Deadtime automatic-optimization system for flyback power supply having primary-side feedback in CCM, control system and method for flyback power supply having primary-side feedback in CCM
An automatic dead zone time optimization system in a primary-side regulation flyback power supply continuous conduction mode (CCM), including a closed loop formed by a control system, including a single output digital to analog converter (DAC) midpoint sampling module, a digital control module, a current detection module, a dead zone time calculation module and a pulse-width modulation (PWM) driving module, and a controlled synchronous rectification primary-side regulation flyback converter. A primary-side current is sampled using a DAC Sampling mechanism to calculate a secondary-side average current, so as to obtain a primary-side average current and a secondary-side average current, in the case of CCM. A secondary-side current is input into the dead zone time calculation module to obtain a reasonable dead zone time; and the PWM driving module is jointly controlled by a primary-side regulation loop and the obtained dead zone time.
1. A deadtime automatic-optimization system of a flyback power supply having a primary-side feedback in a continuous conduction mode (CCM), comprising:
a control system consisting of a single-output digital to analog converter (DAC) midpoint sampling module, a digital control module, a current detection module, a deadtime calculation module, and a pulse-width modulation (PWM) driving module, the control system forming a closed loop with a main topology of a controlled flyback converter having a synchronous-rectification primary-side feedback;
wherein the single-output DAC midpoint sampling module is configured to sample a voltage signal V sense (t mid ) on an auxiliary winding at a midpoint instant of a secondary-side current reset time T r , to output to the digital control module;
the digital control module is configured to calculate an error e(n) between the voltage signal V sense (t mid ) and a system-predetermined fixed value V REF and calculate an input voltage control amount V c (n) for the PWM driving module by using proportion and integration to output to the PWM driving module;
the digital control module is configured to output a digital value V peak_d of a peak voltage on a primary-side current sampling resistor R cs according to a value of the error e(n);
the digital value V peak_d and a voltage V cs at two terminals of the primary-side current sampling resistor R cs are configured to output to the current detection module;
the current detection module is configured to obtain a primary-side average current I mid_p and a secondary-side average current I s (t mid ) in the CCM indirectly by sampling and calculating in a pure digital manner through a DAC, and output the secondary-side average current I x (t mid ) as an output signal to the deadtime calculation module to calculate a reasonable deadtime t d between a turn-off of a secondary-side rectifier SR and a turn-on of a primary-side switching transistor SW;
the PWM driving module is configured to generate duty cycle control signals duty and duty_SR under a common control of the deadtime t d output by the deadtime calculation module and the control amount V c (n) output by the digital control module; and
the duty cycle control signals duty and duty_SR are configured to control switching of the primary-side switching transistor SW and the secondary-side rectifier SR, respectively, to implement an automatic optimization of the deadtime of the flyback power supply having the synchronous-rectification primary-side feedback in the CCM.
2. The deadtime automatic-optimization system of claim 1 , wherein the single-output DAC midpoint sampling module comprises:
a first DAC, a triangular wave generator, a first comparator CMP 1 , a second comparator CMP 2 , a counter, and a feedback amount calculation module;
wherein a voltage signal V sense on the auxiliary winding is connected as an input signal to positive terminals of the first comparator CMP 1 and the second comparator CMP 2 , respectively;
a negative terminal of the first comparator CMP 1 is connected to a voltage signal V ref_slope of a single slope digital wave obtained by superimposition of a digital single sloping wave output by the triangular wave generator and an analog reference voltage output by the first DAC;
a negative terminal of the second comparator CMP 2 is connected to zero voltage;
the first comparator CMP 1 and the second comparator CMP 2 respectively output a feedback comparison signal V ref_comp and a zero-crossing comparison signal V zvs_comp to be connected to the counter;
the counter is configured to count to obtain values of Δt r_half and T r according to changes between high levels and low levels of the feedback comparison signal and the zero-crossing comparison signal V zvs_comp , Δt r half is a total time required for the voltage signal V ref_slope of the single slope digital wave to rise from a position of an initial voltage V initial to a position crossing the voltage signal V sense on the auxiliary winding, and T r is a reset time required for the secondary-side current to drop from a peak value to a lowest point;
the feedback amount calculation module is configured to output a feedback signal V ref initial to be connected to an input terminal of the triangular wave generator and an input terminal of the first DAC, and is configured to adjust a digital value of the initial voltage V initial of the single slope digital wave for a next cycle according to a difference between the values of Δt r half and T r ; and
when the voltage signal V sense on the auxiliary winding is equal to the voltage signal V ref_slope of the single slope digital wave, an instant value of the voltage signal V ref_slope of the single slope digital wave is assigned to the voltage signal V sense (t mid ) at the midpoint instant T mid to output as an output signal of the single-output DAC midpoint sampling module in a current switching cycle.
3. The deadtime automatic-optimization system of claim 1 , wherein the digital control module comprises:
an adder, a subtractor, a multiplier, a register, operational amplifiers K p and K i , and a mode determination module;
wherein an input signal of the digital control module is the voltage signal V sense (t mid ) of the single-output DAC midpoint sampling module, and output signals of the digital control module are the digital value V peak_d of the peak voltage on the primary-side current sampling resistor R cs and the control amount V c (n);
a value of the error e(n) between the voltage signal V sense (t mid ) of the single-output DAC midpoint sampling module and the system-predetermined fixed value V REF is calculated, and the control amount V c (n) is calculated by proportion and integration according to the error e(n) to output; and
the mode determination module is configured to output the digital value V peak_d of the peak value on the primary-side current sampling resistor R cs as an output signal according to the value of the error e(n).
4. The deadtime automatic-optimization system of claim 1 , wherein the current detection module comprises:
a single-input double-output DAC, a third comparator CMP 3 and a fourth comparator CMP 4 , a primary-side current time counting module, and a secondary-side average current calculation module;
wherein the digital value V peak_d of the peak voltage on the primary-side current sampling resistor R cs output by the digital control module is respectively connected to the single-input double-output DAC and the secondary-side average current calculation module;
a positive terminal of the third comparator CMP 3 is connected to the voltage V cs at the two terminals of the primary-side current sampling resistor R cs , and a negative terminal of the third comparator CMP 3 is connected to a voltage analog value V peak on the primary-side current sampling resistor corresponding to a primary-side peak current output by the single-input double-output DAC;
a positive terminal of the fourth comparator CMP 4 is connected to the voltage V cs at the two terminals of the primary-side current sampling resistor R cs , and a negative terminal of the fourth comparator CMP 4 is connected to a voltage analog value V peak_half on the primary-side current sampling resistor corresponding to k times of the voltage analog value V peak on the primary-side current sampling resistor corresponding to the primary-side peak current, and V peak_half =k·V peak , 0<k<1;
the third comparator CMP 3 and the fourth comparator CMP 4 are configured to output comparison signals and V cmp3 and V cmp4 , respectively, and the comparison signals V cmp3 and V cmp4 are connected to the primary-side current time counting module;
the primary-side current time counting module comprises two counters, input signals of the two counters are the comparison signals and V cmp3 and V cmp4 of the comparators CMP 3 and CMP 4 , respectively;
according to changes between high levels and low levels of the comparison signals V cmp3 and V cmp4 , a time t a required by a linear increase of a primary-side current from zero amp or an initial current to a peak current in a discontinuous conduction mode (DCM), and a time t b required by a linear increase of the primary-side current from zero amp or the initial current to the peak current in the CCM are obtained;
the times t a and t b are configured to output to the secondary-side average current calculation module;
according to the input times t a and t b and the digital value V peak_d of the peak voltage on the primary-side current sampling resistor R cs output by the digital control module, the secondary-side average current calculation module is configured to divide V peak_d by a resistance of the primary-side current sampling resistor R cs to obtain a digital value corresponding to a peak current I peak p of a primary-side winding inductor, and the digital value corresponding to the peak current I peak p is substituted into an expression of I s (t mid ):
I
s
(
t
mid
)
=
N
p
N
s
·
(
1
+
k
)
t
b
-
(
1
-
k
)
t
a
2
t
b
·
I
p
e
a
k
-
p
,
wherein N p and N s denote a number of turns of a primary side and a secondary side of a transformer, respectively, and the secondary-side average current I s (t mid ) in the CCM is obtained and output.
5. The deadtime automatic-optimization system of claim 1 , wherein the deadtime calculation module is configured to calculate the reasonable deadtime t d between the turn-off of the secondary-side rectifier SR and the turn-on of the primary-side switching transistor SW according to the secondary-side average current I s (t mid ) output by the current detection module by using a calculation chain comprising an adder, a multiplier, and a divider, and the deadtime t d is calculated according to following formulas:
t
d
=
K
1
+
K
2
+
K
3
+
f
(
I
s
)
,
K
1
=
R
g
Q
g
-
Q
g
d
-
Q
g
s
U
G
S
-
U
P
ln
(
U
g
U
P
)
,
K
2
=
R
g
U
P
Q
gd
,
K
3
=
-
2
R
g
U
P
U
d
g
(
t
)
C
rss
(
t
)
U
D
S
-
I
L
R
d
s
-
U
T
,
f
(
I
s
)
=
m
-
n
m
I
s
-
n
2
2
m
3
I
s
2
,
m
=
U
X
-
U
T
,
n
=
R
d
s
,
in the formulas, U p is a Miller plateau voltage, U g is a gate voltage of the secondary-side rectifier, R g is a gate resistance of the secondary-side rectifier, Q g is a total dissipation charge amount of the gate during the turn-off of the secondary-side rectifier, Q gd is a dissipation charge amount of the gate in a Miller effect phase during the turn-off of the secondary-side rectifier, Q gs is a dissipation charge amount of the gate in a phase that U gs decreases from the Miller plateau voltage U p to 0 during the turn-off of the secondary-side rectifier, I L is a load current, U ds is an input voltage of the secondary-side rectifier, C rss is a reverse transfer capacitance of the secondary-side rectifier, I s is a secondary-side current, U X is an experimental measurement, U τ is a threshold voltage of the secondary-side rectifier, and R ds is a source-drain resistance of the secondary-side rectifier.
6. A control system of a flyback power supply having a primary-side feedback in a continuous conduction mode (CCM), the flyback power supply having the primary-side feedback comprising:
a primary side of a transformer comprising a primary-side winding, a primary-side switching transistor, and a primary-side current sampling resistor connected in series to the primary-side switching transistor;
a secondary side of the transformer comprising a secondary-side winding and a secondary-side rectifier; and
an auxiliary winding;
wherein the control system comprises:
a single-output digital to analog converter (DAC) midpoint sampling module configured to sample a voltage signal V sense (t mid ) on the auxiliary winding at a midpoint instant T r /2 of a secondary-side current reset time T r ;
a digital control module configured to calculate an error e(n) between the voltage signal V sense (t mid ) and a system-predetermined fixed value V REF , calculate an input voltage control amount V c (n) for a PWM driving module by using proportion and integration according to the error e(n), and obtain a digital value V peak_d of a peak voltage on the primary-side current sampling resistor R cs according to the error e(n);
a current detection module configured to obtain a primary-side average current J mid_p and a secondary-side average current I x (t mid ) in the CCM indirectly by sampling and calculating through a digital-to-analog conversion according to the digital value V peak_d and a voltage V cs at two terminals of the primary-side current sampling resistor R cs ;
a deadtime calculation module configured to calculate a deadtime t d between a turn-off of the secondary-side rectifier and a turn-on of the primary-side switching transistor according to the secondary-side average current I x (t mid ); and
the PWM driving module configured to generate a primary-side duty cycle control signal duty and a secondary-side duty cycle control signal duty_SR according to the deadtime t d and the input voltage control amount V c (n), control switching of the primary-side switching transistor according to the primary-side duty cycle control signal duty, and control switching of the secondary-side rectifier according to the secondary-side duty cycle control signal duty_SR.
7. The control system of claim 6 , wherein the single-output DAC midpoint sampling module comprises:
a first DAC, a triangular wave generator, a first comparator CMP 1 , a second comparator CMP 2 , a counter, and a feedback amount calculation module;
wherein a voltage signal V sense on the auxiliary winding is configured to input as input signals to a positive terminal of the first comparator CMP 1 and a positive terminal of the second comparator CMP 2 , respectively;
after superimposition of a digital single sloping wave output by the triangular wave generator and an analog reference voltage output by the first DAC, a voltage signal V ref_slope of a single slope digital wave is obtained and is configured to input to a negative terminal of the first comparator CMP 1 ;
a negative terminal of the second comparator CMP 2 is connected to zero voltage;
the first comparator CMP 1 is configured to output a feedback comparison signal V ref_comp to the counter, and the second comparator CMP 2 is configured to output a zero-crossing comparison signal V zvs_comp to the counter;
the counter is configured to count to obtain values of Δt r half and T r according to changes between high levels and low levels of the feedback comparison signal V ref_comp and the zero-crossing comparison signal V zvs_comp , wherein Δt r half is a total time required for the voltage signal V ref_slope of the single slope digital wave to rise from a position of an initial voltage V initial to a position crossing the voltage signal V sense on the auxiliary winding, and T r is a reset time required for the secondary-side current to drop from a peak value to a lowest point;
according to a difference between the values of Δt r half and T r , the feedback amount calculation module is configured to output a feedback signal V ref initial to an input terminal of the triangular wave generator and an input terminal of the first DAC, and adjust a digital value of the initial voltage V initial for a next cycle;
when the voltage signal V sense on the auxiliary winding is equal to the voltage signal V ref_slope of the single slope digital wave, an instant value of the voltage signal V ref_slope of the single slope digital wave is assigned to the voltage signal V sense (t mid ) to output as an output signal of the single-output DAC midpoint sampling module in a current switching cycle.
8. The control system of claim 6 , wherein the current detection module comprises:
a single-input double-output DAC, a third comparator CMP 3 , a fourth comparator CMP 4 , a primary-side current time counting module, and a secondary-side average current calculation module;
wherein the single-input double-output DAC and the secondary-side average current calculation module are configured to receive the digital value V peak_d output by the digital control module;
a positive terminal of the third comparator CMP 3 and a positive terminal of the fourth comparator CMP 4 are configured to receive the voltage V cs ; a voltage analog value V peak on the primary-side current sampling resistor corresponds to a primary-side peak current output by a first output terminal of the single-input double-output DAC, and the voltage analog value V peak is configured to output to a negative terminal of the third comparator CMP 3 ;
a second output terminal of the single-input double-output DAC is configured to output V peak_half , wherein V peak_half =k·V peak , 0<k<1, and the V peak_half is configured to output to a negative terminal of the fourth comparator CMP 4 ;
the third comparator CMP 3 is configured to output a comparison signal V cmp3 to a first counter of the primary-side current time counting module, and the fourth comparator CMP 4 is configured to output a comparison signal V cmp4 to a second counter of the primary-side current time counting module;
according to changes of high levels and low levels of the comparison signal V cmp3 and the comparison signal V cmp4 , the primary-side current time counting module is configured to obtain a time T q required by a linear increase of a primary-side current from zero amp or an initial current to a peak current in a DCM and a time t b , required by a linear increase of the primary-side current from zero amp or the initial current to the peak current in the CCM, and output the times t a and t b to the secondary-side average current calculation module;
the secondary-side average current calculation module is configured to divide the digital value V peak_d by a resistance of the primary-side current sampling resistor R cs to obtain a digital value I peak p corresponding to a peak current of a primary-side winding inductor, and the digital value I peak p is substituted into an expression of I x (t mid ) along with the times t a and t b ;
I
s
(
t
mid
)
=
N
p
N
s
·
(
1
+
k
)
t
b
-
(
1
-
k
)
t
a
2
t
b
·
I
p
e
a
k
-
p
,
wherein N p and N s denote a number of turns of the primary-side winding and the secondary-side winding of the transformer, respectively, and the secondary-side average current I s (t mid ) in the CCM is obtained and output.
9. The control system of claim 6 , wherein the deadtime calculation module is configured to calculate the deadtime t d according to following formulas:
t
d
=
K
1
+
K
2
+
K
3
+
f
(
I
s
)
,
K
1
=
R
g
Q
g
-
Q
g
d
-
Q
g
s
U
G
S
-
U
P
ln
(
U
g
U
P
)
,
K
2
=
R
g
U
P
Q
gd
,
K
3
=
-
2
R
g
U
P
U
d
g
(
t
)
C
rss
(
t
)
U
D
S
-
I
L
R
d
s
-
U
T
,
f
(
I
s
)
=
m
-
n
m
I
s
-
n
2
2
m
3
I
s
2
,
m
=
U
X
-
U
T
,
n
=
R
d
s
,
in the above formulas, U p is a Miller plateau voltage, U g is a gate voltage of the secondary-side rectifier, R q is a gate resistance of the secondary-side rectifier, Q g is a total dissipation charge amount by the gate during the turn-off of the secondary-side rectifier, Q gd is a dissipation charge amount of the gate in a Miller effect phase during the turn-off of the secondary-side rectifier, Q gs is a dissipation charge amount of the gate in a phase that U gs decreases from the Miller plateau voltage U p to 0 during the turn-off of the secondary-side rectifier, I L is a load current, U ds , is an input voltage of the secondary-side rectifier, C rss is a reverse transfer capacitance of the secondary-side rectifier, I s is a secondary-side current, U X is an experimental measurement, U T : is a threshold voltage of the secondary-side rectifier, and R ds is a source-drain resistance of the secondary-side rectifier.
10. The control system of claim 6 , wherein the PWM driving module comprises:
a sixth comparator, an inverter, a D flip-flop, an OR-gate, and a PWM driving unit;
wherein a positive input terminal of the sixth comparator is configured to receive the deadtime t d , and a negative input terminal of the sixth comparator is connected to zero voltage;
an output terminal of the sixth comparator is connected to an input terminal of the inverter;
an output terminal of the inverter is connected to a D-input terminal of the D flip-flop;
an input signal of the PWM driving unit is the input voltage control amount V c (n);
a first output terminal of the PWM driving unit is configured to output the primary-side duty cycle control signal duty, and a second output terminal of the PWM driving unit is configured to output a signal duty_SRI to a clock control terminal of the D flip-flop;
a Q-output terminal of the D flip-flop is connected to one input terminal of the OR-gate, the signal duty_SRI is configured to input to the other input terminal of the OR-gate, and an output terminal of the OR-gate is configured to output the secondary-side duty cycle control signal duty_SR.
11. The control system of claim 6 , wherein the secondary-side rectifier is a metal oxide semiconductor (MOS) transistor.
12. The control system of claim 6 , wherein the primary-side switching transistor is a MOS transistor, and the primary-side current sampling resistor is connected in series between a source of the primary-side switching transistor and ground.
13. A method of controlling a flyback power supply having a primary-side feedback in a continuous conduction mode (CCM), the flyback power supply having the primary-side feedback comprising:
a primary side of a transformer comprising a primary-side winding, a primary-side switching transistor, and a primary-side current sampling resistor connected in series to the primary-side switching transistor;
a secondary side of the transformer comprising a secondary-side winding and a secondary-side rectifier; and
an auxiliary winding;
wherein the method comprises:
sampling a voltage signal V sense (t mid ) on the auxiliary winding at a midpoint instant T r /2 of a secondary-side current reset time T r ;
calculating an error e(n) between the voltage signal V sense (t mid ) and a system-predetermined fixed value V REF , calculating an input voltage control amount V c (n) for a PWM driving module by using proportion and integration according to the error e(n), and obtaining a digital value V peak_d of a peak voltage on the primary-side current sampling resistor R cs according to the error e(n);
obtaining a primary-side average current I mid p and a secondary-side average current I s (t mid ) in the CCM indirectly by sampling and calculating through a digital-to-analog conversion according to the digital value V peak_d and a voltage V cs at two terminals of the primary-side current sampling resistor R cs ;
calculating a deadtime t d between a turn-off of the secondary-side rectifier and a turn-on of the primary-side switching transistor according to the secondary-side average current I s (t mid );
generating, by the PWM driving module, a primary-side duty cycle control signal duty and a secondary-side duty cycle control signal duty_SR according to the deadtime t d and the input voltage control amount V c (n); and
controlling switching of the primary-side switching transistor according to the primary-side duty cycle control signal duty, and controlling switching of the secondary-side rectifier according to the secondary-side duty cycle control signal duty_SR.
14. The method of claim 13 , wherein the step of sampling the voltage signal V sense (t mid ) on the auxiliary winding at the midpoint instant T r /2 of the secondary-side current reset time T r comprises:
inputting, by a positive terminal of a first comparator CMP 1 , a voltage signal V sense on the auxiliary winding, after superimposition of a digital single sloping wave output by a triangular wave generator and an analog reference voltage output by a first DAC, obtaining a voltage signal V ref_slope of a single slope digital wave to output to a negative terminal of the first comparator CMP 1 , and outputting, by the first comparator CMP 1 , a feedback comparison signal V ref_comp ;
inputting, by a positive terminal of a second comparator CMP 2 , the voltage signal V sense on the auxiliary winding, inputting, by a negative terminal of the second comparator CMP 2 , zero voltage, and outputting, by the second comparator CMP 2 , a zero-crossing comparison signal V zvs_comp ;
counting to obtain values of Δt r half and T r according to changes between high levels and low levels of the feedback comparison signal V ref_comp and the zero-crossing comparison signal V zvs_comp , wherein Δt r half is a total time required for the voltage signal V ref_slope of the single slope digital wave to rise from a position of an initial voltage V initial to a position crossing the voltage signal V sense on the auxiliary winding, and T r is a reset time required for a secondary-side current to drop from a peak value to a lowest point;
outputting a feedback signal V ref initial to an input terminal of the triangular wave generator and an input terminal of the first DAC, and adjusting a digital value of the initial voltage V initial for a next cycle according to a difference between the values of Δt r half and T r ; and
assigning, when the voltage signal V sense on the auxiliary winding is equal to the voltage signal V ref_slope of the single slope digital wave, an instant value of the voltage signal V ref_slope of the single slope digital wave to the voltage signal V sense (t mid ).
15. The method of claim 13 , wherein the step of obtaining the primary-side average current I mid p and the secondary-side average current I s (t mid ) in the CCM indirectly by sampling and calculating through the digital-to-analog conversion according to the digital value V peak_d and the voltage V cs at the two terminals of the primary-side current sampling resistor R cs comprises:
receiving, by a positive terminal of a third comparator CMP 3 and a positive terminal of a fourth comparator CMP 4 , the voltage V cs l
performing a digital-to-analog conversion on the digital value V peak_d to obtain a voltage analog value V peak on the primary-side current sampling resistor corresponding to a primary-side peak current and output the voltage analog value V peak to a negative terminal of the third comparator CMP 3 , and to obtain V peak_half and output the V peak_half to a negative terminal of the fourth comparator CMP 4 , wherein V peak_half =k·V peak , 0<k<1;
obtaining, according to changes between high levels and low levels of a comparison signal V cmp3 output by the third comparator CMP 3 and changes between high levels and low levels of a comparison signal V cmp4 output by the fourth comparator CMP 4 , a time t a required by a linear increase of a primary-side current from zero amp or an initial current to a peak current in a DCM and a time t b required by a linear increase of the primary-side current from zero amp or the initial current to the peak current in the CCM;
dividing the digital value V peak_d by a resistance of the primary-side current sampling resistor R cz to obtain a digital value I peak p of a peak current of a primary-side winding inductor; and
substituting the digital value I peak p , the times t a and t b into an expression of I s (t mid ):
I
s
(
t
mid
)
=
N
p
N
s
·
(
1
+
k
)
t
b
-
(
1
-
k
)
t
a
2
t
b
·
I
p
e
a
k
-
p
,
wherein N p and N s denote a number of turns of the primary-side winding and the secondary-side winding of the transformer, respectively, to obtain the secondary-side average current I x (t mid ) in the CCM.
16. The method of claim 13 , wherein during the step of calculating the deadtime t d between the turn-off of the secondary-side rectifier and the turn-on of the primary-side switching transistor according to the secondary-side average current I s (t mid ), the deadtime T d is calculated according to following formulas:
t
d
=
K
1
+
K
2
+
K
3
+
f
(
I
s
)
,
K
1
=
R
g
Q
g
-
Q
g
d
-
Q
g
s
U
G
S
-
U
P
ln
(
U
g
U
P
)
,
K
2
=
R
g
U
P
Q
gd
,
K
3
=
-
2
R
g
U
P
U
d
g
(
t
)
C
rss
(
t
)
U
D
S
-
I
L
R
d
s
-
U
T
,
f
(
I
s
)
=
m
-
n
m
I
s
-
n
2
2
m
3
I
s
2
,
m
=
U
X
-
U
T
,
n
=
R
d
s
,
in the above formulas, U p is a Miller plateau voltage, U g is a gate voltage of the secondary-side rectifier, R g is a gate resistance of the secondary-side rectifier, Q g is a total dissipation charge amount of the gate during the turn-off of the secondary-side rectifier, Q gd is a dissipation charge amount of the gate in a Miller effect phase during the turn-off of the secondary-side rectifier, Q gs is a dissipation charge amount of the gate in a phase that U gs decreases from the Miller plateau voltage U p to 0 during the turn-off of the secondary-side rectifier, I L is a load current, U ds is an input voltage of the secondary-side rectifier, C rss is a reverse transfer capacitance of the secondary-side rectifier, I s is a secondary-side current, is an experimental measurement, U T is a threshold voltage of the secondary-side rectifier, and R ds is a source-drain resistance of the secondary-side rectifier.