CN217721026U

CN217721026U - PFC (power factor correction) following circuit

Info

Publication number: CN217721026U
Application number: CN202221900201.3U
Authority: CN
Inventors: 高本峰
Original assignee: Dongke Semiconductor Anhui Co ltd
Current assignee: Dongke Semiconductor Anhui Co ltd
Priority date: 2022-07-22
Filing date: 2022-07-22
Publication date: 2022-11-01
Anticipated expiration: 2032-07-22

Abstract

The embodiment of the utility model relates to a PFC following circuit, wherein, two input ends of the rectifier bridge are connected with AC input voltage, a first output end is connected with the input end of the charging circuit, and a second output end is grounded; the input end of the voltage detection circuit is connected with the first output end of the rectifier bridge, and the output end of the voltage detection circuit is connected with the first end of the capacitor C1; the second end of the capacitor C1 is grounded; the non-inverting input end of the voltage follower is connected with the first end of the capacitor C1, and the output end of the voltage follower is connected with the inverting input end of the voltage follower; the input end of the mirror current source is connected with the output end of the voltage follower, and the output end of the mirror current source is connected with the input end of the output circuit; the input end of the output circuit is also connected with the reference voltage of the PFC control chip; the output end of the output circuit outputs the output voltage of the PFC following circuit.

Description

PFC (power factor correction) following circuit

Technical Field

The utility model relates to an electronic circuit technical field especially relates to a power factor correction PFC follower circuit.

Background

Power Factor Correction (PFC) circuits function to reduce distortion of the input current waveform and to keep the current waveform following the voltage waveform to make the load more like a purely resistive load. The switching power supply is a capacitance input type circuit, and the phase difference between the current and the voltage thereof causes the loss of the exchange power, so that the PFC circuit is required to improve the power factor. When the power factor is low, not only the working efficiency of a power grid system is reduced, but also harmonic pollution is generated on a power grid and other equipment connected to the power grid, and the closer the power factor is to 1, the less harmonic components of the current are, and the more active power can be contained in the fundamental component of the current.

For Total Harmonic Distortion (THD), limiting the current harmonic content as early as 2001 has been written in the EN61000-3-2 electrical design specification. Before that, strict specifications have been established for personal consumer electronics such as notebook computers, displays, televisions, etc. in accordance with the relevant specifications, and the harmonic pollution generated by the specifications is required to be strictly limited. Therefore, PFC circuits are widely used in various electronic products.

Most PFC circuits adopt a BOOST framework, and the output voltage of the traditional PFC circuit adopts a fixed voltage mode and is higher than the maximum peak line voltage, for example, for wide-range input application of 85VAC-265VAC range, the output voltage of the BOOST circuit is mostly about 400 VDC. In the PFC circuit of the BOOST architecture, the lower the output voltage is, the lower the required inductance is, i.e., the smaller the required inductance is. In addition, as the output voltage is reduced, the effective value current passing through the power device is also reduced, so that the loss can be reduced, and the power efficiency is improved.

With the higher requirement of people on the quality of power supplies, the switching power supply with high efficiency, small volume and low pollution becomes a mainstream technology for research and development, and the demand for a smaller and lighter high-frequency switch is increasingly strong, however, no matter which circuit structure is adopted, an inductance circuit in the switching power supply can be a great factor for increasing the volume, the weight and the cost of the whole power supply.

The applicant finds through research that if the problem of large inductance caused by the conventional output of a fixed voltage can be avoided, lower switching loss can be obtained.

SUMMERY OF THE UTILITY MODEL

The utility model aims to provide a Power Factor Correction (PFC) following circuit, which adopts a boost conversion circuit following the input voltage, reduces the size of an inductor, improves the power efficiency in the whole input range,

the power factor correction is simply and effectively realized.

Therefore, the embodiment of the utility model provides a PFC follower circuit connects PFC control chip, PFC follower circuit includes: the circuit comprises a rectifier bridge, a charging circuit, a voltage following and mirror image circuit and an output circuit;

two input ends of the rectifier bridge are connected with alternating current input voltage, a first output end of the rectifier bridge is connected with the input end of the charging circuit, and a second output end of the rectifier bridge is grounded;

the charging circuit comprises a voltage detection circuit and a capacitor C1, wherein the input end of the voltage detection circuit is connected with the first output end of the rectifier bridge, and the output end of the voltage detection circuit is connected with the first end of the capacitor C1; the second end of the capacitor C1 is grounded;

the voltage follower and mirror circuit comprises a voltage follower and a mirror current source; the non-inverting input end of the voltage follower is connected with the first end of the capacitor C1, and the output end of the voltage follower is connected with the inverting input end of the voltage follower; the input end of the mirror current source is connected with the output end of the voltage follower, and the output end of the mirror current source is connected with the input end of the output circuit;

the input end of the output circuit is also connected with the reference voltage of the PFC control chip; and the output end of the output circuit outputs the output voltage of the PFC following circuit.

Preferably, the voltage detection circuit includes a first resistor R1, a second resistor R2, and a diode D1;

a first end of the first resistor R1 is connected to the first output end, a second end of the first resistor R1 is connected to a first end of the second resistor R2, and a second end of the second resistor R2 is grounded;

the input end of the diode D1 is connected to the second end of the first resistor R1;

the output end of the diode D1 is connected with the first end of the capacitor C1.

Preferably, the mirror current source comprises a resistor R3, a resistor R4, a transistor Q1 and a transistor Q2;

one end of the resistor R3 is connected with the output end of the voltage follower, the other end of the resistor R is connected with the collector electrode of the triode Q1, and the emitting electrode of the triode Q1 is grounded; the base electrode of the triode Q1 is connected with the base electrode of the triode Q2, the emitting electrode of the triode Q2 is grounded, the collecting electrode of the triode Q2 is connected with one end of the resistor R4, and the other end of the resistor R4 is connected with the input end of the output circuit.

Preferably, the output circuit comprises a resistor R5 and a resistor R6;

one end of the resistor R5 and one end of the resistor R6 are connected to the input end of the output circuit;

the other end of the resistor R6 is grounded;

the other end of the resistor R5 is connected with the output end of the output circuit.

Preferably, the capacitor C1 is a micro-farad capacitor.

The embodiment of the utility model provides a pair of Power Factor Correction (PFC) follower circuit, output voltage can follow the change of input voltage effective value and change, and it is big on the large side to avoid the inductance that traditional output fixed voltage leads to, and efficiency is on the low side problem during the low pressure input. By adopting the boost conversion circuit following the input voltage, the size of the inductor is reduced, the power efficiency in the whole input range is improved, and the power factor correction is simply and effectively realized.

Drawings

FIG. 1 is a circuit diagram of a PFC follower circuit provided by an embodiment of the present invention

Fig. 2 is a graph of output voltage waveform when the input voltage is 100V ac according to an embodiment of the present invention;

fig. 3 is a graph of output voltage waveform when the input voltage is 220V ac according to an embodiment of the present invention.

Detailed Description

The technical solution of the present invention is further described in detail by the accompanying drawings and examples.

The embodiment of the utility model provides a PFC follow circuit is applied to switching power supply, is connected with PFC control chip.

For BOOST converter (BOOST) PFC circuit, inductor L_XThe calculation method of (c) is as follows:

where Vac is the input voltage, vout is the output voltage of the PFC circuit, f is the switching frequency of the power supply, and Pin is the input power of the power supply.

Vout assumes that Lx following the input voltage is smaller than Lx of the fixed output voltage, so that a boost converter circuit employing a voltage following the input voltage can employ a smaller-sized inductor.

For this reason, the PFC follower circuit provided in this embodiment includes: the circuit comprises a rectifier bridge, a charging circuit, a voltage following and mirror image circuit and an output circuit; fig. 1 shows a specific circuit implementation of the present invention. The following description is made with reference to fig. 1.

Two input ends of the rectifier bridge BD1 are connected with alternating current input voltage, a first output end is connected with an input end of the charging circuit, and a second output end is grounded;

the charging circuit includes a voltage detection circuit and a capacitor C1. The input end of the voltage detection circuit is connected with the first output end of the rectifier bridge DB1, the output end of the voltage detection circuit is connected with the first end of the capacitor C1, and the second end of the capacitor C1 is grounded. The voltage detection circuit comprises a first resistor R1, a second resistor R2 and a diode D1. In a specific circuit structure, a first end of a first resistor R1 is connected with a first output end, a second end of the first resistor R1 is connected with a first end of a second resistor R2, and a second end of the second resistor R2 is grounded; the input end of the diode D1 is connected to the second end of the first resistor R1; the output end of the diode D1 is connected with the first end of the capacitor C1.

The voltage follower and mirror circuit comprises a voltage follower U1 and a mirror current source; the non-inverting input end of the voltage follower U1 is connected with the first end of the capacitor C1, and the output end of the voltage follower U1 is connected with the inverting input end of the voltage follower U1; the input end of the mirror current source is connected with the output end of the voltage follower U1, and the output end of the mirror current source is connected with the input end of the output circuit. The mirror current source comprises a resistor R3, a resistor R4, a triode Q1 and a triode Q2. In a specific circuit structure, one end of a resistor R3 is connected with the output end of a voltage follower U1, the other end of the resistor R is connected with the collector of a triode Q1, and the emitter of the triode Q1 is grounded; the base electrode of the triode Q1 is connected with the base electrode of the triode Q2, the emitting electrode of the triode Q2 is grounded, the collecting electrode of the triode Q2 is connected with one end of the resistor R4, and the other end of the resistor R4 is connected with the input end of the output circuit. In the circuit implementation of this embodiment, the transistors Q1 and Q2 both use NPN transistors.

The output circuit comprises a resistor R5 and a resistor R6, and one end of the resistor R5 and one end of the resistor R6 are connected to the input end of the output circuit; the other end of the resistor R6 is grounded; the other end of the resistor R5 is connected with the output end of the output circuit. In addition, the input end of the output circuit is also connected with the reference voltage Vref of the PFC control chip; the output circuit outputs the output voltage of the PFC following circuit through the output end.

Through the circuit, an input alternating current signal is rectified by the rectifier bridge BD1, vin voltage is output from a first output end of the rectifier bridge BD1, and the waveform is an steamed bread wave. The Vin voltage is detected through the voltage division of a resistor R1 and a resistor R2 of the voltage detection circuit, and when the voltage on the resistor R2 is larger than the sum of the forward conduction voltage drop of the diode D1 and the voltage of the capacitor C1, the capacitor C1 is charged through the diode D1. The voltage of the capacitor C1 is output as a follow voltage through the voltage follower U1. In the mirror current source, the triode Q1 and the triode Q2 are of the same type, and the resistor R3 and the resistor R4 are of the same resistance, so that the current flowing through the resistor R3 can be mirrored into the current flowing through the resistor R4, namely I_R3＝I_R4。

In the application of the circuit, the PFC follower circuit is connected to the inverting terminal INV of the internal operation of the PFC control chip, and the forward terminal of the internal operation of the PFC control chip is the reference terminal REF, so that the voltage at the input terminal of the output circuit connected to the output terminal of the mirror current source is always greater than the reference voltage Vref of the PFC control chip.

With the change of the input voltage, the follow-up voltage is changed, the current flowing through the resistor R3 is changed, the current value flowing through the resistor R4 is consistent with the current value flowing through the resistor R3, and therefore the output voltage of the PFC follow-up circuit can be changed along with the change of the input voltage. The following formula is specifically followed:

wherein, V_outAnd Vin is the output voltage of the first output end, VD is the forward conduction voltage drop of the diode D1, and Vref is the reference voltage of the PFC control chip.

The utility model discloses in, input sine wave alternating voltage is when 0 ~ 180 (positive half cycle), and two diodes in the upper right and lower left of rectifier bridge switch on in figure 1, switch on at two diodes in the upper left and lower right of 180 ~ 360 (negative half cycle) time, and input sine wave's positive, negative half cycle all forms the electric current through the diode and supplies power to the load. I.e. the diodes of the rectifier bridge are conducting during the whole power frequency cycle. Because the capacitor C1 can be smaller, 1 muF-2 muF is adopted in practical application, the situation that reverse bias cut-off of a diode in a rectifier bridge is caused by connecting a large capacitor behind a traditional rectifier bridge can not exist, and only the influence of the capacitor C1 is caused, and partial superposition can be generated at a wave crest. Finally, the output waveforms of the PFC follower circuit with sine wave ac as input, after the rectifier bridge and after the final output are shown in fig. 2 and 3.

It can be seen that in the case of inputting an alternating current with a voltage of 100V, a direct current voltage of 230V is outputted as shown in fig. 2. In the case of inputting an ac power having a voltage of 220V, a dc voltage of 350V is outputted as shown in fig. 3.

The embodiment of the utility model provides a pair of Power Factor Correction (PFC) follow circuit, output voltage can follow the change of input voltage effective value and change, and the inductance of avoiding traditional output fixed voltage to lead to is big on the left, efficiency low problem on the left when the low pressure is input. By adopting the boost conversion circuit following the input voltage, the size of the inductor is reduced, the power efficiency in the whole input range is improved, and the power factor correction is simply and effectively realized.

The above-mentioned embodiments, further detailed description of the objects, technical solutions and advantages of the present invention, it should be understood that the above description is only the embodiments of the present invention, and is not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A Power Factor Correction (PFC) following circuit is connected with a PFC control chip and comprises: the circuit comprises a rectifier bridge, a charging circuit, a voltage following and mirror image circuit and an output circuit;

2. The PFC follower circuit of claim 1, wherein the voltage detection circuit comprises a first resistor R1, a second resistor R2, and a diode D1;

3. The PFC follower circuit of claim 1, wherein the mirror current source comprises a resistor R3, a resistor R4, a transistor Q1, and a transistor Q2;

4. The PFC follower circuit of claim 1, wherein the output circuit comprises a resistor R5 and a resistor R6;

the other end of the resistor R6 is grounded;

5. The PFC follower circuit of claim 1, wherein the capacitor C1 is a microfarad capacitor.