Input Line Compensation Circuit and Method

Abstract

The present application relates to an input line compensation circuit and method, including: a current mirror module for generating a second current proportional to a first current on a first resistor; a compensation module and an adjustment module for shunting the second current to form a third current in the adjustment module and a fourth current in the compensation module; a trigger module for detecting the voltage of the compensation module; the adjustment module is also connected to an externally adjustable resistor of a flyback switching power supply to adjust the third current, thereby adjusting the fourth current to control the voltage of the compensation module. When the voltage of the compensation module is greater than the output voltage of the peak current control module of the flyback switching power supply, the trigger module is used to trigger a D flip-flop to control the power tube to turn off; a protection module for connecting the compensation module and the trigger module, and the protection module is used to make the trigger module trigger to turn off the power tube when it detects that the compensation module is in a short-circuit state, which is convenient and fast to protect the power supply circuit.

Description

Technical Field

[0001] The present invention relates to an input line compensation circuit and method, belonging to the technical field of flyback switching power supply control. Background Art

[0002] With the development of technology, power electronics technology is also constantly developing and innovating. Switching power supplies based on power electronics technology have been widely used in various electronic and electrical devices, such as communication devices, military equipment, industrial equipment, household appliances, and digital products. However, for a flyback switching power supply, as Figure 1 shown, the magnitude of its output power is related to the switching frequency of the power supply and the peak current of the coil. And the peak current of the chip is also related to the conduction duration of the primary coil and the magnitude of the input voltage Vin. The longer the conduction time of the primary coil, the higher the peak current; the higher the input voltage Vin, the faster the current of the primary coil rises. When the chip detects that the primary coil reaches the peak current, it will turn off the power transistor Q1. Due to the existence of parasitic capacitance and turn-off delay, even if the power transistor Q1 is turned off, the current of the primary coil will continue to rise until the primary coil is completely turned off. Usually, the delay time of the same system is fixed.

[0003] To ensure that the peak current reached by the primary coil is consistent with the current set by the chip under different input voltages Vin, input line compensation needs to be considered. The input line compensation circuit reduces the influence brought by the turn-off delay of the power transistor Q1 under different input voltages, and it controls the peak current to be consistent with the current set by the chip by compensating the CS voltage in advance. However, when its CS pin is short-circuited to the ground, the source of the power transistor Q1 is always at a low level, and the power transistor Q1 cannot be turned off, resulting in the primary coil being always conducting and the entire power supply will be burned out. Summary of the Invention

[0004] The purpose of the present invention is to provide an input line compensation circuit and method, which can protect the flyback switching power supply to avoid being burned out, and is convenient and fast.

[0005] To achieve the above purpose, the present invention provides the following technical solution: An input line compensation circuit is integrated in the power supply chip of a flyback switching power supply. The flyback switching power supply includes a first resistor connected to an auxiliary coil, a D flip-flop, and a power transistor that is turned on or off under the control of the D flip-flop. The turning on or off of the power transistor controls the power output of the flyback switching power supply. The input line compensation circuit includes:

[0006] A current mirror module, connected to the first resistor, and used to generate a second current proportional to the first current on the first resistor;

[0007] A compensation module and an adjustment module. The compensation module and the adjustment module are connected in parallel and then connected to the current mirror module to shunt the second current so as to form a third current in the adjustment module and a fourth current in the compensation module;

[0008] A trigger module for detecting the voltage of the compensation module;

[0009] The adjustment module is also connected to an external adjustable resistor of the flyback switching power supply. By adjusting the resistance value of the external adjustable resistor, the third current is adjusted, thereby adjusting the fourth current, and further controlling the voltage of the compensation module. When the voltage of the compensation module is greater than the output voltage VCST of the peak current control module of the flyback switching power supply, the trigger module is used to trigger the D flip-flop to control the power tube to turn off;

[0010] The input line compensation circuit further includes a protection module. The protection module is used to connect the compensation module and the trigger module. The protection module is used to trigger the trigger module to turn off the power tube when it detects that the compensation module is in a short-circuit state.

[0011] Further, the adjustment module includes a current-limiting resistor and an adjustment pin COMP. The first end of the current-limiting resistor is connected to the current mirror module, the second end of the current-limiting resistor is connected to the adjustment pin COMP, the adjustment pin COMP is connected to the first end of the external adjustable resistor, and the second end of the external adjustable resistor is grounded.

[0012] Further, the compensation module includes a compensation resistor and a detection pin CS. The first end of the compensation resistor is connected to the current mirror module, the second end of the compensation resistor is connected to the detection pin CS, the detection pin CS is also connected to the first end of a second resistor of the flyback switching power supply, and the second end of the second resistor is grounded.

[0013] Further, the compensation module further includes a first diode. The first end of the first diode is connected to the current mirror module, and the second end of the first diode is connected to the first end of the compensation resistor.

[0014] Further, the trigger module includes a comparator and a logic AND gate. The non-inverting input terminal of the comparator is connected to the output terminal of the peak current control module of the flyback switching power supply, the inverting input terminal of the comparator is connected to the first end of the compensation resistor, the output terminal of the comparator is connected to the first input terminal of the logic AND gate, the second input terminal of the logic AND gate is connected to the first end of the protection module, the output terminal of the logic AND gate is connected to the D flip-flop, and the second end of the protection module is connected to the second end of the compensation resistor.

[0015] Further, the current mirror module includes a first current mirror, a second current mirror, an amplifier, and a follower of the amplifier. The gates and drains of the first current mirror are connected and then connected to the gate of the second current mirror. The sources of the second current mirror and the first current mirror are connected to VDD. The drain of the second current mirror is connected to the adjustment module and the compensation module. The drain of the first current mirror is connected to the drain of the follower. The source of the follower is connected to the inverting input terminal of the amplifier and is connected to one end of the first resistor. A voltage is input to the non-inverting input terminal of the amplifier, and the output terminal of the amplifier is connected to the gate of the follower.

[0016] Further, the first end of the first resistor is connected to the auxiliary coil, the second end of the first resistor is connected to the source of the follower, and the magnitude of the first current is:

[0017]

[0018] where I 1 is the first current, VB is the first input voltage, VNA is the voltage of the auxiliary coil, and R 1 is the first resistor.

[0019] The present invention also provides an input line compensation method applicable to a flyback switching power supply. The method includes the following steps:

[0020] The primary coil conducts, so that the auxiliary coil mutually inducted with the primary coil is negatively charged, and a first current is generated through the first resistor;

[0021] A second current proportional to the first current is formed through the current mirror module;

[0022] The second current is shunted by a first branch and a second branch into a third current and a fourth current, and the magnitude of the third current in the first branch is adjustable;

[0023] Adjust the third current to adjust the magnitude of the fourth current, so as to adjust the voltage drop of the compensation resistor in the second branch;

[0024] When the voltage of the second branch is greater than the output voltage VCST of the peak control circuit of the flyback switching power supply, trigger the D flip-flop of the flyback switching power supply, so that the D flip-flop turns off the power transistor of the flyback switching power supply;

[0025] When the detection pin CS of the second branch is shorted to ground, the second branch triggers the D flip-flop through the protection module, so that the D flip-flop turns off the flyback switching power supply.

[0026] The beneficial effects of the present invention are as follows: by providing a protection module, when the detection pin CS of the flyback switching power supply is short-circuited to ground, the protection module can promptly control the power transistor to turn off through a D flip-flop, and then promptly turn off the flyback switching power supply to protect the flyback switching power supply. At the same time, CS coupling interference is avoided, enhancing the reliability of the circuit;

[0027] By providing an adjustment pin COMP, the adjustment pin COMP is connected to an external adjustable resistor. When the power supply chip and the power transistor are co-packaged and input line compensation cannot be performed through the compensation pin CS, the current can be adjusted by adjusting the external adjustable resistor for compensation, thereby ensuring the effectiveness of the power supply input line compensation.

[0028] The above description is only an overview of the technical solution of the present invention. In order to be able to more clearly understand the technical means of the present invention and implement it in accordance with the content of the specification, the following describes in detail with reference to the preferred embodiments of the present invention and the accompanying drawings. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of a flyback switching power supply in the prior art.

[0030] Figure 2 It is a block diagram of the input line compensation circuit of the present application.

[0031] Figure 3 It is a circuit schematic diagram of the input line compensation circuit of the present application.

[0032] Figure 4 It is an application schematic diagram of the input line compensation circuit of the present application in a flyback switching power supply. Detailed Description of the Embodiment

[0033] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0034] Please refer to Figures 2 to 4 , an input line compensation circuit in a preferred embodiment of the present invention is integrated in the power supply chip of a flyback switching power supply. The flyback switching power supply includes a rectification circuit for converting alternating current to direct current, a first capacitor C1, a second capacitor C2, and a primary coil NP connected to the rectification circuit, a secondary coil NS and an auxiliary coil NA mutually inductive with the primary coil NP, and a power supply chip POWER IC connected to the auxiliary coil NA.

[0035] The flyback switching power supply further includes a fourth resistor R4 connected to both ends of the primary coil NP, a third capacitor C3 connected in parallel with the fourth resistor R4, a sixth diode D6 connected to the circuit of the third capacitor C3 and the primary coil NP, a fifth capacitor C5 connected to both ends of the secondary coil NS, and a seventh diode D7 connected to the circuit of the fifth capacitor C5 and the secondary coil NS.

[0036] The flyback switching power supply further includes a first resistor R1, a second resistor R2, a third resistor R3, a fifth resistor R5, an eighth diode D8, a fourth capacitor C4, and a power transistor Q1. The first end of the first resistor R1 is connected to one end of the auxiliary coil NA, the second end of the first resistor R1 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is connected to the other end of the auxiliary coil NA, the first end of the eighth diode D8 is connected to the first end of the first resistor R1, the second end of the eighth diode D8 is connected to the first end of the fourth capacitor C4, the other end of the fourth capacitor C4 is connected to the second end of the third resistor R3, the first end of the fifth resistor R5 is connected to the regulation pin COMP of the power supply chip, the first end of the second resistor R2 is connected to the detection pin CS of the power supply chip, the second ends of the fifth resistor R5, the second resistor R2, the fourth capacitor C4, and the third resistor R3 are connected in parallel to ground, one pin of the power supply chip is also grounded, the drain of the power transistor Q1 is connected to the DRAIN pin of the power supply chip, the source of the power transistor Q1 is connected to the compensation pin CS of the power supply chip and the first end of the second resistor R2, the gate of the power transistor Q1 is connected to the GATE pin of the power supply chip, and the VS pin of the power supply chip is connected to the second end of the first resistor R1 and the first end of the third resistor R3. In this embodiment, the fifth resistor R5 is an externally adjustable resistor R5, and the resistance value of the fifth resistor R5 is adjustable to thereby adjust the magnitude of the current.

[0037] An error amplifier (EA) connected to the VS pin, a peak current control module (CS) and an oscillation module (OSC) connected to the error amplifier (EA), a D flip-flop connected to the oscillation module (OSC), and a drive module connected to the D flip-flop are integrally provided in the power supply chip. The power transistor Q1 is controlled to be turned on or off through the D flip-flop, thereby controlling the power output of the flyback switching power supply.

[0038] Please refer to Figure 2 and Figure 3, To ensure that the peak current reached by the primary coil NP is consistent with the current set by the power supply chip under different input voltages Vin, therefore, the flyback switching power supply further includes an input line compensation circuit, which specifically includes: a current mirror module 1, an adjustment module 3, a compensation module 2, and a trigger module 4. The current mirror module 1 is connected to the first resistor R1 to generate a second current I2 proportional to the first current I1 on the first resistor R1. The compensation module 2 and the adjustment module 3 are connected in parallel to the current mirror module 1 to shunt the second current I2 to form a third current I3 in the adjustment module 3 and a fourth current I4 in the compensation module 2. The trigger module 4 is used to detect the voltage of the compensation module 2. When the voltage of the compensation module 2 is greater than the output voltage VCST of the peak current control module of the flyback switching power supply, the trigger module 4 is used to trigger the D flip-flop to control the power tube to turn off. The compensation module 2 is also connected to the external adjustable resistor R5 of the flyback switching power supply. As described above, the external adjustable resistor is the fifth resistor R5. Adjusting the resistance value of the external adjustable resistor R5 can adjust the third current I3, thereby adjusting the fourth current I4 to control the voltage of the compensation module 2.

[0039] Specifically, the adjustment module 3 includes a current-limiting resistor RA and an adjustment pin COMP. The first end of the current-limiting resistor RA is connected to the current mirror module 1, the second end of the current-limiting resistor RA is connected to the adjustment pin COMP, the adjustment pin COMP is connected to the first end of the external adjustable resistor R5, and the second end of the external adjustable resistor R5 is grounded.

[0040] The compensation module 2 includes a compensation resistor RB and a detection pin CS. The first end of the compensation resistor RB is connected to the current mirror module 1, the second end of the compensation resistor RB is connected to the detection pin CS, the detection pin CS is also connected to the first end of the second resistor R2 of the flyback switching power supply, and the second end of the second resistor R2 is connected to the second end of the external adjustable resistor R5 and grounded.

[0041] The compensation module 2 further includes a first diode D1, which is used to ensure that when the adjustment pin COMP is short-circuited or the like, it is not difficult to turn off the power tube Q1 through the trigger module 4. Among them, the first end of the first diode D1 is connected to the current mirror module 1, and the second end of the first diode D1 is connected to the first end of the compensation resistor RB.

[0042] The trigger module 4 includes a comparator CMP and a logic AND gate. The non-inverting input terminal of the comparator CMP is connected to the output terminal of the peak current control module CS. The inverting input terminal of the comparator CMP is connected to the first end of the compensation resistor RB. The output terminal of the comparator CMP is connected to the first input terminal of the logic AND gate. The second input terminal of the logic AND gate is connected to the first end of the protection module 5. The output terminal of the logic AND gate is connected to the D flip-flop. The second end of the protection module 5 is connected to the second end of the compensation resistor RB. Among them, the peak current control module CS outputs a VCST voltage signal to the comparator.

[0043] The current mirror module 1 includes a first current mirror M1, a second current mirror M2, an amplifier, and a follower M3 of the amplifier. The gate and drain of the first current mirror M1 are connected and then connected to the gate of the second current mirror M2. The source of the second current mirror M2, the source of the first current mirror M1 are connected to VDD. The drain of the second current mirror M2 is connected to the adjustment module 3 and the compensation module 2. The drain of the first current mirror M1 is connected to the drain of the follower M3. The source of the follower M3 is connected to the inverting input terminal of the amplifier AMP and is connected to one end of the first resistor R1. The non-inverting input terminal of the amplifier AMP inputs a voltage. The output terminal of the amplifier AMP is connected to the source of the follower M3.

[0044] The second end of the first resistor R1 is connected to the source of the follower M3. The magnitude of the first current I1 is:

[0045]

[0046] Among them, I 1 is the first current, VB is the first input voltage, VNA is the voltage of the auxiliary coil, and R 1 is the first resistor.

[0047] The working principle of the input line compensation circuit of this application is as follows: When the primary coil NP is turned on, since the voltage on the auxiliary coil is negative, a first current I1 is generated on the first resistor R1, and the magnitude of the first current I1 is I1 = (VB - VNA) / R1. Due to the mutual inductance between the primary coil NP, the secondary coil NS, and the auxiliary coil NA, the voltage on the auxiliary coil NA and the voltage on the primary coil NP, i.e., the input voltage Vin, are negatively correlated. That is, the larger the input voltage Vin, the smaller the voltage on the auxiliary coil NA, but the absolute value increases proportionally with the increase of Vin. Therefore, the first current I1 changes proportionally with the change of the input voltage Vin. At this time, the second current I2 proportional to the first current I1 can be obtained through the current mirrors M1 and M2. The second current I2 flows through the compensation module 2 and the adjustment module 3 and is divided into two branches to generate a third current I3 and a fourth current I4. Among them, the fourth current I4 of the compensation module 2 flows through the compensation resistor RB to the second resistor R2 connected to the detection pin CS, and the third current I3 of the adjustment module 3 flows through the current limiting resistor RA and the external adjustable resistor R5 to the ground. By adjusting the size of the external adjustable resistor R5, the size of the third current I3 can be adjusted, and then the size of the fourth current I4 can be adjusted. The fourth current I4 can be used to control the voltage △VRB on the compensation resistor RB. When the fourth current I4 is larger, △VRB is larger, and the voltage at the detection pin CS is VCS. Then the voltage VCS + △VRB of the compensation module 2 will reach the voltage of the VCST voltage signal more quickly; when the fourth current I4 is smaller, △VRB is smaller, and the voltage VCS + △VRB of the compensation module 2 will reach the voltage of the VCST voltage signal more slowly. When VCS + △VRB reaches the VCST voltage, the comparator CMP will output a low-level reset signal, and the D flip-flop will output a PWM = 0 signal to turn off the power transistor Q1.

[0048] When the compensation pin CS is shorted to the ground, since no other compensation resistors are connected between the compensation pin CS and the second resistor R2, the protection module can quickly and accurately detect the short circuit of the compensation pin CS and turn off the power transistor Q1 through the D flip-flop in time.

[0049] In order to ensure that when the compensation pin COMP is shorted or the like, the comparator CMP cannot output a low level, and further the D flip-flop cannot turn off the power transistor Q1, a diode D1 needs to be added between RA and RB.

[0050] The present invention also provides an input line compensation method, which is applicable to a flyback switching power supply. The method includes the following steps:

[0051] The primary coil is turned on so that the auxiliary coil mutually inductive with the primary coil is negatively charged, and a first current is generated through the first resistor;

[0052] A second current I2 proportional to the first current I1 is formed through a current mirror module;

[0053] The second current I2 is shunted by a first branch and a second branch into a third current I3 and a fourth current I4, and the magnitude of the third current I3 in the first branch is adjustable;

[0054] Adjust the third current I3 to adjust the magnitude of the fourth current I4, so as to adjust the voltage of the compensation resistor RB in the second branch;

[0055] When the voltage of the second branch is greater than the output voltage VCST of the peak control circuit of the flyback switching power supply, trigger the D flip-flop of the flyback switching power supply, so that the D flip-flop turns off the power transistor of the flyback switching power supply;

[0056] When the detection pin CS of the second branch is shorted to ground, the second branch triggers the D flip-flop through the protection module 5, so that the D flip-flop turns off the flyback switching power supply.

[0057] In summary: By providing the protection module 5, when the detection pin CS of the flyback switching power supply is shorted to ground, the protection module 5 can timely control the power transistor to turn off through the D flip-flop, and then timely turn off the flyback switching power supply to protect the flyback switching power supply. At the same time, CS coupling interference is avoided, and the reliability of the circuit is enhanced.

[0058] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0059] The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be understood as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. An input line compensation circuit is integrated in the power supply chip of a flyback switching power supply. The flyback switching power supply includes a first resistor connected to an auxiliary coil, a D flip-flop, and a power transistor that is turned on or off under the control of the D flip-flop. The turning on or off of the power transistor controls the power output of the flyback switching power supply. An error amplifier, a peak current control module connected to the error amplifier, an oscillation module, a D flip-flop connected to the oscillation module, and a drive module connected to the D flip-flop are integrally arranged in the power supply chip. Characterized in that, the input line compensation circuit includes: a current mirror module, connected to the first resistor, and used to generate a second current proportional to the first current on the first resistor; a compensation module and an adjustment module. The compensation module and the adjustment module are connected in parallel to the current mirror module, used to shunt the second current to form a third current in the adjustment module and a fourth current in the compensation module; a trigger module, used to detect the voltage of the compensation module; the adjustment module is further connected to an externally adjustable resistor of the flyback switching power supply. The resistance value of the externally adjustable resistor is adjusted to adjust the third current, thereby adjusting the fourth current, and further controlling the voltage of the compensation module. When the voltage of the compensation module is greater than the output voltage VCST of the peak current control module of the flyback switching power supply, the trigger module is used to trigger the D flip-flop to control the power transistor to turn off; the input line compensation circuit further includes a protection module. The protection module is used to connect the compensation module and the trigger module. The protection module is used to make the trigger module trigger to turn off the power transistor when it detects that the compensation module is in a short-circuit state.

2. The input line compensation circuit according to claim 1, Characterized in that, the adjustment module includes a current-limiting resistor and an adjustment pin COMP. The first end of the current-limiting resistor is connected to the current mirror module, the second end of the current-limiting resistor is connected to the adjustment pin COMP, the adjustment pin COMP is connected to the first end of the externally adjustable resistor, and the second end of the externally adjustable resistor is grounded.

3. The input line compensation circuit according to claim 1, Characterized in that, the compensation module includes a compensation resistor and a detection pin CS. The first end of the compensation resistor is connected to the current mirror module, the second end of the compensation resistor is connected to the detection pin CS, the detection pin CS is further connected to the first end of a second resistor of the flyback switching power supply, and the second end of the second resistor is grounded.

4. The input line compensation circuit according to claim 3, Characterized in that, the compensation module further includes a first diode. The first end of the first diode is connected to the current mirror module, and the second end of the first diode is connected to the first end of the compensation resistor.

5. The input line compensation circuit according to claim 3, Characterized in that, The trigger module includes a comparator and a logic AND gate. The non-inverting input terminal of the comparator is connected to the output terminal of the peak current control module of the flyback switching power supply. The inverting input terminal of the comparator is connected to the first end of the compensation resistor. The output terminal of the comparator is connected to the first input terminal of the logic AND gate. The second input terminal of the logic AND gate is connected to the first end of the protection module. The output terminal of the logic AND gate is connected to the D flip-flop. The second end of the protection module is connected to the second end of the compensation resistor.

6. The input line compensation circuit according to claim 1, characterized in that the current mirror module includes a first current mirror, a second current mirror, an amplifier and a follower of the amplifier. The gate and drain of the first current mirror are connected and then connected to the gate of the second current mirror. The source of the second current mirror, the source of the first current mirror are connected to VDD. The drain of the second current mirror is connected to the adjustment module and the compensation module. The drain of the first current mirror is connected to the drain of the follower. The source of the follower is connected to the inverting input terminal of the amplifier and is connected to one end of the first resistor. The non-inverting input terminal of the amplifier inputs a voltage. The output terminal of the amplifier is connected to the gate of the follower.

7. The input line compensation circuit according to claim 6, characterized in that the first end of the first resistor is connected to the auxiliary coil, the second end of the first resistor is connected to the source of the follower, and the magnitude of the first current is: Among them, I 1 is the first current, VB is the first input voltage, VNA is the voltage of the auxiliary coil, and R 1 is the first resistor.

8. An input line compensation method for the input line compensation circuit according to any one of claims 1-7, applicable to a flyback switching power supply, characterized in that the method includes the following steps: The primary coil conducts, so that the auxiliary coil mutually inducted with the primary coil is negatively charged, and a first current is generated through the first resistor; A second current proportional to the first current is formed through the current mirror module; The second current is shunted into a third current and a fourth current by a first branch and a second branch, and the magnitude of the third current in the first branch is adjustable; Adjust the third current to adjust the magnitude of the fourth current, so as to adjust the voltage drop of the compensation resistor in the second branch; When the voltage of the second branch is greater than the output voltage VCST of the peak control circuit of the flyback switching power supply, trigger the D flip-flop of the flyback switching power supply, so that the D flip-flop turns off the power transistor of the flyback switching power supply; When the detection pin CS of the second branch is shorted to the ground, the second branch triggers the D flip-flop through the protection module, so that the D flip-flop turns off the flyback switching power supply.

Images