TW201926868A - Voltage compensation circuit of power converter - Google Patents

Abstract

A voltage compensation circuit of a power converter, and the power converter includes an auxiliary winding providing an auxiliary voltage. The voltage compensation circuit includes a resistor network and a switch unit. The resistor network includes a first resistor, a second resistor, and a third resistor, and a feedback voltage is produced at a common connection among the resistors. When the switch unit is turned off, a voltage ratio between the feedback voltage and the auxiliary voltage is determined by the first resistor and the second resistor. When the switch unit is turned on, the voltage ratio between the feedback voltage and the auxiliary voltage is determined by the first resistor, the second resistor, and the third resistor. Accordingly, it is to significantly restrain the influence to the power converter due to a voltage variation of an input voltage.

Description

Power converter circuit

The invention relates to a voltage compensation circuit of a power converter, in particular to a voltage compensation circuit of a power converter controlled by a primary side feedback.

Referring to FIG. 1, it is a circuit diagram of a related art power converter using primary side feedback control. The power converter has a transformer Tr having a primary winding Np (or primary coil, which will not be described below), a primary winding Ns and an auxiliary winding Na. The voltage control of the power converter mainly performs voltage feedback control through the relationship between the auxiliary winding Na and the output side winding, that is, the winding turns ratio between the secondary winding Ns.

Due to the coupling of the coil, the voltage of the auxiliary winding Na, that is, the auxiliary voltage, usually changes as the load changes. Moreover, when an input voltage Vin received by the power converter fluctuates high and the low voltage difference fluctuates, the control stability of the power converter is affected. For example, when the input voltage Vin increases, the auxiliary voltage also rises correspondingly, and thus is divided by a first voltage dividing resistor R1 and a second voltage dividing resistor R2, and then supplied to a controller. For example, the voltage of a pulse width modulation control integrated circuit (PWM IC) will fluctuate, so that the controller will be directly affected by the fluctuation of the input voltage Vin, resulting in a decrease in control stability.

An object of the present invention is to provide a voltage compensation circuit for a power converter that solves the problem of a decrease in control stability when voltage fluctuations occur in an input voltage.

In order to achieve the foregoing, the voltage compensation circuit of the power converter of the present invention has an auxiliary winding that provides an auxiliary voltage. The voltage compensation circuit of the power converter comprises a resistor network and a switching unit. The resistor network includes a first resistor, a second resistor, and a third resistor. The first resistor has a first end and a second end, wherein the first end of the first resistor receives the auxiliary voltage. The second resistor has a first end and a second end, wherein the first end of the second resistor is coupled to the second end of the first resistor, and the second end of the second resistor is grounded. The third resistor has a first end and a second end. The switch unit has a control end and an output end, wherein the output end is coupled to the second end of the third resistor, and the control end is coupled to the auxiliary winding. The second end of the first resistor, the first end of the second resistor, and the first end of the third resistor are coupled to a control unit having a feedback pin, and the feedback pin is received. A feedback voltage. When the switching unit is turned off, the voltage ratio of the feedback voltage to the auxiliary voltage is determined by the first resistor and the second resistor. When the switching unit is turned on, a voltage ratio of the feedback voltage to the auxiliary voltage is determined by the first resistor, the second resistor, and the third resistor.

In an embodiment, when the switch unit is turned off, the magnitude of the feedback voltage is: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, and R4 is the resistance of the second resistor. When the switching unit is turned on, the magnitude of the feedback voltage is: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, R4 is the resistance of the second resistor, and R3 is the resistance of the third resistor.

In one embodiment, the switching unit is a metal oxide semiconductor field effect transistor, a dual carrier junction transistor, or a voltage stabilizing transistor.

In an embodiment, the first end of the first resistor is coupled to a non-ground terminal of the auxiliary winding to receive the auxiliary voltage.

In an embodiment, the voltage compensation circuit of the power converter further includes a voltage dividing resistor network. The voltage dividing resistor network is coupled to the auxiliary winding and the switching unit, and includes a first voltage dividing resistor and a second voltage dividing resistor. The first voltage dividing resistor has a first end and a second end, wherein the first end of the first voltage dividing resistor is coupled to the auxiliary winding to receive the auxiliary voltage. The second voltage dividing resistor has a first end and a second end, wherein the first end of the second voltage dividing resistor is coupled to the second end of the first voltage dividing resistor and the control end of the switching unit The second end of the second voltage dividing resistor is grounded.

In an embodiment, the first voltage dividing resistor and the second voltage dividing resistor divide the auxiliary voltage to provide a control voltage, and the size of the control voltage is: Where V _{C is} the control voltage, V _{AUX is} the auxiliary voltage, R1 is the resistance of the first voltage dividing resistor, and R 2 is the resistance of the second voltage dividing resistor.

In an embodiment, the voltage compensation circuit of the power converter further includes a first diode and a second diode. The first diode has an anode and a cathode, wherein the cathode of the first diode is coupled to a power pin of the control unit. The second diode has an anode and a cathode, wherein the anode of the second diode is coupled to the anode of the first diode and the auxiliary winding, and the cathode of the second diode is coupled The first end of the first voltage dividing resistor.

In an embodiment, when the switching unit is turned off, the voltage dividing resistor network and the resistor network are in a decoupled state; when the switching unit is turned on, the voltage dividing resistor network is coupled to the resistor network. status.

In one embodiment, when the resistance of the first resistor is fixed to the resistance of the second resistor and the switching unit is turned on, the resistance of the third resistor is larger, and the magnitude of the feedback voltage is larger; The smaller the resistance of the third resistor, the smaller the magnitude of the feedback voltage.

In an embodiment, the resistor network, the switch unit, the control unit, and the voltage dividing resistor network are commonly grounded.

With the proposed voltage compensation circuit of the power converter, it is possible to greatly suppress the influence of the fluctuation of the input voltage on the power converter.

In order to further understand the technology, the means and the effect of the present invention in order to achieve the intended purpose, refer to the following detailed description of the invention and the accompanying drawings. The detailed description is to be understood as illustrative and not restrictive.

The technical content and detailed description of the present invention will be described below in conjunction with the drawings.

Referring to FIG. 2, it is a circuit diagram of a first embodiment of a voltage compensation circuit of the power converter of the present invention. The power converter, or a power supply unit, has a transformer Tr having a primary winding Np, a primary winding Ns, and an auxiliary winding Na. The magnitude of the voltage across the windings Np, Ns, Na can be obtained by the relationship of the turns ratio of the windings Np, Ns, Na and the polarity of the transformer Tr. Taking the primary winding Np and the auxiliary winding Na as an example, after the power converter receives an input voltage Vin, a primary side voltage is generated on the primary winding Np after being converted. In Fig. 2, in a manner that simplifies the conversion circuit, only the input voltage Vin is illustrated. The primary side voltage can be coupled to the auxiliary winding Na through the turns ratio of the auxiliary winding Na to the primary winding Np to obtain an auxiliary voltage V _AUX . Therefore, the power converter can provide the auxiliary voltage V _AUX on the auxiliary winding Na.

The power converter has a control unit 13 , which can be a PWM controller for generating a control signal to control switching of a power transfer switch Qm of the power converter, thereby controlling The electrical energy conversion between the primary side and the secondary side of the transformer Tr.

The power converter further provides a voltage compensation circuit with voltage compensation. The voltage compensation circuit includes a resistor network 11 and a switching unit 12. The resistor network 11 is coupled between the auxiliary winding Na of the transformer Tr and the control unit 13. Specifically, the resistor network 11 includes a first resistor R5, a second resistor R4, and a third resistor R3.

The first resistor R5 has a first end and a second end, wherein the first end of the first resistor R5 is coupled to a non-ground end of the auxiliary winding Na. In this embodiment, the non-ground terminal is the A dot polarity end of the auxiliary winding Na, therefore, the first end of the first resistor R5 receives the auxiliary voltage V _AUX .

The second resistor R4 has a first end and a second end, wherein the first end of the second resistor R4 is coupled to the second end of the first resistor R5; the second end of the second resistor R4 Ground. The grounding system is commonly grounded to the primary side of the transformer Tr, and is also grounded together with the control unit 13.

The third resistor R3 has a first end and a second end. The first end of the third resistor R3 is coupled to the second end of the first resistor R5 and the first end of the second resistor R4, and is coupled to a feedback leg of the control unit 13 Bit FB. In addition, the resistor network 11 divides the auxiliary voltage V _AUX to the common contact of the first resistor R5 , the second resistor R4 and the third resistor R3 , that is, coupled to the feedback pin FB The connection is provided with a feedback voltage V _FB , which is described later.

The switch unit 12 has a control end (ie, an input end), a first output end, and a second output end. The first output end of the switch unit 12 is coupled to the second end of the third resistor R3. The second output end of the switch unit 12 is grounded and is also grounded together with the control unit 13. The control terminal of the switch unit 12 is coupled to the auxiliary winding Na. More specifically, the control terminal is coupled to the auxiliary winding Na through a voltage dividing resistor, which will be described later. In this embodiment, the switching unit 12 is a metal oxide semiconductor field effect transistor (MOSFET) Qdm, and the control terminal is a gate, the first output is a source, and the The second output is a drain.

As shown in FIG. 2, the voltage compensation circuit is further coupled to a voltage dividing resistor network 14. Specifically, the voltage dividing resistor network 14 includes a first voltage dividing resistor R1 and a second voltage dividing resistor R2. The first voltage dividing resistor R1 has a first end and a second end, wherein the first end of the first voltage dividing resistor R1 is coupled to the non-grounding end of the auxiliary winding Na (ie, the polarity end of the dot), The auxiliary voltage V _{AUX is} received. The first end of the second voltage dividing resistor R2 is coupled to the second end of the first voltage dividing resistor R1 and is coupled to the control end of the switching unit 12 . The second end of the second voltage dividing resistor R2 is grounded, and is also grounded together with the control unit 13.

The voltage compensation circuit is further coupled to a first diode D1 and a second diode D2. The first diode D1 has an anode and a cathode, and the second diode D2 has an anode and a cathode. The anode of the first diode D1 is coupled to the anode of the second diode D2, and is coupled to the non-ground terminal of the auxiliary winding Na (ie, the polarity end of the dot) to receive the auxiliary voltage V _AUX . The cathode of the first diode D1 is coupled to a power pin VDD of the control unit 13. The cathode of the second diode D2 is coupled to the first end of the first voltage dividing resistor R1. Thereby, the first diode D1 and the second diode D2 provide a current direction of the auxiliary voltage V _AUX power supply loop to prevent the reverse bias voltage from being turned on.

Thereby, the first voltage dividing resistor R1 and the second voltage dividing resistor R2 of the voltage dividing resistor network 14 divide the auxiliary voltage V _AUX to be on the first end of the second voltage dividing resistor R2. A control voltage VC is generated. Wherein, the size of the control voltage VC is:

Where V _{C is} the control voltage, V _{AUX is} the auxiliary voltage, R1 is the resistance of the first voltage dividing resistor, and R 2 is the resistance of the second voltage dividing resistor. Further, the control voltage V _C is used to drive the switch unit 12, and in the embodiment, the gate of the MOSFET Qdm is driven to control the switch unit 12 to be turned on or off. .

When the size of the control voltage V _C is insufficient to drive the switching unit 12 to be turned on, that is, when the switching unit 12 is in an off state, the voltage dividing resistor network 14 and the resistor network 11 are decoupled, and therefore, the back The voltage ratio of the voltage V _FB to the auxiliary voltage V _AUX is determined by the first resistor R5 and the second resistor R4. Specifically, when the switch unit 12 is turned off, the magnitude of the feedback voltage V _FB is: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, and R4 is the resistance of the second resistor.

When the size of the control voltage V _C is sufficient to drive the switch unit 12 to be turned on, that is, when the switch unit 12 is in an on state, the voltage dividing resistor network 14 is coupled to the resistor network 11 , and therefore, the feedback The voltage ratio of the voltage V _FB to the auxiliary voltage V _AUX is determined by the first resistor R5, the second resistor R4, and the third resistor R3. Specifically, when the switch unit 12 is turned on, the magnitude of the feedback voltage V _FB is: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, R4 is the resistance of the second resistor, and R3 is the resistance of the third resistor.

It is worth mentioning that in the voltage compensation circuit of the embodiment, the third resistor R3 plays the key of the voltage compensation amplitude (size), that is, when the resistance of the third resistor R3 is designed to be lower than that of the second resistor R4. When the value is large, the most extreme, when the resistance of the third resistor R3 is much larger than the resistance of the second resistor R4, regardless of whether the switching unit 12 is turned on or off, the magnitude of the feedback voltage V _FB is Approximate That is, the voltage compensation circuit provides a small degree of voltage compensation. In contrast, when the resistance of the third resistor R3 is not much larger than the resistance of the second resistor R4, the magnitude of the feedback voltage V _FB when the switching unit 12 is turned on is smaller than when the switching unit 12 is turned off. The feedback voltage V _{FB is} the size. Furthermore, the resistance of the first resistor R5 is fixed. When the resistance of the third resistor R3 is smaller, the magnitude of the feedback voltage V _FB when the switching unit 12 is turned on is smaller than when the switching unit 12 is turned off. The magnitude of the feedback voltage V _FB , the voltage compensation circuit provides a greater degree of voltage compensation.

In order to clearly illustrate the degree of voltage compensation provided by the voltage compensation circuit, the data presented in Table 1 is presented, but the invention is not limited. Table 1

It can be clearly seen from Table 1 that the larger the resistance value of the third resistor R3 is, the larger the feedback voltage V _FB when the switching unit 12 is turned on, that is, the closer to the feedback when the switching unit 12 is turned off. the magnitude of the voltage V _FB; conversely, the resistance of the third resistor R3 is smaller, the smaller the feedback voltage V _FB at the switch unit 12 is turned on, i.e., farther from the switch unit 12 is turned off when the feedback voltage V The size of the _FB . Furthermore, the greater the resistance of the third resistor R3, the smaller the degree of voltage compensation provided by the voltage compensation circuit; conversely, the smaller the resistance of the third resistor R3 is, the voltage compensation provided by the voltage compensation circuit The greater the degree.

It should be noted that the voltage compensation circuit of the embodiment can be used to solve the influence of the input voltage Vin received by the power converter on the control stability caused by the wave (variable) motion, that is, the voltage compensation circuit can be greatly The influence of the high and low dropout fluctuation of the input voltage Vin on the system control is reduced. As described above, when the resistance value of the third resistor R3 is designed to be larger than the resistance of the second resistor R4, the closer the feedback voltage V _FB when the switching unit 12 is turned on is closer to the switching unit 12 The feedback voltage V _{FB is} the size. Preferably, the resistance of the third resistor R3 can be designed to be much larger than the resistance of the second resistor R4, thereby the third resistor R3 passing through the voltage compensation circuit regardless of the degree of voltage fluctuation of the input voltage Vin. The voltage compensation effect provided can greatly suppress the fluctuation of the input voltage Vin to cause the influence of the power converter.

In other words, regardless of whether the power converter operates at the lower input voltage Vin or the higher input voltage Vin, the resistance of the resistors R5, R4, and R3 through the resistor network 11 can be transmitted according to the needs of the control. The design, in particular, the resistance design of the third resistor R3 relative to the second resistor R4, solves the effect of the lower or higher input voltage Vin on the power converter.

Please refer to FIG. 5, which is a schematic diagram of voltage compensation of the voltage compensation circuit of the present invention. The solid line shown in FIG. 5 is a relationship between the frequency and the load when the switching unit 12 is turned off, that is, a cutoff curve C _OFF ; in addition, the broken line shown is a relationship between the frequency and the load when the switching unit 12 is turned on. That is, a conduction curve C _ON . As described above, the magnitude of the output current can be adjusted through the resistance design of the third resistor R3 compared to the second resistor R4, that is, the feedback voltage V _FB obtained after the voltage division is adjusted, and the conduction is adjusted correspondingly. The degree of offset of the curve C _ON (ie, the degree of compensation). Preferably, if the conduction curve C _ON is controlled to be the same curve as the cutoff curve C _OFF , that is, the power converter is controlled to have the same operation under the lower operation of the input voltage Vin or the higher input voltage Vin. The frequency effect, in other words, the power converter can simultaneously control the lower input voltage Vin or the higher input voltage Vin, so that the power converter can be greatly suppressed not only by the fluctuation of the input voltage Vin. The impact can further simplify the control design of the system.

Referring to FIG. 3, it is a circuit diagram of a second embodiment of the voltage compensation circuit of the power converter of the present invention. Compared with the first embodiment shown in FIG. 2, the switching unit 12 of the present embodiment can replace a metal oxide semiconductor field effect transistor (MOSFET) with a double carrier junction transistor (BJT) Qdb. Correspondingly, the control end is a base, the first output is a collector, and the second output is an emitter. Therefore, unlike the voltage-controlled component-metal oxide semiconductor field effect transistor (MOSFET) employed in the first embodiment shown in FIG. 2, the voltage compensation circuit of the present invention can also use a current-controlled component-double The carrier junction transistor (BJT) can also achieve the same circuit effect as the first embodiment. As for the description of the second embodiment shown in FIG. 3, reference may be made to the first embodiment shown in FIG. 2, and details are not described herein again.

Referring to FIG. 4, it is a circuit diagram of a third embodiment of the voltage compensation circuit of the power converter of the present invention. Compared with the first embodiment shown in FIG. 2, the switching unit 12 of this embodiment can be modified to use a voltage stabilizing transistor Zd. Correspondingly, the control terminal is a reference pole (R), the first output terminal is a cathode (K), and the second output terminal is an anode (A). Therefore, the same circuit effect as that of the first embodiment and the second embodiment can be achieved by the control method of the voltage stabilization. As for the description of the third embodiment shown in FIG. 4, reference may be made to the first embodiment shown in FIG. 2, and details are not described herein again.

In summary, the present invention has the following features and advantages:

1. Through the feedback control on the primary side, the control circuit of the optocoupler and the secondary side can be omitted, thereby reducing the number of circuit components, thereby saving circuit space and circuit cost.

2. The primary side adjustment control function can reduce power consumption to effectively improve power supply efficiency and improve system reliability.

3. Through the design of the resistance of the resistors of the resistor network, especially the resistance design of the third resistor compared to the second resistor, the fluctuation of the input voltage can be greatly suppressed. The influence of the power converter can further simplify the control design of the system.

The above is only the detailed description and the drawings of the preferred embodiments of the present invention, but the invention is not limited thereto, and is not intended to limit the scope of the present invention. The embodiments of the present invention and the similar variations of the scope of the present invention are intended to be included in the scope of the present invention, and any skilled person can easily change or modify them in the field of the present invention. Both can be covered in the following patent scope of this case.

11‧‧‧Resistor network

12‧‧‧Switch unit

13‧‧‧Control unit

14‧‧‧Pressure resistor network

R5‧‧‧First resistance

R4‧‧‧second resistance

R3‧‧‧ third resistor

R1‧‧‧ first voltage divider resistor

R2‧‧‧Second voltage divider resistor

Np‧‧‧ primary winding

Ns‧‧‧ secondary winding

Na‧‧‧Auxiliary winding

V _AUX ‧‧‧Auxiliary voltage

FB‧‧‧reported foot

VDD‧‧‧ power pin

V _FB ‧‧‧Responsive voltage

VC‧‧‧ control voltage

Vin‧‧‧Input voltage

Tr‧‧‧Transformer

Qm‧‧‧Power Transfer Switch

Qdm‧‧‧Metal Oxide Semiconductor Field Effect Transistor

Qdb‧‧‧Double carrier junction transistor

Zd‧‧‧Variable transistor

D1‧‧‧First Diode

D2‧‧‧ second diode

C _OFF ‧‧‧ cutoff curve

C _ON ‧‧‧ conduction curve

Figure 1: Circuit diagram of a power converter using primary side feedback control for the related art.

2 is a circuit diagram of a first embodiment of a voltage compensation circuit of a power converter of the present invention.

3 is a circuit diagram of a second embodiment of a voltage compensation circuit of a power converter of the present invention.

4 is a circuit diagram of a third embodiment of a voltage compensation circuit of a power converter of the present invention.

FIG. 5 is a schematic diagram of voltage compensation of the voltage compensation circuit of the present invention.

Claims (10)

A voltage compensation circuit for a power converter, the power converter having an auxiliary winding for providing an auxiliary voltage, the voltage compensation circuit of the power converter comprising: a resistor network comprising: a first resistor having a first And the second end, wherein the first end of the first resistor receives the auxiliary voltage; the second resistor has a first end and a second end, wherein the first end of the second resistor is coupled The second end of the first resistor is grounded to the second end; and the third resistor has a first end and a second end; and a switch unit having a control end and an output And the output end is coupled to the second end of the third resistor, the control end is coupled to the auxiliary winding; wherein the second end of the first resistor, the first end of the second resistor, and the first The first end of the three resistors is coupled to a control unit having a feedback pin, and the feedback pin receives a feedback voltage; when the switch unit is turned off, the voltage ratio of the feedback voltage to the auxiliary voltage By the first resistor and the second resistor When the switching unit is turned on, the voltage ratio of the feedback voltage to the auxiliary voltage is determined by the first resistor, the second resistor, and the third resistor. The voltage compensation circuit of the power converter according to claim 1, wherein when the switch unit is turned off, the magnitude of the feedback voltage is: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, and R4 is the resistance of the second resistor; when the switching unit is turned on, the magnitude of the feedback voltage for: Where V _{FB is} the feedback voltage, V _{AUX is} the auxiliary voltage, R5 is the resistance of the first resistor, R4 is the resistance of the second resistor, and R3 is the resistance of the third resistor. The voltage compensation circuit of the power converter of claim 1, wherein the switching unit is a metal oxide semiconductor field effect transistor, a double carrier junction transistor or a voltage stabilizing transistor. The voltage compensation circuit of the power converter of claim 1, wherein the first end of the first resistor is coupled to a non-ground terminal of the auxiliary winding to receive the auxiliary voltage. The voltage compensation circuit of the power converter of claim 1, further comprising: a voltage dividing resistor network coupled to the auxiliary winding and the switching unit, the voltage dividing resistor network comprising: a first voltage dividing resistor a first end and a second end, wherein the first end of the first voltage dividing resistor is coupled to the auxiliary winding to receive the auxiliary voltage; and a second voltage dividing resistor has a first end a second end, wherein the first end of the second voltage dividing resistor is coupled to the second end of the first voltage dividing resistor and the control end of the switching unit, the second end of the second voltage dividing resistor Ground. The voltage compensation circuit of the power converter of claim 5, wherein the first voltage dividing resistor and the second voltage dividing resistor divide the auxiliary voltage to provide a control voltage, and the size of the control voltage is : Where V _{C is} the control voltage, V _{AUX is} the auxiliary voltage, R1 is the resistance of the first voltage dividing resistor, and R 2 is the resistance of the second voltage dividing resistor. The voltage compensation circuit of the power converter of claim 5, further comprising: a first diode having an anode and a cathode, wherein the cathode of the first diode is coupled to the control unit And a second diode having an anode and a cathode, wherein the anode of the second diode is coupled to the anode of the first diode and the auxiliary winding, the second The cathode of the diode is coupled to the first end of the first voltage dividing resistor. The voltage compensation circuit of the power converter of claim 5, wherein when the switching unit is turned off, the voltage dividing resistor network and the resistor network are in a decoupled state; when the switching unit is turned on, The voltage dividing resistor network is coupled to the resistor network. The voltage compensation circuit of the power converter of claim 1, wherein when the resistance of the first resistor is fixed to the resistance of the second resistor and the switching unit is turned on, the resistance of the third resistor The larger the value of the feedback voltage is, the smaller the resistance of the third resistor is, and the smaller the magnitude of the feedback voltage is. The voltage compensation circuit of the power converter of claim 5, wherein the resistor network, the switch unit, the control unit, and the voltage dividing resistor network are commonly grounded.