Primary side feedback control circuit

Abstract

The utility model discloses a primary side feedback control circuit. The circuit comprises a primary side power supply circuit, a sampling control circuit, a main control chip and a main power circuit. The primary side power supply circuit supplies power to the primary side circuit, and the voltage of the primary side power supply circuit and the secondary side output voltage form a fixed turn ratio relation. The sampling control circuit carries out sampling and logic control on the output voltage of the primary side power supply circuit and outputs a control signal to the main control chip. The main control chip carries out PWM wave sending according to the control signal, and the purpose of adjusting the output voltage is achieved by adjusting the duty ratio of the main power circuit. Compared with the prior art, by sampling and controlling the voltage of the primary side power supply circuit, the output voltage is equivalently controlled, so that a driving chip originally applied to secondary side feedback control can be directly applied to primary side feedback control, and a primary side and secondary side isolation transmission device is not needed. The circuit is simplified, and meanwhile, the layout space of primary and secondary side isolation transmission is saved.

Description

Technical Field

[0001] This utility model relates to the field of switching power supplies, and in particular to a primary-side feedback control circuit. Background Technology

[0002] In switching power supplies, a common feedback control method involves sampling the output voltage at the output terminal, adjusting the control signal based on the magnitude of the output voltage, and transmitting the control signal to the primary control chip via an optocoupler or other isolated transmission chip. The control chip then adjusts the duty cycle based on the control signal to ultimately adjust the output voltage.

[0003] Therefore, most main control chips on the market are designed according to this logic, resulting in a relatively limited selection of primary-side feedback control chips. Often, these primary-side feedback control chips, due to their inherent characteristics, do not meet the design requirements of developers, forcing them to use secondary-side feedback control chips. Secondary-side feedback control chips typically require the use of optocouplers or other isolation chips to transmit signals from the secondary side to the primary side for the control chip's use, undoubtedly increasing the number of components and costs. Most importantly, optocouplers or isolation chips need to span the isolation band, often resulting in large device sizes and significant PCB space requirements. For high-power-density switching power supplies, PCB space is already very limited; requiring additional space for optocouplers or isolation chips is unacceptable.

[0004] To save board space occupied by optocouplers or isolation chips, some engineers adopt methods such as... Figure 1 Circuit technology:

[0005] It includes an input port Vin, an input ground port GND_in, an output port Vout, an output ground port GND_out, a power supply port Vf, and a control signal output port VCOMP. It also includes a transformer T1, diodes D1 and D2, a MOSFET TR1, capacitors C1 and C2, a driver chip IC1, resistors R1 and R2, and a voltage regulator chip TL431. The same-named terminal of the first primary winding of transformer T1 is connected to the input port Vin. The opposite-named terminal of the first primary winding of transformer T1 is connected to the drain of MOSFET TR1. The gate of MOSFET TR1 is connected to the GATE pin of driver chip IC1, and the source of MOSFET TR1 is connected to the input ground port GND_in. The same-named terminal of the secondary winding of transformer T1 is connected to the output ground port GND_out and one end of capacitor C2. The opposite-named terminal of the secondary winding of transformer T1 is connected to the anode of diode D2. The cathode of diode D2 is connected to the other end of capacitor C2 and the output port Vout. The same-name terminal of the second primary winding of transformer T1 is connected to the input ground port GND_in and one end of capacitor C1. The opposite-name terminal of the second primary winding of transformer T1 is connected to the anode of diode D1. The cathode of diode D1 is connected to the power supply port Vf and the other end of capacitor C1. The power supply port Vf is also connected to one end of resistor R1. The other end of resistor R1 is connected to one end of resistor R2 and the reference terminal of voltage regulator chip TL431. The other end of resistor R2 is connected to the anode of voltage regulator chip TL431 and then connected to the input ground port GND_in. The cathode of voltage regulator chip TL431 is connected to the control signal output port VCOMP.

[0006] This circuit uses resistors R1 and R2 to sample the power supply port Vf, and controls VCOMP through a voltage regulator chip TL431 to regulate the output voltage. This allows for primary-side sampling and output voltage control, saving space on the optocoupler's board layout. However, it has a drawback: due to the characteristics of the TL431 voltage regulator chip, its cathode voltage must be greater than the reference voltage for stable operation. Therefore, if a TL431 with a reference voltage of 2.5V is used, VCOMP can only operate above 2.5V. The output can only operate stably under heavy load conditions. Under light no-load conditions, VCOMP cannot be pulled low enough, preventing the main control chip from achieving a sufficiently small duty cycle, ultimately causing the output voltage to drift and exceed the overvoltage limit. Utility Model Content

[0007] Therefore, the technical problem this invention aims to solve is to directly sample and process signals on the primary side and provide them to the control chip when using a primary-side feedback control chip, thus saving board space for optocouplers or isolation chips. Simultaneously, this invention can stably control the output voltage even under light loads.

[0008] This utility model achieves its purpose through the following technical solution:

[0009] This utility model provides a primary-side feedback control circuit including a primary-side power supply circuit, a sampling control circuit, a main control chip, and a main power circuit. The main control chip is connected to the sampling control circuit and the main power circuit respectively, and the primary-side power supply circuit is connected to the sampling control circuit and the main power circuit respectively.

[0010] The primary-side power supply circuit is used to output a power supply voltage to the primary-side circuit, and the power supply voltage has a fixed turns ratio with the secondary-side output voltage.

[0011] The sampling control circuit is used to sample and logic control the power supply voltage and output a control signal to the main control chip.

[0012] The main control chip is used to generate PWM waves according to the control signal and adjust the duty cycle of the main power circuit to adjust the secondary output voltage.

[0013] Optionally, the main power circuit includes a MOSFET TR1, a transformer T1, a diode D2, and a capacitor C2. The same-name terminal of the first primary winding of the transformer T1 is connected to the voltage input port, the opposite-name terminal of the first primary winding of the transformer T1 is connected to the drain of the MOSFET TR1, the source of the MOSFET TR1 is connected to the input ground port, the opposite-name terminal of the secondary winding of the transformer T1 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to one end of the capacitor C2 and the output port, the same-name terminal of the secondary winding of the transformer T1 is connected to the other end of the capacitor C2 and the output ground port, and the gate of the MOSFET TR1 is connected to the main control chip.

[0014] Optionally, the primary power supply circuit includes a diode D1 and a capacitor C1. The opposite-named terminal of the second primary winding of the transformer T1 is connected to the anode of the diode D1 and connected to the main power circuit. The cathode of the diode D1 is connected to one end of the capacitor C1 and the power supply port, respectively. The other end of the capacitor C1 is connected to the main power circuit and the input ground port, respectively.

[0015] Optionally, the sampling control circuit includes resistors R1, R2, and R3, transistor Q1, and a voltage regulator chip. One end of resistor R1 and the cathode of the voltage regulator chip are both connected to the power supply port. The other end of resistor R1 is connected to the reference terminal of the voltage regulator chip and one end of resistor R2. The other end of resistor R2 is connected to the anode of the voltage regulator chip, one end of resistor R3, and the base of transistor Q1. The other end of resistor R3 is connected to the emitter of transistor Q1 and the input ground port. The collector of transistor Q1 is connected to the control signal port of the main control chip.

[0016] Optionally, the sampling control circuit further includes a resistor R4 and a capacitor C4, wherein the resistor R4 and the capacitor C4 are connected in series and then connected between the cathode and the reference terminal of the voltage regulator chip.

[0017] Optionally, the sampling control circuit further includes a capacitor C3, one end of which is connected to the reference terminal of the voltage regulator chip, and the other end of which is connected to the control signal port of the main control chip.

[0018] The working principle of this invention will be analyzed in conjunction with specific embodiments. Compared with the prior art, this invention has the following beneficial effects:

[0019] 1. This utility model uses a sampling control circuit to sample and control the voltage of the primary-side power supply circuit, thereby effectively controlling the output voltage. This allows the driver chip, which was originally used for secondary-side feedback control, to be directly used for primary-side feedback control. There is no need for primary-secondary isolation transmission devices. The output voltage can be controlled directly from the primary side by sampling the signal. The circuit is simplified, and optocouplers or other isolation chips are saved, thus saving board space.

[0020] 2. Throughout the entire load variation range from no load to full load, the present invention can effectively sample and control the output voltage, with relatively small load regulation and temperature drift. Attached Figure Description

[0021] Figure 1 This is a block diagram illustrating the principle of a primary-side feedback control circuit according to this utility model.

[0022] Figure 2 This is a circuit schematic diagram of existing technology;

[0023] Figure 3 This is a schematic diagram of a first embodiment of a primary-side feedback control circuit according to the present invention;

[0024] Figure 4 This is a schematic diagram of a second embodiment of a primary-side feedback control circuit according to the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] First Embodiment

[0027] Figure 3 The diagram shown is a circuit schematic of this embodiment. In this embodiment, the present invention provides a primary-side feedback control circuit including a primary-side power supply circuit, a sampling control circuit, a main control chip, and a main power circuit. The main control chip is connected to the sampling control circuit and the main power circuit respectively, and the primary-side power supply circuit is connected to the sampling control circuit and the main power circuit respectively.

[0028] The primary-side power supply circuit is used to output a power supply voltage to the primary-side circuit, and the power supply voltage has a fixed turns ratio with the secondary-side output voltage.

[0029] The sampling control circuit is used to sample and logic control the power supply voltage and output a control signal to the main control chip.

[0030] The main control chip is used to generate PWM waves according to the control signal and adjust the duty cycle of the main power circuit to adjust the secondary output voltage.

[0031] The main power circuit includes an input port Vin, an input ground port GND_in, a MOSFET TR1, a transformer T1, a diode D2, a capacitor C2, an output port Vout, and an output ground port GND_out. The same-named terminal of the first primary winding of transformer T1 is connected to the input port Vin, and the opposite-named terminal of the first primary winding of transformer T1 is connected to the drain of MOSFET TR1. The source of transformer T1 is connected to the input ground port GND_in. The opposite-named terminal of the secondary winding of transformer T1 is connected to the anode of diode D2, and the cathode of diode D2 is connected to one end of capacitor C2 and the output port Vout. The same-named terminal of the secondary winding of transformer T1 is connected to the other end of capacitor C2, and then connected to the output ground port GND_out.

[0032] The primary power supply circuit includes a power supply port Vf, an input ground port GND_in, a transformer T1, a diode D1, and a capacitor C1. The opposite-named terminal of the second primary winding of transformer T1 is connected to the anode of diode D1, and the cathode of diode D1 is connected to one end of capacitor C1 and the power supply port Vf. The same-named terminal of the second primary winding of transformer T1 is connected to the other end of capacitor C1, and then connected to the input ground port GND_in.

[0033] The sampling control circuit includes a power supply port Vf, an input ground port GND_in, a control signal port VCOMP, resistors R1, R2, and R3, a transistor Q1, and a voltage regulator chip TL431. The power supply port Vf is connected to one end of resistor R1 and the cathode of the voltage regulator chip TL431. The other end of resistor R1 is connected to the reference terminal of the voltage regulator chip TL431 and one end of resistor R2. The other end of resistor R2 is connected to the anode of the voltage regulator chip TL431. One end of resistor R3 is connected to the base of transistor Q1. The other end of resistor R3 is connected to the emitter of transistor Q1 and then to the input ground port GND_in. The collector of transistor Q1 is connected to the control signal port VCOMP.

[0034] The control signal port VCOMP is connected to the VCOMP pin of the main control chip IC1, and the GATE pin of the main control chip IC1 is connected to the gate of the MOSFET TR1.

[0035] The working process of this embodiment is as follows:

[0036] 1. When hour:

[0037] (Vbe is the turn-on voltage of transistor Q1, approximately 0.7V. Vref is the reference voltage at the reference terminal of the voltage regulator chip TL431.)

[0038] At this time, the voltage difference between pins 1 and 3 of the voltage regulator chip TL431 is less than Vref, and the voltage regulator chip TL431 is in an off state. At this time, the base voltage of transistor Q1 is

[0039] Therefore, it is only necessary to... If the voltage is set to <0.7V, then transistor Q1 is also in an off state. VCOMP will not be pulled low, and the main control chip IC1 outputs a large duty cycle to raise the output voltage Vout and the power supply port voltage Vf.

[0040] 2. When the voltage at the power supply port Vf rises to equal to hour:

[0041] At this point, the voltage difference between pins 1 and 3 of the voltage regulator chip TL431 is exactly equal to Vref, and the TL431 starts to conduct. Current flows from the power supply port Vf through pins 2 and 3 of the TL431 and through resistor R3. The base voltage of transistor Q1 is raised, and transistor Q1 conducts, starting to pull down the VCOMP voltage. The duty cycle of the main control chip IC1 begins to decrease until the final supply voltage Vf stabilizes at Vref. The output voltage Vout is related to the supply voltage Vf by the turns ratio, and eventually it becomes stable.

[0042] Compared to existing technologies, which use a TL431 voltage regulator chip to lower the VCOMP voltage, the TL431's characteristics prevent it from pulling VCOMP below the reference voltage Vref, causing the switching power supply to be unable to operate stably under light no-load conditions. This invention, however, essentially uses a transistor Q1 to lower the VCOMP voltage. Since the saturation conduction voltage drop of a transistor's collector-emitter junction is almost zero, it can completely lower the VCOMP voltage, enabling the switching power supply to operate stably under light no-load conditions.

[0043] Meanwhile, since the main voltage sampling is performed by the voltage regulator chip TL431, the reference temperature drift performance of the voltage regulator chip TL431 is far superior to that of the transistor. Under high and low temperature conditions, the voltage regulation effect of the product using this invention is also very good, and the product temperature drift is relatively small.

[0044] Second Embodiment

[0045] Figure 4 The circuit diagram shown is the schematic diagram of this embodiment 2. In this embodiment, a primary-side feedback control circuit is provided and applied to a switching power supply. It includes a primary-side power supply circuit, a sampling control circuit, a main control chip IC1, and a main power circuit.

[0046] The main power circuit includes an input port Vin, an input ground port GND_in, a MOSFET TR1, a transformer T1, a diode D2, a capacitor C2, an output port Vout, and an output ground port GND_out. The same-named terminal of the first primary winding of transformer T1 is connected to the input port Vin, and the opposite-named terminal of the first primary winding of transformer T1 is connected to the drain of MOSFET TR1. The source of transformer T1 is connected to the input ground port GND_in. The opposite-named terminal of the secondary winding of transformer T1 is connected to the anode of diode D2, and the cathode of diode D2 is connected to one end of capacitor C2 and the output port Vout. The same-named terminal of the secondary winding of transformer T1 is connected to the other end of capacitor C2, and then connected to the output ground port GND_out.

[0047] The primary power supply circuit includes a power supply port Vf, an input ground port GND_in, a transformer T1, a diode D1, and a capacitor C1. The opposite-named terminal of the second primary winding of transformer T1 is connected to the anode of diode D1, and the cathode of diode D1 is connected to one end of capacitor C1 and the power supply port Vf. The same-named terminal of the second primary winding of transformer T1 is connected to the other end of capacitor C1, and then connected to the input ground port GND_in.

[0048] The sampling control circuit includes a power supply port Vf, an input ground port GND_in, a control signal port VCOMP, resistors R1, R2, R3, and R4, capacitors C3 and C4, a transistor Q1, and a voltage regulator chip TL431. The power supply port Vf connects one end of resistor R1, one end of resistor R4, and the cathode of the voltage regulator chip TL431. The other end of resistor R4 connects to one end of capacitor C4. The other end of capacitor C4 connects to one end of capacitor C3, the other end of resistor R1, the reference terminal of the voltage regulator chip TL431, and one end of resistor R2. The other end of resistor R2 connects to the anode of the voltage regulator chip TL431. One end of resistor R3 connects to the base of transistor Q1. The other end of resistor R3 connects to the emitter of transistor Q1 and then to the input ground port GND_in. The other end of capacitor C3 connects to the collector of transistor Q1 and the control signal port VCOMP.

[0049] The control signal port VCOMP is connected to the VCOMP pin of the main control chip IC1, and the GATE pin of the main control chip IC1 is connected to the gate of the MOSFET TR1.

[0050] The working mechanism of this embodiment is basically the same as that of Embodiment 1. The difference is that a resistor R4 and a capacitor C4 are added to form an RC circuit. During the rise of the power supply port voltage Vf, the charging effect of the resistor R4 and capacitor C4 causes the voltage at pin 13 of the voltage regulator chip TL431 to reach Vref earlier. Negative feedback is used to connect in advance to reduce the problem of startup overshoot.

[0051] At the same time, capacitor C3 was added to stabilize the VCOMP voltage and compensate for loop issues, making the VCOMP voltage and loop more stable.

[0052] The above-described embodiments of this utility model are merely illustrative examples and not intended to limit the implementation of this utility model. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this utility model are still within the protection scope of this utility model.

Claims

1. A primary side feedback control circuit, characterized by: The primary side feedback control circuit comprises a primary side power supply circuit, a sampling control circuit, a master control chip and a main power circuit, the master control chip is connected with the sampling control circuit and the main power circuit respectively, and the primary side power supply circuit is connected with the sampling control circuit and the main power circuit respectively. The primary side power supply circuit is used for outputting a power supply voltage to the primary side circuit, and the power supply voltage has a fixed turns ratio relationship with the secondary side output voltage. The sampling control circuit is used for sampling and logically controlling the power supply voltage, and outputting a control signal to the master control chip. The master control chip is used for performing PWM wave generation according to the control signal, and adjusting the duty cycle of the main power circuit to adjust the secondary side output voltage.

2. The primary-side feedback control circuit of claim 1, wherein: The main power circuit comprises a MOS tube TR1, a transformer T1, a diode D2 and a capacitor C2, the same name end of the first primary side winding of the transformer T1 is connected to a voltage input port, the different name end of the first primary side winding of the transformer T1 is connected to the drain of the MOS tube TR1, the source of the MOS tube TR1 is connected to an input ground port, the different name end of the secondary side winding of the transformer T1 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to one end of the capacitor C2 and an output port respectively, the same name end of the secondary side winding of the transformer T1 is connected to the other end of the capacitor C2 and an output ground port respectively, and the gate of the MOS tube TR1 is connected to the master control chip.

3. The primary-side feedback control circuit of claim 1, wherein: The primary side power supply circuit comprises a diode D1 and a capacitor C1, the different name end of the second primary side winding of the transformer T1 is connected to the anode of the diode D1 which is connected to the main power circuit, the cathode of the diode D1 is connected to one end of the capacitor C1 and a power supply port respectively, and the other end of the capacitor C1 is connected to the main power circuit and an input ground port respectively.

4. The primary-side feedback control circuit of claim 1, wherein: The sampling control circuit comprises a resistor R1, a resistor R2, a resistor R3, a triode Q1 and a voltage stabilizing chip, one end of the resistor R1 and the cathode of the voltage stabilizing chip are connected to a power supply port, the other end of the resistor R1 is connected to the reference end of the voltage stabilizing chip and one end of the resistor R2, the other end of the resistor R2 is connected to the anode of the voltage stabilizing chip, one end of the resistor R3 and the base of the triode Q1 respectively, the other end of the resistor R3 is connected to the emitter of the triode Q1 and an input ground port respectively, and the collector of the triode Q1 is connected to the control signal port of the master control chip.

5. The primary side feedback control circuit of claim 4, wherein: The sampling control circuit further comprises a resistor R4 and a capacitor C4, which are connected in series between the cathode and the reference end of the voltage stabilizing chip.

6. The primary side feedback control circuit according to claim 4 or 5, characterized in that: The sampling control circuit further comprises a capacitor C3, one end of the capacitor C3 is connected to the reference end of the voltage stabilizing chip, and the other end of the capacitor C3 is connected to the control signal port of the master control chip.

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