A switching power supply, a power adapter and a charger

Abstract

The present invention provides a switching power supply, a power adapter and a charger. The switching power supply includes a current-type PWM control unit, a transformer, and a DC power supply circuit and a power compensation auxiliary circuit connected in series in sequence. The current-type PWM control unit includes a current detection terminal; the input end of the DC power supply circuit is connected to an auxiliary voltage output terminal, and the auxiliary voltage output terminal outputs an auxiliary voltage associated with the output voltage of the switching power supply, and the auxiliary voltage is used to judge the magnitude relationship between the output voltage and the threshold voltage; when the current output voltage of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates a DC voltage, thereby providing a compensation level to the current detection terminal; otherwise, no compensation level is provided to the current detection terminal. The present invention ensures that when a lower voltage is output, even if a short circuit or other fault occurs, the output current will not be too large, and at the same time, the rated maximum limit power can be output when a higher voltage is output.

Description

Technical Field

[0001] The present invention relates to the field of power supplies, and particularly to a switching power supply, a power adapter, and a charger. Background Art

[0002] Switching power supplies with transformers are widely used in electronic products, such as power adapters or chargers. In some cases, when the load of the switching power supply is overloaded or short-circuited, it may cause the output current of the switching power supply to exceed the rated range, which may pose a safety hazard.

[0003] To solve the above safety problems, the International Electrotechnical Commission (IEC) has specified the tests that a limited power supply (LPS) needs to meet. For example, for a certain type of power supply: the output open-circuit voltage does not exceed 30 Vdc, the maximum output short-circuit current does not exceed 8 A, and the maximum output power does not exceed 100 VA.

[0004] In the prior art, there are usually the following several methods to meet the LPS test or to address the safety problems corresponding to the scenarios of the LPS test:

[0005] (1) Connect a PTC resistor in series on the output loop of the secondary winding of the switching power supply. However, connecting a PTC resistor in series in the power loop will reduce the efficiency of the power converter, which will cause the power converter to fail to meet the six-level energy efficiency requirements.

[0006] (2) Connect a fuse in series on the output loop of the secondary winding of the switching power supply. However, since the fuse after melting is not recoverable, the product reliability is reduced, affecting the after-sales quality of the power converter.

[0007] (3) Adopt a two-stage overcurrent protection circuit. Connect a current sampling resistor in series on the output loop of the secondary winding of the switching power supply, and additionally add peripheral devices such as a comparator for the second-stage overcurrent protection. However, this is not conducive to the miniaturization design of the product and will increase the cost at the same time.

[0008] To improve safety and meet the LPS test, Chinese Patent Document CN101783595B discloses a method for over-power compensation of a flyback power supply. The embodiments of its background art respectively introduce the following two solutions: 1. As shown in this patent document Figure 3 shown, introduce a compensation level from the input voltage of the primary winding of the transformer to the current detection pin CS of the PWM chip, so as to achieve power compensation for the PWM chip; however, this power compensation continues all the time. 2. As shown in this patent document Figure 4 shown, when it is detected that the output voltage Vout increases, turn on the power compensation circuit.

[0009] With the development of consumer electronics, the application of 5G and high-capacity batteries, the market demand for super-fast charging switching power supplies with high power density is increasing. For example, fast charging chargers or adapters with a wide output voltage (5V - 24V) and an output power greater than 50W. However, for these switching power supplies with a wide output range, this power compensation method is not suitable. Summary of the Invention

[0010] Based on the above situation, the main object of the present invention is to provide a switching power supply, a power adapter and a charger, so that even if a fault such as a short circuit occurs when the output voltage is low, the output current will not be too large, thereby improving the safety performance of the product, and at the same time, the rated maximum limit power can also be output when the output voltage is high.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A switching power supply includes a current-mode PWM control unit and a transformer. The current-mode PWM control unit includes a current detection terminal Is. The current detection terminal Is is used to detect the primary winding current of the transformer to control power transmission. The switching power supply further includes a DC power supply circuit and a power compensation auxiliary circuit connected in series in sequence. The input end of the DC power supply circuit is connected to an auxiliary voltage output terminal, and the auxiliary voltage output terminal outputs an auxiliary voltage Vi associated with the output voltage v0 of the switching power supply. The output end of the power compensation auxiliary circuit is connected to the current detection terminal Is. The power compensation auxiliary circuit is used to judge the output voltage of the DC power supply circuit, that is, when the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates a DC voltage to provide a compensation level to the current detection terminal Is; when the current output voltage V0 of the switching power supply is greater than the threshold voltage, the power compensation auxiliary circuit does not generate the DC voltage and does not provide a compensation level to the current detection terminal Is; wherein, the threshold voltage is within the output voltage range of the switching power supply.

[0013] Preferably, the transformer further includes a first auxiliary winding and a second auxiliary winding; the first auxiliary winding has a first auxiliary voltage output terminal for generating a first auxiliary voltage VL associated with the output voltage V0; the second auxiliary winding has a second auxiliary voltage output terminal for generating a second auxiliary voltage VH associated with the output voltage V0, and the first auxiliary voltage VL is less than the second auxiliary voltage VH; the power compensation auxiliary circuit includes a switch K, a comparator A1 and a level generation circuit; the DC power supply circuit includes a first circuit, a second circuit and a third circuit; the input terminal of the first circuit is connected to the first auxiliary voltage output terminal or the second auxiliary voltage output terminal, and the output terminal of the first DC circuit, the switch, the level generation circuit and the current detection terminal Is are connected in sequence; the input terminal of the third circuit is connected to the first auxiliary voltage output terminal, and the output terminal is connected to the first input terminal of the comparator A1; the input terminal of the second circuit is connected to the second auxiliary voltage output terminal, and the output terminal is connected to the second input terminal of the comparator A1; the comparator A1 is used to compare the voltage output by the third circuit and the voltage output by the second circuit. When the current output voltage of the switching power supply is not greater than the threshold voltage, an output control signal is used to control the switch K to conduct, and the level generation circuit generates an output voltage, so as to provide a compensation level to the current detection terminal; when the current output voltage of the switching power supply is greater than the threshold voltage, an output control signal is used to control the switch K to disconnect, and the level generation circuit does not generate an output voltage, so as not to provide a compensation level to the current detection terminal.

[0014] Preferably, the power compensation auxiliary circuit includes a P-type semiconductor switch tube. The DC power supply circuit provides a second voltage VA and a first voltage VB to the current inflow terminal and the control terminal of the P-type semiconductor switch tube respectively, and at least one of the second voltage VA and the first voltage VB is related to the current output voltage V0 of the switching power supply; when the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is greater than the conduction voltage between the current inflow terminal and the control terminal of the P-type semiconductor switch tube, and the P-type semiconductor switch tube conducts, and the power compensation auxiliary circuit generates a DC voltage, so as to provide a compensation level to the current detection terminal; when the current output voltage V0 of the switching power supply is greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is less than the conduction voltage between the current inflow terminal and the control terminal of the P-type semiconductor switch tube, and the P-type semiconductor switch tube turns off, and the power compensation auxiliary circuit does not generate a DC voltage, so as not to provide a compensation level to the current detection terminal.

[0015] Preferably, the P-type semiconductor switch tube includes a PNP triode or a P-channel field effect transistor; the current input end and the control end of the PNP triode are the emitter and the base respectively; the current input end and the control end of the P-channel field effect transistor are the source and the gate respectively.

[0016] Preferably, the power compensation auxiliary circuit further includes a resistor voltage division module, the resistor voltage division module includes a first resistor R1 and a second resistor R2, the collector of the PNP triode is connected to the current detection terminal Is through the second resistor, and the current detection terminal Is is connected to the sampling resistor Rs of the primary winding of the transformer through the first resistor; when the PNP triode Q2 is turned on, the second voltage VA provides a compensation level to the current detection terminal by applying voltages on the first resistor R1 and the second resistor R2.

[0017] Preferably, the transformer further includes a first auxiliary winding and a second auxiliary winding. The first auxiliary winding is used to generate a first auxiliary voltage VL associated with the output voltage; the second auxiliary winding is used to generate a second auxiliary voltage VH associated with the output voltage, and the first auxiliary voltage VL is less than the second auxiliary voltage VH; the DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit. The first DC power supply circuit is used to output a first voltage VB according to the input first auxiliary voltage VL; the second DC power supply circuit is used to output a second voltage VA according to the input second auxiliary voltage VH.

[0018] Preferably, the second DC power supply circuit includes a third resistor R3, an N-channel MOS transistor Q3, a first zener diode ZD1, and a capacitor C1, and the first DC power supply circuit includes a second zener diode ZD2; the second auxiliary voltage VH is grounded through the third resistor R3 and the first zener diode ZD1, and the anode of the first zener diode ZD1 is grounded; the drain, gate, and source of the N-channel MOS transistor Q3 are connected to the second auxiliary voltage VH, the cathode of the first zener diode ZD1, and the emitter of the PNP triode Q2 respectively, wherein the emitter of the PNP triode Q2 outputs the second voltage VA; the first auxiliary voltage VL is connected to the base of the PNP triode Q2 through the second zener diode ZD2, and the anode of the second zener diode ZD2 is connected to the first auxiliary voltage VL, wherein the voltage of the base of the PNP triode Q2 is the first voltage VB.

[0019] Preferably, the second DC power supply circuit includes a voltage regulator chip, and the first DC power supply circuit includes a second zener diode ZD2; the voltage regulator chip outputs the second voltage VA according to the input second auxiliary voltage VH, where the second voltage VA is a set voltage value or a voltage value associated with the second auxiliary voltage VH; the first auxiliary voltage VL is connected to the base of the PNP transistor Q2 through the second zener diode ZD2, and the cathode of the second zener diode ZD2 is connected to the base of the PNP transistor Q2, where the voltage of the base of the PNP transistor Q2 is the first voltage VB.

[0020] Preferably, the transformer further includes an auxiliary winding for generating an auxiliary voltage Vi associated with the output voltage of the switching power supply; the DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit, the first DC power supply circuit is used to output a first voltage VB according to the input auxiliary voltage Vi; the second DC power supply circuit is used to output a second voltage VA according to the input auxiliary voltage Vi.

[0021] Preferably, the voltage regulation value of the second zener diode ZD2 is determined according to the threshold voltage.

[0022] Preferably, the switching power supply further includes a third zener diode ZD3 and a fourth zener diode ZD4; the second voltage VA is connected to the power supply terminal VCC of the PWM control unit through the third zener diode ZD3, and the first auxiliary voltage VL is connected to the power supply terminal VCC of the PWM control unit through the fourth zener diode ZD4, and the cathodes of the third zener diode ZD3 and the fourth zener diode ZD4 are connected to the power supply terminal VCC of the PWM control unit; the voltage regulation value of the first zener diode ZD1 is determined by the power supply range of the power supply terminal VCC of the PWM control unit.

[0023] Preferably, the output voltage range of the switching power supply is 5 - 24V, or at least partially overlaps with the voltage range of 5 - 24V.

[0024] The present invention also provides a power adapter or charger, including the switching power supply described in any one of the foregoing.

[0025]

Beneficial effects

[0026] By setting the above-mentioned threshold voltage, when the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates an output voltage, thereby providing a compensation level to the current detection terminal Is. This compensation level is superimposed on the voltage across the current sampling resistor, causing the level detected by the PWM control unit through the current detection terminal Is to increase. As a result, at a relatively small power below the maximum limit output power, the duty cycle of the PWM signal is reduced, ultimately maintaining the power of the primary winding at this relatively small power, that is, maintaining the output power at a smaller value, and further maintaining the output current at a smaller value, making it easier to meet the requirements of the LPS test or reducing the safety risk in practical applications. Additionally, since the power compensation auxiliary circuit stops providing the compensation level to the current detection terminal Is when the output voltage V0 is greater than the threshold voltage, the actual output power of the switching power supply in this output voltage range will not be reduced (for example, the output of the switching power supply can reach its maximum limit output power), improving the charging efficiency, which is particularly important for fast charging power adapters. At the same time, stopping the supply of the compensation level can reduce power consumption and improve the energy efficiency of the switching power supply.

[0027] In some embodiments, compared with a switching power supply that does not adopt the power compensation auxiliary circuit of the present invention, the output voltage ripple is smaller and the audible noise is smaller.

[0028] In a preferred solution, the P-type semiconductor switch (such as a PNP triode) serves both as a device for comparing the magnitudes of the first voltage VB and the second voltage VA to further compare the magnitudes of the output voltage V0 and the threshold voltage, and as a switch for controlling the power supply channel of the DC power supply circuit to the power compensation auxiliary circuit, with a simple circuit structure, relatively small volume and power consumption.

[0029] Other beneficial effects of the present invention will be described in the specific implementation manners through the introduction of specific technical features and technical solutions. Those skilled in the art should be able to understand the beneficial technical effects brought by these technical features and technical solutions through the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following will describe the preferred embodiments according to the present invention with reference to the drawings. In the figures:

[0031] Figure 1 is a schematic diagram of a switching power supply according to a preferred embodiment of the present invention

[0032] Figure 2 is a schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0033] Figure 3 is a schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0034] Figure 4 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0035] Figure 5 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0036] Figure 6 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0037] Figure 7 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0038] Figure 8 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0039] Figure 9 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0040] Figure 10 Schematic diagram of a switching power supply according to another preferred embodiment of the present invention

[0041] Figure 11 Waveform diagram of the output current and output voltage of a switching power supply that does not adopt the present invention

[0042] Figure 12 Output voltage ripple of a switching power supply that does not adopt the present invention

[0043] Figure 13 Waveform diagram of the output current and output voltage of an embodiment of the switching power supply adopting the present invention

[0044] Figure 14 Output voltage ripple of an embodiment of the switching power supply adopting the present invention Specific implementation mode

[0045] Figure 1 Schematic diagram of a switching power supply of an embodiment of the present invention, the switching power supply has a wide output voltage, that is, the output voltage range is relatively wide, such as 2 - 30V, or 5 - 24V, or variable output voltage (5V - 9V / 5V - 11V / 5V - 12V / 5V - 15V / 5V - 20V), or its output voltage range V min -V max Overlaps at least partially with the voltage range of 5 - 24V. This switching power supply is particularly suitable for fast - charging power adapters or chargers with high power density and wide output voltage.

[0046] The switching power supply includes a current-mode PWM control unit (such as a current-mode PWM control chip), a transformer T, a power switch Q1, a current sampling resistor Rs, a DC power supply circuit, a power compensation auxiliary circuit, a clamping circuit, a filtering circuit, and a voltage feedback circuit (not shown in the figure). The primary winding NP of the transformer T inputs the rectified DC voltage Vbulk (the DC voltage Vbulk is obtained through AC rectification and filtering). The clamping circuit is connected in parallel with the primary winding to provide clamping protection. The secondary winding NS outputs the voltage V0 through the filtering circuit. The primary winding is grounded through the power switch Q1 and the current sampling resistor Rs connected in series in sequence. The current-mode PWM control unit also includes a voltage detection terminal (not shown in the figure) and a current detection terminal Is. The voltage feedback signal obtained by the output voltage V0 through the voltage feedback circuit is input to the voltage detection terminal. The PWM control unit generates a corresponding PWM control signal according to the voltage feedback signal, so as to control and maintain the output voltage at the required output voltage V0. The current detection terminal Is is used to detect the primary winding current of the transformer T by detecting the voltage on the current sampling resistor Rs. When the detected voltage is greater than the set voltage, the duty cycle of the PWM signal controlling the power switch Q1 is reduced to control the primary winding current, that is, to control the power of the primary winding, and further control the power transmission of the transformer T, thus controlling the output power.

[0047] The DC power supply circuit, the power compensation auxiliary circuit, and the current detection terminal Is are connected in series in sequence. The input end of the DC power supply circuit is connected to the auxiliary voltage output end. The auxiliary voltage output end outputs an auxiliary voltage Vi associated with the output voltage V0 of the switching power supply. The output end of the power compensation auxiliary circuit is connected to the current detection terminal Is. As Figure 3 shown, the voltage Vi can be the output voltage VH or VL of the auxiliary winding.

[0048] A threshold voltage is preset within the output voltage range (V min -V max ) of the switching power supply. The threshold voltage is greater than V min and less than V max . For example, the threshold voltage can be approximately equal to V max / 2.

[0049] Since the PWM control unit actually controls the output power by controlling the power of the primary winding, the PWM control unit only limits the maximum output power. For a switching power supply with a wide output voltage range, when the output voltage is at a relatively low value, if the load is overloaded or short-circuited, the output current will become very large, which may exceed the range specified by the LPS test, or this large current may pose a safety hazard in actual applications. For example, for a switching power supply with an output range of 5 - 20V and a maximum limit power of 60W, when the output voltage is 5V, if the load is short-circuited, the output current can reach 12A before the PWM control unit triggers the power protection action of reducing the PWM duty cycle. However, 12A is greater than the 8A required by the LPS test, resulting in failure to pass the LPS test, or bringing great safety risks to actual applications. When the output voltage is 20V, even if the load is short-circuited, once the maximum output current reaches 60W / 20V = 3A, the power protection action of the PWM control unit is triggered, and this maximum current does not exceed the requirements of the LPS test, and the risk in actual applications is also relatively low. It can be seen that in such switching power supplies with a wide output voltage range, when the output voltage is relatively low, the output current is more likely to exceed the safe range. As long as the output current when the voltage is low is controlled not to exceed the safe range, the output current when the voltage is high will not exceed the safe range either.

[0050] To solve the above problems, the present invention provides the above-mentioned threshold voltage. When the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates a DC voltage, thereby providing a compensation level to the current detection terminal Is. This compensation level is superimposed on the voltage across the current sampling resistor Rs, making the level detected by the PWM control unit through the current detection terminal Is larger. As a result, the duty cycle of the PWM signal is reduced at a relatively small power below the maximum limit output power, ultimately maintaining the power of the primary winding at this smaller power, that is, maintaining the output power at a smaller value, and further maintaining the output current at a smaller value, making it easier to meet the requirements of the LPS test or reducing safety risks in actual applications. Additionally, when the output voltage V0 is greater than the threshold voltage, the power compensation auxiliary circuit does not generate a DC voltage, thereby stopping providing the compensation level to the current detection terminal Is. Therefore, the actual output power of the switching power supply in this output voltage range will not be reduced (for example, the output of the switching power supply can reach its maximum limit output power of 60W. When the output voltage V0 is greater than the threshold voltage, the switching power supply can output 60W. However, when the output voltage V0 is less than the threshold voltage, the power that the switching power supply can output is less than 60W). This improves the charging efficiency, which is particularly important for fast charging power adapters or chargers. Additionally, stopping providing the compensation level can reduce power consumption and improve the energy efficiency of the switching power supply.

[0051] The magnitude of the compensation level can be where V RSis the voltage across the sampling resistor Rs when the switching power supply outputs the maximum limited output power without the power compensation auxiliary circuit, V min is the minimum value of the output voltage range of the switching power supply, I max is the maximum limited output current.

[0052] For example, when the output range is 5 - 20V, V RS = 1V, P max = 60W, I max = 8A:

[0053] V min ·I max = 5v * 8A = 40W,

[0054] Then the compensation level can be taken as 330mV. In some specific applications, the compensation level can be between 50mV - 700mV.

[0055] Figure 2 is a more preferred embodiment of the switching power supply of the present invention. The power compensation auxiliary circuit includes a PNP transistor Q2 and a resistor voltage division module. The DC power supply circuit provides a second voltage VA and a first voltage VB to the emitter and base of the PNP transistor Q2 respectively according to the input voltage Vi. The input end of the resistor voltage division module is connected to the collector of the PNP transistor Q2, and the output is connected to the current detection terminal Is. At least one of the second voltage VA and the first voltage VB is related to the current output voltage V0 of the switching power supply. When the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is greater than the conduction voltage between the emitter and base of the PNP transistor Q2 (this conduction voltage is usually about 0.7V), the PNP transistor Q2 conducts, and the power compensation auxiliary circuit generates an output voltage, thereby providing a compensation level to the current detection terminal Is through the resistor voltage division module; when the current output voltage V0 of the switching power supply is greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is less than the conduction voltage V EB between the emitter and base of the PNP transistor Q2, the PNP transistor Q2 turns off, and the power compensation auxiliary circuit does not generate an output voltage, thereby not providing a compensation level to the current detection terminal Is. The PNP transistor Q2 serves both as a device for comparing the magnitudes of the first voltage VB and the second voltage VA and thus comparing the output voltage V0 with the threshold voltage, and as a switch for controlling the power supply channel of the DC power supply circuit to the power compensation auxiliary circuit. The circuit structure is simple, and the volume and power consumption are relatively small.

[0056] In some embodiments, the second voltage VA is a fixed value, while the first voltage VB is a voltage positively correlated with the output voltage V0, such as a multiple of the output voltage V0;

[0057] In some other embodiments, the first voltage VB is a fixed value, while the second voltage VA is a voltage related to the output voltage V0.

[0058] Figure 4 This is a more preferred embodiment of the switching power supply of the present invention. The power compensation auxiliary circuit further includes a resistor voltage division module. The resistor voltage division module includes a first resistor R1 and a second resistor R2. The collector of the PNP transistor Q2 is connected to the current detection terminal Is through the second resistor R2, and the current detection terminal Is is connected to the sampling resistor Rs of the primary winding of the transformer T through the first resistor R1. When the PNP transistor Q2 is turned on, the second voltage VA provides a compensation level to the current detection terminal Is by applying voltages on the first resistor R1 and the second resistor R2. The magnitude of the compensation level is:

[0059]

[0060] Figure 5 This is a more preferred embodiment of the switching power supply of the present invention. The transformer T further includes a first auxiliary winding and a second auxiliary winding. The first auxiliary winding has a first auxiliary voltage output terminal and is used to generate a first auxiliary voltage VL associated with the output voltage (for example, with a magnitude equal to V0) (the induced electromotive force generated on the first auxiliary winding passes through the first diode D1 and the capacitor C1 to generate the first auxiliary voltage VL). The second auxiliary winding has a second auxiliary voltage output terminal and is used to generate a second auxiliary voltage VH associated with the output voltage. The first auxiliary voltage VL is less than the second auxiliary voltage VH (for example, with a magnitude equal to 3V0) (the induced electromotive force generated on the second auxiliary winding passes through the second diode D2 and the capacitor C2 to generate the second auxiliary voltage VH). The DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit. The first DC power supply circuit is used to output the first voltage VB according to the input first auxiliary voltage VL. The second DC power supply circuit is used to output the second voltage VA according to the input second auxiliary voltage VH.

[0061] Figure 6This is a more preferred embodiment of the switching power supply of the present invention. The second DC power supply circuit includes a third resistor R3, an N-channel MOS transistor Q3, a first zener diode ZD1, and a capacitor C3. The first DC power supply circuit includes a second zener diode ZD2; the second auxiliary voltage VH is grounded through the third resistor R3 and the first zener diode ZD1, and the anode of the first zener diode ZD1 is grounded; the drain, gate, and source of the N-channel MOS transistor Q3 are connected to the second auxiliary voltage VH, the cathode of the first zener diode ZD1, and the emitter of the PNP transistor Q2, respectively, where the emitter of the PNP transistor Q2 outputs the second voltage VA; the first auxiliary voltage VL is connected to the base of the PNP transistor Q2 through the second zener diode ZD2, and the anode of the second zener diode ZD2 is connected to the first auxiliary voltage VL, where the voltage of the base of the PNP transistor Q2 is the first voltage VB. When VH≥V ZD1 , the first zener diode ZD1 is reversely broken down, the gate voltage of Q3 is clamped at V ZD1 , and Q3 is turned on. VH starts to charge the capacitor C3 until the voltage of the capacitor C3 reaches V ZD1 -Vth (Vth is the gate-source conduction threshold voltage of Q3), the Q3 transistor is turned off, and the magnitude of the first voltage VA is maintained at V ZD1 -Vth. When VH<V ZD1 , the first zener diode ZD1 cannot be broken down, the gate voltage of Q3 is maintained at VH, Q3 remains turned on, and the magnitude of the first voltage VA is maintained at VH-Vth. When:

[0062] VA-V EB -VL≥V ZD2 When,

[0063] the PNP transistor Q2 is turned on, otherwise it is turned off, where V EB is the conduction voltage between the emitter and collector of the PNP transistor Q2, and V ZD2 is the reverse breakdown voltage of the second zener diode ZD2).

[0064] In one embodiment, if: VH = 3V0, VL = V0, and the reverse breakdown voltage of the first zener diode ZD1 is 16V;

[0065] (1) When VH≥16V (i.e., V0≥16 / 3V = 5.3v),

[0066] When the PNP transistor Q2 is turned on, there is the following relationship: VA-VB≥0.7,

[0067] and VA = 16-Vth, VB = V ZD2 +V0,

[0068] That is: (16-Vth)-(VZD2 (+V0) ≥ 0.7,

[0069] 16 - Vth - 0.7 - V0 ≥ V ZD2 Therefore, V0 ≤ 15.3 - Vth - V ZD2 ,

[0070] That is, the threshold voltage is: 15.3 - Vth - V ZD2 ;

[0071] If V ZD2 is set to 5V and Vth is 2.5V, then the threshold voltage is 7.8V. That is, when the output voltage is between 5.3V - 7.8V, power compensation is required. When the output voltage is greater than 7.8V, no power compensation is required.

[0072] (2) When VH < 16V (i.e., V0 < 16 / 3V = 5.3),

[0073] The situation where the PNP transistor Q2 conducts has the following relationship: VA - VB ≥ 0.7,

[0074] And VA = 3V0 - Vth, VB = V ZD2 +V0,

[0075] (3V0 - Vth) - (V ZD2 +V0) ≥ 0.7, that is: 2V0 - Vth - 0.7 ≥ V ZD2 Therefore,

[0076] (Vth + 0.7 + V ZD2 ) / 2 ≤ V0.

[0077] If V ZD2 is set to 5V and Vth is 2.5V, (Vth + 0.7 + V ZD2 ) / 2 = 4.4V, and the minimum value of the output voltage is 5V. So, when the output voltage is between 5V - 5.3V, power compensation is required. When the output voltage is less than 5V, it will not work properly.

[0078] In summary, when the output voltage is between 5V - 7.8V, power compensation is required; when the output voltage is greater than 7.8V, no power compensation is required. Therefore, when the output voltage V0 is not greater than the threshold voltage (15.3 - Vth - V ZD2 ), to make the PNP transistor Q2 conduct, power compensation is required.

[0079] It can be seen that for a determined VA and the first auxiliary voltage VL, the designed threshold voltage determines the reverse breakdown voltage V ZD2 of the second voltage regulator diode ZD2 to be selected.

[0080] Figure 7 is a more preferred embodiment of the switching power supply of the present invention. This switching power supply is basically similar to Figure 6 , and the main differences include the differences in the second DC power supply circuit. The second DC power supply circuit includes a voltage stabilizing chip, and the first DC power supply circuit includes a second zener diode ZD2; the voltage stabilizing chip outputs a stable second voltage VA according to the input second auxiliary voltage VH, where the second voltage VA is a set voltage value (for example, 15 - 17V); the first auxiliary voltage VL is connected to the base of the PNP transistor Q2 through the second zener diode ZD2, and the cathode of the second zener diode ZD2 is connected to the base of the PNP transistor Q2. Among them, the voltage of the base of the PNP transistor Q2 is the first voltage VB.

[0081] Figure 8 is a more preferred embodiment of the switching power supply of the present invention. This switching power supply is generally similar to the Figure 6 switching power supply, and the main differences include the differences in the auxiliary winding and the DC power supply circuit. The transformer T also includes an auxiliary winding, and the auxiliary winding is used to generate an auxiliary voltage Vi associated with the output voltage of the switching power supply; the DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit. The first DC power supply circuit is used to output a first voltage VB according to the input auxiliary voltage Vi; the second DC power supply circuit is used to output a second voltage VA according to the input auxiliary voltage Vi. For example, the second DC power supply circuit of this embodiment can use a voltage stabilizing chip to output a second voltage VA with a fixed voltage value, and the first DC power supply circuit can use the first DC power supply circuit as shown in Figure 7 .

[0082] Figure 9 is a more preferred embodiment of the switching power supply of the present invention. The switching power supply further includes a third zener diode ZD3, a fourth zener diode ZD4, and a fourth resistor R4; the second voltage VA is connected to the power supply terminal VCC of the PWM control unit through the third zener diode ZD3, the first auxiliary voltage VL is connected to the power supply terminal VCC through the fourth zener diode ZD4, the cathodes of the third zener diode ZD3 and the fourth zener diode ZD4 are connected to the power supply terminal VCC of the PWM control unit, and the voltage stabilizing value of the first zener diode ZD1 is determined by the power supply range of the power supply terminal VCC of the PWM control unit. In addition, the first auxiliary voltage VL is grounded through the fourth resistor R4.

[0083] According to Figure 6 the embodiment, when VH≥V ZD1 , the voltage of the second voltage VA is maintained at V ZD1 -Vth, and when VH<V ZD1 , the voltage of the second voltage VA is maintained at VH - Vth.

[0084] (1) When VA > VL, VCC = VA - V ZD3 = V ZD1 - Vth - V ZD3 ,

[0085] It can be seen that the regulated voltage value of the first voltage - regulating diode ZD1 is determined by the power - supply range of the power - supply terminal VCC of the PWM control unit, where V ZD3 is the forward conduction voltage of the third voltage - regulating diode ZD3, usually about 0.7V;

[0086] (2) When VA ≤ VL, VCC = VL - V ZD4 (V ZD4 is the forward conduction voltage of the fourth voltage - regulating diode ZD4, usually about 0.7V).

[0087] Specific examples are as follows: If VH = 3V0, VL = V0, Vth = 2.5V,

[0088] (1) When V0 = 5V, VA = 15V - 2.5V = 12.5V, VL = 5V,

[0089] Therefore, VCC = VA - V ZD3 = 12.5V - 0.7V = 11.8V;

[0090] (2) When V0 = 20V, VA = 16V - 2.5V = 13.5V, VL = 20V,

[0091] Therefore, VCC = VL - V ZD4 = 12V - 0.7V = 11.3V.

[0092] Figure 3This is a more preferred embodiment of the switching power supply of the present invention. The transformer T further includes a first auxiliary winding and a second auxiliary winding; the first auxiliary winding has a first auxiliary voltage output terminal for generating a first auxiliary voltage VL associated with the output voltage; the second auxiliary winding has a second auxiliary voltage output terminal for generating a second auxiliary voltage VH associated with the output voltage, and the first auxiliary voltage VL is less than the second auxiliary voltage VH; the power compensation auxiliary circuit includes a switch K, a comparator A1, and a level generation circuit; the DC power supply circuit includes a first DC power supply circuit, a second DC power supply circuit, and a third DC power supply circuit; the input terminal of the first DC power supply circuit is connected to the first auxiliary voltage output terminal or the second auxiliary voltage output terminal, and the output terminal of the first DC power supply circuit, the switch K, the level generation circuit, and the current detection terminal Is are connected in sequence; the input terminal of the third DC power supply circuit is connected to the first auxiliary voltage output terminal, and the output terminal is connected to the first input terminal (such as the inverting input terminal) of the comparator A1 to input the first auxiliary voltage VL; the input terminal of the second DC power supply circuit is connected to the second auxiliary voltage output terminal, and the output terminal is connected to the second input terminal (such as the non-inverting input terminal) of the comparator A1; the comparator A1 is used to compare the voltage output by the third DC power supply circuit and the voltage output by the second DC power supply circuit, so that when the current output voltage V0 of the switching power supply is not greater than the threshold voltage, an output control signal is output to control the switch K to conduct, and the level generation circuit generates an output voltage, thereby providing a compensation level to the current detection terminal Is; when the current output voltage V0 of the switching power supply is greater than the threshold voltage, the output control signal controls the switch K to disconnect, and the level generation circuit does not generate an output voltage, thereby not providing a compensation level to the current detection terminal Is. The above second DC power supply circuit can adopt Figure 6 The second DC power supply circuit in, so the magnitude of the voltage input to the non-inverting input terminal is the second voltage VA. The above first DC power supply circuit can adopt a resistor, so the magnitude of the voltage input to the inverting input terminal is VL. The level generation circuit can adopt Figure 4 The resistor voltage division module in.

[0093] Figure 10 This is a more preferred embodiment of the switching power supply of the present invention. This embodiment is substantially the same as Figure 4 The switching power supply, and the main difference includes replacing the PNP triode Q2 with the P-channel field effect transistor Q4. As Figure 10As shown in the figure, the power compensation auxiliary circuit includes a P-channel field effect transistor Q4. The DC power supply circuit provides a second voltage VA and a first voltage VB to the source and gate of the P-channel field effect transistor Q4 respectively. At least one of the second voltage VA and the first voltage VB is related to the current output voltage V0 of the switching power supply. When the current output voltage V0 of the switching power supply is not greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is greater than the conduction voltage between the source and gate of the P-channel field effect transistor Q4, and the P-channel field effect transistor Q4 is turned on. The power compensation auxiliary circuit generates an output voltage, thereby providing a compensation level to the current detection terminal. When the current output voltage V0 of the switching power supply is greater than the threshold voltage, the difference between the second voltage VA and the first voltage VB is less than the conduction voltage between the source and gate of the P-channel field effect transistor Q4, and the P-channel field effect transistor Q4 is turned off. The power compensation auxiliary circuit does not generate an output voltage, thereby not providing a compensation level to the current detection terminal.

[0094] Figure 11 is a waveform diagram of the output current and output voltage of the switching power supply without adopting the present invention. In the figure, curve 2 and curve 1 are the output current and output voltage of the switching power supply respectively. It can be seen that the output current reaches a maximum of 9.54 A before entering the current limiting protection, which does not meet the LPS test requirement of less than 8 A. Figure 12 is the output voltage ripple of the switching power supply without adopting the present invention. It can be seen from the figure that the output voltage ripple reaches 184 mV.

[0095] Figure 13 is a waveform diagram of the output current and output voltage of an embodiment of the switching power supply adopting the present invention. In the figure, curve 2 and curve 1 are the output current and output voltage of the switching power supply respectively. It can be seen that the output current enters the current limiting protection when it reaches 6.6 A, which meets the LPS test requirement of less than 8 A. Figure 14 is the output voltage ripple of the switching power supply adopting the present invention. It can be seen from the figure that the output voltage ripple is only 124 mV. It can be seen that the present invention can also reduce the output voltage ripple.

[0096] Those skilled in the art can understand that on the premise of no conflict, the above preferred solutions can be freely combined and superimposed.

[0097] It should be understood that the above embodiments are exemplary rather than restrictive. Without departing from the basic principles of the present invention, various obvious or equivalent modifications or substitutions made by those skilled in the art to the above details will be included within the scope of the claims of the present invention.

Claims

1. A switching power supply includes a current-mode PWM control unit and a transformer. The transformer includes a primary winding and a secondary winding. The current-mode PWM control unit includes a current detection terminal, and the current detection terminal is used to detect the primary winding current of the transformer so as to control power transmission. Characterized in that, The switching power supply further includes a DC power supply circuit and a power compensation auxiliary circuit connected in series in sequence. The input end of the DC power supply circuit is connected to an auxiliary voltage output end, and the auxiliary voltage output end outputs an auxiliary voltage associated with the output voltage of the switching power supply. The output end of the power compensation auxiliary circuit is connected to the current detection terminal. The power compensation auxiliary circuit is used to judge the output voltage of the DC power supply circuit. That is, when the current output voltage of the switching power supply is not greater than the threshold voltage, the power compensation auxiliary circuit generates a DC voltage to provide a compensation level to the current detection terminal. When the current output voltage of the switching power supply is greater than the threshold voltage, the power compensation auxiliary circuit does not generate the DC voltage and thus does not provide a compensation level to the current detection terminal. Wherein, the threshold voltage is within the output voltage range of the switching power supply.

2. The switching power supply according to claim 1, Characterized in that, The transformer further includes a first auxiliary winding and a second auxiliary winding. The first auxiliary winding has a first auxiliary voltage output end and is used to generate a first auxiliary voltage associated with the output voltage. The second auxiliary winding has a second auxiliary voltage output end and is used to generate a second auxiliary voltage associated with the output voltage, and the first auxiliary voltage is less than the second auxiliary voltage. The power compensation auxiliary circuit includes a switch, a comparator and a level generation circuit. The DC power supply circuit includes a first circuit, a second circuit and a third circuit. The input end of the first circuit is connected to the first auxiliary voltage output end or the second auxiliary voltage output end, and the output end of the first circuit, the switch, the level generation circuit and the current detection terminal are connected in sequence. The input end of the third circuit is connected to the first auxiliary voltage output end, and the output end is connected to the first input end of the comparator. The input end of the second circuit is connected to the second auxiliary voltage output end, and the output end is connected to the second input end of the comparator. The comparator is used to compare the voltage output by the third circuit and the voltage output by the second circuit. When the current output voltage of the switching power supply is not greater than the threshold voltage, it outputs a control signal to control the switch to conduct, and the level generation circuit generates an output voltage to provide a compensation level to the current detection terminal. When the current output voltage of the switching power supply is greater than the threshold voltage, it outputs a control signal to control the switch to disconnect, and the level generation circuit does not generate an output voltage and thus does not provide a compensation level to the current detection terminal.

3. The switching power supply according to claim 1, Characterized in that, The power compensation auxiliary circuit includes a P-type semiconductor switch. The DC power supply circuit provides a second voltage and a first voltage to the current input end and the control end of the P-type semiconductor switch respectively, and at least one of the second voltage and the first voltage is related to the current output voltage of the switching power supply. When the current output voltage of the switching power supply is not greater than the threshold voltage, the difference between the second voltage and the first voltage is greater than the conduction voltage between the current input end and the control end of the P-type semiconductor switch, and the P-type semiconductor switch is turned on. The power compensation auxiliary circuit generates a DC voltage, thereby providing a compensation level to the current detection end. When the current output voltage of the switching power supply is greater than the threshold voltage, the difference between the second voltage and the first voltage is less than the conduction voltage between the current input end and the control end of the P-type semiconductor switch, and the P-type semiconductor switch is turned off. The power compensation auxiliary circuit does not generate a DC voltage, thereby not providing a compensation level to the current detection end.

4. The switching power supply according to claim 3, wherein, the P-type semiconductor switch includes a PNP triode or a P-channel field effect transistor; the current input end and the control end of the PNP triode are the emitter and the base respectively; the current input end and the control end of the P-channel field effect transistor are the source and the gate respectively.

5. The switching power supply according to claim 4, wherein, the power compensation auxiliary circuit further includes a resistor voltage division module. The resistor voltage division module includes a first resistor and a second resistor. The collector of the PNP triode is connected to the current detection end through the second resistor, and the current detection end is connected to the sampling resistor of the primary winding of the transformer through the first resistor; when the PNP triode is turned on, the second voltage provides a compensation level to the current detection end by applying voltages on the first resistor and the second resistor.

6. The switching power supply according to claim 4, wherein, the transformer further includes a first auxiliary winding and a second auxiliary winding. The first auxiliary winding is used to generate a first auxiliary voltage associated with the output voltage; the second auxiliary winding is used to generate a second auxiliary voltage associated with the output voltage, and the first auxiliary voltage is less than the second auxiliary voltage; the DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit. The first DC power supply circuit is used to output a first voltage according to the input first auxiliary voltage; the second DC power supply circuit is used to output a second voltage according to the input second auxiliary voltage.

7. The switching power supply according to claim 6, wherein, the second DC power supply circuit includes a third resistor, an N-channel MOS transistor, a first voltage stabilizing diode, and a capacitor. The first DC power supply circuit includes a second voltage stabilizing diode; The second auxiliary voltage is grounded through a third resistor and a first zener diode, and the anode of the first zener diode is grounded; the drain, gate, and source of the N-channel MOS transistor are respectively connected to the second auxiliary voltage, the cathode of the first zener diode, and the emitter of the PNP transistor, wherein the emitter of the PNP transistor outputs the second voltage; The first auxiliary voltage is connected to the base of the PNP transistor through the second zener diode, and the anode of the second zener diode is connected to the first auxiliary voltage, wherein the voltage of the base of the PNP transistor is the first voltage.

8. The switching power supply according to claim 6, characterized in that the second DC power supply circuit includes a voltage stabilizing chip, and the first DC power supply circuit includes a second zener diode; the voltage stabilizing chip outputs the second voltage according to the input second auxiliary voltage, wherein the second voltage is a set voltage value or a voltage value associated with the second auxiliary voltage; The first auxiliary voltage is connected to the base of the PNP transistor through the second zener diode, and the cathode of the second zener diode is connected to the base of the PNP transistor, wherein the voltage of the base of the PNP transistor is the first voltage.

9. The switching power supply according to claim 3, characterized in that the transformer further includes an auxiliary winding for generating an auxiliary voltage associated with the output voltage of the switching power supply; the DC power supply circuit includes a first DC power supply circuit and a second DC power supply circuit. The first DC power supply circuit is used to output a first voltage according to the input auxiliary voltage; the second DC power supply circuit is used to output a second voltage according to the input auxiliary voltage.

10. The switching power supply according to claim 7 or 8, characterized in that the voltage stabilizing value of the second zener diode is determined according to the threshold voltage.

11. The switching power supply according to claim 7, characterized in that the switching power supply further includes a third zener diode and a fourth zener diode; the second voltage is connected to the power supply terminal of the PWM control unit through the third zener diode, the first auxiliary voltage is connected to the power supply terminal of the PWM control unit through the fourth zener diode, and the cathodes of the third zener diode and the fourth zener diode are connected to the power supply terminal of the PWM control unit; the voltage stabilizing value of the first zener diode is determined by the power supply range of the power supply terminal of the PWM control unit.

12. The switching power supply according to any one of claims 1-9, 11, characterized in that the output voltage range of the switching power supply is 5-24V, or at least partially overlaps with the voltage range of 5-24V.

13. A power adapter or charger, characterized in that it includes the switching power supply according to any one of claims 1-12.

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