CN206433225U - A piecewise linear constant current LED drive circuit - Google Patents

Abstract

The utility model discloses a kind of piecewise linearity constant current LED drive circuit, it includes rectifier bridge and carries out full-wave rectification to 220V/50Hz sinusoidal voltage waveform, is connect with high voltage stabilizing reduction voltage circuit and LED series winding；High voltage stabilizing reduction voltage circuit：RC circuits are charged using high-voltage LDMOS pipe, regulated output voltage is obtained by linear voltage-stabilizing circuit, is connected with output reference voltage circuit；Output reference voltage circuit：Output reference voltage, is connected with linear constant current circuit；Linear constant current circuit：Managed by the use of integrated high-voltage power pipe as adjustment, adjusted and managed by feedback control, realize constant current output；The LED drive circuit for solving prior art has used electrochemical capacitor, easily influenceed by operating temperature, the volatilization of generation electrolyte, leakage, the problems such as capacitance declines causes capacitance aging, service life is substantially reduced, the service life of driving power supply is have impact on, and then reduces the technical problems such as the service life of the whole lamps of LED.

Description

A piecewise linear constant current LED drive circuit

technical field

The utility model belongs to the technology of LED drive power supply, in particular to a segmented linear constant current LED drive circuit.

Background technique

In the 21st century, as a solid-state light source, LED is a typical green lighting source, which has the characteristics of long life, high luminous efficiency, and low power consumption. In LED lighting technology, the driving of the power supply is very important, which involves the service life of the LED lamp and various electrical properties. So far, LED driving power has been roughly developed into switching power supply and linear power supply. Switching power supply has the advantages of high efficiency and low power consumption. However, due to the circuit structure, the circuit has serious interference. These switching interferences may be connected to the power grid in series. Interfere with nearby electrical equipment and affect the normal operation of other electrical appliances. The linear power supply has almost no electromagnetic interference problem, and the output current and voltage ripple is small. In the occasions where the quality of engineering applications is high, the linear power supply has obvious advantages. LED is a current type device, which has high requirements for constant current, so LED drive is generally a constant current drive power supply. The service life of the LED light source is generally 30000-50000h, so the service life of the driving power supply is required to be higher than the service life of the LED light source in order to ensure the service life of the entire LED light. However, due to the use of electrolytic capacitors in the circuit, they are easily affected by the working temperature. Problems such as electrolyte volatilization, leakage, and capacitance drop cause the capacitor to age, and the service life is greatly reduced, which affects the service life of the driving power supply, thereby reducing the LED lamp. Therefore, the performance of the driving power supply is an important factor affecting the development of LED lighting.

Utility model content

The technical problem to be solved by the utility model: provide a piecewise linear constant current LED driving circuit to solve the problem that the LED driving circuit in the prior art uses electrolytic capacitors, which are easily affected by the working temperature, and the electrolyte volatilization and leakage occur, and the capacitance Problems such as capacity reduction lead to aging of the capacitor and a greatly reduced service life, which affects the service life of the driving power supply, thereby reducing the service life of the LED lamp and other technical problems.

Technical scheme of the utility model:

A segmented linear constant current LED drive circuit, which includes:

Rectifier bridge: perform full-wave rectification on the sinusoidal voltage waveform of 220V/50Hz, and connect with the high-voltage voltage regulator and step-down circuit and LED light string;

High-voltage voltage regulator and step-down circuit: use high-voltage LDMOS tube to charge the RC circuit, obtain a stable output voltage through a linear voltage regulator circuit, and connect it to the output reference voltage circuit;

Output reference voltage circuit: output reference voltage, connected with linear constant current circuit;

Linear constant current circuit: use the integrated high-voltage power tube as the adjustment tube, and control the adjustment tube through the feedback signal to achieve constant current output.

It also includes protection circuits that provide undervoltage protection, overtemperature protection, overvoltage protection, and overcurrent protection.

The rectifier bridge is a full-wave rectifier bridge, which converts 220V/50Hz alternating current into 0-311V direct current pulsating high voltage.

The high-voltage stabilizing and step-down circuit includes a resistor R0, which provides the gate terminal voltage for the LDMOS0 tube, the resistor R1 and the capacitor C0 are connected in series to the source terminal of the LDMOS0 tube, the drain terminal of the LDMOS0 tube is connected to the input voltage, and the voltage at both ends of the capacitor C0 is The voltage is stabilized by resistor R2 and Zener diode Zener1, P-type field effect transistors Mp1, Mp2, Mp4, Mp5 and N-type field effect transistors Mn1, Mn2, Mn3, Mn4 form a cascode structure, and resistors R3 and R4 are common The source common gate structure provides bias, the bases of the bipolar transistors Q1 and Q2 are connected to the ground, and the P-type field effect transistors Mp3 and Mp6 form a current mirror. The mirror current obtains the reference voltage Vref1 through the resistor R6 and the bipolar transistor Q3, and the error amplifier The inverting terminal of OPA0 is connected to the reference voltage Vref1, the resistors R7 and R8 are connected in series to form a feedback network, the feedback voltage on the resistor R8 is connected to the non-inverting terminal of the error amplifier OPA0, and the output terminal of the error amplifier OPA0 is connected to the gate terminal of the power transistor Mp40.

The output reference voltage circuit includes P-type field effect transistors Mp7, Mp8, Mp9, Mp10, P-type field effect transistors Mp7, Mp8, Mp9, Mp10 and N-type field effect transistors Mn5, Mn6, Mn7, Mn8 form a cascode structure, Resistors R11 and R12 provide bias for the cascode structure, the bases of bipolar transistors Q4 and Q5 are connected to ground, P-type field effect transistor Mp11 and P-type field effect transistor Mp12 form a current mirror, and the mirror current flows through resistors R10 and The transistor Q6 obtains the reference voltage of the first-order temperature compensation, and the reference voltage of the first-order temperature compensation passes through the unity gain buffer formed by the error amplifier OPA5 to obtain the reference voltage Vref2, and the resistors R13, R14, R15, R16, and R17 form a resistor divider structure , four reference voltages can be obtained, the N-type field effect transistor Mn13 is connected in parallel with the resistor R13, and the gate terminal of the N-type field effect transistor Mn13 is connected to the output signal EN of the level conversion circuit.

The linear constant current circuit includes LED light strings, LDMOS tubes, operational amplifiers and external sampling resistors. When the input external voltage reaches the forward conduction voltage drop of the LED light strings, the LDMOS tubes and the external sampling resistors form a path, and the sampling A voltage drop is generated on the resistor, and the voltage value is connected to the reverse terminal of the operational amplifier as a feedback signal. The same direction terminal of the operational amplifier is connected to a corresponding reference voltage in the reference voltage circuit, and the output terminal of the operational amplifier is connected to the grid terminal of the LDMOS transistor.

The reference voltage circuit includes at least four reference voltage outputs, and a level conversion circuit is externally connected to the enable end of the output reference voltage circuit to control the voltage value of the reference voltage output, thereby generating two sets of output reference voltages, providing two Set different reference voltages.

The beneficial effects of the utility model:

The segmented linear constant current LED driving circuit of the utility model adopts an internal step-down method, integrates a high-voltage power tube inside, and integrates the driving power on a chip. Small interference and other characteristics; the circuit can be directly applied to the mains, the AC input voltage range is wide, and the operating temperature range is wide, and the protection circuit is perfect; it solves the problem that the LED drive circuit in the prior art uses electrolytic capacitors and is easily affected by the operating temperature , Electrolyte volatilization, leakage, capacitor capacity decline and other problems lead to capacitor aging, greatly reducing the service life, affecting the service life of the driving power supply, and further reducing the service life of the LED lamp and other technical problems.

Description of drawings

Fig. 1 is a schematic structural representation of the utility model principle;

Figure 2 and Figure 3 are schematic diagrams of device wiring in the embodiment of the present invention;

FIG. 4 is a schematic diagram of input voltage and output current waveforms according to an embodiment of the present invention.

detailed description

A segmented linear constant current LED drive circuit, which includes (see Figure 1):

Rectifier bridge: perform full-wave rectification on the sinusoidal voltage waveform of 220V/50Hz, and connect with the high-voltage voltage regulator and step-down circuit and LED light string;

High-voltage voltage regulator and step-down circuit: use high-voltage LDMOS tube to charge the RC circuit, obtain a stable output voltage through a linear voltage regulator circuit, and connect it to the output reference voltage circuit;

The reference voltage circuit is a multi-value output reference voltage circuit, including at least four reference voltage outputs, and a level conversion circuit is externally connected to the enable end of the output reference voltage circuit to control the voltage value of the reference voltage output, thereby generating two sets of output reference voltages, Two sets of different reference voltages are provided for the linear constant current circuit.

Linear constant current circuit: use the integrated high-voltage power tube as the adjustment tube, and control the adjustment tube through feedback to achieve constant current output.

It also includes protection circuits that provide undervoltage protection, overtemperature protection, overvoltage protection, and overcurrent protection.

The rectifier bridge is a full-wave rectifier bridge, which converts 220V/50Hz alternating current into 0-311V direct current pulsating high voltage. The reverse withstand voltage of the diode on each bridge arm is above 700V, and the forward current capacity is above 300mA.

The high-voltage voltage stabilizing and step-down circuit includes an LDMOS tube and an external capacitor C. The LDMOS tube and the external capacitor C form an RC charging branch, and the voltage stabilization value is obtained through the Zener diode Zener1 for the front reference voltage source and the linear voltage regulator. The regulator works, the pre-reference voltage source generates the voltage Vref1 as the reference voltage of the linear regulator, and the voltage across the capacitor C is used as the input voltage of the linear regulator.

The technical scheme of the utility model is described in detail below through specific embodiments (see Fig. 2, Fig. 3):

The rectifier bridge adopts a full-wave rectifier bridge, which converts 220V/50Hz AC power into 0-311V DC pulsating high voltage; the reverse withstand voltage of the diode on each bridge arm is required to be above 700V, and the forward current capacity is above 300mA.

High-voltage regulator step-down circuit 2, the LDMOS tube used in the circuit is a high-voltage LDMOS0 and an external capacitor C0 to form an RC charging branch, and the regulated value is obtained through the Zener diode Zener1 for the pre-reference voltage source and linear regulator Work, the pre-reference voltage source generates the reference voltage Vref1 as the reference voltage of the linear regulator, the error amplifier OPA0 adjusts the gate voltage of the power transistor Mp40 according to the change of the feedback voltage, so that the output voltage VDD is stable, and the appropriate parameters of the power transistor Mp40 are set. The output voltage VDD has a certain load capacity and is used as the working voltage of the low-voltage module of the chip.

The specific structure of the high-voltage voltage regulator and step-down circuit is as follows: the resistor R0 provides the gate terminal voltage for the LDMOS0 tube, the resistor R1 and the capacitor C0 are connected in series to the source terminal of the LDMOS0 tube, the drain terminal of the LDMOS0 tube is connected to the input voltage, and the voltage at both ends of the capacitor C0 is passed through Resistor R2 and Zener diode Zener1 stabilize the voltage, P-type field effect transistors Mp1, Mp2, Mp4, Mp5 and N-type field effect transistors Mn1, Mn2, Mn3, Mn4 form a cascode structure, and resistors R3 and R4 are common sources The common gate structure provides bias. The emitter junction area of the bipolar transistor Q1 is 8 times that of the bipolar transistor Q2. The bases of the bipolar transistors Q1 and Q2 are connected to the ground. The resistance value of the resistor R5 can change the reference current of the circuit. P-type field effect transistors Mp3 and Mp6 form a current mirror, and the mirror current passes through the resistor R6 and the bipolar transistor Q3 to obtain the reference voltage Vref1 for first-order temperature compensation, the inverting terminal of the error amplifier OPA0 is connected to the reference voltage Vref1, resistors R7, R8 The feedback network is formed in series, the feedback voltage on the resistor R8 is connected to the non-inverting terminal of the error amplifier OPA0, and the output terminal of the error amplifier OPA0 is connected to the gate terminal of the power transistor Mp40 (the D-S withstand voltage of the power transistor Mp40 is 40V), and the operational amplifier adjusts the power according to the feedback voltage The gate-source voltage of the tube Mp40 makes the power tube Mp40 in a linear state, making the output voltage VDD stable.

The output reference voltage circuit is a multi-value output reference voltage circuit, including a bandgap reference voltage source, a buffer, a resistor divider network and an enabling terminal, and the working voltage of the output reference voltage circuit is the output voltage of a linear voltage regulator, with The gap reference voltage source outputs the reference voltage, and the four output reference voltages are obtained after the buffer and the resistor divider network, and an enabling terminal is added to the resistor divider network to control the voltage value of the four output reference voltages, thereby generating two groups of four output reference voltage.

In this embodiment, the output reference voltage circuit 3 is mainly composed of three parts: a reference voltage source, a buffer and a resistor divider network. The reference voltage source uses the weight of the voltage with the opposite temperature coefficient to be added in an appropriate ratio to obtain a reference voltage with zero temperature coefficient, and is less affected by input voltage fluctuations. The reference voltage Vref2 can be obtained through the buffer, and the voltage is divided proportionally by the resistor Finally, multiple reference voltages can be obtained, and the buffer ensures that the characteristics of the reference voltages are the same as those of the reference voltage Vref2. A switch tube Mn13 is added to the resistor voltage divider network, which can control the switch tube Mn13 to be turned on and off according to the enable signal EN, thereby changing the ratio of the resistor voltage divider network to change the output reference voltage. The enable signal has two states, so the reference voltage will output two sets of different voltage values accordingly.

Specific circuit structure: P-type field effect transistors Mp7, Mp8, Mp9, Mp10 and N-type field effect transistors Mn5, Mn6, Mn7, and Mn8 form a cascode structure, and resistors R11 and R12 provide bias for the cascode structure. The emitter junction area of the bipolar transistor Q4 is 8 times that of the bipolar transistor Q5. The bases of the bipolar transistor Q4 and Q5 are connected to the ground. The resistance value of the resistor R9 can change the reference current of the circuit. The P-type field effect transistors Mp11 and P Type field effect transistor Mp12 constitutes a current mirror, and the mirror current flows through resistor R10 and transistor Q6 to obtain a reference voltage for first-order temperature compensation. , R14, R15, R16, and R17 form a resistor divider structure to obtain four reference voltages. The N-type field effect transistor Mn13 is connected in parallel with R13, and the gate terminal of the N-type field effect transistor Mn13 is connected to the output signal EN of the level conversion circuit.

The linear constant current circuit includes an LED light string, an LDMOS tube, an operational amplifier and an external sampling resistor. When the input external voltage reaches the forward conduction voltage drop of the LED light string, the LDMOS tube and the external sampling resistor form a path, and A voltage drop is generated on the sampling resistor, and the voltage value is connected to the reverse terminal of the operational amplifier as a feedback signal, the same direction terminal of the operational amplifier is connected to the corresponding reference voltage in the reference voltage circuit, and the output terminal of the operational amplifier is connected to the grid terminal of the LDMOS transistor.

The linear constant current circuit 4 in this embodiment is mainly composed of an operational amplifier OPA1, a high voltage LDMOS1 and a sampling resistor Rsen. When the input voltage does not reach the forward conduction voltage value of the first string of LED lights N1, no current flows through the sampling resistor, and the voltage drop is 0, so the operational amplifier OPA1 outputs a high level, making the gate-source voltage of the high-voltage LDMOS1 greater than the threshold voltage ;When the input voltage rises to the forward voltage drop of the first string of LED lights N1, the drain-source current of LDMOS1 starts to increase and flows through the sampling resistor, and the voltage drop on the sampling resistor also gradually rises and is fed back to the inverting terminal of the op amp , OPA1 adjusts LDMOS1 to stabilize the output current through the change of the input terminal voltage, so that the LED light string 1 works with a constant current. The linear constant current circuits 4, 5, 6, and 7 work on the same principle.

Circuit structure: The positive terminal of LED light string N1 is connected to the input voltage, the reverse terminal is connected to the drain of LDMOS1, the source of LDMOS1 is connected to the sampling resistor Rsen, and the voltage drop of the resistor Rsen is connected to the inverting terminal of the operational amplifier OPA1 as the feedback voltage. The same-phase terminal of OPA1 is connected to the reference voltage V1 or V11 (V1 and V11 are controlled by the enable signal EN), the output of the operational amplifier is connected to the gate terminal of LDMOS1, and the output of OPA1 controls the on-resistance of LDMOS1 through the feedback voltage change, and the circuit realizes constant Stream work, Out_pt is connected with the protection module to realize the protection function. The linear constant current circuits 4, 5, 6, and 7 in Fig. 2 and Fig. 3 have the same structure.

The input signal of the level conversion circuit is an external induction signal, and the output signal controls the enable terminal in the reference voltage circuit, thereby generating two sets of output reference voltages, providing two sets of different reference voltages for the linear constant current circuit;

In the level conversion circuit 8 in this embodiment, the external induction signal EN_Vin can be adjusted to be consistent with the working voltage level of the chip after the external induction signal EN_Vin passes through the level conversion circuit to obtain the output enable signal EN. The output enable signal EN reflects the external induction signal, and by controlling the enable terminal of the output reference voltage circuit, the output reference voltage circuit outputs two sets of different reference voltages, and the switchable LED is in two different working states.

Circuit structure: the gate terminals of the P-type field effect transistor Mp13 and the N-type field effect transistor Mn9 are connected, and the drain terminals are connected to form an inverter, and the input of the inverter is connected to EN_Vin. The gate terminal of the N-type field effect transistor Mn10 is connected to the input end of the inverter, and the gate terminal of the N-type field effect transistor Mn11 is connected to the output end of the inverter. Under the external induction signal EN_Vin signal, the N-type field effect transistor Mn10 and the N-type Only one of the FET Mn11 will be turned on, the P-type FET Mp14 is connected to the drain end of the N-type FET Mn10, the P-type FET Mp15 is connected to the drain end of the N-type FET Mn11, and the P-type FET is connected to the drain end of the N-type FET Mn11. The gate terminal of Mp14 is connected to the drain terminal of the N-type field effect transistor Mn11, the gate terminal of the P-type field effect transistor Mp15 is connected to the drain terminal of the N-type field effect transistor Mn10, and a voltage Vx consistent with the EN_Vin signal level can be obtained at point X ( Vx high level is VDD, low level is GND), P-type field effect transistor Mp16 is connected to N-type field effect transistor Mn12 gate to form a first-stage inverter, P-type field effect transistor Mp17 and N-type field effect The gates of the transistors Mn13 are connected to form a second-stage inverter. The two-stage inverters can play a shaping role, and the enable signal EN is obtained at the drain terminals of the P-type field effect transistor Mp17 and the N-type field effect transistor Mn13.

The protection circuit 9 is composed of an over-temperature protection circuit, an over-voltage protection circuit and an over-current protection circuit. When the circuit operation exceeds the limit set by the protection circuit, the protection circuit will be triggered to generate the protection enable signal out_pt, thereby controlling the operation of the power tube and preventing the chip from being damaged due to abnormal operation.

The working principle of the utility model: after the AC power of the input city power is 220V/50Hz is rectified by the rectifier bridge, a pulsating DC high voltage can be obtained at the two output ports of the rectifier bridge. pulsating voltage. This voltage not only provides the working voltage for the high-voltage voltage regulator and step-down circuit, but also serves as the input voltage of the LED light source. The high-voltage stabilizing and step-down circuit can stabilize the working voltage of the output chip before the first string of lamp beads are forward-conducting, so as to ensure the normal operation of the chip. The multi-value output reference voltage circuit generates four reference voltages as the reference voltages of the four sets of linear constant current circuits (V1<V2<V3<V4), which are respectively connected to the same direction terminals of the operational amplifiers in the four sets of linear constant current circuits. , the input terminals of the power tubes of the four linear constant current circuits are respectively connected to a set of LED light strings, and the four sets of LED light strings are connected in series (attached drawings 1 and 3). Since the input voltage does not reach the forward conduction voltage of the lamp bead, there is no current flowing in the circuit, the voltage on the sampling resistor is zero, that is, the feedback voltage is zero, so the output of the op amp is all high level, so that the gate-source of the four LDMOS voltages are greater than the threshold voltage.

In the rising stage of the input voltage, when the input voltage rises to the forward voltage drop of the LED lamp string N1, the LDMOS1 in the first group of linear constant current circuits is in the conduction state, the LED lamp string N1 is lit, and the current is controlled by the first group of linear constant current circuits. Constant current circuit control, the current value is V1/Rsen. When the input voltage reaches the forward conduction voltage of the light string N1 and the LED light string N2, due to the increase of the current of the branch circuit, the feedback voltage becomes larger, so that the output of the operational amplifier of the first group of linear constant current circuits is low level, thus The LDMOS1 of the first group is turned off, and the LED light string N1, the LED light string N2 and LDMOS2 form a branch circuit, and the current is controlled by the second linear constant current circuit, and the current value is V2/Rsen. When the input voltage rises to the forward conduction voltage of LED light string N1, LED light string N2 and LED light string N3, due to the increase of branch current, the feedback voltage becomes larger, thus turning off the second group of LDMOS2, LED light string N1, LED light string N2, LED light string N3 and LDMOS3 form a branch circuit, the current is controlled by the third linear constant current circuit, and the current value is V3/Rsen. As the input voltage rises to the forward conduction voltage of LED light string N1, LED light string N2, LED light string N3 and LED light string N4, turn off the third group of LDMOS3, LED light string N1, LED light string N2, LED light string N3, LED light string N4 and LDMOS4 form a branch circuit, the current is controlled by the fourth linear constant current circuit, and the current value is V4/Rsen. In the stage of input voltage drop, the working order of the four sets of linear constant current circuits is opposite to that of the input voltage rise stage. Since the multi-value output reference voltage voltage can be controlled by the enable terminal, when the enable signal is invalid, the circuit output reference voltage is V1:V2:V3:V4, and the output current is V1/Rsen:V2/Rsen:V3/Rsen:V4 /Rsen. When the enable signal is valid, the circuit output reference voltage is V11:V22:V33:V44, and the output current is V11/Rsen:V22/Rsen:V33/Rsen:V44/Rsen. In this way, the circuit can work in two working current modes. The circuit can change the working current of the circuit by adjusting the resistance value of the external sampling resistor Rsen according to the application occasion and the specification of the LED lamp bead.

Claims (7)

1. a kind of piecewise linearity constant current LED drive circuit, it includes：

Rectifier bridge：Full-wave rectification is carried out to 220V/50Hz sinusoidal voltage waveform, with high voltage stabilizing reduction voltage circuit and LED string Connection；

High voltage stabilizing reduction voltage circuit：RC circuits are charged using high-voltage LDMOS pipe, stable export is obtained by linear voltage-stabilizing circuit Voltage, is connected with output reference voltage circuit；

Output reference voltage circuit：Output reference voltage, is connected with linear constant current circuit；

Linear constant current circuit：Manage, by feedback signal control adjustment pipe, realize permanent by the use of integrated high-voltage power pipe as adjustment Stream output.

2. a kind of piecewise linearity constant current LED drive circuit according to claim 1, it is characterised in that：It also includes protection Circuit, the protection circuit provides under-voltage protection, overheat protector, overvoltage protection and overcurrent protection.

3. a kind of piecewise linearity constant current LED drive circuit according to claim 1, it is characterised in that：The rectifier bridge is Full-wave rectification bridge, 220V/50Hz alternating current is converted to 0-311V DC pulse high pressure.

4. a kind of piecewise linearity constant current LED drive circuit according to claim 1, it is characterised in that：The high voltage stabilizing Reduction voltage circuit includes resistance R0, and resistance R0 provides grid end voltage for LDMOS0 pipes, and resistance R1 and electric capacity C0 series connections are in LDMOS0 The source of pipe, the drain terminal of LDMOS0 pipes connects input voltage, and the voltage at electric capacity C0 two ends is through resistance R2 and Zener diode Zener1 Voltage stabilizing is carried out, p-type FET Mp1, Mp2, Mp4, Mp5 and N-type FET Mn1, Mn2, Mn3, Mn4 constitute cascade knot Structure, resistance R3, R4 provide biasing for cascode structure, and bipolar transistor Q1, Q2 base stage, which are connected, to be grounded, p-type FET Mp3 and Mp6 constitutes current mirror, and image current obtains reference voltage V ref1, error amplification through resistance R6 and bipolar transistor Q3 Device OPA0 anti-phase termination reference voltage V ref1, resistance R7, R8 connect to form feedback network, and the feedback voltage on resistance R8 connects It is connected to error amplifier OPA0 in-phase end, error amplifier OPA0 output termination power tubes Mp40 grid end.

5. a kind of piecewise linearity constant current LED drive circuit according to claim 1, it is characterised in that：Output reference voltage Circuit includes p-type FET Mp7, Mp8, Mp9, Mp10, p-type FET Mp7, Mp8, Mp9, Mp10 and N-type FET Mn5, Mn6, Mn7, Mn8 constitute cascode structure, and resistance R11, R12 provide biasing, bipolar transistor for cascode structure Pipe Q4, Q5 base stage, which are connected, to be grounded, and p-type FET Mp11 and Mp12 constitute current mirror, and image current flows through resistance R10 and crystal Pipe Q6 obtains the reference voltage of temperature first compensation phase, the list that the reference voltage of temperature first compensation phase is constituted through error amplifier OPA5 After the gain buffer of position, reference voltage V ref2 is obtained, resistance R13, R14, R15, R16, R17 composition electric resistance partial pressure structure can Four road reference voltages are obtained, N-type FET Mn13 is in parallel with resistance R13, N-type FET Mn13 grid end connects level conversion The output signal EN of circuit.

6. a kind of piecewise linearity constant current LED drive circuit according to claim 1, it is characterised in that：Linear constant current circuit Including LED string, LDMOS pipes, amplifier and external sampling resistor, when the external voltage of input reaches the forward conduction of LED string During pressure drop, LDMOS pipes and external sampling resistor constitute path, and produce on sampling resistor pressure drop, and the magnitude of voltage is used as feedback Signal is connected in the backward end of amplifier, the termination reference voltage circuit in the same direction of amplifier corresponding reference voltage all the way, amplifier output Terminate the grid end of LDMOS pipes.

7. a kind of piecewise linearity constant current LED drive circuit according to claim 5, it is characterised in that：Reference voltage circuit At least include four tunnel reference voltage outputs, in the external level shifting circuit of output reference voltage circuit Enable Pin, control ginseng The magnitude of voltage of voltage output is examined, and then produces two groups of output reference voltages, two groups of different ginsengs are provided for linear constant current circuit Examine voltage.