TW201607228A - Primary-side regulated flyback converter and power control integrated circuit thereof - Google Patents

Abstract

A primary-side regulated flyback converter and a power control circuit thereof are provided in the present invention. The primary-side regulated flyback converter includes a transformer, a switching element, a voltage divider and a power control IC. The transformer includes a primary winding, a secondary winding and an auxiliary winding. The first terminal of the switching element is coupled between the primary winding and a common voltage. The input terminal of the voltage divider is coupled to the first terminal of the auxiliary winding, and the output terminal of the voltage divider outputs a divided voltage. When the switching element is turned off, the control IC adjusts the duty cycle of the PWM signal according to the divided voltage received from the feedback terminal of the power control IC. When the switching element is turned on, the feedback terminal outputs a constant current and receives the divided voltage. When the divided voltage is greater than a reference voltage, the control IC enters a protection mode.

Description

Back-side converter with primary feedback control and power control circuit used therefor

The present invention relates to a technique for a flyback converter, and more particularly to a flyback converter for primary side feedback control and a power supply control circuit therefor.

The flyback converter is widely used in the low voltage power supply market due to its simple structure and low production cost. A general flyback converter feedback circuit must use an expensive optocoupler and a TL431 stabilized integrated circuit to achieve electrical isolation. This not only increases the circuit cost, but also increases the circuit volume and power consumption. The primary side feedback control flyback converter achieves the effect of stabilizing the output voltage by detecting the auxiliary winding voltage. Since the detection auxiliary winding and the pulse width modulation power supply integrated circuit are located on the primary side, the use of expensive components is avoided, which is beneficial to the overall cost, efficiency and volume of the flyback converter.

Assume that the flyback converter of the primary side feedback control operates in discontinuous conduction mode (Discontinuous Conduction mode) Mode, DCM). However, when the input line voltage is too low, the duty cycle of the output Pulse Width Modulation (PWM) signal is too large and the inductor current is increased. This situation will cause the flyback converter to enter the Continuous Conduction Mode (CCM) from the discontinuous conduction mode, and the feedback compensation mechanism will be destroyed. Therefore, the flyback converter of the primary side feedback control needs a detection mechanism to avoid the above situation.

It is an object of the present invention to provide a flyback converter for primary side feedback control and a power supply control circuit therefor, by adding an input voltage detection mechanism to the feedback portion of the primary side. When the input voltage is too low, the power control circuit enters the protection mode.

In view of the above, the present invention provides a flyback converter for primary side feedback control, the flyback converter of the primary side feedback control includes a transformer, a switching element, a voltage dividing circuit and a power control product. Body circuit. The transformer includes a primary side winding, a secondary side winding, and an auxiliary winding. The switching element includes a first end, a second end, and a control end, wherein the first end of the switching element is coupled to the second end of the primary winding of the transformer, and the second end of the switching element is coupled to a common voltage. The voltage dividing circuit includes an input end and an output end, wherein the input end of the voltage dividing circuit is coupled to the first end of the auxiliary winding, and the output end of the voltage dividing circuit outputs a divided voltage. The power control integrated circuit includes a switch control end and a feedback end, wherein the switch control end of the power control integrated circuit is coupled to the control of the switch element The terminal end of the power control integrated circuit is coupled to the output end of the voltage dividing circuit.

When the switching element is turned off, the feedback terminal of the power control integrated circuit receives the divided voltage to adjust the duty cycle of a pulse width modulation signal outputted by the switch control terminal. When the switching element is turned on, the feedback terminal of the power control integrated circuit outputs a fixed current and receives the divided voltage. When the divided voltage is greater than a reference voltage, the power control integrated circuit enters a protection mode.

The invention further provides a power control integrated circuit, which is suitable for a back-side converter of primary side feedback control, the reverse-side converter of the primary side feedback control comprises a transformer, a switching element and a voltage dividing circuit . The transformer includes a primary side winding, a secondary side winding, and an auxiliary winding. The switching element includes a first end, a second end, and a control end, wherein the first end of the switching element is coupled to the second end of the primary winding of the transformer, and the second end of the switching element is coupled to a common voltage. The voltage dividing circuit includes an input end and an output end, wherein the input end of the voltage dividing circuit is coupled to the first end of the auxiliary winding, and the output end of the voltage dividing circuit outputs a divided voltage.

The power control integrated circuit of the present invention comprises a switch control terminal, a feedback terminal, a pulse width modulation circuit, a feedback circuit, a current supply circuit and a voltage detection circuit. The switch control end is coupled to the control end of the switching element. The feedback end is coupled to the output of the voltage dividing circuit. The pulse width modulation circuit is coupled to the switch control end for outputting a pulse width modulation signal. The feedback circuit is coupled to the feedback terminal, wherein when the switching element is turned off, the duty cycle of the pulse width modulation circuit is determined according to the divided voltage. Electricity The flow providing circuit is coupled to the feedback end. When the switching element is turned on, the current supply circuit outputs a fixed current to the output terminal of the voltage dividing circuit. The voltage detection circuit is coupled to the feedback terminal. When the switching element is turned on, the voltage detecting circuit receives the divided voltage, and when the divided voltage is greater than a reference voltage, a protection signal is enabled. When the protection signal is enabled, the power control integrated circuit enters a protection mode.

According to the first-side feedback control of the flyback converter and the power control integrated circuit according to the preferred embodiment of the present invention, the power control integrated circuit includes a fixed current source and a first switch. A fixed current source is used to provide the above fixed current. The first end of the first switch is coupled to the fixed current source, and the second end of the first switch is coupled to the feedback end of the power control integrated circuit. When the switching element is turned on, the first switch is turned on, and the fixed current flows from the first end of the first switch to the second end of the first switch to increase the divided voltage. In a preferred embodiment, when the voltage dividing voltage is greater than a reference voltage for more than N times, the power control integrated circuit enters the protection mode, and the power control integrated circuit stops outputting the pulse width modulation signal, wherein N is A natural number greater than 1.

According to the first-side feedback control of the flyback converter and the power control integrated circuit according to the preferred embodiment of the present invention, the voltage detecting circuit includes a sample and hold circuit and a comparison circuit. The sample and hold circuit includes a second switch and a sampling capacitor. The second switch includes a first end and a second end, wherein the first end of the second switch is coupled to the fixed current source. The first end of the sampling capacitor is coupled to the second end of the second switch, and the second end of the sampling capacitor is coupled to the common voltage. The comparison circuit includes a first input terminal, a second input terminal, and an output terminal, wherein the first input of the comparison circuit The terminal is coupled to the first end of the sampling capacitor, the second input of the comparison circuit is coupled to a reference voltage, and the output of the comparison circuit outputs a comparison signal.

According to the first-side feedback control of the flyback converter and the power control integrated circuit according to the preferred embodiment of the present invention, the power control integrated circuit further includes a counting circuit. The counting circuit includes an input and an output. The input end of the counting circuit is coupled to the output of the comparison circuit. The counting circuit is configured to calculate the number of times the voltage at the input end of the counting circuit is changed from the first logic voltage to the second logic voltage as a count value. At each preset time, the count value of the counting circuit is reset to a pre-designed value. When the count value is greater than a predetermined value, the power control integrated circuit enters the protection mode and stops outputting the pulse width modulation signal.

The spirit of the present invention is to detect the input voltage by using a feedback circuit on the primary side. When the main switch is turned off, the general output voltage is fed back. When the main switch is turned on, the coil of the auxiliary winding reflects the input voltage, but the voltage is a negative voltage. At this time, the power control circuit outputs a fixed current to the feedback terminal and detects the feedback voltage. When this feedback voltage is maintained at a negative value, it indicates that the input voltage is sufficient. When this voltage is converted to a positive voltage due to the above fixed current and larger than the reference voltage inside the wafer, it indicates that the input voltage is insufficient. At this point, the power control circuit can enter the protection mode in time to avoid damage.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

101‧‧‧Transformer

102‧‧‧Switching elements

103‧‧‧voltage circuit

104‧‧‧Power Control Integrated Circuit

105‧‧‧Secondary side rectifier circuit

106‧‧‧Auxiliary winding rectifier circuit

R _HV ‧‧‧ high voltage resistor

R _CS ‧‧‧current sense resistor

HV‧‧‧High-voltage starter

GND‧‧‧Common voltage terminal

SW‧‧‧Switch control terminal

FB‧‧‧reporting end

L _P ‧‧‧ primary winding

L _S ‧‧‧ secondary winding

L _AUX ‧‧‧Auxiliary winding

V _CC ‧‧‧ Operating voltage of the power control integrated circuit 104

V _FB ‧‧‧voltage voltage

V _O ‧‧‧voltage of the secondary winding L _S

V _AUX ‧‧‧Auxiliary winding L _AUX voltage

V _OUT ‧‧‧ output voltage

D1‧‧‧ diode

201‧‧‧ Pulse width modulation circuit

202‧‧‧Return circuit

203‧‧‧Voltage detection circuit

204‧‧‧ Current supply circuit

PWM‧‧‧ pulse width modulation signal

I _LS ‧‧‧fixed current

205‧‧‧Fixed current source

SW1, SW2‧‧‧ switch

R _FB1 , R _FB2 ‧ ‧ two resistors for the voltage divider circuit

V _IN ‧‧‧ input voltage

LVS‧‧‧ protection signal

301‧‧‧ comparator

302‧‧‧Sampling capacitor

V _ref ‧‧‧reference voltage

303‧‧‧Counting circuit

FIG. 1 is a circuit diagram of a flyback converter of a primary side feedback control according to a preferred embodiment of the present invention.

2 is a circuit diagram of a flyback converter and a partial power control integrated circuit of a partial primary side feedback control according to a preferred embodiment of the present invention.

FIG. 3 is a circuit diagram of a flyback converter and a partial power control integrated circuit of a partial primary side feedback control according to a preferred embodiment of the present invention.

FIG. 1 is a circuit diagram of a flyback converter of a primary side feedback control according to a preferred embodiment of the present invention. Referring to FIG. 1 , the primary side feedback control of the flyback converter includes a transformer 101 , a switching element 102 , a voltage dividing circuit 103 , a power control integrated circuit 104 , and a secondary side rectifying circuit 105 . auxiliary winding rectifying circuit 106, resistors R _HV high voltage and a current sensing resistor R _CS. The power control integrated circuit 104 includes a high voltage start terminal HV, a common voltage terminal GND, a switch control terminal SW, and a feedback terminal FB. The transformer 101 includes a primary side winding L _P , a secondary side winding L _S and an auxiliary winding L _AUX . The auxiliary winding rectifying circuit 106 is mainly used to rectify the voltage of the auxiliary winding L _AUX and supply the operating voltage V _{CC of the} power control integrated circuit 104. The voltage dividing circuit 103 is composed of two resistors for dividing the voltage of the auxiliary winding 107 and outputting the divided voltage V _FB .

Since this circuit is a flyback converter controlled by the primary side feedback, the power supply control integrated circuit 104 needs to detect the above-mentioned divided voltage V _FB as a reference for the output voltage. When the switching element 102 of the flyback converter of this primary side feedback control is turned off, the transformer 101 releases the stored energy to the secondary side winding L _S and the auxiliary winding L _AUX . At this time, the voltage V _{O of the} secondary side winding L _{S is} in a turn ratio relationship with the voltage V _{AUX of the} auxiliary winding L _AUX (V _AUX =V _O ×N _AUX /N _S ). Thereby, the power supply control integrated circuit 104 can know the change of the output voltage V _OUT as long as the divided voltage V _FB is detected. In general, the magnitude of the divided voltage V _FB does not fully represent the output voltage V _OUT . Due to the secondary side rectifying circuit 105, when the magnitude of the output current is different, the voltage across the diode D1 will fluctuate accordingly. Therefore, the flyback converter of the primary side feedback control needs to compensate for this.

In addition, when the switching element 102 of the flyback converter of the primary side feedback control is turned on, the input current flows through the transformer 101 to store energy for the transformer 101. At this time, the voltage of the auxiliary winding L _AUX is approximately (V _AUX =-V _IN ×N _AUX /N _S ). The control circuit can check whether the input voltage V _IN is sufficient by detecting the divided voltage V _FB . However, detecting the negative voltage is a problem for the power supply control circuit 104 which does not have a negative voltage itself. The following embodiments illustrate how the present invention detects this negative voltage to determine if the input voltage is sufficient.

2 is a circuit diagram of a flyback converter and a partial power control integrated circuit of a partial primary side feedback control according to a preferred embodiment of the present invention. Referring to FIG. 2, the power control integrated circuit includes a pulse width modulation circuit 201, a feedback circuit 202, a voltage detection circuit 203, and a current supply circuit 204. The coupling relationship of the pulse width modulation circuit 201, the feedback circuit 202, the voltage detection circuit 203, and the current supply circuit 204 is as shown. The pulse width modulation circuit 201 is configured to output a pulse width modulation signal PWM. When the switching element 102 is turned off, the feedback circuit 202 determines the duty cycle of the pulse width modulation signal PWM outputted by the pulse width modulation circuit 201 based on the divided voltage V _FB .

The current supply circuit 204 is configured to provide a fixed current I _LS to the voltage dividing circuit 103 when the switching element 102 is turned on. In this embodiment, the current supply circuit 204 includes a fixed current source 205 and a switch SW1. In this embodiment, the switch SW1 is controlled by the pulse width modulation signal PWM outputted by the pulse width modulation circuit 201. In other words, when the switching element 102 is turned on by the pulse width modulation signal PWM, the switch SW1 is also turned on at the same time. At this time, the fixed current I _{LS is} output to the voltage dividing circuit 103. The divided voltage V _FB can be mathematically expressed as follows:

Wherein the resistance R _FB1 and R _FB2 is two resistor voltage dividing circuit; I _LS represents the fixed current; V _IN represents the input voltage. The voltage detecting circuit 203 is configured to detect the divided voltage V _FB . When the divided voltage is too high V _FB , the input voltage V _{IN is} too low. At this time, the voltage detecting circuit 203 outputs a protection signal LVS, and the power control product The body circuit 104 is turned off in the protection mode and stops outputting the pulse width modulation signal PWM.

FIG. 3 is a circuit diagram of a flyback converter and a partial power control integrated circuit of a partial primary side feedback control according to a preferred embodiment of the present invention. Referring to FIG. 3, in this embodiment, the voltage detecting circuit 203 includes a comparator 301, a sampling capacitor 302, and a switch SW2. By the same token, the switch SW2 is controlled by the pulse width modulation signal PWM outputted by the pulse width modulation circuit 201. In other words, when the switching element 102 is turned on by the pulse width modulation signal PWM, the switch SW2 is also turned on at the same time. Capacitor 302 and switch SW2 form a sample and hold circuit. When the switching element 102 is turned on by the pulse width modulation signal PWM, the switch SW2 is turned on. At this time, the capacitor 302 samples the divided voltage V _FB . The positive input terminal of the comparator 301 receives the above-mentioned divided voltage V _FB , and the negative input terminal of the comparator 301 receives the reference voltage V _ref .

In general, the fixed current I _{LS is} output to the voltage dividing circuit 103, and the divided voltage V _{FB is} thus increased. However, when the input voltage V _{IN is} sufficiently high, the divided voltage V _FB is still negative even if a fixed current I _{LS is} present. At this time, the comparator 301 outputs a logic low voltage. When the input voltage V _IN drops, the divided voltage V _FB turns from a negative voltage to a positive voltage. When the divided voltage V _{FB is} smaller than the reference voltage V _ref , it indicates that the input voltage V _IN is still sufficiently high, and at this time, the comparator 301 outputs a logic low voltage. When the input voltage V _{IN is} too low, the divided voltage V _FB will be greater than the reference voltage V _ref . At this time, the comparator 301 outputs a logic high voltage.

However, in this embodiment, the instantaneous input voltage is too low and the power control integrated circuit 104 is not immediately brought into the protection mode. If the voltage is unstable for a while, the entire power supply will be protected, which will cause inconvenience to the user. When the power supply is unstable, it will generally recover instantaneously. Therefore, in this embodiment, a counting circuit 303 is configured. The counting circuit 303 is configured to count the number of times the comparator 301 outputs a logic high voltage when the switching element 102 is turned on by the pulse width modulation signal PWM. If the number of times is greater than a predetermined number of times, for example, 10 or 20 times, it indicates that the unstable state of the input voltage V _IN continues to occur. At this time, the counting circuit 303 outputs the protection signal LVS, and the power control integrated circuit 104 is turned off in the protection mode and stops outputting the pulse width modulation signal PWM.

In addition, the counting circuit 303 resets every preset time. At this time, the number of times the comparator 301 calculated by the counting circuit 303 outputs the logic high voltage is reset to zero. In other words, if the input voltage V _IN does not continue to be too low for a period of time, and the divided voltage V _FB does not continue to be greater than the reference voltage V _ref , the power control integrated circuit 104 does not enter the protection mode, thereby preventing the user from feeling The power supply was turned off for unknown reasons.

In summary, the spirit of the present invention is to detect the input voltage by using a feedback circuit on the primary side. When the main switch is turned off, the general output voltage is fed back. When the main switch is turned on, the coil of the auxiliary winding reflects the input voltage, but the voltage is a negative voltage. At this time, the power control circuit outputs a fixed current to the feedback terminal and detects the feedback voltage. When this feedback voltage is maintained at a negative value, it indicates that the input voltage is sufficient. When this voltage is converted to a positive voltage due to the above fixed current and larger than the reference voltage inside the wafer, it indicates that the input voltage is insufficient. At this point, the power control circuit can enter in time. Protect the mode from damage.

The specific embodiments of the present invention are intended to be illustrative only and not to limit the invention to the above embodiments, without departing from the spirit of the invention and the following claims. The scope of the invention and the various changes made are within the scope of the invention. Therefore, the scope of the invention is defined by the scope of the appended claims.

201‧‧‧ Pulse width modulation circuit

202‧‧‧Return circuit

203‧‧‧Voltage detection circuit

204‧‧‧ Current supply circuit

205‧‧‧Fixed current source

I _LS ‧‧‧fixed current

LVS‧‧‧ protection signal

PWM‧‧‧ pulse width modulation signal

R _FB1 , R _FB2 ‧ ‧ two resistors for the voltage divider circuit

SW1‧‧‧ switch

V _FB ‧‧‧voltage voltage

V _IN ‧‧‧ input voltage

Claims (10)

A flyback converter for primary side feedback control, comprising: a transformer comprising a primary side winding, a secondary side winding and an auxiliary winding; a switching element comprising a first end, a second end and a control The first end of the switching element is coupled to the second end of the primary winding of the transformer, the second end of the switching element is coupled to a common voltage; a voltage dividing circuit includes an input end and an output The input end of the voltage dividing circuit is coupled to the first end of the auxiliary winding, the output end of the voltage dividing circuit outputs a divided voltage; and a power control integrated circuit includes a switch control end and a switching end, wherein the switch control end of the power control integrated circuit is coupled to the control end of the switching element, and the feedback end of the power control integrated circuit is coupled to the output end of the voltage dividing circuit, wherein When the switching element is turned off, the feedback terminal of the power control integrated circuit receives the divided voltage to adjust a duty cycle of a pulse width modulation signal output by the switch control terminal, wherein when the switching element is turned on The power supply control integrated circuit, the feedback end outputs a constant current, and receives the divided voltage when the divided voltage is greater than a reference voltage, the power supply control integrated circuit enters a protection mode. The flyback converter of the primary side feedback control according to the first aspect of the patent application, wherein the power control integrated circuit comprises: a fixed current source for providing the fixed current; a first switch comprising a first end and a second end, wherein the first end of the first switch is coupled to the fixed current source, the first switch The second end is coupled to the feedback end of the power control integrated circuit; a voltage detecting circuit is coupled to the feedback end of the power control integrated circuit, wherein when the switching element is turned on, the first switch is turned on, A fixed current flows from the first end of the first switch to the second end of the first switch to increase the divided voltage. The flyback converter of the primary side feedback control as recited in claim 1, wherein the power control integrated circuit enters a protection mode when the divided voltage is greater than a reference voltage for more than N times, and The power control integrated circuit stops outputting the pulse width modulation signal, where N is a natural number. The counter-rotating converter of the primary-side feedback control as described in claim 2, wherein the voltage detecting circuit comprises: a sample-and-hold circuit comprising: a second switch comprising a first end and a first a second end, wherein the first end of the second switch is coupled to the fixed current source; and a sampling capacitor includes a first end and a second end, wherein the first end of the sampling capacitor is coupled to the second end a second end of the switch, the second end of the sampling capacitor is coupled to the common voltage; a comparison circuit includes a first input terminal, a second input terminal, and an output terminal, wherein the first input end of the comparison circuit is coupled to the first end of the sampling capacitor, and the second input end of the comparison circuit is coupled Connected to a reference voltage, the output of the comparison circuit outputs a comparison signal. The flyback control circuit of the primary side feedback control as described in claim 4, wherein the power control integrated circuit further comprises: a counting circuit comprising an input end and an output end, wherein the counting circuit The input end is coupled to the output end of the comparison circuit, wherein the counting circuit is configured to calculate a number of times the voltage of the input end of the counting circuit is converted from a first logic voltage to a second logic voltage as a count value; Each preset time, the count value of the counting circuit is reset to a pre-designed value, wherein when the count value is greater than a preset value, the power control integrated circuit enters the protection mode and stops outputting the pulse Wave width modulation signal. The utility model relates to a power control integrated circuit, which is suitable for a back-side converter of primary side feedback control. The reverse-side converter of the primary side feedback control comprises: a transformer comprising a primary side winding, a secondary side winding and a An auxiliary winding; a switching element comprising a first end, a second end and a control end, wherein the first end of the switching element is coupled to the second end of the primary winding of the transformer, and the second end of the switching element The terminal is coupled to a common voltage; a voltage dividing circuit includes an input end and an output end, wherein an input end of the voltage dividing circuit is coupled to the first end of the auxiliary winding, and an output end of the voltage dividing circuit outputs a divided voltage; The power control integrated circuit includes: a switch control end coupled to the control end of the switch element; a feedback end coupled to the output end of the voltage dividing circuit; a pulse width modulation circuit coupled The switch control terminal is configured to output a pulse width modulation signal; a feedback circuit coupled to the feedback terminal, wherein when the switching element is turned off, the pulse width is determined according to the voltage division voltage a duty cycle of the modulation circuit; a current supply circuit coupled to the feedback terminal, wherein the current supply circuit outputs a fixed current to the output terminal of the voltage dividing circuit when the switching element is turned on; and a voltage a detection circuit coupled to the feedback terminal, wherein the voltage detection circuit receives the divided voltage when the switching element is turned on, wherein when the divided voltage is greater than a reference voltage, a protection signal is enabled, wherein When the protection signal is enabled, The power supply control integrated circuit enters a protection mode. The power control integrated circuit of claim 6, wherein the current supply circuit comprises: a fixed current source for providing the fixed current; and a first switch comprising a first end and a second End, where, the The first end of the first switch is coupled to the fixed current source, and the second end of the first switch is coupled to the feedback end of the power control integrated circuit; wherein, when the switching element is turned on, the first switch is turned on, The fixed current flows from the first end of the first switch to the second end of the first switch to increase the divided voltage. The power control integrated circuit as described in claim 6, wherein when the voltage dividing voltage is greater than a reference voltage for more than N times, the power control integrated circuit enters a protection mode, and the power control integrated circuit Stop outputting the pulse width modulation signal, where N is a natural number. The power control integrated circuit as described in claim 6 , wherein the voltage detecting circuit comprises: a sample and hold circuit, comprising: a second switch comprising a first end and a second end, wherein the a first end of the second switch is coupled to the fixed current source; and a sampling capacitor includes a first end and a second end, wherein the first end of the sampling capacitor is coupled to the second end of the second switch, The second end of the sampling capacitor is coupled to the common voltage; and a comparison circuit includes a first input terminal, a second input terminal, and an output terminal, wherein the first input end of the comparison circuit is coupled to the sampling The first end of the capacitor is coupled to a reference voltage, and the output of the comparator outputs a comparison signal. The power control integrated circuit as described in claim 9 , wherein the power control integrated circuit further comprises: a counting circuit comprising an input end and an output end, wherein the input end of the counting circuit is coupled to the Comparing the output end of the circuit, wherein the counting circuit is configured to calculate a number of times the voltage at the input end of the counting circuit is converted from a first logic voltage to a second logic voltage as a count value; wherein, each preset time, The count value of the counting circuit is reset to a pre-designed value, wherein when the count value is greater than a predetermined value, the counting circuit enables the protection signal, and the power control integrated circuit enters the protection mode, and Stop outputting the pulse width modulation signal.