CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the priority of the Chinese Patent Application No. 202010333412.2, filed on Apr. 24, 2020 and titled CIRCUIT FOR CONTROLLING SWITCHING POWER SUPPLY AND METHOD FOR CONTROLLING SWITCHING POWER SUPPLY BY USING CIRCUIT, and the content of which is incorporated by reference herein in its entirety, the specification of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a power supply circuit and a control method for using the power supply. The disclosure belongs to the technical field of the switching power supplies.

BACKGROUND

As one of the important components in various electric devices and electric apparatuses, a switching power supply is widely used in various fields of the prior art due to its advantages of small size, fast transient response and low loss. However, smart electricity meters have a special problem in utilizing switching power supplies. That is, when the electricity meter is interfered by an outside strong magnetic field, a normal operation of a switching power supply device or a module inside the electricity meter will be affected, thus disabling the electricity meter to accurately measure an amount of electricity, and further exasperating electricity theft and affecting national economic construction and social stability.

Regarding this problem, some corresponding technical solutions have also appeared in the industry. The solutions mainly include providing a magnetic field shielding shell outside the meter, or designing and manufacturing an inductance or transformer in the switching power supply with special materials and by special processes. In practical application, persons skilled in the art found that although the above technical solutions can reduce interference of the magnetic field on the switching power supply to a certain extent, a size of the meter and whole manufacturing costs of the switching power supply are greatly increased.

Along with continuous updating and iteration of technology, in order to better solve the above technical problems, some switching power supplies with anti-magnetic interference capabilities have also appeared in the industry. For example, in Chinese Patent Application 106655823A, an anti-magnetic interference switching power supply, a control circuit and a control method therefor are provided. In this control circuit, a magnetic field detection unit determines whether the power supply is affected by an external magnetic field on the basis of detecting a magnitude of a value of an error amplification signal COMP and a gradient Rcs of a current detection signal CS. When a result of the determination is that the power supply is interfered by the external magnetic field, an operating frequency of the switching power supply will be increased to N times. To some extent, this solution can effectively improve a load capacity of the switching power supply in the magnetic field and reduce the interference of the magnetic field on the switching power supply.

However, it should be noted that this control circuit still has some significant deficiencies in a manner of detecting the magnetic field and frequency doubling. Specifically, firstly, in this solution, there is no direct corresponding relationship between a magnitude of the external magnetic field and the value of the error amplification signal COMP, and the accuracy of the result of the determination is questionable. Secondly, input voltages and inductance values of magnetic elements of different switching power supplies are also tremendously different, which also causes the gradient Rcs of the current detection signal CS to show different values under a same intensity of the external magnetic field. In this case, if the control circuit determines the interference of the external magnetic field merely on the basis of variations in an output voltage and the gradient of the current detection signal of the switching power supply, problems of false detections or low detection accuracy will occur in some application scenarios that are sensitive to the intensity of the external magnetic field. Further, when the control circuit detects the interference of external magnetic field, the operating frequency will be changed to N times of the original frequency abruptly. Such an adjustment method will undoubtedly affect an overall stability of the switching power supply, and even cause the switching power supply to fail to operate normally in the worst case.

In summary, no matter which prior art are applied, there are many problems that need to be solved and improved. Therefore, it has become an urgent problem to be solved by the persons skilled in the art on how to propose a novel, self-adaptive technology for the switching power supply that can overcome the above mentioned defects on the basis of an existing research foundation.

SUMMARY

In view of the above defects in the prior art, an objective of the present disclosure is to provide a circuit for controlling a switching power supply and a method for controlling a switching power supply by using the circuit.

A circuit for controlling a switching power supply, configured to control a power stage circuit of a converter of the switching power supply, and includingan external magnetic field direct detection unit configured to: detect an intensity of an external magnetic field directly, and generate a corresponding logic signal to control a switching frequency output by the operating frequency unit and to adjust a current limit threshold in the current limit threshold unit,a current limit threshold unit configured to receive an output signal of the external magnetic field direct detection unit and limit a maximum current flowing through a magnetic element in the power stage circuit,an operating frequency unit controlled by the external magnetic field direct detection unit and a feedback signal processed by a feedback loop, and configured to generate a corresponding frequency signal to control a power switching transistor in the power stage circuit to turn on or off,a pulse width unit configured to receive the feedback signal processed by the feedback loop and a sampling signal at a current sampling terminal, and control an on-off duty ratio of the power switching transistor in the power stage circuit,a logic unit configured to receive output signals from the current limit threshold unit, the operating frequency unit and the pulse width unit, and perform a logic processing and generate a corresponding driving signal to control the power switching transistor in the power stage circuit to turn on or be offThe external magnetic field direct detection unit includes a Hall device and a Hall detection component.The Hall device is configured to detect the intensity of the external magnetic field directly and convert the intensity of the external magnetic field into an internal voltage signal.The Hall detection component is configured to receive the internal voltage signal generated by the Hall device, and generate the corresponding logic signal after amplification and comparison.

In an embodiment, the power stage circuit includes at least the magnetic element, an output unit, the power switching transistor, a sampling resistor, and the converter of the switching power supply includes the feedback loop.The power switching transistor is electrically connected to the sampling resistor, and a position in a connection between the power switching transistor and the sampling resistor is the current sampling terminal of the circuit for controlling the switching power supply.The feedback loop is electrically connected to the operating frequency unit and the pulse width unit respectively.

In an embodiment, an input end of the external magnetic field direct detection unit is magnetically connected to the external magnetic field, and an output end of the external magnetic field direct detection unit is electrically connected to a first input end of the current limit threshold unit and a first input end of the operating frequency unit respectively.The first input end of the current limit threshold unit is electrically connected to the output end of the external magnetic field direct detection unit, a second input end of the current limit threshold unit is electrically connected to the current sampling terminal; and an output end of the current limit threshold unit is electrically connected to a first input end of the logic unit.The first input end of the operating frequency unit is electrically connected to the output end of the external magnetic field direct detection unit, a second input end of the operating frequency unit is electrically connected to an output end of the feedback loop, and an output end of the operating frequency unit is electrically connected to a second input end of the logic unit.A first input end of the pulse width unit is electrically connected to the output end of the feedback loop, a second input end of the pulse width unit is electrically connected to the current sampling terminal, and an output end of the pulse width unit is electrically connected to a third input end of the logic unit.The first input end of the logic unit is electrically connected to the output end of the current limit threshold unit, the second input end of the logic unit is electrically connected to the output end of the operating frequency unit, the third input end of the logic unit is electrically connected to the output end of the pulse width unit, and the output end of the logic unit is electrically connected to the power switching transistor.

In an embodiment, the Hall device is a chip-level Hall device integrated in a switching power supply chip, and an integrated Hall device is formed by combining one or more process devices.

In an embodiment, an external shape of the Hall device is center symmetrical and has four ports for connection; a first port and a second port are arranged along a diagonal direction of the Hall device; and a third port and a fourth port are arranged in another diagonal direction of the Hall device.

In an embodiment, the Hall detection component includes a first current source, a first amplifier, and a first comparator.An output of the first current source is electrically connected to the first port of the Hall device, and the second port of the Hall device is electrically connected to a ground potential.A first input end of the first amplifier is electrically connected to the third port of the Hall device; a second input end of the first amplifier is electrically connected to the fourth port of the Hall device, a first output end of the first amplifier is electrically connected to a first input end of the first comparator, and a second output end of the first amplifier is electrically connected to a second input end of the first comparator.The first input end of the first comparator is electrically connected to the first output end of the first amplifier, the second input end of the first comparator is electrically connected to the second output end of the first amplifier, and an output end of the first comparator serves as the output end of the external magnetic field direct detection unit and is electrically connected to the first input end of the current limit threshold unit and the first input end of the operating frequency unit respectively.

In an embodiment, the current limit threshold unit includes an overcurrent threshold selector and an OCP comparator.A first input end of the overcurrent threshold selector serves as the first input end of the current limit threshold unit and is electrically connected to the output end of the first comparator, a second input end of the overcurrent threshold selector is electrically connected to the first threshold voltage, a third input end of the overcurrent threshold selector is electrically connected to the second threshold voltage, and an output end of the overcurrent threshold selector is electrically connected to a first input end of the OCP comparator.The first input end of the OCP comparator is electrically connected to the output end of the overcurrent threshold selector, a second input end of the OCP comparator serves as the second input end of the current limit threshold unit and is electrically connected to the current sampling terminal, and an output end of the OCP comparator serves as the output end of the current limit threshold unit and is electrically connected to the first input end of the logic unit.

In an embodiment, the operating frequency unit includes a second comparator, a third comparator, an RS trigger, a second current source, a third current source, and a first switch, a second switch, a first capacitor, a third switch, a voltage-controlled current source and a subtracter.A first input end of the second comparator is electrically connected to a third threshold voltage, a second input end of the second comparator is electrically connected to an end of the first capacitor, and an output end of the second comparator is electrically connected to a first input end of the RS trigger.A first input end of the third comparator is electrically connected to the second input end of the second comparator, a second input end of the third comparator is electrically connected to a fourth threshold voltage, and an output end of the third comparators is electrically connected to a second input end of the RS trigger.The first input end of the RS trigger is electrically connected to the output end of the second comparator, the second input end of the RS trigger is electrically connected to the output end of the third comparator, and an output end of the RS trigger is electrically connected to a third connection end of the first switch and a third connection end of the second switch respectively.An end of the second current source is electrically connected to an internal power supply, and another end of the second current source is electrically connected to a first connection end of the first switch.An end of the third current source is electrically connected to a second connection end of the second switch, and another end of the third current source is electrically connected to the ground potential.The first connection end of the first switch is electrically connected to the second current source, a second connection end of the first switch is electrically connected to the second input end of the second comparator, and the third connection end of the first switch is electrically connected to the output end of the RS trigger.A first connection end of the second switch is electrically connected to the second input end of the second comparator, the second connection end of the second switch is electrically connected to the third current source, and the third connection end of the second switch is electrically connected to the output end of the RS trigger.An end of the first capacitor is electrically connected to the second input end of the second comparator, and another end of the first capacitor is electrically connected to the ground potential.A first connection end of the third switch is electrically connected to a fourth connection end of the voltage-controlled current source, a second connection end of the third switch is electrically connected to the second input end of the second comparator, and a third connection end of the third switch is electrically connected to the output end of the first comparator.A first connection end of the voltage-controlled current source is electrically connected to an output end of the subtracter, a second connection end of the voltage-controlled current source is electrically connected to the ground potential, a third connection end of the voltage-controlled current source is electrically connected to the internal power supply, and the fourth connection end of the voltage-controlled current source is electrically connected to the first connection end of the third switch.A first input end of the subtracter is electrically connected to the output end of the feedback loop, a second input end of the subtracter is electrically connected to a fifth threshold voltage, and the output end of the subtracter is electrically connected to the first connection end of the voltage-controlled current source.

A method for controlling a switching power supply by using the circuit for controlling the switching power supply described above is provided. The method includes the following steps.Power on and start the circuit for controlling the switching power supply,Detect, by the external magnetic field direct detection unit, the intensity of the external magnetic field directly, and compare detected intensity of the external magnetic field with a preset magnetic field intensity threshold.If the detected intensity of the external magnetic field is greater than the preset magnetic field intensity threshold, set the switching power supply in a strong magnetic field operating mode, in which the current limit threshold unit adjusts a current limit threshold voltage from a first threshold voltage to a second threshold voltage, and the voltage-controlled current source in the operating frequency unit is then turned on. A value of the second threshold voltage is not less than a value of the first threshold voltage.If the detected intensity of the external magnetic field is not greater than the preset magnetic field intensity threshold, keep the switching power supply always in a normal operating mode, in which the current limit threshold unit keeps the current limit threshold voltage being the first threshold voltage, and the voltage-controlled current source in the operating frequency unit remains off.

Advantages of the present disclosure are mainly reflected in the following aspects.

In accordance with the circuit for controlling the switching power supply of the present disclosure, the intensity of the external magnetic field can be detected directly at the chip level, and the operating mode of the switching power supply system can be adjusted timely. Compared with a traditional technical solution, a judgment is made without detecting other signals inside the control circuit, thereby not only ensuring accuracy of a detection result, but also greatly reducing the number of discrete components in an external magnetic field detection section of the switching power supply, and reducing a whole cost for manufacturing the switching power supply system.

Moreover, in accordance with the circuit for controlling the switching power supply of the present disclosure, after the intensity of the external magnetic field is detected, and the voltage-controlled current source in the operating frequency unit is turned on, a maximum frequency output by the operating frequency unit will be linearly controlled by the feedback signal, rather than the frequency is simply changed from a first preset value to a second preset value abruptly. Such an operation mode can improve operating stability of the switching power supply system effectively and avoid system oscillations.

The circuit for controlling the switching power supply of the present disclosure can be directly applied to a smart electric meter interfered by the external magnetic field. When there is no magnetic field outside the smart electric meter or the intensity of the magnetic field is not greater than a threshold, the switching power supply system is in the normal operating mode; while when the intensity of the magnetic field outside the smart electric meter is greater than the threshold, the switching power supply system is switched to the strong magnetic field operating mode. By switching between the above operating modes, the operating stability of the switching power supply can be effectively improved and interference of the magnetic field on the switching power supply can be reduced.

Embodiments of the present disclosure will be further described in detail below with reference to the drawings of the embodiments, so as to make it easier to understand and comprehend the technical solutions of the present disclosure.

