Constant on-time control circuit and power conversion circuit

Abstract

This invention discloses a constant on-time control circuit and a power conversion circuit, belonging to the field of switching power supply technology. It includes: the output terminal of a first operational amplifier connected to the first terminal of a fourth transistor; the second terminal of the fourth transistor connected to the second terminal of the first transistor, the first terminal of the first transistor, the first terminal of the second transistor, and the first terminal of a third transistor; the second terminal of a third resistor connected to the first terminal of a third capacitor and the positive terminal of a first comparator; the second terminal of the third transistor connected to the second terminal of a sixth transistor; the third terminal of the sixth transistor connected to the negative terminal of the first comparator, the first terminal of the fourth capacitor, and the second terminal of a seventh transistor; the first terminal of the seventh transistor connected to the second terminal of a first inverter; and the output terminal of the first comparator connected to the first terminal of a buck converter. This invention can effectively counteract the effects of efficiency, duty cycle, and operating condition variations on the switching frequency, improving power conversion efficiency and output voltage stability.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, and in particular to a constant on-time control circuit and a power conversion circuit. Background Technology

[0002] Constant On-Time (COT) control circuits are control circuits used in switching power supplies that maintain a constant on-time and dynamically adjust the off-time. Compared to traditional constant frequency control circuits, this circuit can quickly adjust the inductor current by changing the off-time when the load undergoes transient changes, exhibiting superior transient response performance. Therefore, it is widely used in power supply systems for digital chips such as central processing units (CPUs), graphics processing units (GPUs), field-programmable gate arrays (FPGAs), and application-specific integrated circuits (ASICs).

[0003] While traditional constant on-time control circuits offer fast response times, their switching frequency varies significantly with load and input / output conditions. This not only increases the difficulty of inductor selection but also complicates electromagnetic interference (EMI) handling. To mitigate frequency fluctuations, existing technologies often employ adaptive constant on-time control circuits, achieving relative stability of the switching frequency while retaining fast response characteristics.

[0004] However, existing adaptive constant on-time control circuits still have significant drawbacks: their switching frequency is easily affected by actual operating conditions such as power conversion efficiency, switching transistor drive conditions, and operating temperature. When the load changes, the drive voltage changes, or the ambient temperature fluctuates, the system conversion efficiency changes, leading to a significant shift in the switching frequency. This makes it difficult to maintain a constant frequency under complex operating conditions and still has adverse effects on inductor parameter matching and electromagnetic interference suppression, failing to meet the requirements of high-precision and high-stability power supply applications. Summary of the Invention

[0005] The present invention aims to provide a constant on-time control circuit and a power conversion circuit.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A constant on-time control circuit is applied to a power conversion circuit. The power conversion circuit includes a constant on-time control circuit and a buck converter. The constant on-time control circuit includes a second resistor, a first terminal of which is connected to the input voltage, a second terminal of which is connected to the first terminal of a fourth resistor and the positive terminal of a first operational amplifier, the second terminal of which is grounded, the negative terminal of the first operational amplifier connected to the third terminal of a fourth transistor and the first terminal of the first resistor, the second terminal of which is grounded, the output terminal of the first operational amplifier connected to the first terminal of the fourth transistor, and the second terminal of the fourth transistor connected to the second terminal of the first transistor, the first terminal of the first transistor, the first terminal of the second transistor, and the first terminal of the third transistor. The third terminal of the first transistor is connected to the third terminal of the second transistor and the third terminal of the third transistor. The second terminal of the second transistor is connected to the second terminal of the fifth transistor. The third terminal of the fifth transistor is connected to the first terminal of the fifth resistor and the first terminal of the third resistor. The second terminal of the fifth resistor is grounded. The second terminal of the third resistor is connected to the first terminal of the third capacitor and the positive terminal of the first comparator. The second terminal of the third capacitor is grounded. The second terminal of the third transistor is connected to the second terminal of the sixth transistor. The third terminal of the sixth transistor is connected to the negative terminal of the first comparator, the first terminal of the fourth capacitor, and the second terminal of the seventh transistor. The second terminal of the fourth capacitor is connected to the third terminal of the seventh transistor and grounded. The first terminal of the seventh transistor is connected to the second terminal of the first inverter.

[0008] Furthermore, the positive terminal of the first comparator is a compensation voltage, and the first comparator outputs a conduction signal with a fixed conduction time; the conduction signal with the fixed conduction time is input to the buck converter to control the conduction time of the buck converter's switching transistor.

[0009] Furthermore, the expression for the compensation voltage is:

[0010] ,

[0011] in, This is the actual duty cycle. For the efficiency under the corresponding working conditions, For output voltage, Input voltage, As the first reference current, k This is the proportionality coefficient. Ron This is the resistance value of the fifth resistor. R 1 represents the resistance value of the first resistor.

[0012] Furthermore, the expression for the fixed conduction time is:

[0013] ,

[0014] in, For the efficiency under the corresponding working conditions, For output voltage, Input voltage, Ron This is the resistance value of the fifth resistor. Con This is the capacitance value of the fourth capacitor.

[0015] Furthermore, the actual switching frequency expression of the buck converter is:

[0016] ,

[0017] in, TON represents the actual duty cycle and the fixed on-time. For the efficiency under the corresponding working conditions, For output voltage, Input voltage, k This is the proportionality coefficient. Ron This is the resistance value of the fifth resistor. Con This is the capacitance value of the fourth capacitor.

[0018] Furthermore, a first signal is input to the fifth transistor, the sixth transistor, and the first terminal of the first inverter.

[0019] Furthermore, the first signal is a pre-stage drive signal for the switching transistors generated inside the buck converter, used to drive the upper and lower switching transistors of the buck converter.

[0020] Furthermore, the first transistor, the second transistor, and the third transistor are P-type MOS transistors, with the first terminal of the first transistor, the second transistor, and the third transistor being the gate, the second terminal of the first transistor, the second transistor, and the third transistor being the drain, and the third terminal of the first transistor, the second transistor, and the third transistor being the source.

[0021] Furthermore, the fourth, fifth, sixth, and seventh transistors are N-type MOS transistors, with the first terminal of each transistor serving as the gate, the second terminal as the drain, and the third terminal as the source.

[0022] A power conversion circuit is provided in which a buck converter completes stable power conversion and load power supply output based on the turn-on signal output by a constant on-time control circuit; a boost converter is also applicable to the power conversion circuit.

[0023] Beneficial effects: This invention provides a constant on-time control circuit and power conversion circuit. By using a current mirror to generate a reference current proportional to the input voltage, and combining it with a PWM signal-controlled switching circuit, a compensation voltage related to the actual duty cycle is generated, which is used as a comparison threshold for on-time timing. At the same time, the on-time is determined by using a constant current to charge the capacitor to the compensation voltage. This allows the buck converter to maintain the advantage of fast transient response with constant on-time while effectively offsetting the influence of efficiency, duty cycle, and operating condition changes on the switching frequency. It achieves stable and constant switching frequency under all operating conditions, improves power conversion efficiency and output voltage stability, and the overall circuit structure is simple, easy to integrate, and has high control precision.

[0024] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0025] Figure 1 This is a circuit topology diagram of a constant on-time control circuit according to the present invention.

[0026] Figure 2 This is a circuit topology diagram of a first specific embodiment of a power conversion circuit according to the present invention.

[0027] Figure 3 This is a circuit topology diagram of a second specific embodiment of a power conversion circuit according to the present invention. Detailed Implementation

[0028] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Figure 1 This is a circuit topology diagram of a constant on-time control circuit according to the present invention. Figure 1 As shown, a constant on-time control circuit 1 includes a resistor R2, the first end of which is connected to the input voltage V. INThe second terminal of resistor R2 is connected to the first terminal of resistor R4 and the positive terminal of operational amplifier AMP. The second terminal of resistor R4 is grounded. The negative terminal of operational amplifier AMP is connected to the third terminal of transistor MN1 and the first terminal of resistor R1. The second terminal of resistor R1 is grounded. The output terminal of operational amplifier AMP is connected to the first terminal of transistor MN1. The second terminal of transistor MN1 is connected to the second terminal of transistor MP1, the first terminal of transistor MP1, the first terminal of transistor MP2, and the first terminal of transistor MP3. The third terminal of transistor MP1 is connected to the third terminal of transistor MP2 and the third terminal of transistor MP3. The second terminal of transistor MP2... Connect the second terminal of transistor MN2. Connect the third terminal of transistor MN2 to the first terminal of resistor Ron and the first terminal of resistor R3. The second terminal of resistor Ron is grounded. Connect the second terminal of resistor R3 to the first terminal of capacitor C3 and the positive terminal of comparator Comp. The second terminal of capacitor C3 is grounded. Connect the second terminal of transistor MP3 to the second terminal of transistor MN3. Connect the third terminal of transistor MN3 to the negative terminal of comparator Comp, the first terminal of capacitor Con, and the second terminal of transistor MN4. Connect the second terminal of capacitor Con to the third terminal of transistor MN4 and grounded. Connect the first terminal of transistor MN4 to the second terminal of inverter INV1.

[0030] Furthermore, transistors MP1, MP2, and MP3 are P-type MOS transistors, with the first terminal of each transistor being the gate, the second terminal being the drain, and the third terminal being the source.

[0031] Furthermore, transistors MN1, MN2, MN3, and MN4 are N-type MOS transistors, with the first terminal of each transistor being the gate, the second terminal being the drain, and the third terminal being the source.

[0032] Figure 2 This is a circuit topology diagram of a first specific embodiment of a power conversion circuit according to the present invention. Figure 2 As shown, a power conversion circuit includes a constant on-time control circuit 1 and a buck converter 2; the first terminal of the buck converter 2 is connected to the output terminal of the comparator Comp; the buck converter 2 completes stable power conversion and load power supply output according to the on-time signal output by the constant on-time control circuit 1.

[0033] Furthermore, the signal PWM1 is input to the first terminal of transistors MN2 and MN3 and inverter INV1.

[0034] Furthermore, signal PWM1 is the pre-stage drive signal for the switching transistors generated inside the buck converter 2, used to drive the upper and lower switching transistors of the buck converter, and is also multiplexed as the timing control signal for the constant on-time control circuit.

[0035] Furthermore, the positive terminal of the comparator Comp is the compensation voltage V. o_new The comparator Comp outputs a turn-on signal PWM2 with a fixed turn-on time.

[0036] Furthermore, a fixed-time conduction signal PWM2 is input to buck converter 2 to control the conduction duration of the switching transistor in buck converter 2.

[0037] The following is combined with Figure 2 This invention introduces the working principle of a constant on-time control circuit. Resistors R2 and R4 are used to control the input voltage V. IN Voltage divider, resistor , ,in k This is the proportionality coefficient. R The resistance is a unit value. Divide the voltage into units. After voltage clamping and impedance isolation by the operational amplifier AMP, the input is fed to a 1:1 proportional current mirror composed of transistors MP1 and MP2. Through the mirroring effect of the current mirror, a reference current proportional to the input voltage is generated in the MP2 branch. Reference current The expression is:

[0038] .

[0039] Generated reference current After passing through transistor MN2, which is controlled by signal PWM1, the current flows through resistor Ron. In the switching power supply, the duty cycle of the PWM signal differs from the actual duty cycle of the buck converter. Maintain consistency, actual duty cycle The expression is:

[0040] ,

[0041] in, For the efficiency under the corresponding working conditions, For output voltage, This is the input voltage.

[0042] When signal PWM1 is high, the upper transistor of the buck converter is turned on and the lower transistor is turned off. At this time, the voltage is smoothed by the low-pass filter formed by resistor R3 and capacitor C3 to obtain the compensation voltage V. o_new Its expression is:

[0043] ,

[0044] in, This is the actual duty cycle. For the efficiency under the corresponding working conditions, For output voltage, This is the input voltage.

[0045] When signal PWM1 is low, the buck converter operates in the off-time TOFF state; at this time, the gate voltage of transistor MN4 is high and it is turned on, and the upper plate of capacitor Con is short-circuited to ground through transistor MN4, and its voltage is reset to zero. When signal PWM1 is high, transistor MN4 is turned off and transistor MN3 is turned on. Transistor MP3 and transistor MP1 are mirrored in a 1:1 ratio to obtain the reference current. ,therefore Reference current As capacitor Con is charged, the voltage across it gradually rises to reach the compensation voltage V. o_new When the comparator Comp detects that the positive terminal voltage is equal to the negative terminal voltage, the output state immediately jumps to the opposite level, controlling the upper transistor of the buck converter to turn off.

[0046] Therefore, it can be seen that during the period when signal PWM1 is at a high level, the reference current... The duration of charging capacitor Con is the fixed on-time TON of the upper transistor in the buck converter, and its expression is:

[0047] ,

[0048] Right now .

[0049] Furthermore, the actual switching frequency expression of the buck converter is:

[0050] ,

[0051] Therefore, by applying this control circuit and eliminating the influence of non-ideal factors, the final switching frequency is only related to the parameters of capacitor Con and resistor Ron.

[0052] Figure 3 This is a circuit topology diagram of a second specific embodiment of a power conversion circuit according to the present invention. Figure 3 As shown, a power conversion circuit includes a constant on-time control circuit 1 and a boost converter 3; the first terminal of the boost converter 3 is connected to the output terminal of the comparator Comp; the boost converter 3 completes stable power conversion and load power supply output according to the on-time signal output by the constant on-time control circuit 1. Figure 3 Working principle and Figure 2 The same applies, so I won't go into details here.

[0053] This invention discloses a constant on-time control circuit and a power conversion circuit. By using a current mirror to generate a reference current proportional to the input voltage, and combining it with a PWM signal-controlled switching circuit, a compensation voltage related to the actual duty cycle is generated, which is used as a comparison threshold for on-time timing. Simultaneously, the on-time is determined by using a constant current to charge the capacitor to the compensation voltage. This allows the buck converter to maintain the advantage of constant on-time and fast transient response while effectively offsetting the influence of efficiency, duty cycle, and operating condition changes on the switching frequency. It achieves stable and constant switching frequency under all operating conditions, improves power conversion efficiency and output voltage stability, and the overall circuit structure is simple, easy to integrate, and has high control precision.

[0054] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A constant on-time control circuit, applied to a power conversion circuit, the power conversion circuit comprising a constant on-time control circuit and a buck converter, characterized in that, The constant on-time control circuit includes: a second resistor, a first terminal of which is connected to the input voltage; a second terminal of which is connected to the first terminal of a fourth resistor and the positive terminal of a first operational amplifier; the second terminal of the fourth resistor is grounded; the negative terminal of the first operational amplifier is connected to the third terminal of a fourth transistor and the first terminal of the first resistor; the second terminal of the first operational amplifier is grounded; the output terminal of the first operational amplifier is connected to the first terminal of the fourth transistor; the second terminal of the fourth transistor is connected to the second terminal of a first transistor, the first terminal of the first transistor, the first terminal of the second transistor, and the first terminal of a third transistor; the third terminal of the first transistor is connected to the third terminal of the second transistor and the third terminal of the third transistor; the second terminal of the second transistor is connected to the second terminal of a fifth transistor; the third terminal of the fifth transistor is connected to the first terminal of a fifth resistor and the first terminal of the third resistor; the second terminal of the fifth resistor is grounded; the second terminal of the third resistor is connected to the first terminal of a third capacitor and the positive terminal of a first comparator; the second terminal of the third capacitor is grounded; the second terminal of the third transistor is connected to the second terminal of a sixth transistor; the third terminal of the sixth transistor is connected to the negative terminal of the first comparator, the first terminal of the fourth capacitor, and the second terminal of a seventh transistor; the second terminal of the fourth capacitor is connected to the third terminal of the seventh transistor and grounded; and the first terminal of the seventh transistor is connected to the second terminal of a first inverter.

2. The constant on-time control circuit as described in claim 1, characterized in that, The positive terminal of the first comparator is a compensation voltage, and the first comparator outputs a conduction signal with a fixed conduction time; the conduction signal with the fixed conduction time is input to the buck converter to control the conduction time of the buck converter's switching transistor.

3. The constant on-time control circuit as described in claim 2, characterized in that, The expression for the compensation voltage is: ， in, This is the actual duty cycle. For the efficiency under the corresponding working conditions, For output voltage, Input voltage, As the first reference current, k This is the proportionality coefficient. Ron This is the resistance value of the fifth resistor. R 1 represents the resistance value of the first resistor.

4. The constant on-time control circuit as described in claim 3, characterized in that, The expression for the fixed conduction time is: ， in, For the efficiency under the corresponding working conditions, For output voltage, Input voltage, Ron This is the resistance value of the fifth resistor. Con This is the capacitance value of the fourth capacitor.

5. The constant on-time control circuit as described in claim 4, characterized in that, The actual switching frequency expression for a buck converter is: ， in, TON represents the actual duty cycle and the fixed on-time. For the efficiency under the corresponding working conditions, For output voltage, Input voltage, k This is the proportionality coefficient. Ron This is the resistance value of the fifth resistor. Con This is the capacitance value of the fourth capacitor.

6. The constant on-time control circuit as described in claim 1, characterized in that, A first signal is input to the fifth transistor, the sixth transistor, and the first terminal of the first inverter.

7. The constant on-time control circuit as described in claim 6, characterized in that, The first signal is a pre-stage drive signal for the switching transistors generated inside the buck converter, used to drive the upper and lower switching transistors of the buck converter.

8. The constant on-time control circuit as described in claim 7, characterized in that, The first transistor, the second transistor, and the third transistor are P-type MOS transistors. The first terminal of the first transistor, the second transistor, and the third transistor is the gate, the second terminal of the first transistor, the second transistor, and the third transistor is the drain, and the third terminal of the first transistor, the second transistor, and the third transistor is the source.

9. The constant on-time control circuit as described in claim 8, characterized in that, The fourth, fifth, sixth, and seventh transistors are N-type MOS transistors. The first terminal of the fourth, fifth, sixth, and seventh transistors is the gate, the second terminal of the fourth, fifth, sixth, and seventh transistors is the drain, and the third terminal of the fourth, fifth, sixth, and seventh transistors is the source.

10. A power conversion circuit, characterized in that, The buck converter completes stable power conversion and load power supply output according to the turn-on signal output by the constant on-time control circuit as described in any one of claims 1-9.

11. A constant on-time control circuit, applied to a power conversion circuit, the power conversion circuit comprising a constant on-time control circuit and a boost converter, characterized in that, The constant on-time control circuit includes: a second resistor, a first terminal of which is connected to the input voltage; a second terminal of which is connected to the first terminal of a fourth resistor and the positive terminal of a first operational amplifier; the second terminal of the fourth resistor is grounded; the negative terminal of the first operational amplifier is connected to the third terminal of a fourth transistor and the first terminal of the first resistor; the second terminal of the first operational amplifier is grounded; the output terminal of the first operational amplifier is connected to the first terminal of the fourth transistor; the second terminal of the fourth transistor is connected to the second terminal of a first transistor, the first terminal of the first transistor, the first terminal of the second transistor, and the first terminal of a third transistor; the third terminal of the first transistor is connected to the third terminal of the second transistor and the third terminal of the third transistor; the second terminal of the second transistor is connected to the second terminal of a fifth transistor; the third terminal of the fifth transistor is connected to the first terminal of a fifth resistor and the first terminal of the third resistor; the second terminal of the fifth resistor is grounded; the second terminal of the third resistor is connected to the first terminal of a third capacitor and the positive terminal of a first comparator; the second terminal of the third capacitor is grounded; the second terminal of the third transistor is connected to the second terminal of a sixth transistor; the third terminal of the sixth transistor is connected to the negative terminal of the first comparator, the first terminal of the fourth capacitor, and the second terminal of a seventh transistor; the second terminal of the fourth capacitor is connected to the third terminal of the seventh transistor and grounded; and the first terminal of the seventh transistor is connected to the second terminal of a first inverter.

12. The constant on-time control circuit as described in claim 11, characterized in that, The positive terminal of the first comparator is a compensation voltage, and the first comparator outputs a conduction signal with a fixed conduction time; the conduction signal with the fixed conduction time is input to the boost converter to control the conduction time of the switch of the boost converter.

13. The constant on-time control circuit as described in claim 11, characterized in that, A first signal is input to the fifth transistor, the sixth transistor, and the first terminal of the first inverter.

14. The constant on-time control circuit as described in claim 13, characterized in that, The first signal is a pre-stage drive signal for the switching transistors generated inside the boost converter, used to drive the upper and lower switching transistors of the boost converter.

15. A power conversion circuit, characterized in that, The boost converter completes stable power conversion and load power supply output according to the turn-on signal output by the constant on-time control circuit as described in any one of claims 11-14.

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