TWI323551B - Synchronous rectification circuit for power converters - Google Patents

Description

IX. INSTRUCTIONS: TECHNICAL FIELD OF THE INVENTION The present invention relates to power converters and, more particularly, to a control circuit for a switched power converter. [Prior Art]

Referring to the first figure, a circuit diagram of a power conversion benefit of a synchronous rectifier having improved power conversion efficiency is known. As shown, the hybrid device, such as the loader 1 (), includes a secondary side winding and a secondary side winding. The switch 15 is connected to the primary side winding core to switch the transformer and the power converter's turn-out c-side side miscellaneous over-current shut-off plus capacitors to the turn-off of the power conversion 11. The electric shutdown 20 and its main body are reduced by 25 for the step rectifier, operation. The voltage % is applied to the primary side winding Np according to the opening M 15 during the magnetization period. Therefore, the charging current Ic will be generated according to the voltage Ve and the inductance of the primary side winding side winding Np. At the same time, magnetization electric power s Vs is generated in the secondary side winding Ns. Once the switch 15 is open, the buffer 10 U will be transmitted to the power converter through the secondary winding (4) and the power switch 2 , to the output. Therefore, the demagnetization period _ demagnetization voltage (output voltage v.) will be applied to the two-person side, and the Ns» discharge current Id will be generated according to the demagnetization voltage and the inductance of the secondary side winding claw. Charging current I. The discharge current Id can be obtained from equations (1) and (2), respectively: V〇 "j~ x Tdischarge — _ (2) The eight Lp and Ls cutters are the inductance coefficients of the secondary side winding Np and the secondary side winding 变压器 of the transformer 1Q. Τ_Ε is the magnetization period; and Td_ge is the demagnetization period. In the continuous electric circuit (c: Qntin_s flap ntmQde; (ΧΜ) the material is transformed (4) completely before the closing of the 15 will (8) in the discontinuous current mode (discGnti_s encode; hall) operation, before the start of the next switching cycle transformer 10 The 1323551 energy is completely demagnetized. Please refer to the waveform diagrams of continuous current mode and discontinuous current mode in Figure 2A and Figure 2. If the power switch 20 is not disconnected after the transformer 10 is completely demagnetized, then a reverse The reverse current will discharge capacitor 30 through power switch 20. This reverse current reduces the efficiency of the power converter. To avoid reverse current, conventional techniques are described, for example, in U.S. Patent No. 6,995 to Yang et al. As described in "PWM controller for synchronous rectifier of flyback power converter", the resistor 40 and the control circuit 45 are used to turn off the synchronous rectification method of the power switch 20 when the discharge current ID is lower than the critical value. And, in the continuous current mode. During operation, the phase-locked circuit turns off the power switch 20 before the start of the next switching cycle. However, the current sensing circuit and the phase-locked circuit will be produced. Power loss increases the complexity of the system. In addition, a wide-variable frequency system such as a 'resonant p0wer converter' will cause a phase locking problem. SUMMARY OF THE INVENTION The present invention provides a synchronous rectification The circuit 'is suitable for a power converter operating at a fixed frequency and/or a variable frequency. The synchronous rectification circuit of the present invention does not require a current sensing circuit or a phase lock circuit. The synchronous rectification circuit of the present invention includes: a power switch coupled To the transformer (magnetic device) for rectification. The signal generating circuit is configured to generate a control signal according to the magnetization voltage of the transformer, the demagnetization voltage of the transformer and the magnetization period of the transformer. The control signal is coupled to control the power switch to be turned on. The enable period is related to the demagnetization period of the transformer. In addition, the control signal is increased according to the increase of the magnetization voltage. The control signal is reduced according to the decrease of the magnetization period of the transformer. In addition, the control signal responds to the increase of the demagnetization voltage. And reduce. Hyun makes the review board of the invention Further understanding and understanding of the structural features and the achieved efficiencies will be provided with better implementation and detailed explanations, as explained below. [Embodiment] π Referring to the third figure, the preferred embodiment of the synchronous rectification circuit of the present invention is included. Example of a switched power conversion pirate circuit diagram. This synchronous rectification circuit is suitable for a power converter operating at a fixed frequency and/or a variable frequency of 1323551, and does not require a current sensing circuit or a phase-locked circuit. The power switch 20 is coupled to a transformer (magnetic device) 10 for rectification. The switching control circuit 100 generates a control signal s outputted from the output terminal OUT in accordance with the magnetization voltage (Vs) of the transformer 10, the demagnetized voltage, and the magnetized time. The control signal is coupled to turn on the power switch 2〇. The enable period of the control signal S» is related to the demagnetized time of the transformer. When the switch 15 is turned on, a voltage Vos (not shown) is generated between the secondary winding Ns and the power switch 2A. The voltage Vds is related to the magnetization voltage % of the transformer 1Q. The magnetization voltage ^ can be known from equation (3):

Vs = Vds - Vo ^ (3) When the s switch 15 is turned off (turn 0ff), the output voltage v〇 is applied to the secondary side winding claws for demagnetization. Therefore, the output voltage v. It is related to the demagnetization voltage of the transformer 1G. The input terminal S of the switching control circuit 100 detects the ink I through the resistors 50 and 55. The diode 60 is stepped into the secondary winding (1) to accelerate the detection of the voltage (4). The other input & The turn-off coupled to the power converter for receiving the output voltage V. The transformer, equal to the demagnetizing flux, is known by the following equation, Φ = Β ^ Ac _______ N (5)

Ve

Vo

^-XTCHARGE =^7"XTDISCI

Ns

CHARGE (6)

V E x T CHARGE N, Nl x v,

T

DISCHARGE (7)

Ve

Vs----

Np

Ns Γ 8 ) f is the flux density, and Ae is the cross-sectional area of the transformer.) 'T is the magnetization period of the transformer (Tc瞧) or the winding of the voltage regulator. Week (Tm_E), N is variable According to equation (7)*(8), the demagnetization period of the transformer 1〇 (five) can be obtained. 7 (9)

Tdischarge =-^-xTcHARGE

Vo can be pre-determined by the magnetization voltage Vs and the demagnetization voltage v. And the magnetization cycle (w) can be repeated. According to equations (3) and (9), the demagnetization period (τ_bottle) can be re-expressed as equation (10) as follows:

Tdischarge = V°)

Vo

X TcHARGE (10) Generates the activation period of the control signal & according to the demagnetization period (T_RGE) of the transformer. Therefore, the enable period of the control signal Sw increases in accordance with an increase in the magnetization voltage Vs. The activation of the control signal S, is reduced according to the decrease of the 1G Wei period (τ_). In addition to this, the enable period of the 'control signal S» is decreased in accordance with the increase in the demagnetization voltage Vg. Please refer to the circuit diagram of the preferred embodiment of the sigma control circuit (10). As shown, the input circuit of the switching control circuit 100 is operated by the operational amplifiers 11〇, 12〇, the diodes 115, 125' voltage-current conversion The circuit 14〇, 15〇, the impedance skirt m, 1〇2 and the hysteresis buffer circuit 180. The operational amplifier and the diode 115 form a first unit gain slow lung. The reference minus Vr is provided to the first light weight The second unity gain buffer is formed by the operational amplifier 120 and the diode 125. The second unity gain buffer is coupled to the input terminal S2 through the impedance devices 101 and 102. The output of the first unity gain buffer and the second unity gain The output of the buffer is combined to generate a signal Vb. The minimum value of the signal % is clamped by the reference signal VR. The signal VB is connected to the voltage-current conversion circuit 15 to generate the second signal I2 and the third signal according to the output voltage V. I3. The minimum value of the second signal Iz is determined by a limit value. The input terminal S generates a voltage signal Va, which is connected to the voltage_current conversion circuit 14 to generate a first signal L· according to the voltage Vds. The buffer circuit 18 is coupled to the input terminal S to generate the switching signal Sgn according to the magnetization period of the transformer 10. The first signal h, the second signal h, the third signal I3, and the switching signal Son are coupled to the signal generating circuit 2 to generate Control signal S. Please refer to the fifth and sixth figures, and the fifth and sixth figures are respectively circuit diagrams of the preferred embodiments of the voltage-current conversion circuits 140 and 150 of the present invention. Please refer to the fifth figure, voltage Va 丄 milk 551 To the operational amplifier 141. The operational amplifier 141 is connected to the transistor 143 and the resistor 142 to generate a current Im according to the voltage VA. The current U is connected to the transistors 145 and 146 to generate a first signal L. See Fig. 6, voltage VB Connected to operational amplifier 151. Operational amplifier 151 is coupled to transistor 153 and resistor 152' to generate current Ii53 from voltage Vb. Current I! 53 is coupled to transistors 155 and 156 to generate current 1156. Current 1, 56 is further connected to The transistors 157, 158, and 159 are used to generate the second signal ι2 and the third signal 丨 3. Therefore, the first current [is generated according to the voltage VA. The second signal ι2 and the third signal h are generated according to the voltage Vb.

Please refer to the seventh circuit diagram of a preferred embodiment of the signal generating circuit 2 of the present invention. Capacitor 220 is used to determine the period of control signal S». The first switch 21 is coupled between the first signal 电容器 and the capacitor 220. The second switch 215 is coupled between the second signal ι2 and the capacitor 220. The first comparator 230 is coupled to the capacitor 220 to generate a first control signal at the output of the first comparator 23A when the voltage of the capacitor 220 is higher than the first reference voltage VR1. by

The output circuit formed by the inverter 231 and the AND gate 232 is coupled to generate a first discharge signal at the output of the AND gate 232 according to the activation of the first control signal and the switching signal 5 (the disablement of the switching gate STM). Coupling to control the first switch 21A. The first switch 21A is turned on according to the activation of the switching signal Son. The first discharge signal is coupled to control the second switch 215. The second switch 215 is turned on according to the activation of the first discharge signal. The first signal L is used to charge the capacitor 220. The second signal h is used to discharge the capacitor 22A. The third signal Ia is further consumed by the first signal 以ι to reduce the value of the first signal h. klx voltage Vds Decide on the first signal h.

Yds Rl42 signal l· can be expressed as equation (11) as ----------------------- (11) Output voltage V. The determined second signal l2 and the third signal h can be expressed by the following equations (10), (1)): h = k2 > Vo < - Rl52 sS--- L· = k3 x Vo RlS2 The voltage on the capacitor 220 can be expressed by equation (10) For: kl x Yds (12) (13)

Vc = II b c x Ton =

Rl42 kl^V〇

xT〇N (14)^23551, where W, k2, and k3 are constants, such as the ratio of the impedance device and/or the gain of the current mirror 'C is the capacitance value of the capacitor 220, and T()N is the activation time of the switching signal Sw (Charging time of the capacitor 220), Rl42 is the resistance value of the resistor 142, "is the electric I5 of the resistor 152 and the value. The discharge time T〇FF of the capacitor 220 is expressed by the following equation:

Toff =

Cx Vc C x Vc h k2x

Vo Rl52 (15)

By appropriately selecting Id, k2, k3, "and Rl52, the discharge time of capacitor 22Q can be rearranged to equation (16) according to equations (14) and (15).

Vds Vo Toff = K x—xTon Vo (16) Therefore, the discharge time of the capacitor 220 T〇F# transformer 1〇 demagnetization period 7_caffe correlation. The demagnetization period Tdischarge can be expressed by equation (17) as: TDISCHARGE = K :

Vs

X TcHARGE where K is a constant. The second comparator 240 is coupled to the capacitor 220 for generating a second at the output of the second comparator 240 when the voltage of the capacitor --- (17) 220 is higher than the first reference voltage VR2 Control signal.

Another output circuit formed by the inverter 241 and the brain 250 is coupled to generate a second discharge signal at the output of the AND gate 25A in accordance with the enable of the second control signal and the disable of the switching signal Son. The control signal S» can be generated according to the first discharge signal or the second discharge signal. In this embodiment, the second discharge signal is used to generate a control signal & The second reference voltage ~ is higher than the first reference voltage VR1. Therefore, before the transformer 1 () is magnetized, the control signal & disable, and the power switch 20 is turned off. π Referring to the waveforms of the synchronous rectification circuits of equations (16) and 8, the period of the control signal & is controlled by the discharge time T() FF of the capacitor 22G (voltage V.). The period of the control signal & is reduced in accordance with the decrease in the charging time Tdn of the capacitor H220. The period of the control signal Sw is based on the output voltage V. The decrease is increased. The charging time T〇N is controlled by switching between the start and the fourth (four). The enable time of the switching signal Son is controlled to be related to the magnetization period (Tcharge). ^^551 Guozhan ΐΐΓΓ ΐΐΓΓ 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏 掏The embodiment is not intended to limit the use of the present invention. The invention is based on the fineness and spirit of the patent application of the present invention. The Wei Na decoration, the touch of the tree cap flip = the internal feature 1323551 [Simple description of the figure] It is a circuit diagram of a conventional power converter with a synchronous rectifier. The second A and second B graphs are waveform diagrams of the continuous current mode and the discontinuous current mode, respectively. The second figure is a circuit diagram of a switched power converter incorporating a preferred embodiment of the synchronous rectification circuit of the present invention. The fourth figure is a circuit diagram of a preferred embodiment of the switching control circuit of the present invention. The fifth and sixth figures are circuit diagrams of a preferred embodiment of the voltage-current conversion circuit of the present invention, respectively. Figure 7 is a circuit diagram of a preferred embodiment of the signal generating circuit of the present invention. Figure 8 is a waveform diagram of a synchronous rectification circuit in accordance with a preferred embodiment of the present invention.

[Main component symbol description] 10 transformer 30 capacitor 15 switch 40 resistor 55 resistor 100 control circuit 110 operational amplifier 101 impedance device 140 voltage-current conversion circuit 141 operational amplifier 143 transistor 146 transistor 2 power switch 45 control circuit 25 Diode 50 Resistor 60 Diode 102 Impedance Device 125 Diode 115 Diode 120 Operational Amplifier 142 Resistor 145 Transistor ^0 Voltage · Current Conversion Circuit 1323551

151 operational amplifier 153 transistor 156 transistor 158 transistor 180 hysteresis buffer circuit 210 first switch 220 capacitor 231 inverter 240 second comparator 250 AND gate 12 second signal Ic charging current 1143 current 1156 current NS secondary Side winding S2 input terminal Sw control signal Vb voltage V 〇 output voltage VR1 first reference voltage Vs magnetization voltage GND ground terminal 152 resistor 155 transistor 157 transistor 159 transistor 200 signal generation circuit 215 second switch 230 first comparator 232 AND gate 241 inverter I! first signal 13 third signal Id discharge current Il53 current Np - secondary winding Si input terminal S〇N switching signal vA voltage Ve voltage VR reference signal VR2 second reference voltage OUT output terminal 13

Claims (1)

April Yin Correction Replacement Page->-;1 X. Patent Application Range: 1. A synchronous rectifier circuit for a power converter, comprising: a power switch 'which is coupled to a transformer for rectification; and a "knife a control temple circuit, which generates a control signal according to a magnetization voltage of the transformer, a demagnetization waste of the transformer, and a magnetization period of the transformer, wherein the control signal is engaged to control the power switch' The enable period of the control signal is related to a demagnetization period of the Weiler. 2. The synchronous rectification circuit of claim 7, wherein the enable period of the miscellaneous signal is increased according to the increase of the magnetization voltage, and the enable period of the control signal is according to the magnetization period of the rabbit voltage Decreasing and decreasing, the enable period of the control signal decreases corresponding to an increase in the demagnetization voltage. 3. The synchronous rectification circuit as described in U.S. U. 1, the switch control circuit includes: - an input circuit, which generates - a __ signal, a second signal, a third signal, and a - switching signal; And a nickname generating circuit coupled to the input circuit to generate the control signal; wherein the first signal is related to a voltage of the transformer, and the second signal and the second signal are related to an output voltage of the power converter, And the switching signal is generated according to the magnetization period of the transformer. 4. As claimed in the patent application S3, the towel generation circuit includes: a capacitor; a first switch 'coupling between the first signal and the capacitor; a second a switch coupled between the second signal and the capacitor; a first comparator coupled to the capacitor and generating a first control signal when the voltage of the capacitor is higher than the first reference voltage; and an output a circuit that is coupled to generate a first discharge signal according to the activation of the first control signal and the disable of the switching signal; wherein the first switch is turned on according to the activation of the switching signal, and the second switch is based on the first The first signal transmits the capacitor, the second signal discharges the capacitor, and the third signal is further coupled to the first signal to reduce the value of the first signal. 5. The synchronous rectification circuit of claim 4, wherein the signal generation circuit further comprises: a second comparator coupled to the capacitor to be higher than the second reference voltage when the voltage of the capacitor is higher than the second reference voltage A second control signal is generated, wherein the control signal is generated according to the first discharge signal or the second discharge signal. 6. The synchronous rectification circuit of claim 1, wherein the power switch is turned off before the transformer is magnetized. 7. The synchronous rectification circuit of claim 3, wherein the minimum value of the second signal is clamped to a limit value. 8. A synchronous rectifying device for a power converter, comprising: a power switch coupled to a magnetic device for rectification, and a switching control circuit 'based on a magnetizing voltage of the magnetic device and the magnetic device The magnetization cycle generates a control signal, and the control signal is lightly controlled to control the power switch; wherein an enable period of the control signal is related to a demagnetization period of the magnetic device. 9. The synchronous rectifying device of claim 8, wherein a demagnetization voltage of the magnetic farm is further used to determine the activation period of the control signal. The synchronous rectifying device of claim 8, wherein the activation period of the control signal is increased according to the increase of the magnetization voltage, and the activation period of the control signal is small according to the Wei apparatus of the magnetic device. The shout is small, and the period of the control cage number is decreased according to the increase of the demagnetization voltage. 11. The synchronous rectifying device of claim 8, wherein the power switch is turned off before the magnetic device is magnetized.