A circuit for dynamically regulating output voltage in a switching power supply

Abstract

The utility model provides a kind of circuit of dynamic regulation output voltage in switching power supply, the input end of low pass filter circuit in this circuit is connected TRIM voltage signal, output connects the source of NMOS switch tube, the drain of NMOS switch tube is connected the feedback port of PWM control chip and the output port of output voltage setting circuit after a fourth resistance, the output positive terminal of switching power supply is connected the input port of output voltage setting circuit, the input of delay open circuit is connected TRIM voltage signal, output connects the gate of NMOS switch tube, the TRIM voltage signal is the square waveform of adjustable duty ratio, the voltage of PWM control chip feedback port is controlled at 0.8V by PWM control chip inside;The utility model provides this kind of circuit of dynamic regulation output voltage in switching power supply, for dynamic external TRIM voltage signal, the up-regulation or down-regulation of switching power supply output voltage is realized by simple circuit, safe and reliable, easy to realize, low in cost.

Description

Technical Field

[0001] This utility model relates to the field of switching power supplies, and in particular to a circuit for dynamically adjusting the output voltage in a switching power supply. Background Technology

[0002] In switching power supply applications, the client adjusts the output voltage as needed. In a typical switching power supply circuit, there is a TRIM PIN in the output pin. The TRIM PIN is connected to the output voltage control loop circuit through an external resistor. Pulling up a resistor between the TRIM PIN and the positive terminal of the output voltage can increase the output voltage, while connecting a resistor between the TRIM PIN and the negative terminal of the output voltage can decrease the output voltage. In this type of application, the client requires a fixed output voltage. The value of the pull-up or pull-down resistor is determined by comparing the client's required voltage with the module's default output voltage. In the conventional applications described above, the voltage signal fed back to the voltage loop from the TRIM PIN is a stable voltage signal. However, in some applications, customers require the output voltage of the switching power supply module to be dynamically adjustable. For example, the output voltage should be adjusted promptly under light and heavy load conditions. The microcontroller in the customer's system circuit issues a dynamic PWM signal based on the load conditions. The customer wants to directly use the dynamic PWM signal to adjust the output voltage of the switching power supply module, with different PWM duty cycles resulting in different output voltages. In this case, for the switching power supply, the TRIM signal is the PWM signal issued by the customer's microcontroller. The PWM signal is a dynamic duty cycle signal, and using the dynamic PWM duty cycle signal to directly adjust the output voltage makes the traditional voltage TRIM circuit no longer suitable.

[0003] To address the aforementioned problems, this invention provides a circuit for dynamically adjusting the output voltage in a switching power supply. Utility Model Content

[0004] The technical problem solved by this utility model is to provide a circuit for dynamically adjusting the output voltage in a switching power supply.

[0005] The technical solution adopted by this utility model to solve the above-mentioned technical problems is as follows: a circuit for dynamically adjusting the output voltage in a switching power supply. The circuit includes a low-pass filter circuit, an NMOS switch, a delay turn-on circuit, an output voltage setting circuit, and a PWM control chip. The input terminal of the low-pass filter circuit is connected to a TRIM voltage signal, and the output is connected to the source of the NMOS switch. The drain of the NMOS switch is connected to the feedback port of the PWM control chip and the output port of the output voltage setting circuit through a fourth resistor. The input port of the output voltage setting circuit is connected to the positive output terminal of the switching power supply. The input of the delay turn-on circuit is connected to a TRIM voltage signal, and the output is connected to the gate of the NMOS switch. The TRIM voltage signal is a square wave with an adjustable duty cycle. The voltage at the feedback port of the PWM control chip is controlled internally by the PWM control chip at 0.8V.

[0006] Furthermore, the low-pass filter circuit includes a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, and a comparator. One end of the first resistor is connected to one end of the second resistor and the TRIM voltage signal. The other end of the second resistor is connected to one end of the third resistor and one end of the second capacitor. The other end of the third resistor and one end of the first capacitor are connected to the positive input terminal of the comparator. The negative input terminal of the comparator is connected to the output terminal of the comparator, the other end of the second capacitor, and the source of the NMOS switch. The other end of the first capacitor and the other end of the first resistor are grounded.

[0007] Furthermore, the delayed turn-on circuit includes a diode, a fifth resistor, a sixth resistor, and a third capacitor. The anode of the diode is connected to the TRIM voltage signal, the cathode is connected to one end of the fifth resistor, the other end of the fifth resistor is connected to the gate of the NMOS switch, and the sixth resistor and the third capacitor are connected in parallel between the gate of the NMOS switch and ground.

[0008] Furthermore, the output voltage setting circuit includes a seventh resistor, an eighth resistor, a ninth resistor, and a fourth capacitor. One end of the seventh resistor is connected to the positive output terminal of the switching power supply, and the other end is connected to one end of the eighth resistor and the feedback port of the PWM control chip. The ninth resistor is connected in series with the fourth capacitor and then in parallel across the seven resistor. The other end of the eighth resistor is grounded.

[0009] Furthermore, the PWM control chip is an analog control chip.

[0010] The technical advantages achieved by this utility model compared to existing designs are as follows:

[0011] The circuit for dynamically adjusting the output voltage in a switching power supply provided by this utility model can achieve the upward or downward adjustment of the output voltage of the switching power supply using a simple circuit for dynamic external TRIM voltage signals. It is safe, reliable, and low in cost. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the circuit structure for dynamically adjusting the output voltage in the switching power supply provided by this utility model. Detailed Implementation

[0013] The embodiments of the circuit of this utility model are given below with reference to the accompanying drawings to illustrate the technical solution of this utility model in detail.

[0014] as follows Figure 1 This invention provides a circuit for dynamically adjusting the output voltage in a switching power supply. The circuit includes a low-pass filter circuit 10, an NMOS switch Q1, a delay-on circuit 20, an output voltage setting circuit 30, and a PWM control chip. The input of the low-pass filter circuit 10 is connected to a TRIM voltage signal, and its output is connected to the source of the NMOS switch Q1. The drain of Q1 is connected to the feedback port of the PWM control chip and the output port of the output voltage setting circuit 30 via a fourth resistor R4. The input port of circuit 30 is connected to the positive output terminal Vout+ of the switching power supply. The input of the delay-on circuit 20 is connected to the TRIM voltage signal, and its output is connected to the gate of Q1. The TRIM voltage signal is a square wave with an adjustable duty cycle. The voltage at the feedback port of the PWM control chip is internally controlled at 0.8V.

[0015] The low-pass filter circuit 10 includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, and a comparator IC1. One end of R1 is connected to one end of R2 and the TRIM voltage signal. The other end of R2 is connected to one end of R3 and one end of C2. The other end of R3 and one end of C1 are connected to the positive input terminal IN+ of IC1. The negative input terminal IN- of IC1 is connected to the output terminal of IC1, the other end of C2, and the source of Q1. The other end of C1 and the other end of R1 are grounded.

[0016] The delayed turn-on line 20 includes a diode CR1, a fifth resistor R5, a sixth resistor R6, and a third capacitor C3. The anode of CR1 is connected to the TRIM voltage signal, the cathode of CR1 is connected to one end of R5, the other end of R5 is connected to the gate of the NMOS switch Q1, and R6 and C3 are connected in parallel between the gate of Q1 and ground.

[0017] The output voltage setting line 30 includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, and a fourth capacitor C4. One end of R7 is connected to the positive output terminal Vout+ of the switching power supply, and the other end is connected to one end of R8 and the feedback port of the PWM control chip. R9 is connected in series with C4 and then in parallel across the two ends of R7. The other end of R8 is grounded.

[0018] The TRIM voltage signal is a square wave with an adjustable duty cycle. After passing through low-pass filter circuit 10, the TRIM signal reaches the source of Q1. The source voltage of Q1, VQ1_S, is equal to the TRIM amplitude multiplied by the TRIM duty cycle. Q1 is the switching transistor for the TRIM signal. When there is no TRIM voltage or the duty cycle is extremely small, the TRIM function is disabled, allowing the module to output a normal voltage. Circuit 20 controls the on / off state of Q1. Due to the presence of relevant RC parameters such as CR1, R5, R6, and C3, it serves to perform peak charging and delay the on / off of Q1 when a TRIM signal is present. This prevents the module from triggering overvoltage protection and shutting down when the switching power supply intervenes with the voltage loop too quickly at the moment of TRIM power-on.

[0019] The feedback port of the PWM control chip is connected to the inverting input of an internal error amplifier. The voltage at the non-inverting input of the error amplifier is stabilized at 0.8V by the internal reference voltage of the PWM control chip. The virtual short and virtual open characteristics of the error amplifier input ensure that the voltage at the inverting input is stabilized at 0.8V, i.e., the voltage of FB is stabilized at 0.8V, thus achieving the purpose of controlling and regulating the output voltage. The voltages at the drains of line 30 and Q1 are superimposed using the superposition theorem to ensure that the target voltage of the feedback signal FB is 0.8V.

[0020] While specific embodiments of this utility model have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of this utility model. Therefore, the scope of protection of this utility model is defined by the appended claims.

Claims

1. A circuit for dynamically adjusting the output voltage in a switching power supply, characterized in that, The circuit includes a low-pass filter circuit, an NMOS switch, a delay turn-on circuit, an output voltage setting circuit, and a PWM control chip. The input of the low-pass filter circuit is connected to the TRIM voltage signal, and the output is connected to the source of the NMOS switch. The drain of the NMOS switch is connected to the feedback port of the PWM control chip and the output port of the output voltage setting circuit through a fourth resistor. The input port of the output voltage setting circuit is connected to the positive output of the switching power supply. The input of the delay turn-on circuit is connected to the TRIM voltage signal, and the output is connected to the gate of the NMOS switch. The TRIM voltage signal is a square wave with an adjustable duty cycle; The voltage at the feedback port of the PWM control chip is controlled internally at 0.8V.

2. The circuit for dynamically adjusting the output voltage in a switching power supply as described in claim 1, characterized in that, The low-pass filter circuit includes a first resistor, a second resistor, a third resistor, a first capacitor, a second capacitor, and a comparator. One end of the first resistor is connected to one end of the second resistor and the TRIM voltage signal. The other end of the second resistor is connected to one end of the third resistor and one end of the second capacitor. The other end of the third resistor and one end of the first capacitor are connected to the positive input terminal of the comparator. The negative input terminal of the comparator is connected to the output terminal of the comparator, the other end of the second capacitor, and the source of the NMOS switch. The other end of the first capacitor and the other end of the first resistor are grounded.

3. The circuit for dynamically adjusting the output voltage in a switching power supply as described in claim 1, characterized in that, The delayed turn-on circuit includes a diode, a fifth resistor, a sixth resistor, and a third capacitor. The anode of the diode is connected to the TRIM voltage signal, the cathode is connected to one end of the fifth resistor, the other end of the fifth resistor is connected to the gate of the NMOS switch, and the sixth resistor and the third capacitor are connected in parallel between the gate of the NMOS switch and ground.

4. The circuit for dynamically adjusting the output voltage in a switching power supply as described in claim 1, characterized in that, The output voltage setting circuit includes a seventh resistor, an eighth resistor, a ninth resistor, and a fourth capacitor. One end of the seventh resistor is connected to the positive output terminal of the switching power supply, and the other end is connected to one end of the eighth resistor and the feedback port of the PWM control chip. The ninth resistor is connected in series with the fourth capacitor and then in parallel across the seven resistor. The other end of the eighth resistor is grounded.

5. The circuit for dynamically adjusting the output voltage in a switching power supply as described in claim 1, characterized in that, The PWM control chip is an analog control chip.

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