JP2012055094A - Power supply control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent circuit malfunction.SOLUTION: A power supply control circuit comprises an IC for inputting a DC voltage converted from an AC voltage and supplied from a power source input line via an input terminal connected to the power source input line, and can output a DC voltage whose value is converted by operation of the IC. The IC is operable when a voltage equal to or higher than a predetermined threshold value is fed from an enable terminal. The power supply control circuit comprises an enable control circuit for lowering a voltage fed to the enable terminal below the threshold value when a DC voltage fed from the input terminal to the IC decreases below the predetermined value.

Description

  The present invention relates to a power supply control circuit.

  A so-called DC / DC converter that converts the value of an input DC voltage and outputs a different DC voltage to a subsequent circuit is known. The DC / DC converter includes an IC that forms the center of the DC / DC converter.

The purpose is to prevent flutter (malfunction) when shifting from on to off, and when the low-voltage cutoff circuit changes from on to off, the transistor that creates hysteresis changes from on to off. The drain voltage of the transistor rises due to the coupling capacitance between the gate and drain, but it cancels out by lowering the drain voltage with a capacitor corresponding to the coupling capacitance between the gate and drain of the transistor, and the rise in the gate voltage of the transistor There is known a power supply control circuit that prevents the low-voltage cutoff circuit from fluttering (see Patent Document 1).
Also, when the AC power supply is turned off or when the AC power supply is turned off for a moment due to a momentary power failure, etc., the power supply is supplied from the power supply to the microcomputer IC for the purpose of preventing the malfunction of the microcomputer IC. The detected power supply voltage is detected using the negative voltage of the output of the power transformer, and the detected voltage is fed back to the microcomputer IC to reset the microcomputer IC when the power supply voltage becomes a predetermined value or less. A configuration of a power reset circuit that stops data transmission from the microcomputer IC is disclosed (see Patent Document 2).
In addition, the input voltage of the primary winding of the transformer has become lower than a predetermined potential in order to prevent the control IC from malfunctioning even when the input voltage is dropped and then turned on again. In such a case, a configuration of a DC power supply device provided with voltage drop means for drawing out the charge of the smoothing capacitor of the rectifier circuit and dropping the voltage supplied to the control circuit is disclosed (see Patent Document 3).

JP 2000-197356 A JP 2002-158572 A JP 2010-11563 A

  In an electrical appliance with a built-in DC / DC converter as described above, when the power supply by the power cord (AC cord) is cut off (the AC cord is disconnected from the power outlet), the above-mentioned DC / DC converter is instantaneously Ideally, the input voltage to the IC is 0V. However, in the DC / DC converter, when the power supply by the AC cord is cut off, the input voltage does not immediately decrease to 0V, but substantially maintains a certain voltage for a certain period (for example, about 400 msec), and thereafter A phenomenon of 0V was observed. The design of the DC / DC converter is such that the minimum operating voltage value is set for the input voltage. One of the conditions under which the IC operates is that the input voltage is equal to or higher than the minimum operating voltage value. Therefore, there is a period in which the input voltage fluctuates in the vicinity of the minimum operating voltage value in an unstable manner (approximately holds the vicinity of the minimum operating voltage value) until the input voltage becomes 0 V after the power supply by the AC cord is cut off. In the meantime, an unstable operation (malfunction, also referred to as chattering) in which the DC / DC converter repeatedly turns on and off the output voltage may occur.

  The present invention has been made to solve the above-described problems, and provides a power supply control circuit capable of reliably preventing a malfunction that has been conventionally seen when power supply is interrupted.

  One aspect of the present invention includes an IC that inputs a DC voltage converted from an AC voltage and supplied by a power supply input line through an input terminal connected to the power supply input line. Is a power supply control circuit that is operable when a voltage equal to or higher than a predetermined threshold value is input from an enable terminal, and is input to the IC from the input terminal. And an enable control circuit for lowering the voltage input to the enable terminal below the threshold when the DC voltage to be applied falls below a predetermined value.

  According to this configuration, when the DC voltage input from the input terminal to the IC falls below a predetermined value, the voltage input to the enable terminal falls below the threshold value. Therefore, after the supply of the AC voltage is interrupted, a voltage that causes the IC to operate in an unstable manner is input from the input terminal until the DC voltage input from the input terminal to the IC becomes 0V. Even in this state, the IC becomes inoperable, and as a result, malfunction due to unstable operation of the IC does not occur.

It is a figure which shows schematically the circuit structure etc. of a power supply control circuit. It is a figure which shows the voltage change before and after the AC cord in this embodiment was removed. It is a figure which shows the voltage change before and after the conventional AC cord was removed.

As an embodiment of the present invention, the enable control circuit includes a Zener diode having a cathode connected to the power input line side and an anode connected to the enable terminal side, and the Zener diode receives the input DC voltage as described above. A configuration may be adopted in which voltage input to the enable terminal is cut off when the value falls below a predetermined value.
Further, as a more detailed embodiment of the present invention, it includes an IC that inputs a DC voltage converted from an AC voltage and supplied by a power input line via an input terminal connected to the power input line. When a DC voltage whose value has been stepped down by operation can be output, the IC inputs a DC voltage that is equal to or higher than the minimum operating voltage value from the input terminal and a voltage that exceeds a predetermined threshold value from the enable terminal. A power control circuit operable, wherein a Zener diode having a cathode connected to the power input line side and an anode connected to the enable terminal side is disposed in the middle of the signal line connecting the power input line and the enable terminal. The zener diode is configured such that the supply of the AC voltage is interrupted and the DC voltage input from the input terminal to the IC is the minimum operating voltage value. When below the remote high predetermined value, the voltage input to the enable terminal may be configured to be lower than the threshold value by blocking the input voltage to the enable terminal.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 schematically shows a power supply control circuit 10 according to the present embodiment. The power supply control circuit 10 is a DC / DC converter that inputs a DC voltage DC from a power supply input circuit 20 through a power supply input line 13, converts the value, and outputs a different DC voltage DC to a subsequent circuit (not shown). Function. The power supply input circuit 20 inputs an AC voltage via an AC cord 21 inserted into a commercial AC voltage power outlet, and performs voltage conversion, rectification, smoothing, etc. on the input AC voltage to thereby generate a DC voltage. The DC is taken out and the DC voltage DC is input to the power supply control circuit 10. The power supply control circuit 10 and the power supply input circuit 20 constitute a power supply circuit mounted on an electrical product. Various products such as a television, a DVD player / recorder, and a Blu-ray disc (BD) player / recorder are mounted on the power control circuit 10 and the like.

  The power supply control circuit 10 includes an IC 11 that plays a central role as a DC / DC converter. The IC 11 is a one-chip IC (for example, an IC having a model name BD9326EFJ) including a MOSFET, and includes a plurality of terminals (pins). The input terminal VIN of the IC 11 is connected to the power input line 13. Under a situation where the AC cord 21 is inserted into the power outlet (a situation where an AC voltage is supplied), a DC voltage DC of about + 12V is supplied from the power input circuit 20 to the power input line 13, and this DC The voltage DC is input to the input terminal VIN via the power input line 13. Note that a resistor, a capacitor for smoothing (see FIG. 1), and the like can be appropriately connected to the power input line 13. The IC 11 inputs the DC voltage DC from the input terminal VIN and operates to output a pulse signal having a predetermined duty ratio from the switch terminal SW. Then, the DC voltage DC stepped down (converted) according to the duty ratio of the pulse signal is output to the subsequent stage of the choke coil L.

  In the IC 11, the minimum operating voltage value Vmin is set with respect to the voltage input from the input terminal VIN, and the condition that the IC 11 operates as described above is that the input voltage is equal to or higher than the minimum operating voltage value Vmin. It has become one. The minimum operating voltage value Vmin is, for example, about 4 to 6V. Further, an enable signal (voltage) is input to the enable terminal EN of the IC 11, and the IC 11 is operable when an enable signal whose voltage is equal to or higher than a predetermined threshold is input. Yes. That is, the IC 11 operates only when an enable signal equal to or higher than the threshold is applied to the enable terminal EN and a voltage equal to or higher than the minimum operating voltage value Vmin is applied to the input terminal VIN. In addition, the IC 11 includes a soft start terminal SS, a phase correction terminal COM, a feedback terminal FB, a boost terminal BST, and a ground terminal G. In FIG. 1, not all the connection states between the terminals and the surroundings are shown, but the portions necessary for this embodiment are shown as appropriate.

The feature of this embodiment is that an enable control circuit 12 is provided between the power input line 13 and the enable terminal EN. Conventionally, such an enable control circuit 12 is not provided, and a configuration in which the power input line 13 and the enable terminal EN are directly connected is adopted, and the voltage on the power input line 13 is also applied to the enable terminal EN. It had been.
The enable control circuit 12 includes a Zener diode Z having a cathode connected to the power input line 13 side and an anode connected to the enable terminal EN side in the middle of a signal line connecting the connection point 13a on the power input line 13 and the enable terminal EN. (+ Zener diode Z reversely connected to the power supply). Further, the enable control circuit 12 is provided with a resistor R1 [100Ω] for preventing overcurrent between the anode of the Zener diode Z and the enable terminal EN, and further, a connection point 12a between the resistor R1 and the enable terminal EN side. Is grounded via a resistor R2 [1 kΩ]. The resistor R2 is a resistor provided to allow a current to flow stably through the Zener diode Z.

  The Zener diode Z has a characteristic of flowing a current when a voltage equal to or higher than a predetermined value Vs (Zener voltage) is applied, and the predetermined value Vs is, for example, about + 9.1V. Therefore, under the situation where the AC cord 21 is inserted into the power outlet as described above, the Zener diode Z passes a current because the DC voltage DC of about + 12V is supplied to the power input line 13, and as a result, A voltage of about + 9V is input to the enable terminal EN as an enable signal. Since such an enable signal is equal to or greater than the threshold value, the IC 11 operates normally, and as a result, the DC / DC converter outputs a stepped-down DC voltage DC (the output voltage Vout from the DC / DC converter is can get).

  On the other hand, when the AC cord 21 is disconnected from the power outlet and the supply of AC voltage is interrupted, the voltage on the power input line 13 decreases from about + 12V to 0V. In this process, at the moment when the voltage applied to the Zener diode Z falls below the predetermined value Vs, the Zener diode Z stops flowing current, and the voltage supply to the enable terminal EN is cut off. That is, the enable signal is 0 V, which is lower than the threshold value. That is, at the instant when the AC cord 21 is disconnected from the power outlet and the potential at the connection point 13a on the power input line 13 falls below the predetermined value Vs, the enable signal is cut off and the operation of the IC 11 is stopped. The IC 11 may simply stop its operation when the enable signal becomes 0V.

  As described above, in the DC / DC converter, even when the AC cord is disconnected and the external power supply is cut off, the voltage on the power supply line does not immediately decrease to 0 V, and the minimum operating voltage for a certain period. A voltage near the value Vmin may be substantially maintained. For this reason, conventionally, there has been a problem of malfunction caused by the IC operating unstablely because the voltage near the minimum operating voltage value Vmin is substantially held. However, according to the present embodiment, the moment when the AC cord 21 is disconnected from the power outlet and the voltage on the power input line 13 (voltage input to the input terminal VIN) falls below the predetermined value Vs higher than the minimum operating voltage value Vmin. Further, since the operation of the IC 11 is forcibly stopped, the malfunction is surely prevented.

  FIG. 2 shows the measurement results of the voltage change of the input terminal VIN of the IC 11 and the change of the output voltage Vout before and after the AC cord 21 is pulled out when this embodiment is employed. FIG. 3 shows the measurement results of the change in the voltage at the input terminal VIN and the change in the output voltage Vout before and after the AC cord is pulled out when the conventional configuration (configuration without the enable control circuit 12) is adopted. ing. As shown in FIG. 3, it takes some time for the voltage at the input terminal VIN to reach 0 V even after the AC cord is disconnected, and in this process, the voltage at the input terminal VIN is substantially held around the minimum operating voltage value Vmin. There is a period to do. Therefore, it can be seen that the operation / non-operation of the IC is repeated after the AC cord is removed, and the output voltage Vout is repeatedly turned on / off (the malfunction of the DC / DC converter occurs). In this case, the threshold for the enable signal is lower than the minimum operating voltage value Vmin. On the other hand, FIG. 2 is the same as FIG. 3 in that after the AC cord 21 is disconnected, there is a period during which the voltage at the input terminal VIN substantially holds around the minimum operating voltage value Vmin. However, as described above, in this embodiment, since the operation of the IC 11 is forcibly stopped before the voltage of the input terminal VIN becomes near the minimum operating voltage value Vmin, such a minimum operation of the voltage of the input terminal VIN is performed. The above malfunction does not occur regardless of instability near the voltage value Vmin.

DESCRIPTION OF SYMBOLS 10 ... Power supply control circuit, 11 ... IC, 12 ... Enable control circuit, 20 ... Power supply input circuit, 21 ... AC code

Claims (3)

Includes an IC that inputs a DC voltage converted from an AC voltage and supplied by a power supply input line via an input terminal connected to the power supply input line, and can output a DC voltage whose value is converted by the operation of the IC. The IC is a power supply control circuit operable when a voltage equal to or higher than a predetermined threshold is input from an enable terminal,
A power supply control circuit comprising: an enable control circuit that reduces a voltage input to the enable terminal below the threshold when a DC voltage input to the IC from the input terminal falls below a predetermined value.   The enable control circuit includes a Zener diode having a cathode connected to the power input line side and an anode connected to the enable terminal side, and the Zener diode is connected when the input DC voltage falls below the predetermined value. The power supply control circuit according to claim 1, wherein the voltage input to the enable terminal is cut off. Includes an IC that inputs a DC voltage converted from an AC voltage and supplied by a power supply input line via an input terminal connected to the power supply input line, and can output a DC voltage whose value is stepped down by the operation of the IC The IC is a power supply control circuit operable when a DC voltage equal to or higher than the minimum operating voltage value is input from the input terminal and a voltage equal to or higher than a predetermined threshold is input from the enable terminal.
A zener diode having a cathode connected to the power input line side and an anode connected to the enable terminal side is disposed in the middle of the signal line connecting the power input line and the enable terminal, and the zener diode is supplied with the AC voltage. When the DC voltage input to the IC from the input terminal is dropped below a predetermined value higher than the minimum operating voltage value, the voltage input to the enable terminal is cut off to be input to the enable terminal. A power supply control circuit, wherein the voltage is lowered below the threshold value.

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