Starting circuit and switching power supply

Abstract

The utility model discloses a starting circuit and a switching power supply, the starting circuit comprises a time-delay circuit, the input end of the time-delay circuit is used for connecting the input end of the switching power supply, the grounding end of the time-delay circuit is used for connecting the grounding end of the switching power supply, and the output end of the time-delay circuit is used for connecting the enabling end of a control chip; the output slow start circuit comprises a slow start capacitor, a reference current source, a reference voltage source and a comparator, and the output end of the reference current source is connected with one end of the slow start capacitor and the first in-phase input end of the comparator at the same time; the other end of the slow start capacitor is connected with one end of the reference voltage source and then used for being connected with the grounding end of the switching power supply, the second in-phase input end of the comparator is connected with the other end of the reference voltage source, and the inverted input end of the comparator is used for inputting a feedback signal representing the magnitude of the output voltage of the switching power supply. The utility model can solve the problem of overlarge peak at the starting moment of the switching power supply.

Description

TECHNICAL FIELD

[0001] The utility model relates to power supply technical field especially relates to a starting circuit and switching power supply. BACKGROUND

[0002] With the increase of the degree of electrification of human, the requirement of power supply is also higher and higher. The input and output end of common switching power supply system often sets up the filter capacitor of larger capacitance value, and the capacitor will be charged at the power-on moment of power supply system, which will cause great starting peak current. Although the current engineer will choose to add the slow starting MOS pipe before the input and add a capacitor between the gate and source of MOS pipe, and the capacitor slowly opens the MOS pipe to realize the function of slow starting. But this method cannot realize the delay of several hundred milliseconds. In the case of such as coal mine and other intrinsic safety power supply, the peak current of starting moment cannot be effectively controlled, which will cause the restart of the front stage equipment, and even endanger the personal safety. SUMMARY

[0003] Therefore, the utility model provides a starting circuit and switching power supply, which at least solves the above technical problems to some extent.

[0004] As a first aspect of the utility model, the technical scheme of the provided starting circuit is as follows:

[0005] A starting circuit, the starting circuit is applied to switching power supply, the switching power supply realizes energy conversion by the control chip control main power switch tube conduction and cut-off, the switching power supply includes input filter capacitor and / or output filter capacitor, wherein, the starting circuit includes:

[0006] Delay circuit, the input end of delay circuit is used for connecting the input end of switching power supply, the ground end is used for connecting the ground end of switching power supply, the output end is used for connecting the enable end of control chip, the delay circuit controls the time when the control chip starts to work by the level signal state of its output end when the switching power supply works, thereby realizing the delay starting of switching power supply;

[0007] An output slow start circuit, which comprises a slow start capacitor, a reference current source, a reference voltage source and a comparator, the output of the reference current source is connected to one end of the slow start capacitor and the first non-inverting input of the comparator, the other end of the slow start capacitor and one end of the reference voltage source are connected together and used to connect the ground of the switching power supply, the second non-inverting input of the comparator is connected to the other end of the reference voltage source, the inverting input of the comparator is used to input a feedback signal representing the output voltage of the switching power supply, the comparator outputs a control signal following the change of the output voltage of the switching power supply when the switching power supply is working, the control chip generates a PWM signal to control the turn-on and turn-off of the main power switch according to the control signal, so as to realize the slow rising of the output of the switching power supply until stable.

[0008] Preferably, the delay circuit comprises:

[0009] An RC charging circuit, the input of the RC charging circuit is the input of the delay circuit, the ground of the RC charging circuit is the ground of the delay circuit, and the output of the RC charging circuit outputs a voltage signal;

[0010] A switching circuit, the first input of the switching circuit is connected to the output of the RC charging circuit, the second input of the switching circuit is connected to the input of the delay circuit, the ground of the switching circuit is connected to the ground of the delay circuit, and the output of the switching circuit is the output of the delay circuit;

[0011] When the switching power supply is working, the output voltage of the switching circuit is low during the initial stage of the delay power-on, the control chip does not work, and as the voltage signal output by the output of the RC charging circuit rises to a set value, the output of the switching circuit becomes floating, and the control chip starts to work.

[0012] Preferably, the RC charging circuit comprises a resistor R15 and a capacitor C11, one end of the resistor R15 is the input of the RC charging circuit, the other end of the resistor R15 and one end of the capacitor C11 are connected together to be the output of the RC charging circuit, and the other end of the capacitor C11 is the ground of the RC charging circuit.

[0013] Preferably, the RC charging circuit further comprises a discharge circuit, the discharge circuit is connected to the capacitor C11 and used to discharge the energy stored in the capacitor C11 after the switching power supply is started.

[0014] Further, the discharge circuit comprises a diode D14, one end of the capacitor C11 is connected to the anode of the diode D14, and the cathode of the diode D14 is connected to the input of the RC charging circuit.

[0015] Preferably, the switch circuit comprises resistance R21, resistance R22, resistance R24, resistance R25, triode Q21 and triode Q22; one end of the resistance R21 is the first input end of the switch circuit, the other end of the resistance R21 is connected with one end of the resistance R22, the base of the triode Q21 and one end of the resistance R25 at the same time, one end of the resistance R24 is the second input end of the switch circuit, the other end of the resistance R24 is connected with the collector of the triode Q21 and the base of the triode Q22 at the same time, the other end of the resistance R25 and the collector of the triode Q22 are connected together to be the output end of the switch circuit, the other end of the resistance R22, the emitter of the triode Q21 and the emitter of the triode Q22 are connected together to be the ground end of the switch circuit.

[0016] Further, the switch circuit further comprises diode D23, one end of the diode D23 is connected with one end of the resistance R25, the other end of the diode D23 is connected with the connection point of the other end of the resistance R21, one end of the resistance R22 and the base of the triode Q21.

[0017] Further, the switch circuit further comprises voltage stabilizing diode D22, the anode of the voltage stabilizing diode D22 is connected with the base of the triode Q21, the cathode of the voltage stabilizing diode D22 is connected with the connection point of the other end of the resistance R21, one end of the resistance R22 and one end of the resistance R25.

[0018] Further, the switch circuit further comprises capacitor C22, the capacitor C22 is connected with the resistance R22 in parallel.

[0019] As a second aspect of the utility model, the embodiment technical scheme of the switch power supply is as follows:

[0020] A switch power supply, the switch power supply realizes energy conversion by controlling the conduction and turn-off of main power switch tube controlled by control chip, the switch power supply comprises input filter capacitor and / or output filter capacitor, wherein: the switch power supply further comprises the starting circuit in any one of the first aspect.

[0021] Compared with the prior art, the utility model has the following advantages and beneficial effects:

[0022] The embodiment of the utility model successfully realizes the output of switching power supply is compared with the delay start of input and the slow rise of output voltage, specifically: the delay circuit is arranged in starting circuit, the delay circuit controls the time that the control chip in switching power supply starts to work through the level signal state of its output end when switching power supply works, thereby realizing the delay start of switching power supply, the output slow start circuit is also arranged in starting circuit simultaneously, the comparator will output a control signal that follows the change of switching power supply output voltage when switching power supply works, and the control chip generates PWM signal according to the control signal to control the conduction and cut-off of main power switch tube in switching power supply, thereby realizing the slow rise of switching power supply output until stable. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is the principle block diagram of the starting circuit of the first embodiment of the utility model;

[0024] Figure 2 It is the principle block diagram of a specific embodiment of the delay circuit in Figure 1

[0025] Figure 3 It is the principle block diagram of a specific embodiment of RC charging circuit in Figure 2

[0026] Figure 4 It is the principle block diagram of a specific embodiment of switch circuit in Figure 2

[0027] Figure 5 It is the principle block diagram of a specific embodiment of switching power supply of the second embodiment of the utility model. DETAILED DESCRIPTION

[0028] In order to make the above purpose, features and advantages of the utility model more apparent, obvious and easy to understand, the specific embodiment of the utility model is described in detail below with reference to the drawings, obviously, the described embodiment is a part of the embodiment of the utility model, rather than all the embodiments. Based on the embodiment in the application, all other embodiments obtained by the person skilled in the art without making creative labor should belong to the protection scope of the application.

[0029] It should be noted that the terms "include" and "have" and any change of them described in the specification and claims of the application are intended to cover the non-exclusive inclusion, for example, the inclusion of a series of components, unit circuits or control time sequence should not be limited to the clearly listed components, unit circuits or control time sequence, but can include the components, unit circuits or control time sequence that are not clearly listed or inherent to these circuits. ​​​

[0030] In addition, the embodiments in the present application and the features in the embodiments can be combined with each other in the case of no conflict.

[0031] It should be understood that, in the description and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0032] First embodiment

[0033] The embodiment provides a starting circuit applied to a switching power supply, energy conversion is realized by controlling a main power switch tube to be turned on and turned off by a control chip, the switching power supply comprises an input filter capacitor and / or an output filter capacitor, Figure 1 For the starting circuit principle block diagram of the first embodiment of the utility model, please refer to Figure 1 The starting circuit comprises:

[0034] The delay circuit is used for connecting the input end of the switching power supply, the ground end is used for connecting the ground end of the switching power supply, and the output end is used for connecting the enable end of the control chip; when the switching power supply works, the delay circuit controls the time when the control chip starts to work through the level signal state of the output end, so that the switching power supply realizes delay starting.

[0035] The output slow starting circuit comprises a slow starting capacitor, a reference current source, a reference voltage source and a comparator; the output end of the reference current source is connected to one end of the slow starting capacitor and the first non-inverting input end of the comparator; the other end of the slow starting capacitor and one end of the reference voltage source are connected together and then used for connecting the ground end of the switching power supply; the second non-inverting input end of the comparator is connected to the other end of the reference voltage source; the inverting input end of the comparator is used for inputting a feedback signal representing the size of the output voltage of the switching power supply; when the switching power supply works, the comparator will output a control signal following the change of the output voltage of the switching power supply; the control chip generates a PWM signal to control the main power switch tube to be turned on and turned off according to the control signal, so that the output voltage of the switching power supply slowly rises until it is stable.

[0036] It should be understood that, in the description and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0032] First embodiment

[0033] The embodiment provides a starting circuit applied to a switching power supply, energy conversion is realized by controlling a main power switch tube to be turned on and turned off by a control chip, the switching power supply comprises an input filter capacitor and / or an output filter capacitor, Figure 1 For the starting circuit principle block diagram of the first embodiment of the utility model, please refer to Figure 1 The starting circuit comprises:

[0034] The delay circuit is used for connecting the input end of the switching power supply, the ground end is used for connecting the ground end of the switching power supply, and the output end is used for connecting the enable end of the control chip; when the switching power supply works, the delay circuit controls the time when the control chip starts to work through the level signal state of the output end, so that the switching power supply realizes delay starting.

[0035] The output slow starting circuit comprises a slow starting capacitor, a reference current source, a reference voltage source and a comparator; the output end of the reference current source is connected to one end of the slow starting capacitor and the first non-inverting input end of the comparator; the other end of the slow starting capacitor and one end of the reference voltage source are connected together and then used for connecting the ground end of the switching power supply; the second non-inverting input end of the comparator is connected to the other end of the reference voltage source; the inverting input end of the comparator is used for inputting a feedback signal representing the size of the output voltage of the switching power supply; when the switching power supply works, the comparator will output a control signal following the change of the output voltage of the switching power supply; the control chip generates a PWM signal to control the main power switch tube to be turned on and turned off according to the control signal, so that the output voltage of the switching power supply slowly rises until it is stable.

[0036] It should be understood that, in the description and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0032] First embodiment

[0033] The embodiment provides a starting circuit applied to a switching power supply, energy conversion is realized by controlling a main power switch tube to be turned on and turned off by a control chip, the switching power supply comprises an input filter capacitor and / or an output filter capacitor, Figure 1 For the starting circuit principle block diagram of the first embodiment of the utility model, please refer to Figure 1 The starting circuit comprises:

[0034] The delay circuit is used for connecting the input end of the switching power supply, the ground end is used for connecting the ground end of the switching power supply, and the output end is used for connecting the enable end of the control chip; when the switching power supply works, the delay circuit controls the time when the control chip starts to work through the level signal state of the output end, so that the switching power supply realizes delay starting.

[0035] The output slow starting circuit comprises a slow starting capacitor, a reference current source, a reference voltage source and a comparator; the output end of the reference current source is connected to one end of the slow starting capacitor and the first non-inverting input end of the comparator; the other end of the slow starting capacitor and one end of the reference voltage source are connected together and then used for connecting the ground end of the switching power supply; the second non-inverting input end of the comparator is connected to the other end of the reference voltage source; the inverting input end of the comparator is used for inputting a feedback signal representing the size of the output voltage of the switching power supply; when the switching power supply works, the comparator will output a control signal following the change of the output voltage of the switching power supply; the control chip generates a PWM signal to control the main power switch tube to be turned on and turned off according to the control signal, so that the output voltage of the switching power supply slowly rises until it is stable.

[0036] It should be understood that, in the description and claims, when it is described that an element is "connected" to another element, the element can be "directly connected" to the other element, or "connected" to the other element through a third element; when it is described that a step is followed by another step, the step can be directly followed by the other step, or followed by the other step through a third step.

[0032] First embodiment Figure 1

[0037] The starting circuit of the embodiment successfully realizes the delayed starting of the output of the switching power supply compared with the input and the slow rising of the output voltage, specifically: the delay circuit is arranged in the starting circuit, and the delay circuit controls the time when the control chip starts to work in the switching power supply by controlling the level signal state of the output end of the delay circuit when the switching power supply works, so as to realize the delayed starting of the switching power supply; meanwhile, the output slow starting circuit is arranged in the starting circuit, and the comparator will output a control signal following the change of the output voltage of the switching power supply when the switching power supply works, and the control chip generates the PWM signal to control the turn-on and turn-off of the main power switch tube in the switching power supply according to the control signal, so as to realize the slow rising of the output of the switching power supply until the output is stable. The starting circuit of the embodiment can effectively solve the problem of the excessively large peak at the starting moment of the switching power supply.

[0038] Figure 2 For Figure 1 , the principle block diagram of a specific embodiment of the delay circuit is shown in Figure 2 , wherein the delay circuit comprises:

[0039] The RC charging circuit has an input end, a ground end and an output end, wherein the input end is the input end of the delay circuit, the ground end is the ground end of the delay circuit, and the output end outputs a voltage signal.

[0040] The switching circuit has a first input end, a second input end, a ground end and an output end, wherein the first input end is connected with the output end of the RC charging circuit, the second input end is connected with the input end of the delay circuit, the ground end is connected with the ground end of the delay circuit, and the output end is the output end of the delay circuit.

[0041] When the switching power supply works, the output end voltage of the switching circuit is low at the initial stage of the delay power-on, and the control chip does not work. With the rising of the voltage signal outputted by the output end of the RC charging circuit to the set value, the output end of the switching circuit becomes in a floating state, and the control chip starts to work.

[0042] Figure 3 For Figure 2 , the principle block diagram of a specific embodiment of the RC charging circuit is shown in Figure 3 , wherein the RC charging circuit comprises a resistor R15 and a capacitor C11, one end of the resistor R15 is the input end of the RC charging circuit, the other end and one end of the capacitor C11 are connected together to be the output end of the RC charging circuit, and the other end of the capacitor C11 is the ground end of the RC charging circuit.

[0043] Please continue to refer to Figure 3 , wherein the RC charging circuit further comprises a discharging circuit connected with the capacitor C11, which is used for discharging the energy stored in the capacitor C11 after the switching power supply completes the starting, so that the delay circuit can work normally when the switching power supply starts next time.

[0044] Please continue to refer to Figure 3The discharge circuit includes a diode D14. The anode of diode D14 is connected to one end of capacitor C11, and the cathode of diode D14 is connected to the input terminal of the RC charging circuit. When the switching power supply is turned off, the capacitor C11, which has stored a certain amount of charge, continues to supply power to the subsequent circuits through diode D14. The power-down retention time of the switching power supply can be obtained. In practical applications, the amount of energy that capacitor C11 needs to store can be obtained by calculating the product of the power P required for the switching power supply to continue working and the time Tb required for power-down retention, thereby calculating the required capacitance value of capacitor C11.

[0045] Figure 4 for Figure 2 For a schematic diagram of a specific implementation of the switching circuit, please refer to [link / reference]. Figure 4 The switching circuit includes resistors R21, R22, R24, and R25, transistors Q21 and Q22. One end of resistor R21 is the first input terminal of the switching circuit, and the other end of resistor R21 is connected to one end of resistor R22, the base of transistor Q21, and one end of resistor R25. One end of resistor R24 ​​is the second input terminal of the switching circuit, and the other end of resistor R24 ​​is connected to the collector of transistor Q21 and the base of transistor Q22. The other end of resistor R25 is connected to the collector of transistor Q22 as the output terminal of the switching circuit. The other end of resistor R22, the emitter of transistor Q21, and the emitter of transistor Q22 are connected together as the ground terminal of the switching circuit.

[0046] Figure 3 RC charging circuit and Figure 4 The working principle of achieving delayed startup of a switching power supply by combining switching circuits is as follows:

[0047] In the initial stage of power-on of the switching power supply: The input terminal of the RC charging circuit is connected to the input terminal of the switching power supply, so it starts charging capacitor C11 through resistor R15. The voltage across capacitor C11 begins to increase. The voltage at the output terminal of the RC charging circuit is divided by resistors R21 and R22, and the voltage across resistor R22 is relatively low. As a result, NPN transistor Q21 is turned off because the voltage VBE1 between its base and emitter does not reach the turn-on voltage. At the same time, the second input terminal of the switching circuit is connected to the input terminal of the switching power supply, so it generates a bias current at the base of NPN transistor Q22 through resistor R24. NPN transistor Q22 turns on and operates in saturation, pulling down the output terminal of the switching circuit (i.e., the collector of NPN transistor Q22) to a low level, and the control chip does not work.

[0048] After the switch power supply is powered on for a time T: at this time, the voltage across the capacitor C11 increases to a voltage divided across the resistor R22, which is greater than the turn-on voltage between the base and the emitter of the NPN transistor Q21. The NPN transistor Q21 is turned on and works in a saturated state. The emitter voltage of the NPN transistor Q21 is substantially equal to the collector voltage. Since the emitter of the NPN transistor Q21 is connected to the ground, the collector voltage of the NPN transistor Q21 is substantially 0. Since the base of the NPN transistor Q22 is connected to the collector of the NPN transistor Q21, the base voltage of the NPN transistor Q22 is substantially 0. The NPN transistor Q22 is turned off. The output end of the switch circuit (i.e. the collector of the NPN transistor Q22) is suspended. The control chip starts to work.

[0049] The time T is the delay time of the delay start of the switch power supply. By selecting the parameter of the resistor R15, the charging speed of the capacitor C11 can be adjusted, so as to adjust the delay time of the delay start of the switch power supply.

[0050] Please go back to Figure 4The switch circuit further comprises a diode D23, an anode of the diode D23 is connected to one end of the resistor R25, a cathode of the diode D23 is connected to the other end of the resistor R21, one end of the resistor R22 and the connection point of the base of the triode Q21; the diode D23 is arranged to set a voltage hysteresis, so that the input voltage of the switch power supply for starting the work of the control chip is greater than the input voltage of the switch power supply for stopping the work of the control chip, and the stability of the circuit work is improved; the specific working principle is as follows: assuming that the voltage just making the triode Q21 conduct is VBE1, when the control chip is to be started, the triode Q22 is saturated and conducts, the enable signal EN is basically 0, the voltage of the enable signal EN fed back to the base of the triode Q21 through the resistor R25 and the diode D23 is basically 0, VBE1 can only be divided by the resistors R21 and R22, and the input voltage when the voltage across the resistor R22 is just VBE1 after voltage division is Vin1; when the control chip is to be stopped, because the triode Q22 is cut off, the enable signal EN is floating or pulled up to a voltage by the chip, so the voltage of the enable signal EN fed back to the base of the triode Q21 through the resistor R25 and the diode D23 is no longer 0, VBE1 is superimposed by the voltage fed back by the enable signal EN and the voltage divided by the resistors R21 and R22 at this time, because only the voltage greater than VBE1 can make the triode Q21 conduct and the voltage less than VBE1 can make the triode Q21 cut off, the voltage divided by the resistors R21 and R22 does not need to be as high as before to reach VBE1 because of the voltage superimposed by the enable signal EN at the base of the triode Q21, and the input voltage when the voltage across the resistor R22 is just VBE1 after voltage division at this time is Vin2, so Vin2 also does not need to be as high as before, that is, Vin2 is less than Vin1, so the input voltage for starting the work of the control chip and the input voltage for stopping the work of the control chip are inconsistent, that is, there is a voltage hysteresis.

[0051] Please continue to see Figure 4Wherein the switch circuit further comprises a Zener diode D22, the anode of the Zener diode D22 is connected to the base of the triode Q21, the cathode of the Zener diode D22 is connected to the joint of the other end of the resistor R21, the one end of the resistor R22 and the one end of the resistor R25, the purpose of arranging the Zener diode D22 is that when the voltage divided on the resistor R22 rises to the Zener voltage of the Zener diode D2, the voltage across the resistor R22 no longer changes with the voltage across the capacitor C11, since the anode of the Zener diode D22 is connected to the base of the triode Q21, the positive temperature characteristic of the Zener voltage of the low-voltage Zener diode can be used to compensate the negative temperature characteristic of the PN junction voltage of the triode Q21, so that the starting delay time of the whole circuit can be kept better consistency in a wider temperature range, and meanwhile the triode Q21 can be saturated only when the voltage across the capacitor C11 is higher, so that the delay time of the delay starting is longer.

[0052] Please continue to see Figure 4 Wherein the switch circuit further comprises a capacitor C22, the capacitor C22 is connected in parallel with the resistor R22, the purpose is to filter the ripple noise of the voltage divided on the resistor R22, to avoid the triode Q21 base voltage from being mis-conducted due to the ripple noise when being in the critical conduction, so as to make the triode Q21 and the switch circuit work abnormally.

[0053] Second embodiment

[0054] The embodiment provides a switching power supply, the switching power supply is controlled by a control chip to realize energy conversion by controlling the conduction and turn-off of a main power switch tube, and the switching power supply comprises an input filter capacitor and / or an output filter capacitor, wherein: the switching power supply further comprises the starting circuit in any one of the first embodiments.

[0055] Figure 5 It is a principle block diagram of a specific implementation mode of the switching power supply of the second embodiment of the utility model, and it should be noted that the switching power supply of the embodiment omits the delay circuit in the starting circuit, and in addition, the circuit topology in the embodiment is only a schematic diagram, and the application is not limited to the circuit topology in the specific implementation.

[0056] Figure 5 The switching power supply comprises a 3uA reference current source and a 0.8V reference voltage source, a comparator (also referred to as an error amplifier), a sawtooth signal generator, a PWM comparator, a logic controller, a slow-start capacitor C42, upper and lower switching elements MOS tubes, an inductor, a filter network and an output sampling feedback network, the reference current source charges the capacitor C42 with a current of 3uA, the voltage U across the capacitor C42 slowly rises, and the relationship expression of the voltage U across the capacitor C42 and the time t and the capacitance C of the capacitor C42 is 42 ​The voltage of the capacitor C42 rises to 0.8V when the output is stable, and the time of slowly rising of the output voltage is adjusted by adjusting the capacitance of the capacitor C42.

[0057] The output of the error amplifier is connected to the non-inverting input of the PWM comparator, the inverting input of the PWM comparator is connected to the sawtooth signal, the output of the PWM comparator is connected to the logic controller, the logic controller generates complementary pulse signals to control the turn-on and turn-off of the upper and lower MOS tubes, the upper and lower MOS tubes are N tubes, the D terminal of the upper tube is connected to the DC input VDC of the switching power supply, the S terminal of the upper tube is connected to the D terminal of the lower tube and one end of the inductor, the S terminal of the lower tube is connected to the ground, the other end of the inductor is connected to the output filter network and the sampling feedback network, when the output of the error amplifier is greater than the sawtooth signal, the output is high, and the upper tube is turned on, when the output of the error amplifier is less than the sawtooth signal, the output is low, and the upper tube is turned off, it can be seen that the period of the output pulse is the same as that of the sawtooth signal, and the duty cycle D is determined by the output of the error amplifier, and then the conduction time of the switching device is determined, so as to control the size of the output voltage.

[0058] The above is only the embodiment of the present application, and it should be particularly pointed out that the above embodiment should not be regarded as the limitation of the present application, and for ordinary skilled in the technical field, some improvements and decorations can be made without departing from the spirit and scope of the present application, and these improvements and decorations should also be regarded as the protection scope of the present application.

Claims

1. A starting circuit applied to a switching power supply, the switching power supply controlled by a control chip to turn on and off a main power switch tube to realize energy conversion, the switching power supply comprising an input filter capacitor and / or an output filter capacitor, characterized in that, The starting circuit comprises: a delay circuit, an input end of the delay circuit being connected to an input end of the switching power supply, a ground end of the delay circuit being connected to a ground end of the switching power supply, and an output end of the delay circuit being connected to an enable end of the control chip, the delay circuit controlling the time when the control chip starts to work by controlling the level signal state of the output end of the delay circuit when the switching power supply works, so as to realize the delay starting of the switching power supply; an output slow starting circuit, the output slow starting circuit comprising a slow starting capacitor, a reference current source, a reference voltage source and a comparator, the output end of the reference current source being connected to one end of the slow starting capacitor and the first non-inverting input end of the comparator, the other end of the slow starting capacitor and one end of the reference voltage source being connected together and then connected to the ground end of the switching power supply, the second non-inverting input end of the comparator being connected to the other end of the reference voltage source, the inverting input end of the comparator being used for inputting a feedback signal representing the size of the output voltage of the switching power supply, the comparator outputting a control signal following the change of the output voltage of the switching power supply when the switching power supply works, and the control chip generating a PWM signal to control the turn-on and turn-off of the main power switch according to the control signal, so as to realize the slow rising of the output of the switching power supply until the output is stable.

2. The start-up circuit of claim 1, wherein The delay circuit comprises: an RC charging circuit, an input end of the RC charging circuit being the input end of the delay circuit, a ground end of the RC charging circuit being the ground end of the delay circuit, and an output end of the RC charging circuit outputting a voltage signal; a switching circuit, a first input end of the switching circuit being connected to the output end of the RC charging circuit, a second input end of the switching circuit being connected to the input end of the delay circuit, a ground end of the switching circuit being connected to the ground end of the delay circuit, and an output end of the switching circuit being the output end of the delay circuit; when the switching power supply works, the output end voltage of the switching circuit is low during the initial stage of the delay power-on, the control chip does not work, and the output end of the switching circuit becomes in a floating state as the voltage signal outputted by the output end of the RC charging circuit rises to a set value, and the control chip starts to work.

3. The start-up circuit of claim 2, wherein: The RC charging circuit comprises a resistor R15 and a capacitor C11, one end of the resistor R15 being the input end of the RC charging circuit, the other end of the resistor R15 and one end of the capacitor C11 being connected together as the output end of the RC charging circuit, and the other end of the capacitor C11 being the ground end of the RC charging circuit.

4. The start-up circuit of claim 3, wherein: The RC charging circuit further comprises a discharging circuit, the discharging circuit being connected to the capacitor C11 and being used for discharging the energy stored in the capacitor C11 after the switching power supply completes starting.

5. The start-up circuit of claim 4, wherein: The discharging circuit comprises a diode D14, one end of the diode D14 being connected to one end of the capacitor C11, and the other end of the diode D14 being connected to the input end of the RC charging circuit.

6. The start-up circuit of claim 2, wherein: The switch circuit comprises resistors R21, R22, R24, R25, a transistor Q21 and a transistor Q22; one end of the resistor R21 is a first input end of the switch circuit, the other end of the resistor R21 is connected with one end of the resistor R22, the base of the transistor Q21 and one end of the resistor R25, one end of the resistor R24 is a second input end of the switch circuit, the other end of the resistor R24 is connected with the collector of the transistor Q21 and the base of the transistor Q22, the other end of the resistor R25 and the collector of the transistor Q22 are connected together as an output end of the switch circuit, the other end of the resistor R22, the emitter of the transistor Q21 and the emitter of the transistor Q22 are connected together as a ground end of the switch circuit.

7. The start-up circuit of claim 6, wherein: The switch circuit further comprises a diode D23, one end of the diode D23 is connected with one end of the resistor R25, the other end of the diode D23 is connected with the other end of the resistor R21, one end of the resistor R22 and the base of the transistor Q21.

8. The start-up circuit of claim 6, wherein: The switch circuit further comprises a voltage stabilizing diode D22, the base of the transistor Q21 is connected with the anode of the voltage stabilizing diode D22, the cathode of the voltage stabilizing diode D22 is connected with the connection point of the other end of the resistor R21, one end of the resistor R22 and one end of the resistor R25.

9. The start-up circuit of claim 6, wherein: The switch circuit further comprises a capacitor C22, the capacitor C22 is connected with the resistor R22 in parallel.

10. A switching power supply, which is controlled by a control chip to control the turn-on and turn-off of a main power switch tube to realize energy conversion, and comprises an input filter capacitor and / or an output filter capacitor, characterized in that: The switch power supply further comprises the starting circuit according to any one of claims 1 to 9.

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