JP2011146985A - Voltage detection circuit and power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely discharge a reset capacitor without shutting off power for every instantaneous interruption. <P>SOLUTION: The invention relates to a voltage detection circuit 53 for detecting drop of an input voltage to a switching control circuit 5 and operating a discharging circuit 55 for discharging a reset capacitor C2 provided in the switching control circuit 5, wherein a signal for comparison is produced from the input voltage in such a way that its voltage reaches a recovery determination value Vr after the lapse of a predetermined time Ta from the time of recovery after the detection of the input voltage drop, and the reset capacitor C2 is discharged by operating the discharging circuit 55 continuously from the detection of the input voltage drop until the voltage of the signal for comparison exceeds the recovery determination value Vr. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for reliably discharging a reset capacitor provided in an electric circuit when a momentary power failure occurs.

  Some power supply apparatuses have an input voltage range that can be normally output and a minimum input voltage. For example, in a switching power supply device, in general, a control circuit that controls the switching operation and resets when the reset capacitor is discharged, and detects that the input voltage is below the minimum input voltage, and discharges the reset capacitor. And a voltage detection circuit (input monitoring circuit) that prevents a malfunction of the control circuit by discharging the reset capacitor when the input power is interrupted or restored.

By the way, if the voltage detection circuit is configured to stop the discharge of the reset capacitor in accordance with the recovery of the input power, when the power failure / recovery of the input power occurs instantaneously (hereinafter referred to as “instantaneous power failure”). ) The reset capacitor may not be sufficiently discharged, and the control circuit may not reset.
Therefore, a power supply circuit having a function of delaying the power failure recovery for a predetermined time when the voltage detection circuit detects the power failure recovery has been proposed (for example, Patent Document 1 (paragraph numbers 0043 to 0045, FIG. 5)). reference). According to such a power supply circuit, even when the input voltage recovers before the reset capacitor is sufficiently discharged, the power supply circuit is stopped for a predetermined time, so that the reset capacitor is discharged and the control circuit is reliably reset. it can.

JP 2002-165155 A

However, since the power supply circuit is stopped every time a momentary power failure occurs, the conventional configuration has a problem that the operation of all the circuits that operate by receiving power supply from the power supply circuit is stopped for a predetermined time. For this reason, it may be necessary to separately supply power to a circuit that does not require a reset operation.
The present invention has been made in view of the above-described circumstances, and includes a voltage detection circuit that can reliably discharge a reset capacitor without interrupting power every momentary power failure, and the voltage detection circuit. An object is to provide a power supply device.

  In order to achieve the above object, the present invention provides a voltage detection circuit that detects a drop in an input voltage to an electric circuit and activates a discharge circuit that discharges a reset capacitor provided in the electric circuit. A comparison signal in which the voltage reaches the power recovery determination value after a predetermined time from power recovery after detection of the input voltage drop is generated from the input voltage, and the voltage of the comparison signal is recovered from the time of detection of the input voltage drop. The discharge capacitor is discharged by continuing the operation of the discharge circuit until a power determination value is exceeded.

  In the voltage detection circuit, the present invention further includes a comparator that compares the voltage of the comparison signal and the power recovery determination value, and the connection node that inputs the comparison signal to the comparator includes the input voltage. A charge / discharge circuit is provided that charges the battery based on the input voltage applied to the connection node while discharging when detecting a drop in the voltage.

  The present invention is also characterized in that the voltage detection circuit further comprises a zero voltage maintaining circuit for connecting the connection node to the ground side for a predetermined time from the time when the drop in the input voltage is detected.

  In order to achieve the above object, the present invention provides a switching power supply that controls on / off of a switching element provided on a primary side of a transformer and obtains an output voltage on a secondary side of the transformer. A switching control circuit having a reset capacitor, a discharge circuit for discharging the reset capacitor, a drop in input voltage to the primary side, and operating the discharge circuit to control the reset capacitor A voltage detection circuit for discharging, and the voltage detection circuit generates a comparison signal from the input voltage that reaches a power recovery determination value after a predetermined time from power recovery after detection of a drop in the input voltage, The operation of the discharge circuit is continued until the voltage of the comparison signal exceeds the power recovery determination value from the time when the input voltage drop is detected. Characterized by discharging the capacitor.

  According to the present invention, even when a momentary power failure occurs, the comparison signal reaches the power recovery determination value over a predetermined time, and thus the discharge of the reset capacitor is continued for the predetermined time. It can be surely discharged. In addition, the power recovery is determined based on the comparison signal generated from the input voltage, so that the power recovery can be reliably detected, and the operation of the discharge circuit is stopped based on the comparison signal, so that the electric circuit is supplied with power. The reset operation can be performed reliably without interruption.

It is a circuit diagram which shows the structure of the power supply device which concerns on embodiment of this invention. It is a circuit diagram which expands and shows a voltage detection circuit. It is a timing chart which shows operation | movement of the switching power supply device at the time of input power input (at the time of power recovery). It is a timing chart which shows operation | movement of the switching power supply device at the time of a momentary power failure. It is a circuit diagram which shows the structure of the voltage detection circuit which concerns on the modification of this invention. It is a timing chart which shows the operation | movement at the time of the momentary power failure of the voltage detection circuit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a voltage detection circuit that resets a switching control circuit of a switching power supply device is illustrated.

FIG. 1 is a circuit diagram showing a configuration of a switching power supply device 1 according to the present embodiment.
The switching power supply device 1 is a so-called forward switching power supply. That is, the switching power supply device 1 includes a transformer T1, and a switching element 3 such as a MOSFET is connected in series to a primary winding 2 of the transformer T1, and switching control for turning on / off the switching element 3 is performed. A circuit 5 is provided. When the switching element 3 is turned on / off, an electromotive voltage is generated in the primary winding 2 by the input voltage Va input from the primary side input terminal 7, and an induction voltage is generated in the secondary winding 9. Generate voltage.

  The secondary winding 9 of the transformer T1 includes diodes 11 and 13 as rectifying elements, a smoothing choke coil 15, and an electrolytic capacitor 17, and rectifies the induced electromotive voltage generated in the secondary winding 9 to generate a DC output voltage. A rectifying / smoothing circuit 19 that outputs Vb to the output terminal 21 is provided. By connecting a load to the output terminal 21, the output voltage Vb having a predetermined voltage value is applied to the load.

Further, the switching power supply device 1 includes an input smoothing circuit 23 and an excitation reset circuit 25 on the primary side.
The input smoothing circuit 23 smoothes and outputs an input voltage, and includes a diode 27 and an electrolytic capacitor C1.
The excitation reset circuit 25 is a circuit that discharges residual excitation power accumulated in the transformer T1, and is connected in series to the tertiary winding 29 as a reset winding provided in the transformer T1 and the tertiary winding 29. A resistor 31, a diode 33, and an electrolytic capacitor 35 are provided, and the residual excitation power of the transformer T1 is stored in the electrolytic capacitor 35. The input terminal of the electrolytic capacitor 35 is connected to the primary-side input terminal 7 via a resistor 37 so that the power stored in the electrolytic capacitor 35 is returned to the input side as a result. The stored power of the electrolytic capacitor 35 is also supplied to the switching control circuit 5 and functions as an auxiliary battery that supplies power to the switching control circuit 5 when the input power is cut off.

  On the secondary side, an overvoltage detection circuit 39 is provided between the output terminal 21 on the secondary side and the rectifying / smoothing circuit 19. The overvoltage detection circuit 39 is a circuit that detects an overvoltage at the output terminal 21, and resistors 41 and 43 provided between the terminals of the output terminal 21, and the voltage between the terminals becomes an overvoltage value defined by the resistors 41 and 43. A shunt regulator 45 that is turned on when the shunt regulator 45 is turned on, a light emitting diode 47 that emits light when the shunt regulator 45 is turned on, and a current limiting resistor 49 that limits a current to the light emitting diode 47 are provided. The overvoltage at the output terminal 21 is detected by the light emission of the light emitting diode 47.

  The DC voltage at the output terminal 21 of the switching power supply device 1 is defined by the frequency and duty ratio at which the switching control circuit 5 turns on / off the switching element 3. In order to keep the voltage value of the DC voltage constant, a feedback circuit (not shown) that feedback-controls the switching control circuit 5 based on the voltage value of the DC voltage is provided. Further, the switching control circuit 5 is provided with a reset capacitor C2, and is configured to reset a feedback value or the like when the reset capacitor C2 is discharged. The reset capacitor C2 is charged with the input power from the input terminal 7 of the switching power supply 1. Once discharged, the reset capacitor C2 is not charged unless the input power is restored.

  Further, the switching power supply device 1 is provided with a power-on reset circuit 51 that discharges the reset capacitor C2 and resets the switching control circuit 5 in the event of a power failure. The power-on reset circuit 51 includes a voltage detection circuit 53 that detects a power failure / recovery based on the input voltage Va of the input power, and a discharge circuit 55 that discharges the reset capacitor C2 based on the detection of the voltage detection circuit 53. I have.

The voltage detection circuit 53 normally outputs the detection signal VCo at the H level, sets the detection signal VCo to the L level when detecting a power failure of the input power to the switching power supply 1, and detects the power failure when the power is restored. This is a circuit for returning the detection signal VCo to the H level on condition that a predetermined time Ta (FIG. 3) has passed since the start. As described above, since the time for which the detection signal VCo is set to the L level is always secured for a predetermined time, the reset capacitor C2 can be reliably discharged.
The discharge circuit 55 discharges the input side node N1 of the reset capacitor C2 connected to the ground side (earth side) over a period in which the detection signal VCo is at the L level. Specifically, the discharging circuit 55 turns on the switching element 57 provided between the input side node N1 of the reset capacitor C2 and the ground side and the switching element 57 in accordance with the transition of the detection signal VCo to the L level. And a switching element 59 that is turned off with the level transition. The potential for turning on the switching element 57 is supplied from the electrolytic capacitor 35 of the excitation reset circuit 25 described above, and is configured to operate reliably when the input power is cut off. In the figure, resistors 61 to 67 included in the discharge circuit 55 are current limiting resistors.

FIG. 2 is an enlarged circuit diagram showing the voltage detection circuit 53.
The voltage detection circuit 53 includes a comparator 60. On the plus side of the comparator 60, an input voltage Vin based on the input voltage Va at the input terminal 7 of the switching power supply device 1 is input via the resistor R1, and on the minus side. Is inputted with a power recovery judgment value Vr which is a voltage threshold value regarded as a power failure / power recovery. That is, the comparator 60 compares the voltage VCi of the signal (hereinafter referred to as “comparison signal”) of the plus-side connection node N2 with the power recovery determination value Vr, and the voltage VCi of the comparison signal is recovered. An H level signal is output as the detection signal VCo during the determination value Vr or higher, and the detection signal VCo is set to the L level when the voltage VCi becomes lower than the power recovery determination value Vr.
The voltage VCi of the comparison signal fluctuates up and down following the voltage fluctuation of the input voltage Vin to the voltage detection circuit 53, but is connected to the connection node N2 so as to fluctuate gently at each timing at the time of power failure and power recovery. The first charging / discharging circuit 63 and the second charging / discharging circuit 65 are connected to each other.

The first charge / discharge circuit 63 is a parallel circuit of a capacitor C3 and a resistor R3, and is provided between the positive connection node N2 of the comparator 60 and the output node N3. That is, the capacitor C3 of the first charging / discharging circuit 63 is charged by applying the input voltage Vin to the connection node N2 and maintains a predetermined potential, and the voltage VCi of the connection node N2 has the power recovery determination value Vr. It is discharged when the output node N3 of the comparator 60 becomes L level (ground potential).
The second charging / discharging circuit 65 is a parallel circuit of the capacitor C4 and the resistor R2, and is provided between the positive connection node N2 of the comparator 60 and the ground. That is, the capacitor C4 of the second charge / discharge circuit 65 is charged by applying the input voltage Vin to the connection node N2, holds a predetermined potential, and discharges as the input voltage Vin decreases.

  By the first charging / discharging circuit 63 and the second charging / discharging circuit 65, when the power failure occurs, the first charging / discharging circuit 63 and the second charging / discharging circuit 65 discharge electric power, so that the voltage VCi of the connection node N2 becomes the ground potential. Descent promptly. On the other hand, at the time of power recovery, the voltage VCi of the connection node N2 also increases as the input voltage Vin increases. At this time, the increase in the voltage VCi at the connection node N2 is accompanied by the charging of the first charge / discharge circuit 63 and the second charge / discharge circuit 65 connected to the connection node N2, and therefore rises more slowly than the voltage of the input voltage Vin. It will be.

FIG. 3 is a timing chart showing the operation of the switching power supply device 1 when input power is turned on (when power is restored).
When the input voltage Vin of the voltage detection circuit 53 rises as the input power is turned on (power recovery), as described above, the voltage VCi at the connection node N2 on the plus side of the comparator 60 starts to rise gently, and reaches a predetermined time Ta. To reach the power recovery judgment value Vr. When the voltage VCi at the connection node N2 reaches the power recovery determination value Vr, the output of the comparator 60, that is, the detection signal VCo of the voltage detection circuit 53 transitions to the H level.

  When the detection signal VCo of the voltage detection circuit 53 reaches the H level from the L level, the discharge circuit 55 cuts off the reset capacitor C2 and the ground side, thereby starting the charging of the reset capacitor C2. When the potential of the reset capacitor C2 rises to the switching operation voltage Vs, the switching control circuit 5 starts the switching operation, and accordingly, the output voltage Vb is generated on the output side of the switching power supply device 1. The capacity of the reset capacitor C2 is set to be smaller than the capacities of the capacitors C3 and C4 included in the first charging / discharging circuit 63 and the second charging / discharging circuit 65 so that the switching operation can be started quickly upon power recovery. Yes.

Next, the operation when the voltage VCi of the connection node N2 in the voltage detection circuit 53 rises will be described in detail.
As shown in FIG. 3, in a predetermined time Ta until the voltage VCi reaches the power recovery determination value Vr, an initial rising period Tb that rises very slowly at the start of the rising, and a rising period Tc that gradually rises thereafter. And are included. The initial rising period Tb is a period during which the capacitors C3 and C4 of both the first charging / discharging circuit 63 and the second charging / discharging circuit 65 are charged. The charging voltage of the capacitors C3 and C4 is the voltage VCi of the connection node N2. It becomes. In the present embodiment, the capacity of the capacitor C4 of the second charging / discharging circuit 65 is made smaller than that of the capacitor C3 of the first charging / discharging circuit 63, and the charging of the capacitor C4 of the second charging / discharging circuit 65 is completed. The initial rising period Tb shifts to the rising period Tc.

In the rising period Tc, the capacitor C3 of the first charging / discharging circuit 63 is continuously charged, and the charging voltage of the capacitor C3 becomes the voltage VCi of the connection node N2.
The charging time is adjusted by adjusting the capacities of the capacitors C3 and C4, and a predetermined time Ta is required until the charging voltage of the capacitors C3 and C4 reaches from 0 volt to the power recovery determination value Vr. .

FIG. 4 is a timing chart showing the operation of the switching power supply device 1 at the momentary power failure.
When a power failure / recovery of input power to the switching power supply 1 occurs instantaneously due to a momentary power failure, the input voltage Va of the switching power supply 1 instantaneously becomes zero as shown in FIG. Along with this, the input voltage Vin of the voltage detection circuit 53 drops, and when the voltage VCi of the comparison signal based on the input voltage Vin drops to the power recovery determination value Vr, the comparator 60 outputs an L level detection signal VCo. (Input power failure detection t1). Accordingly, the discharge circuit 55 connects the reset capacitor C2 to the ground, so that the reset capacitor C2 starts discharging.
In the voltage detection circuit 53, when the comparator 60 outputs an L level detection signal VCo, the positive connection node N2 of the comparator 60 is short-circuited via the capacitor C3, and the voltage VCi of the connection node N2 is short-circuited. Becomes zero volts.

Next, when the input voltage Va of the switching power supply device 1 is restored by power recovery, the input voltage Vin of the voltage detection circuit 53 increases. At this time, in the voltage detection circuit 53, the voltage VCi of the comparison signal of the comparator 60 is the comparator until a predetermined time Ta elapses from the input power failure detection t1 and reaches the power recovery determination value Vr as described above. 60 continues to output the L level detection signal VCo. Thereby, even if the input power of the switching power supply 1 is restored, the discharging of the reset capacitor C2 is continued. Then, when the voltage of the reset capacitor C2 falls below the switching stop voltage Vt, the switching control circuit 5 stops the switching operation, whereby the output voltage Vb also decreases to zero volts.
When the predetermined time Ta has elapsed from the input power failure detection t1 and the comparator 60 outputs the H level detection signal VCo, the discharge circuit 55 cuts off the reset capacitor C2 from the ground, thereby charging the reset capacitor C2. When the voltage of the reset capacitor C2 reaches the switching operation voltage Vs, the switching control circuit 5 starts the switching operation, and a predetermined output voltage Vb is output.

As described above, according to the present embodiment, the connection signal N2 that inputs a signal to the comparator 60 is connected to the comparison signal in which the voltage reaches the power recovery determination value Vr after a predetermined time Ta from the time of power recovery after the drop in the input voltage Vin is detected. Is generated from the input voltage Vin, and the operation of the discharge circuit 55 is continued until the voltage VCi of the comparison signal exceeds the power recovery determination value Vr from when the drop of the input voltage Vin is detected, and the reset capacitor C2 is discharged. .
According to this configuration, even when a momentary power failure occurs, the comparison signal reaches the power recovery determination value Vr over a predetermined time Ta, so that the discharge of the reset capacitor C2 continues over the predetermined time Ta. Therefore, it can be surely discharged. Further, since the power recovery determination is performed based on the comparison signal generated from the input voltage Vin, the power recovery can be reliably detected. In addition, since the operation of the discharge circuit 55 is stopped using the comparison signal, the switching control circuit 5 can be reliably reset without shutting off the power supply to the switching power supply device 1.

Further, according to the present embodiment, the connection node N2 that inputs the comparison signal to the comparator 60 is charged based on the input voltage Vin applied to the connection node N2 while discharging when the drop of the input voltage Vin is detected. The second charge / discharge circuits 63 and 65 are provided.
With this configuration, it is possible to generate a comparison signal in which the voltage reaches the power recovery determination value Vr after a predetermined time Ta from the time of power recovery after the detection of the drop in the input voltage Vin with a simple circuit. The predetermined time Ta can be easily changed by appropriately setting the capacitances of the capacitors C3 and C4 included in the circuits 63 and 65.

  The above-described embodiment is merely an example of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.

For example, in the above-described embodiment, the voltage detection circuit 53 includes the first charging / discharging circuit 63 and the second charging / discharging circuit 65, but the configuration is not limited thereto.
FIG. 5 is a circuit diagram showing a configuration of the voltage detection circuit 153 according to the present modification. In addition, in the same figure, the same code | symbol is attached | subjected about what was demonstrated in 1st Embodiment, and the description is abbreviate | omitted.
The voltage detection circuit 153 is obtained by providing a zero voltage maintaining circuit 70 in place of the first charge / discharge circuit 63 in the voltage detection circuit 53 shown in the first embodiment. The zero voltage maintaining circuit 70 is a circuit that maintains the voltage VCi of the comparison signal at zero volts for a predetermined time Td from when the voltage VCi of the detection signal falls below the power recovery determination value Vr.

  Specifically, the zero voltage maintaining circuit 70 is a switching element that connects the connection node N2 to the ground when the voltage VCi of the detection signal falls below the power recovery determination value Vr and the comparator 60 outputs the L level detection signal VCo. Q1 and Q2, and a capacitor C5 that is charged over a predetermined time Td when power is restored after the comparator 60 outputs the L level detection signal VCo, and the switch element Q2 is charged when the capacitor C5 is fully charged. Turn off to disconnect the connection node N2 from the ground. Resistors R4 to R7 shown in the figure are current limiting resistors. The input power of the switching power supply device 1 is used for charging the capacitor C5 and driving the switch elements Q1 and Q2.

FIG. 6 is a timing chart showing the operation at the momentary power failure of the voltage detection circuit 153 according to this modification.
When a momentary power failure occurs, in the voltage detection circuit 153, after the voltage VCi of the comparison signal falls below the power recovery determination value Vr and the detection signal VCo output from the comparator 60 becomes L level, the zero voltage maintenance circuit 70, the voltage VCi of the comparison signal is maintained at zero volts for a predetermined time Td. Thereafter, charging of the second charging / discharging circuit 65 is started, and when the voltage VCi of the connection node N2 reaches the power recovery determination value Vr accompanying this charging, the detection signal VCo of the comparator 60 transitions to the H level.

  As described above, in the present modification, since the zero voltage maintaining circuit 70 that connects the connection node N2 to the ground side for a predetermined time Td from the time when the drop in the input voltage Vin is detected is provided, after the drop in the input voltage Vin is detected. The predetermined time Te from the time of power recovery until the voltage VCi reaches the power recovery determination value Vr is always longer than the predetermined time Td, and the reset capacitor C2 can be discharged reliably.

  In the embodiment and the modification described above, the case where the present invention is applied to the reset operation of the switching control circuit of the switching power supply device is illustrated. However, the present invention can be applied to any circuit as long as it is an electric circuit including a reset capacitor. Can be applied.

DESCRIPTION OF SYMBOLS 1 Switching power supply device 3 Switching element 5 Switching control circuit (electric circuit)
51 Power-on Reset Circuit 53, 153 Voltage Detection Circuit 55 Discharge Circuit 60 Comparator 63 First Charge / Discharge Circuit 65 Second Charge / Discharge Circuit 70 Zero Voltage Maintenance Circuit C2 Reset Capacitor C3-C4 Capacitor N2 Connection Node T1 Transformer Ta, Td, Te predetermined time Tb initial rising period Tc rising period t1 input power failure detection VCi voltage for comparison signal VCo detection signal Vin input voltage to voltage detection circuit Vr power recovery judgment value

Claims (4)

A voltage detection circuit that detects a drop in input voltage to an electric circuit and operates a discharge circuit that discharges a reset capacitor provided in the electric circuit,
A comparison signal in which the voltage reaches a power recovery determination value after a predetermined time from power recovery after detection of the input voltage drop is generated from the input voltage, and the voltage of the comparison signal is detected from the time of detection of the input voltage drop. A voltage detection circuit characterized in that the operation of the discharge circuit is continued until the power recovery judgment value is exceeded, thereby discharging the reset capacitor. A comparator for comparing the voltage of the comparison signal and the power recovery determination value;
The connection node that inputs the comparison signal to the comparator is provided with a charge / discharge circuit that is charged based on the input voltage applied to the connection node while discharging when the input voltage drop is detected. The voltage detection circuit according to claim 1.   The voltage detection circuit according to claim 1, further comprising: a zero voltage maintaining circuit that connects the connection node to the ground side for a predetermined time from the time when the drop in the input voltage is detected. In a power supply device for controlling on / off of a switching element provided on the primary side of the transformer and obtaining an output voltage on the secondary side of the transformer,
A switching control circuit for controlling the switching element and having a reset capacitor;
A discharge circuit for discharging the reset capacitor;
A voltage detection circuit that detects a drop in the input voltage to the primary side and operates the discharge circuit to discharge the reset capacitor;
The voltage detection circuit includes:
A comparison signal in which the voltage reaches a power recovery determination value after a predetermined time from power recovery after detection of the input voltage drop is generated from the input voltage, and the voltage of the comparison signal is detected from the time of detection of the input voltage drop. The power supply device, wherein the discharge capacitor is discharged by continuing the operation of the discharge circuit until a power recovery judgment value is exceeded.

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