Switching power source control circuit and switching power source

[0032] In order to have a clearer understanding of the technical features, objectives and effects of the present invention, the present invention will now be described in further detail with reference to the drawings and embodiments.

[0033] In view of the problems in the prior art, the present invention proposes a switching power supply control circuit. The switching power supply control circuit samples the voltage output by the switching power supply and feeds it back to the control circuit to adjust the current of the transformer primary winding, thereby adjusting the transformer. The output voltage of the auxiliary winding can provide a suitable working voltage for the control circuit, so that the control circuit can work within the normal working range, reduce loss and extend the service life of the switching power supply.

[0034] Such as figure 1 As shown, in the switching power supply control circuit of the present invention, the switching power supply control circuit includes:

[0035] Transformer T101, which includes primary winding, secondary winding and auxiliary winding;

[0036] The power supply circuit 103, connected to the auxiliary winding, is used to input the auxiliary voltage output by the auxiliary winding, and output the power supply voltage based on the auxiliary voltage;

[0037] The power switch 102 is connected to the primary winding;

[0038] The output circuit 105 is connected to the secondary winding;

[0039] The sampling feedback circuit 104 is connected to the output circuit 105 to output a feedback signal;

[0040] The control circuit 101 is respectively connected with the sampling feedback circuit 104, the power switch 102 and the power supply circuit 103, and controls the current in the primary winding through the power switch 102 based on the feedback signal, so that the secondary winding outputs a variable power supply voltage and at the same time makes the auxiliary The auxiliary voltage output by the winding provides a supply voltage to the control circuit 102 through the power supply circuit 103.

[0041] Further, the switching power supply control circuit of the present invention further includes a rectifier circuit 106, connected between the AC mains output terminal and the primary winding of the transformer T101, for inputting AC voltage, and rectifying and outputting the rectified voltage to the original transformer T101 based on the AC voltage. The side windings supply power to the transformer T101.

[0042] In the embodiment of the present invention, the switching power supply control circuit further includes an overvoltage detection circuit 107, which is connected to the auxiliary winding for inputting the auxiliary voltage output by the second auxiliary winding and outputting the detection voltage to the control circuit 106; If the control circuit 106 detects that the detection voltage is higher than the safe working voltage of the control circuit 106, the control circuit 106 outputs a stop control signal inside it to stop the control circuit 106 from working, thereby ensuring that the control circuit 106 is within the safe working voltage. Work to ensure the safety of the switching power supply and improve the safety performance of the switching power supply.

[0043] specifically:

[0044] The primary winding of the transformer T101 is used to charge and store energy in each cycle of the AC voltage and during the turn-on process, and the control circuit 101 controls the turn-on and turn-off through the power switch 102. Preferably, the transformer T101 of the present invention is a flyback transformer. According to the working principle of the flyback transformer, when the primary winding of the transformer T101 is in the charging process, the secondary winding and auxiliary winding are not working, and the transformer T101 During the charging process of the primary winding, energy is stored in the gap of the transformer T101. When the primary winding of the transformer T101 is disconnected from the power supply, that is, the control circuit 101 controls the primary winding of the transformer T101 to be disconnected through the power switch 102. At this time, energy is transferred to the secondary winding and the auxiliary winding, in other words, in the transformer When the primary winding of T101 is disconnected from the power supply, the secondary winding and auxiliary winding start to work at the same time, generating an induced voltage. Preferably, the voltage output by the secondary winding is used as the power supply voltage of the switching power supply. In the embodiment of the present invention, figure 1 It can be seen that the voltage output by the secondary winding is output by the output circuit 105 to output the power supply voltage. The auxiliary voltage output by the auxiliary winding is used as the power supply voltage of the control circuit 101, and the power supply voltage is output to the control circuit 101 via the power supply circuit 103.

[0045] by figure 1 It can be seen that, in the embodiment of the present invention, the auxiliary winding of the transformer T101 includes a first auxiliary winding and a second auxiliary winding, which are respectively connected to the power supply circuit 103. Preferably, the number of turns of the first auxiliary winding is greater than the number of turns of the second auxiliary winding, and the number of turns of the first auxiliary winding and the number of turns of the second auxiliary winding are wound in a preset ratio. It is understandable that the preset ratio of the number of turns of the coils wound by the first auxiliary winding and the second auxiliary winding is determined according to the power supply voltage output by the switching power supply, which is not specifically limited in the present invention.

[0046] Further, in the embodiment of the present invention, the auxiliary winding and the secondary winding of the transformer T101 are in the same phase, and the voltage output by the auxiliary winding varies with the power supply voltage output by the output circuit 105. For example, when the power supply voltage output by the output circuit 105 is 5V, according to the requirements of the circuit design, the output voltage of the auxiliary winding is 15V. The parameters such as the number of turns of the auxiliary winding coil and the diameter of the wire can be selected according to actual requirements, which are not required by the present invention.

[0047] Such as figure 2 As shown, the power supply circuit 103 includes a first power supply circuit 1031 and a second power supply circuit 1032. The first power supply circuit 1031 is connected to the first auxiliary winding for inputting the auxiliary voltage output by the first auxiliary winding, and according to the first auxiliary voltage output by the first auxiliary winding, outputting the first supply voltage to supply power to the control circuit 101. The second power supply circuit 1032 is connected to the second auxiliary winding for outputting the second auxiliary voltage output by the second auxiliary winding, and outputs the second supply voltage according to the second auxiliary voltage output by the second auxiliary winding to supply power to the control circuit 101. Understandably, when the first power supply circuit 1031 supplies power to the control circuit 101, the second power supply circuit 1032 does not work; when the second power supply circuit 1032 supplies power to the control circuit 101, the first power supply circuit 1031 does not work.

[0048] In the embodiment of the present invention, since the first power supply circuit 1031 is provided with the voltage stabilization circuit 200, the first power supply voltage output by the first power supply circuit is stabilized near the voltage stabilization value set by the voltage stabilization circuit 200. The voltage stabilization value of the voltage stabilization circuit 200 is usually determined by the relationship between the minimum voltage output by the switching power supply and the auxiliary voltage. For example, the minimum voltage output by the output circuit 105 is 5V. According to the requirements of the circuit design, the auxiliary voltage output by the auxiliary winding of the transformer T101 is 15V. At this time, the voltage stabilizing value set by the stabilizing circuit 200 in the first power supply circuit 1031 The voltage value of the first power supply voltage is maintained at about 15V due to the function of the voltage stabilizing circuit 200, and because the second power supply circuit 1032 is not provided with the voltage stabilizing circuit 200, and the number of turns of the second auxiliary winding is smaller than that of the first auxiliary winding. The number of turns of the winding. At this time, the second auxiliary voltage output by the second auxiliary winding is less than 15V, that is, the second power supply voltage output by the second power supply circuit is less than 15V. The first power supply circuit 1031 supplies power to the control circuit 101. The power supply circuit 1032 does not work. When the power supply voltage output by the switching power supply continues to rise, due to the function of the voltage stabilizing circuit 200, the voltage output by the first power supply circuit is maintained at about 15V, and the second auxiliary voltage increases in proportion to the power supply voltage output by the switching power supply. When the second auxiliary voltage rises to greater than 15V, the output voltage of the second power supply circuit is greater than 15V. At this time, the first power supply circuit 1031 does not work, and the second power supply circuit 1032 supplies power to the control circuit 101.

[0049] Preferably, the auxiliary voltage output by the auxiliary winding of the transformer T101 is determined by the voltage generated by the secondary winding of the transformer T101. In the embodiment of the present invention, assuming that the power supply voltage output by the output circuit 105 is 5V-20V, the power supply voltage can be segmented. Generally, the power supply voltage 5V-15 can be a low voltage, and 15V-20V can be a high voltage. Therefore, if the secondary winding of the transformer T101 produces a high voltage, that is, the power supply voltage output by the output circuit 105 is 15V-20V, due to the voltage stabilization effect of the voltage stabilizing circuit 200 in the first power supply circuit 1031, the first power supply circuit outputs The first power supply voltage is maintained at about 15V (the voltage stabilization value of the stabilizing circuit 200 is set to 15V). At this time, the first power supply voltage is smaller than the second power supply voltage. At this time, the first power supply circuit 1031 does not work, and the second The power supply circuit 1032 supplies power to the control circuit 101. If the secondary winding of the transformer T101 generates a low voltage, that is, the power supply voltage output by the output circuit 105 is 5V-15V, due to the voltage stabilization effect of the voltage stabilization circuit 200 in the first power supply circuit 1031, the voltage output by the first power supply circuit remains At about 15V, the first power supply voltage is greater than the second power supply voltage. At this time, the second power supply circuit 1032 does not work, and the first power supply circuit 1031 supplies power to the control circuit 101.

[0050] The power switch 102 is a MOS tube, the gate of the MOS tube is connected to the control circuit 101, and the drain of the MOS tube is connected to the primary winding of the transformer T101. The MOS tube is used to control the conduction and disconnection of the primary winding of the transformer T101, and the conduction or disconnection of the MOS tube is controlled by the control circuit 101.

[0051] The control circuit 101 is used to output a control signal to the power switch 102 according to the feedback signal returned by the sampling feedback circuit 104 to control the turning on and off of the power switch 102, thereby controlling the current in the primary winding of the transformer T101, and making the transformer T101 secondary winding output The adjustable voltage is changed, and at the same time, the auxiliary winding of the transformer T101 can output a changed working voltage suitable for the operation of the control circuit 101, that is, the supply voltage of the control circuit 101. Preferably, the control circuit 101 includes a reference voltage generating circuit 300 and a control module 400. The reference voltage generating circuit 300 is used to generate a reference voltage according to the primary winding of the transformer T101 during the energy storage process; the control module 400 is used to detect the reflection of the primary winding When the voltage signal of the medium current reaches the reference voltage, the power switch 102 is controlled to cut off the current in the primary winding. Understandably, the reference voltage generation circuit 300 collects the current in the primary winding of the transformer T101 during the energy storage process to generate a reference voltage and transmits it to the detection pin of the control module 400. When the detection pin of the control module 400 detects When the voltage signal is equal to the reference voltage transmitted by the reference voltage generating circuit 300, the output control signal controls the power switch 102 to turn off, so that the primary winding of the transformer T101 is energized and the current in the primary winding is cut off.

[0052] The sampling feedback circuit 104 is used to collect the power supply voltage output by the output circuit 105 and output a feedback signal to the control circuit 101 based on the power supply voltage. The control circuit 101 outputs a PWM control signal with an adjustable duty cycle change based on the feedback signal.

[0053] Specifically, if the feedback signal output by the sampling feedback circuit 104 is a low-voltage signal, the control circuit 101 processes based on the low-voltage signal, and adjusts the output PWM control signal, that is, reduces the pulse width and outputs a signal corresponding to the low-voltage signal. The first PWM control signal is sent to the power switch 102 to control the current of the primary winding so that the secondary winding generates a low voltage. At this time, the first power supply circuit 1031 supplies power to the control circuit 101. In other words, when the power supply voltage output by the output circuit 105 is a low voltage, in the embodiment of the present invention, it is assumed that the low voltage is 5V-15V. At this time, the sampling feedback circuit 104 collects the voltage and outputs a low-voltage feedback signal to return to The control circuit 101, after receiving the low voltage feedback signal, the control circuit 101 processes according to the low voltage feedback signal, reduces the pulse width of the PWM control signal, and outputs the first PWM control signal. Understandably, the first PWM control signal is The PWM control signal with a small pulse width corresponding to the pulse width and the low voltage feedback signal controls the on-time of the power switch 102, and then controls the current in the primary winding of the transformer T101 so that the output secondary voltage corresponds to the power supply voltage, namely The secondary winding generates a low voltage. At this time, due to the characteristics of the first auxiliary winding and the second auxiliary winding and the characteristics of the first power supply circuit, the first power supply circuit 1031 supplies power to the control circuit 101.

[0054] If the feedback signal output by the sampling feedback circuit 104 is a high voltage signal, the control circuit 101 processes based on the high voltage signal and adjusts the output PWM control signal, that is, increases the pulse width, and outputs the second PWM corresponding to the low voltage signal The control signal is sent to the power switch 102 to control the current of the primary winding so that the secondary winding generates a high voltage. At this time, the second power supply circuit 1032 supplies power to the control circuit 101. In other words, when the power supply voltage output by the output circuit 105 is a high voltage, in the embodiment of the present invention, it is assumed that the high voltage is 15V to 20V. At this time, the sampling feedback circuit 104 collects the voltage and outputs the high voltage feedback signal to The control circuit 101, after receiving the high voltage feedback signal, the control circuit 101 processes the high voltage feedback signal, increases the pulse width of the PWM control signal, and outputs the second PWM control signal. Understandably, the second PWM control signal is a PWM control signal with a pulse width and a large pulse width corresponding to the high voltage feedback signal, which controls the on-time of the power switch 102, and then controls the current in the primary winding of the transformer T101 to output The secondary voltage corresponds to the power supply voltage, that is, the secondary winding generates a high voltage. At this time, due to the characteristics of the first auxiliary winding and the second auxiliary winding and the characteristics of the first power supply circuit, the second power supply circuit 1032 controls The circuit 101 supplies power.

[0055] It can be understood that the pulse width of the first PWM control signal is smaller than the pulse width of the second PWM control signal, in other words, the duty cycle of the first PWM control signal is smaller than the duty cycle of the second PWM control signal. By adjusting the duty cycle of the PWM control signal, the voltage output by the primary winding of the transformer T101 is adjusted, and the power supply voltage provided by the power supply circuit 103 to the control circuit 101 is adjusted, so that the power supply voltage of the control circuit 101 meets the working requirements.

[0056] Such as figure 2 Shown is the circuit principle diagram of the switching power supply control circuit of the present invention.

[0057] Specifically, the power supply circuit 103 includes a first power supply circuit 1031 and a second power supply circuit 1032. The first power supply circuit 1031 includes a voltage stabilizing circuit 200, a resistor R106, a diode D104, a capacitor C103, and a diode D106. The voltage stabilizing circuit 200 includes a transistor Q102, a resistor R108, and a voltage stabilizing diode ZD101. The first end of the resistor R106 is connected to the first auxiliary winding, the second end is connected to the anode of the diode D104, the cathode of the diode D104 is connected to the collector of the transistor Q102, and the node between the cathode of the diode D104 and the collector of the transistor Q102 is connected to the capacitor C103. One end is connected, the second end of capacitor C103 is connected to the reference ground; resistor R108 is connected between the base and collector of transistor Q102, the cathode of Zener diode ZD101 is connected to the base of transistor Q102, and the anode of Zener diode ZD102 is connected Reference ground; the first end of the diode D106 is connected to the emitter of the transistor Q102, and the second end of the diode D106 is connected to the second power supply circuit 1032.

[0058] The second power supply circuit 1032 includes a resistor R107 and a diode D105. The first end of the resistor R107 is connected to the second auxiliary winding, the second end of the resistor R107 is connected to the anode of the diode D105, and the cathode of the diode D105 is connected to the cathode of the diode D106.

[0059] In the embodiment of the present invention, a resistor R109 and a capacitor C104 are also connected between the power supply circuit 103 and the control circuit 101. The first end of the resistor R109 is connected to the node between the cathode of the diode D105 and the cathode of the diode D106, and the resistor R109 The second end of the capacitor C104 is connected to the control circuit 101; the first end of the capacitor C104 is connected to the first end of the resistor R109, and the second end of the capacitor C104 is connected to the reference ground. The resistor R109 and the capacitor C104 form a filter circuit, so that the power supply voltage provided by the first power supply circuit 1031 and the second power supply circuit 1032 to the control circuit 101 is smoother.

[0060] Understandably, when the power supply voltage output by the output circuit 105 is a low voltage, the first auxiliary voltage output by the first auxiliary winding is greater than the second auxiliary voltage output by the second auxiliary winding, that is, the first power supply voltage output by the first power supply circuit. The first power supply circuit 1031 supplies power to the control circuit 101 if the second power supply voltage is greater than the second power supply voltage output by the second power supply circuit. That is, at this time, resistor R106, diode D104, capacitor C103, resistor R108, transistor Q102, Zener diode ZD101, and diode D106 supply power to control circuit 101 through resistor R109 and capacitor C104. Zener diode ZD101 can make transistor Q102 turn on stably. The diode D104 and the resistor R106 form a rectifier and filter circuit, which converts the AC first auxiliary voltage into a DC voltage, and at the same time makes the voltage in the first power supply circuit smoother. When the power supply voltage output by the output circuit 105 is a high voltage, due to the stabilizing effect of the first power supply circuit, the first power supply voltage output by the first power supply circuit is maintained at about 15V, at this time the second power supply voltage output by the second power supply circuit The second power supply circuit 1032 supplies power to the control circuit 101 if it is greater than the first power supply voltage output by the first power supply circuit. That is, power is supplied by the resistor R107 and the diode D105 at this time.

[0061] The power switch 102 includes a MOS transistor Q101, the gate of the MOS transistor Q101 is connected to the control circuit 101, the drain of the MOS transistor Q101 is connected to the primary winding of the transformer T101, and the source of the MOS transistor Q101 is connected to the reference voltage generating circuit 300.

[0062] The control circuit 101 includes a reference voltage generating circuit 300 and a control module 400. The reference voltage generating circuit 300 includes a resistor R116 and a resistor R117. The first end of the resistor R116 is connected to the source of the MOS transistor Q101, the second end of the resistor R116 is connected to the reference ground; the resistor R117 is connected in parallel with the resistor R116. The control module 400 includes a control chip U101, a resistor R112, a resistor R113, a resistor R114, a capacitor C105, and a resistor C106. The PIN8 pin of the control chip U101 is the start pin, which is used to receive the start voltage when the AC mains is connected, and control The chip U101 starts to work after the PIN8 pin receives the starting voltage. The PIN5 pin of the control chip U101 is connected to the first end of the resistor R112, the second end of the resistor R112 is connected to the first end of the resistor R113, the second end of the resistor R113 is connected to the gate of the MOS transistor Q101; the diode D107 is connected to the resistor R113 is connected in parallel, and the anode of diode D107 is connected to the gate of MOS transistor Q101; resistor R114 is connected between the gate and source of MOS transistor Q101; the PIN3 pin (detection pin) of control chip U101 is connected to the first of resistor R115 The second end of the resistor R115 is connected between the source of the MOS transistor Q101 and the resistor R116; the PIN3 pin of the control chip U101 is also connected to the reference ground through the capacitor C106; the PIN4 pin of the control chip U101 (grounded Pin) is connected to the reference ground; the PIN2 pin of the control chip U101 is connected to the sampling feedback circuit for receiving the feedback signal output by the sampling feedback circuit. Preferably, in the embodiment of the present invention, the feedback signal output by the sampling feedback circuit is a voltage signal. The PIN2 pin of the control chip U101 is also connected to the reference ground through the capacitor C105; the PIN1 pin (the overvoltage monitoring pin) of the control chip U101 is connected to the overvoltage detection circuit 107; the PIN6 pin of the control chip U101 (power supply pin, That is, the VDD pin is connected to the node between the cathode of the diode D106 and the cathode of the diode D105 via the resistor R109.

[0063] The overvoltage detection circuit 107 includes a resistor R110 and a resistor R111, and the resistor R110 and the resistor R111 are connected in series between the second auxiliary winding and the PIN1 pin of the control chip U101.

[0064] The following pairs figure 2 The working principle of the circuit is further explained:

[0065] When there is AC_IN input, the PIN8 pin (ie, the start pin) of the control chip U101 receives the start voltage, and the control chip U101 starts to work after the PIN8 pin receives the start voltage, and outputs the start signal through the resistor R112, The resistor R113 is sent to the gate of the MOS transistor Q101 to turn on the MOS transistor Q101. At the same time, the rectifier circuit 106 rectifies the received AC mains and outputs the rectified voltage to the primary winding of the transformer T101. At this time, the primary winding of the transformer T101 Start charging. During the charging process, the secondary winding and auxiliary winding do not work, and the electric energy generated by the primary winding of the transformer T101 is stored in its gap; and during the charging process of the primary winding of the transformer T101, the reference voltage generation circuit 300 The resistor R116 and the resistor R117 collect the voltage output by the primary winding to generate a reference voltage and transmit it to the PIN3 pin (detection pin) of the control chip U101 through the resistor R115. Preferably, the reference voltage generated by the reference voltage generating circuit 300 changes with the current of the primary winding, that is, the reference voltage is a changing voltage. When the PIN3 pin of the control chip U101 detects that the reference voltage meets the requirements, the control chip U101 outputs control The signal is sent to the MOS tube Q101 to disconnect it, so that the primary winding stops charging. In other words, when the PIN3 pin of the control chip U101 detects that the reference voltage reflects the voltage signal of the current in the primary winding, that is, the value of the reference voltage reflects that the voltage generated by the primary winding meets the output requirements, that is, the primary winding is cut off In the current, the primary winding stops working. When the primary winding stops working, the secondary winding, the first auxiliary winding, and the second auxiliary winding of the transformer T101 start to work. The secondary winding outputs the secondary voltage according to the energy transferred by the primary winding and outputs the power supply voltage through the output circuit 106 to supply power to the load. The first auxiliary winding and the second auxiliary winding respectively output the first auxiliary voltage and the second auxiliary voltage. When the first power supply voltage is greater than the second power supply voltage, the first power supply circuit 1031 supplies power to the control chip U101 via the resistor R109, and vice versa , The second power supply circuit 1031 supplies power to the control chip U101 via the resistor R109.

[0066] The power supply voltage output by the switching power supply control circuit of the present invention is a variable voltage, and the secondary winding, the first auxiliary winding, and the second auxiliary winding are in the same phase. When the secondary winding outputs the secondary voltage (equivalent to the output circuit 105 When the output power supply voltage) increases, the VDD voltage of the control chip U101 also increases in the same proportion, that is, the auxiliary voltage output by the auxiliary winding also increases in the same proportion. In the embodiment of the present invention, it is assumed that the power supply voltage output by the output circuit 105 is 5V-20V, and the high and low voltages are divided, low voltage: 5V-15V, high voltage: 15V-20V. It can be seen from the foregoing that when the power supply voltage changes from 5V to 20V, the sampling feedback circuit 104 outputs a low voltage feedback signal to the PIN2 pin of the control chip U101 according to the change in the power supply voltage, and the control chip U101 receives low voltage feedback according to the PIN2 pin. The signal is processed, the pulse width of the output PWM control signal is reduced, and the first PWM control signal corresponding to the low voltage signal is output to the gate of the MOS transistor Q101. The MOS transistor Q101 controls the current of the primary winding according to the first PWM control signal , The secondary winding generates a low voltage. At this time, due to the stabilizing effect of the voltage stabilizing circuit 200 in the first power supply circuit 1031, the first power supply voltage output by the first power supply circuit is maintained at about 15V, and the first auxiliary winding The number of coil turns is greater than that of the second auxiliary winding. Therefore, the first power supply voltage is greater than the second power supply voltage. The first power supply circuit 1031 supplies power to the control chip U101, that is, the first auxiliary voltage passes through the resistor R106, the diode D104, and the capacitor. C103, transistor Q102, resistor R108, Zener diode ZD101, diode D106 output the first power supply voltage and provide the power supply pin (VDD pin) of the control chip U101 through resistor R109. When the power supply voltage output by the output circuit 105 is a high voltage, that is, 15V~20V, the sampling feedback circuit collects the voltage and outputs a high voltage feedback signal back to the PIN2 pin of the control chip U101, and the control chip U101 receives the PIN2 pin After the high-voltage feedback signal, it is processed according to the high-voltage feedback signal, the pulse width of the PWM control signal is increased, and the second PWM control signal is output. The second PWM control signal is a large pulse width corresponding to the pulse width of the high-voltage feedback signal The second PWM control signal is sent to the gate of the MOS transistor Q101. The MOS transistor Q101 controls the current of the primary winding according to the second PWM control signal, so that the primary winding generates a high voltage. At this time, the first The power supply voltage remains at about 15V, and the second auxiliary winding increases in proportion to the output power supply voltage. The second power supply voltage output by the second power supply circuit is greater than the first power supply voltage output by the first power supply circuit. The second power supply circuit 1032 supplies power to the control chip U101, that is, the second auxiliary voltage outputs the second supply voltage through the resistor R107 and the diode D105 and is provided to the power supply pin (VDD pin) of the control chip U101 through the resistor R109. Thus, the requirement for power supply of the switching power supply control chip is met when the power supply voltage changes within a certain range.

[0067] Because in the original power supply circuit, when the output power supply voltage rises and is higher than the stabilized voltage of the stabilized circuit 200, power is supplied to the control chip at this time, and the voltage loaded on the power device (transistor Q102) is too high, which will cause power The device generates large heat and high loss. For example, when the power supply voltage is 20V, the voltage output from the auxiliary winding of the transformer T101 to the resistor R106 is as high as 40V or more. At this time, the voltage stabilized voltage set by the voltage stabilizer circuit 200 formed by the resistor R108, the transistor Q102 and the Zener diode ZD101 At 15V, the voltage drop on the transistor Q102 is as high as 40-15=25V. At this time, the heat generation of the transistor Q102 is greatly increased, and the loss is very large, so it is not suitable for the current circuit design requirements of switching power supplies. The switching power supply control circuit of the present invention provides a flexible power supply requirement for the control chip U101 of the switching power supply by adding an auxiliary winding (that is, adding a second auxiliary winding). When the power supply voltage changes, as the power supply voltage changes, the circuit can choose whether to supply power to the control chip U101 from the first power supply circuit 1031 or the second power supply circuit 1032. That is, when the power supply voltage is low, the first power supply circuit 1031 supplies power to the control chip U101, and the second power supply circuit U1032 does not work; when the power supply voltage is high, the second power supply circuit 1032 supplies power to the control chip U101. The first power supply circuit 1031 does not work, which effectively solves the problems of high heat generation and high loss of the transistor Q102 of the first power supply circuit 1031 when the power supply voltage is high, resulting in high switching power supply loss, shortened service life, and low safety. In addition, the selection of the first power supply circuit 1031 and the second power supply circuit 1032 of the present invention is automatically selected by the circuit. When the first power supply voltage is greater than the second power supply voltage, the first power supply circuit 1031 is automatically selected for power supply. When the voltage is less than the second power supply voltage, the second power supply circuit 1032 is automatically selected for power supply without the need for additional switching devices or selection control circuits to select the power supply circuit 103. Therefore, the circuit structure design is simple, which simplifies the structure of the switching power supply control circuit and saves Cost and takes up less space. Moreover, the switching power supply control circuit of the present invention also connects the overvoltage detection circuit 107 to the output end of the second auxiliary winding to monitor whether the power supply voltage provided by the second power supply circuit 1032 to the control chip 101 exceeds the normal working range of the control chip 101 to ensure control The chip 101 can work within a safe working voltage, which further improves the safety of the circuit.

[0068] The present invention also provides a switching power supply. The switching power supply includes the above-mentioned switching power supply control circuit. The switching power supply can make the switching power supply work normally and stably by providing the above-mentioned switching power supply control circuit with low loss, low cost, small size and safety. High performance and longer service life.

[0069] The above embodiments are only to illustrate the technical ideas and features of the present invention, and their purpose is to enable those familiar with the art to understand the content of the present invention and implement them accordingly, and cannot limit the protection scope of the present invention. All equivalent changes and modifications made to the scope of the claims of the present invention shall fall within the scope of the claims of the present invention.

[0070] It should be understood that those of ordinary skill in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the protection scope of the appended claims of the present invention.