JP2001057778A - Switching power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a switching power source, which can suppress the current applied steadily on a load to be a small value, simplify specifications and realize size reduction and cost reduction of the device itself. SOLUTION: There are provided in a switching power source having an overcurrent detection circuit, which sets an overcurrent detection point iref for an output current I0 supplied to a load 20, an output current detection circuit detects the output current I0 supplied to the load 20 and a control unit 4 which monitors the output current I0 detected by the output current detection circuit, and when the average value of the output current over a certain period exceeds a certain value, the overcurrent detection point iref is changed to a value lower than the normal value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply used for an information processing apparatus and the like, and more particularly to a switching power supply having improved overcurrent measures.

[0002]

2. Description of the Related Art In order to limit the output power of a conventional switching power supply, an overcurrent detection circuit is generally used to limit the output current to a certain value or less.

In this overcurrent detection circuit, an overcurrent detection value is set mainly for protection of a switching element in a power supply device and protection of a load. Since this overcurrent detection value is usually set to a constant value, the power supply unit must be designed to always be able to cope with the peak load current. Will flow.

A conventional example of such a switching power supply will be described with reference to FIG.

The conventional switching power supply device shown in FIG. 6 supplies a DC voltage from a DC power supply E to the primary side of a transformer T as a pulsed voltage via a switching element Q that is turned on and off under the control of a PWM control unit 10. Then, the transformed AC output induced on the secondary side of the transformer T is rectified by the diodes D1 and D2, further smoothed by the inductor L and the electrolytic capacitor C, and supplied to the load 20 with the DC output voltage and the output current I. It is supposed to.

In this switching power supply device, a resistor Rai is connected in series with the switching element Q, and the resistor Rai is connected to a comparator 21 constituting an overcurrent detection circuit.
And the preset overcurrent detection value ire
f, and when the current flowing through the resistor Rai becomes larger than the overcurrent detection value iref, the overcurrent detection signal is output from the comparator 21 as PW
The switching element Q is turned off under the control of the PWM control unit 10 so as to prevent the output current I supplied to the load 20 from exceeding a certain value. Further, the switching power supply device is characterized in that the output voltage and a preset voltage value vre
and a comparator 22 that constitutes a voltage detection circuit that compares the signal f with the f and sends a voltage detection signal to the PWM control unit 10.

[0007]

However, in the case of the above-described conventional switching power supply, the overcurrent detection point is a constant value, that is, the overcurrent detection value iref is a constant value, and the load 20 is, for example, a hard disk drive. When a rush current flows, such as a motor load or a capacitor load for driving the motor, the overcurrent detection value iref is set to be equal to or more than the maximum peak value.

As a result, the specifications of the switching power supply and the load 20 must be adjusted so that the safety is not impaired even if the current of the current level immediately before the overcurrent detection value iref flows constantly. There has been a problem that the configuration becomes large and the price is high.

The present invention has been made in view of the above circumstances, and it is possible to reduce the current that can constantly flow through the switching power supply itself and the load, thereby simplifying the specifications and improving the apparatus itself. It is an object of the present invention to provide a switching power supply device capable of realizing miniaturization and cost reduction of a power supply.

[0010]

According to the first aspect of the present invention,
In a switching power supply device provided with an overcurrent detection circuit for performing an overcurrent detection by setting an overcurrent detection point for an output current supplied to a load, an output current detection circuit for detecting an output current supplied to the load; The output current by the current detection circuit is monitored, and the average value of the output current over a certain period of time is obtained. If this average value exceeds a certain value, the overcurrent detection point of the overcurrent detection circuit is changed to a lower value than usual. And a control unit.

According to the present invention, based on the output current from the output current detection circuit, the control unit obtains an average value of the output current for a predetermined time, and when the average value exceeds a predetermined value, the overcurrent detection circuit Since the overcurrent detection point is changed to a lower value than usual, it is possible to suppress the output current that can constantly flow to the load, thereby reducing the size and cost of circuit elements such as a transformer and a smoothing capacitor. Thus, the specifications of the device itself can be simplified, and the size and cost of the device itself can be reduced.

According to a second aspect of the present invention, there is provided a switching power supply device having an overcurrent detection circuit for performing an overcurrent detection by setting an overcurrent detection point for an output current supplied to a load. An output current detection circuit that detects the output voltage, an output voltage detection circuit that detects the output voltage supplied to the load, and an output current that is monitored by the output current detection circuit. In a case where the output voltage exceeds the predetermined value, the overcurrent detection point of the overcurrent detection circuit is changed to a value lower than usual. And a control unit that controls to stop the operation.

According to the present invention, in addition to exhibiting the same function as the first aspect of the present invention, the operation of the switching power supply is stopped when the output voltage becomes insufficient. It is possible to avoid a situation in which the operation of the switching power supply device is continued in an abnormal state of occurrence of an undervoltage, and a normal operation state of the switching power supply device can be secured for a long period of time, thereby improving durability.

According to a third aspect of the present invention, in the switching power supply device according to the first or second aspect, the control unit changes a value of an overcurrent detection point of the overcurrent detection circuit to a value lower than a normal value, and then lapses a predetermined time. The overcurrent detection point is returned to a normal value later.

According to this invention, the same operation as in the case of the switching power supply according to claim 1 or 2 is exhibited, and after the overcurrent detection point is changed to a value lower than usual,
Since the overcurrent detection point is returned to the normal state after a lapse of a certain time, it is possible to cope with a sudden or instantaneous overcurrent occurrence state, and it is possible to ensure smooth operation of the switching power supply.

[0016]

Embodiments of the present invention will be described below in detail.

FIG. 1 is a circuit diagram showing the configuration of the switching power supply of the present embodiment. In this switching power supply, the basic configuration is the same as that of the conventional switching power supply shown in FIG. Those having the function of are denoted by the same reference numerals.

The switching power supply according to the present embodiment
As in the conventional switching power supply device, the DC voltage from the DC power supply E is supplied to the primary side of the transformer T as a pulsed voltage via the switching element Q that is turned on and off under the control of the PWM control unit 10. The transformed AC output induced on the secondary side is rectified by diodes D1 and D2, and further smoothed by an inductor L and an electrolytic capacitor C to supply a DC output voltage and an output current I to a load 20. I have. Further, a detection resistor RS is connected between the electrolytic capacitor C and the load 20.

Further, the switching power supply of the present embodiment is characterized in that the output voltage and the preset voltage value v
ref and a comparator 22 that constitutes a voltage detection circuit that sends a voltage detection signal to the PWM control unit 10.

Further, in the switching power supply of the present embodiment, the output current I and the overcurrent whose value (current value) is changed in two stages of Ipeak and Irest are detected by the comparator 1 constituting the overcurrent detection circuit. It comprises a comparator 1 which constitutes an overcurrent detection circuit for comparing a detection point iref with a current detection signal to send a current detection signal to a PWM control unit 10, and an amplifier 2 having a detection resistor RS (resistance value rs) and an amplification factor K. An output current detection circuit, an A / D converter 3 for converting a value detected by the output current detection circuit into digital data, and digital data sent from the A / D converter 3 are taken in and monitored.
If the average value exceeds a certain value (Iave), the overcurrent detection point iref set in the comparator 1 of the overcurrent detection circuit is changed to a lower value (Irest) than usual. And a D / A converter 3 that converts digital data from the control unit 4 into analog data and sends the analog data to the comparator 1. The control unit 4 includes a RAM used for obtaining a time average of data, a ROM for storing a program describing a calculation method for obtaining an average value of the output current I over a certain time, a microprocessor, and the like.

The amplifier 2 takes in a voltage (rS.IO) corresponding to the output current I flowing through the detection resistor RS via the input resistor R1 and the input resistor R2, amplifies the voltage by K times, and A / D
Send to converter 3. The A / D converter 3 outputs the output current I
Is converted into digital data and sent to the control unit 4. In FIG. 1,
R3 is a feedback resistor.

Here, Ipeak is Ipeak max shown in FIG.
Irest means Ire of a value smaller than Ipeak max.
The following is explained as meaning stricted.

Next, the operation of the switching power supply of this embodiment will be described with reference to the waveform diagrams of the output current I and the output voltage shown in FIGS. 2 to 4 and the flowchart shown in FIG.

During normal operation of the switching power supply, the overcurrent detection point iref of the output current I is set to ipeak shown in FIG. 2 (step S1).

In this state, the amplifier 2 is connected to the detection resistor RS.
The voltage (rS.IO) corresponding to the output current I flowing through the A / D converter is taken in, amplified K times, and sent to the A / D converter 3. A /
The D converter 3 outputs a voltage (K · rs ·
IO) is converted into digital data and sent to the control unit 4.

The control unit 4 captures and monitors digital data of a voltage (K · rs · IO) corresponding to the output current I sent from the A / D converter 3 (step S2),
An average value of the output current I during a certain time (t1) (this is defined as Iin) is obtained (step S3), and the average value I
If in exceeds the constant value (Iave) shown in FIG. 2 (step S4), the overcurrent detection point iref set in the comparator 1 in the overcurrent detection circuit is changed to a value Irest lower than the normal Ipeak. Is sent to the DA converter 5.

Thus, the operation of the DA converter 5 sets the overcurrent detection point iref = Irest in the comparator 1 (step S5).

The time at which the overcurrent detection point iref = Irest lasts, for example, t2, as shown in FIG. 3 (step S6), and thereafter, the control unit 4 responds to a change in the output current I.
As shown in FIG. 3, the overcurrent detection point i of the comparator 1
ref is returned to Ipeak (step S7).

As described above, according to the switching power supply device of the present embodiment, the current flows to the load 20 constantly in response to the change of the output current I, especially when an overcurrent is generated or the possibility is high. It is possible to reduce the output current I to be obtained, thereby making it possible to use small and inexpensive circuit elements such as the transformer T and the smoothing capacitor C, to simplify the specifications of the device itself, The size and cost of the device itself can be reduced.

In the example shown in FIG. 2, at time A, the average output current I during the time t1 exceeds Iave, so that the overcurrent detection point iref is lowered to Irest.

In the example shown in FIG. 2, the output current I is I
As a result of being limited to rest, the output voltage decreases, and the under-voltage detection function of the comparator 22 constituting the voltage detection circuit operates,
This is to stop the switching power supply. As a result, it is possible to avoid a situation in which the operation of the switching power supply device is continued in an abnormal state of occurrence of an undervoltage, to secure a normal operation state by the switching power supply device for a long time, and to improve durability.

The example shown in FIG. 3 shows a limit state, in which the output current average value during the time t1 exceeds Iave, but the output current I thereafter is smaller than Irest. In this case, the overcurrent detection point ire of the comparator 1 after t2
f is returned to Ipeak. Thereby, it is possible to cope with a sudden and instantaneous overcurrent occurrence state, and it is possible to always ensure a smooth operation.

FIG. 4 shows that the output current average value is a constant value Iave.
Is instantaneously exceeded, but since it is extremely short, the overcurrent detection point iref of the comparator 1 is kept at Ipeak.

[0034]

According to the first aspect of the present invention, it is possible to reduce the output current that can constantly flow to the load, thereby reducing the size and cost of circuit elements such as a transformer and a smoothing capacitor. This makes it possible to provide a switching power supply device that can be used, can simplify the specifications of the device itself, and can reduce the size and cost of the device itself.

According to the second aspect of the present invention, there is provided a switching power supply capable of avoiding a situation in which operation is continued in an abnormal state of occurrence of undervoltage, maintaining a normal operation state for a long time, and improving durability. Can be provided.

According to the third aspect of the present invention, the same effect as the first or second aspect of the present invention is obtained, and after the overcurrent detection point is changed to a lower value than usual, the overcurrent detection is performed after a lapse of a predetermined time. Since the point is returned to the normal state, it is possible to provide a switching power supply device that can cope with an overcurrent occurrence state that occurs suddenly and instantaneously and that can ensure smooth operation.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a switching power supply according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a change in output current and output voltage waveforms, an overcurrent detection point, and a power supply stop state of the switching power supply device of the present embodiment.

FIG. 3 is an explanatory diagram illustrating a state of changing an output current and an overcurrent detection point of the switching power supply device according to the present embodiment.

FIG. 4 is an explanatory diagram in a case where an overcurrent detection point of the switching power supply device of the present embodiment is not changed.

FIG. 5 is a flowchart illustrating an operation of changing an overcurrent detection point of the switching power supply according to the present embodiment.

FIG. 6 is a circuit diagram showing a conventional switching power supply device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Comparator 2 Amplifier 3 AD converter 4 Control part 5 DA converter 10 PWM control part 20 Load 22 Comparator E DC power supply Q Switching element T Transformer D1 Diode D2 Diode L Inductor C Electrolytic capacitor RS Detection resistance

Claims (3)

[Claims] 1. A switching power supply device comprising an overcurrent detection circuit for performing an overcurrent detection by setting an overcurrent detection point for an output current supplied to a load, wherein the output current detection detects an output current supplied to the load. And an output current detected by the output current detection circuit, and an average value of the output current over a certain period of time is calculated. When the average value exceeds a certain value, the overcurrent detection point of the overcurrent detection circuit is set higher than usual. A switching power supply, comprising: a control unit that changes the value to a low value. 2. A switching power supply device comprising an overcurrent detection circuit for performing an overcurrent detection by setting an overcurrent detection point for an output current supplied to a load, wherein the output current detection detects an output current supplied to the load. Circuit, an output voltage detection circuit that detects the output voltage supplied to the load, and an output current that is monitored by the output current detection circuit. Changing the overcurrent detection point of the overcurrent detection circuit to a value lower than normal, and when the detection voltage by the output voltage detection circuit becomes an undervoltage of a certain value or less,
A switching power supply, comprising: a control unit that controls to stop the operation of the switching power supply. 3. The control unit changes the overcurrent detection point of the overcurrent detection circuit to a value lower than normal, and then returns the overcurrent detection point to a normal value after a lapse of a predetermined time. Item 3. The switching power supply device according to Item 1 or 2.