Disclosure of Invention
In order to solve the above problem, the present invention provides a Buck circuit implemented by soft switching, which includes:
a main circuit comprising, in the main circuit:
a direct current power supply;
the main power switch tube is connected in series with the positive end of the direct-current power supply;
a main inductor connected in series with the main power switch tube;
the capacitor is connected with the main inductor in series, and a load resistor is connected in parallel at two ends of the capacitor; and a synchronous rectification switching tube connected in parallel to the series branch of the main inductor and the capacitor, an
An auxiliary circuit further connected in parallel across a main inductance L of the main circuit, the auxiliary circuit comprising:
a first auxiliary power switch tube, an auxiliary inductor and a second auxiliary power switch tube which are connected in series in turn,
before the main switching tube is conducted, the first auxiliary power switching tube and the second auxiliary power switching tube are controlled to be conducted, so that the sum of the current flowing through the auxiliary electric tube and the current flowing through the main inductor reaches a reverse maximum value, and the current in the body diodes which are connected in parallel reversely on the synchronous rectification switching tube is offset.
According to an embodiment of the present invention, it is preferable that the current change rate of the auxiliary inductor on the auxiliary circuit before the main switching tube is turned on satisfies the following equation:
wherein, U0Lr is the inductance of the auxiliary inductor, itotalIs the total current flowing on the main circuit, iLrTo assist the current flowing in the inductor, iLIs the current flowing through the main inductor.
According to one embodiment of the present invention, when the total current reaches the reverse maximum, the synchronous rectifier is turned off, and the body diode thereon is blocked by the reverse voltage formed by the reverse current, so that the change of the current on the main inductor satisfies the following relation:
wherein, UDCIs the voltage on the dc power supply.
According to an embodiment of the present invention, it is preferable that the time length d after the synchronous rectification power switch tube is turned off and before the main switch is turned onrT is set to satisfy the following relationship:
according to one embodiment of the present invention, it is preferable that before controlling the synchronous rectifier to conduct, a dead time is set to prevent the main switch from being inserted through the synchronous rectifier, and a duration of the dead time is in a range of 95-105 ns.
The invention has the beneficial technical effects that: according to the novel soft switch Buck circuit provided by the invention, the auxiliary inductor and the auxiliary switch are added, so that zero-voltage switching-on and zero-current switching-off are realized, and the novel soft switch Buck circuit has important significance for reducing switching loss and improving efficiency. Compared with most of the existing soft switch Buck circuits, the circuit has a wide voltage working range and strong power supply adaptability. The effect same as a theoretical result is obtained through simulation experiments, and ideal zero-voltage switching-on and zero-current switching-off effects can be achieved. Although the circuit has multiple points of the auxiliary switching tube, the efficiency is high, the operation is stable, the circuit can be widely applied to various DC/DC circuits, the soft switching effect is obvious when the circuit is applied to medium and high power occasions, and the power consumption can be greatly reduced.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
The invention provides a novel soft switching Buck circuit, namely a Buck circuit realized by soft switching, and a topological diagram of the Buck circuit is shown in figure 1. In fig. 1, a Buck circuit is shown comprising: a main circuit comprising, in the main circuit: a direct current power supply; the main power switch tube is connected in series with the positive end of the direct-current power supply; a main inductor connected in series with the main power switch tube; the capacitor is connected with the main inductor in series, and a load resistor is connected in parallel at two ends of the capacitor; and the synchronous rectification switching tube is connected in parallel with a series branch of the main inductor and the capacitor, and the auxiliary circuit is further connected in parallel with the main inductor L of the main circuit.
As shown in fig. 1, the auxiliary circuit includes: the synchronous rectification circuit comprises a first auxiliary power switch tube, an auxiliary inductor and a second auxiliary power switch tube which are sequentially connected in series, wherein before the main switch tube is conducted, the first auxiliary power switch tube and the second auxiliary power switch tube are controlled to be conducted, so that the sum of the current flowing through the auxiliary power switch tube and the current flowing through the main inductor reaches a reverse maximum value, and the current in body diodes which are reversely connected in parallel on the synchronous rectification switch tube is offset.
The invention is characterized in that the zero-voltage switching-on and zero-current switching-off of the technology is realized without depending on a resonance principle. The circuit can work at constant frequency and wide voltage working range, and meanwhile, on the basis of no additional passive device, the circuit has low switching loss and high efficiency, is suitable for medium and large power occasions, and has great advantages.
Compared with the traditional soft switch Buck circuit, the novel topological structure provided by the invention is different from the traditional structure. In addition, in order to further improve the efficiency, the freewheeling diodes in all the non-isolated topologies are replaced by MOSFET power switch tubes, the bootstrap driver is assisted to realize synchronous rectification, and the Buck circuit has the advantages of high efficiency and low cost, so that the advantages of the circuit are more obvious.
In one embodiment of the present invention, in order to avoid the main switching tube and the synchronous rectification switch from being directly connected, a dead time with a certain length is added in the switching process of the two switching tubes, and the duration of the dead time can be set between the range of 95-105ns, for example. Therefore, when the main switch is switched on, the parasitic anti-parallel diode of the synchronous rectification switch tube continues current like a common DC/DC converter.
Because the continuous conduction mode of the inductive current in actual work is mainly considered, the diode current of the synchronous rectifier tube body is not zero at the moment when the main switching tube is switched on, and the common working loss shows that the switching action causes larger reverse recovery loss of the diode and hard switching loss of the main switching tube.
To eliminate the reverse recovery loss of the diode, a soft switching circuit is added as shown in fig. 1. The current of the Q2 is reduced to be below zero through a certain control mode, and then the Q1 is switched on. At this time, the body diode of Q1 freewheels, so that the voltage across the body diode drops to approximately zero volts, and zero-voltage turn-on is realized.
The soft switch Buck circuit of the invention is divided into different stages, FIGS. 2a to 2f are equivalent circuits of each stage, and FIG. 3 is a theoretical waveform of the soft switch Buck circuit of the invention when in operation.
The working process of each stage of the soft switching circuit is analyzed according to the Buck circuit working principle. Although parasitic capacitance, namely output capacitance Coss, exists at the drain-source two poles of the MOSFET, the stored energy is small, so that the influence of the Coss on the working process can be ignored.
Stage t 0-t 1: at the time t0, the main switch Q1 is controlled to be turned off, the current of the inductor L rises to the maximum value, the body diode of the synchronous rectifier Q2 continues current until the time t1, Q2 is turned on, the voltage at two ends of Q2 drops to be close to 0V, and the equivalent circuit at the stage is shown in figure 2a, and the stages from t0 to t1 are dead time added for preventing the through short circuit.
Stage t 1-t 2: at time t1, the synchronous rectifier Q2 is turned on linearly and enters the ohmic region, and the current of the main inductor L gradually decreases due to the reverse voltage applied thereto, and the equivalent circuit at this stage is as shown in fig. 2 b. If the corresponding on-resistance at the driving voltage is rds (on), the voltage drop across Q2 and the slope of the current of the main inductor L can be expressed as the following equations:
uDS2=-iL*RDS(on) (1)
stage t 2-t 3: at time t2, the auxiliary switches Qr1 and Qr2 are turned on, the auxiliary inductor Lr is subjected to a forward voltage and the current rises, and the main inductor L current continues to change regularly in the formula (2). Assume that the current i in Lr at a time t23 between t2 and t3LrCurrent i rising to and LLEquality, after which the auxiliary switch is kept on until time t3, iLrGreater than iLThen the total current itotalReversal to a negative maximum iinv,max. The equivalent circuit is shown in fig. 2c, and the change rate of the Lr current at this stage satisfies the following equation:
stage t 3-t 4: at time t3, itotal reverses, turning off the synchronous rectifier Q2, the parasitic diode of which is blocked by the reverse voltage formed by the reverse current, itotal forms a loop with the input power source through the Q1 body diode freewheeling path, and the equivalent circuit is as shown in fig. 2 (d). Neglecting the short switching time for the Q1 body diode to turn on, since time t3, the voltage drops to approximately 0V across Q1, inductor L experiences the forward input voltage, current iL starts to increase, iLr starts to decrease because the input voltage is opposite to its reference direction, and the following equation is satisfied:
stage t 4-t 5: at time t4, the main switch Q1 is turned on, and in the previous stage, the anti-parallel diode of Q1 is turned on, and the voltage across the anti-parallel diode is already approximately reduced to 0V, so that Q1 is turned on at zero voltage, and the circuit in this stage is equivalent to that in fig. 2 e. The current in the main inductor L and the auxiliary inductor Lr continues to change in slope in the above stage. In order for Q1 to satisfy the zero voltage turn-on condition, then the total current must satisfy before Q1 turns on:
itotal<0 (7)
from the equation (7), the time length drT of the t 3-t 4 phase satisfies the following constraint:
stage t 5-t 0: at the time t5, the Lr current is 0, in order to prevent the Lr current from reversing, the auxiliary switches Qr1 and Qr2 are turned off, only the current of the main inductor is increased under the action of forward voltage, the circuit enters the closing stage of the main switch of the common Buck circuit until the time t0, the equivalent circuit is as shown in FIG. 2f, and the L current change rate keeps the formula (2-6). If the total duration of the interval from t3 to t0 is dcT and the average current of the inductor L is IL, it can be known that the peak current of the main inductor is:
in fig. 3, the time length of the dead time inserted for preventing the main switch and the synchronous rectifier from being connected in series from the stage t0 to t1 is about 100ns, which is extremely short compared with the 10us switching period, and the stage time is amplified for clearly showing the waveform.
By using the MATLAB simulation platform, a Buck circuit without a soft switch and a Buck circuit simulation model with a soft switch can be built. The parameter settings are shown in table 1:
TABLE 1 Main operating parameters of the circuit
Circuit parameter
|
Numerical value
|
Input voltage (V)
|
50
|
Output voltage (V)
|
30
|
L(μH)
|
42
|
Co(μF)
|
80
|
Lr(μH)
|
2
|
R(Ω)
|
10
|
Ddis
|
0.3
|
f(KHz)
|
100 |
Comparing the input current Iin simulation waveform under the soft switching condition with the theoretical analysis result, the simulation result is consistent with the theoretical analysis result, the valley current is close to zero, and the zero current switching-on of the switching tube Q1 is approximately realized.
According to the novel soft switch Buck circuit provided by the invention, the auxiliary inductor and the auxiliary switch are added, so that zero-voltage switching-on and zero-current switching-off are realized, and the novel soft switch Buck circuit has important significance for reducing switching loss and improving efficiency.
Compared with most of the existing soft switch Buck circuits, the circuit has a wide voltage working range and strong power supply adaptability. The effect same as a theoretical result is obtained through simulation experiments, and ideal zero-voltage switching-on and zero-current switching-off effects can be achieved. Although the circuit is provided with multiple points of the auxiliary switching tube, the efficiency is high, the operation is stable, the circuit can be widely applied to various DC/DC circuits, the effect of applying the sub-soft switching in medium and high power occasions is particularly obvious, and the power consumption can be greatly reduced.
It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures, process steps, or materials disclosed herein but are extended to equivalents thereof as would be understood by those ordinarily skilled in the relevant arts. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase "one embodiment" or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.
Although the embodiments of the present invention have been described above, the above description is only for the convenience of understanding the present invention, and is not intended to limit the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.