A synchronous converter control circuit

Abstract

The present invention provides a synchronous converter control circuit, comprising: a power switch unit, the power switch unit comprising a power tube, a synchronous rectifier tube, a first controller and a second controller; a zero-crossing detection unit, the detection end of the zero-crossing detection unit is connected to a switch node, and the output end of the zero-crossing detection unit is connected to the second controller; an output unit, the first end of the output unit is connected to the switch node, and the second end of the output unit is connected to the second end of the synchronous rectifier tube; a synchronous rectification control unit, the two current detection ends of the synchronous rectification control unit are connected to the power switch unit or the output unit, and the output end of the synchronous rectification control unit is connected to the second controller. Comparing the inductor current with the corresponding threshold value is used to determine whether the synchronous rectifier tube is turned on in the current cycle, so that the synchronous converter or controller can achieve efficient operation in the DCM mode.

Description

Technical Field

[0001] The present invention relates to the field of control circuits, and more particularly to a synchronous converter control circuit. Background Art

[0002] When an existing synchronous buck converter or controller operates in DCM mode, under different loads and different input and output voltages, the synchronous rectifier (freewheeling tube) is turned on in the PWM off stage until the inductor current passes through zero, using the low Ron of the switch tube to save conduction loss; however, there will be switching loss when the synchronous rectifier is turned on once in a cycle. When the inductor current is less than a certain value, the switching loss will exceed the freewheeling loss of the body diode, so turning on the synchronous rectifier will be counterproductive. Summary of the invention

[0003] An object of the present invention is to provide a synchronous converter control circuit.

[0004] The present invention aims to solve the problem of how to improve the operating efficiency of the synchronous converter in the DCM mode.

[0005] Compared with the prior art, the technical solution of the present invention and its beneficial effects are as follows:

[0006] A synchronous converter control circuit comprises: a power switch unit, wherein the power switch unit comprises a power tube, a synchronous rectifier tube, a first controller and a second controller; a zero-crossing detection unit, wherein a detection end of the zero-crossing detection unit is connected to a switch node, and an output end of the zero-crossing detection unit is connected to the second controller; an output unit, wherein a first end of the output unit is connected to the switch node, and a second end of the output unit is connected to a second end of the synchronous rectifier tube; and a synchronous rectification control unit, wherein two current detection ends of the synchronous rectification control unit are connected to the power switch unit or the output unit, and an output end of the synchronous rectification control unit is connected to the second controller.

[0007] As a further improvement, the two current detection terminals of the synchronous rectification control unit are connected to the output unit; a sampling resistor is provided between the first and second terminals of the output unit; the two current detection terminals of the synchronous rectification control unit are connected to the two ends of the sampling resistor; the synchronous rectification control unit includes an amplifier, a voltage comparator and an operation unit, the positive phase input terminal and the negative phase input terminal of the amplifier serve as the two current detection terminals of the synchronous rectification control unit; the positive phase input terminal of the voltage comparator is connected to the output terminal of the amplifier, the negative phase input terminal of the voltage comparator is connected to the operation unit, and the output terminal of the voltage comparator is connected to the second controller.

[0008] As a further improvement, the two current detection terminals of the synchronous rectification control unit are connected to the output unit; a second inductor is provided between the first and second terminals of the output unit; the two current detection terminals of the synchronous rectification control unit are connected to the two ends of the second inductor; the synchronous rectification control unit includes an amplifier, a voltage comparator and an operation unit, the positive phase input terminal and the negative phase input terminal of the amplifier serve as the two current detection terminals of the synchronous rectification control unit; the positive phase input terminal of the voltage comparator is connected to the output terminal of the amplifier, the negative phase input terminal of the voltage comparator is connected to the operation unit, and the output terminal of the voltage comparator is connected to the second controller.

[0009] As a further improvement, the two current detection ends of the synchronous rectification control unit are connected to the power switch unit; the two current detection ends of the synchronous rectification control unit are connected to the two ends of the power tube; the synchronous rectification control unit includes an amplifier, a voltage comparator and an operation unit, the positive phase input end and the negative phase input end of the amplifier serve as the two current detection ends of the synchronous rectification control unit, and the control end of the power tube is connected to the control end of the amplifier; the positive phase input end of the voltage comparator is connected to the output end of the amplifier, the negative phase input end of the voltage comparator is connected to the operation unit, and the output end of the voltage comparator is connected to the second controller.

[0010] As a further improvement, the output unit also includes: a first inductor, which is connected in series between the switch node and the sampling resistor; a capacitor, which is connected in series between the sampling resistor and the second end of the synchronous rectifier; and a load resistor, which is connected in parallel to both ends of the capacitor.

[0011] As a further improvement, the operation unit is of the first type or the second type; the first type is a numerical operation unit and a DAC; the second type is an analog operation unit.

[0012] As a further improvement, the conduction loss of the body diode W1 = Vdiode*ipeak*0.5*(Δtfw / T); the loss when the synchronous rectifier is turned on W2 = W 导通损耗 +W 开关损耗 =(1 / 4)*ipeak 2 *Ron*(Δtfw / T)+Vin*(Qg / T); when W1>W2, the synchronous rectifier is turned on; when W1<W2, the synchronous rectifier is turned off.

[0013] As a further improvement, the power tube is an enhanced NMOS tube, and the synchronous rectifier tube is an enhanced NMOS tube.

[0014] As a further improvement, the zero-crossing detection unit includes a voltage comparator, a positive phase input terminal of the voltage comparator is connected to the switch node, a negative phase input terminal of the voltage comparator is grounded, and an output terminal of the voltage comparator is connected to the second controller.

[0015] As a further improvement, the first controller and the second controller are integrated into the same controller.

[0016] The beneficial effect of the present invention is that the comparison between the inductor current and the corresponding threshold is used to determine whether the synchronous rectifier is turned on in the current cycle, so that the synchronous converter or controller can achieve high-efficiency operation in the DCM mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a synchronous converter control circuit diagram provided in Embodiment 1 of the present invention.

[0018] Figure 2 is a schematic diagram of a first type of computing unit provided in an embodiment of the present invention.

[0019] Figure 3 is a schematic diagram of a second type of computing unit provided in an embodiment of the present invention.

[0020] Figure 4 This is a partial synchronous converter control circuit diagram provided in Embodiment 2 of the present invention.

[0021] Figure 5 This is a partial synchronous converter control circuit diagram provided in Embodiment 3 of the present invention.

[0022] Figure 6 yes Figure 1 The signal timing diagram of each device in the circuit diagram shown.

[0023] In the figure: 1. Power switch unit 11. First controller 12. Second controller 13. Power tube

[0024] 14. Synchronous rectifier 2. Zero-crossing detection unit 3. Output unit

[0025] 4. Synchronous rectification control unit 41. Amplifier 42. Voltage comparator

[0026] 43. Arithmetic unit DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0029] Reference Figures 1 to 6 As shown, a synchronous converter control circuit includes: a power switch unit 1, wherein the power switch unit 1 includes a power tube 13, a synchronous rectifier tube 14, a first controller 11 and a second controller 12; a zero-crossing detection unit 2, wherein the detection end of the zero-crossing detection unit 2 is connected to a switch node, and the output end of the zero-crossing detection unit 2 is connected to the second controller 12; the switch node is located between the power tube 13 and the synchronous rectifier tube 14; an output unit 3, wherein the first end of the output unit 3 is connected to the switch node, and the second end of the output unit 3 is connected to the second end of the synchronous rectifier tube 14; a synchronous rectification control unit 4, wherein the two current detection ends of the synchronous rectification control unit 4 are connected to the power switch unit 1 or the output unit 3, and the output end of the synchronous rectification control unit 4 is connected to the third control end of the second controller 12. The first end of the power tube 13 is connected to the first power supply, the second end of the power tube 13 is connected to the switch node, and the control end of the power tube 13 is connected to the first controller 11; the first end of the synchronous rectifier tube 14 is connected to the switch node, the second end of the synchronous rectifier tube 14 is connected to the reference ground, and the control end of the synchronous rectifier tube 14 is connected to the second controller 12. Figure 1As shown, the output end of the zero-crossing detection unit 2 is connected to the second control end of the second controller 12, and PWM_IN is used as an external control, connected to the first control end of the first controller 11, and also connected to the first control end of the second controller 12. The inductor current is compared with the corresponding threshold to determine whether the synchronous rectifier 14 is turned on in the current cycle, so that the synchronous converter or controller can achieve efficient operation in the DCM mode.

[0030] Reference Figure 1 As shown, the two current detection terminals of the synchronous rectification control unit 4 are connected to the output unit 3; a sampling resistor is provided between the first terminal and the second terminal of the output unit 3; the two current detection terminals of the synchronous rectification control unit 4 are connected to the two ends of the sampling resistor; the synchronous rectification control unit 4 includes an amplifier 41, a voltage comparator 42 and an operation unit 43, and the positive phase input terminal and the negative phase input terminal of the amplifier 41 serve as the two current detection terminals of the synchronous rectification control unit 4; the positive phase input terminal of the voltage comparator 42 is connected to the output terminal of the amplifier 41, the negative phase input terminal of the voltage comparator 42 is connected to the operation unit 43, and the output terminal of the voltage comparator 42 is connected to the second controller 12, that is, the output terminal of the voltage comparator 42 serves as the output terminal of the synchronous rectification control unit 4.

[0031] Reference Figure 1 As shown, the output unit 3 also includes: a first inductor, which is connected in series between the switch node and the sampling resistor; a capacitor, which is connected in series between the sampling resistor and the second end of the synchronous rectifier 14; and a load resistor, which is connected in parallel to both ends of the capacitor.

[0032] Reference Figures 2 to 3 As shown, the operation unit 43 is of the first type or the second type; the first type is a numerical operation unit 43 and a DAC; the second type is an analog operation unit 43.

[0033] Reference Figure 1 As shown, in the PWM_ON stage, when the inductor current is detected to exceed a certain set threshold value (as shown by COMP2 voltage comparator 42), the synchronous rectifier tube 14LS of the current cycle will be turned on. If it is less than this threshold value, the LS of the current cycle will not be turned on, and the inductor current will continue to flow using the body diode D2 of the synchronous rectifier tube 14. This control method is essentially a control method that selects the least loss in the switching loss and the diode conduction loss to achieve efficient operation.

[0034] The theoretical calculation is as follows: In the PWM_OFF stage, Vdiode is negligible compared to Vout, so the time required for the inductor peak current Ipeak to discharge to 0A is: Δtfw (freewheeling time) = L*ipeak / Vout;

[0035] When the diode is used for freewheeling, its conduction loss W1 = Vdiode * ipeak * 1 / 2 * (Δtfw / T);

[0036] When the synchronous rectifier tube 14 is turned on, the total loss W2 = W 导通损耗 +W 开关损耗 =(1 / 4)*ipeak 2 *Ron*(Δtfw / T)+Vin*(Qg / T);

[0037] When W1 < W2, Vdiode * ipeak * 1 / 2 * (Δtfw / T) < 1 / 4 * ipaek 2 *Ron*(Δtfw / T)+Vin*(Qg / T), where, at low current, the conduction loss of Ron can be neglected compared with the switching loss, then Vdiode * ipeak * 1 / 2 * (Δtfw / T) < Vin * (Qg / T), Ipeak < (2 * Qg / Vdiode) 1 / 2 *(Vout * Vin / L) 1 / 2 .

[0038] In summary, the current I flip threshold corresponding to the Comp2 comparator is (2 * Qg / Vdiode) 1 / 2 *(Vout * Vin / L) 1 / 2 , when the current I exceeds this threshold, the synchronous rectifier tube 14 in the current cycle is normally turned on for freewheeling until the zero-crossing detection unit 2; if the current I does not exceed this threshold, the synchronous rectifier tube 14 in the current cycle is not turned on, that is, the inductor current uses the body diode for freewheeling.

[0039] Referring to Figure 4 shown, in the second embodiment, the two current detection ends of the synchronous rectification control unit 4 are connected to the output unit 3; a second inductor is provided between the first end and the second end of the output unit 3; the two current detection ends of the synchronous rectification control unit 4 are connected to both ends of the second inductor; the synchronous rectification control unit 4 includes an amplifier 41, a voltage comparator 42 and an arithmetic unit 43, the positive input terminal and the negative input terminal of the amplifier 41 are used as the two current detection ends of the synchronous rectification control unit 4; the positive input terminal of the voltage comparator 42 is connected to the output terminal of the amplifier 41, the negative input terminal of the voltage comparator 42 is connected to the arithmetic unit 43, and the output terminal of the voltage comparator 42 is connected to the second controller 12.

[0040] Referring to Figure 5As shown, in Example 3, the two current detection ends of the synchronous rectification control unit 4 are connected to the power switch unit 1; the two current detection ends of the synchronous rectification control unit 4 are connected to the two ends of the power tube 13; the synchronous rectification control unit 4 includes an amplifier 41, a voltage comparator 42 and an operation unit 43, the positive phase input end and the negative phase input end of the amplifier 41 serve as the two current detection ends of the synchronous rectification control unit 4, and the control end of the power tube 13 is connected to the control end of the amplifier 41; the positive phase input end of the voltage comparator 42 is connected to the output end of the amplifier 41, the negative phase input end of the voltage comparator 42 is connected to the operation unit 43, and the output end of the voltage comparator 42 is connected to the second controller 12.

[0041] Reference Figure 1 As shown, the power tube 13 is an enhanced NMOS tube, and the synchronous rectifier tube 14 is an enhanced NMOS tube.

[0042] Reference Figure 1 As shown, the zero-crossing detection unit 2 includes a voltage comparator 42 , a positive phase input terminal of the voltage comparator 42 is connected to the switch node, a negative phase input terminal of the voltage comparator 42 is grounded, and an output terminal of the voltage comparator 42 is connected to the second controller 12 .

[0043] The first controller 11 and the second controller 12 are integrated into the same controller.

[0044] The working principle of a synchronous converter control circuit provided by the present invention is: the operation unit 43 obtains an output voltage through operation according to the inductance size of Qg and the diode conduction voltage Vdiode, which is used as the judgment threshold of the COMP2 voltage comparator 42; the voltage signal of the sampled current is compared with the voltage of the operation unit 43, and a control signal is output to the second controller 12; the second controller 12 selects whether the synchronous rectifier tube 14 of the current cycle is turned on according to the signal of the COMP2 voltage comparator 42 and PWM_IN.

[0045] It should be noted that the difference between the second embodiment and the third embodiment and the first embodiment is that the output units 3 of the different embodiments are different, and the connection methods of the output unit 3 and the power switch unit 1 are different. In the three embodiments, the power switch unit 1, the zero-crossing detection unit 2 and the synchronous rectification control unit 4 are all the same.

[0046] The working principle and working process of this embodiment can refer to the corresponding contents of the above-mentioned embodiments.

[0047] The same or similar parts between the above-mentioned embodiments in this specification can be referenced to each other, and each implementation method focuses on the differences from other implementation methods, but it is not limited to the differences that cannot be replaced or superimposed on each other.

[0048] The above embodiments are only used to explain the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that any modification and equivalent substitution that does not depart from the spirit and scope of the present invention should fall within the protection scope of the claims of the present invention.

Claims

1. A synchronous converter control circuit, characterized in that: include: A power switch unit, the power switch unit comprising a power tube, a synchronous rectifier tube, a first controller and a second controller; A zero-crossing detection unit, wherein a detection end of the zero-crossing detection unit is connected to a switch node, and an output end of the zero-crossing detection unit is connected to the second controller; An output unit, wherein a first end of the output unit is connected to the switch node, and a second end of the output unit is connected to a second end of the synchronous rectifier tube; A synchronous rectification control unit, wherein two current detection terminals of the synchronous rectification control unit are connected to the power switch unit or the output unit, and an output terminal of the synchronous rectification control unit is connected to the second controller; The two current detection terminals of the synchronous rectification control unit are connected to the output unit; a sampling resistor or a second inductor is provided between the first terminal and the second terminal of the output unit; the two current detection terminals of the synchronous rectification control unit are connected to the two ends of the sampling resistor or the second inductor; Or, The two current detection terminals of the synchronous rectification control unit are connected to the power switch unit; the two current detection terminals of the synchronous rectification control unit are connected to the two ends of the power tube; the synchronous rectification control unit includes an amplifier, a voltage comparator and an operation unit, the positive phase input terminal and the negative phase input terminal of the amplifier are used as the two current detection terminals of the synchronous rectification control unit, and the control terminal of the power tube is connected to the control terminal of the amplifier; the positive phase input terminal of the voltage comparator is connected to the output terminal of the amplifier, the negative phase input terminal of the voltage comparator is connected to the operation unit, and the output terminal of the voltage comparator is connected to the second controller; The operation unit calculates an output voltage based on the input information according to the inductance of Qg and the diode conduction voltage Vdiode, which serves as the judgment threshold of the COMP2 voltage comparator; compares the voltage signal of the sampled current with the voltage of the operation unit, and outputs a control signal to the second controller; the second controller selects whether the synchronous rectifier tube of the current cycle is turned on based on the signal of the COMP2 voltage comparator and PWM_IN.

2. A synchronous converter control circuit according to claim 1, characterized in that: The output unit also includes: A first inductor, wherein the first inductor is connected in series between the switch node and the sampling resistor; A capacitor, the capacitor is connected in series to the sampling resistor and the second end of the synchronous rectifier; A load resistor is connected in parallel to both ends of the capacitor.

3. A synchronous converter control circuit according to claim 1, characterized in that: The operation unit is of the first type or the second type; the first type is a numerical operation unit and a DAC; the second type is an analog operation unit.

4. The synchronous converter control circuit according to claim 1, characterized in that: The conduction loss of the body diode W1 = Vdiode*ipeak*0.5*(Δtfw / T); The loss when the synchronous rectifier is turned on is W2 = W 导通损耗 +W 开关损耗 =(1 / 4)*ipeak 2 *Ron*(Δtfw / T)+Vin*(Qg / T); When W1>W2, the synchronous rectifier is turned on; When W1<W2, the synchronous rectifier is turned off.

5. The synchronous converter control circuit according to claim 1, characterized in that: The power tube is an enhanced NMOS tube, and the synchronous rectifier tube is an enhanced NMOS tube.

6. The synchronous converter control circuit according to claim 1, characterized in that: The zero-crossing detection unit includes a voltage comparator, a positive phase input terminal of the voltage comparator is connected to the switch node, a negative phase input terminal of the voltage comparator is grounded, and an output terminal of the voltage comparator is connected to the second controller.

7. The synchronous converter control circuit according to claim 1, characterized in that: The first controller and the second controller are integrated into the same controller.

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