CN103763820A - Load sampling circuit of isolation-type LED drive circuit - Google Patents

Abstract

The invention provides a load sampling circuit of an isolation-type LED drive circuit, and belongs to the technical field of LED lighting drive circuits. The load sampling circuit comprises an LED drive circuit and a sampling circuit, wherein the sampling circuit is connected with a primary side winding of the LED drive circuit, the sampling circuit comprises a first resistor R1, a second resistor R2 and a first capacitor C1, one end of the first resistor R1 serves as one input end of the sampling circuit and is connected with the other input end of a primary side winding of a first flyback transformer T1, the other end of the first resistor R1 is connected with one end of the first capacitor C1, the other end of the first capacitor C1 is connected with one end of the second resistor R2 and a drive chip U1 and serves as the output end of the sampling circuit, and the other end of the second resistor R2 is grounded. The load sampling circuit has the advantages of being free of an auxiliary winding and an opto-coupler, high in collecting precision, simple in structure, easy to achieve and capable of being used for the drive circuit of a continuous current mode or an intermittent current mode.

Description

The load sample circuit of isolated LED drive circuit

Technical field

The invention belongs to LED illumination driving circuit technical field, relate to a kind of load sample circuit of isolated LED drive circuit, relate in particular to the auxiliary winding of a kind of nothing or without the load sample circuit of the isolated LED drive circuit of photoelectric coupled circuit.

Background technology

Traditional LED drive circuit or DC/DC electric power management circuit need adopt auxiliary winding or photoelectric coupled circuit to gather load voltage.As shown in Figure 5, LED drive circuit is by driving chip U1, the second flyback transformer T2, the first metal-oxide-semiconductor M1, the 3rd resistance R 3, the 4th resistance R 4, the 6th resistance R 6, the 7th resistance R 7, the second capacitor C 2, the 3rd capacitor C 3, the 4th capacitor C 4, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, the 5th diode D5 and LED lamp string DL to form, wherein, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4 form a rectifier bridge, connect external communication power supply.The second described flyback transformer T2 has three windings: former limit, secondary and auxiliary winding.Former limit is the switch loop for providing energy to be fed to, and the inductance on former limit, in the switching process of the first metal-oxide-semiconductor M1, completes from power supply energy storage with to the function of secondary delivery of energy; The effect of secondary is to carrying out rectification from the electromotive force of former limit induction, offering LED lamp string DL or other loads after filtering; The effect of auxiliary winding is the collection of secondary voltage and the overvoltage protection of secondary.The effect that drives chip U1 is by gathering the size of secondary current or voltage, to control the switching time of former limit the first metal-oxide-semiconductor M1, with this, reaches the electric current of constant LED lamp string DL or the object of constant other load output voltages.Yet, at the auxiliary winding of above-mentioned traditional employing, gather load voltage V _lEDreverse excitation circuit structure in, the existence of auxiliary winding causes circuit to have following defect: more or less have leakage inductance, the precision of voltage regulation is declined, consistency variation; In circuit, use auxiliary winding, except increasing manufacturing cost, also can occupying volume outer volume, and the circuit board finite volume that LED fluorescent tube can hold, if certain parameter that particularly circuit board length and width are high is mated not good with the size of LED fluorescent tube, also can affect the heat dispersion of circuit board, thereby reduce the life-span of driving power; In addition, auxiliary winding also can make the structure of transformer become complicated, and the restriction being subject to during circuit design increases, and it is large that the difficulty of light source design also becomes thereupon.Fig. 6 has illustrated a kind of electrical schematic diagram that gathers load voltage by optocoupler, this circuit comprises: drive chip U1, the first flyback transformer T1, the first metal-oxide-semiconductor M1, the 3rd resistance R 3, the 4th resistance R 4, the second capacitor C 2, the 3rd capacitor C 3, the 4th capacitor C 4, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, the 5th diode D5, LED lamp string DL and optocoupler OC, wherein the difference of the first flyback transformer T1 and the second flyback transformer T2 is not assist winding, this circuit gathers load voltage V by optocoupler OC _lED, but there is equally defect: cost of manufacture rises, and increases larger power consumption, thereby affects power-efficient, in addition, the sensitivity of optocoupler is poor, the aging accuracy of sampled voltage and the stability of overvoltage protection of also can affecting of optocoupler.

In view of above-mentioned prior art, be necessary to be improved, for this reason, the applicant has done useful design, and technical scheme described below produces under this background

Summary of the invention

The object of the present invention is to provide a kind of load sample circuit of isolated LED drive circuit, without auxiliary winding or optic coupling element, acquisition precision is high, simple in structure, be easy to realize, and can be used for the drive circuit of continuous current mode (CCM) or interrupted (discontinuous) current-mode (DCM).

The object of the invention is to reach like this, a kind of load sample circuit of isolated LED drive circuit, comprise LED drive circuit and sample circuit, described sample circuit is connected with the former limit winding of LED drive circuit, and described LED drive circuit comprises driving chip U1, the first flyback transformer T1, the first metal-oxide-semiconductor M1, the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5, the second capacitor C 2, the 3rd capacitor C 3, the 4th capacitor C 4, the 5th capacitor C 5, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, the 5th diode D5, the 6th diode D6 and LED lamp string DL, the negative pole of the first described diode D1 and the negative pole of the second diode D2, one end of the 3rd resistance R 3, one end of the 3rd capacitor C 3, one end of the 5th capacitor C 5, one end of the former limit winding of one end of the 5th resistance R 5 and the first flyback transformer T1 connects, the positive pole of the first diode D1 and the negative pole of the 3rd diode D3 are connected one end of external ac power source jointly, the positive pole of the second diode D2 and the negative pole of the 4th diode D4 are connected the other end of external ac power source jointly, the other end of the 3rd resistance R 3 is connected with one end of the second capacitor C 2, and connection drives chip U1, the other end of the 5th capacitor C 5 is connected with the other end of the 5th resistance R 5 and the negative pole of the 6th diode D6, the drain electrode of the positive pole of the 6th diode D6 and the first metal-oxide-semiconductor M1, the other end of the former limit winding of the first flyback transformer T1 connects, and connect an input of sample circuit, the grid of the first metal-oxide-semiconductor M1 connects driving chip U1, the source electrode of the first metal-oxide-semiconductor M1 is connected with one end of the 4th resistance R 4, and connection drives chip U1, one output of the first flyback transformer T1 secondary winding is connected with the positive pole of the 5th diode D5, and the negative pole of the 5th diode D5 connects one end of the 4th capacitor C 4 and the positive input terminal of LED lamp string DL, the positive pole of the 3rd diode D3, the positive pole of the 4th diode D4, the other end of the second capacitor C 2, the other end of the 3rd capacitor C 3, the other end of the 4th resistance R 4, another output of the secondary winding of the first flyback transformer T1, the negative input end common ground of the other end of the 4th capacitor C 4 and LED lamp string DL, is characterized in that: described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

In a specific embodiment of the present invention, described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

In another specific embodiment of the present invention, described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

In another specific embodiment of the present invention, described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

The present invention is owing to having adopted said structure, compared with prior art, the beneficial effect having is: described sample circuit is only connected with the former limit winding of the first flyback transformer T1, thereby do not affect the isolation of circuit, this sample circuit can be sampled to the load voltage of isolated LED drive circuit at the state of continuous current mode, in addition, by increasing by the second metal-oxide-semiconductor M2, also can sample to the load voltage of the isolated LED drive circuit of discontinuous current mode; It gathers secondary voltage from former limit, to determine secondary load condition, acquisition precision is high, and described sample circuit do not need auxiliary winding and optocoupler, thereby simple in structure, easily realize, and cost of manufacture is lower.

Accompanying drawing explanation

Fig. 1 is the electrical schematic diagram of one embodiment of the invention.

Fig. 2 is the current-voltage waveform figures of one embodiment of the invention under stable state.

Fig. 3 is the electrical schematic diagram of another embodiment of the present invention.

Fig. 4 is the current-voltage waveform figure of another embodiment of the present invention under stable state.

Fig. 5 is the electrical schematic diagram that the auxiliary winding of utilization of the prior art gathers LED drive circuit load voltage.

Fig. 6 is the electrical schematic diagram that utilizes optocoupler to gather LED drive circuit load voltage of the prior art.

Embodiment

In order to make the public can fully understand technical spirit of the present invention and beneficial effect; applicant will describe in detail the specific embodiment of the present invention below by reference to the accompanying drawings; but applicant is not the restriction to technical scheme to the description of embodiment, anyly according to the present invention design, changes in the form rather than substance all and should be considered as protection scope of the present invention.

Embodiment 1:

Refer to Fig. 1, a kind of load sample circuit of isolated LED drive circuit, comprises LED drive circuit and sample circuit, and described sample circuit is connected with the former limit winding of LED drive circuit.Described LED drive circuit comprises driving chip U1, the first flyback transformer T1, the first metal-oxide-semiconductor M1, the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5, the second capacitor C 2, the 3rd capacitor C 3, the 4th capacitor C 4, the 5th capacitor C 5, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, the 5th diode D5, the 6th diode D6 and LED lamp string DL, wherein, the first diode D1, the second diode D2, the 3rd diode D3 and the 4th diode D4 form a rectifier bridge.Described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output (sampled point shown in figure) of sample circuit, the other end ground connection of the second resistance R 2.

Please continue to refer to Fig. 1 and in conjunction with Fig. 2, the operation principle of the present embodiment is described.Described sample circuit is only connected with the former limit winding of the first flyback transformer T1, thereby do not affect the isolation of circuit, this sample circuit can be sampled to the load voltage of isolated LED drive circuit at the state of continuous current mode or discontinuous current mode, in the present embodiment, be to take the state of continuous current mode to describe as example.In the situation that described LED drive circuit is in stable condition, if the first metal-oxide-semiconductor M1 conducting, electric current is from the positive output end of rectifier bridge, successively through the former limit of the first flyback transformer T1 winding, the first metal-oxide-semiconductor M1 and the 4th resistance R 4(sampling resistor) get back to the negative output terminal of rectifier bridge.When electric current increases to after certain threshold value, the first metal-oxide-semiconductor M1 cut-off, the secondary loop conducting of the first flyback transformer T1.When the electric current in secondary loop is reduced to zero, the first metal-oxide-semiconductor M1 conducting again.Especially, suppose the first metal-oxide-semiconductor M1 conducting when secondary current zero passage, when the voltage of the 4th resistance R 4 reaches certain threshold values, end, circuit working is also suitable for the present embodiment in the critical condition of continuous current mode and discontinuous current mode.The time durations of establishing again the first metal-oxide-semiconductor M1 maintenance conducting is T ₁, the time durations of the first metal-oxide-semiconductor M1 remain off is T ₂, the former limit inductance size of the first flyback transformer T1 is L, the current peak on former limit is I _pEAK, the DC input voitage of external communication voltage after rectifier bridge rectification is V _iN, the voltage at the first resistance R 1 two ends is V _r1, the voltage at the second resistance R 2 two ends is V _r2, the voltage at the first capacitor C 1 two ends is V _c1, the output voltage values of LED lamp string DL is V _lED, former limit and the secondary turn ratio of the first flyback transformer T1 are N, obtain

$T_1=\frac{L\·I_{\mathrm{PEAK}}}{V_{\mathrm{IN}}}---\left(1\right)$

$T_2=\frac{L\·I_{\mathrm{PEAK}}}{N\·V_{\mathrm{LED}}}---\left(2\right)$

To T ₁, T ₂ask ratio, obtain

$\frac{T_1}{T_2}=\frac{N\·V_{\mathrm{LED}}}{V_{\mathrm{IN}}}---\left(3\right)$

$\frac{T_2}{T_1+T_2}=\frac{V_{\mathrm{IN}}}{N\·V_{\mathrm{LED}}+V_{\mathrm{IN}}}---\left(4\right)$

Because at T ₂in section, in figure, the voltage at A point place is V during this time _iN+ NV _lED, and at T ₁in section, A point and the earth equipotential, be about 0 during this time, therefore the voltage V in the first capacitor C 1 _c1the mean value of A point voltage:

$T_{C1}=\frac{T_2}{T_1+T_2}\·(V_{\mathrm{IN}}+N\·V_{\mathrm{LED}})=\frac{V_{\mathrm{IN}}}{V_{\mathrm{IN}}+N\·V_{\mathrm{LED}}}(V_{\mathrm{IN}}+N\·V_{\mathrm{LED}})=V_{\mathrm{IN}}---\left(5\right)$

If RC time constant (R1+R2) C1 of described sample circuit is far longer than the switching frequency of the first metal-oxide-semiconductor M1, the voltage V in the first capacitor C 1 _c1stabilize to V _iN, again due to

V _R1+V _R2+V _C1=N·V _LED+V _IN （6）

Therefore,

V _R1+V _R2=N·V _LED （7）

Because the voltage on the first resistance R 1 and second voltage R2 is according to the proportional distribution of their resistance value, the voltage that therefore can obtain in the second resistance R 2 is

$V_{R2}=\frac{R_2}{R_1+R_2}\·N\·V_{\mathrm{LED}}---\left(8\right)$

As shown from the above formula, described sampled voltage, i.e. the voltage V at the second resistance R 2 two ends _r2voltage V with secondary load LED lamp string DL two ends _lEDlinear, the coefficient of this linear relationship is only relevant with the first resistance R 1, the resistance of the second resistance R 2 and the turn ratio N of the first flyback transformer T1, therefore can realize the accurate collection of load end output voltage.

Embodiment 2:

Refer to Fig. 3, described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output (sampled point shown in figure) of sample circuit, the other end ground connection of the second resistance R 2.

Please continue to refer to Fig. 3 and in conjunction with Fig. 4, the operation principle of the present embodiment is described.In this embodiment, by setting up the second metal-oxide-semiconductor M2, can to the load voltage of isolated LED drive circuit, sample at the state of discontinuous current mode.In the situation that described LED drive circuit is in stable state, when the electric current of secondary winding reduces to zero, not conducting immediately of the first metal-oxide-semiconductor M1, but through conducting after a period of time.When the first metal-oxide-semiconductor M1 normally and cut-off, suppose that it is T that the first metal-oxide-semiconductor M1 keeps the time durations of conducting ₃, the time durations of the first metal-oxide-semiconductor M1 remain off is T ₄, the time durations of reducing to 0 to first metal-oxide-semiconductor M1 conducting from the first flyback transformer T1 secondary current is T ₅, in addition, with embodiment 1, suppose that the size of the former limit inductance of the first flyback transformer T1 is L, the peak current by the first former limit of flyback transformer T1 is I _pEAK, circuit input voltage is V _iN, the voltage at the first resistance R 1 two ends is V _r1, the voltage at the second resistance R 2 two ends is V _r2, the voltage at the first capacitor C 1 two ends is V _c1, the output voltage of load LED lamp string DL is V _lED, former limit and the secondary turn ratio of the first flyback transformer T1 are N, obtain

$T_3=\frac{L\·I_{\mathrm{PEAK}}}{V_{\mathrm{IN}}}---\left(9\right)$

$T_4=\frac{L\·I_{\mathrm{PEAK}}}{N\·V_{\mathrm{LED}}}---\left(10\right)$

To T ₃, T ₄ask ratio, obtain

$\frac{T_3}{T_4}=\frac{N\·V_{\mathrm{LED}}}{V_{\mathrm{IN}}}---\left(11\right)$

$\frac{T_4}{T_3+T_4}=\frac{V_{\mathrm{IN}}}{N\·V_{\mathrm{LED}}+V_{\mathrm{IN}}}---\left(12\right)$

If at T ₅during this time, the grid voltage of the second metal-oxide-semiconductor M2 becomes low level, at T ₄voltage V during this time in the first capacitor C 1 _c1for

$V_{C1}=\frac{T_4}{T_3+T_4}\·(V_{\mathrm{IN}}+N\·V_{\mathrm{LED}})=\frac{V_{\mathrm{IN}}}{V_{\mathrm{IN}}+N\·V_{\mathrm{LED}}}(V_{\mathrm{IN}}+N\·V_{\mathrm{LED}})=V_{\mathrm{IN}}---\left(13\right)$

With the deriving analysis in embodiment 1, can be at T ₄during this time,

V _R1+V _R2=N·V _LED （14）

$V_{R2}=\frac{R_2}{R_1+R_2}\·N\·V_{\mathrm{LED}}---\left(15\right)$

As shown from the above formula, identical with embodiment 1, described sampled voltage, i.e. the voltage V at the second resistance R 2 two ends _r2voltage V with secondary load LED lamp string DL two ends _lEDlinear, the coefficient of this linear relationship is only relevant with the first resistance R 1, the resistance of the second resistance R 2 and the turn ratio N of the first flyback transformer T1, therefore can realize the accurate collection of load end output voltage.

Embodiment 3:

In the present embodiment, described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.All the other all, with the description of embodiment 1, repeat no more herein.

Embodiment 4:

In the present embodiment, described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.All the other all, with the description of embodiment 2, repeat no more herein.

Claims (4)

1. a load sample circuit for isolated LED drive circuit, comprises LED drive circuit and sample circuit, and described sample circuit is connected with the former limit winding of LED drive circuit, and described LED drive circuit comprises driving chip U1, the first flyback transformer T1, the first metal-oxide-semiconductor M1, the 3rd resistance R 3, the 4th resistance R 4, the 5th resistance R 5, the second capacitor C 2, the 3rd capacitor C 3, the 4th capacitor C 4, the 5th capacitor C 5, the first diode D1, the second diode D2, the 3rd diode D3, the 4th diode D4, the 5th diode D5, the 6th diode D6 and LED lamp string DL, the negative pole of the first described diode D1 and the negative pole of the second diode D2, one end of the 3rd resistance R 3, one end of the 3rd capacitor C 3, one end of the 5th capacitor C 5, one end of the former limit winding of one end of the 5th resistance R 5 and the first flyback transformer T1 connects, the positive pole of the first diode D1 and the negative pole of the 3rd diode D3 are connected one end of external ac power source jointly, the positive pole of the second diode D2 and the negative pole of the 4th diode D4 are connected the other end of external ac power source jointly, the other end of the 3rd resistance R 3 is connected with one end of the second capacitor C 2, and connection drives chip U1, the other end of the 5th capacitor C 5 is connected with the other end of the 5th resistance R 5 and the negative pole of the 6th diode D6, the drain electrode of the positive pole of the 6th diode D6 and the first metal-oxide-semiconductor M1, the other end of the former limit winding of the first flyback transformer T1 connects, and connect an input of sample circuit, the grid of the first metal-oxide-semiconductor M1 connects driving chip U1, the source electrode of the first metal-oxide-semiconductor M1 is connected with one end of the 4th resistance R 4, and connection drives chip U1, one output of the first flyback transformer T1 secondary winding is connected with the positive pole of the 5th diode D5, and the negative pole of the 5th diode D5 connects one end of the 4th capacitor C 4 and the positive input terminal of LED lamp string DL, the positive pole of the 3rd diode D3, the positive pole of the 4th diode D4, the other end of the second capacitor C 2, the other end of the 3rd capacitor C 3, the other end of the 4th resistance R 4, another output of the secondary winding of the first flyback transformer T1, the negative input end common ground of the other end of the 4th capacitor C 4 and LED lamp string DL, is characterized in that: described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

2. the load sample circuit of isolated LED drive circuit according to claim 1, it is characterized in that described sample circuit comprises the first resistance R 1, the second resistance R 2 and the first capacitor C 1, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

3. the load sample circuit of isolated LED drive circuit according to claim 1, it is characterized in that described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first resistance R 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first resistance R 1 is connected with one end of the first capacitor C 1, the other end of the first capacitor C 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

4. the load sample circuit of isolated LED drive circuit according to claim 1, it is characterized in that described sample circuit comprises the first resistance R 1, the second resistance R 2, the first capacitor C 1 and the second metal-oxide-semiconductor M2, one end of the first capacitor C 1 connects another input of the former limit winding of the first flyback transformer T1 as an input of sample circuit, the other end of the first capacitor C 1 is connected with one end of the first resistance R 1, the other end of the first resistance R 1 is connected with the drain electrode of the second metal-oxide-semiconductor M2, the grid of the second metal-oxide-semiconductor M2 connects driving chip U1 as another input of sample circuit, the source electrode of the second metal-oxide-semiconductor M2 is connected with one end and the driving chip U1 of the second resistance R 2, and become the output of sample circuit, the other end ground connection of the second resistance R 2.

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