TW201838309A - Control apparatus and control method - Google Patents

Abstract

The present disclosure provides a control apparatus and a control method for a flyback converter including an auxiliary switch. The control apparatus includes an output voltage integral unit and a comparing control unit. The output voltage integral unit integrates an output voltage of the flyback converter for achieving the amplitude of an excitation negative current of the flyback converter. The comparing control unit compares the achieved amplitude of the excitation negative current with a standard value of the excitation negative current and controls the switching of the auxiliary switch according to the comparing result. The present disclosure can realizes the zero-voltage-switching of the primary-side switching tube of the flyback converter under different voltage.

Description

Control device and control method

This case relates to the field of power electronics technology, in particular to a control device and control method applied to a flyback converter.

At present, quasi-resonant flyback converters are the most popular circuit topology applied to small power switching power supplies. The quasi-resonant flyback converter can realize the primary-side power switch when the low-voltage input (V _bus <nV _o , where: V _bus is the input voltage; n is the turns ratio of the primary winding of the transformer; V _o is the output voltage) The zero-voltage turn-on (ZVS) can achieve valley turn-on of the primary-side power switch when high-voltage input (V _bus > nV _o ), which can significantly reduce switching losses. However, with the development of high frequency, although the quasi-resonant flyback converter can achieve valley turn-on at high voltage input, the turn-on loss has become larger and larger, which seriously affects the efficiency of the converter. In order to solve the problem that the quasi-resonant flyback converter cannot fully realize the zero-voltage turn-on (ZVS) of the primary-side power switch at the high-voltage input, the conventional technology proposes new control methods such as the delayed conduction of the secondary-side synchronous rectifier tube, and New circuit topologies such as active clamp flyback converters.

However, the conventional technology is only applicable to a case where the output voltage is constant, and in the case of a variable output voltage application, it cannot guarantee that the zero-voltage turn-on of the primary-side power switch can be achieved under all operating conditions.

Therefore, how to develop a control device and a control method that can improve the lack of the conventional technology is an urgent need at present.

The purpose of this case is to provide a control device and a control method, so as to at least to some extent overcome one or more problems caused by the limitations and defects of the related technology.

An embodiment of the present invention provides a control device applied to a flyback converter. The flyback converter includes an auxiliary switch. The control device includes: an output voltage integration unit configured to pass the output voltage of the flyback converter. Performing integration to obtain the magnitude of the negative excitation current in the flyback converter; and a comparison control unit for comparing the obtained magnitude of the negative excitation current with a reference value of the negative excitation current, and controlling the assistance based on the comparison Switch off.

Among them, the auxiliary switch is a synchronous rectifier tube, a clamp tube, a switch connected in parallel on the secondary side rectifier unit of the flyback converter, or a switch connected in series with the auxiliary winding of the flyback converter.

Among them, the working mode of the flyback converter is discontinuous mode or critical continuous mode.

Wherein, integrating the output voltage of the flyback converter includes: starting the output voltage integration unit through an enable signal, and resetting the output voltage integration unit through a reset signal.

Among them, in the discontinuous mode, an enable signal is obtained by detecting the opening signal of the auxiliary switch; and in the critical continuous mode, the enable signal is obtained by detecting the zero-crossing point of the negative excitation current.

Among them, detecting the zero-crossing point of the negative excitation current includes: detecting the zero-crossing point of the negative excitation current through a current transformer, a sampling resistor, or the internal resistance of the auxiliary switch.

The reset signal is obtained by detecting the off signal of the auxiliary switch.

The comparison control unit is configured to control the auxiliary switch to be turned off when the amplitude of the negative excitation current is greater than or equal to the reference value of the negative excitation current.

Among them, the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter.

The control device further includes: a first excitation negative current reference setting unit, configured to set a reference value of the excitation negative current based on the input voltage of the flyback converter.

The control device further includes: a second excitation negative current reference setting unit, configured to set a reference value of the excitation negative current based on the input voltage and the output voltage of the flyback converter.

Among them, the output voltage of the flyback converter is variable.

Among them, the output voltage of the flyback converter is 5V, 9V, 15V or 20V.

Another aspect of the present invention provides a switching power supply, including the control device according to any one of the above.

Another implementation aspect of the present case provides a control method applied to a flyback converter. The flyback converter includes an auxiliary switch. The control method includes: integrating the output voltage of the flyback converter to obtain a flyback converter. The magnitude of the negative exciting current in the converter; comparing the obtained magnitude of the negative exciting current with the reference value of the negative exciting current; and controlling the turning-off of the auxiliary switch to realize the primary side of the flyback converter according to the comparison result The zero voltage of the power switch is turned on.

Among them, the auxiliary switch is a synchronous rectifier tube, a clamp tube, a switch connected in parallel on the secondary side rectifier unit of the flyback converter, or a switch connected in series with the auxiliary winding of the flyback converter.

Among them, the working mode of the flyback converter is discontinuous mode or critical continuous mode.

The integrating the output voltage of the flyback converter includes: starting to integrate the output voltage of the flyback converter through an integration line in response to an enable signal; and resetting the integration line in response to a reset signal.

Among them, in the discontinuous mode, an enable signal is obtained by detecting the opening signal of the auxiliary switch; and in the critical continuous mode, the enable signal is obtained by detecting the zero-crossing point of the negative excitation current.

Among them, the zero crossing of the negative excitation current is detected by the current transformer, the sampling resistor or the internal resistance of the auxiliary switch.

The reset signal is obtained by the off signal of the auxiliary switch.

Among them, implementing the zero-voltage turn-on of the primary-side power switch of the flyback converter includes: realizing zero of the primary-side power switch of the flyback converter through resonance of the magnetic field inductance and parasitic capacitance in the flyback converter. Voltage is on.

Among them, controlling the turning off of the auxiliary switch to realize the zero-voltage turning on of the primary-side power switch of the flyback converter according to the comparison result further includes: when the amplitude of the negative exciting current is greater than or equal to the reference value of the negative exciting current, controlling the auxiliary Switch off.

Among them, the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter.

The control method further includes: setting a reference value of the exciting negative current based on the input voltage of the flyback converter.

Wherein, setting the reference value of the negative excitation current based on the input voltage of the flyback converter includes: setting the reference value of the negative excitation current based on the maximum value of the input voltage of the flyback converter.

The control method further includes: setting a reference value of the exciting negative current based on an input voltage and an output voltage of the flyback converter.

Among them, the output voltage of the flyback converter is variable.

Among them, the output voltage of the flyback converter is 5V, 9V, 15V or 20V.

According to the control device and control method of the present embodiment, the amplitude of the negative excitation current in the flyback converter is obtained by integrating the output voltage of the flyback converter, and the amplitude of the obtained negative excitation current is obtained. Compare it with the reference value of the excitation negative current, and control the turning off of the auxiliary switch according to the comparison result. On the one hand, by integrating the output voltage of the flyback converter to obtain the amplitude of the negative excitation current in the flyback converter, the amplitude of the negative excitation current under different output voltages can be obtained in real time; , Comparing the amplitude of the obtained negative excitation current with the reference value of the negative excitation current, and controlling the turn-off of the auxiliary switch according to the comparison result, the primary-side switch tube at different output voltages can be achieved by rationally setting the reference value of the negative excitation current Turn on at zero voltage.

It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and should not limit the case.

A typical embodiment embodying the features and advantages of this case will be described in detail in the following paragraphs with reference to the drawings. It should be understood that the present case can have various changes in different aspects, all of which do not depart from the scope of the present case, and that the descriptions and drawings therein are essentially for the purpose of illustration, rather than limiting the case.

In addition, the drawings in this case are only schematic diagrams and are not necessarily drawn to scale. The same notes in the drawings represent the same or similar parts, and thus repeated descriptions thereof will be omitted. Some block diagrams shown in the figures are functional entities and do not necessarily have to correspond to physically or logically independent entities. Software can be used to implement these functional entities, or to implement these functional entities in one or more hardware modules or integrated circuits, or to implement these functions in different networks and / or processor devices and / or microcontroller devices entity.

Figure 1 is a circuit diagram of an active clamp flyback converter in a technical solution. The active clamp flyback converter can achieve zero voltage turn-on (ZVS) of the primary-side power switch S _1. The conventional control method is: control the clamp S ₂ only before the primary-side power switch S _{1 is} turned on. Turn on for a set time, as shown by t2-t3 in the control waveform diagram shown in Figure 2.

FIG. 3 shows a circuit diagram of an RCD clamp flyback converter in a technical solution. The RCD clamp flyback converter realizes zero-voltage turn-on (ZVS) of the primary-side power switch S ₁ by delaying the secondary-side synchronous rectifier S _{R of the} quasi-resonant flyback converter. conduction delay control method of the synchronous rectifier is S _R: S _R synchronous rectifier control after the secondary-side current i _s turned to zero continues for a set time, the control waveform diagram as shown in FIG. 4 of t1-t2 .

The above two methods for realizing the zero-voltage turn-on (ZVS) of the primary-side power switch S ₁ are achieved by controlling the synchronous rectifier S _R or the clamp S _{2 to be} turned on for a set time. This is for the application of fixed output voltage The situation is applicable.

However, with the development of power supplies, especially the popularization and popularization of USB-PD Type-C, the application of variable output voltage has become increasingly popular. For the application of variable output voltage, the above control method will no longer be applicable, because: whether it is an RCD clamp flyback converter or an active clamp flyback converter, it implements the primary-side power switch The basic principle of zero voltage turn-on (ZVS) is as follows: before the primary-side power switch S _{1 is turned on} , a negative excitation current I _{m_n} is generated on the excitation inductance L _m of the transformer, and the primary side is realized with the help of the negative excitation current I _{m_n} . The zero-voltage turn-on (ZVS) of the power switch S ₁ is determined by the following formula: (1) where: L _m is the excitation inductance of the transformer, n is the turns ratio of the transformer, V _o is the output voltage value of the converter, I _{m_n} (t) is the amplitude of the negative excitation current, and t is the value of the auxiliary switch On-time (referred to as the delayed on-time for synchronous rectifiers of quasi-resonant flyback converters, and on-time for the clamps of active-clamp flyback converters).

It can be seen from the above formula that for a fixed design, the excitation inductance value L _m and the turns ratio n are fixed. If the output voltage Vo is fixed, it can be known from formula (1) that the fixed on-time t means a fixed negative amplitude of the magnetizing current. Therefore, by controlling the synchronous rectifier tube S _R or the clamp tube S _{2 to be} turned on for a set time t It is suitable for the application of fixed output voltage. If the output voltage is variable, a fixed on-time means that the magnitude of the negative magnetizing current will change as the output voltage changes. Taking the application of USB-PD Type-C as an example, the minimum output voltage is 5V and the maximum output voltage is 20V. If the control method of fixed on-time is used, it will cause one of the following two results: A: If the set on- The time can just meet the condition of zero-voltage turn-on (ZVS) of the primary-side power switch when the output voltage is 5V. When the output voltage is 20V, the amplitude of the negative excitation current will be 4 times that when the output voltage is 5V. Excessive negative excitation current will introduce additional losses and affect the efficiency of the converter. B: If the set on-time exactly meets the condition of zero-voltage turn-on (ZVS) of the primary-side power switch when the output voltage is 20V, then when the output voltage is 5V, the amplitude of the negative excitation current will only be the output voltage of 1/4 at 20V, too small excitation negative current amplitude will cause the primary-side power switch to achieve zero voltage turn-on.

Based on the above, in a preferred embodiment of the present case, a control device is first provided. The control device 600 is used to control a flyback converter 610, where the flyback converter 610 includes an auxiliary switch. As shown in FIG. 6, the control device 600 may include an output voltage integration unit 620 and a comparison control unit 630. Wherein: the output voltage integration unit 620 is configured to obtain the amplitude of the negative excitation current in the flyback converter 610 by integrating the output voltage of the flyback converter 610; and the comparison control unit 630 is configured to use the obtained The amplitude of the negative excitation current is compared with a reference value of the negative excitation current, and the auxiliary switch is turned off according to the comparison result.

According to the control device 600 of this embodiment, on the one hand, by integrating the output voltage of the flyback converter 610 to obtain the magnitude of the exciting negative current in the flyback converter 610, it is possible to obtain different output voltages in real time. On the other hand, the obtained amplitude of the negative excitation current is compared with the reference value of the negative excitation current, and the turn-off of the auxiliary switch is controlled according to the comparison result. The reasonable value of the negative excitation current reference can be set. Value to achieve zero-voltage turn-on of the primary-side switch at different output voltages.

In this embodiment, the flyback converter 610 further includes a primary-side switching unit, a secondary-side rectifying unit, a transformer, and an output capacitor (not shown), wherein the primary-side switching unit includes a primary-side power switching tube, and a secondary The side rectifier unit includes a first end and a second end, and the first end and the second end are electrically connected to the transformer and the output capacitor, respectively. In order to adapt to the application of variable output voltage, to achieve zero voltage turn-on (ZVS) of the primary-side power switch in the full input voltage range (for example, 90 ~ 264Vac) and full load range under different output voltages, it is necessary to control the excitation negative The amplitude of the current reaches a set value. According to the following formula (2): (2), the product of the output voltage V _o is detected by the time t and the amplitude can be detected indirectly exciting the negative current, and the physical meaning of the output voltage V _o and the time t is the product of the output voltage Vo is integrated over time t. Therefore, the basic principle of this case is that before the primary-side power switch is turned on, by controlling the on and off of the auxiliary switch, a negative magnetic current is generated in the flyback converter 610. By detecting the output voltage and performing integral control on the output voltage, the information I _{m_n} (t) of the magnitude of the negative excitation current is obtained. A reference value I _{m_N of the} negative excitation current is set. When the amplitude of the negative excitation current is greater than or equal to the reference value, the comparison control unit 630 outputs a control signal to turn off the auxiliary switch. Then, based on the excitation negative current as the initial value, the zero-voltage turn-on (ZVS) of the primary-side power switch is achieved through the resonance of the excitation inductance L _m and the parasitic capacitance C _EQ of the primary line. By properly setting the reference value of the negative excitation current, the zero-voltage turn-on (ZVS) of the primary-side power switch can be achieved in the full input voltage range and the full load range of different output voltages. In this embodiment, the parasitic capacitance C _{EQ is} composed of the parasitic capacitance of the primary-side power switch S1 and the parasitic capacitance of the primary-side coil of the transformer T.

It should be noted that, in this embodiment, the output voltage of the flyback converter 610 is variable. For example, the output voltage of the flyback converter 610 may be 5V, 9V, 15V, or 20V, etc., this case does not make any special limited.

In addition, as shown in FIG. 7, in a preferred embodiment of the present case, in order to reasonably set the reference value of the excitation negative current, the control device 600 may further include an excitation negative current reference setting unit 640 for use in a flyback-based converter. An input voltage or output voltage of 610 sets the reference value of the exciting negative current.

In addition, in some embodiments, the flyback converter 610 may be an active clamp flyback converter as shown in FIG. 1 or an RCD clamp flyback as shown in FIGS. 3 and 5. Converter, but the flyback converter in the preferred embodiment of the present invention is not limited to this.

Further, in some embodiments, the auxiliary switch of the flyback converter 610 may be a clamp tube S ₂ as shown in FIG. ₁ or a synchronous rectifier tube S _R as shown in FIG. 3. The auxiliary switch in the preferred embodiment is not limited to this. For example, as shown in Fig. 5, the secondary side is a diode-rectified RCD clamp flyback converter. The auxiliary switch may be a switch S _aux connected in parallel to the diode D1, or The auxiliary switch may be a switch S _{aux_VCC} connected in series to the auxiliary winding W _aux . It should be noted that, in the preferred embodiment of this case, the control device 600 may be applicable to different working modes, including discontinuous mode and critical continuous mode, which is not specifically limited in this case.

In some embodiments, the voltage integration function can be implemented in multiple ways, for example, digital circuits can be used, or analog lines can be used. An example of an analog line is described below. The voltage integration circuit as shown in FIG. 8 includes amplifiers and resistors R ₁ -R ₄ to Rsense, but is not limited thereto. From the circuit principle, as long as the following formula is satisfied: (3) That is, R ₁ = R ₂ , R ₃ = R ₄ , then: (4)

Since R _sense is a known fixed value, equation (4) coming into the voltage signal V _o signal current I _sense. To a charging capacitor C _sense signal current I _sense, the voltage on the capacitor C _sense signal that is reflected in the integration of the output voltage V _o (5) Available: (6) Since the C _sense and R _sense is a known parameter, therefore the output voltage of the integrator can be obtained by detecting the output signal V _sense voltage V _o.

FIG. 8 is a voltage integration circuit diagram of another preferred embodiment of the present invention. As shown in Figure 8: the enable signal acts on the switch S ₁ and is set to be active low: when the enable signal is high, the switch S _{1 is} closed, and the integration line does not work at this time; When the energy signal is at a low level, the switch S ₁ is turned off, and the integration line starts to work. The reset signal acts on the switch S ₂ and is set to be active high: when the reset signal is low, the switch S ₂ is turned off and the capacitor C _sense is charged to detect the voltage integration signal V _sense and the integration line remains Working state; when the reset signal is high, the switch S _{2 is} closed and the capacitor C _sense is fully discharged. At this time, the voltage integration signal V _sense is 0, the integration line is reset, and the integration circuit stops working. In another embodiment, the effective level signal of the integration signal may also be a high level, and the effective level signal of the reset signal may also be a low level, which is not limited herein. In another embodiment, it is not necessary to set the switch S1 and the enable signal, and the working state of the integration circuit can also be controlled.

It should be noted that, in some embodiments, for the intermittent operation mode, the enable signal of the integration unit may be obtained by the opening signal of the auxiliary switch. As shown in FIG. ₂ , the rising edge transition signal of the S ₂ driving signal at time t2 is the opening signal of the auxiliary switch. As shown in FIG. 9, the rising edge transition signal of the S _R driving signal at time t 2 is the auxiliary signal. The enable signal of the switch can be obtained by detecting this rising edge transition signal. It should be noted that the enable signal may also be synchronized with this rising edge transition signal, or may be obtained by delaying the rising edge transition signal with a certain delay.

Further, in some embodiments, for the critical continuous mode, the enable signal of the integration circuit may be detected by detecting the zero crossing of the negative excitation current (as shown in FIG. 4 and time t1; as shown in FIG. 10 and time t1). obtain. Specifically, the detection of the zero crossing point of the negative excitation current can be achieved by a current transformer, a sampling resistor or an internal resistance of the power device such as the internal resistance of the auxiliary switch.

It should be noted that, in some embodiments, the reset signal of the integration unit may be turned off by the auxiliary switch (such as the falling edge transition signal of the S ₂ driving signal at time t3 in FIG. ₂ , such as t2 in FIG. 4). The falling edge transition signal of the driving signal at time S _R , such as the falling edge transition signal of the driving signal of S _R at time t3 in FIG. 9, such as the falling edge transition signal of the driving signal of S ₂ at time t _{2 in} FIG. 10). For example, it can be synchronized with the shutdown signal of the auxiliary switch, or obtained by delaying the shutdown signal.

FIG. 11 is a specific embodiment of a control device. As shown in FIG. 11, the control device 1100 is used to control the flyback converter 1110. The control device 1100 includes an output voltage integration unit 1120, a comparison control unit 1130, and an excitation negative current reference setting unit 1140. The flyback converter 1110 is an RCD clamped flyback converter, including a primary-side switching unit, a secondary-side rectifying unit, a transformer T, and an output capacitor C _o , wherein the primary-side switching unit includes a primary-side power switch S ₁ The secondary-side rectifier unit includes a synchronous rectifier S _R , and the secondary-side rectifier unit is electrically connected to the transformer T and the output capacitor C _o respectively. In this embodiment, the flyback converter 1110 operates in a discontinuous mode.

In this embodiment, the control device 1100 uses the second turn-on signal of the synchronous rectifier tube S _R , such as the S _R driving signal at time t ₂ shown in FIG. 9, to obtain an enable signal. The output voltage integration unit 1120 can integrate the output voltage integration unit 1120 according to the received output voltage signal V _o , and obtain the amplitude I _{m_n of the} primary-side coil exciting negative current according to formula (2), and send it to the comparison control unit. 1130; the comparison control unit 1130 compares the excitation negative current amplitude I _{m_n} with the reference value I _{m_N of the} excitation negative current reference setting unit 1140, and when I _{m_n} reaches the reference value I _{m_N} , that is, when I _{m_n is} greater than or equal to the reference value I _{m_N} The comparison control unit 1130 outputs a control signal to turn off the synchronous rectifier S _R. At the same time, the comparison control unit 1130 outputs a reset signal according to the shutdown signal of the synchronous rectifier S _R to reset the output voltage integration unit 1120.

Fig. 12 is another specific embodiment of a control device. As shown in FIG. 12, the control device 1200 is used to control the flyback converter 1210. The control device 1200 includes: an output voltage integration unit 1220, a comparison control unit 1230, and an excitation negative current reference setting unit 1240. The flyback converter 1210 is an active clamp flyback converter, including a primary-side switching unit, a secondary-side rectifying unit, a transformer T, and an output capacitor C _o , wherein the primary-side switching unit includes a primary-side power switch S ₁ and clamp tube S ₂ , the secondary-side rectifier unit includes a synchronous rectifier tube S _R , and the secondary-side rectifier unit is electrically connected to the transformer T and the output capacitor C _o respectively. In this embodiment, the flyback converter operates in a discontinuous mode.

In this embodiment, the control device 1200 obtains the integration unit enable signal from the turn-on signal of the clamp tube S ₂ , such as the turn-on signal of S ₂ at time t 2 in FIG. ₂ , and the enable signal is used to enable the output voltage. Integrating unit 1220; the output voltage signal V _{o is} transmitted to the output voltage integrating unit 1220; the output voltage integrating unit 1220 integrates according to the output voltage signal V _o to obtain the amplitude I _{m_n of the} negative exciting current of the primary coil, and sends it to The comparison control unit 1230; the comparison control unit 1230 compares the excitation negative current amplitude I _{m_n} with the reference value I _{m_N of the} excitation negative current reference setting unit 1240, and when I _{m_n} reaches the reference value I _{m_N} , the comparison control unit 1230 outputs a control signal to Turn off the clamp tube S ₂ . At the same time, the comparison control unit 1230 outputs an integration unit reset signal according to the turn-off signal of the clamp tube S ₂ to reset the output voltage integration unit 1220.

For the setting of the reference value of the negative excitation current, it is known through research that at the low-voltage input (V _bus <nV _o ), the zero-voltage turn-on (ZVS) of the primary-side power tube can be achieved without the help of the negative excitation current; at the high-voltage input (V _bus ＞ nV _o ), in order to achieve the zero-voltage turn-on (ZVS) of the primary-side power tube, the minimum amplitude of the negative excitation current must meet: (7)

According to the above formula (7), for a specific circuit design, the transformer's turns ratio n, the magnetizing inductance L _m and the parasitic capacitance C _EQ are fixed. In order to achieve the zero-voltage turn-on of the primary-side power tube ( ZVS), the reference value of the negative excitation current I _{m_N is} related to the input voltage V _bus and the output voltage V _O. Therefore, the excitation negative current reference setting unit can adjust the excitation negative current reference value I _{m_N in} real time based on the input voltage V _bus and the output voltage V _{O of the} flyback converter.

However, using the above method, in order to adjust the excitation negative current reference value I _{m_N} in real time, two variables need to be monitored in real time: the input voltage V _bus and the output voltage V _O. This will increase the complexity of control. Further research shows that when the flyback converter is operated with a high-voltage input (V _bus > nV _o ), the influence of the output voltage on the reference value of the negative excitation current can be ignored, that is, the reference value of the negative excitation current is only related to the input voltage. , Which greatly simplifies the setting of the reference value of the negative excitation current. (8)

In some embodiments, the following two setting methods can be used for setting the reference value of the negative excitation current: Fixed reference value setting method: In order to achieve zero voltage turn-on (ZVS) of the primary-side power switch in the full input voltage range, The reference value of the negative excitation current is set according to the maximum input voltage, that is: (9) where: V _{bus_max} is the maximum input voltage.

For the fixed reference value setting method, when the input voltage is the maximum value V _{bus_max} , it can just meet the zero-voltage turn-on (ZVS) of the primary-side power switch; but when the input voltage is low, the control method produces The amplitude of the negative excitation current is greater than the amplitude of the negative excitation current required for the zero-voltage turn-on (ZVS) of the primary-side power tube, which will cause additional losses and is not conducive to efficiency optimization. Of course, in applications where efficiency requirements are not very high, a fixed reference value setting method can be used.

For applications with high efficiency requirements, the setting method of the reference value of the negative magnetic current with input voltage can be adopted to optimize the efficiency of the converter. Therefore, the reference value of the negative excitation current can be set as: (10) Where: Im_N (V _bus ) is the reference value of the negative excitation current.

For a specific circuit design, the magnetizing inductance L _m and the parasitic capacitance C _EQ are fixed. From the above formula (10), it can be known that the reference value of the negative excitation current is proportional to the input voltage V _bus , and the reference value of the negative excitation current is set. The unit can directly calculate the reference value of the excitation negative current I _{m_N} according to the input voltage value V _bus detected by the input voltage detection unit.

FIG. 13 is another specific embodiment of a control device. FIG. 13 is similar to the structure in FIG. 11, but FIG. 13 further includes a specific example of the excitation negative current reference setting unit. As shown in FIG. 13, the control device 1300 further includes an input voltage detection unit 1360. In this embodiment, the input voltage detection unit 1360 includes a first resistor R ₁ and a second resistor R ₂ , and the first resistor R ₁ and The second resistor R ₂ divides the voltage to detect the input voltage information V _bus . The excitation negative current reference setting unit 1340 receives the input voltage information V _bus from the input voltage detection unit 1360 and is used to set the excitation negative current reference value I _{m_N} . The excitation negative current reference value is sent to the comparison control unit 1330; the output voltage integration unit 1320 Integrate according to the input output voltage signal to obtain the amplitude I _{m_n of the} primary-side coil exciting negative current, and send it to the comparison control unit 1330. The comparison control unit 1330 compares the excitation negative current amplitude I _{m_n} obtained from the output voltage integration unit 1320 with the excitation negative current reference value I _{m_N of the} excitation negative current reference setting unit 1340, and waits for I _{m_n} to reach the excitation negative current reference value I _{m_N} The comparison control unit 1330 outputs a control signal to turn off the synchronous rectifier S _R , and at the same time, outputs an integration unit reset signal to reset the output voltage integration unit 1320. At the same time, the integration unit enable signal is obtained by the secondary conduction turn-on signal of the synchronous rectifier tube (FIG. 9, _SR drive signal at time t2), and the output voltage integration unit 1320 is enabled by the enable signal.

Fig. 14 shows a further specific embodiment of a control device. FIG. 14 is similar to the structure in FIG. 11, but FIG. 14 further includes a specific example of the excitation negative current reference setting unit. As shown in FIG. 14, the control device 1400 further includes an input voltage detection unit 1460. In this embodiment, the input voltage detection unit 1460 includes a first resistor R ₁ and a second resistor R ₂ , and is detected by a resistance voltage division method. Input voltage information V _bus . The input voltage detection unit 1460 inputs the input voltage information V _bus to the excitation negative current reference setting unit 1440 for setting the reference value; the turning-on signal of the clamp tube S ₂ is used to obtain the integration unit enable signal, and the output is enabled by the enable signal The voltage integration unit 1420; the output voltage signal Vo is sent to the output voltage integration unit 1420; the output voltage integration unit 1420 integrates according to the input output voltage signal to obtain the amplitude I _{m_n of the} primary-side coil exciting negative current, and sends it to The comparison control unit 1430; the comparison control unit 1430 compares the excitation negative current amplitude I _{m_n} obtained from the output voltage integration unit 1420 with the reference value I _{m_N of the} excitation negative current reference setting unit 1440, and when I _{m_n} reaches the reference value I _{m_N} , The comparison control unit 1430 outputs a control signal to turn off the clamp tube S ₂ , and simultaneously outputs an integration unit reset signal to reset the output voltage integration unit 1420.

In addition, in the preferred embodiment of the present case, a control method is also provided. The control method can be applied to the flyback converter shown in FIG. 6 to FIG. 14. The flyback converter includes an auxiliary switch. Referring to FIG. 15, the control method may include the following steps: Step S1510: Obtain the amplitude of the exciting negative current in the flyback converter by integrating the output voltage of the flyback converter; Step S1520: The obtained amplitude value of the negative excitation current is compared with a reference value of the negative excitation current; and step S1530: controlling the turning-off of the auxiliary switch according to the comparison result to realize the zero-voltage turning on of the primary-side power switch of the flyback converter.

According to the control method of this embodiment, on the one hand, by integrating the output voltage of the flyback converter to obtain the magnitude of the exciting negative current in the flyback converter, the exciting negative at different output voltages can be obtained in real time. The amplitude of the current; on the other hand, the obtained amplitude of the negative excitation current is compared with the reference value of the negative excitation current, and the turn-off of the auxiliary switch is controlled according to the comparison result, which can be achieved by appropriately setting the reference value of the negative excitation current In the full input voltage range (for example, 90 ~ 264Vac), the primary-side switch is turned on at zero voltage under different output voltages.

Further, in some embodiments, the control method may further include: comparing the obtained amplitude of the negative excitation current with a reference value of the negative excitation current, and controlling when the amplitude of the negative excitation current is greater than the reference value of the negative excitation current. Turn off the auxiliary switch.

Further, in some embodiments, the control method may further include: setting a reference value of the exciting negative current based on the input voltage of the flyback converter.

Further, in some embodiments, setting the reference value of the exciting negative current based on the input voltage of the flyback converter may include: setting the reference value of the exciting negative current based on the maximum value of the input voltage of the flyback converter.

In addition, in some embodiments, the control method may further include: setting a reference value of the exciting negative current based on an input voltage and an output voltage of the flyback converter.

It should be noted that, in some embodiments, the flyback converter is an RCD clamped flyback converter or an active clamped flyback converter.

It should be noted that, in some embodiments, the operating mode of the flyback converter is a discontinuous mode or a critical continuous mode.

It should be noted that, in some embodiments, the auxiliary switch is a synchronous rectifier tube, a clamp tube, or a switch connected in parallel to the secondary-side rectifier unit of the flyback converter.

Further, in some embodiments, integrating the output voltage of the flyback converter includes: starting to integrate the output voltage of the flyback converter through an integration circuit in response to an enable signal, and in response to a reset signal Reset the integration circuit.

Further, in some embodiments, in the discontinuous mode, the enable signal is obtained by an on signal of an auxiliary switch; and in the critical continuous mode, an enable signal is obtained by detecting a zero-crossing point of a negative excitation current.

Further, in some embodiments, the zero crossing of the negative excitation current is detected by a current transformer, a sampling resistor, or the internal resistance of the auxiliary switch.

Further, in some embodiments, the reset signal is obtained by an off signal of the auxiliary switch.

Further, in some embodiments, implementing the zero-voltage turn-on of the primary-side power switch tube of the flyback converter includes: realizing the flyback converter by resonance of an excitation inductance and a parasitic capacitance in the flyback converter. The zero-voltage of the primary-side power switch is turned on.

After considering the specification and practicing the invention of the present invention, those skilled in the art will easily think of other embodiments of the present invention. This application is intended to cover any alterations, uses, or adaptations to the present application. These alterations, uses, or adaptations follow the general principles of the present application and include techniques known in the art that are not disclosed in this application. And the description and examples in this case are only considered as exemplary, and the scope of the present invention is determined by the scope of the attached patent application.

It should be understood that the present application is not limited to the precise structure that has been described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of this case is limited only by the scope of the attached patent application.

S ₁ ‧‧‧ Switch tube

S ₂ ‧‧‧Clamp

t, t ₀ , t ₁ , t ₂ , t ₃ , t ₄ , t ₅ ‧‧‧ time

S _R ‧‧‧Synchronous Rectifier

L _m ‧‧‧ Excitation inductance

I _{m_n} ‧‧‧Negative excitation current

n‧‧‧turn ratio

V _o ‧‧‧ output voltage

I _{m_n} (t) ‧‧‧ amplitude of negative excitation current

600, 1100, 1200, 1300, 1400‧‧‧ control devices

610, 1110, 1210‧‧‧ Flyback Converter

620, 1120, 1220, 1320, 1420‧‧‧‧ output voltage integration unit

630, 1130, 1230, 1330, 1430‧‧‧‧Comparison control unit

640, 1140, 1240, 1340, 1440‧‧‧ Excitation negative current reference setting unit

1360, 1460‧‧‧ input voltage detection unit

I _{m_N} ‧‧‧ reference value

C _EQ ‧‧‧ Parasitic capacitance

T‧‧‧Transformer

D1‧‧‧Diode

S _aux , S _{aux_VCC} ‧‧‧ switch

W _aux ‧‧‧ auxiliary winding

R ₁ , R ₂ , R ₃ , R ₄ , R _sense ‧‧‧ resistance

I _sense ‧‧‧ current signal

C _sense ‧‧‧ capacitor

V _sense ‧‧‧Voltage integral signal

C _o ‧‧‧ output capacitor

V _bus ‧‧‧ input voltage

V _{bus_max ‧‧‧Maximum} input voltage

S1510, S1520, S1530‧‧‧ steps

Figure 1 is a circuit diagram of an active clamp flyback converter in a technical scheme; Figure 2 is a discontinuous mode control waveform diagram of an active clamp flyback converter in a technical scheme; Figure 3 is a circuit diagram of an RCD clamp flyback converter in a technical scheme; Figure 4 is a critical continuous mode control waveform diagram of an RCD clamp flyback converter in a technical scheme; Figure 5 is FIG. 6 is a circuit diagram of an RCD clamp flyback converter in another technical solution; FIG. 6 is a schematic diagram of a control principle of a control device of a preferred embodiment of the present invention; FIG. 7 is a schematic view of another preferred embodiment of the present invention. Schematic diagram of the control principle of the control device; Figure 8 is a voltage integration circuit diagram of yet another preferred embodiment of the present invention; Figure 9 is a discontinuous mode control of an RCD clamp flyback converter according to yet another preferred embodiment of the present invention Waveform diagram; Figure 10 is a critical continuous mode control waveform diagram of an active clamp flyback converter according to another preferred embodiment of the present invention; Figure 11 is an RCD clamp return of another preferred embodiment of the present invention Voltage Integral Detection and Control of Gallop Converter FIG. 12 is a specific embodiment of the on-time detection control method of an active clamp flyback converter according to another preferred embodiment of the present invention; FIG. 13 is another preferred embodiment of the present invention. A specific embodiment of a method for setting a reference value of an RCD clamp flyback converter according to an embodiment to change with an input voltage. FIG. 14 is a specific embodiment of a method for setting a reference value of an active clamp flyback converter with input voltage according to another preferred embodiment of the present invention; and FIG. 15 is another preferred implementation of the present invention. Example control method flowchart.

Claims (29)

A control device is applied to a flyback converter. The flyback converter includes an auxiliary switch. The control device includes: an output voltage integration unit for performing an output voltage on the flyback converter. Integrate to obtain the amplitude of a negative excitation current in the flyback converter; and a comparison control unit for comparing the obtained amplitude of the negative excitation current with a reference value of the negative excitation current, and according to The comparison results turn off the auxiliary switch. The control device according to item 1 of the scope of patent application, wherein the auxiliary switch is a synchronous rectifier tube, a clamp tube, a switch connected in parallel to the primary side rectifier unit of the flyback converter, or connected in series to the flyback Switch of an auxiliary winding of the converter. The control device according to item 1 of the scope of patent application, wherein the operating mode of the flyback converter is discontinuous mode or critical continuous mode. The control device according to item 3 of the scope of patent application, wherein integrating the output voltage of the flyback converter includes: activating the output voltage integrating unit by an enable signal, and outputting the output voltage by a reset signal. The integration unit is reset. The control device according to item 4 of the scope of patent application, wherein in the discontinuous mode, the enable signal is obtained by detecting an on signal of the auxiliary switch; and in the critical continuous mode, the over-excitation negative current is detected. The zero point gets this enable signal. The control device according to item 5 of the scope of patent application, wherein detecting the zero-crossing point of the negative excitation current includes detecting the zero-crossing point of the negative excitation current through a current transformer, a sampling resistor, or an internal resistance of the auxiliary switch. The control device according to item 4 of the scope of patent application, wherein the reset signal is obtained by detecting an off signal of the auxiliary switch. The control device according to item 1 of the scope of patent application, wherein the comparison control unit is configured to control the auxiliary switch to be turned off when the amplitude of the negative excitation current is greater than or equal to the reference value of the negative excitation current. The control device according to item 1 of the scope of patent application, wherein the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter. The control device according to item 1 of the scope of patent application, wherein the control device further comprises: a first excitation negative current reference setting unit for setting the reference value of the excitation negative current based on an input voltage of the flyback converter . The control device according to item 1 of the patent application scope, wherein the control device further comprises: a second excitation negative current reference setting unit for setting the excitation based on an input voltage and the output voltage of the flyback converter Negative current reference value. The control device according to item 1 of the scope of patent application, wherein the output voltage of the flyback converter is variable. The control device according to item 12 of the scope of patent application, wherein the output voltage of the flyback converter is 5V, 9V, 15V, or 20V. A switching power supply includes the control device described in any one of claims 1-13 of the scope of patent application. A control method is applied to a flyback converter, the flyback converter includes an auxiliary switch, wherein the control method includes: obtaining the flyback type by integrating an output voltage of the flyback converter The amplitude of a negative excitation current in the converter; comparing the obtained amplitude of the negative excitation current with a reference value of a negative excitation current; and controlling the turning-off of the auxiliary switch to implement the flyback type according to the comparison result Zero voltage of a primary-side power switch of the converter is turned on. The control method according to item 15 of the scope of patent application, wherein the auxiliary switch is a synchronous rectifier tube, a clamp tube, a switch connected in parallel to the primary side rectifier unit of the flyback converter, or connected in series to the flyback Auxiliary winding switch of the converter. The control method according to item 15 of the scope of patent application, wherein the operating mode of the flyback converter is discontinuous mode or critical continuous mode. The control method according to item 17 of the scope of patent application, wherein the integrating the output voltage of the flyback converter includes: responding to an enable signal through an integration line to start the The output voltage is integrated, and the integration line is reset in response to a reset signal. The control method according to item 18 of the scope of patent application, wherein in the discontinuous mode, the enable signal is obtained by detecting an on signal of the auxiliary switch; and in the critical continuous mode, the excessive negative current is detected by detecting The zero point gets this enable signal. The control method according to item 19 of the scope of patent application, wherein the zero crossing of the negative excitation current is detected by a current transformer, a sampling resistor or the internal resistance of the auxiliary switch. The control method as described in claim 18, wherein the reset signal is obtained by an off signal of the auxiliary switch. The control method according to item 15 of the scope of patent application, wherein implementing the zero-voltage turn-on of the primary-side power switch of the flyback converter includes: passing a magnetizing inductance and a parasitic capacitance in the flyback converter To achieve zero voltage turn-on of the primary-side power switch of the flyback converter. The control method according to item 15 of the scope of patent application, wherein the zero-voltage turn-on of the primary-side power switch tube of the flyback converter is controlled by controlling the turning-off of the auxiliary switch according to the comparison result, further comprising: When the amplitude of the current is greater than or equal to the reference value of the exciting negative current, the auxiliary switch is controlled to be turned off. The control method according to item 15 of the scope of patent application, wherein the flyback converter is an RCD clamp flyback converter or an active clamp flyback converter. The control method according to item 15 of the scope of patent application, wherein the control method further comprises: setting the reference value of the exciting negative current based on an input voltage of the flyback converter. The control method as described in claim 25, wherein setting the reference value of the excitation negative current based on the input voltage of the flyback converter includes: setting the maximum value of the input voltage based on the flyback converter; Excitation negative current reference value. The control method according to item 15 of the scope of patent application, wherein the control method further comprises: setting the reference value of the exciting negative current based on an input voltage and the output voltage of the flyback converter. The control method according to item 15 of the scope of patent application, wherein the output voltage of the flyback converter is variable. The control method as described in item 28 of the scope of patent application, wherein the output voltage of the flyback converter is 5V, 9V, 15V, or 20V.