TW201724720A - Isolated converter and isolated converter control method - Google Patents

Abstract

An isolated converter control method adapted to an isolated converter. The isolated converter includes a first switch, a second switch, a third switch, a fourth switch, a first resonant component and a transformer. In the isolated converter control method, the first switch and the fourth switch are conducted in the first period. Then the second switch and the fourth switch are conducted in the second period. In the third period, the second switch and the third switch are conducted. In the fourth period, the second switch and the fourth switch are conducted.

Description

Isolated converter and control method thereof

The present invention relates to an isolated converter and a control method therefor.

In the past isolated converters, at least one transformer was included to boost the voltage, and an output voltage higher or lower than the input voltage was obtained by adjusting the turns ratio of the transformer. In some implementations, multiple windings can be wound around the transformer to output a variety of voltage values. In general, the power conversion mode of the isolated converter is "DC-AC-DC" conversion. In the process of conversion to AC, resonance or capacitance is often used to generate resonance for zero current or zero voltage switching. That is, the on and off of the switch occurs at the zero current point and the zero voltage point to form a lossless switch.

However, the residual energy is stored in the inductor or capacitor used for resonance, so that in the circuit operation interval, the reverse resonant current is transmitted to the input power source side, resulting in an increase in the effective value of the resonant current, and the net power must be increased on the input power supply side. To offset the energy of the reverse virtual power.

The invention provides an isolated converter control method suitable for an isolated converter. The isolated converter includes a first switch and a second switch connected in series across the power supply, a third switch and a fourth switch connected in series across the power supply, a first resonant unit and a transformer. There is a first node between the first switch and the second switch. There is a second node between the third switch and the fourth switch. The first side of the transformer is coupled in series with the first resonant unit between the first node and the second node. The isolated converter control method turns on the first switch and the fourth switch in the first period. The second switch and the fourth switch are turned on in the second period. The second switch and the third switch are turned on in the third period. The second switch and the fourth switch are turned on in the fourth period.

The invention discloses an isolated converter coupled between a power source and a load. The isolated converter includes a transformer, a first conversion module, a first resonance unit, and a second conversion module. The first conversion module is coupled to the transformer. The second conversion module is coupled to the transformer and is located on the second side. The first resonant unit is coupled between the first side of the transformer and the first node. The transformer has a first side and a second side. The first conversion module includes a first switch and a second switch connected in series at both ends of the power supply, and a third switch and a fourth switch connected in series at both ends of the power supply. There is a first node between the first switch and the second switch, and a second node between the third switch and the fourth switch. The first side of the transformer is coupled to the first resonant unit and the second node. The first switch, the second switch, the third switch, and the fourth switch are respectively controlled to be selectively turned on by the plurality of first control signals. The second conversion module includes a fifth switch and a sixth switch connected in series at both ends of the load, and a seventh switch and an eighth switch connected in series at both ends of the power supply. There is a third node between the fifth switch and the sixth switch. There is a fourth node between the seventh switch and the eighth switch. The second side of the transformer is coupled between the third node and the fourth node. The fifth switch, the sixth switch, the seventh switch, and the eighth switch are respectively controlled to be selectively turned on by the plurality of second control signals. In the first period, the first switch and the fourth switch are turned on. In the second period, the second switch and the fourth switch are turned on. During the third period, the second switch and the third switch are turned on. In the fourth period, the second switch and the fourth switch are turned on.

The above description of the present invention and the following description of the embodiments of the present invention are intended to illustrate and explain the spirit and principles of the invention.

The detailed features and advantages of the present invention are set forth in the Detailed Description of the Detailed Description of the <RTIgt; </ RTI> <RTIgt; </ RTI> </ RTI> </ RTI> <RTIgt; The objects and advantages associated with the present invention can be readily understood by those skilled in the art. The following examples are intended to describe the present invention in further detail, but are not intended to limit the scope of the invention.

Please refer to FIG. 1 and FIG. 2 for illustration. FIG. 1 is a schematic circuit diagram of an isolated converter according to an embodiment of the invention. 2 is a flow chart of a method for controlling an isolated converter according to an embodiment of the invention. The present invention provides an isolated converter control method which is suitable for the isolated converter 1 shown in FIG. The isolated converter 1 is coupled between the power source 4 and the load 3. More specifically, the isolated converter 1 has a transformer 11 which is provided on the primary side of the transformer 11, and the load 3 is provided on the secondary side of the transformer 11. Hereinafter, an example in which the power source 4 is a DC power source and the load 3 is a DC load will be described, but in practice, it is not limited thereto.

As shown in FIG. 1 , the first resonating unit 13 and the first conversion module 15 are also disposed on the first side of the transformer 11 . The first resonating unit 13 is coupled between the first node N1 and the end point 111 of the transformer 11 . The first conversion module 15 includes a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4. The first switch S1 is coupled between the first end of the power source 4 and the first node N1. The second switch S2 is coupled between the second end of the power source 4 and the first node N1. The third switch S3 is coupled between the first end of the power source 4 and the second node N2. The fourth switch S4 is coupled between the second end of the power source 4 and the second node N2. The end point 112 of the transformer 11 is coupled to the second node N2. The first switch S1, the second switch S2, the third switch S3 and the fourth switch S4 are, for example, a single transistor or a switching circuit composed of a plurality of electronic components, followed by an N-type metal oxide field effect transistor (Metal -Oxide-Semiconductor Field-Effect Transistor, MOSFET) is illustrated, but not limited to.

In addition, in the embodiment shown in FIG. 1 , the first resonant unit 13 has a first inductor Lr1 and a first capacitor Cr1 , and the first inductor Lr1 is coupled to the first capacitor Cr1 . The secondary side of the transformer 11 is further provided with a rectifier 17, which is coupled to the terminals 113, 114 of the transformer. The rectifier 17 includes, for example, diodes D1 to D4. The input capacitor Ci and the output capacitor Co are included in the isolated transformer 1 or included in the power source 4 and the load 3, respectively. The above is only an example, but it is not limited to this.

The first conversion module 15 is controlled by the first control signals SC1 SC SC4 to selectively turn on different current paths to convert the DC power provided by the power source 4 into AC power in cooperation with the first resonance unit 13 . The first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are respectively selectively controlled by the first control signals SC1, SC2, SC3, and SC4. The first resonating unit 13 is used to determine the quality factor of the isolated converter 1. The transformer 11 is configured to convert the converted AC power to the secondary side, and to adjust the voltage level of the AC power, and selectively output the current along the first current direction according to the duty cycle of the isolated converter 1. Or current in the second direction. The rectifier 17 is configured to rectify the current in the first current direction or the current in the second direction into a direct current and supply it to the load 3. Here, the current flowing through the first resonating unit 13 is defined as the resonant current ir, and the current output from the rectifier 17 is defined as the output current is for subsequent explanation. The resonant current ir has peaks Irp1 and Irp2, and the turns ratio of the transformer 11 is 1:n. Therefore, the peak value of the output current is is one-nth of the peak value of the resonant current ir. Where n is a positive integer.

The step S201 of the isolated converter control method provided by the present invention is to turn on the first switch S1 and the fourth switch S4 in the first period to convert the direct current power to the second side, and output the second side according to the second side. Current in the direction of the first current. In step S203, in the second period, the second switch S2 and the fourth switch S4 are turned on to release the first resonating unit 13. Next, in step S205, in the third period, the second switch S2 and the third switch S3 are turned on to convert the direct current power to the second side, and accordingly, the current in the second current direction is output by the second side. Then, in step S207, in the fourth period, the second switch S2 and the fourth switch S4 are turned on to release the first resonating unit 13.

Please refer to FIG. 3 for further explanation. FIG. 3 is a timing diagram of the isolated converter illustrated in FIGS. 1 and 2 according to the present invention. Corresponding to the above-described isolated converter control method, the first control signals SC1 to SC4 respectively have corresponding voltage levels in the first period T1 to the fourth period T4 in the first duty cycle T. The following is a description of the different time periods in the first work cycle T.

It should be noted that, as described above, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are exemplified as N-type metal oxide field effect transistors, so When the corresponding first control signals SC1 to SC4 are at the high voltage level, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are turned on correspondingly. Actually, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are electrically connected according to the voltage level. Those who have the general knowledge in the field can be freely designed after reading this specification. There are no restrictions.

In the first time period T1, the first control signals SC1, SC4 are at a high voltage level, and the first switch S1 and the fourth switch S4 are turned on. The power source 4, the first switch S1, the first resonating unit 13, the transformer 11 and the fourth switch S4 form a first current path. At this time, the isolated converter 1 converts the direct current power supplied from the power source 4 to the secondary side. The first resonating unit 13 stores energy to cause the isolated converter 1 to resonate. And the transformer 11 outputs a current in the first current direction to the rectifier 17.

In the second time period T2, the first control signals SC2, SC4 are at a high voltage level, and the second switch S2 and the fourth switch S4 are turned on. The second switch S2, the first resonating unit 13, the transformer 11 and the fourth switch S4 form a short-circuit current path. At this time, the first resonating unit 13 releases the electric energy stored in the first resonating unit 13 by the short-circuit current path.

In the third time period T3, the first control signals SC2, SC3 are at a high voltage level, and the second switch S2 and the third switch S3 are turned on. The power source 4, the third switch S3, the transformer 11, the first resonating unit 13 and the second switch S2 form a second current path. At this time, the isolated converter 1 converts the direct current power supplied from the power source 4 to the secondary side. The first resonating unit 13 stores energy to cause the isolated converter 1 to resonate. And the transformer 11 outputs a current in the second current direction to the rectifier 17.

In the fourth time period T4, the first control signals SC2, SC4 are at a high voltage level, and the second switch S2 and the fourth switch S4 are turned on. The second switch S2, the first resonating unit 13, the transformer 11 and the fourth switch S4 form a short-circuit current path. At this time, the first resonating unit 13 releases the electric energy stored in the first resonating unit 13 by the short-circuit current path.

By the short-circuit current path that is turned on by the second time period T2 and the fourth time period T4, the first resonating unit 13 can release the stored residual energy to avoid generating and first when switching the first current path and the second current path. A resonant current ir whose current path is opposite to the direction of the current on the second current path. Under the conventional control method, the DC power to be converted is depleted due to the resonant current ir in the opposite direction, so that the output current or the output voltage of the power source 4 must be further increased, and the isolated converter 1 can output the desired voltage. Or current to load 3. However, this will inevitably increase the peaks 値Irp1 and Irp2 of the resonant current ir. The resonant current rm ^{rms is} related to the peaks Irp1 and Irp2 of the resonant current. The expression of the effective value of the resonant current ir ^rms is as shown in Equation 1: (Equation 1) Therefore, when the peaks 値Irp1 and Irp2 of the resonance current ir are increased, the resonance current effective value ir ^{rms is} also correspondingly increased.

Please refer to FIG. 4 to illustrate the difference in performance of the isolated converter control method provided by the present invention compared to the conventional control method in an embodiment. FIG. 4 is an isolated type according to an embodiment of the invention. Schematic diagram of the performance of the converter control method. In FIG. 4, the effective value ir ^rms of the resonant current ir generated by the isolated converter 1 under different load conditions is shown in a solid line, and the isolated converter 1 is shown by a broken line. The effective value of the resonant current ir, ir, con ^rms , produced under different loads under conventional control methods. Among them, the horizontal axis is the percentage of the load to the rated load, the vertical axis is the current 値, and the vertical axis is the ampere. As shown in Fig. 4, when the isolated converter 1 is at a medium-high load, the resonant current effective 値 ir ^rms caused by the control method of the present invention is approximately the effective resonant current caused by the conventional control method 値 ir, nine percent of the con ^rms Ten to eighty-eight.

Continuing from the above, the present invention further provides an isolated converter. 5A and 5B are schematic diagrams, FIG. 5A is a circuit diagram of an isolated converter according to another embodiment of the present invention, and FIG. 5B is an isolated diagram according to another embodiment of the present invention. Schematic diagram of the converter. As shown in FIGS. 5A and 5B, the structure of the isolated converter 2 on the left side of the transformer 21 is similar to that of the primary side of the isolated converter 1, and the related structure will not be repeated here. In contrast to the structure of the secondary side of the isolated converter 1, the isolated converter 2 is further provided with a second conversion module 29 on the right side of the transformer 21. The second conversion module 29 includes a fifth switch S5', a sixth switch S6', a seventh switch S7', and an eighth switch S8'. The fifth switch S5' is coupled between the first end of the load 3 and the third node N3. The sixth switch S6' is coupled between the second end of the load 3 and the third node N3. The seventh switch S7' is coupled between the first end of the load 3 and the fourth node N4. The eighth switch S8' is coupled to the fourth node N4 and the second end of the load 3. The end points 213 and 214 of the transformer 21 are coupled to the third node N3 and the fourth node N4, respectively.

The second conversion module 29 selectively turns on different current paths in accordance with the second control signals SC5' to SC8'. The fifth switch S5', the sixth switch S6', the seventh switch S7', and the eighth switch S8' correspond to the second control signals SC5', SC6', SC7', SC8', respectively. As shown in FIG. 5A, in an embodiment, the second conversion module 29 is configured to convert AC power from the transformer 21 into DC power to the load 3. Among them, the load 3 is located on the right side of the transformer 21 as shown in FIG. 5A. The load 3 is, for example, a battery that is charged. The power source 4 is used to provide the charging power required by the load 3, such as a discharged battery or other device or component that can provide DC power. In this embodiment, the output voltage of the power source 4 is greater than the terminal voltage of the load 3, and the power source 4 thus charges the load 3.

In one implementation, the user can selectively turn on the first switch S1', the second switch S2', the third switch S3', or the fourth switch S4', respectively, to convert the DC power provided by the power source 4 into AC power. The AC power is converted by the transformer 21 from the first side to the second side, that is, the AC power is converted to the right side of the transformer 21 by the left side of the transformer 21 as shown in FIG. 5A. In another method, the user may also selectively turn on the fifth switch S5', the sixth switch S6', the seventh switch S7' or the eighth switch S8', respectively, to supply the power provided by the power source 4 by the transformer 21. The first side is switched to the second side of the transformer 21.

As shown in Fig. 5B, in another embodiment, the second conversion module 29 is for converting DC power from the power source 4' into AC power to the transformer 21 to supply power to the load 3'. As shown in Fig. 5B, the power source 4' is located on the right side of the transformer 21, and the load 3' is located on the left side of the transformer 21. Similarly to Fig. 5A, the load 3' in Fig. 5B is, for example, a charged battery. The power source 4' is used to provide the charging power required for the load 3', such as a discharged battery or other device or component that can provide electrical energy. Unlike Fig. 5A, in the embodiment shown in Fig. 5B, the electric energy is transmitted from the right side of the transformer 21 to the left side of the transformer 21, and the output voltage of the power source 4' is not necessarily larger than the terminal voltage of the load 3'. The operation mode of the embodiment shown in FIG. 5B will be described with reference to FIG. 6. FIG. 6 is a timing diagram of the isolated converter shown in FIG. 5B according to the present invention. As shown in the figure, the timings of the second control signals SC5' to SC8' are similar to those of the first control signals SC1 to SC4 in Fig. 3, and the details are not repeated here. The timing of the first control signals SC1' to SC4' will be explained below.

In the first period T1', the first control signals SC2', SC4' are at a high voltage level, and the second switch S4' and the fourth switch S4' are turned on. The second switch S2', the first resonating unit 23, the transformer 21, and the fourth switch S4' form a short-circuit current path. At this time, the AC power converted from the secondary side is stored in the first resonance unit 23 by the short-circuit current path.

In the second time period T2', the first control signals SC1' to SC4' are at a low voltage level. The first switch S1', the second switch S2', the third switch S3', and the fourth switch S4' are not turned on. At this time, the parasitic diode of the first resonating unit 23, the second switch S2', the transformer 21, and the parasitic diode of the third switch S3' form a first charging path with the load 3'. At this time, the first resonating unit 23 is discharged by the first charging path to charge the load 3'.

In the third period T3', the first control signals SC2', SC4' are at a high voltage level, and the second switch S2' and the fourth switch S4' are turned on. The second switch S2', the first resonating unit 23, the transformer 21, and the fourth switch S4' form a short-circuit current path. At this time, the AC power converted from the secondary side is stored in the first resonance unit 23 by the short-circuit current path.

In the fourth period T4', the first control signals SC1' to SC4' are at a low voltage level. The first switch S1', the second switch S2', the third switch S3', and the fourth switch S4' are not turned on. At this time, the first resonating unit 23, the parasitic diode of the first switch S1', the parasitic diode of the power source 4, and the fourth switch S4' form a second charging path with the transformer 21. At this time, the first resonating unit 23 is discharged by this second charging path to charge the load 3'.

From another point of view, by the structure of the isolated converter provided by the present invention, the first control signals SC1', SC2', SC3', SC4' and the second control signals SC5', SC6', SC7' are adjusted. The relative timing of the SC8' can be switched to allow the power supply 4 to supply power to the load 3 or the power supply 4' to charge the load 3'. In addition, in an embodiment, as long as the resonance parameter of the first resonating unit 23 is properly adjusted, even if the output voltage of the power source 4' is smaller than the output voltage of the load 3', the power source 4' can be placed on the load by the isolated converter 2. 3' power or charge.

Corresponding to the above, the isolated converter provided by the present invention has another embodiment, which will be described with reference to FIG. 7. FIG. 7 is a circuit diagram of an isolated converter according to a further embodiment of the present invention. schematic diagram. The isolated converter 2 further includes a second resonating unit 26 as compared to FIG. As shown in the figure, one end of the second resonating unit 26 is coupled to the end point 211 of the transformer 21, and the other end of the second resonating unit 26 is coupled to both ends of the power source 4 via the diodes D5 and D6. When the isolated converter 2 supplies power to the load 3 in accordance with the power source 4, the isolated converter 2 forms a current path on the primary side with the first resonance unit 23. When the isolated converter 2 charges the power source 4 according to the load 3, the isolated converter 2 forms a current path on the primary side with the equivalent resonance unit composed of the first resonance unit 23 and the second resonance unit 26. Thereby, the user can design the quality factor of the isolated converter 2 when the power supply 4 is powered and the power supply 4 is charged by adjusting the component parameters 第一 in the first resonating unit 23 and the second resonating unit 26, respectively. The performance of the isolated converter 2 is either powered by the power supply 4 or the isolated converter 2 is charged to the power supply 4.

In summary, the present invention provides a short circuit path to the first resonating unit in the circuit in the current direction switching interval, allowing the first resonating unit to release energy to eliminate the reverse resonant energy and avoid the reverse resonant current. Thereby, the switching loss is reduced and the circuit energy utilization is improved. At the same time, according to such a control manner, the present invention further provides an isolated converter, which changes the resonant energy or stores the resonant energy mode by performing corresponding timing control on the conversion modules on both sides of the transformer. Achieve the function of two-way energy transmission.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

1, 2‧‧‧ Isolated conversion circuit
11, 21‧‧‧ Transformers
End points 111, 112, 113, 114, 211, 212, 213, 214‧‧
13, 23‧‧‧First Resonant Unit
15, 25‧‧‧ first conversion module
17‧‧‧Rectifier
26‧‧‧Second Resonance Unit
29‧‧‧Second conversion module
3‧‧‧load
4‧‧‧Power supply
Cr1, Cr1'‧‧‧ first capacitor
Cr2'‧‧‧second capacitor
Ci‧‧‧ input capacitor
Co‧‧‧ output capacitor
D1, D2, D3, D4, D5, D6‧‧‧ diodes
Ir‧‧‧Resonance current
Ir,con ^rms ,ir ^rms ‧‧‧Resonant current effective 値
Irp1, Irp2‧‧‧Resonance current peak
Is‧‧‧output current
Lr1'‧‧‧First Inductor
Lr2'‧‧‧second inductance
N1‧‧‧ first node
N2‧‧‧ second node
N3‧‧‧ third node
N4‧‧‧ fourth node
T1, T1'‧‧‧ first time
T2, T2'‧‧‧ second period
T3, T3'‧‧‧ third period
T4, T4'‧‧‧ fourth period
T‧‧‧ work cycle
S1, S1'‧‧‧ first switch
S2, S2'‧‧‧ second switch
S3, S3'‧‧‧ third switch
S4, S4'‧‧‧ fourth switch
S5'‧‧‧ fifth switch
S6'‧‧‧ sixth switch
S7'‧‧‧ seventh switch
S8'‧‧‧ eighth switch
SC1, SC2, SC3, SC4, SC1', SC2', SC3', SC4'‧‧‧ first control signal
SC5', SC6', SC7', SC8'‧‧‧ second control signal
S201~S207‧‧‧Step procedure

1 is a circuit diagram of an isolated converter according to an embodiment of the invention. 2 is a flow chart of a method for controlling an isolated converter according to an embodiment of the invention. FIG. 3 is a timing diagram of the isolated converter illustrated in FIGS. 1 and 2 according to the present invention. FIG. 4 is a schematic diagram showing the performance of an isolated converter control method according to an embodiment of the invention. FIG. 5A is a schematic circuit diagram of an isolated converter according to another embodiment of the invention. FIG. 5B is a schematic circuit diagram of an isolated converter according to still another embodiment of the present invention. FIG. 6 is a timing diagram of the isolated converter illustrated in FIG. 5B according to the present invention. FIG. 7 is a circuit diagram of an isolated converter according to a further embodiment of the present invention.

Claims (13)

An isolated converter control method is applicable to an isolated converter, wherein the isolated converter comprises a first switch and a second switch connected in series at a power supply end, and a third switch and a series connected to the two ends of the power supply a fourth switch, a first resonating unit and a transformer, the first switch and the second switch have a first node, the third switch and the fourth switch have a second node, the first of the transformer The first and second resonant units are connected in series between the first node and the second node, and the isolated converter control method includes: turning on the first switch and the fourth switch in a first period; Turning on the second switch and the fourth switch in a second time period; turning on the second switch and the third switch in a third time period; and turning on the second switch and the first time in a fourth time period Four switches. The isolated converter control method of claim 1, wherein the isolated converter has a duty cycle, the work cycle including the first time period, the second time period, the third time period, and the fourth time period, The first time period plus the second time period is a half period of the working period, and the third time period plus the fourth time period is another half period of the working period. The isolated converter control method of claim 1, wherein the second side of the transformer is further provided with a rectifier coupled to both ends of the second side of the transformer. The isolated converter control method of claim 1, wherein the first resonant unit comprises a first inductor and a first capacitor. The isolated converter control method of claim 1, wherein the isolated converter comprises a fifth switch and a sixth switch connected in series at a load end, and a seventh switch connected to the two ends of the power supply and a first switch An eighth switch, the fifth switch and the sixth switch have a third node, the seventh switch and the eighth switch have a fourth node, and the second side of the transformer is coupled to the third node and the first Four nodes. The isolated converter control method of claim 5, wherein the isolated converter further comprises a second resonating unit coupled between the first side of the transformer and the power source. The isolated converter control method of claim 6, wherein the second resonant unit comprises a second inductor and a second capacitor. An isolated converter is coupled between a power source and a load, and includes: a transformer having a first side and a second side; a first conversion module coupled to the transformer and located on the first side a first switch and a second switch connected in series at the two ends of the power supply, a third switch and a fourth switch connected in series at the two ends of the power supply, the first switch and the second switch having a first node, A first node is coupled between the third switch and the fourth switch, the first side is coupled to the first node and the second node, the first switch, the second switch, the third switch, and the fourth The switches are respectively controlled to be selectively turned on by the plurality of first control signals; a first resonant unit coupled between the transformer and the first node; and a second conversion module coupled to the transformer Located on the second side, a fifth switch and a sixth switch connected in series across the load, a seventh switch and an eighth switch connected in series across the power supply, and the fifth switch and the sixth switch have a third node, the seventh switch and the eighth The switch has a fourth node, the second side is coupled to the third node and the fourth node, and the fifth switch, the sixth switch, the seventh switch, and the eighth switch are respectively controlled by multiple The second control signal is selectively turned on, wherein the first switch and the fourth switch are turned on during a first time period, and the second switch and the fourth switch are turned on during a second time period. During the third period, the second switch and the third switch are turned on, and in a fourth period, the second switch and the fourth switch are turned on. The isolated converter of claim 8, wherein the sixth switch and the eighth switch are turned on during the first time period and the third time period. The isolated converter of claim 8, wherein the isolated converter has a duty cycle, the duty cycle including the first time period, the second time period, the third time period, and the fourth time period, wherein the The first time period plus the second time period is a half period of the working period, and the third time period plus the fourth time period is a half period of the working period. The isolated converter of claim 8, wherein the first resonant unit comprises a first inductor and a first capacitor. The isolated converter of claim 8, wherein the isolated converter further comprises a second resonant unit coupled between the first side of the transformer and the power source. The isolated converter of claim 12, wherein the second resonant unit comprises a second inductor and a second capacitor.