Triangular wave control circuit with small duty ratio compensation

Abstract

The utility model discloses a triangular wave control circuit with small duty ratio compensation, which comprises a power supply end, a grounding end, an input end, a triangular wave circuit and a small duty ratio compensation circuit, the triangular wave circuit comprises a capacitor and a first resistor, the power supply end is used for providing reference voltage to charge the capacitor of the triangular wave circuit, and the grounding end is used for providing reference voltage to charge the capacitor of the triangular wave circuit. The first resistor is used for controlling the charging speed of the capacitor, the input end inputs a pulse signal to the triangular wave circuit, and the small duty ratio compensation circuit is arranged between the power supply end and the triangular wave circuit and used for providing small duty ratio compensation for the triangular wave circuit. According to the utility model, through the small duty ratio compensation circuit, when the power supply end provides a very small reference voltage, the triangular wave control circuit can also acquire the required voltage, and good adjustment can be carried out when the duty ratio is small.

Description

Technical Field

[0001] The utility model relates to the technical field of triangular wave control circuits, and particularly relates to a triangular wave control circuit with small duty cycle compensation. Background Art

[0002] In a switching power supply circuit, PWM control is the most commonly used control method. Among them, the triangular wave circuit is one of the most important circuits affecting the output ripple and accuracy in PWM control. As Figure 1 shown, the traditional triangular wave control circuit consists of a reference voltage plus a square wave with a custom input frequency. The reference voltage charges the capacitor, and the charging speed is determined by the resistor. The waveform measured at the positive pole of the capacitor is the triangular wave. Then, this triangular wave and another custom DC reference voltage pass through a comparator. When the reference voltage is higher than the triangular wave voltage, the desired PWM wave is generated.

[0003] In an actual triangular wave circuit, at the bottom triangle of the triangular wave circuit, the voltage waveform is not an ideal acute angle waveform. Due to the characteristics of the resistor and capacitor, the waveform is similar to a "U" shape. In this case, at a small duty cycle, the reference voltage is very low and often reaches the bottom of the triangular wave. The required voltage cannot be sampled in the circular part of the "U" shape, which causes the PWM wave to be fully on or fully off in this area, generating very large ripple and voltage spikes for the whole machine and affecting the indicators. Summary of the Utility Model

[0004] The purpose of the utility model is to provide a triangular wave control circuit with small duty cycle compensation in order to overcome the deficiencies of the prior art.

[0005] The utility model discloses a triangular wave control circuit with small duty cycle compensation, including a power supply terminal, a grounding terminal, an input terminal, a triangular wave circuit, and a small duty cycle compensation circuit. The triangular wave circuit includes a capacitor and a first resistor. The power supply terminal is used to provide a reference voltage to charge the capacitor of the triangular wave circuit. The first resistor is used to control the capacitor charging speed. The input terminal inputs a pulse signal to the triangular wave circuit. The small duty cycle compensation circuit is arranged between the power supply terminal and the triangular wave circuit and is used to provide a small duty cycle compensation signal for the triangular wave circuit.

[0006] Further, the small duty cycle compensation circuit includes a diode and a second resistor. The positive pole of the diode is connected to the PWM compensation signal, the negative pole of the diode is connected to the second resistor, and the other end of the second resistor is connected between the power supply terminal and the first resistor.

[0007] Further, the frequency of the PWM compensation signal is consistent with the frequency of the pulse signal.

[0008] Further, the diode is an anti-reverse diode, which is used to prevent the reverse flow of the triangular wave voltage.

[0009] Advantages of the present utility model:

[0010] The present utility model provides a small duty cycle compensation signal through a small duty cycle compensation circuit. The small duty cycle compensation signal is emitted after the pulse signal, and its duty cycle is very small. The frequency of the small duty cycle compensation signal is the same as that of the pulse signal. When charging the capacitor of the triangular wave circuit, it will increase the slope of the bottom of the triangular wave, and the waveform at the bottom of the triangular wave becomes a "V" shape. When the power supply terminal provides a very small reference voltage, the triangular wave control circuit can also acquire the required voltage, enabling the triangular wave control circuit to perform good regulation at a small duty cycle. Description of the drawings

[0011] Figure 1 is a traditional triangular wave control circuit.

[0012] Figure 2 is a triangular wave control circuit with small duty cycle compensation disclosed by the present utility model.

[0013] Figure 3 are various waveforms simulated according to the circuit of the present utility model.

[0014] Figure 4 is a partial enlarged view of the change in the bottom slope of the triangular wave after small duty cycle compensation of the present utility model, forming a "V" shape. Detailed implementation manners

[0015] The following will describe in detail the embodiments of the present utility model. These embodiments are implemented on the premise of the technical solution of the present utility model, and detailed implementation manners and specific operation processes are given. However, the protection scope of the present utility model is not limited to the following embodiments.

[0016] Such as Figure 2As shown in the figure, the utility model discloses a triangular wave control circuit with small duty cycle compensation, including: a power supply terminal, a ground terminal, an input terminal, a triangular wave circuit, and a small duty cycle compensation circuit. The triangular wave circuit includes a first capacitor C1, a second capacitor C2, and a first resistor R1. The negative electrodes of the first capacitor C1 and the second capacitor C2 are connected to the ground terminal, the positive electrodes of the first capacitor C1 and the second capacitor C2 are connected together, one end of the first resistor R1 is connected to the power supply terminal, and the other end is connected to the node between the positive electrodes of the first capacitor C1 and the second capacitor C2. The power supply terminal is used to provide a reference voltage to charge the first capacitor C1 and the second capacitor C2 of the triangular wave circuit, and the first resistor R1 is used to control the charging speed of the first capacitor C1 and the second capacitor C2. The input terminal inputs a pulse signal to the positive electrodes of the first capacitor C1 and the second capacitor C2 of the triangular wave circuit, and the waveform measured at the positive electrodes of the first capacitor C1 and the second capacitor C2 is the triangular wave. The first resistor R1 is the triangular wave charging resistor, and its resistance value is set according to the time requirement of the triangular wave slope, without specific resistance value requirements. The small duty cycle compensation circuit is arranged between the power supply terminal and the triangular wave circuit and is used to provide a small duty cycle compensation signal to the triangular wave circuit. The small duty cycle compensation circuit includes a diode D1 and a second resistor R2. The positive electrode of the diode D1 is connected to the PWM compensation signal, the negative electrode of the diode D1 is connected to the second resistor R2, and the other end of the second resistor R2 is connected to the node between the power supply terminal and the first resistor R1. The second resistor R2 is the current limiting resistor of the PWM compensation signal, and generally about a few hundred ohms can be set. The diode D1 is an anti-reverse diode, which is used to prevent the reverse flow of the triangular wave voltage.

[0017] The PWM compensation signal is sent after the pulse signal. The duty cycle of the PWM compensation signal is very small, and the frequency of the PWM compensation signal is the same as that of the pulse signal. When charging the triangular wave circuit, it will increase the slope of the bottom of the triangular wave, and the bottom waveform of the triangular wave becomes a "V" shape. At a very small reference voltage, the required voltage can also be obtained, and it can be well adjusted at a small duty cycle.

[0018] As Figure 3As shown, in this embodiment, taking the resistance value of the first resistor R1 as 2.2 Ω, the resistance value of the second resistor R2 as 200 Ω, the diode D1 as 1N4007 diode, and the pulse signal as a 100KHz pulse square wave (100KHz_Square) as an example, the PWM compensation signal is a small duty cycle compensation square wave (PWM_COM) with the same frequency as the pulse signal. The small duty cycle compensation square wave is not a specific value and the parameters of the peripheral devices need to be changed according to the requirements of the actual circuit. It must be emitted with a value having the same frequency as the pulse square wave. Otherwise, it will cause damage to the machine. The value of the pulse square wave is determined by the switching tube frequency, chip capabilities, magnetic devices, etc. By controlling the charge and discharge processes of the first capacitor C1 and the second capacitor C2, after the 100KHz pulse square wave is emitted, the small duty cycle compensation square wave is emitted. A triangular wave is measured as a sawtooth wave at the positive poles of the first capacitor C1 and the second capacitor C2. Due to the limited bandwidth of the control chip and the limited sampling accuracy of the sampling circuit, when sampling at the bottom of the triangular wave circuit, without this compensation circuit, it can be seen from the waveform that its slope is relatively gentle. Assuming that the sampling range on the X-axis is 0.1 - 0.2, the voltage on the Y-axis may only rise by 0.01, and this 0.01V has a negligible change after passing through the sampling circuit and cannot be recognized by the main control chip. It can be seen from the green sawtooth wave waveform in the figure that the triangular wave with the small duty cycle compensation circuit rises along the bottom. At this time, the sawtooth wave is not a pure triangular waveform, but in the process of rising from the bottom, at the just rising stage, the slope changes and the waveform becomes steeper. When the X-axis changes by 0.1, the change amount on the Y-axis may reach 0.05 or more, so that it can be recognized by the main control chip after passing through the sampling circuit. As Figure 4 shown, assuming that the original slope angle of the triangular wave rises at 45°, then at the initial stage of just rising, the slope may be 80°, forming a "V" shape. When sampling at a very low voltage, a very small voltage change will result in a relatively obvious change in the range value, so it facilitates the sampling accuracy and thus improves the overall accuracy. The yellow line shows the reference voltage output of the AD5660 digital-to-analog conversion. This voltage is adjustable and is compared with the triangular wave. In a common comparator circuit, the comparator normally outputs a high level. When the triangular wave waveform reaches a part higher than the yellow line, the voltage output of the comparator flips, forming a drive waveform.

[0019] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A triangular wave control circuit with small duty cycle compensation, characterized in that: include: A power supply end, a ground end, an input end, a triangular wave circuit and a small duty cycle compensation circuit, wherein the triangular wave circuit includes a capacitor and a first resistor, the power supply end is used to provide a reference voltage to charge the capacitor of the triangular wave circuit, the first resistor is used to control the capacitor charging speed, the input end inputs a pulse signal to the triangular wave circuit, and the small duty cycle compensation circuit is arranged between the power supply end and the triangular wave circuit, and is used to provide a small duty cycle compensation signal for the triangular wave circuit.

2. The triangular wave control circuit with small duty cycle compensation according to claim 1, characterized in that: The small duty cycle compensation circuit includes a diode and a second resistor, wherein the anode of the diode is connected to the PWM compensation signal, the cathode of the diode is connected to the second resistor, and the other end of the second resistor is connected between the power supply terminal and the first resistor.

3. The triangular wave control circuit with small duty cycle compensation according to claim 2, characterized in that: The frequency of the PWM compensation signal is consistent with the frequency of the pulse signal.

4. The triangular wave control circuit with small duty cycle compensation according to claim 2, characterized in that: The diode is an anti-reverse diode, which is used to prevent the triangular wave voltage from flowing back.

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