JPH04123407U - Switching power supply input voltage monitoring circuit - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an input voltage monitoring circuit for a switching power supply that ensures the operation of the power supply as much as possible even when the input voltage drops and can be used for general purposes regardless of the type of power supply device. . [Structure] It has a switching element that inputs a DC voltage supplied from an external power supply, and an output circuit that rectifies and smoothes the signal output from this switching element and supplies it to the load side, and outputs an error signal of this output voltage. error amplifier,
A switching power supply having a control circuit that outputs an on/off control signal in the direction of reducing this error signal, a level determination circuit that compares this error signal with a low threshold voltage, and a low threshold voltage that is determined by this level determination circuit. The apparatus includes a duration determination circuit that outputs an alarm signal when a state in which the value of the error signal is determined to be lower than the voltage is longer than a reference time.

Description

[Detailed explanation of the idea]

0001

[Industrial application field]

The present invention relates to an input voltage monitoring circuit for a switching power supply, and is particularly applicable to input voltage monitoring circuits for switching power supplies. The present invention relates to an improvement suitable for use in detecting the operating limit of a power supply device.

0002

[Conventional technology]

Detecting a drop in input voltage can be accomplished, for example, by the method proposed by the applicant of the present invention. This method is known from Japanese Patent No. 84579 and the like. For industrial control equipment, etc., power outages can be detected in advance. It is easy to detect this, take necessary measures such as saving data, and start control when power is restored. We are taking care to ensure that

0003

[Problem that the idea aims to solve]

However, if such an input voltage monitoring circuit is applied directly to a power supply, the following will occur. There were such inconveniences. The operating state of the power supply depends on the load current, etc. Immediately stopping operation just because the input voltage has fallen below a certain value is not correct. If it is possible to continue, it will place an unnecessary burden on the load. Also, as disclosed in Utility Model Application Publication No. 2-32137 proposed by the present applicant. , Direct monitoring of the input voltage is also practiced, but it has the disadvantages mentioned above and , the use of a current transformer is limited to AC power, and DC power is used for input. There was a problem that it could not be used if the

0004 This invention solves these problems and allows the power supply to operate even if the input voltage drops. It ensures operation as much as possible and can be used universally regardless of the type of power supply. The purpose of this invention is to provide an input voltage monitoring circuit for a switching power supply.

[0005]

[Means to solve the problem]

FIG. 1 is a block diagram of the structure of the present invention that achieves the above object. In the diagram, external Input the DC voltage supplied from the power supply and turn on/off according to the on/off control signal. It has a switching element (Q1) that outputs a signal from the switching element. An output circuit (12) that rectifies and smoothes and supplies it to the load side, and an output voltage of this output circuit. An error amplifier (14) that compares the voltage with the reference voltage and outputs an error signal, and a switching control circuit that outputs the on/off control signal in the direction of decreasing the signal; The switching power supply has (16). Also, a level determination circuit (32) for comparing this error signal with a low threshold voltage; , this level judgment circuit judges that the error signal value is lower than the low threshold voltage. a duration determination circuit (34) that outputs an alarm signal when the condition is longer than the reference time; ).

[0006]

[Effect]

Each component of the present invention operates as follows. Switching power supplies are common be. The level judgment circuit indirectly determines the output voltage from the error signal output from the error amplifier. is detected and determines whether or not it is in a low voltage state. The duration judgment circuit detects the low voltage state. If it continues for a certain period of time, an alarm signal is given to the load side and measures such as power outage countermeasures are taken. Let them know you need it.

[0007]

【Example】

The present invention will be explained below using the drawings. FIG. 2 is a circuit diagram showing an embodiment of the present invention. Note that in Figure 2, the same as Figure 1 above is used. Components that have one effect are given the same reference numerals and their explanations will be omitted. Output circuit 12 is an external power supply The DC current supplied from the The predetermined voltage is obtained by In other words, an external power supply is connected to the emitter terminal, and the base Switching voltage is supplied from the collector terminal according to the on/off control signal supplied to the collector terminal. The current is output. The cathode terminal of diode D1 is connected to this collector terminal. , whose anode terminal is grounded and performs rectification. Choke coil L1 is adjusted Remove high frequency components from the flowing switching signal and smooth it with capacitor C1 The output voltage is supplied to the main device 20.

[0008] The error amplifier 14 compares the output voltage of the output circuit 12 with the threshold voltage and generates an error signal. This outputs the following. Voltage dividing resistors R1 and R2 change the level of the output voltage to an appropriate voltage. A capacitor is connected in parallel with resistor R1 to reduce the influence of noise components. C2 is provided. The OP amplifier U1 has a positive terminal divided by voltage dividing resistors R1 and R2. The reference voltage Vre is applied using a zener diode etc. to the negative terminal. f is applied and the difference voltage is output as an error signal. Resistance R3, R4, R5 is a voltage dividing resistor that converts the level of the error signal to an appropriate voltage. Resistor R5 is a capacitor. This capacitor C5 absorbs steep changes in the error signal. are doing.

[0009] The switching control circuit 16 sends an on/off control signal in a direction that reduces the error signal. This is what is output. Comparator U2 is connected to the negative terminal through resistor R3. A triangular wave generator U3 inputs a signal and generates a triangular wave of a constant frequency at the positive terminal. It is connected. The on/off element Q2 is the on/off control output from the comparator U2. Input the signal to the base terminal, and connect the base terminal and collector terminal of switching element Q1. is connected to drive the switching element Q1.

[0010] The voltage monitoring circuit 30 outputs an alarm signal indicating the occurrence of a power outage to the main device 20 when the output voltage decreases. FIG. 3 is an explanatory diagram of the operation of the voltage monitoring circuit 30. Among the error signals output from the error amplifier 14, the voltage generated at the resistor R5 is input as the feedback error signal _VFB . The level determination circuit 32 determines whether the error signal V _FB is lower than the low threshold voltage V _FBL . The duration determination circuit 34 generates an alarm signal when this low state continues for longer than a reference time Δt _PE (protection enable time). This logical condition is V _FB ≦V _FBL and Δt≧Δt _PE . Here, Δt is the time during which the error signal V _FB continues to be lower than the low threshold voltage V _FBL . When this condition is met, an alarm signal is sent to the main device 20. Note that the voltage monitoring circuit 30 may be configured using an IC, or may be implemented using software using a microprocessor.

[0011]The operation of the device configured as described above will be explained next. Figure 4 is a waveform diagram explaining the operation during a power outage. (A) is the output waveform and error signal of the triangular wave oscillator U3, (B) is the alarm signal ALARM* (low-active), and (C) is the external Indicates the input voltage supplied from the power supply. When the output voltage deviates from the reference voltage due to load fluctuations or the like, feedback acts in the direction of stabilizing the output voltage by the error amplifier and switching control circuit. The reference time Δt _PE is determined so that no alarm signal is generated in such a mode. Therefore, even if the error signal temporarily drops below the low threshold voltage, an alarm will not be generated because the duration is short.

0012 Next, if there is a power outage with the external power source or the storage battery is exhausted, the error will occur constantly. The difference signal will fall below the low threshold voltage and the duration will be longer than the reference time. So An alarm is then generated to alert the main device 20.

[0013]

[Effect of the idea]

As explained above, according to the present invention, the voltage monitoring circuit 30 is used to monitor the error signal. Input voltage malfunctions are detected from the signal and duration, so if the input voltage is DC, It can be detected in the same way as AC, and it can be activated in the optimal condition depending on the load condition. A alarm signal can be generated, and the practical effect is great.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram of the present invention.

FIG. 2 is a circuit diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of the operation of the voltage monitoring circuit 30.

FIG. 4 is a waveform diagram illustrating operation during a power outage.

[Explanation of symbols]

12...Output circuit 14...Error amplifier 16...Switching control circuit 20...Main device 30...Voltage monitoring circuit 32...Level judgment circuit 34... Duration determination circuit

Claims (1)

[Scope of utility model registration request] Claim 1: A switching element (Q1) that receives a DC voltage supplied from an external power source and turns on and off according to an on/off control signal, rectifies and smoothes the signal output from this switching element, and supplies the signal to the load side. an error amplifier (14) that compares the output voltage of this output circuit with a reference voltage and outputs an error signal; and a switching device that outputs the on/off control signal in a direction that reduces this error signal. A switching power supply having a control circuit (16), a level determination circuit (32) for comparing this error signal with a low threshold voltage, and a level determination circuit (32) that compares the error signal with a low threshold voltage. 1. An input voltage monitoring circuit for a switching power supply, comprising: a duration determination circuit (34) that outputs an alarm signal when a state determined to be low is longer than a reference time.