CN211046758U - Switching power supply frequency modulation circuit - Google Patents

Switching power supply frequency modulation circuit Download PDF

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CN211046758U
CN211046758U CN201922017600.XU CN201922017600U CN211046758U CN 211046758 U CN211046758 U CN 211046758U CN 201922017600 U CN201922017600 U CN 201922017600U CN 211046758 U CN211046758 U CN 211046758U
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resistor
capacitor
pin
pwm
pwm modulation
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田新凯
潘成章
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Mornsun Guangzhou Science and Technology Ltd
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Mornsun Guangzhou Science and Technology Ltd
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Abstract

The utility model discloses a switching power supply frequency modulation circuit, its characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1, a capacitor C2 and a capacitor C3; one end of the resistor R1 is connected with a pin pfcout of the PWM modulation chip, and the other end of the resistor R1 is simultaneously connected with one ends of the capacitor C1, the capacitor C2 and the resistor R4; one end of a resistor R2 is connected with a PWM modulation chip pin Vref, and the other end of a resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of a resistor R3; the other end of the resistor R3 is simultaneously connected with a PWM modulation chip pin RAMP and one end of a capacitor C3; the other ends of the resistor R4, the capacitor C2 and the capacitor C3 are simultaneously connected to the pin GND of the PWM modulation chip. The utility model discloses a with PWM modulation chip pin pfc out output half-wave sine law change PWM pulse integral back, obtain half-wave sine's pulsating voltage to through the oscillation frequency of PWM modulation chip pin RAMP modulation PWM modulation chip, make PWM modulation chip operating frequency change according to sine law, thereby can improve the electromagnetic compatibility performance of product.

Description

Switching power supply frequency modulation circuit
Technical Field
The utility model relates to an AC-DC, DC-DC circuit, in particular to switching power supply operating frequency modulation, tremble circuit frequently.
Background
In the field of switching power supplies, various electromagnetic compatibility tests are often required to be met, including conduction and radiation, and the traditional method for modifying conduction and radiation mainly comprises the following steps: the coupling approach is to adjust a common-mode inductor, adapt a safety capacitor, sleeve a magnetic bead on a pin of a power device, sleeve a magnetic bead on a pin of a Y capacitor (safety capacitor), increase shielding and the like.
The Frequency Jitter technique (Frequency Jitter) can effectively solve the EMI problem, and the principle is as follows: the harmonic interference energy is dispersed by utilizing the characteristic of changing the working frequency, two quantization standards, namely quasi-peak value (QP) and Average Value (AV), are usually provided for conduction and radiation tests, and the harmonic quasi-peak value (QP) and the Average Value (AV) are obviously reduced by comparing the test with the harmonic quasi-peak value (QP) and the Average Value (AV) when the frequency jitter technology is adopted compared with the harmonic quasi-peak value (QP) and the Average Value (AV) when the frequency jitter technology is not adopted.
However, a part of PWM modulation chips do not have frequency dithering technology, especially a switching power supply with PFC function, and harmonics generated by a PFC circuit have the characteristics of narrow frequency band and large amplitude, and cover the whole conduction and radiation test frequency band, such as CM6800UXIS model PWM modulation chips of rainbow crown brand.
SUMMERY OF THE UTILITY MODEL
With this in mind, the present invention is to provide a switching power supply frequency modulation circuit, which reduces the quasi-peak value (QP) and the Average Value (AV) of the conduction and radiation of the switching power supply.
The utility model discloses an inventive concept can realize that switching power supply operating frequency can change for the oscillation frequency setting pin in utilizing the PWM modulation chip to reach the effect of frequency jitter technique. Specifically, the PWM pulse (including the PWM pulse which is output by the PFC output drive pin and changes regularly) output by the PWM output drive pin in the PWM modulation chip is integrated to obtain the pulsating voltage, and the operating frequency of the switching power supply is modulated by modulating the oscillation frequency setting pin of the PWM modulation chip.
In order to solve the above technical problem, the utility model provides a first technical scheme as follows:
a switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1, a capacitor C2 and a capacitor C3; one end of the resistor R1 is used for connecting a PFC output driving pin of the PWM modulation chip, and the other end of the resistor R1 is simultaneously connected with one end of the capacitor C1, one end of the capacitor C2 and one end of the resistor R4; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3.
In order to solve the above technical problem, the utility model provides a second technical scheme as follows:
a switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a capacitor C1, a capacitor C2, a capacitor C3, a diode D1 and a diode D2; the anode of the diode D2 is used for being connected with a PFC output driving pin of the PWM modulation chip, the cathode of the diode D2 is connected with one end of a resistor R1, and the other end of the resistor R1 is simultaneously connected with one end of a capacitor C1, one end of a capacitor C2, one end of a resistor R4 and one end of a resistor R5; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3; the anode of the diode D1 is used for connecting the PWM output driving pin of the PWM modulation chip, and the cathode of the diode D1 is connected to the other end of the resistor R5.
In order to solve the above technical problem, the utility model provides a third technical scheme as follows:
a switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a capacitor C2, a capacitor C3, a diode D1 and a diode D2; the anode of the diode D2 is used for connecting a PFC output driving pin of the PWM modulation chip, the cathode of the diode D2 is connected with one end of a resistor R1, and the other end of the resistor R1 is simultaneously connected with one end of a resistor R6, one end of a capacitor C2, one end of a resistor R4 and one end of a resistor R5; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the resistor R6 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3; the anode of the diode D1 is used for connecting the PWM output driving pin of the PWM modulation chip, and the cathode of the diode D1 is connected to the other end of the resistor R5.
The utility model relates to a PWM modulation chip and the relevant pin of present case innovation point and its meaning as follows:
(1) oscillation frequency setting pin: the pin is an oscillator timer node in the PWM chip, and the oscillation frequency of the PWM chip can be set through an external timing resistor and a timing capacitor, for example, the English code of the pin in the CM6800UXIS chip is RAMP, and the English code of the pin in the UC3854 chip is CT;
(2) internal reference voltage output pin: the pin outputs a reference voltage inside the PWM chip, and the English code of the universal pin is Vref;
(3) PFC output drive pin: the pin outputs a driving signal of a power tube in the PFC circuit, for example, the english code of the pin in the CM6800UXIS chip is PFC out, and the english code of the pin in the UC3854 chip is GTDRV:
(4) PWM output drive pin: the pin outputs a driving signal of a power tube in the main power circuit, for example, the English code of the pin in a CM6800UXIS chip is pwm out, and the English code of the pin in an NCP1252E chip is Drv;
(5) a grounding pin: the pin is used for realizing the internal grounding of the PWM chip, and the English code of the universal pin is GND;
the utility model relates to an other pins of PWM modulation chip and circuit connection do not be in the utility model discloses an in the innovation scope, consequently, do not give unnecessary details its meaning.
The utility model discloses specially adapted does not have the PWM modulation chip of integrated frequency jitter technique. Of course, in order to further improve the electromagnetic compatibility (EMI) performance of the product, the circuit of the present invention can also be applied to a PWM modulation chip integrated with a frequency jitter technique. The utility model discloses an analysis of realization principle and detailed theory of operation will combine specific embodiment to explain, will not be repeated here.
The beneficial effects of the utility model are summarized as follows:
(1) the working frequency of the PWM modulation chip is modulated to change according to a sine rule, harmonic interference energy is dispersed, and the quasi-peak value (QP) and the Average Value (AV) of conduction and radiation are reduced.
(2) When the load is abnormal, the working frequency of the switching power supply is instantly improved, and the instant overload capacity of the switching power supply is improved.
(3) When the input voltage of the switching power supply is reduced, the working frequency of the switching power supply is improved, and the load capacity of the switching power supply when the input voltage is reduced is improved.
Drawings
Fig. 1 is a schematic circuit diagram of a first embodiment of the present invention;
fig. 2 is a conductive diagram of a 320W switching power supply without the circuit of the present invention;
FIG. 3 is a conduction diagram of a 320W switching power supply after application of the first embodiment circuit;
fig. 4 is a schematic circuit diagram of a second embodiment of the present invention;
fig. 5 is a schematic circuit diagram of a third embodiment of the present invention.
Detailed Description
The utility model discloses a with PWM modulation chip pin pfc out output half-wave sine law change PWM pulse integral back, obtain half-wave sine's pulsating voltage to through the oscillation frequency of PWM modulation chip pin RAMP modulation PWM modulation chip, make PWM modulation chip operating frequency change according to sine law, thereby can improve the electromagnetic compatibility performance of product. In order to make the present invention easier to understand for those skilled in the art, the present invention will be described below with reference to specific embodiments.
First embodiment
Fig. 1 shows a schematic circuit diagram of the present invention, the PWM modulation chip U1 connected to the switching power supply frequency modulation circuit of this embodiment is a CM6800UXIS model chip of the iris brand, and according to its technical manual, the pin setting and meaning are as follows:
pin 1 IEAO: a transconductance error amplifier output terminal for the PFC current;
pin 2 IAC: PFC increases and overflows the control reference input;
pin 3 ISENSE: the current detection input is sent to a current limiting comparator of the PFC part;
pin 4 VRMS: an RMS line voltage comparator input to the PFC;
pin 5 SS: a soft start capacitor terminal of the PWM section;
pin 6 VDC: a PWM partial voltage feedback input end;
pin 7 RAMP: the oscillator timer contact is arranged by external RT and CT;
pin 8 RAMP: in the current mode of operation, as a current sense input. In the voltage mode operation mode, as PWM input from the PFC output, (feed forward ramp);
a 9 th pin DC I L IMIT, the input end of a PWM current-limiting comparator;
a 10 th pin GND which is a ground terminal;
pin 11 pwm out: PWM output driving;
pin 12 pfc out: PFC output drive;
pin 13 VCC: a supply voltage positive terminal;
14 th pin Vref: an internal 7.5V reference voltage output terminal;
pin 15 VFB: the input end of a transconductance error amplifier for PFC output voltage feedback;
pin 16, VEAO: and the output end of the transconductance error amplifier is used for PFC output voltage feedback.
The switching power supply frequency modulation circuit of the embodiment comprises: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1, a capacitor C2 and a capacitor C3.
The circuit connection relation is as follows: one end of the resistor R1 is connected with a 12 th pin pfc out of the PWM chip U1, and the other end of the resistor R1 is simultaneously connected with one end of the capacitor C1, one end of the capacitor C2 and one end of the resistor R4; one end of the resistor R2 is connected with the 14 th pin Vref of the PWM modulation chip U1, and the other end of the resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is simultaneously connected with a 7 th pin RAMP of the PWM chip U1 and one end of the capacitor C3; the other end of the resistor R4, the other end of the capacitor C2 and the other end of the capacitor C3 are simultaneously connected to the 10 th pin GND of the PWM modulation chip U1.
The implementation principle of the embodiment is as follows: the 14 th pin Vref of the PWM chip U1 is a reference voltage output end, the capacitor C3 is charged through the resistor R2 and the resistor R3, the resistance value of the resistor R2 can be adjusted to set the lowest working frequency of the PWM chip U1, and the PWM chip U1 can normally work in the no-load or starting process. After a half-wave sine-law changing PWM pulse is output by a 14 th pin pfcout of the PWM modulation chip U1 and is integrated, a half-wave sine-shaped pulsating voltage is obtained, and the oscillation frequency of the PWM modulation chip U1 is modulated by a 7 th pin RAMP of the PWM modulation chip U1, so that the working frequency of the PWM modulation chip U1 is changed according to the sine law, harmonic interference energy is dispersed, and quasi-peak value (QP) and Average Value (AV) of conduction (EMI) and radiation (EMI) are reduced.
The detailed working principle analysis is as follows:
(1) when the power supply is started, the 14 th pin Vref of the PWM chip U1 charges the capacitor C1 through the resistor R2 and the resistor R3, so that the internal oscillator of the PWM chip U1 starts oscillation, and the PWM chip U1 can work normally.
(2) After the power supply is started, a 12 th pin pfc out of the PWM modulation chip U1 outputs a half-wave sine-law-changing PWM pulse, and the capacitor C2 is charged through the resistor R1 for integration, the resistor R4 is connected in parallel with the capacitor C2 to discharge for C2, and a half-wave sine-like ripple voltage waveform can be obtained at two ends of the capacitor C2.
(3) The pulsating voltage at the two ends of the capacitor C2 is coupled by the capacitor C1, the capacitor C3 is charged through the resistor R3, the charging current is superposed with the charging current of the capacitor C3 through the resistor R2 on the 14 th pin Vref of the PWM chip U1, and the charging current of the capacitor C3 is changed along with the change of the amplitude value of the half-wave sinusoidal pulsating voltage because the two ends of the capacitor C2 are the half-wave sinusoidal pulsating voltage, so that the working frequency of the PWM chip U1 is changed along with the change of the amplitude value of the half-wave sinusoidal pulsating voltage, and the purpose of modulating the working frequency of the switching power supply is achieved.
FIG. 2 is a graph showing the conduction of 320W switching power supply without the circuit of the present invention, and FIG. 3 is a graph showing the conduction of 320W switching power supply after the circuit of the first embodiment is applied, it can be seen from the test waveform of FIG. 2 that the harmonic band is extremely narrow, but the quasi-peak (QP) amplitude is larger, and the Average (AV) in the harmonic band has exceeded the limits of the CISPR32EN55032, C L ASS class B standard, while it can be seen from the test waveform of FIG. 3 that the harmonic band is broadened, and the maximum quasi-peak (QP) amplitude is also reduced by about 2dB to 3dB as compared with FIG. 2, leaving a margin of about 10dB or more between the measured Average (AV) value and the limits of the CISPR32EN55032, C L ASSB standard over the entire test band.
The comparison shows that the implementation effect of the embodiment is very obvious, the quasi-peak value (QP) and the Average Value (AV) of the conduction (EMI) are effectively reduced, and the practical effect of the Frequency Jitter technique (Frequency Jitter) is achieved.
In this embodiment, the lowest operating frequency of the switching power supply can be set by adjusting the resistance values of the R2 and the resistor R3 in the circuit, and the operating frequency range and the frequency change rate of the switching power supply can be adjusted by adjusting the values of the R1, the resistor R4, the resistor R3, the capacitor C2, and the capacitor C1 in the circuit, so as to achieve the effect of reducing the quasi-peak value (QP) and the Average Value (AV) of conduction (EMI) and radiation (EMI).
Second embodiment
As shown in fig. 4, a schematic circuit diagram of a second embodiment of the present invention is provided, in which a diode D1, a diode D2, and a resistor R5 are added to the circuit based on the first embodiment.
The circuit connection relationship is different from that of the first embodiment in that: the anode of the diode D1 is connected to the 11 th pin PWM out of the PWM modulating chip U1, the cathode of the diode D1 is connected to one end of the resistor R5, and the other end of the resistor R5 is connected to one end of the resistor R4; the resistor R1 has one end connected to the cathode of the diode D2, and the anode of the diode D2 is connected to the 12 th pin pfc out of the PWM modulation chip U1.
The implementation principle of the embodiment is as follows: on the basis of the first embodiment, the PWM pulse output from the 11 th pin PWM out of the PWM modulation chip U1 is superimposed and integrated with the PWM pulse output from the 14 th pin pfc out of the PWM modulation chip U1, so as to obtain a pulsating voltage having the characteristics of the PWM pulse output from the 11 th pin PWM out of the PWM modulation chip U1 and the PWM pulse output from the 14 th pin pfc out of the PWM modulation chip U1, the oscillating frequency of the PWM modulation chip U1 is modulated by the 7 th pin RAMP of the PWM modulation chip U1, except that when the switching power supply normally works, the operating frequency of the PWM modulation chip U1 is varied according to the wave sine law, when the load is abnormal, for example, when the switching power supply outputs an abrupt overload, the duty ratio of the PWM pulse output from the 11 th pin PWM out of the PWM modulation chip U1 is increased and the PWM pulse output from the 14 th pin pfc of the PWM modulation chip U1 is superimposed and integrated, the amplitude of the obtained pulsating voltage is suddenly increased, the 7 th pin RAMP of the PWM chip U1 is used for modulating to enable the oscillation frequency of the PWM chip U1 to be instantly increased, the working frequency of the switching power supply is instantly increased, and the instant overload capacity of the switching power supply is improved.
The detailed operation principle of the circuit of the second embodiment is similar to that of the circuit of the first embodiment, and the differences are as follows:
(1) on the basis of the circuit of the first embodiment, a pulse voltage with characteristics of a PWM pulse output by the 11 th pin PWM out of the PWM modulation chip U1 and a PWM pulse output by the 14 th pin pfc out of the PWM modulation chip U1 are added, the PWM pulse output by the 11 th pin PWM out of the PWM modulation chip U1 passes through the diode D1 and the resistor R5, and the PWM pulse output by the 14 th pin pfc out of the PWM modulation chip U1 passes through the diode D2 and the resistor R1 to integrate charging currents of the capacitor C2 after being superimposed, the resistor R4 is connected in parallel with the capacitor C2 and discharges the capacitor C2, and two ends of the capacitor C2 can obtain the pulse voltage with characteristics of a PWM pulse output by the 11 th pin PWM out of the PWM modulation chip U1 and a.
(2) The pulsating voltage waveform at two ends of the capacitor C2 is coupled by the capacitor C1 and charges the capacitor C3 through the resistor R3, the charging current is superposed with the charging current of the capacitor C3 through the resistor R2 and the resistor R2 at the 14 th pin Vref of the PWM chip U1, and the amplitude of the charging current pulsating voltage for the capacitor C3 changes due to the fact that the two ends of the capacitor C2 are pulsating voltage with variable amplitude, so that the working frequency of the PWM chip U1 also changes along with the amplitude of the pulsating voltage, and the variable working frequency of the switching power supply is achieved.
(3) If the switching power supply output belt is in instantaneous overload, the duty ratio of PWM pulse output by the 11 th pin PWM out of the PWM modulation chip U1 is instantaneously increased, so that the amplitude of pulsating voltage at two ends of the capacitor C2 is suddenly increased, and by (2) in the working principle analysis, the working principle is the 2 nd, the working frequency of the PWM modulation chip U1 is also suddenly increased, the working frequency of the switching power supply can be known to be increased by the switching power supply principle, so that the output power of the switching power supply can be increased, and the instantaneous overload capacity of the switching power supply is increased.
In the present embodiment, since the PWM pulse output from the 11 th pin pwmout of the PWM modulation chip U1 and the PWM pulse output from the 14 th pin pfc out of the PWM modulation chip U1 are simultaneously applied to the circuit of the second embodiment, in order to avoid the PWM pulses interfering with each other, the diode D1 and the diode D2 are added to the circuit of the second embodiment to isolate the two PWM pulses. The second embodiment improves the instantaneous overload capability of the switching power supply while achieving the effect of reducing the quasi-peak value (QP) and Average Value (AV) of conduction (EMI) and radiation (EMI).
Third embodiment
As shown in fig. 5, a schematic circuit diagram of a third embodiment of the present invention is different from the second embodiment in that a capacitor C1 is replaced by a resistor R6, and the electrical connection relationship is not changed.
The implementation principle of the embodiment is as follows: on the basis of the second embodiment, the capacitor C1 is replaced by the resistor R6, when the input voltage of the switching power supply is reduced, the duty ratio of the PWM pulse output by the 14 th pin pfc out of the PWM modulation chip U1 is increased and is integrated after being superposed with the PWM pulse output by the 11 th pin PWM out of the PWM modulation chip U1, the amplitude of the obtained pulsating voltage is also increased, the oscillation frequency of the PWM modulation chip U1 is increased through the RAMP modulation of the 7 th pin RAMP of the PWM modulation chip U1, the working frequency of the switching power supply is increased, the working frequency higher than before is maintained, and the load capacity of the switching power supply when the input voltage is reduced is improved.
The detailed operation principle of the circuit of the third embodiment is similar to that of the circuit of the second embodiment, and the differences are as follows:
if the input voltage of the switching power supply is reduced, the duty ratio of the PWM pulse with the half-wave sinusoidal variation output from the 14 th pin pfc out of the PWM modulation chip U1 is increased, and a larger duty ratio is maintained, which results in an increase in the amplitude of the ripple voltage at the two ends of the capacitor C2, the working principle of the second embodiment and the replacement of the capacitor C1 with the resistor R6 change the coupling mode in which the ripple voltage at the two ends of the capacitor C2 charges the capacitor C3 through the resistor R3, and it is known that the working frequency of the PWM modulation chip U1 is also increased, and a higher working frequency than before is maintained, and it is known from the switching power supply principle to increase the working frequency of the switching power supply, so that the output power of the switching power supply can be increased, and the load capacity of the switching.
The third embodiment improves the load capacity of the switching power supply at low input voltage while achieving the effect of reducing quasi-peak values (QP) and Average Values (AV) of conduction (EMI) and radiation (EMI).
The above is the preferred embodiment of the present invention, and it should be noted that the application of the present invention is not limited to the PWM modulation chip of CM6800UXIS model mentioned in the specific embodiment, and other PWM modulation chips designed with the oscillation frequency setting pin, the internal reference voltage output pin, the PFC output driving pin, the PWM output driving pin, and the ground pin also have feasibility of application. In addition, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also considered as the protection scope of the present invention.

Claims (3)

1. A switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a capacitor C1, a capacitor C2 and a capacitor C3; one end of the resistor R1 is used for connecting a PFC output driving pin of the PWM modulation chip, and the other end of the resistor R1 is simultaneously connected with one end of the capacitor C1, one end of the capacitor C2 and one end of the resistor R4; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3.
2. A switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a capacitor C1, a capacitor C2, a capacitor C3, a diode D1 and a diode D2; the anode of the diode D2 is used for being connected with a PFC output driving pin of the PWM modulation chip, the cathode of the diode D2 is connected with one end of a resistor R1, and the other end of the resistor R1 is simultaneously connected with one end of a capacitor C1, one end of a capacitor C2, one end of a resistor R4 and one end of a resistor R5; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the capacitor C1 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3; the anode of the diode D1 is used for connecting the PWM output driving pin of the PWM modulation chip, and the cathode of the diode D1 is connected to the other end of the resistor R5.
3. A switching power supply frequency modulation circuit is characterized in that: the circuit comprises a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a capacitor C2, a capacitor C3, a diode D1 and a diode D2; the anode of the diode D2 is used for connecting a PFC output driving pin of the PWM modulation chip, the cathode of the diode D2 is connected with one end of a resistor R1, and the other end of the resistor R1 is simultaneously connected with one end of a resistor R6, one end of a capacitor C2, one end of a resistor R4 and one end of a resistor R5; one end of the resistor R2 is used for connecting an internal reference voltage output pin of the PWM modulation chip, and the other end of the resistor R2 is simultaneously connected with the other end of the resistor R6 and one end of the resistor R3; the other end of the resistor R3 is used for connecting an oscillation frequency setting pin of the PWM modulation chip, and the other end of the resistor R3 is also connected with one end of a capacitor C3; the other end of the resistor R4 is used for connecting a grounding pin of the PWM modulation chip, and the other end of the resistor R4 is also simultaneously connected with the other end of the capacitor C2 and the other end of the capacitor C3; the anode of the diode D1 is used for connecting the PWM output driving pin of the PWM modulation chip, and the cathode of the diode D1 is connected to the other end of the resistor R5.
CN201922017600.XU 2019-11-20 2019-11-20 Switching power supply frequency modulation circuit Active CN211046758U (en)

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CN201922017600.XU CN211046758U (en) 2019-11-20 2019-11-20 Switching power supply frequency modulation circuit

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