down due to a decrease in the input voltage, and to increase the availability of the power supply circuit.

1 is a configuration diagram of a power supply circuit according to a first embodiment. 3 is a timing chart of the power supply circuit according to the first embodiment. It is a block diagram of the power supply circuit which concerns on 2nd Embodiment. It is a timing chart of the power supply circuit which concerns on 2nd Embodiment.

<First Embodiment>
FIG. 1 is a configuration diagram of a power supply circuit according to the first embodiment. The power source main circuit 1 steps down the DC voltage Vin input from, for example, a battery or an AC adapter, and outputs a DC voltage Vout. The power supply main circuit 1 enters a shutdown state when the signal SD is active (for example, at H level) for a certain period of time, for example, for a start-up time until the voltage Vout exceeds 0 V from the output lower limit voltage. Further, the power supply main circuit 1 is released from the shutdown state when the signal RST becomes active (for example, H level). The power source main circuit 1 can be constituted by, for example, a step-down DC-DC converter.

  The reset circuit 4 activates the reset signal RST when the voltage Vin is lower than the input lower limit voltage. The input lower limit voltage is, for example, a voltage that is slightly higher than the lower limit value of the operating voltage of the power supply main circuit 1.

  The output short circuit protection circuit 5 activates the short circuit detection signal SH (for example, H level) when the voltage Vout is lower than the output lower limit voltage. The output lower limit voltage is, for example, 70% of the target output voltage. Further, the output short circuit protection circuit 5 is reset when the signal RST is active, and makes the signal SH inactive (for example, L level).

  The difference voltage detection circuit 6 activates the difference voltage detection signal DEF (for example, H level) when the voltage difference between the voltage Vin and the voltage Vout is lower than the maximum difference. The maximum difference is, for example, 0.5V.

  The control circuit 7 activates the shutdown signal SD when the signal SH is active and the signal DEF is inactive (for example, L level). Specifically, the control circuit 7 can be composed of a NOT circuit 70 and an AND circuit 71, for example.

  Next, the operation of the power supply circuit according to the present embodiment will be described with reference to FIG. For convenience, each signal is active at H level and inactive is L level. At time t0, the voltage Vin and the voltage Vout are both 0V. Signals RST, SH, DEF, SD are all at L level.

  When the voltage Vin exceeds the input lower limit voltage and the signal RST becomes L level, the voltage Vout increases. As a result, the signal SD becomes H level, but the power source main circuit 1 does not shut down because the time for maintaining the H level is less than the startup time. When the voltage Vin and the voltage Vout exceed the respective lower limit voltages, the power supply main circuit 1 enters a normal state.

  When an output short circuit or overload droop occurs, the voltage Vout decreases and falls below the output lower limit voltage at time t1. Then, the signal SH becomes H level and the signal SD becomes H level. From time t1 to time t2, since the signal SD is at the H level continuously for the activation time or longer, the power supply main circuit 1 is shut down. After the shutdown, a restart operation is performed and the voltage Vin decreases. When the voltage Vin falls below the input lower limit voltage at time t2, the signal RST becomes H level. As a result, the shutdown state is released and the output short circuit protection circuit 5 is reset, so that the signal SH becomes L level and the signal SD becomes L level. If the voltage Vin starts to increase at time t3 due to the restart operation and the output short circuit, overload drooping, or the like is resolved, the power supply main circuit 1 is in a normal state.

  When the voltage Vin decreases due to battery consumption or the like, the voltage Vout also decreases, and the signal DEF becomes H level immediately before time t4. When the voltage Vout falls below the output lower limit voltage at time t4, the signal SH becomes H level. However, since the signal DEF is at H level, the signal SD remains at L level. Therefore, the power supply main circuit 1 does not shut down and continues to output the voltage Vout while being lower than the output lower limit voltage. After that, when the voltage Vin starts to recover by connecting the power source to, for example, an AC adapter, the voltage Vout also recovers accordingly.

  As described above, according to the present embodiment, the power supply main circuit 1 shuts down when the state in which only the voltage Vout is lowered while the voltage Vin remains unchanged continues for a certain time or more. That is, the power supply main circuit 1 does not shut down when the voltage Vin decreases.

  As the overcurrent protection function, the power supply main circuit 1 may be configured to have a characteristic that both the output voltage and the output current decrease in the overcurrent region, for example. According to this, when the voltage Vin is low and an output short-circuit occurs, the power supply circuit can be protected from destruction or the like without being shut down.

<Second Embodiment>
FIG. 3 is a configuration diagram of a power supply circuit according to the second embodiment. Hereinafter, differences from the first embodiment will be described.

  The control circuit 7A activates the stop signal ST (for example, H level) when the signal RST is active or when both the signal SH and the signal DEF are active. That is, the signal ST also serves as the signal RST. Specifically, the circuit portion related to the output of the signal ST in the control circuit 7A can be configured by, for example, an AND circuit 72 and an OR circuit 73. When the signal ST is active, the power supply main circuit 1 enters an output stop state that does not require restarting.

  Next, the operation of the power supply circuit according to the present embodiment will be described with reference to FIG. The operation from time t0 to time t1 is the same as the operation from time t0 to time t4 in FIG. When the voltage Vout falls below the output lower limit voltage at time t1, the signal SH becomes H level, and the signal DEF is H level, so that the signal ST becomes H level. As a result, the power supply main circuit 1 is in an output stop state, and the voltage Vout further decreases.

  When the voltage Vout decreases, at time t2, the signal DEF becomes L level, the signal SD becomes H level, and the signal ST becomes L level. Therefore, the output stop state is canceled and the voltage Vout increases. When the voltage Vout rises, the signal DEF becomes H level, the signal SD becomes L level, the signal ST becomes H level, and the power supply main circuit 1 is again in the output stop state. Thereafter, the same operation is repeated. Thereafter, when the voltage Vin recovers, the voltage Vout also returns.

  As described above, according to the present embodiment, when the voltage Vout decreases as the voltage Vin decreases, an output stop state that does not require restart is set. When the voltage Vin is restored, the voltage Vout is also automatically restored. In addition, when the voltage Vout decreases as the voltage Vin decreases, the power supply main circuit 1 repeats output and stop, so that when the voltage Vin recovers, a soft start can be applied, and the output load is reduced. Inrush current can be suppressed.

  In each of the above embodiments, the power supply main circuit 1 has been described as a step-down DC-DC converter for convenience, but a step-up DC-DC converter may be used. In addition, although the power-up main circuit 1 counts the startup time, the output short-circuit protection circuit 5 may count the startup time. That is, the output short circuit protection circuit 5 may activate the signal SH when the state where the voltage Vout is lower than the output lower limit voltage continues for the start time or longer. In this case, the power supply main circuit 1 is shut down as soon as the signal SD becomes active.

  The power supply circuit according to the present invention can prevent the power supply circuit from frequently shutting down due to a decrease in input voltage, and thus is useful for electronic devices to which various power supply voltages such as a battery and an AC adapter are connected. .

DESCRIPTION OF SYMBOLS 1 Power supply main circuit 4 Reset circuit 5 Output short circuit protection circuit 6 Differential voltage detection circuit 7, 7A Control circuit SH Short circuit detection signal (1st signal)
DEF differential voltage detection signal (second signal)

Claims (4)

A power supply main circuit that transforms a DC input voltage to generate a DC output voltage;
An output short circuit protection circuit that activates an output when the output voltage is lower than a first voltage;
A differential voltage detection circuit that activates an output when a differential voltage between the input voltage and the output voltage is lower than a second voltage;
When the output of the output short circuit protection circuit is active and the output of the differential voltage detection circuit is inactive, a control circuit that puts the power supply main circuit into a shutdown state that requires restarting;
And a reset circuit for canceling the shutdown state when the input voltage is lower than a third voltage. The power supply circuit according to claim 2, wherein
The control circuit puts the power supply main circuit into an output stop state that does not require restart when the output of the output short circuit protection circuit is active and the output of the differential voltage detection circuit is active. circuit. The power supply circuit according to claim 1, wherein
The control circuit sets the power supply main circuit to the shutdown state when the output of the output short circuit protection circuit is active and the output of the differential voltage detection circuit is inactive for a predetermined time or more. Power supply circuit. A method for controlling the output of a power supply circuit that transforms a DC input voltage to generate a DC output voltage,
Activating a first signal when the output voltage is lower than a first voltage;
Activating a second signal when a difference voltage between the input voltage and the output voltage is lower than a second voltage;
When the first signal is active and the second signal is inactive, the power supply circuit is placed in a shutdown state that needs to be restarted;
And a step of canceling the shutdown state when the input voltage is lower than a third voltage.

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