TW201113531A - Apparatus and method for output current sense at primary side in a flyback converter - Google Patents

Abstract

A method for output current sense at primary side in a flyback converter detects the current on a primary winding and the resetting duration of the inductor current on a secondary winding, and then determines a sensing signal related to the output current of the flyback converter according thereto. The detection is not made at secondary side in the flyback converter, and thus requires lower cost.

Description

201113531 VI. Description of the invention: [Technical field to which the invention pertains] The present invention relates to the placement and method of the transmission (four) flow of the secret-return type, and in particular to an output current applied to the primary side of the flyback converter Sensing device and method. [Prior Art] In the conventional off-line switching voltage converter, in order to adjust the output and output current, an output voltage and current sensor are required on the secondary side thereof to obtain a feedback signal related to the output voltage and current. For example, a shunt regulator, a current sense resistor, and an optocoupler. 1 is a conventional fly-back type switching voltage converter in which a transformer T1 has a primary side coil Lp connected between a voltage input terminal Vin and a power switch S1, and a secondary side coil Ls connected to a voltage output via a diode Do. The terminal Vo and the auxiliary coil Laux are connected to a pole body Daux' Pulse Width Modulation (PWM) controller 10 provides a control signal Vgs switching switch S1 to convert the input voltage vin into an output voltage Vo supply load RL, and The combination of the current sensing resistor Rcs, the optical combiner 12 and the voltage regulator 14 senses the output voltage v〇 and the output current 1〇 to provide a feedback signal Vfb to the PWM controller 1 for regulating the output voltage ν〇 and the output. The current is 1 〇. This output current sensing requires the addition of an additional current sense resistor Res and circuitry on the secondary side, and requires the optocoupler 12 to deliver an output current sense signal between the primary side and the primary side, thus requiring higher cost. SUMMARY OF THE INVENTION 201113531 Low-cost output current sense One of the objects of the present invention is to provide a measuring device. The object of the present invention is to provide a wheel current sensing device and method for the primary side of the flyback conversion. ,

According to the invention, the _back converter - the output power of the secondary side is a hunger sensing device, and the flyback converter includes a secondary side shaft, a secondary side coil, and a power switch connected to the secondary side coil. Controlling the signal switching to cause the secondary side line to generate an induced current, the output current sensing device comprising: sampling and maintaining circuit sampling to generate a second signal with a peak of the first signal related to the current line line current; detecting the off signal The resetting duration of the induced current generates a second signal 'the third scale of the weekly scale in the period of the control stealing number, and the working time is the resetting touch time of the current; the touch connection connects the sampling and sustaining circuit and the detect According to the second job and the fourth signal, the fourth signal has the same cycle and working time as the third signal and the peak value is determined by the second signal; and the low passer connection The buffer, filtering the fourth signal, produces a sensed signal associated with an output current of the flyback converter. According to the present invention, an output current sensing method applied to a primary side of a flyback converter includes a primary side coil, a secondary side coil, and a power switch connected to the primary side coil in response to a control signal switching And causing the secondary side coil to generate an induced current, the output current sensing method includes: sensing a current of the primary side coil to generate a first signal; sampling a peak of the first signal to generate a second signal, detecting a weight of the induced current The duration of the second signal is generated, the period of the third signal is equal to the period of the control signal, and the working time 201113531 is equal to the reset duration of the induced current; and the fourth signal is generated according to the second signal and the third signal, The period and operating time of the fourth signal are the same as the third signal and the peak value is determined by the second signal; and chopping the fourth signal produces a sensing signal associated with the wheel current of the flyback converter. According to the present invention, an output current sensing device is applied to a jumpback converter-subsequent side, the flyback converter includes a primary side coil and a connection to the primary side line _ work __ should be touched, the output current The sensing device includes: a first sampling and a rotating circuit sampling the axis of the first - § § associated with the current of the extracted coil: the second sampling and the rotating circuit sampling the valley value of the first signal, and the force Π method is connected to the The first and second sampling and switching circuits combine to generate the second signal according to the peak and the bottom value; the buffer is connected to the adding method, and the third signal is generated according to the second signal and the control signal, the period of the third signal and the control #号同' is the same as the non-weize time of the control signal, and the peak value is determined by the second money; and a low-pass filter is connected to the buffer, and the third signal is generated and the return-to-return converter Output current related sensing signals. According to the present invention, the output of the flyback converter - the secondary side of the output power / melon sense / square] 4 of the flyback converter includes - the secondary side coil and the power of the one side of the side of the open switch _ should be controlled Signal switching, the output current sensing method includes: sensing a current of the primary side coil to generate a first signal; sampling a peak and a bottom value of the first signal; adding the peak value to the valley value to generate a second signal; The second signal and the control signal generate a third signal, the third signal is controlled by the same 彳5, the guard time is the same as the non-operation time of the control signal, and the peak value is determined by the second signal; The third signal r 201113531 produces a sensed signal associated with the output current of the flyback converter. According to the present invention, an output current sensing device applied to a primary side of a flyback converter includes a primary side coil, a secondary side coil, and a power switch connected to the primary side coil in response to a control signal switching Having the secondary side coil generate an induced current, the output current sensing device comprising: a first sampling and maintaining circuit sampling a peak of a first signal related to a current of the primary side coil; and a second sampling and maintaining circuit The valley value of the signal; the adder connects the 3H-and the second sampling and sustaining circuit, and combines the peak and the valley to generate a first parameter, and the detector detects the reset duration of the induced current to generate a second No. The period of the third signal is equal to the period of the control signal, and the working time is equal to the reset duration of the induced current; the buffer is connected to the adder and the side device, and the fine signal is generated according to the second signal and the third signal. , the fourth signal of the occupation and the guard __ third health _, and the peak is caused by the second signal mosquito; and the low-order wave contact, filtering the fourth signal to generate the same F stream output of the phase converter __ signal. According to the present invention, the output current sensing method applied to the primary side of the flyback converter 'the flyback type conversion H includes a secondary side coil, a secondary side coil, and a power switch connected to the secondary side coil Controlling signal switching to cause the human-side line to generate an induced current, the output current sensing method comprising: sensing a current of the secondary-side coil to generate a first signal; sampling a peak and a valley of the first signal; Adding a peak value to the valley value to generate a second signal; _ the resetting duration of the inductive power generating a third signal, the period of the third signal being equal to the period of the control signal, U being equal to the reset duration of the induced current Time; root _ second letter of the third record produces fine money, the fourth letter 201113531, the period and working time is the same as the third signal, the m value is determined by the second signal; and the fourth signal is crossed A sense signal associated with the current of the % return converter is generated. Since the present invention does not require the use of a current sensing circuit on the secondary side to sense the wheel current, cost can be saved. [Embodiment] As shown in Fig. 2, 'in a flyback converter', a transformer τι has a __ under-side coil Lp connected between a voltage input terminal vin and a power switch S1, and a secondary-side coil Ls via a diode Do Connected to the voltage output terminal v〇, and the auxiliary coil Laux is connected to the diode Daux' primary side coil Lp, secondary side coil Ls and auxiliary coil Laux, the turns ratio is Np: Ns : Naux, and the PWM controller 20 has control The terminal Gate provides a control signal Vgs switching power switch si, a detecting terminal Vdet detecting voltage Vaux on the auxiliary coil Laux, and a voltage Vcs on the sensing terminal CS sensing resistor R1 to sense the current Ids of the power switch si. 3 is a waveform diagram of the flyback converter of FIG. 2 operating in a discontinuous current mode (DCM), wherein waveform 22 is voltage Vds on power switch S1, waveform 24 is control signal Vgs, and waveform 26 is The voltage Vaux on the auxiliary coil Laux, the waveform 28 is the current Ids of the power switch S1, the waveform 30 is the induced current i__Do through the diode d〇, and the waveform 32 is the leading edge masking signal LEB. At time t1, as indicated by waveforms 24 and 28, control signal Vgs turns to a high level and on) power switch S1 is turned on, so current Ids rises. When the power switch si is just turned on, the current Ids may appear as a glitch, so the leading edge occlusion signal LEB is used to shield the possible glitch, 201113531 to avoid malfunction due to the glitch. At time t2, the control signal Vgs turns to a low level and turns off the power switch si, at which time the current Ids falls to zero, and the secondary side coil Ls generates an induced current l_D〇 through the diode Do, inducing current I_Do starts to drop from the peak I_Do_pk. When the induced current l_Do falls to zero, as indicated by time t4, the voltage Vds will produce a sine wave oscillation due to the magnetizing inductance Lm and the discrete electric valley Ceq, as shown by the waveform 22. Output current of the flyback converter in DCM mode

Io=Ids_j)kxNp/Nsx〇.5xT〇ff/Ts . Equation 1 where Ids-pk is the peak value of the current ids, Ts is the period of the control signal Vgs, and Toff is the resetting duration of the induced current i_D〇 . Since Np and Ns are fixed values, Equation 1 can be rewritten as

Io=KlxIds_pkxT〇fJ/Ts, where Equation 2 where Kl=Np/Nsx〇.5. Figure 4 is a first embodiment of the wheel current sensing device of the present invention,

The output current sensing device includes a sampling and maintaining circuit 4 〇 sampling sensing terminal cs voltage Vcs peak generating signal Vcs pk, reset duration detector 46 detecting reset The duration Toff generates signals Sc3 and Sc4, the buffer 42 generates a signal Sc5 according to the numbers Vcs_pk, Sc3, and Sc4, and the low pass [S 8 201113531 filter 44 filters the wave signal Sc5 to generate a sensing signal related to the output current ι〇 Io_signa In the sample and hold circuit 40, the switch S2 is connected between the sensing terminal CS and the capacitor Cshl, and the control signal VgS controls the switching of the switch S2 to sample the peak value of the voltage Vcs. In order to avoid the influence of the glitch when the power switch S1 is just turned on, the switch S3 is connected in parallel with the capacitor Cshl, and the leading edge occlusion signal LEB switches the switch S3. There are many ways to detect the reset current of the induced current i__d〇 in the DCM operation. The more common method is to detect the knee value of the voltage Vaux on the auxiliary coil Laux, as shown in the waveform of Figure 3. 26 is shown. The reset duration detector 46 includes the knee value detecting voltage Vaux of the knee value circuit 52 to generate the knee value signal SK, and the flip-flop 54 determines the signal Scl 'comparator according to the inverted signal Vgs_B of the control signal Vgs and the knee value signal SK. The comparison voltage Vaux and the preset value Vref1 generate the signal Sc2' and the gate 58 generates the signal Sc3 based on the signals Sc1 and Sc2, and the inverter 60 generates the signal Sc4 based on the signal Sc3. • Figure 5 is a waveform diagram of the circuit of Figure 4, where waveform 62 is a signal

The Vgs_B' waveform 64 is the knee value signal SK, the waveform 66 is the signal Sc1, the waveform 68 is the signal Sc2, the waveform 70 is the signal Sc3, and the waveform 72 is the signal Sc5. Referring to Figures 4 and 5' at time t5, as shown by waveforms 62 and 66, signal Vgs_B is switched to a level, so that signal scl at output q of flip-flop 52 also transitions to a high level. At time t7, as indicated by waveforms 64 and 66, knee circuit 50 detects the knee value of voltage Vaux, thereby generating knee signal sk to reset terminal C of flip flop 52 and reset signal Scl. In general, the reset current duration Toff of the induced current is the time from the peak jjQO-pk to 〇. However, as shown in time t2 to t3 of Fig. 3, after the control signal Vgs is turned to the low level, it takes a period of time for the induced current I_Do to start falling from the peak I_Do_pk. Therefore, in order to obtain a more accurate reset duration Toff, the reset duration detector 46 compares the voltage Vaux with the preset value Vref1 using the comparator 54. In this embodiment, the preset value Vref1 is 0. When the voltage Vaux is greater than 0, as shown by time t6 of FIG. 5, the signal Sc2 is turned to a high level, and at time t8, the voltage Vaux is less than 0, so "s The number Sc2 changes to a low level as shown by waveform 68. Finally, the re-use and gate 58 generate a signal Sc3 based on the signals Sc 1 and Sc2. As shown by the waveform 70, the period of the signal Sc3 is Ts, and the operation time of the signal Sc3 is almost equal to the reset duration T〇ff. In fact, the time t2 to t3 疋 is relatively short, and can be ignored, so that the comparator 54 in the reset duration detector 46 can be omitted. Referring to Figures 4 and 5, in the buffer 42, the amplifier 48 amplifies the signal Vcsjk from the sample and hold circuit 40 by K2, and the switch S4 is connected between the amplifier 牝 and the output 50 of the buffer 42 'switch S5 Connected between the round end 5〇 and the ground end qnd of the buffer 42, the signals Sc3 and Sc4 from the reset duration detector 46 switch the switches S4 and S5, respectively, and thus at the output of the buffer 42. 5 〇 produces 彳s number Se5 as shown by waveform 72. The peak value of the signal Sc5 is K2xVcs_pk, the period is Ts, and the working time is T〇ff. The low pass filter 44 filters the signal Sc5 to generate a sensing signal. Equation 3 I〇_signal=K^xVcs_pkxToff/Ts. 201113531 As can be seen from Figure 2, the signal Vcs_pk = Ids_pkxRl, so Equation 3 can be rewritten as

Io_signal=K3><Ids_pkxToff/Ts » Equation 4 where K3=K2xRl. It can be seen from Equation 2 and Equation 4 that the sense signal Io_signal has a proportional relationship with the output current 1〇, so that the change of the output current 1〇 can be known by the sense signal Io_signal. 6 is a waveform diagram of the continuous current mode (CCM) of the flyback converter of FIG. 2, wherein the waveform 80 is the control signal Vgs, the waveform 81 is the voltage Vaux, and the waveform 82 is the diode Do. The induced current I_Do, the waveform 84 is the leading edge masking signal LEB, the waveform 86 is the signal LEB_D, the waveform 88 is the signal Sc5 of the buffer output 50, and the waveform 90 is the sensing signal Io_signal. As can be seen from waveform 82, the output current of the flyback converter operating at CCM φ

Io = 0.5x (Ids_pk + Ids_valley) x Np / Ns > Toff / Ts » Equation 5 where Ids_valley is the valley of the current Ids. Since Np and Ns are fixed values, Equation 5 can be rewritten as

Io=Klx(Ids_pk+Ids_valley)xTofE/Ts. Equation 6 11 201113531 as shown in waveforms 80 and 82 'When the flyback converter operates at ccm, the current I is sensed. The reset continuation of the coffee TGff is determined by the non-working time of the control ship number ** so that the time Toff can be obtained directly with the control signal Vgs. Figure 7 is a second embodiment of the output current sensing device of the present invention applied to a CCM flyback converter. The output money sensing device of FIG. 7 includes the sample and hold circuit 40 and the buffer 42 as well as the circuit of FIG. 4, and further includes a delay 92, a sample and hold circuit 94, an adder 96, and a second-order low pass filter 98. In the sampling and sustaining circuit 94, one end of the switch S6 is connected to the sensing terminal CS via the switch S2, and the other end is connected to the capacitor Csh2, and the signal LEB_D is controlled by the switch S6 to generate a signal by the valley of the sampling voltage vcs.

Vcs_valley. As mentioned before, when the power switch si is just turned on, the voltage vcs may generate a surge 'to avoid sampling and maintaining the circuit 94 from incorrect sampling due to the glitch'. The delay is used to delay the leading edge occlusion signal LEB to generate a signal. LEB_D' causes sample and hold circuit 94 to sample voltage Vcs after the leading edge masking signal LEB has ended, as shown by waveforms 84 and 86 of FIG. Adder 96 combines signals Vcs_pk and Vcs_valley to generate signal Vadd. In the buffer 42, the amplifier 48 amplifies the signal Vadd by K2, and the switches S4 and S5 are switched in response to the control signal Vgs and its inverted signal Vgs_B, respectively, thereby generating a signal Sc5 at the output 50 of the buffer 42, as in the waveform 88. Show. The peak value of the signal Sc5 is K2x (Vcs_pk+Vcs_valley), the period is Ts, and the working time is Toff. The second-order low-pass filter 98 filters the signal Sc5 to generate a sensing signal

Io_signal=K2x(Vcs_pk+Vcs_valley)xToff/Ts. The formula ' 12 201113531 Since 'is said Vcs pk=Ids pkxRl , and the number \^3 乂 &116丫=1 as a 乂&14>^111, the formula 7 can be rewritten as

Io-signal=K3x(Ids_pk+Ids_valley)xToff/Ts. Equation 8 From Equations 6 and 8, it can be seen that the sense signal i〇-signai has a proportional relationship with the output current Ιο, so that the change of the output current Ιο can be known by the sense signal I〇_signal. Figure 8 is a third embodiment of the output current sensing device of the present invention for use in a flyback converter that can operate in DCM and CCM. The output current sensing device of FIG. 8 includes the delay device %, the sample and hold circuit 94, and the adder of FIG. 7 in addition to the sample hold circuit 4A of FIG. 4, the buffer 42 and the reset duration side 46. 96 and second order low pass filter 98. Referring to Figures 3 and 8 'When the flyback converter operates in DCM, since the valley value of the current operation is 〇' as shown by waveform 28, the valley of the voltage Vcs is also 〇, = by addition H 96 Output Vadd=Ves』k, while resetting the duration state 46 by detecting the electrical waste Vaux on the auxiliary coil Laux, obtaining the signal Sc3 whose period is equal to the reset duration Toff and its S phase L number Sc4 . The buffer 42 generates a signal Sc5 based on the signals Vadd, Sc3, and Sc4. Signal Sc5 is shown as waveform 72 of Fig. 5 and has a period Ts, an operating time Toff, and a value ♦ K2xVcs_pk. The last-order low-pass filter 98 filter signal Sc5 produces a sensed signal associated with the output current, lG-signa, as shown in Equation 4. ^ 13 201113531 > Fig. 6 and Fig. 8 'When the flyback converter operates at cCM, the sampling and sustaining circuits 4G and 94 respectively sample the peaks and valleys of the voltage Ves, so the round of the force processor 96 is Vadd=Vcs 』k+Vcs_valley. As the waveform 81 does not have a valley value due to the voltage Vaux, the reset duration of the output Scl of the flip-flop 54 in the detector 46 will remain at the high level signal S c 3 which will be determined by the signal s c 2 . Assuming that the pre-6 value Vrefl of the inverting input of the comparator 56 is 〇, it can be seen from the waveforms 81 and 82 that the period of the signal is Ts and the operating time is almost equal to the reset duration Toff of the induced current ^Do, so the signal Sc3 The period is Ts and the working time is Toff. The buffer 42 generates an apostrophe Sc5 based on the signals Vadd, Sc3, and Sc4, as shown by the waveform 88 of Fig. 6, having a period ts, an operating time Toff, and a peak K2x (Vcs_pk + Vcs_valley). The last second-order low-pass filter 98 filter signal Sc5 produces a sense signal I〇_signal associated with the output current ι0, as shown in Equation 8. The output current sensing device of the present invention can more accurately sense the load state. The determined sensing signal can be used to implement many applications, for example, overload protection, constant current control, frequency adjustment control, front-end converter. Voltage regulation and load status indicators, etc. 9 is an embodiment of an overload protection using the output current sensing device of the present invention, which includes a comparator 1 〇〇 compare sense signal I 〇 — signal and a preset value V ref 2 , and a delay device 102 connected to the comparator 100 . When the sense signal Io_signal continues to be greater than the preset value Vref2 for more than a predetermined period of time, the delayer 102 sends a fault signal Fault to turn off the flyback converter. 10 is an embodiment of a constant current control using the output current sensing device of the present invention. The circuit of FIG. 2 includes a PWM controller 2, a 201113531 transformer T1 and a power switch SI, and a constant voltage loop 106. The measured output voltage Vo generates a feedback signal to the feedback terminal Vfb of the PWM controller 20, and the constant current loop 104 adjusts the feedback signal of the feedback terminal Vfb according to the sensing signal I〇_signal to achieve constant current control. In this embodiment, the constant current loop 104 includes resistor Reel and Rcc2 voltage-divided sensing signals i〇_signai to generate a divided voltage to control the current through the transistor Qcc, thereby adjusting the feedback signal of the feedback terminal vfb. When the sense signal Io_signal rises, the current through the transistor qcc increases 'so the feedback signal of the feedback terminal Vfb drops to decrease the output current 1〇; conversely, when the sense signal Io_signal falls, the feedback terminal vfb The feedback signal rises to cause the output current to rise. Since the sensing signal I〇_signal is related to the output current Ιο, it is also related to the load state. Therefore, by using the sensing signal 1〇 signal to adjust the switching frequency of the power switch S1, the switching frequency can be improved during heavy loading to improve The performance of the flyback converter, and reduce the switching frequency at light load to reduce the switching loss' as shown in the relationship between the switching frequency and the sensing signal in Figure 11. Figure 12 is an embodiment of a front-end converter voltage regulation using the output current sensing device of the present invention, which, in addition to the circuit of Figure 2, includes a PWM controller 20, a transformer T1, and a power switch S1. In this flyback converter, the front end converter 108 converts the alternating current voltage vin_AC into a direct current voltage Vin_Dc to the primary side coil of the transformer τι, the resistor R2 and an equivalent resistor 11 composed of the resistors R3, R4 and the transistor ^ 〇Divided voltage Vin_DC production (4) Grant Vpfe-& to the surface device ι〇8 to adjust the voltage Vin_DO sensing signal I〇~signal control the switching of the transistor to change the resistance of the equivalent resistance 110, and then adjust the voltage Vin—Dc. Referring to Figure 12, a load status indicator is included in the PWM control 20 to turn off the 15 201113531 front end converter 108. The load status indicator is shown in Figure 13, which includes the comparator 112 comparing the sense signal 1 - Signal and the preset value Vref3 and sending the comparison result to the delay 114. When the sensing signal I 〇 -Signal continues to be greater than the preset value Vref3 exceeds the expected time of the segment, the delay device 114 sends a load status signal

Status is _ front-end converter, which achieves good green power efficiency. The above description of the preferred embodiments of the present invention is intended to be illustrative of the invention and is not intended to be in the form of the disclosure, and is modified or changed based on the above teachings or learning from the present invention. It is possible that the embodiments are for explaining the invention and that the skilled person selects and narrates in actual use of the present invention in various embodiments, and the technical scope of the present invention seeks (4) Equal to decide. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a conventional flyback switching voltage converter; Lutu 2 is a flyback converter; FIG. 3 is a waveform diagram of the flyback converter operating in DCM of FIG. 2; 4 is a waveform diagram of the circuit of FIG. 4; FIG. 2 is a waveform diagram of the flyback converter of FIG. 2 operating at CCM; FIG. 2 is a diagram of the wheel current sensing device of the present invention Second Embodiment; FIG. 9 is a third embodiment of the wheel current sensing device of the present invention; FIG. 9 is a diagram showing the use of the wheel current sensing device of the present invention to achieve overload protection. The output current sensing device implements a constant current control embodiment; FIG. 11 is a relationship between the switching frequency and the sensing signal I〇_signal; FIG. 12 is a front-end converter voltage adjustment using the output current sensing device of the present invention. Embodiments; and Figure 13 is an embodiment of implementing a load status indicator using the output current sensing device of the present invention. [Main component symbol description] 10 PWM controller 12 Optical clutch 14 Voltage regulator 20 PWM controller 22 Voltage Vds waveform 24 Control signal Vgs waveform 26 Voltage Vaux waveform 28 Current Ids waveform 30 Induced current I_Do waveform 32 Waveform of leading edge masking signal LEB 40 Sample and hold circuit 42 Buffer 44 Low pass filter 46 Reset duration detector 48 Amplifier 17 201113531

50 Buffer output 52 Knee circuit 54 Rectifier 56 Comparator 58 and Gate 60 Inverter 62 Signal Vgs_B waveform 64 Knee signal SK waveform 66 Signal Scl waveform 68 Signal Sc2 waveform 70 Signal Sc3 Waveform 72 Signal Sc5 waveform 80 Control signal Vgs waveform 81 Voltage Vaux waveform 82 Induced current I_Do waveform 84 Front edge masking signal LEB waveform 86 Signal LEB_D waveform 88 Signal Sc5 waveform 90 Sensing signal I〇_signal Waveform 92 Delay 94 Sample and Hold Circuit 96 Adder 98 Second-Order Low-Pass Filter 100 Comparator 18 201113531 102 Tin-Chip 104 Constant Current Loop 106 Constant Voltage Loop 108 Front-End Converter 110 Equivalent Resistor 112 Comparator 114 Delayer

Claims (1)

201113531 VII. Patent application scope: 1. An output current sensing device applied to the primary side of a flyback converter, the flyback converter including a primary side coil, a secondary side coil, and a power switch connected to the primary side coil In response to the control signal switching to cause the secondary side coil to generate an induced current, the output current sensing device includes: the sampling and sustaining circuit 'sampling the first "number of values associated with the current of the primary side coil to generate a second signal; The detector 'detects the reset duration of the induced current to generate a third signal'. The period of the third signal is equal to the period of the control signal, and the working time is equal to the reset duration of the induced current; The sampling and maintaining circuit and the detector generate a fourth signal according to the second and third signals, wherein the period and the working time of the fourth signal are the same as the third signal, and the peak value is determined by the second signal; And a low pass filter is coupled to the buffer, and filtering the fourth signal to generate a sense signal associated with an output current of the flyback converter. The output current sensing device of claim 1, wherein the sampling and maintaining circuit comprises: an input terminal, receiving the first signal; a capacitor; a switch connected to the fa1 of the hybrid terminal and the capacitor, wherein the (four) signal makes the first signal The second signal is generated by charging the capacitor. 3. The output current measuring device of claim 1 further includes an auxiliary line _ connected to the primary side coil to generate a voltage for the detector to determine the third signal. 20 201113531 4. The output current sensing device of claim 3, wherein the detector comprises: a knee value circuit connected to the auxiliary coil, detecting a voltage knee value on the auxiliary coil to generate a knee value signal; the flip-flop connecting the knee value a circuit, determining a sixth signal according to a fifth signal inverted from the control signal and the knee value signal; a comparator connecting the auxiliary coil, comparing a voltage on the auxiliary coil with a preset value to generate a seventh signal; And a gate connected to the flip-flop and the comparator, and generating the third signal according to the sixth and seventh signals. 5. The output current sensing device of claim 3, wherein the detector comprises: a knee value circuit connecting the auxiliary coil 'debt measuring a voltage knee value on the auxiliary coil to generate a knee value signal; and a flip-flop connection The knee value circuit determines the third signal based on the fifth signal inverted from the control signal and the knee value signal. The output current sensing device of claim 1, wherein the buffer comprises: an amplifier connected to the sampling and maintaining circuit, the second signal is amplified to generate a fifth signal; and the switch is connected to the amplifier and the output end of the buffer And the first switch is connected between the round and the ground of the money punch; the middle 'pair' and the second open coffee should switch the third signal to generate the fourth signal at the output of the buffer . The secondary side coil and the connection of the one ==Yu!|-force (10) input (four) subtraction method, the flyback converter includes the primary side coil 21, the power switch of the 201113531 secondary side coil is switched according to the control signal to make the second The side coil generates an induced current'. The round current sensing method comprises the following steps: (A) sensing a current of the primary side coil to generate a first signal; (B) sampling a peak of the first signal to generate a second signal; (C) Detecting a reset duration of the induced current to generate a third signal, the period of the second signal being equal to a period of the control signal, and the working time being equal to a reset duration of the induced current; (D) according to the second signal And the third signal generates a fourth signal, the period and working time of the fourth signal are the same as the third signal, and the peak value is determined by the second signal; and (E) filtering the fourth signal to generate the reciprocal conversion The sense signal associated with the current of the wheel. 8. The output current sensing method of claim 7, wherein the step B comprises controlling the charging of the capacitor by the first signal by the control 彳§ to obtain the second apostrophe. The output current sensing method of claim 7, wherein the step c comprises determining the third signal according to the control signal and a voltage on the auxiliary coil coupled to the primary side coil. 10. The output current sensing method of claim 9, wherein the step c comprises: detecting a voltage knee value on the auxiliary coil to generate a knee value signal; and a fifth signal inverted from the control signal and the knee value signal Determining a sixth signal; comparing the voltage on the auxiliary coil with a preset value to generate a seventh signal; and generating the third signal according to the sixth and seventh signals. 22 201113531 11. The output current sensing method of claim 9, wherein the step c comprises: detecting a voltage knee value on the auxiliary coil to generate a knee value signal; according to a fifth signal inverted from the control signal and the knee The value signal determines the third signal. 12. The output current sensing method of claim 7, wherein the step D comprises: Amplifying the 5th first signal generates a fifth signal; and switching a switch that receives the fifth signal from one end according to the third signal to generate the fourth signal at the other end of the switch. 13. An output current sensing device applied to a primary side of a flyback converter, the flyback converter comprising a secondary side coil and a power switch connected to the primary side coil in response to a control signal switching, the output current sensing The device comprises: a first sampling and maintaining circuit for sampling a peak of a first signal related to the current of the secondary scale; a second sampling and maintaining circuit for sampling a valley of the first signal; an adder connecting the first and the third a second sampling and switching circuit, combined with the peak and the bottom to generate a second signal; a buffer connected to the adder, generating a third signal according to the second signal and the control signal, the third signal has the same period, the control signal is the same, working The time is the same as the non-working time of the control signal, and the peak value is determined by the second signal; and the low-pass filter is connected to the buffer, and the third signal is sensed by the third signal generator and the output current of the _ return converter signal. t S 13 wheel current sensing device 'where the first sampling and dimension $ 23 201113531 wheeled end, receiving the first signal; capacitance; and the switch is connected between the input terminal and the capacitor, due to the control signal The first 彳§ number charges the first electric valley to obtain a peak of the first signal. The output current sensing device of μ, wherein the second sampling and maintaining circuit comprises: ' ' input terminal, receiving the first signal; a capacitor; and a switch connected between the input terminal and the capacitor, corresponding to The fourth signal causes the first signal to charge the capacitor to obtain a valley of the first signal. 16. The input device of claim 13 wherein: the amplifier is coupled to the adder, the second signal is amplified to generate a fourth signal; and the switch is coupled between the amplifier and the output of the buffer. And a second switch connected between the output end of the buffer and the ground; wherein the first switch and the second switch are controlled to switch to generate the third signal at the output of the buffer. 17. - Seed system (4) shouting — II - pick-up current sensing method, the fly-back converter includes a primary side coil and a power switch connected to the primary side coil in response to a control signal switching, the output current sensing method includes The following steps: (Α) sensing the current of the primary side coil to generate a first signal; (Β) sampling the peak and valley of the first signal; (C) adding the peak value to the valley value to generate a second signal; 24 201113531 CD) Root_Second money and (4) Money generates a third money, the period of the third signal is the same as the control signal, the working time is the same as the non-working time of the control signal, and the peak value is the same as the E) Filtering the third recording produces a sensed signal associated with the output current of the flyback (four). The output current sensing method of the second item 17 wherein the step b includes: Controlling the charge of the first capacitor by the control signal_first signal to obtain the peak of the first signal; delaying the leading edge masking signal to generate a fourth signal; and by using the fourth money control_first-money pair Charging the two capacitors to obtain the valley of the first signal. 19. The method as claimed in claim 17, wherein the step D comprises: amplifying the second signal to generate a fourth signal; The signal determines to switch a switch that receives the fourth signal at one end according to the control signal to generate the third signal at the other end of the Luhai switch. 20. An output current sensing device applied to a primary side of a flyback converter, the flyback converter comprising a primary side coil, a secondary side coil, and a power switch connected to the one side coil to switch according to a control signal In order to cause the secondary side coil to generate an induced current, the output current sensing device includes: a first sampling and maintaining circuit that samples a peak of a first signal related to a current of the primary side coil; a second sampling and sustaining circuit, sampling a valley value of the first signal; an adder connecting the first and second sampling and sustaining circuits 'in combination with the peak 25 201113531 and a valley value to generate a second signal; and a detector for detecting a reset duration of the induced current The third signal 'the period of the third signal is equal to the period of the control signal, and the working time is equal to the reset duration of the induced current; the buffer is connected to the adder and the detector, according to the second signal and the second k No. generating a fourth signal, the period and working time of the fourth signal being the same as the third signal, and the peak value is determined by the second signal; A buffer connected to the filter, filtering the fourth signal to generate an output current to the Chi of the back converter associated sensing signal. 21. The output current sensing device of claim 20, wherein the first sampling and maintaining circuit comprises: an input terminal, receiving the first signal; a capacitor; and a switch connection between the input terminal and the capacitor 'corresponding to control The signal causes the first 彳 § to charge the first capacitor to obtain a peak of the first signal. 22. The output current sensing device of claim 2, wherein the second sampling and maintaining circuit comprises: an input terminal, receiving the first signal; a capacitor; and a switch connection between the human terminal and the capacitor The fifth signal causes the number to charge the valley to obtain the valley of the first signal. 23. The output current measuring device of claim 20, further comprising an auxiliary line _ connected to the Γ 26 201113531 - the secondary side coil button - for the _ rectifying the third signal. 24. The output current sensing device of claim 23, wherein the debt detector comprises: a knee value circuit connecting the help coil, the voltage knee value on the shed assist coil generating a knee value signal; The fifth signal of the control signal and the signal of the knee determine the sixth signal; the comparator is connected to the auxiliary coil, the voltage on the auxiliary coil is compared with the preset value to generate a seventh signal; and the gate is connected to the flip-flop and The comparator generates the third signal according to the sixth and seventh signals. The output current sensing device of claim 20, wherein the buffer comprises: an amplifier connected to the sampling and maintaining circuit, the second signal is amplified to generate a fifth signal; and the switch is connected to the output of the amplifier and the buffer Between the ends; and a second switch connected between the output of the buffer and the ground; wherein 'the first and second switches are switched by the third signal to generate the fourth at the output of the buffer signal. 26. A method for applying a flyback converter-sub-contact (four) over-the-counter, the primary-side coil, the secondary-side coil, and a power switch connected to the primary-side coil are switched in response to a control signal to enable The secondary side coil generates an induced current. The output current sensing method comprises the following steps: (A) sensing a current of the primary side coil to generate a first signal; (B) sampling a peak and a bottom value of the first signal; 201113531 (c) adding the peak value to the valley value to generate a second signal; (D) detecting a reset duration of the induced current to generate a third mark, ▲ ★ a period of the three signals - a period of the control signal, And the operation 3 is equal to the reset duration of the induced current; 曰(E) generates a fourth signal according to the second signal and the third signal, and the period of the fourth sound signal and the time I is the same as the third signal, : the second signal is determined; (F) Filtering the fourth money produces a sensed signal associated with the wheel of the flyback converter. The output current sensing method of claim 26, wherein the step B comprises: controlling the charging of the _ capacitor by the money control by the control to obtain the peak of the first signal; masking the leading edge The signal generates a fifth signal; and charging by the second pass of the second pass to obtain the valley of the first signal. 28. The output current sensing method of claim 26, wherein the step d comprises determining the third signal based on the control signal and a voltage on the auxiliary coil that is coupled to the primary side coil. 29. The output current sensing method of claim 28, wherein the step d comprises: _ the voltage knee value on the auxiliary coil generates a knee value signal; and the fifth money and the knee value signal are determined according to the control Six signals; comparing the position and the preset value on the auxiliary axis to generate a seventh signal, and generating the third signal according to the sixth and seventh signals. 28 201113531 30. The output current sensing method of claim 26, wherein the step E comprises: amplifying the second signal to generate a fifth signal; and switching a switch that receives the fifth signal at one end according to the third signal, The other end of the switch produces the fourth signal. 29