CN115765464A - Flyback conversion circuit, control method, converter, servo motor and driver - Google Patents
Flyback conversion circuit, control method, converter, servo motor and driver Download PDFInfo
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- CN115765464A CN115765464A CN202210787293.7A CN202210787293A CN115765464A CN 115765464 A CN115765464 A CN 115765464A CN 202210787293 A CN202210787293 A CN 202210787293A CN 115765464 A CN115765464 A CN 115765464A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Abstract
The invention discloses a flyback conversion circuit, a control method, a converter, a servo motor and a driver thereof.A first switch is connected with a bus at one end and connected with a second end of a primary coil of a transformer at the other end; one end of the second switch is connected with the first end of the primary coil, and the other end of the second switch is grounded; the first diode and the third switch are connected in series between the bus and the first end of the primary coil, the third switch is connected in parallel with the first absorption circuit, and the second diode and the fourth switch are connected in series between the second end of the primary coil and the ground; the fourth switch is connected with the second absorption circuit in parallel; when the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch and the fourth switch to be switched on to form a first clamping circuit and a second clamping circuit of the primary coil, and when the bus sampling voltage is less than the threshold voltage, the voltage comparison circuit controls the third switch and the fourth switch to be switched off to form a first clamping absorption circuit of the primary coil and a second clamping absorption circuit of the primary coil.
Description
Technical Field
The invention relates to the field of DC-DC, in particular to a flyback conversion circuit, a control method, a converter, a servo motor and a driver thereof.
Background
The flyback converters may be classified into a double-tube flyback converter and a single-tube flyback converter from the viewpoint of the number of switches connected in series with the primary coil and the connection structure.
Fig. 1 is a circuit diagram of a dual-transistor flyback converter in the prior art, and since a continuous current of a primary coil (which is caused by an induced electromotive force generated by a leakage inductance of the primary coil, etc.) can return to a bus through clamping two-position transistors D1 and D2, so that switching transistors Q1 and Q2 only need to bear a voltage substantially equal to a bus voltage Vin, the dual-transistor flyback converter is more easily applied to a high input voltage condition. However, under the condition of low-voltage input, that is, when the bus voltage is lower than the voltage reflected by the secondary winding to the primary winding, the clamping diode returns the energy which should be originally transmitted to the secondary winding to the primary winding in a forward mode, so that the secondary winding can only output an output voltage slightly lower than the winding ratio of the bus voltage, that is, if the winding ratio of the primary winding and the secondary winding of the transformer is n:1, the secondary output voltage is: vo = Vin/n-VD (Vo, vin and VD are the output voltage, the input voltage of the bus and the voltage drop of the rectifier diode D, respectively).
Fig. 2 is a circuit diagram of a single-tube flyback converter in the prior art, because the switching tubes Q1 and Q2 having serial primary coils need to bear the bus voltage, the secondary coil reflects to the primary coil voltage (i.e., the reflected voltage) through the transformer, and the voltage value obtained by superimposing the peak voltage (induced electromotive force generated by the leakage inductance of the primary coil) generated by turning off the switching tubes Q1 and Q2, under the condition of high input voltage, the voltage that the switching tubes Q1 and Q2 need to bear is larger, which makes the highest input voltage of the single-tube flyback converter significantly limited. However, under the condition of low-voltage input, the circuit still can normally output under the condition of extremely low input voltage theoretically only by reasonable design.
The problems can occur when the existing double-tube flyback converter is input with low voltage, a designer can only avoid the voltage range when designing the double-tube flyback converter, and determines the lowest input voltage, and cannot take into account the lowest and highest input voltages in wide-range input. In summary, a single-tube flyback converter has no advantage at high input voltages, while a dual-tube flyback converter has problems at low input voltages.
For example, supercapacitors have now become widespread as backup power sources for servo drives, such as backup voltages for wind power pitch servo drives. Under the condition that alternating current is provided for a power grid, the three-phase alternating current of 400Vac is input into an alternating current rectification circuit, and the direct current voltage on a rectified bus can reach 800Vdc under the limit condition; under the condition of power failure of a power grid, a backup power supply super capacitor starts to work, in order to utilize the energy of the super capacitor to the maximum extent, the voltage of the super capacitor needs to be released as low as possible (ideally, the voltage is released to zero), and it can be seen that the working voltage of the bus voltage has a variation range between dozens of volts and 800Vdc, but the existing double-tube flyback converter and the existing single-tube flyback converter are difficult to work in the variation range.
Disclosure of Invention
In view of the above-mentioned situation, a primary object of the present invention is to provide a flyback converter circuit, a control method, a converter, a servo motor and a driver thereof, which can normally operate at a wide input voltage and can lower withstand voltage values of a first switch and a second switch.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a flyback converter circuit comprises a first switch, a second switch, a first diode and a second diode, and further comprises: the circuit comprises a third switch, a fourth switch, a voltage comparison circuit, a first absorption circuit and a second absorption circuit, wherein the first absorption circuit comprises a first absorption capacitor and a first absorption resistor, and the second absorption circuit comprises a second absorption capacitor and a second absorption resistor; one end of the first switch is connected with the bus, and the other end of the first switch is connected with the second end of the primary coil of the transformer; one end of the second switch is connected with the first end of the primary coil, and the other end of the second switch is grounded; the first diode and the third switch are connected in series between the bus and the first end of the primary coil, the third switch is connected in parallel with the first absorption circuit, and the first absorption capacitor and the first absorption resistor in the first absorption circuit are connected in parallel; the second diode and the fourth switch are connected between the second end of the primary coil and the ground in series; the fourth switch is connected with the second absorption circuit in parallel, and the second absorption capacitor and the second absorption resistor in the second absorption circuit are connected in parallel; the voltage comparison circuit compares a bus sampling voltage with a threshold voltage, and when the bus sampling voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to be conducted, so that the first diode and the third switch form a first clamping circuit of the primary coil, the current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode to the cathode of the first diode, and the third switch is enabled to short-circuit the first absorption circuit; the voltage comparison circuit also controls the fourth switch to be conducted, so that the second diode and the fourth switch form a second clamping circuit of the primary coil, the current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode to the second end of the primary coil, and the fourth switch is enabled to short circuit the second absorption circuit; when the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to be switched off, so that the first diode and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the voltage comparison circuit also controls the fourth switch to be switched off, so that the second diode and the second absorption circuit form a second clamping absorption circuit of the primary coil.
Preferably, the flyback converter circuit further includes a third diode and a fourth diode, the first absorption circuit is connected in series with the third diode and then connected in parallel with the third switch, and at the moment when the third switch is turned on, the third diode is used for preventing the electric quantity of the first absorption capacitor from discharging through the third switch; the third diode forms part of the first clamp after the third switch is turned off; the second absorption circuit is connected with the fourth diode in series and then connected with the fourth switch in parallel, and at the moment that the fourth switch is switched on, the fourth diode is used for preventing the electric quantity of the second absorption capacitor from discharging through the fourth switch; the fourth diode forms part of the second clamp after the fourth switch is turned off.
Preferably, the flyback converter circuit further includes a control unit, and the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control unit is used for: when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, updating the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k × n (Vo + Vd); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1); and outputting the updated threshold voltage to the voltage comparison circuit.
Preferably, the flyback converter circuit further includes a control unit, and the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control unit is used for: when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, updating the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k (n (Vo + Vd) + V1); wherein Vth, vo and Vd are respectively: v1 is a constant between 5V and 10V, n is a turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1); and outputting the updated threshold voltage to the voltage comparison circuit.
The invention also provides a control method of the flyback conversion circuit, which adopts the flyback conversion circuit and comprises the following steps: the voltage comparison circuit compares a bus sampling voltage with a threshold voltage, and when the bus sampling voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to be conducted, so that the first diode and the third switch form a first clamping circuit of the primary coil, the current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode to the cathode of the first diode, and the third switch is enabled to short-circuit the first absorption circuit; the voltage comparison circuit further controls the fourth switch to be conducted, so that the second diode and the fourth switch form a second clamping circuit of the primary coil, the current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode to the second end of the primary coil, and the fourth switch short-circuits the second absorption circuit; when the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to be switched off, so that the first diode and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the voltage comparison circuit also controls the fourth switch to be switched off, so that the second diode and the second absorption circuit form a second clamping absorption circuit of the primary coil.
Preferably, the flyback converter circuit further includes a control unit, and the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control method further comprises the following steps: when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k × n (Vo + Vd); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1); the control unit outputs the updated threshold voltage to the voltage comparison circuit.
Preferably, the flyback converter circuit further includes a control unit, and the secondary winding of the transformer outputs the output voltage through a rectifier diode; the control method further comprises the following steps: when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k (n (Vo + Vd) + V1); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, V1 is a constant between 5V and 10V, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1); the control unit outputs the updated threshold voltage to the voltage comparison circuit.
The invention also provides a flyback converter, which comprises a transformer and any flyback conversion circuit.
The invention also provides a servo motor driver, which comprises a transformer and any flyback conversion circuit.
The invention also provides a servo motor which comprises the servo motor driver.
[ PROBLEMS ] the present invention
Under the condition that the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch and the fourth switch to be conducted, so that the first diode and the third switch form a first clamping circuit of the primary coil, the second diode and the fourth switch form a second clamping circuit of the primary coil, the voltage comparison circuit is similar to a double-tube flyback converter, and the withstand voltage values of the first switch and the second switch can be lower; when the bus sampling voltage is smaller than the threshold voltage, the voltage comparison circuit controls the third switch to be switched off and the fourth switch to be switched off, so that the first diode and the first absorption circuit form a first clamping absorption circuit of the primary coil, the second diode and the second absorption circuit form a second clamping absorption circuit of the primary coil, and the first end and the second end of the primary coil of the transformer cannot be clamped, so that the problem that the energy of the secondary coil is transmitted back to the primary coil in a forward mode, and the secondary coil can only be slightly lower than the output voltage of the bus voltage in turn ratio is avoided.
Other advantages of the present invention will be described in the detailed description, and those skilled in the art will understand the technical features and technical solutions presented in the description.
Drawings
A preferred embodiment of a flyback converter circuit of the present invention will be described below with reference to the accompanying drawings. In the figure:
fig. 1 is a circuit topology diagram of a dual-transistor flyback converter circuit in the prior art;
fig. 2 is a circuit topology diagram of a single-tube flyback conversion circuit in the prior art;
fig. 3 is a flyback converter circuit according to a preferred embodiment of the present invention;
fig. 4 is a flyback converter circuit according to another preferred embodiment of the present invention;
fig. 5 is a flyback converter circuit according to another preferred embodiment of the present invention;
fig. 6 is a flyback converter circuit according to another preferred embodiment of the present invention;
fig. 7 is a flyback converter circuit according to another preferred embodiment of the present invention;
fig. 8 is a flyback converter circuit according to another preferred embodiment of the present invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth in order to avoid obscuring the nature of the present invention, well-known methods, procedures, and components have not been described in detail.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
The flyback conversion circuit is very suitable for a scene with a wide input voltage variation range, and products applying the flyback conversion circuit can be as follows: the device comprises a switching power supply, a frequency converter, a servo driver, a UPS, an inverter, an energy storage device and the like. Fig. 3 is a flyback converter circuit according to an embodiment of the present invention, the flyback converter circuit is configured to convert a voltage on a bus thereof into an output voltage Vo to be provided to a load, for example, a servo motor (correspondingly, the flyback converter circuit is a component of a servo driver).
The flyback conversion circuit comprises a control unit (not shown in the figure), a driving unit (not shown in the figure), a bus capacitor C1, a first switch Q1, a second switch Q2, a first diode D1 (freewheeling diode), a second diode D2 (freewheeling diode), a third switch Q3, a fourth switch Q4, a voltage comparison circuit, a first absorption circuit, a second absorption circuit, a transformer T, a rectifier diode D and an output filter capacitor C2, wherein the first absorption circuit comprises a first absorption capacitor C3 and a first absorption resistor R1, and the second absorption circuit comprises a second absorption capacitor C4 and a second absorption resistor R2. The first switch Q1, the second switch Q2, the third switch Q3 and the fourth switch Q4 may be MOS transistors, such as N-channel MOS transistors or P-channel MOS transistors, and IGBT (insulated gate bipolar transistors).
The bus of the flyback converter circuit is grounded through a bus capacitor C1, and the voltage on the bus is derived from the output voltage of the previous stage circuit, which is the input voltage of the flyback converter circuit. The range of the output voltage of the present front-stage circuit is greatly changed, for example, the range of the output voltage is 20V-800V. The front-stage circuit can be a super capacitor (namely a standby power supply) and an alternating current rectification circuit, and the super capacitor and the alternating current rectification circuit respectively work under corresponding conditions; when the power grid is electrified, the alternating current rectifying circuit works, and converts alternating current voltage into direct current voltage to be supplied to the bus; when the power grid is out of power, the super capacitor works and outputs direct current voltage to the bus.
One end of the first switch Q1 is connected with the bus, and the other end of the first switch Q1 is connected with a second end T2 of a primary coil of the transformer T; one end of the second switch Q2 is connected with the first end T1 of the primary coil, and the other end is grounded.
The first diode D1 and the third switch Q3 are connected in series between the bus bar and the first end T1 of the primary coil. As shown in fig. 3, in one embodiment, the third switch Q3 is connected in series between the first terminal T1 of the primary coil and the anode of the first diode D1; in another embodiment, as shown in fig. 4, a third switch Q3 is connected in series between the bus bar and the cathode of the first diode D1. The third switch Q3 is connected in parallel with the first absorption circuit, and the first absorption capacitor C3 and the first absorption resistor R1 in the first absorption circuit are connected in parallel.
The second diode D2 and the fourth switch Q4 are connected in series between the second end T2 of the primary coil and ground. In one embodiment, as shown in fig. 3, a fourth switch Q4 is connected in series between the anode of the second diode D2 and ground. In another embodiment, as shown in fig. 6, the fourth switch Q4 is connected in series between the second terminal T2 of the primary winding and the cathode of the second diode D2. The fourth switch Q4 is connected in parallel with the second absorption circuit, and the second absorption capacitor C4 in the second absorption circuit is connected in parallel with the second absorption resistor R2.
The voltage comparison circuit compares the bus sampling voltage (namely the sampling voltage of the input voltage) with the threshold voltage, when the bus sampling voltage is larger than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to be conducted, the fourth switch Q4 to be conducted, so that the first diode D1 and the third switch Q3 form a first clamping circuit of the primary coil, the second diode D2 and the fourth switch Q4 form a second clamping circuit of the primary coil, and the current (also called continuous current, the current generated when the first switch Q1 and the second switch Q2 are turned off in the switching action period of the first switch Q1 and the second switch Q2) in the first clamping circuit is in the direction from the first end T1 of the primary coil, the third switch Q3 and the anode of the first diode D1 to the cathode of the first diode D1, and the third switch Q3 is used for short-circuiting the first absorption circuit; the current in the second clamp circuit is in the direction from the fourth switch Q4, the anode of the second diode D2, the cathode of the second diode D2 to the second end T2 of the primary winding, and the fourth switch Q4 is caused to short-circuit the second snubber circuit.
When the bus sampling voltage is smaller than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to be switched off and the fourth switch Q4 to be switched off, so that the first diode D1 and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the second diode D2 and the second absorption circuit form a second clamping absorption circuit of the primary coil. As shown in fig. 3, in one embodiment, the voltage comparison circuit uses a comparator, one end of which inputs a bus sampling voltage (i.e. a sampling voltage of the input voltage) V' in, the other end of which inputs a threshold voltage, and the output end outputs a comparison result signal, for example, when the input voltage is greater than the threshold voltage, the comparison result signal is at a high level, and when the input voltage is less than the threshold voltage, the comparison result signal is at a low level. In some embodiments, the flyback converter further includes a driving circuit, which converts the comparison result signal into a driving signal for driving the third switch Q3 and the fourth switch Q4, and inputs the driving signal to the control terminal of the third switch Q3 and the control terminal of the fourth switch Q4, respectively, so as to control the third switch Q3 to be turned on or off and the fourth switch Q4 to be turned on or off. For example, the third switch Q3 is a MOS transistor, the driving signal is input to the gate of the MOS transistor, and a resistor R3 is connected between the gate and the source, so as to provide both a bias voltage for the gate of the third switch Q3 and a quick release path for the accumulated charges on the gate. Similarly, the fourth switch Q4 is a MOS transistor, the driving signal is input to a gate of the MOS transistor, and a resistor R4 is connected across between the gate and a source, so as to provide a bias voltage for the gate of the fourth switch Q4 and provide a fast discharging channel for the accumulated charges on the gate.
One end of a secondary winding of the transformer T is connected with the positive output end Vo + through the rectifier diode D, the other end of the secondary winding of the transformer T is connected with the negative output end Vo-, two ends of the filter capacitor C2 are respectively connected with the positive output end Vo + and the negative output end Vo-, and output voltage Vo between the positive output end Vo + and the negative output end Vo-is supplied to a load.
Under the condition that the bus sampling voltage is larger than the threshold voltage, the voltage comparison circuit compares the bus sampling voltage with the threshold voltage to obtain a comparison result, and then controls the third switch Q3 and the fourth switch Q4 to be conducted respectively, so that the third switch Q3 short-circuits the first absorption circuit, and the fourth switch Q4 short-circuits the second absorption circuit. The following describes the operation of the flyback converter circuit in the operating cycle in detail: (1) The control unit controls the first switch Q1 and the second switch Q2 to be switched on through a driving unit (not shown in the figure), current flows out from a bus and flows into the ground through the first switch Q1, the primary coil and the second switch Q2, the current excites the transformer T in the process, electric energy is converted into magnetic energy, the rectifier diode D is switched off (namely switched off), and no current exists in the secondary coil. At this time, the voltage of the cathode of the second diode D2 is greater than the voltage of the anode thereof, and thus the second diode D2 is turned off (i.e., turned off); the voltage of the cathode of the first diode D1 is greater than the voltage of the anode thereof, so that the first diode D1 is turned off (i.e., turned off); (2) After the step (1) lasts for a certain time, the control unit controls the first switch Q1 and the second switch Q2 to be switched off through a driving unit (not shown in the figure), the magnetic energy in the transformer T starts to be converted into electric energy, the rectifier diode D is switched on, and the secondary side coil has current; in addition, because the first switch Q1 and the second switch Q2 are disconnected instantly, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback conversion circuit generates a reflected voltage at the primary coil due to the turn ratio of the transformer T (the turn ratio between the primary coil and the secondary coil), and thus the voltage difference between both ends of the primary coil is the sum of the induced electromotive force and the reflected voltage. The voltage of the first end T1 of the primary coil is clamped to the sum of the input voltage and the voltage drop of the first diode D1 (namely Vin + VD 1) due to the clamping of the first diode D1; the voltage of the second end T2 of the primary coil is clamped between 0 and the voltage drop difference (namely-VD 2) of the second diode D2 due to the clamping of the second diode D2; therefore, the continuous current on the primary coil flows out from the first end T1, flows into the bus through the first diode D1, charges the bus capacitor C1, and returns to the second end T2 of the primary coil through the bus capacitor C1 and the second diode D2 to form a continuous current loop.
Under the condition that the bus sampling voltage is smaller than the threshold voltage, the voltage comparison circuit compares the bus sampling voltage with the threshold voltage to obtain a comparison result, and then controls the third switch Q3 and the fourth switch Q4 to be switched off respectively, so that the first diode D1 and the first absorption circuit form a first clamping absorption circuit (RCD circuit) of the primary coil, and the second diode D2 and the second absorption circuit form a second clamping absorption circuit (RCD circuit) of the primary coil.
The following describes the operation of the flyback converter circuit in the operating cycle in detail: (1) The control unit controls the first switch Q1 and the second switch Q2 to be switched on through a driving unit (not shown in the figure), current flows out from a bus and flows into the ground through the first switch Q1, the primary coil and the second switch Q2, the current excites the transformer T in the process, electric energy is converted into magnetic energy, the rectifier diode D is switched off (namely switched off), and no current exists in the secondary coil. At this time, the voltage of the cathode of the second diode D2 is greater than the voltage of the anode thereof, and thus the second diode D2 is turned off (i.e., turned off); the voltage of the cathode of the first diode D1 is greater than the voltage of the anode thereof, so that the first diode D1 is turned off (i.e., turned off); (2) After the step (1) lasts for a certain time, the control unit controls the first switch Q1 and the second switch Q2 to be switched off through a driving unit (not shown in the figure), the magnetic energy in the transformer T starts to be converted into electric energy, the rectifier diode D is switched on, and the secondary side coil has current; in addition, because the first switch Q1 and the second switch Q2 are disconnected instantly, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback conversion circuit generates a reflection voltage at the primary coil due to the turn ratio of the transformer T (the turn ratio between the primary coil and the secondary coil), that is, the voltage difference between two ends of the primary coil is the sum of the induced electromotive force and the reflection voltage, the first diode D1 and the second diode D2 are conducted, the continuous current on the primary coil flows out from the first end T1, the first absorption capacitor C3 starts to charge, the charging current flows back to the bus after passing through the first absorption capacitor C3 and the first diode D1 and charges the bus capacitor C1, in addition, the second absorption capacitor C4 also starts to charge, the charging current flows out from the ground and flows back to the second end T2 of the primary coil through the second absorption capacitor C4 and the second diode D2. Due to the charging effect of the first absorption capacitor C3 and the second absorption capacitor C4, voltage peaks caused by induced electromotive force in the voltages of the first end T1 of the primary coil and the second end T2 of the primary coil are also absorbed and become gentle; (3) When the first absorption capacitor C3 is charged to a certain voltage (i.e., stores a certain corresponding electric quantity), and the voltage difference between the low-potential end P31 and the bus voltage is smaller than the turn-on voltage drop of the first diode D1, the first absorption capacitor C3 is charged to a certain voltage (i.e., stores a certain corresponding electric quantity), at this time, the second absorption capacitor C4 is charged to a certain voltage (i.e., stores a certain corresponding electric quantity), the voltage difference between the high-potential end P33 and the second end T2 of the primary coil is smaller than the turn-on voltage drop of the second diode D2, and the second absorption capacitor C4 is charged to a certain voltage (i.e., is turned off); (4) The first absorption capacitor C3 can discharge through the first absorption resistor R1, and a discharge current flows out from a high potential end P32 (the end connected to the first end T1 of the primary coil) of the first absorption capacitor C3, passes through the first absorption resistor R1, and then flows into a low potential end P31 (the end sharing the anode of the first diode D1) of the first absorption capacitor C3; similarly, the second snubber capacitor C4 can discharge through the second snubber resistor R2, the discharge current flows out from the high potential end P34 (the end connected to ground) of the second snubber capacitor C4, flows into the low potential end P33 (the end in common with the anode of the second diode D2) of the second snubber capacitor C4 after passing through the second snubber resistor R2, and after discharging to a certain voltage value, the flyback converter circuit starts to enter the steps (1) - (3) of the next cycle again, wherein in the step (1) of the next cycle, the cathode voltage of the first diode D1 is the bus voltage, the anode voltage thereof is the voltage of the low potential end P31, and at this time, the first diode D1 is turned off; the cathode voltage of the second diode D2 is the voltage of the second end T2 of the primary coil, and the anode voltage thereof is the negative voltage of the low potential end P33, at which time the second diode D2 is turned off; after step (3) of the next cycle, the first absorption capacitor C3 and the second absorption capacitor C4 start to charge again; therefore, when the bus sampling voltage is smaller than the threshold voltage, during the operation of the flyback converter circuit, the voltage at the low potential end P31 of the first absorption capacitor C3 can be stably maintained at least at a certain voltage value (i.e., at least a certain amount of electric energy can be stored in the first absorption capacitor C3) (similarly, the voltage VC3 at the high potential end P32 can be stably maintained at least at a certain voltage value) related to the capacitance value of the first absorption capacitor C3, the resistance value of the first absorption resistor R1, and the duty ratio of the on-time of the first switch Q1 and the second switch Q2; similarly, the voltage VC4 at the low potential terminal P33 of the second absorption capacitor C4 can be stably maintained at least below a voltage value (negative value) (i.e., at least a certain amount of stored electric energy) related to the capacitance value of the second absorption capacitor C4, the resistance value of the second absorption resistor R2, and the duty ratio of the on-time of the first switch Q1 and the second switch Q2. Therefore, under the condition that the bus sampling voltage is less than the threshold voltage, the voltage difference of the primary coil cannot be clamped at the input voltage, so that the flyback conversion circuit can work normally, and the problem that the energy of the secondary coil is transmitted back to the primary coil in a forward mode, so that the secondary coil can only obtain the output voltage slightly lower than the turn ratio of the bus voltage is solved.
In some embodiments, the output voltage Vo of the flyback converter circuit (which is output by the secondary winding of the transformer T through the rectifier diode D) is generally adjustable, for example, 20V needs to be output in some scenarios, and 48V needs to be output in some scenarios, and the control unit may adjust the output voltage Vo of the flyback converter circuit to a new voltage value by adjusting the duty ratios of the on-time of the first switch Q1 and the second switch Q2. When the output voltage Vo is adjusted to a new voltage value, the control unit updates the threshold voltage and outputs the updated threshold voltage to the voltage comparison circuit; wherein the control unit updates the threshold voltage to a greater threshold voltage when the output voltage Vo is adjusted to a greater voltage value, and updates the threshold voltage to a smaller threshold voltage when the output voltage Vo is adjusted to a smaller voltage value; and finally, the control unit outputs the updated threshold voltage to the voltage comparison circuit. And the voltage comparison circuit controls the third switch Q3 and the fourth switch tube Q4 to be switched on or switched off according to the updated threshold voltage.
In some embodiments, the magnitude of the determined threshold voltage Vth is calculated by the output voltage Vo and the voltage drop VD of the rectifying diode D: vth = k × n (Vo + VD); wherein n is the turn ratio of the primary coil and the secondary coil of the transformer T, k is a sampling coefficient, and the value range is (0,1), that is, k = V 'in/Vin (Vin is the bus voltage, and V' in is the bus sampling voltage). In the above relation, when the first switch Q1 and the second switch Q2 are turned off, instantaneous oscillation or fluctuation of the voltage difference between the two ends of the primary winding of the transformer T is ignored, and it is roughly considered that the threshold voltage Vth = k × n (Vo + VD) is quite appropriate, the flyback conversion circuit normally operates between the input voltage intervals vin.min-Vth, and the voltage of the second end of the primary winding of the transformer T is not clamped at-VD 2; the voltage-stabilizing circuit has the advantages of a traditional double-tube flyback conversion circuit when the voltage is input within the interval Vth-vin.max; wherein vin.min and vin.max are the minimum and maximum values of the input voltage, respectively.
In some embodiments, when considering the transient oscillation or fluctuation of the voltage difference across the primary winding of the transformer T when the first switch Q1 and the second switch Q2 are turned off, some margin may be added to the threshold voltage Vth, that is, the magnitude of the threshold voltage Vth is calculated and determined by the output voltage Vo and the voltage drop VD of the rectifier diode D: vth = k (n (Vo + VD) + V1); wherein V1 is a constant between 5V-10V.
As described above, in the embodiment shown in fig. 4, the third switch Q3 may be disposed between the cathode of the first diode D1 and the bus, the anode of the first diode D1 is connected to the first terminal T1 of the primary coil, the third switch Q3 is connected in parallel to the first absorption circuit, the first absorption capacitor C3 and the first absorption resistor R1 are connected in parallel in the first absorption circuit, and the fourth switch is disposed between the anode of the second diode D2 and the ground. The working process of the flyback converter circuit in the working period is the same as that of the flyback converter circuit in fig. 3 in principle, and the specific process is different, for example, when the bus sampling voltage is less than the threshold voltage, and when the first absorption capacitor C3 is charged to a certain voltage in the working process step (3), the voltage difference between the high potential end P32 (correspondingly, P31 is the low potential end) and the first end T1 of the primary coil is less than the on-state voltage drop of the first diode D1, the charging of the first absorption capacitor C3 is cut off.
In some embodiments, as shown in fig. 5, the flyback converter further includes a third diode D3 and a fourth diode D4, the first absorption circuit is connected in series with the third diode D3 and then connected in parallel with a third switch Q3, and at the moment when the third switch Q3 is turned on, the third diode D3 is used to prevent the electric quantity of the first absorption capacitor C3 from discharging through the third switch Q3; the third diode D2 forms part of the first clamp after the third switch Q3 is turned off. For example, the cathode of the third diode D3 is connected to the anode of the first diode D1, and the anode is connected to the low potential terminal P31 of the snubber circuit. For another example, the cathode of the third diode D3 is connected to the high potential terminal P32, and the anode is connected to the first terminal T1 of the primary winding (not shown). The second absorption circuit is connected in series with a fourth diode D4 and then connected in parallel with a fourth switch Q4, and at the moment when the fourth switch Q4 is turned on, the fourth diode D4 is used for preventing the electric quantity of the second absorption capacitor C4 from discharging through the fourth switch Q4; after the fourth switch Q4 is turned off, the fourth diode D4 forms part of the second clamp. For example, the cathode of the fourth diode D4 is connected to the anode of the second diode D2, and the anode is connected to the high potential terminal P33 of the snubber circuit. For another example, the cathode of the fourth diode D4 is connected to the high potential terminal P34 of the snubber circuit, and the anode is connected to ground (not shown). As mentioned above, when the bus sampling voltage is smaller than the threshold voltage, the first absorption capacitor C3 has a voltage value, and when the bus sampling voltage changes to be larger than the threshold voltage, the third switch Q3 is controlled to be turned on, and due to the presence of the third diode D3, the voltage on the first absorption capacitor C3 is discharged through the first absorption resistor R1; otherwise, if the third diode D3 does not exist, at the moment when the third switch Q3 is controlled to be turned on, the third switch Q3 is turned on to short-circuit the first absorption capacitor C3, and the voltage of the first absorption capacitor C3 is instantaneously loaded on the third switch Q3, so that an instantaneous high voltage is generated, thereby causing damage to the third switch Q3. Similarly, in the case that the bus sampling voltage is smaller than the threshold voltage, the second absorption capacitor C4 has a voltage value, when the bus sampling voltage changes to be larger than the threshold voltage, the third switch Q4 is controlled to be turned on, and due to the presence of the fourth diode D4, the voltage on the second absorption capacitor C4 is discharged through the second absorption resistor R2; otherwise, if the fourth diode D4 does not exist, at the moment when the fourth switch Q4 is controlled to be turned on, the fourth switch Q4 is turned on to short-circuit the second absorption capacitor C4, and the voltage of the second absorption capacitor C4 is instantaneously loaded on the fourth switch Q4, an instantaneous high voltage is generated, so that the fourth switch Q4 is damaged. Similarly, the flyback converter circuit in fig. 4 may also include a third diode D3 and a fourth diode D4, which are not described herein again.
Fig. 6 is a flyback converter circuit according to another embodiment of the present invention, which is substantially similar to fig. 3, and the main differences include: the relative positional relationship of the first diode D1 and the third switch Q3, and the relative positional relationship of the second diode D2 and the fourth switch Q4.
Specifically, as shown in fig. 6, the third switch Q3 is connected in series between the bus bar and the cathode of the first diode D1, the anode of the first diode D1 is connected to the first terminal T1 of the primary winding, and the fourth switch Q4 is connected in series between the cathode of the second diode D2 and the second terminal T2 of the primary winding.
The voltage comparison circuit compares the bus sampling voltage (i.e. the sampling voltage of the input voltage) V' in with a threshold voltage, when the bus sampling voltage is greater than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to be turned on, the fourth switch Q4 to be turned on, so that the first diode D1 and the third switch Q3 form a first clamping circuit of the primary coil, the fourth switch Q4 and the second diode D2 form a second clamping circuit of the primary coil, and the current (also called continuous current, current generated when the first switch Q1 and the second switch Q2 are turned off in the switching action period of the first switch Q1 and the second switch Q2) in the first clamping circuit is in the direction from the first end T1 of the primary coil, the anode of the first diode D1, the cathode of the first diode D1 to the first switch Q3, and the third switch Q3 short-circuits the first absorption circuit; the direction of the current in the second clamping circuit is the anode of the second diode D2, the cathode of the second diode D2, from the fourth switch Q4 to the second end T2 of the primary winding, and causes the fourth switch Q4 to short circuit the second snubber circuit. When the bus sampling voltage is smaller than the threshold voltage, the voltage comparison circuit controls the third switch Q3 to be switched off and the fourth switch Q4 to be switched off, so that the first diode D1 and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the second diode D2 and the second absorption circuit form a second clamping absorption circuit of the primary coil.
Under the condition that the bus sampling voltage is larger than the threshold voltage, after the comparison result is obtained by comparing the bus sampling voltage with the threshold voltage, the voltage comparison circuit respectively controls the third switch Q3 to be conducted, the third switch Q3 short-circuits the first absorption circuit, controls the fourth switch Q4 to be conducted, and the fourth switch Q4 short-circuits the second absorption circuit. The following describes the operation of the flyback converter circuit in the operating cycle in detail: (1) The control unit controls the first switch Q1 and the second switch Q2 to be switched on through a driving unit (not shown in the figure), current flows out from a bus and flows into the ground through the first switch Q1, the primary coil and the second switch Q2, the current excites the transformer T in the process, electric energy is converted into magnetic energy, at the moment, the rectifier diode D is cut off (namely switched off), and no current flows in the secondary coil. At this time, the voltage of the cathode of the second diode D2 is greater than the voltage of the anode thereof, and thus the second diode D2 is turned off (i.e., turned off); the voltage of the cathode of the first diode D1 is greater than the voltage of the anode thereof, so that the first diode D1 is turned off (i.e., turned off); (2) After the step (1) lasts for a certain time, the control unit controls the first switch Q1 and the second switch Q2 to be switched off through a driving unit (not shown in the figure), the magnetic energy in the transformer T starts to be converted into electric energy, the rectifier diode D is switched on, and the secondary side coil has current; in addition, because the first switch Q1 and the second switch Q2 are disconnected instantly, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback conversion circuit generates a reflected voltage at the primary coil due to the turn ratio of the transformer T (the turn ratio between the primary coil and the secondary coil), and thus the voltage difference between both ends of the primary coil is the sum of the induced electromotive force and the reflected voltage. The voltage of the first end T1 of the primary coil is clamped to the sum of the input voltage and the voltage drop of the first diode D1 (namely Vin + VD 1) due to the clamping of the first diode D1; the voltage of the second end T2 of the primary coil is clamped between 0 and the voltage drop difference (namely-VD 2) of the second diode D2 due to the clamping of the second diode D2; therefore, the continuous current on the primary coil flows out from the first end T1, flows into the bus through the first diode D1, charges the bus capacitor C1, and returns to the second end T2 of the primary coil through the bus capacitor C1 and the second diode D2 to form a continuous current loop.
Under the condition that the bus sampling voltage is smaller than the threshold voltage, the voltage comparison circuit compares the bus sampling voltage with the threshold voltage to obtain a comparison result, and then controls the third switch Q3 to be switched off and the fourth switch Q4 to be switched off respectively, so that the first diode D1 and the first absorption circuit form a first clamping absorption circuit (RCD circuit) of the primary coil, and the second diode D2 and the second absorption circuit form a second clamping absorption circuit (RCD circuit) of the primary coil.
The following describes the operation of the flyback converter circuit in the operating cycle in detail: (1) The control unit controls the first switch Q1 and the second switch Q2 to be switched on through a driving unit (not shown in the figure), current flows out from a bus and flows into the ground through the first switch Q1, the primary coil and the second switch Q2, the current excites the transformer T in the process, electric energy is converted into magnetic energy, at the moment, the rectifier diode D is cut off (namely switched off), and no current flows in the secondary coil. At this time, the voltage of the cathode of the second diode D2 is greater than the voltage of the anode thereof, and thus the second diode D2 is turned off (i.e., turned off); the voltage of the cathode of the first diode D1 is greater than the voltage of the anode thereof, so that the first diode D1 is turned off (i.e., turned off); (2) After the step (1) lasts for a certain time, the control unit controls the first switch Q1 and the second switch Q2 to be switched off through a driving unit (not shown in the figure), the magnetic energy in the transformer T starts to be converted into electric energy, the rectifier diode D is switched on, and the secondary side coil has current; in addition, because the first switch Q1 and the second switch Q2 are disconnected instantly, the leakage inductance of the primary coil generates a large induced electromotive force; the output voltage Vo of the flyback conversion circuit generates a reflected voltage at the primary coil due to the turn ratio of the transformer T (the turn ratio between the primary coil and the secondary coil), that is, the voltage difference between the two ends of the primary coil is the sum of the induced electromotive force and the reflected voltage. The first diode D1 is conducted, the first absorption capacitor C3 starts to be charged, the charging current flows out from the first end T1 of the primary coil, the first absorption capacitor C3 is charged and flows back after passing through the first diode D1, in addition, the second diode D2 is conducted, the second absorption capacitor C4 starts to be charged, the charging current charges the second absorption capacitor C4 through the second diode D2, and the charging current flows back to the second end T2 of the primary coil. Due to the charging effect of the first absorption capacitor C3 and the second absorption capacitor C4, voltage spikes caused by induced electromotive force in the voltages of the first end T1 and the second end T2 of the primary coil are also absorbed and become gentle (3) when the first absorption capacitor C3 is charged to a certain voltage and the voltage difference between the high potential end P32 and the first end of the primary coil is smaller than the conduction voltage drop of the first diode D1, the charging of the first absorption capacitor C3 is cut off (i.e., turned off), at this time, the second absorption capacitor C4 is charged to a certain voltage and the voltage difference between the high potential end P34 and the ground is smaller than the conduction voltage drop of the second diode D2, the charging of the second absorption capacitor C4 is cut off (i.e., turned off); (4) The first absorption capacitor C3 can discharge through the first absorption resistor R1, and a discharge current flows from a high potential end P32 (one end that is in common with the cathode of the first diode) of the first absorption capacitor C3, passes through the first absorption resistor R1, and then flows into a low potential end P31 (one end connected to the bus) of the first absorption capacitor C3; similarly, the second absorption capacitor C4 can discharge through the second absorption resistor R2, the discharge current flows out from the high potential end P34 (the end that is in common with the cathode of the second diode) of the second absorption capacitor C4, flows into the low potential end P33 (the end connected to the second end of the primary winding) of the second absorption capacitor C4 through the second absorption resistor R2, and after discharging to a certain voltage value, the flyback converter circuit starts to enter the steps (1) - (3) of the next cycle again, wherein in the step (1) of the next cycle, the cathode voltage of the first diode D1 is the voltage of the high potential end P32, the anode voltage thereof is the voltage of the first end T1 of the primary winding, and at this time, the first diode D1 is turned off; the cathode voltage of the second diode D2 is the voltage of the high potential terminal P34, and the anode voltage thereof is ground, at which time the second diode D2 is turned off; after step (3) of the next cycle, the first absorption capacitor C3 and the second absorption capacitor C4 start to charge again; therefore, in the case where the bus sampling voltage is smaller than the threshold voltage, during the operation of the flyback converter circuit, the voltage VC3 of the high potential terminal P32 of the first absorption capacitor C3 can be stably maintained at least above a certain voltage value (i.e., at least a certain amount of electric energy can be stored) related to the capacitance value of the first absorption capacitor C3, the resistance value of the first absorption resistor R1, and the duty ratio of the on time of the first switch Q1 and the second switch Q2, and similarly, the voltage of the low potential terminal P33 of the second absorption capacitor C4 can be stably maintained at least below a certain voltage value (negative value) (i.e., at least a certain amount of electric energy can be stored) related to the capacitance value of the second absorption capacitor C4, the resistance value of the second absorption resistor R2, and the duty ratio of the on time of the first switch Q1 and the second switch Q2. Therefore, under the condition that the bus sampling voltage is less than the threshold voltage, the voltage difference of the primary coil cannot be clamped at the input voltage, so that the flyback conversion circuit can work normally, and the problem that the energy of the secondary coil is transmitted back to the primary coil in a forward mode, so that the secondary coil can only obtain the output voltage slightly lower than the turn ratio of the bus voltage is solved.
As described above, in the embodiment shown in fig. 7, the third switch Q3 may be disposed between the anode of the first diode D1 and the first end T1 of the primary coil, and the cathode of the first diode D1 is connected to the bus bar. The fourth switch Q4 may be disposed between the second terminal T2 of the primary coil and the cathode of the second diode D2, and the anode of the second diode D2 is grounded. The working process of the flyback conversion circuit in the working period is the same as that of the flyback conversion circuit in the working period in fig. 6 in principle, and the specific process is different.
In some embodiments, as shown in fig. 8, the flyback converter further includes a third diode D3 and a fourth diode D4, the first absorption circuit is connected in series with the third diode D3 and then connected in parallel with the third switch Q3, a cathode of the third diode D3 and the third switch Q3 have a common end, and a current direction in the first absorption circuit is from an anode of the third diode D3 to a cathode of the third diode D3. The function of the fourth diode D4 is described in detail in the related embodiments, and is not described in detail herein. Similarly, the flyback converter circuit in fig. 7 may also include a third diode D3 and a fourth diode D4, which are not described in detail herein.
It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.
It will be appreciated by those skilled in the art that the above-described preferred embodiments may be freely combined, superimposed, without conflict.
It will be understood that the embodiments described above are illustrative only and not restrictive, and that various obvious and equivalent modifications and substitutions for details described herein may be made by those skilled in the art without departing from the basic principles of the invention.
Claims (10)
1. A flyback converter circuit comprises a first switch, a second switch, a first diode and a second diode, and is characterized by further comprising: the circuit comprises a third switch, a fourth switch, a voltage comparison circuit, a first absorption circuit and a second absorption circuit, wherein the first absorption circuit comprises a first absorption capacitor and a first absorption resistor, and the second absorption circuit comprises a second absorption capacitor and a second absorption resistor;
one end of the first switch is connected with the bus, and the other end of the first switch is connected with the second end of the primary coil of the transformer; one end of the second switch is connected with the first end of the primary coil, and the other end of the second switch is grounded;
the first diode and the third switch are connected in series between the bus and the first end of the primary coil, the third switch is connected in parallel with the first absorption circuit, and the first absorption capacitor and the first absorption resistor in the first absorption circuit are connected in parallel;
the second diode and the fourth switch are connected between the second end of the primary coil and the ground in series; the fourth switch is connected with the second absorption circuit in parallel, and the second absorption capacitor and the second absorption resistor in the second absorption circuit are connected in parallel;
the voltage comparison circuit compares a bus sampling voltage with a threshold voltage, and when the bus sampling voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to be conducted, so that the first diode and the third switch form a first clamping circuit of the primary coil, the current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode to the cathode of the first diode, and the third switch is enabled to short-circuit the first absorption circuit; the voltage comparison circuit also controls the fourth switch to be conducted, so that the second diode and the fourth switch form a second clamping circuit of the primary coil, the current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode to the second end of the primary coil, and the fourth switch is enabled to short-circuit the second absorption circuit;
when the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to be switched off, so that the first diode and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the voltage comparison circuit also controls the fourth switch to be switched off, so that the second diode and the second absorption circuit form a second clamping absorption circuit of the primary coil.
2. The flyback converter of claim 1,
a third diode and a fourth diode are also included,
the first absorption circuit is connected with the third diode in series and then connected with the third switch in parallel, and at the moment when the third switch is turned on, the third diode is used for preventing the electric quantity of the first absorption capacitor from discharging through the third switch; the third diode forms part of the first clamp after the third switch is turned off;
the second absorption circuit is connected in series with the fourth diode and then connected in parallel with the fourth switch, and at the moment when the fourth switch is turned on, the fourth diode is used for preventing the electric quantity of the second absorption capacitor from discharging through the fourth switch; the fourth diode forms part of the second clamp after the fourth switch is turned off.
3. The flyback converter of claim 1,
the secondary coil of the transformer outputs the output voltage through a rectifier diode;
the control unit is used for:
when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, updating the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k × n (Vo + Vd); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1);
and outputting the updated threshold voltage to the voltage comparison circuit.
4. The flyback converter of claim 1,
the secondary coil of the transformer outputs the output voltage through a rectifier diode;
the control unit is used for:
when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, updating the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k (n (Vo + Vd) + V1); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, V1 is a constant between 5V and 10V, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1);
and outputting the updated threshold voltage to the voltage comparison circuit.
5. A control method of a flyback converter circuit, characterized in that the flyback converter circuit of claim 1 is used, the control method comprising the steps of:
the voltage comparison circuit compares a bus sampling voltage with a threshold voltage, and when the bus sampling voltage is greater than the threshold voltage: the voltage comparison circuit controls the third switch to be conducted, so that the first diode and the third switch form a first clamping circuit of the primary coil, the current direction in the first clamping circuit is from the first end of the primary coil, the anode of the first diode to the cathode of the first diode, and the third switch is enabled to short-circuit the first absorption circuit; the voltage comparison circuit also controls the fourth switch to be conducted, so that the second diode and the fourth switch form a second clamping circuit of the primary coil, the current direction in the second clamping circuit is from the anode of the second diode, the cathode of the second diode to the second end of the primary coil, and the fourth switch is enabled to short-circuit the second absorption circuit;
when the bus sampling voltage is less than the threshold voltage: the voltage comparison circuit controls the third switch to be switched off, so that the first diode and the first absorption circuit form a first clamping absorption circuit of the primary coil, and the voltage comparison circuit also controls the fourth switch to be switched off, so that the second diode and the second absorption circuit form a second clamping absorption circuit of the primary coil.
6. The control method according to claim 5,
the flyback conversion circuit also comprises a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode;
the control method further comprises the following steps:
when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k × n (Vo + Vd); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1);
the control unit outputs the updated threshold voltage to the voltage comparison circuit.
7. The control method according to claim 5,
the flyback conversion circuit also comprises a control unit, and the secondary coil of the transformer outputs the output voltage through a rectifier diode;
the control method further comprises the following steps:
when the output voltage of the flyback conversion circuit is adjusted to a new voltage value, the control unit updates the threshold voltage according to the following relation between the threshold voltage and the output voltage: vth = k (n (Vo + Vd) + V1); wherein Vth, vo and Vd are respectively: the threshold voltage, the output voltage and the voltage drop of the rectifier diode, V1 is a constant between 5V and 10V, n is the turn ratio of a primary coil and a secondary coil of the transformer, k is a sampling coefficient, and the value range is (0,1);
the control unit outputs the updated threshold voltage to the voltage comparison circuit.
8. A flyback converter comprising a transformer and further comprising a flyback converter circuit as claimed in any of claims 1-4.
9. A servo motor driver comprising a transformer, further comprising a flyback converter circuit as claimed in any of claims 1-4.
10. A servo motor comprising the servo motor driver as claimed in claim 9.
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|---|---|---|---|
| CN202210787293.7A CN115765464A (en) | 2022-07-04 | 2022-07-04 | Flyback conversion circuit, control method, converter, servo motor and driver |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210787293.7A CN115765464A (en) | 2022-07-04 | 2022-07-04 | Flyback conversion circuit, control method, converter, servo motor and driver |
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| CN115765464A true CN115765464A (en) | 2023-03-07 |
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| CN202210787293.7A Pending CN115765464A (en) | 2022-07-04 | 2022-07-04 | Flyback conversion circuit, control method, converter, servo motor and driver |
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