Output voltage regulating circuit and switching power supply

Abstract

The utility model discloses an output voltage regulation circuit and a switching power supply, and the output voltage regulation circuit comprises a voltage division circuit which comprises a first voltage division device and a second voltage division device, one end of the first voltage dividing device is connected with the output end of the switching power supply, the other end of the first voltage dividing device is connected with one end of the second voltage dividing device and then connected with the reference end of the TL431, and the other end of the second voltage dividing device is used for being connected with the signal ground of the switching power supply; the digital adjusting circuit is connected with the second voltage dividing device in parallel and comprises a switching device and an energy storage device, the control end of the switching device is used for inputting a controllable duty ratio signal, and the charging, discharging and open-circuit states of the energy storage device can be changed by changing the duty ratio of the duty ratio signal, so that the energy storage device can be switched on or switched off. Therefore, the magnitude of the output voltage of the switching power supply is adjusted. A production end is easy to operate, and ripple and dynamic performance are good.

Description

Technical Field

[0001] The utility model relates to the technical field of power supply, in particular to an output voltage regulating circuit and a switching power supply. Background Art

[0002] The switching power supply with regulated output will achieve output voltage stability through the control loop. The control loop generally compares the output voltage of the switching power supply with the reference voltage through TL431, and adjusts the current of the feedback pin of the control IC according to the comparison result, so as to achieve the output voltage stability of the switching power supply. However, different devices and scenarios often have certain requirements for the power supply voltage. Therefore, the switching power supply generally requires an output voltage regulation circuit to adjust the output voltage, and the corresponding load can be connected only after the required voltage is obtained.

[0003] The existing switching power supply output voltage regulation circuit design generally uses Figure 1 In the circuit shown, the optocoupler U2 and the left side thereof are the feedback circuit of the switching power supply, which can provide a feedback signal to the control IC of the main power switch tube of the switching power supply by adjusting the size of the FB current, so as to realize the closed-loop control of the switching power supply; the main function of the resistor R6 is to ensure that the working current is provided to the TL431 device U1; the resistor R5, the capacitor C2 and the TL431 device U1 are the loop module of the switching power supply, which constitute the feedback circuit to realize the effective feedback of the voltage loop; the resistor R1, the resistor R2 and the potentiometer R3 are the output voltage adjustment circuit, which are used to adjust the output voltage of the switching power supply.

[0004] Figure 1 The working principle of the circuit regulating the output voltage of the switching power supply is: the potentiometer R3 is connected in series to the output voltage sampling circuit composed of the resistor R1 and the resistor R2, and different lower bias resistances are obtained by adjusting the resistance value of the potentiometer R3, so as to adjust the current flowing through the upper bias resistance, thereby realizing the output voltage regulation function. This circuit structure is very simple, but the potentiometer R3 needs to be adjusted manually, and the voltage adjustment is relatively troublesome, so it is not easy to operate during the production process.

[0005] There is also a commonly used output voltage regulation circuit in the prior art, such as Figure 2 As shown in the figure, the output voltage of the switching power supply is adjusted by the operational amplifier control method. Since this circuit uses an operational amplifier for comparison control, the operational amplifier itself has a slow adjustment speed, so the ripple and dynamic performance are poor. Utility Model Content

[0006] In view of this, the technical problem to be solved by the present invention is to provide an output voltage regulation circuit and a switching power supply, which can at least solve the deficiencies of the above-mentioned prior art to a certain extent.

[0007] As a first aspect of the present invention, the technical solution of the embodiment of the output voltage regulation circuit provided is as follows:

[0008] An output voltage regulating circuit is applied to a switching power supply. The switching power supply compares the output voltage of the switching power supply with a reference voltage through a TL431, and adjusts the current of a feedback pin of a control IC according to the comparison result, thereby achieving control of the output voltage stability of the switching power supply. The output voltage regulating circuit includes:

[0009] The voltage divider circuit comprises a first voltage divider device and a second voltage divider device; one end of the first voltage divider device is used to connect to the output end of the switching power supply; the other end of the first voltage divider device and one end of the second voltage divider device are connected together as the output end of the voltage divider circuit, which is used to connect to the reference end of the TL431; the other end of the second voltage divider device is used to connect to the signal ground of the switching power supply;

[0010] The digital regulation circuit is connected in parallel with the second voltage divider device, and includes a switch device and an energy storage device. The control end of the switch device is used to input a controllable duty cycle signal. By changing the duty cycle of the duty cycle signal, the charging, discharging and open circuit states of the energy storage device can be changed, thereby changing the current flowing through the first voltage divider device, thereby adjusting the output voltage of the switching power supply.

[0011] Preferably, the first voltage divider is a resistor R1.

[0012] Preferably, the second voltage divider is a resistor R2.

[0013] Preferably, the digital adjustment circuit also includes a resistor R3 and a resistor R4, one end of the resistor R3 is connected to one end of the second voltage divider device, the other end of the resistor R3 and one end of the energy storage device are simultaneously connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the switching device, and the other end of the energy storage device and the other end of the switching device are simultaneously connected to the other end of the second voltage divider device.

[0014] Preferably, the first voltage divider is a resistor R1, and the second voltage divider is a resistor R2;

[0015] The digital adjustment circuit also includes a resistor R3 and a resistor R4, one end of the resistor R3 is connected to one end of the second voltage divider device, the other end of the resistor R3 and one end of the energy storage device are simultaneously connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the switch device, and the other end of the energy storage device and the other end of the switch device are simultaneously connected to the other end of the second voltage divider device.

[0016] Preferably, the switching device is a MOS tube.

[0017] Preferably, the energy storage device is a capacitor C1.

[0018] As a second aspect of the present invention, the technical solution of the embodiment of the switching power supply provided is as follows:

[0019] A switching power supply, which compares the output voltage of the switching power supply with a reference voltage through TL431, and adjusts the current of a feedback pin FB of a control IC according to the comparison result, thereby achieving control of the output voltage stability of the switching power supply, wherein: the switching power supply also includes the output voltage regulation circuit described in any one of the first aspects above.

[0020] Furthermore, the switching device is controlled to be turned on and off by a digital chip.

[0021] The beneficial effects of the utility model are:

[0022] (1) Compared with using a potentiometer to adjust the output voltage, the output voltage adjustment circuit embodiment of the utility model can not only set the output voltage by setting a fixed duty cycle, but also control the duty cycle by setting the output voltage. When the output voltage is larger than the set value, the duty cycle can be increased, and when the output voltage is smaller than the set value, the duty cycle can be reduced, so as to achieve the purpose of easy operation at the production end, greatly shorten the production operation time and meet the requirements of high-precision output;

[0023] (2) Compared with the use of an op amp to adjust the output voltage, the output voltage adjustment circuit embodiment of the utility model adopts the control method of TL431, which has a faster response speed and better ripple and dynamic performance than the op amp control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The circuit diagram of the prior art adopting a potentiometer to adjust the output voltage of a switching power supply;

[0025] Figure 2 The circuit diagram is for adjusting the output voltage of the switching power supply by using the operational amplifier control method;

[0026] Figure 3 The utility model is a schematic diagram of a specific output voltage regulating circuit for controlling the output voltage of a switching power supply. DETAILED DESCRIPTION

[0027] In order to make the above-mentioned purposes, features and advantages of the utility model more obvious and easy to understand, the specific implementation methods of the utility model are described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the utility model, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0028] It should be noted that the terms "including" and "having" and any variations thereof described in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, the inclusion of a series of components, unit circuits or control timings is not necessarily limited to those components, unit circuits or control timings clearly listed, but may include components, unit circuits or control timings that are not clearly listed or inherent to these circuits.

[0029] In addition, the embodiments and features of the embodiments in this application may be combined with each other if there is no conflict.

[0030] It should be understood that, in the specification and the claims, when an element is described as being “connected” to another element, the element may be “directly connected” to the other element, or be “connected” to the other element through a third element; when a step is described as being continued to another step, the step may be directly continued to the other step, or be continued to the other step through a third step.

[0031] First embodiment

[0032] The present embodiment provides an output voltage regulation circuit, which is applied to a switching power supply. The switching power supply compares the output voltage of the switching power supply with a reference voltage through TL431, and adjusts the current of the feedback pin of the control IC according to the comparison result, thereby achieving the output voltage stability of the switching power supply. Figure 3 The following is a schematic diagram of a specific output voltage regulating circuit of the utility model for controlling the output voltage of a switching power supply, wherein the output voltage regulating circuit includes:

[0033] The voltage divider circuit comprises a first voltage divider device and a second voltage divider device; one end of the first voltage divider device is used to connect to the output end of the switching power supply; the other end of the first voltage divider device and one end of the second voltage divider device are connected together as the output end of the voltage divider circuit, which is used to connect to the reference end of TL431; the other end of the second voltage divider device is used to connect to the signal ground of the switching power supply;

[0034] The digital regulation circuit is connected in parallel with the second voltage divider device, and includes a switching device and an energy storage device. The control end of the switching device is used to input a controllable duty cycle signal. By changing the duty cycle of the duty cycle signal, the charging, discharging and open circuit states of the energy storage device can be changed, thereby changing the current flowing through the first voltage divider device, thereby adjusting the output voltage of the switching power supply.

[0035] The operating method of the output voltage regulation circuit of this embodiment when performing voltage regulation at the production end is: the duty cycle of the switch drive signal when the switching power supply outputs the rated voltage is set as a reference value. When the required output voltage is higher than the rated voltage, it can be achieved by increasing the duty cycle of the switch drive signal; when the required output voltage is lower than the rated voltage, it can be achieved by reducing the duty cycle of the switch drive signal.

[0036] Compared with using a potentiometer to adjust the output voltage, the output voltage regulation circuit of this embodiment can not only set the output voltage by setting a fixed duty cycle, but also control the duty cycle by setting the output voltage. When the output voltage is larger than the set value, the duty cycle can be increased, and when the output voltage is smaller than the set value, the duty cycle can be reduced, thereby achieving the purpose of easy operation at the production end, greatly shortening the production operation time and meeting the requirements of high-precision output; compared with using an op amp to adjust the output voltage, the TL431 control method is adopted, and the response speed is faster than the op amp control method, and the ripple and dynamic performance effects are better.

[0037] Please continue to see Figure 3 , wherein the first voltage divider device is a resistor R1.

[0038] Please continue to see Figure 3 , wherein the second voltage divider device is a resistor R2.

[0039] Please continue to see Figure 3 , wherein the digital adjustment circuit also includes a resistor R3 and a resistor R4, one end of the resistor R3 is connected to one end of the second voltage divider device, the other end of the resistor R3 and one end of the energy storage device are simultaneously connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the switch device, and the other end of the energy storage device and the other end of the switch device are simultaneously connected to the other end of the second voltage divider device.

[0040] Please continue to see Figure 3 , where the switching device is MOS tube Q1.

[0041] Please continue to see Figure 3 , where the energy storage device is capacitor C1.

[0042] Below Figure 3 Taking this as an example, the working principle of the output voltage regulation circuit of this embodiment is described as follows:

[0043] The output voltage Vo of the switching power supply has the following relationship with the resistance value R1 of the resistor R1, the current flowing through the resistor R1, and the voltage V1 at the connection point between the other end of the resistor R1 and one end of the resistor R2:

[0044] Vo=V1+R1×I1······Relation 1

[0045] According to Kirchhoff's current law, the current I1 flowing through the resistor R1, the current I2 flowing through the resistor R2, and the current I3 flowing through the resistor R3 satisfy the following relationship:

[0046] I1=I2+I3·······Relation 2

[0047] Substituting equation 2 into equation 1, we can get the following equation:

[0048] Vo=V1+R1×(I2+I3)······Relation 3

[0049] Since the voltage at the reference end of the TL431 device U1 is a fixed voltage, V1 is a fixed value; the resistance value R1 of the resistor R1 is a fixed value; since V1 is a fixed value and the resistance value R2 of the resistor R2 is a fixed value, it can be known from Ohm's law that the current I2 flowing through the resistor R2 is I1 / R2, so I2 is a fixed value; therefore, there is only one variable I3 on ​​the right side of the equation in Relationship 3, so it is necessary to change the current I3 flowing through the resistor R3 to change the output voltage of the switching power supply, and the larger I3 is, the larger the output voltage is, and vice versa, the smaller I3 is, the smaller the output voltage is. Since I3 changes the output voltage of the switching power supply by affecting I1, it can be known from Relationship 1 and Relationship 2 that Figure 3 The circuit can also be considered as changing the output voltage of the switching power supply by changing I1, and the larger the I1, the larger the output voltage, and vice versa, the smaller the I1, the smaller the output voltage.

[0050] It can be seen from Relationship 2 that changing the current I3 flowing through the resistor R3 will change the current I1 flowing through the resistor R1 , and further, according to Relationship 1, it can be seen that the output voltage of the switching power supply is changed.

[0051] The current relationship between the other end of resistor R3, one end of capacitor C1 and one end of resistor R4 can be divided into two cases:

[0052] (1) When the drive signal given by the microcontroller to the gate of MOS tube Q1 is low

[0053] MOS tube Q1 is turned off. At this time, capacitor C1 is in a charging state. The charging circuit is the output of the switching power supply → resistor R1 → resistor R3 → capacitor C1 → ground. The current I3 flowing through resistor R3 is equal to the charging current IC1+ of capacitor C1. As capacitor C1 is continuously charged, capacitor C1 gradually tends to saturation, IC1+ decreases continuously, and therefore IC decreases continuously until the voltage on capacitor C1 reaches V1. At this time, capacitor C1 stops charging and I3 decreases to 0.

[0054] (2) When the drive signal given by the microcontroller to the gate of MOS tube Q1 is high

[0055] MOS tube Q1 is turned on, and the charge stored in capacitor C1 is discharged through resistor R4. The discharge loop is capacitor C1→resistor R4→MOS tube Q1→capacitor C1. The sum of the voltage across capacitor C1 and the voltage across resistor R3 is V1. As capacitor C1 is continuously discharged, the voltage across capacitor C1 gradually decreases. In order to maintain V1 unchanged, the voltage across resistor R3 needs to be gradually increased. Since the resistance value of resistor R3 remains unchanged, the current flowing through resistor R3 needs to be gradually increased until the voltage VC1 on capacitor C1 satisfies VC1 / R4=V1 / (R3+R4). At this time, capacitor C1 stops discharging, IC1- is 0, and the current I3 flowing through resistor R3 and the current I4 flowing through resistor R4 are equal and no longer change.

[0056] As analyzed above, the larger the I3 is, the larger the output voltage is, and vice versa, the smaller the I3 is, the smaller the output voltage is. Since I3 gradually decreases when the driving signal of the MOS tube Q1 is at a low level, the output voltage of the switching power supply will be reduced. When the driving signal of the MOS tube Q1 is at a high level, I3 gradually decreases, which will cause the output voltage of the switching power supply to rise. Therefore, in order to achieve output voltage regulation, the known strategy of the MOS tube Q1 is: the duty cycle of the driving signal of the MOS tube Q1 when the switching power supply outputs the rated voltage is set as a reference value, for example, 50%. When the required output voltage is higher than the rated voltage, it can be achieved by increasing the duty cycle of the driving signal of the MOS tube Q1 so that the time of I3 increasing in each working cycle becomes longer and the time of I3 decreasing becomes shorter; when the required output voltage is lower than the rated voltage, it can be achieved by reducing the duty cycle of the driving signal of the MOS tube Q1 so that the time of I3 decreasing in each working cycle becomes longer and the time of I3 increasing becomes shorter. When the duty cycle of the driving signal of the MOS tube Q1 is reduced to 0, the capacitor C1 is in an open circuit state, and the output voltage of the switching power supply is the lowest at this time.

[0057] Second embodiment

[0058] The present embodiment provides a switching power supply, which compares the output voltage of the switching power supply with a reference voltage through TL431, and adjusts the current of the feedback pin FB of the control IC according to the comparison result, thereby achieving the output voltage stability of the switching power supply, wherein: the switching power supply also includes any output voltage regulation circuit of the first aspect mentioned above.

[0059] Since the switching power supply of this embodiment includes any output voltage regulation circuit of the first aspect mentioned above, it is easy to operate at the production end when adjusting the output voltage, which can greatly shorten the production operation time and meet the requirements of high-precision output, and has better ripple and dynamic performance effects.

[0060] Preferably, the switching device is controlled to be turned on and off by a digital chip.

[0061] The above are only implementation modes of the present invention. It should be pointed out that the above implementation modes should not be regarded as limitations of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An output voltage regulation circuit is applied to a switching power supply, wherein the switching power supply compares the output voltage of the switching power supply with a reference voltage through a TL431, and adjusts the current of the feedback pin of the control IC according to the comparison result, thereby achieving the control of the output voltage stability of the switching power supply, characterized in that: The output voltage regulation circuit comprises: The voltage divider circuit comprises a first voltage divider device and a second voltage divider device; one end of the first voltage divider device is used to connect to the output end of the switching power supply; the other end of the first voltage divider device and one end of the second voltage divider device are connected together as the output end of the voltage divider circuit, which is used to connect to the reference end of the TL431; the other end of the second voltage divider device is used to connect to the signal ground of the switching power supply; The digital regulation circuit is connected in parallel with the second voltage divider device, and includes a switch device and an energy storage device. The control end of the switch device is used to input a controllable duty cycle signal. By changing the duty cycle of the duty cycle signal, the charging, discharging and open circuit states of the energy storage device can be changed, thereby changing the current flowing through the first voltage divider device, thereby adjusting the output voltage of the switching power supply.

2. The output voltage regulation circuit according to claim 1, characterized in that: The first voltage dividing device is a resistor R1.

3. The output voltage regulation circuit according to claim 1, characterized in that: The second voltage divider is a resistor R2.

4. The output voltage regulation circuit according to claim 1, characterized in that: The digital adjustment circuit also includes a resistor R3 and a resistor R4, one end of the resistor R3 is connected to one end of the second voltage divider device, the other end of the resistor R3 and one end of the energy storage device are simultaneously connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the switch device, and the other end of the energy storage device and the other end of the switch device are simultaneously connected to the other end of the second voltage divider device.

5. The output voltage regulation circuit according to claim 1, characterized in that: The first voltage divider is a resistor R1, and the second voltage divider is a resistor R2; The digital adjustment circuit also includes a resistor R3 and a resistor R4, one end of the resistor R3 is connected to one end of the second voltage divider device, the other end of the resistor R3 and one end of the energy storage device are simultaneously connected to one end of the resistor R4, the other end of the resistor R4 is connected to one end of the switch device, and the other end of the energy storage device and the other end of the switch device are simultaneously connected to the other end of the second voltage divider device.

6. The output voltage regulating circuit according to any one of claims 1 to 5, characterized in that: The switch device is a MOS tube.

7. The output voltage regulating circuit according to any one of claims 1 to 5, characterized in that: The energy storage device is a capacitor C1.

8. A switching power supply, wherein the switching power supply compares the output voltage of the switching power supply with a reference voltage through TL431, and adjusts the current of the feedback pin FB of the control IC according to the comparison result, thereby achieving the control of the output voltage of the switching power supply to be stable, characterized in that: The switching power supply further comprises the output voltage regulating circuit as claimed in any one of claims 1 to 7.

9. The switching power supply according to claim 8, characterized in that: The switching device is controlled to be turned on and off by a digital chip.

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