A power supply circuit, a control circuit, and a switching power supply

Abstract

The application discloses a power supply circuit, a control circuit and a switching power supply, which comprise a first switch and a voltage detection circuit. A first end of the first switch is a power supply access end for receiving a power supply voltage. A second end of the first switch is used as a power supply output end for supplying power to a to-be-powered circuit. The voltage detection circuit samples the voltage of the first end or the second end of the first switch to obtain a voltage sampling signal. The voltage sampling signal is compared with a first threshold value, and the voltage detection circuit outputs a first control signal. When the voltage sampling signal is lower than the first threshold value, the first control signal represents a low-power-consumption trigger instruction. The application can realize stable power supply, is beneficial to the normal work of the to-be-powered circuit, and has few peripheral devices.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and particularly to a power supply circuit, a control circuit, and a switching power supply. Background Technology

[0002] In the prior art, when using a switching power supply to power a load, the inductor current and output voltage are typically sampled, and feedback is performed based on the corresponding sampling signals to achieve regulation of the output current or output voltage.

[0003] In isolated switching power supplies, when the input terminal uses an electrolytic capacitor, it is generally used in low power factor scenarios where the bus voltage fluctuation is small and the input voltage VIN will not fall below the normal operating voltage range of the control circuit. However, when the input capacitor is small, especially in high power factor scenarios, the input voltage VIN fluctuates significantly, such as... Figure 1 As shown, the input voltage VIN is close to or equal to zero, and the normal operating voltage of the control circuit needs to be higher than V1. It is very easy for it to be lower than the chip supply voltage and fall below the normal operating range. Therefore, when the input voltage VIN is lower than V1, it may cause the control circuit or chip to lose power and fail to work properly. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a stable power supply circuit, control circuit, and switching power supply to solve the technical problem of potential power loss in the control circuit or chip in the prior art.

[0005] To achieve the above objectives, the present invention provides a power supply circuit, including a first switch and a voltage detection circuit. The first end of the first switch is a power supply input terminal, receiving a power supply voltage, and the second end of the first switch is a power supply output terminal, supplying power to the circuit to be powered. The voltage detection circuit samples the voltage at the first or second end of the first switch to obtain a voltage sampling signal, compares the voltage sampling signal with a first threshold, and outputs a first control signal. When the voltage sampling signal is lower than the first threshold, the first control signal represents a trigger command.

[0006] Optionally, the first switch is a transistor, which is turned on under controlled or uncontrolled conditions to supply power to the circuit to be powered, wherein the turning on is fully turned on or partially turned on.

[0007] Optionally, the transistor is a junction field-effect transistor (JFET), which turns on when the supply voltage is lower than the pinch-off voltage of the JFET.

[0008] Optionally, the voltage detection circuit includes a first comparator, a first terminal of the first comparator receiving the voltage sampling signal, a second terminal of the first comparator receiving the first threshold, and an output terminal of the first comparator outputting the first control signal.

[0009] The present invention provides a control circuit, including any of the above-mentioned power supply circuits and a circuit to be powered, wherein the power supply circuit supplies power to the circuit to be powered.

[0010] The present invention also provides a switching power supply, including any of the above-described power supply circuits, a circuit to be powered, and a switching circuit. The power supply circuit receives the bus voltage of the switching power supply and supplies power to the circuit to be powered. The circuit to be powered outputs a second control signal for controlling the switching state of the switching circuit.

[0011] Optionally, the power supply circuit includes a voltage detection circuit, which samples the voltage at the first or second terminal of the first switch to obtain a voltage sampling signal. The voltage detection circuit outputs a first control signal. When the voltage sampling signal is lower than a first threshold, the first control signal represents a trigger command. When the circuit to be powered receives the trigger command, it controls the switching circuit to operate at a reduced frequency or stop operating.

[0012] Optionally, the circuit to be powered includes a logic circuit and a reference generation circuit. The reference generation circuit receives a current reference signal and a first voltage signal representing the peak value of the inductor current. The first voltage signal is converted to an average value signal representing the average inductor current. A reference signal is obtained based on the current reference signal and the average value signal. The logic circuit receives the reference signal. In the logic circuit, the reference signal is compared with a ramp signal to determine the turn-off time of the main switch and is represented by a second control signal. The output terminal of the logic circuit is connected to the driver.

[0013] Optionally, the circuit to be powered further includes a zero-crossing detection circuit, the input of which is connected to the control terminal of the main switch transistor, and the output of which is connected to the logic circuit.

[0014] Compared with existing technologies, the technical solution of this invention has the following advantages: This invention is used to detect the voltage of the power supply circuit. When the voltage is lower than the normal operating voltage of the control circuit, the first control signal represents a low-power trigger command. The circuit to be powered receives the low-power trigger command and controls the switching circuit to enter a low-power mode (including but not limited to frequency reduction operation and shutdown) to prevent the circuit to be powered from losing power. This invention can achieve stable power supply, which is beneficial to the normal operation of the circuit to be powered, and requires fewer external components. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the input voltage waveform in the prior art;

[0016] Figure 2 This is a schematic diagram of the circuit principle of the switching power supply of the present invention;

[0017] Figure 3 This is a schematic diagram of the power supply circuit of the present invention;

[0018] Figure 4 This is a schematic diagram of the circuit structure of the overvoltage protection module. Detailed Implementation

[0019] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0020] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0021] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0022] like Figure 2 The diagram illustrates the circuit principle of the switching power supply of the present invention. Based on the Flyback topology, a rectifier bridge is set at the front end of the switching power supply, and the LED is used as the load, which can be used as an LED driving circuit.

[0023] In this invention, the power supply circuit and the circuit to be powered constitute a control circuit. The control circuit is in the form of an integrated circuit, but is not limited to using an integrated circuit. The VIN pin of the chip integrating the control circuit serves as the power supply input terminal of the power supply circuit. The GATE pin of the chip is a control pin used to transmit control signals to the main switch M. The CS pin is a sampling pin, which samples the voltage drop across resistor R1 or the current flowing through resistor R1. The OVP pin is an overvoltage protection pin, and the trigger voltage for overvoltage protection can be set by an external resistor R2. GND is a conventional ground pin.

[0024] like Figure 3The diagram illustrates the circuit structure of the power supply circuit of the present invention. The power supply circuit of the present invention includes a first switch J and a voltage detection circuit U01. The first terminal of the first switch J is a power supply input terminal, receiving a power supply voltage VIN, and the second terminal of the first switch J serves as a power supply output terminal to supply power to the circuit to be powered. The voltage detection circuit samples the voltage at either the first or second terminal of the first switch J to obtain a voltage sampling signal Vs. The voltage sampling signal Vs is compared with a first threshold V1, and the voltage detection circuit outputs a first control signal Vctrl1. When the voltage sampling signal Vs is lower than the first threshold V1, the first control signal Vctrl1 represents a low-power trigger command. The voltage detection circuit includes a first comparator. The first terminal of the first comparator receives the voltage sampling signal Vs, the second terminal of the first comparator receives the first threshold V1, and the output terminal of the first comparator outputs the first control signal Vctrl1.

[0025] The first switch J is a transistor, which conducts under controlled or uncontrolled conditions to supply power to the circuit to be powered. This conduction can be fully or partially turned on. If a controlled transistor is used, a MOSFET can be employed, controlling its full or partial conduction; if an uncontrolled transistor is used, a JFET can be employed. Using a JFET is more effective. Taking a high-voltage JFET as an example, when the supply voltage VIN is lower than the pinch-off voltage of the high-voltage JFET, the JFET conducts; conversely, it is turned off, thus preventing the supply voltage VIN from becoming too high. The control circuit (IC) only requires a very small filter capacitor or capacitor as the filtering unit, or may not require a capacitor at all, saving on external power supply capacitors.

[0026] When the first control signal Vctrl1 represents a trigger command, the trigger command has a mode switching function. Taking entering a low-power mode as an example, the logic circuit receives the trigger command. The logic circuit is part of the circuit to be powered, and the power supply of the entire control chip mainly relies on the power supply circuit of this invention. The logic circuit outputs a second control signal Vctrl2, which controls the switching state of the switching circuit. When the first control signal Vctrl1 represents a low-power trigger command, the second control signal Vctrl2 controls the switching circuit to enter a low-power mode, which includes frequency reduction operation or complete shutdown.

[0027] This invention is applied to a switching power supply, which includes a power supply circuit, a circuit to be powered, and a switching circuit. The switching transistor M is a secondary-side switching transistor. The power supply circuit receives the bus voltage of the switching power supply, i.e., the supply voltage VIN, and supplies power to the circuit to be powered. The circuit to be powered outputs a second control signal Vctrl2 to control the switching state of the switching circuit. To improve the efficiency of the switching power supply, the switching power supply using this invention can operate in critical conduction mode (BCM). The turn-off time of the primary side of the switching circuit is determined by the reference generation circuit. The circuit to be powered includes a logic circuit and a reference generation circuit. The reference generation circuit receives a current reference signal and a first voltage signal representing the peak value of the inductor current. The first voltage signal is converted to an average value signal representing the average inductor current. Based on the current reference signal and the average value signal, a reference signal is obtained. The logic circuit receives the reference signal and compares it with a ramp signal to determine the turn-off time of the main switching transistor, which is then represented by the second control signal. The output terminal of the logic circuit is connected to a driver, which is connected to the control terminal of the main switching transistor M. Because a critical conduction mode is used, it is necessary to detect the zero-crossing point of the inductor current. Existing technology controls the switch M to turn on by sampling the current flowing through the inductor, that is, when the secondary inductance drops to zero. The zero-crossing detection circuit of this invention detects the zero-crossing point of the inductor current by detecting the voltage at the control terminal of the switch M. The principle is that when the inductor current crosses zero, resonance occurs. When resonance occurs, a negative voltage is generated at the control terminal of the primary switch. Therefore, the zero-crossing point is detected by detecting the voltage at the control terminal of the switch M.

[0028] like Figure 4 The diagram illustrates the circuit structure of the overvoltage protection module. This invention also includes an overvoltage protection function. The input terminal of the overvoltage protection module OVP is connected to the high-potential terminal of the input voltage VIN. The overvoltage protection module samples the input voltage VIN, proportionally adjusts the sampled signal Vs1 (this sampled signal can be the same as the voltage sampling signal Vs, or they can be sampled separately as different sampling signals), and compares it with the corresponding overvoltage reference signal V. OVP_REF A comparison is performed to determine whether an overvoltage has occurred. This comparison is completed in the second comparator COMP2, whose output is connected to a logic circuit to trigger overvoltage protection in case of overvoltage. The proportional adjustment uses a proportional coefficient directly proportional to the duty cycle of the main power transistor, ensuring that the adjusted signal represents the output voltage of the switching power supply. The overvoltage reference signal is generated by a reference signal generation circuit, which includes an off-chip overvoltage protection resistor R3.

[0029] Although the embodiments are described and illustrated separately above, some common technologies are involved. Those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.

[0030] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. A power supply circuit, characterized in that, The system includes a first switch and a voltage detection circuit. The first terminal of the first switch is a power supply input terminal, receiving the power supply voltage. The second terminal of the first switch serves as a power supply output terminal, supplying power to the circuit to be powered. The circuit to be powered controls the switching state of the switch circuit, and the bus voltage of the switch circuit is the power supply voltage. The voltage detection circuit samples the voltage at either the first or second terminal of the first switch to obtain a voltage sampling signal. The voltage sampling signal is compared with a first threshold, and the voltage detection circuit outputs a first control signal. When the voltage sampling signal is lower than the first threshold, the first control signal represents a low-power trigger command. The circuit to be powered receives the low-power trigger command to control the switch circuit to switch to a low-power mode to prevent power loss in the circuit to be powered. The switching circuit includes an isolated switching power supply, which operates in a scenario with high power factor and low input capacitance.

2. The power supply circuit according to claim 1, characterized in that, The first switch is a transistor, which is turned on under controlled or uncontrolled conditions to supply power to the circuit to be powered, and the turning on can be fully turned on or partially turned on.

3. The power supply circuit according to claim 2, characterized in that, The transistor is a junction field-effect transistor (JFET). When the supply voltage is lower than the pinch-off voltage of the JFET, the JFET is turned on.

4. The power supply circuit according to claim 1, 2, or 3, characterized in that, The voltage detection circuit includes a first comparator, a first terminal of which receives the voltage sampling signal, a second terminal of which receives the first threshold, and an output terminal of which outputs the first control signal.

5. A control circuit, characterized in that, It includes a power supply circuit and a circuit to be powered as described in any one of claims 1-4, wherein the power supply circuit supplies power to the circuit to be powered.

6. A switching power supply, characterized in that, The device includes a power supply circuit, a circuit to be powered, and a switching circuit as described in any one of claims 1-4. The power supply circuit receives the bus voltage of the switching power supply and supplies power to the circuit to be powered. The circuit to be powered outputs a second control signal to control the switching state of the switching circuit.

7. The switching power supply according to claim 6, characterized in that, The power supply circuit includes a logic circuit and a reference generation circuit. The reference generation circuit receives a current reference signal and a first voltage signal representing the peak value of the inductor current. The first voltage signal is converted to an average value signal representing the average inductor current. A reference signal is obtained based on the current reference signal and the average value signal. The logic circuit receives the reference signal. In the logic circuit, the reference signal is compared with a ramp signal to determine the turn-off time of the main switch and is represented by a second control signal. The output terminal of the logic circuit is connected to the driver.

8. The switching power supply as described in claim 7, characterized in that, The circuit to be powered also includes a zero-crossing detection circuit. The input terminal of the zero-crossing detection circuit is connected to the control terminal of the main switch transistor, and the output terminal of the zero-crossing detection circuit is connected to the logic circuit.

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