TWI420956B - Led driver and start-up feedback circuit therein - Google Patents

Description

LED driver and its start feedback circuit

This invention relates to a drive circuit and, more particularly, to a light emitting diode driver.

In general, a light emitting diode (LED) driver converts an input voltage to a desired output voltage to drive one or more connected light emitting diodes. However, LED drivers often fail to start properly due to certain conditions (such as receiving an unstable start input voltage) during startup, which often causes the LED to fail as expected. working normally.

It is an object of the present invention to provide a start feedback circuit in a light emitting diode driver to ensure that the light emitting diode driver can be normally started.

Another object of the present invention is to provide a light emitting diode driver for driving a light emitting diode in a normally stable operation.

One aspect of the present invention relates to a start feedback circuit in a light emitting diode driver, and the start feedback circuit includes at least one feedback subcircuit. The feedback subcircuit includes a first current unit, a second current unit, a third current unit, a fourth current unit, and a mirror unit. The first current unit is biased by a ground voltage to generate a first current. The second current unit is configured to generate a second current according to the first current. The third current unit is configured to receive the LED feedback voltage to generate the first current and the first control voltage. The fourth current unit is configured to receive the first control voltage to generate a third current that is mirrored by the second current, and induce a fourth current corresponding to the first control voltage. The mirroring unit is configured to generate a fourth current and mirror the fourth current to generate an output current corresponding to the fourth current, wherein the output current is converted into a feedback voltage to boost the output voltage of the LED driver and The light-emitting diode feedback voltage corresponding to the output voltage.

Another aspect of the present invention is directed to a start feedback circuit in a light emitting diode driver, and the start feedback circuit includes at least one feedback subcircuit. The feedback subcircuit includes a first P-type transistor, a first N-type transistor, a second P-type transistor, a second N-type transistor, and a mirror unit. The first P-type transistor has a first control end and a first end, wherein the first control end is biased by a low level supply voltage, and the first end is coupled to the high level supply voltage via the first current source. The first N-type transistor has a second control end and a second end, wherein the second control end is coupled to the first end of the first P-type transistor, and the second end is coupled to the high level via the second current source voltage. The second P-type transistor has a third control end and a third end, wherein the third control end is configured to receive the LED feedback voltage, and the third end is coupled to the high level supply voltage via the first current source. The second N-type transistor has a fourth control end and a fourth end, wherein the fourth control end is coupled to the third end of the second P-type transistor, and the fourth end is mirrored by the second current source The third current source is coupled to the high level supply voltage. The mirror unit is composed of a third P-type transistor and a fourth P-type transistor, wherein the third P-type transistor has a fifth control end and a fifth end, and the fifth control end is coupled to the fifth end and coupled Connected to the fourth end of the second N-type transistor, and the fourth P-type transistor has a sixth control end and a sixth end, and the sixth control end is coupled to the fifth control end of the third P-type transistor. The sixth end is coupled to the low level supply voltage via the resistor unit and generates an output current, and the output current is converted by the resistance unit into a feedback voltage to boost the output voltage of the LED driver and the corresponding output voltage. The diode feedback voltage.

Yet another aspect of the present invention is directed to a light emitting diode driver including a start feedback circuit, an operation feedback circuit, and a multiplexer. The start feedback circuit has a plurality of first ends for receiving a plurality of LED feedback voltages, wherein each of the LED feedback voltages is transmitted by at least one LED, and the LEDs are illuminated The pole system is coupled to the output end of the LED driver for outputting the output voltage, and the start feedback circuit generates the initial feedback voltage according to the LED feedback voltage. The operation feedback circuit has a plurality of second ends for receiving the LED feedback voltage, and the operation feedback circuit generates an operation feedback voltage according to the LED feedback voltage. The multiplexer is coupled to the start feedback circuit and the operation feedback circuit to select the start feedback voltage or the operation feedback voltage. Wherein, when the LED driver starts to start, the multiplexer selects to initiate the feedback voltage to start to push up the output voltage, and when the output voltage increases to a specific value, the multiplexer selects the operation feedback voltage. Push up the output voltage.

Still another aspect of the present invention relates to a light emitting diode driver including a start feedback circuit, an operation feedback circuit, a multiplexer, and a compensation unit. The first feedback system has a plurality of first ends, and each of the first ends is coupled to the output terminal of the LED driver for outputting an output voltage via at least one light emitting diode, and the first end system is The method is configured to receive a plurality of light-emitting diode feedback voltages, and each of the light-emitting diode feedback voltages is transmitted by the light-emitting diodes, wherein the start feedback circuit is based on the light-emitting diode feedback voltage The initial feedback voltage is generated. The operation feedback circuit has a plurality of second ends, and each of the second ends is coupled to the output end of the LED driver via the LED, and the second end is configured to receive the LED feedback voltage And each of the light-emitting diode feedback voltages is transmitted by the light-emitting diodes, wherein the operation feedback circuit generates the operation feedback voltage according to the light-emitting diode feedback voltage. The multiplexer is used to select the start feedback voltage when the LED driver starts to start, or to select the operation feedback voltage when the output voltage is increased to a specific value. The compensation unit is configured to compare the initial feedback voltage and the reference voltage to output a compensation signal for the initial push-up action of the output voltage, or to compare the operation feedback voltage and the reference voltage to output a compensation signal for the output voltage connection. Push up the action.

According to the technical content of the present invention, the light-emitting diode driver and the start-up feedback circuit thereof can be used to ensure that the LED driver is normally and well operated when the LED driver is started, thereby stably driving the LED. Diode.

FIG. 1 is a block diagram showing a light emitting diode (LED) driver according to an embodiment of the invention. The LED driver 100 converts the input voltage VIN to an output voltage VOUT, thereby driving one or more LEDs 102 channels, each of which includes one or more LEDs 102 connected in series. In one embodiment, the LED driver 100 is configured to drive channels formed by eight white LEDs, and each of the channels includes a plurality of white LEDs connected in series. Further, the LED driver 100 can be designed as an integrated circuit (IC) wafer.

The LED driver 100 includes a driving unit 110, a transistor switch 120, a comparator 130, a compensation unit (such as an error amplifier 140), a start feedback circuit 150, an operation feedback circuit 160, and a multiplexer 170.

The start feedback circuit 150 has a plurality of first ends 152, and each of the first ends 152 is correspondingly coupled to a channel formed by one of the LEDs 102. The operation feedback circuit 160 has a plurality of second ends 162, and each of the second ends 162 is correspondingly coupled to one LED 102 channel. In other words, each of the LEDs 102 is coupled to one of the first ends 152 and one of the second ends 162 and coupled to an output for outputting the output voltage VOUT.

The first end 152 of the start feedback circuit 150 receives the plurality of LED feedback voltages LFB transmitted by the LEDs 102, respectively, such that the start feedback circuit 150 thereby generates the start feedback voltage SFB. Here, as shown in FIG. 1, the LED feedback voltage LFB refers to the cathode voltage of the first LED 102 connected to the start feedback circuit 150 and the operation feedback circuit 160, or a voltage corresponding to the cathode voltage thereof. . Similarly, the second end 162 of the operational feedback circuit 160 receives the LED feedback voltage LFB transmitted by the LED 102, respectively, such that the operational feedback circuit 160 thereby generates the operational feedback voltage OFB. In one embodiment, the operational feedback circuit 160 generates an operational feedback voltage OFB based on the minimum LED feedback voltage of the received LED feedback voltage.

The multiplexer 170 is coupled to the start feedback circuit 150 and the operation feedback circuit 160 for selecting the start feedback voltage SFB or the operation feedback voltage OFB as the compensation feedback voltage FB. The error amplifier 140 is for comparing the compensated feedback voltage FB and the reference voltage VREF to output a compensation signal VC (typically a voltage signal). The comparator 130 compares the compensation signal VC with the oscillating signal OS and produces a comparison signal CS. The driving unit 110 then receives the comparison signal CS and thus outputs the pulse driving signal PS, thereby turning on the transistor switch 120.

The duty ratio of the transistor switch 120 determines the proportional relationship between the output voltage VOUT and the input voltage VIN. When the pulse driving signal PS turns on the transistor switch 120, the input voltage VIN charges the inductor 104; conversely, when the transistor switch 120 is not turned on by the pulse driving signal PS, the inductor 104 transmits the induced current IL, thereby generating The voltage VOUT is output and a diode current IOUT flowing through the LED 102 is generated in each channel, and the brightness of the LED 102 varies according to the magnitude of the diode current IOUT through which it flows.

In operation, when the LED driver 100 starts to start, the multiplexer 170 selects the start feedback voltage SFB as the compensation feedback voltage FB for the initial push-up action of the output voltage VOUT, and when the output voltage VOUT is increased to At a specific value, the multiplexer 170 selects the operation feedback voltage OFB as the compensation feedback voltage FB for the successive push-up operation of the output voltage VOUT.

Specifically, when the LED driver 100 starts to start, the compensation feedback voltage FB is 0V, and the reference voltage VREF gradually increases from 0V, so that the compensation signal VC is generated, and the output voltage VOUT thus gradually increases from 0V. When the output voltage VOUT is increased to a specific value, the LED feedback voltage LFB is thereby generated and gradually increased. At this time, the start feedback circuit 150 correspondingly generates the start feedback voltage SFB, and is selectively released by the multiplexer 170 as the compensation feedback voltage FB.

When the start feedback voltage SFB and the reference voltage VREF are increased to a certain value, the so-called soft-start program of the conventional knowledge is completed, and the slow start signal SEL is transmitted to the multiplexer 170. The multiplexer 170 is caused to switch, and the operation feedback voltage OFB generated by the operation feedback circuit 160 is selected as the compensation feedback voltage FB, and the push-up operation of the output voltage VOUT is continued.

FIG. 2 is a block diagram showing a start feedback circuit as shown in FIG. 1 according to an embodiment of the invention. The start feedback circuit may further include a plurality of feedback sub-circuits 200 connected in parallel with each other and a resistance unit 210 (eg, a resistor R) connected to the feedback sub-circuit 200, wherein each of the feedback sub-circuits 200 receives one The corresponding LEDs feedback the voltage LFB and thereby output an output current. In the present embodiment, the start feedback circuit includes eight feedback sub-circuits 200, wherein the first feedback circuit 200 outputs an output current IS1, the second feedback circuit 200 outputs an output current IS2, and so on. Then, the resistance unit 210 converts the total current composed of the currents IS1, IS2, ..., and IS8 into the start feedback voltage SFB.

FIG. 3 is a block diagram showing a feedback sub-circuit as shown in FIG. 2 according to an embodiment of the invention. The feedback sub-circuit 200 includes a first current unit 310, a second current unit 320, a third current unit 330, a fourth current unit 340, and a mirror unit 350. The first current unit 310 is biased by a low level supply voltage (eg, ground voltage GND) to assert the first current source I1. The second current unit 320 generates a second current source I2 according to the first current source I1. The third current unit 330 receives one of the LED feedback voltages LFB to generate a first current and a first control voltage FC. The fourth current unit 340 receives the first control voltage FC to generate a third current source I3 mirrored by the second current source I2, and induces a fourth current I4 corresponding to the first control voltage FC. The mirroring unit 350 generates a fourth current I4 (or a mirror current) and mirrors the fourth current I4 to generate an output current IS corresponding to the fourth current I4, thereby generating a start feedback voltage SFB. In the present embodiment, when the LED feedback voltage LFB is increased, the first control voltage FC is increased, so that the fourth current I4 and the start feedback voltage SFB are thus increased.

In this embodiment, the first current unit 310 further includes a first P-type transistor (eg, a P-type metal oxide semiconductor field effect transistor MP1), wherein the gate of the transistor MP1 is biased by the ground voltage GND. The source of the transistor MP1 is coupled to the high level supply voltage VD via the first current source I1, and the drain of the transistor MP1 is coupled to the ground voltage GND. The second current unit 320 further includes a first N-type transistor (eg, an N-type metal oxide semiconductor field effect transistor MN1), wherein the gate of the transistor MN1 is coupled to the source of the transistor MP1, and the transistor MN1 The drain is coupled to the high level supply voltage VD via the second current source I2, and the source of the transistor MN1 is coupled to the ground voltage GND.

The third current unit 330 further includes a second P-type transistor (eg, P-type metal oxide semiconductor field effect transistor MP2), wherein the gate of the transistor MP2 receives the LED feedback voltage LFB, and the source of the transistor MP2 is via The first current source I1 is coupled to the high level supply voltage VD, and the drain of the transistor MP2 is coupled to the ground voltage GND. The fourth current unit 340 further includes a second N-type transistor (eg, an N-type metal oxide semiconductor field effect transistor MN2), wherein the gate of the transistor MN2 is coupled to the source of the transistor MP2, and the transistor MN2 The drain is coupled to the high level supply voltage VD via the third current source I3, and the source of the transistor MN2 is coupled to the ground voltage GND.

The mirror unit 350 is composed of a third P-type transistor (such as a P-type metal oxide semiconductor field effect transistor MP3) and a fourth P-type transistor (such as a P-type metal oxide semiconductor field effect transistor MP4). The gate of the transistor MP3 is coupled to the drain and coupled to the drain of the transistor MN2, the gate of the transistor MP4 is coupled to the gate of the transistor MP3, and the drain of the transistor MP4 is via the resistor unit. The 210 is coupled to the ground voltage GND and generates an output current IS corresponding to the fourth current I4 generated by the transistor MP3, and the sources of the transistors MP3 and MP4 are coupled to the high level supply voltage VD. In an embodiment, the size of the transistor MN1 is the same as the size of the transistor MN2.

In operation, when the LED driver starts to start, the transient voltage of the LED feedback voltage LFB is 0V. At this time, the fourth current I4 and the output current IS have not yet been generated. Then, as the voltage LFB gradually increases, the voltage FC increases, so that the current I4 is thus generated and gradually increased, and the current IS is also generated and gradually increased. In this way, the feedback voltage SFB can be correspondingly generated and gradually increased, thereby being selected as the compensation feedback voltage FB (as shown in FIG. 1). Then, when the feedback voltage SFB is increased to a certain value, the slow start procedure is completed. The voltage OFB is then replaced by the voltage SFB for selection as the compensated feedback voltage FB (as described above). Therefore, the feedback voltage SFB generated by the start feedback circuit can be used to ensure that the LED driver can operate or start normally when starting up, regardless of whether the operation feedback circuit is associated with the LED driver startup procedure.

According to the embodiment of the present invention, the LED driver and the initiating feedback circuit thereof can ensure that the LED driver is normally and well operated when the LED driver starts to be activated, thereby stably Drive the light-emitting diode.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

100. . . LED driver

102. . . Light-emitting diode

104. . . inductance

110. . . Drive unit

120. . . Transistor switch

130. . . Comparators

140. . . Error amplifier

150. . . Start feedback circuit

152. . . Start the first end of the feedback circuit

160. . . Operation feedback circuit

162. . . Operating the second end of the feedback circuit

170. . . Multiplexer

200. . . Feedback subcircuit

210. . . Resistor unit

310. . . First current unit

320. . . Second current unit

330. . . Third current unit

340. . . Fourth current unit

350. . . Mirror unit

FIG. 1 is a block diagram showing a light emitting diode (LED) driver according to an embodiment of the invention.

FIG. 2 is a block diagram showing a start feedback circuit as shown in FIG. 1 according to an embodiment of the invention.

FIG. 3 is a block diagram showing a feedback sub-circuit as shown in FIG. 2 according to an embodiment of the invention.

100. . . LED driver

102. . . Light-emitting diode

104. . . inductance

110. . . Drive unit

120. . . Transistor switch

130. . . Comparators

140. . . Error amplifier

150. . . Start feedback circuit

152. . . Start the first end of the feedback circuit

160. . . Operation feedback circuit

162. . . Operating the second end of the feedback circuit

170. . . Multiplexer

Claims (20)

A start feedback circuit in a light-emitting diode driver, the start feedback circuit comprising at least one feedback circuit comprising: a first current unit biased by a ground voltage to Generating a first current; a second current unit for generating a second current according to the first current; and a third current unit for receiving a light-emitting diode feedback voltage to generate the first current and a first control voltage; a fourth current unit for receiving the first control voltage to generate a third current that is mirrored by the second current, and inducing a corresponding one of the first control voltages a fourth current; and a mirror unit for generating the fourth current, and mirroring the fourth current to generate an output current corresponding to one of the fourth currents, the output current is converted into a feedback voltage to boost The output voltage of one of the LED drivers and the LED feedback voltage corresponding to the output voltage. The initiation feedback circuit of claim 1, wherein the feedback voltage and the fourth current increase when the feedback voltage of the LED is increased. The initiation feedback circuit of claim 1, wherein the first current unit comprises a first P-type transistor, the first P-type transistor is biased by the ground voltage, and the third current unit comprises A second P-type transistor is used to receive the LED feedback voltage. The initiation feedback circuit of claim 3, wherein the first P-type transistor and the second P-type transistor are P-type metal oxide semiconductor field effect transistors. A start feedback circuit in a light-emitting diode driver, the start feedback circuit comprising at least one feedback circuit comprising: a first P-type transistor having a first control terminal and a first end, the first control end is biased by a low level supply voltage, the first end is coupled to a high level supply voltage via a first current source; a first N-type transistor having a second control end coupled to the first end of the first P-type transistor, the second end coupled to the high level via a second current source a power supply voltage; a second P-type transistor having a third control end and a third end, the third control end is configured to receive a light-emitting diode feedback voltage, the third end is via the first The current source is coupled to the high-level power supply voltage; a second N-type transistor has a fourth control end and a fourth end, the fourth control end is coupled to the second P-type transistor a third end, the fourth end is mirrored by the second current source, and a third current source is coupled to the a level power supply voltage; and a mirror unit, comprising a third P-type transistor and a fourth P-type transistor, the third P-type transistor having a fifth control end and a fifth end, The fifth control end is coupled to the fifth end and coupled to the fourth end of the second N-type transistor, the fourth P-type transistor has a sixth control end and a sixth end, the sixth The control end is coupled to the fifth control end of the third P-type transistor, and the sixth end is coupled to the low-level power supply voltage via a resistor unit and generates an output current, wherein the output current is generated by the resistor The unit is converted to a feedback voltage to boost the output voltage of one of the LED drivers and the LED feedback voltage corresponding to the output voltage. The initiation feedback circuit of claim 5, wherein the third P-type electro-crystal system generates a mirror current corresponding to the output current according to the LED feedback voltage. The initiation feedback circuit of claim 6, wherein the mirror current and the feedback voltage increase when the feedback voltage of the LED is increased. The initiation feedback circuit of claim 5, wherein the first, second, third, and fourth P-type transistors are P-type metal oxide semiconductor field effect transistors, the first and second N The type of transistors are all N-type metal oxide semiconductor field effect transistors. A light-emitting diode driver includes: a start feedback circuit having a plurality of first ends for receiving a plurality of light-emitting diode feedback voltages, each of the light-emitting diode feedback voltages being at least one The light emitting diode is coupled to the light emitting diode driver for outputting an output voltage output terminal, and the starting feedback circuit is based on the light emitting diodes The feedback voltage generates a start feedback voltage; an operation feedback circuit has a plurality of second ends for receiving the light-emitting diode feedback voltages, and the operation feedback circuit is based on the light-emitting diodes The voltage is generated to generate an operation feedback voltage; and a multiplexer coupled to the start feedback circuit and the operation feedback circuit to select the initial feedback voltage or the operation feedback voltage; wherein the illumination When the diode driver starts to start, the multiplexer selects the start feedback voltage to start to push up the output voltage, and when the output voltage increases to a specific value, the multiplexer selects the operation feedback voltage to continue Push up the output voltage. The light-emitting diode driver of claim 9, wherein the start feedback circuit further comprises a plurality of feedback sub-circuits, each of the feedback sub-circuits comprising: a first current unit, which is performed by a ground voltage Biasing to generate a first current; a second current unit for generating a second current according to the first current; and a third current unit for receiving one of the LED feedback voltages And generating a first current and a first control voltage; a fourth current unit for receiving the first control voltage to generate a third current mirrored by the second current, and inducing Corresponding to a fourth current of the first control voltage; and a mirroring unit for generating the fourth current and mirroring the fourth current to generate an output current corresponding to one of the fourth currents. The illuminating diode driver of claim 10, wherein the start feedback circuit further comprises a resistor unit, wherein the resistor unit is configured to form one of the output currents generated by the feedback subcircuits The total current is converted to the initial feedback voltage. The illuminating diode driver of claim 10, wherein the initial feedback voltage and the fourth current increase when the illuminating diode feedback voltage received by the third current unit increases. The illuminating diode driver of claim 9, wherein the start feedback circuit further comprises a plurality of feedback subcircuits, each of the feedback subcircuits comprising: a first P-type transistor having a first a control terminal and a first terminal, the first control terminal is biased by a low level power supply voltage, the first end is coupled to a high level power supply voltage via a first current source; a first N type The transistor has a second control end coupled to the first end of the first P-type transistor, and the second end is coupled via a second current source The second P-type transistor has a third control terminal and a third terminal, and the third control terminal is configured to receive one of the LED feedback voltages. The third end is coupled to the high level power supply voltage via the first current source; the second N type transistor has a fourth control end and a fourth end, and the fourth control end is coupled to the first The third end of the second P-type transistor, the fourth end is mirrored by the second current source a three current source coupled to the high level supply voltage; and a mirror unit comprising a third P-type transistor and a fourth P-type transistor, the third P-type transistor having a fifth control terminal And a fifth end, the fifth control end is coupled to the fifth end and coupled to the fourth end of the second N-type transistor, the fourth P-type transistor has a sixth control end and a a sixth end, the sixth control end is coupled to the fifth control end of the third P-type transistor, the sixth end is coupled to the low level power supply voltage via a resistor unit and generates a corresponding fourth One of the currents outputs current. The illuminating diode driver of claim 9, wherein the operation feedback circuit generates the operational feedback voltage according to one of the minimum illuminating diode feedback voltages of the illuminating diode feedback voltages. The illuminating diode driver of claim 9, wherein the start feedback circuit further comprises a plurality of feedback subcircuits coupled in parallel with each other. A light-emitting diode driver includes: a start-up feedback circuit having a plurality of first ends, each of the first ends being coupled to the LED driver via at least one light-emitting diode Outputting an output voltage, the first end is configured to receive a plurality of LED feedback voltages, and each of the LED feedback voltages is transmitted by the LED The start feedback circuit generates a start feedback voltage according to the LED feedback voltages; an operation feedback circuit has a plurality of second ends, each of the second ends is via the illumination The diode is coupled to the output end of the LED driver, and the second ends are configured to receive the LED feedback voltages, and each of the LED feedback voltages is configured by the LEDs Transmitted by the LED, the operation feedback circuit generates an operation feedback voltage according to the LED feedback voltages; a multiplexer is selected when the LED driver starts to start The start feedback voltage, or the output voltage is increased to one Selecting the operation feedback voltage when setting; and a compensation unit for comparing the initial feedback voltage and a reference voltage to output a compensation signal for the initial push-up action of the output voltage, or comparing the operation The voltage and the reference voltage are fed back to output the compensation signal for the successive push-up action of the output voltage. The light-emitting diode driver of claim 16, wherein the start feedback circuit further comprises a plurality of feedback sub-circuits, each of the feedback sub-circuits comprising: a first current unit, which is performed by a ground voltage Biasing to generate a first current; a second current unit for generating a second current according to the first current; and a third current unit for receiving one of the LED feedback voltages And generating a first current and a first control voltage; a fourth current unit for receiving the first control voltage to generate a third current mirrored by the second current, and inducing Corresponding to a fourth current of the first control voltage; and a mirroring unit for generating the fourth current and mirroring the fourth current to generate an output current corresponding to one of the fourth currents. The illuminating diode driver of claim 17, wherein the starting feedback circuit further comprises a resistor unit, wherein the resistor unit is configured to form one of the output currents generated by the sub-circuits The total current is converted to the initial feedback voltage. The illuminating diode driver of claim 16, wherein the start feedback circuit further comprises a plurality of feedback sub-circuits coupled in parallel with each other. The light-emitting diode driver of claim 16, wherein the start feedback circuit further comprises a plurality of feedback sub-circuits, each of the feedback sub-circuits comprising: a first P-type transistor having a first a control terminal and a first terminal, the first control terminal is biased by a low level power supply voltage, the first end is coupled to a high level power supply voltage via a first current source; a first N type The transistor has a second control end coupled to the first end of the first P-type transistor, and the second end is coupled via a second current source The second P-type transistor has a third control terminal and a third terminal, and the third control terminal is configured to receive one of the LED feedback voltages. The third end is coupled to the high level power supply voltage via the first current source; the second N type transistor has a fourth control end and a fourth end, and the fourth control end is coupled to the first The third end of the second P-type transistor, the fourth end is mirrored by the second current source a three current source coupled to the high level supply voltage; and a mirror unit comprising a third P-type transistor and a fourth P-type transistor, the third P-type transistor having a fifth control terminal And a fifth end, the fifth control end is coupled to the fifth end and coupled to the fourth end of the second N-type transistor, the fourth P-type transistor has a sixth control end and a a sixth end, the sixth control end is coupled to the fifth control end of the third P-type transistor, the sixth end is coupled to the low level power supply voltage via a resistor unit and generates a corresponding fourth One of the currents outputs current.