CN201805600U - A LED driver primary side constant current control device - Google Patents

Abstract

The utility model discloses a constant current control device for the primary side of an LED driver. The existing constant current control device is prone to the problem of optocoupler aging and the circuit is relatively complicated. The output terminal of the peak sampling and holding module in the utility model is connected to the input terminal of the secondary current simulation module, the output terminal of the secondary current simulation module is connected to the input terminal of the average current loop, and the output terminal of the average current loop is connected to an input of the comparison module terminal, the other input terminal of the comparison module is connected to the output terminal of the sawtooth wave generation module, the output terminal of the comparison module is connected to one input terminal of the drive pulse generation module, and the other input terminal of the drive pulse generation module is connected to the inductor current zero-crossing detection module The output terminal, the output terminal of the driving pulse generating module is connected to the driving module. The utility model can realize high power factor and output constant current control.

Description

A LED driver primary side constant current control device

technical field

The utility model belongs to the technical field of switching power supplies and relates to a primary side constant current control device of an LED driver.

Background technique

Current high-power LED drivers usually need to meet the following requirements: output constant current, high power factor and electrical isolation. Among them, the output constant current is determined by the characteristics of the LED itself, the high power factor is to reduce the pollution of the driver to the public grid, and the electrical isolation is for safety considerations. Electrical isolation is usually achieved by using a high-frequency transformer. In order to achieve output constant current control, the usual practice is to collect the output current signal, and then transmit it to the primary side control circuit through the optocoupler. The existence of the secondary current sampling circuit and the optocoupler increases the complexity of the circuit. Furthermore, due to the aging problem of the optocoupler, the stability and service life of the circuit are affected to a certain extent.

One solution is to use primary side constant current control, that is, without secondary side current sampling and optocoupler components, directly obtain output current information on the primary side of the isolation transformer or use constant power control to achieve output constant current. In addition, in order to meet the requirements of high power factor, the control circuit also needs to be able to realize the power factor correction function. At present, there are control chips that can realize primary-side constant current control and high power factor requirements, mainly including PI's LNK-PH series and Infineon's ICL8001G. These two chips can basically meet the primary-side constant current control and high power factor requirements. But performance may not be optimal.

Therefore, it is a very practical work to study the primary side constant current control device of the isolated high power factor flyback LED driver with simple structure and high performance.

Contents of the invention

The purpose of the utility model is to provide a constant current control device for the primary side of an LED driver, which does not need a multiplier and has a very simple structure, aiming at the shortcomings of the prior art.

The technical scheme that the utility model solves the technical problem that takes is:

The utility model comprises a peak sampling and holding module, a secondary side current simulation module, an average current loop, a sawtooth wave generation module, a comparison module, an inductor current zero-crossing detection module, a driving pulse generation module and a driving module.

The output terminal of the peak sample and hold module is connected to the input terminal of the secondary current analog module, the output terminal of the secondary current analog module is connected to the input terminal of the average current loop, the output terminal of the average current loop is connected to an input terminal of the comparison module, and the output terminal of the comparison module is The other input terminal is connected to the output terminal of the sawtooth wave generating module, the output terminal of the comparison module is connected to one input terminal of the driving pulse generating module, the other input terminal of the driving pulse generating module is connected to the output terminal of the inductor current zero-crossing detection module, and the driving pulse The output terminal of the generating module is connected to the driving module.

The secondary side current analog module can be implemented using the following six technical solutions

Option 1: The secondary current simulation module includes a resistor R ₁₁ and a switch S ₁₁ ; one end of the resistor R ₁₁ is connected to the output terminal of the peak sampling and holding module, and the other end of the resistor R ₁₁ is connected to one end of the switch S ₁₁ as a secondary current simulation module The output terminal of the switch S ₁₁ is grounded, and the control terminal of the switch S ₁₁ is connected to the positive phase output terminal Q of the drive generation module.

Scheme 2: The secondary current simulation module includes a resistor R ₁₁ , a switch S ₁₁ and an inverter U ₁₁ , one end of the resistor R ₁₁ is connected to the output end of the peak sampling and holding module, the other end of the resistor R ₁₁ is connected to one end of the switch S ₁₁ and As the output terminal of the secondary current simulation module, the other end of the switch _S11 is grounded, the control terminal of the switch _S11 is connected _to the output terminal of the inverter U11, and the input terminal of the inverter _U11 is connected to the inverting phase of the driving pulse generation module output

Scheme 3: The secondary side current simulation module includes a switch S ₄₄ , a switch S ₅₅ and an inverter U ₂₂ , one end of the switch S ₅₅ is connected to the output end of the peak sampling and holding circuit, and the other end of the switch S ₅₅ is connected to one end of the switch S ₄₄ Finally, as the output terminal of the secondary current analog module circuit, the other end of the switch _S44 is grounded, the control terminal of the switch _S44 is connected to the positive phase output terminal Q of the drive pulse generation module, and the control signal of _S55 is determined by the positive phase output terminal Q of the drive pulse generation module. The output terminal Q is obtained after being inverted by the inverter _U22 .

Solution 4: The secondary current simulation module includes a switch _S44 and a switch _S55 , one end of the switch _S55 is connected to the output end of the peak sampling and holding circuit, and the other end of the switch _S55 is connected to one end of the switch _S44 as a secondary current simulation The output terminal of the module circuit, the other end of the switch _S44 is grounded, the control terminal of the switch _S44 is connected to the positive phase output terminal Q of the drive pulse generation module, and the control terminal of the switch _S55 is connected to the inverting output terminal of the drive pulse generation module

Scheme 5: The secondary current simulation module includes a switch S ₆₆ and a resistor R ₆₆ , one end of the switch S ₆₆ is connected to the output terminal of the peak sampling and holding circuit, and the other end of the switch S ₆₆ is connected to one end of the resistor R ₆₆ as a secondary current simulation The output end of the module circuit, the other end of the resistor R ₆₆ is grounded, and the control end of the switch S ₆₆ is directly connected to the inverting output end of the drive pulse generation module

Scheme 6: The secondary side current simulation module includes a switch S ₆₆ , a resistor R ₆₆ and an inverter U ₃₃ , one end of the switch S ₆₆ is connected to the output end of the peak sampling and holding circuit, the other end of the switch S ₆₆ is connected to one end of the resistor R ₆₆ Finally, as the output terminal of the secondary current analog module circuit, the other end of the resistor R ₆₆ is grounded, and the control signal of the switch S ₆₆ is obtained by inverting the positive phase output terminal Q of the driving pulse generation module through the inverter U ₃₃ .

The average current loop includes an input resistor _R22 , a compensation network, a voltage reference Vref and an operational amplifier, the output of the secondary current analog module is connected to the negative terminal input of the operational amplifier in the average current loop through the resistor _R22 , and the positive input of the operational amplifier is The terminal input is connected to the voltage reference Vref, one end of the compensation network is connected to the negative input of the operational amplifier, and the other end of the compensation network is connected to the output terminal of the operational amplifier.

The voltage reference Vref can adopt the following three technical solutions:

Solution 1: The voltage reference Vref adopts a DC voltage source.

Scheme 2: The voltage reference Vref includes a divider, a resistor R _a1 , a resistor R _a2 , a resistor R _a3 , a resistor R _a4 and a capacitor C _a1 ; one end of R _a1 is connected to the high-level output end of the flyback LED driver input rectifier B ₁ , The other end is connected to one end of the parallel branch of the resistor R _a3 and the capacitor C _a1 , and then connected to the divisor terminal B of the divider, the other end of the parallel connection of the resistor R _a3 and the capacitor C _a1 is grounded, one end of the resistor R _a2 , one end of the resistor R _a4 Connect with the dividend end A of the divider, the other end of the resistor R _a2 is connected to the high level output end of the flyback LED driver input rectifier _B1 , the other end of the resistor R _a4 is grounded, and the output of the divider is used as the output of the voltage reference Vref , which is a sine half-wave signal with constant amplitude and the same frequency and phase as the output of the input rectifier _B1 .

Scheme 3: The voltage reference Vref includes a divider, a transistor Q _b1 , a resistor R _b1 , a resistor R _b2 , a resistor R _b3 , a capacitor C _b1 , a first mirror current source and a second mirror current source; one end of the resistor R _b1 is connected to a flyback type The LED driver is input to the high-level output terminal of the rectifier _B1 , the other end of the resistor R _b1 is connected to the collector and base of the transistor Q _b1 , and the emitter of the transistor Q _b1 is grounded; the collector and base of the transistor Q _b1 are respectively connected to the first The input terminals of the mirror current source and the second mirror current source, the output terminal of the first mirror current source are connected with one end of the resistor R _b2 , one end of the capacitor C _b1 , and the divisor terminal B of the divider, and the other end of the resistor R _b2 is connected with the capacitor The other end of C _b1 is grounded; the output end of the second mirror current source is connected to one end of the resistor R _b3 and the dividend end A of the divider; the other end of the resistor R _b3 is grounded, and the output of the divider is used as the output of the voltage reference Vref, which is A sine half-wave signal with constant amplitude and the same frequency and phase as the output of the input rectifier _B1 .

The sawtooth wave generation module includes a DC voltage source V _DD , a DC current source I _DC , a capacitor C ₃₃ and a switch S ₃₃ ; the input terminal of the DC current source I _DC is connected to the DC voltage source V _DD , and the output terminal is connected to the capacitor C ₃₃ One end of the capacitor C33 and one end of the switch _S33 are used as the output end of the sawtooth wave generation module; the other end of the capacitor _C33 is connected to the other end of the switch _S33 and then grounded, and the control end of the switch _S33 is connected to the inverting output of the drive generation module end

The comparison module includes a first comparator U ₁ , the negative terminal input of the first comparator U ₁ is connected to the output terminal of the average current loop, and the positive terminal input of the first comparator U ₁ is connected to the output of the sawtooth wave generating module.

The inductance current zero-crossing detection module includes a second comparator _U2 and a delay module, the negative terminal input of the second comparator _U2 is connected to the opposite end of the auxiliary winding of the flyback LED driver transformer, and the positive terminal of _U2 The input is grounded; one end of the delay module is connected to the output end of the second comparator U ₂ , and the other end of the delay module is used as the output end of the inductor current zero-crossing detection module.

The drive pulse generation module uses an RS flip-flop, the R pin of the RS flip-flop is connected to the output end of the comparison module, and the S pin of the RS flip-flop is connected to the output end of the inductor current zero-crossing detection module. The output of the driving pulse generating module is sent to the gate of the flyback LED driver primary switch _Q1 through the driving module, and the output of the driving pulse generating module is also used as the control signal of the switch in the secondary current analog module.

The utility model is used as a control device of an isolated flyback LED driver, and together with a main circuit of the flyback LED driver, the utility model constitutes a switching power supply. The main circuit of a traditional single-tube flyback LED driver includes an input rectifier, an input capacitor, a snubber network, a transformer, a primary switching tube, a primary current sampling network, an output rectifier, and an output capacitor. The input capacitor is a capacitor with a very small capacity, which mainly plays a filtering role and basically has no effect on the half-sine wave waveform output by the input rectifier. The main circuit of the flyback LED driver of the present utility model can also be a traditional single-tube flyback topology and other variable structure topologies, such as a double-tube flyback converter.

The peak sampling and holding module is connected with the primary current sampling network of the main circuit of the flyback LED driver, performs peak sampling and holding on the primary current sampling signal in each switching cycle, and extracts the peak value of the primary current sampling signal.

After the secondary current simulation module is connected to the peak sample and hold module, it is used to simulate the secondary output rectifier current. The envelope of the current waveform of the output rectifier is a half-sine wave, specific to a single switching cycle, and the current waveform of the output rectifier on the secondary side is a right-angled triangle with a linearly decreasing slope. The output waveform of a single switching period of the secondary side current analog module is a rectangular wave, the width is equal to the turn-off time of the primary side switch tube (approximately equal to the conduction time of the secondary side output rectifier), and the amplitude is equal to the single switching period of the primary side current sampling signal peak voltage, so the area is proportional to twice the area of the secondary output rectifier current waveform.

The average current loop compares the average value of the output signal of the secondary current analog module with the voltage reference and amplifies the error between the two.

The sawtooth wave generation module generates a sawtooth wave when the primary switch of the flyback LED driver is turned on; and the sawtooth wave generation module outputs a low level when the primary switch is turned off.

The input of the comparison module is the output signal of the sawtooth wave generation module and the output signal of the average current loop respectively. The comparison module compares the output signal of the sawtooth wave generation module with the output signal of the average current loop. When the output signal of the sawtooth wave generation module rises to be equal to the output signal of the average current loop, the output of the comparison module turns from low to high. level.

The inductance current zero-crossing detection module detects the transformer auxiliary winding voltage signal of the flyback LED driver, and indirectly detects the zero-crossing point of the excitation inductance current of the transformer. When the transformer auxiliary winding voltage signal drops to zero, the inductor current zero-crossing detection module outputs a high level.

The drive pulse generation module generates a pulse signal according to the output level signals of the comparison module and the inductance current zero-crossing detection module: when the comparison module generates a low-level to high-level reversal, the pulse signal of the drive pulse generation module is generated by Reset from high level to low level; when the inductance current zero-crossing detection module generates a low level to high level inversion, the pulse signal of the driving pulse generation module is set from low level to high level; pulse train.

The driving module is used to enhance the driving capability of the driving pulse generating module.

Wherein, the flyback LED driver works in Boundary Discontinuous Mode (BCM).

Wherein, the secondary current simulation module may adopt any one of the six technical solutions.

Wherein, the voltage reference of the average current loop can be the DC voltage reference described in Scheme 1, or it can be the same frequency and phase as the output voltage of the flyback LED driver input rectifier bridge generated by the scheme 2 or 3. Fixed-amplitude half-sine wave voltage reference.

Wherein, the operational amplifier of the average current loop can be a voltage type or a current type (transconductance type).

Further, the compensation network of the average current loop may be a pure integral link, or a proportional integral link, or a proportional integral differential link, which belongs to the known technology.

Wherein, the driving module may be a push-pull structure (totem pole structure) composed of two bipolar transistors or metal oxide semiconductor field effect transistors, which belongs to the known technology.

Wherein, the switch may be a single bipolar transistor, metal oxide semiconductor field effect transistor or a combined switch realized by multiple bipolar transistors or metal oxide semiconductor field effect transistors.

Based on the above description, the core idea of the present invention is to detect the zero-crossing point of the inductance current of the flyback LED driver transformer through the inductance current zero-crossing detection module, and turn on the primary switch tube when the transformer inductance current crosses zero, so that the flyback The LED driver works in current critical discontinuous mode (BCM); the peak value sampling and holding of the primary current sampling signal is carried out by the peak sampling and holding module to obtain the peak envelope of the primary current sampling signal; obtain the primary current sampling After the peak envelope of the signal, through the secondary current simulation module, a signal whose area is proportional to twice the area of the secondary diode current is simulated; the output signal of the secondary current simulation module is sent to the average current loop, Utilizing the average value filter function of the average current loop itself, a sine half-wave signal proportional to the average value of the output current is obtained at the input end of the average current loop, and compared with the voltage reference, the error signal of the two is passed through the average current loop The compensation network is amplified to obtain an error-amplified DC signal; the sawtooth wave generated by the sawtooth wave generation module is compared with the DC signal output by the average current loop to obtain the turn-off trigger signal of the primary switch tube. Since the slope of the sawtooth wave is fixed, In this way, the conduction time of the primary side switch tube is a constant value in the entire power frequency cycle; when the sinusoidal half-wave voltage output by the input rectifier acts on both ends of the primary side transformer for a constant time, the peak envelope of the primary side current sampling signal is a sine half wave, In this way, the high power factor of the flyback LED driver is realized; when the output current fluctuates, the amplitude of the output DC signal of the average current loop changes, thereby changing the conduction time of the primary switch tube, making the average value of the output current tend to be stable, and realizing output constant current. The constant current value of the output current can be realized by changing the sampling coefficient of the primary current or changing the voltage reference in the average current loop.

The beneficial effect of the utility model is that: the primary side constant current control device of the isolated high power factor flyback LED driver with constant conduction time proposed by the utility model can realize high power without optocoupler and secondary side feedback circuit. factor and output constant current control. Compared with the same type of high power factor primary side constant current control circuit, the multiplier is omitted, and the structure is simpler; further, the primary side core control circuit can be integrated into a single chip.

Description of drawings

Fig. 1 is the schematic diagram of the main circuit connection of the utility model and the flyback LED driver;

Fig. 2 is the schematic diagram of the first specific embodiment of the utility model;

Fig. 3 is the waveform analysis diagram of the working principle of the present utility model;

Fig. 4 is six kinds of specific implementation schemes of the secondary side current simulation module in the utility model;

Fig. 5 is the schematic diagram of the second specific embodiment of the present utility model;

Fig. 6 is the schematic diagram of the third specific embodiment of the present utility model;

FIG. 7 is a schematic diagram of the connection between the utility model and the main circuit of the non-isolated buck-boost circuit.

Detailed ways

The content of the utility model will be described in detail below in conjunction with the block diagram of the utility model and the schematic diagram of specific embodiments.

Referring to Fig. 1, a constant current control device for the primary side of an LED driver includes: a peak sampling and holding module 100, a secondary side current simulation module 200, an average current loop 300, a sawtooth wave generation module 400, a comparison module 500, and an inductor current zero-crossing detection module 600. A driving pulse generating module 700 and a driving module 800.

The output terminal of the peak sampling and holding module 100 is connected to the input terminal of the secondary current simulation module 200, the output terminal of the secondary current simulation module 200 is connected to the input terminal of the average current loop 300, and the output terminal of the average current loop 400 is connected to an input of the comparison module terminal, the other input terminal of the comparison module 500 is connected to the output terminal of the sawtooth wave generation module 400, the output terminal of the comparison module 500 is connected to an input terminal of the drive pulse generation module 700, and the other input terminal of the drive pulse generation module 700 is connected to the inductor current The output terminal of the zero-crossing detection module 600 and the output terminal of the driving pulse generating module 700 are connected to the driving module 800 .

The application object of the utility model is the main circuit of the flyback LED driver, including the input rectifier bridge B ₁ , the input capacitor C _in , the transformer T, the absorption network, the primary switch tube Q ₁ , the primary current sampling network, and the output rectifier ( Choose diode D ₁ ) and output capacitor C ₀ .

With reference to the schematic diagram of the first specific embodiment of Fig. 2:

The peak sampling and holding module 100 is connected to the primary current sampling network of the main circuit of the flyback LED driver, performs peak sampling and holding on the primary current sampling signal in each switching cycle, and extracts the peak value of the primary current sampling signal; wherein, the peak sampling and holding Specifically, the module can use the peak sample and hold circuit disclosed in the Chinese patent (publication number: CN101615432).

The secondary side current simulation module 200 includes: a resistor R ₁₁ and a switch S ₁₁ ; one end of the resistor R ₁₁ is connected to the output of the peak sampling and holding module 100, the other end of the resistor R ₁₁ is connected to one end of the switch S ₁₁ , and the connection point of the two serves as a secondary The output of the edge current simulation module 200, the other end of the switch _S11 is grounded, the control terminal of the switch _S11 is connected to the positive phase output terminal Q of the drive generation module 700, when the level of the control terminal is high, the switch _S11 is turned on, When the level of the control terminal is low, the switch _S11 is turned off; the output of the secondary current simulation module 200 is a square wave signal.

The average current loop 300 includes an input resistor R ₂₂ , a compensation network, a voltage reference Vref and an operational amplifier. The output of the secondary current simulation module 200 is connected to the negative terminal input of the operational amplifier in the average current loop 300 through the resistor _R22 , and the positive terminal input of the operational amplifier is connected to the voltage reference Vref. Since the average current loop has a switching cycle average value filtering effect, the input signal of the negative terminal of the operational amplifier of the average current loop 300 is the average value of the output signal of the secondary current simulation module 200 after filtering the switching cycle ripple. The signal is compared with the voltage reference Vref, and the error between the two is amplified by the compensation network and the operational amplifier to output a DC level signal superimposed with low-frequency ripple and high-frequency switching ripple twice the frequency of the AC grid.

当控制端电平为高电平，开关S₃₃导通，将电容C₃₃两端电压保持为零；当控制端电平为低电平，开关S₃₃关断，直流电流源I_DC给电容C₃₃充电，产生锯齿波信号。The sawtooth wave generating module 400 includes a DC voltage source V _DD , a DC current source I _DC , a capacitor C ₃₃ and a switch S ₃₃ ; wherein the DC voltage source V _DD and the DC current source I _DC can be obtained by known techniques; the DC current source I _DC The input end is connected to the DC voltage source _VDD , the output end is connected to one end of the capacitor _C33 and one end of the switch _S33 as the output end of the sawtooth wave generating module 400, and the other end of the capacitor _C33 is connected to the other end of the switch _S33 Grounded, the control terminal of the switch _S33 is connected to the inverting output terminal of the driving generation module 700

When the level of the control terminal is high, the switch _S33 is turned on, and the voltage across the capacitor _C33 is kept at zero; when the level of the control terminal is low, the switch _S33 is turned off, and the DC current source I _DC supplies the capacitor C ₃₃ is charged to generate a sawtooth wave signal.

The comparison module 500 includes a first comparator U ₁ , the negative terminal of U ₁ is connected to the output of the average current loop 300 , and the positive terminal of U ₁ is connected to the output of the sawtooth wave generation module 400 . When the sawtooth wave signal generated by the sawtooth wave generation module 400 reaches the output level of the average current loop 300 , the output level of the comparison module 500 is turned from low level to high level. Since the output level of the average current loop 300 basically has the same amplitude in the entire power frequency cycle, the slope of the sawtooth signal generated by the sawtooth wave generating module 400 is also fixed, and the width of the sawtooth signal corresponds to that of the primary switch tube Q ₁ Therefore, for a specific output level amplitude of the average current loop 300, the conduction time of the primary switch tube _Q1 is constant. When the conduction time of the primary switch tube _Q1 is constant, the current waveform envelope of the primary switch tube follows the output of the flyback LED driver input rectifier _B1 , which is the same frequency as the output of the flyback LED driver input rectifier _B1 Sine half waves in phase.

The inductor current zero-crossing detection module 600 includes a second comparator _U2 and a delay module. The negative terminal input of _U2 is connected to the opposite end of the auxiliary winding of the flyback LED driver transformer, and the positive terminal input of _U2 is grounded; through the detection transformer The zero-crossing point of the auxiliary winding voltage signal can indirectly detect the zero-crossing point of the transformer inductor current. When it is detected that the voltage signal of the auxiliary winding of the transformer crosses zero, the second comparator U ₂ outputs a high level. Since there is a certain time difference between the zero-crossing point of the auxiliary winding voltage signal of the flyback LED driver transformer and the bottom of the resonant voltage valley between the drain and source (or collector and emitter) of the primary switch tube, that is, the auxiliary winding voltage signal of the flyback LED driver transformer The zero-crossing point should be slightly ahead of the bottom of the resonant voltage between the drain and source of the primary switching tube. By compensating the time difference through the delay module, the bottom of the resonant voltage between the drain and the source of the primary switching tube can be turned on.

Furthermore, the positive terminal input of the second comparator U ₂ in the inductor current zero-crossing detection module 600 can also be connected to a low-amplitude DC voltage source to reduce errors caused by ground wire interference.

The driving pulse generating module 700 is realized by RS flip-flop, wherein the R pin is connected to the output of the comparison module 500, and the S pin is connected to the output of the inductor current zero-crossing detection module 600: when the comparison module 500 generates a low-level to high-level reversal , the output signal of the driving pulse generation module 800 is reset from high level to low level; The level is set to a high level, and this cycle repeats to generate an output pulse sequence.

The output of the driving pulse generating module 700 is sent to the gate of the primary side switching tube _Q1 of the flyback LED driver through the driving module 800, and the output of the driving pulse generating module 700 is directly used as the switch _S11 in the secondary current simulation module 200 at the same time. control signal.

Fig. 3 is the key waveform of the primary and secondary sides of the flyback LED driver working in the current critical discontinuous mode. Referring to Fig. 3, the working principle of the utility model is described in detail:

In Fig. 3, V _comp is the output waveform of the average current loop 300, V _saw is the output waveform of the sawtooth wave generating module 400, V _{GS_Q1} and _{V GS_s11} are the driving waveform and switching The waveform of the control terminal of S ₁₁ ; i _pri is the current waveform of the switch tube on the primary side of the flyback LED driver; i _sec is the current waveform of the output rectifier on the secondary side of the flyback LED driver; V _samp1e is the output waveform of the peak sample and hold module 100; V _{DS_S11} is the voltage waveform at both ends of the switch _S11 , that is, the output waveform of the secondary current simulation module 200 . According to Fig. 3, it can be seen that since the output waveform V _comp of the average current loop 300 is a DC level, and the slope of the sharp tooth wave V _saw is constant, the turn-on time of the primary side switch _Q1 of the flyback LED driver is constant, and the primary side switch The waveform envelope of the tube current i _pri is a half-sine wave; since the inductor current zero-crossing detection module 600 makes the flyback LED driver work in the current critical discontinuous mode, the current waveform i _sec envelope of the secondary output rectifier is also It is a sine half wave; the output waveform V _samp1e of the peak sample and hold module 100 is a ladder wave, and the amplitude of each step corresponds to a different primary sampling current peak value; the output waveform V _{DS_s11} of the secondary current analog module 200 is a variable amplitude Rectangular wave, the amplitude corresponds to the peak value of different primary current sampling signals; it can be seen from Figure 3:

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}}_{\mathrm{<span\; class="notranslate">\; DS</span>}<span\; class="notranslate">\; \_</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="11"\; label="S"\; filenames="HSA00000291937200051.png"\; state="\{\{state\}\}">S</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}}_{\mathrm{<span\; class="notranslate">\; sec</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}$

为副边电流模拟模块200的输出波形V_{DS_s11}的平均值，

为副边输出整流器的电流平均值。从上式可以看出副边电流模拟模块200的输出波形V_{DS_s11}的平均值正比于输出电流平均值I_o；因此只要将

送入平均电流环300，与设定的基准Vref进行比较，即可间接调节输出平均电流，从而实现输出电流恒流。由于平均电流环自身具有滤波功能，只要将V_{DS_s11}送入平均电流环300，即可在平均电流环300的运算放大器输入端获得V_{DS_s11}的平均值

进一步，也可以在副边电流模拟模块200的输出和平均电流环300增加一级滤波电路，但对电路功能基本没有影响。Among them, K ₁ is the primary current sampling coefficient, N _s is the number of turns of the secondary side of the transformer, N _p is the number of turns of the primary side of the transformer,

is the average value of the output waveform V _{DS_s11} of the secondary current simulation module 200,

is the average current of the secondary output rectifier. It can be seen from the above formula that the average value of the output waveform V _{DS_s11} of the secondary current analog module 200 is proportional to the average value of the output current I _o ; therefore, as long as the

Sending it into the average current loop 300 and comparing it with the set reference Vref can indirectly adjust the output average current, thereby realizing a constant output current. Since the average current loop itself has a filtering function, as long as V _{DS_s11} is sent to the average current loop 300, the average value of V _{DS_s11} can be obtained at the input terminal of the operational amplifier of the average current loop 300

Furthermore, a filter circuit may be added to the output of the secondary current analog module 200 and the average current loop 300, but this has basically no effect on the circuit function.

The average current loop 300 reference is usually set as a DC voltage reference; in addition, the average current waveform i _sec of the flyback LED driver secondary output rectifier current waveform after switching cycle filtering is approximately a half-sine wave, so the average current loop 300 reference can also be Set as a sine half-wave reference with the same frequency and phase as the output waveform of the flyback LED driver input rectifier bridge, and constant amplitude.

图4(e)中副边电流模拟模块200由开关S₆₆和电阻R₆₆组成，开关S₆₆的一端接峰值采样保持电路100的输出，开关S₆₆的另一端与接电阻R₆₆的一端后作为副边电流模拟模块200电路的输出端，电阻R₆₆的另一端接地，开关S₆₆的控制端直接接驱动脉冲产生模块的反相输出端

图4(f)中副边电流模拟模块200电路结构与图4(e)中相同，区别在于开关S₆₆的控制信号由驱动脉冲产生模块的正相输出端Q经反相器U₃₃反相之后得到。Figure 4 shows several specific implementation circuits of the secondary current simulation module 200, wherein the circuit structure shown in Figure 4(a) is the same as that of the secondary current simulation module 200 in Figure 2; the circuit structure shown in Figure 4(b) is the same as The circuit shown in Figure 4(a) has a similar structure and is also composed of a resistor R ₁₁ and a switch S _11. The difference is that the control signal of S ₁₁ is the inverting output terminal of the drive pulse generation module Obtained after being inverted by the inverter _U11 ; the secondary current analog module 200 in Figure 4(c) is composed of switches _S44 , _S55 and inverter _U22 , and one end of _S55 is connected to the output of the peak sample-and-hold circuit 100 , the other end of _S55 is connected to one end of switch _S44 as the output end of the secondary current analog module 200 circuit, the other end of switch _S44 is grounded, and the control end of switch _S44 is connected to the positive phase output end Q of the drive pulse generation module , the control signal of _S55 is obtained by the positive-phase output terminal Q of the driving pulse generating module after being inverted by the inverter _U22 ; the circuit structure of the secondary current analog module 200 in Fig. 4(d) is the same as that in Fig. , the difference is that the control terminal of _S55 is connected to the inverting output terminal of the driving pulse generation module

In Fig. 4 (e), the secondary side current simulation module 200 is composed of a switch _S66 and a resistor _R66 . One end of the switch _S66 is connected to the output of the peak sampling and holding circuit 100, and the other end of the switch _S66 is connected to one end of the resistor _R66 . As the output terminal of the secondary current simulation module 200 circuit, the other end of the resistor R ₆₆ is grounded, and the control terminal of the switch S ₆₆ is directly connected to the inverting output terminal of the driving pulse generation module

The circuit structure of the secondary current analog module 200 in Fig. 4(f) is the same as that in Fig. 4(e), the difference is that the control signal of the switch _S66 is inverted by the non-phase output terminal Q of the drive pulse generation module through the inverter _U33 get after.

Fig. 5 is the second specific embodiment of the present utility model, and main circuit and main control part are all identical with the embodiment shown in Fig. 2, and the difference with Fig. 2 is that the voltage reference Vref of the average current loop 300 in Fig. 5 adopts amplitude A sine half-wave reference module with constant value is provided, and a specific implementation is given. Referring to Fig. 5, the sine half-wave reference module Vref includes a divider, a resistor R _a1 , a resistor R _a2 , a resistor R _a3 , a resistor R _a4 and a capacitor C _a1 ; wherein, one end of the resistor R _a1 is connected to the flyback LED driver input rectifier B ₁ The high-level output terminal of the resistor R _a3 and capacitor C _a1 is connected in parallel with one end of the parallel branch and then connected to the divisor terminal B of the divider, the other end of the parallel connection of resistor R _a3 and capacitor C _a1 is grounded, and the resistor R _a1 , The electrical network formed by _the resistor R _{a3 and} the capacitor C _a1 divides and filters the output voltage _of the positive terminal of the input rectifier _B1 . DC voltage, the average value of which is proportional to the peak value of the input AC voltage of the flyback LED driver. One end of the resistor R _a2 is connected to the high-level output end of the input rectifier _B1 , the other end is connected to the resistor R _a4 , and the other end of the resistor R _a4 is grounded. The dividend terminal A of the divider is connected to the connection point of R _a2 and R _a4 , and the phase division (A/B) is performed in the divider, so that the output of the divider has a constant amplitude and is the same as the output of the flyback LED driver input rectifier A sinusoidal half-wave signal with the same frequency and phase.

Fig. 6 is the main circuit of the third specific embodiment of the present utility model, and the main circuit and the main control part are all the same as the embodiment shown in Fig. 5, and the difference with Fig. 5 is that the reference Vref of the average current loop 300 in Fig. 6 adopts Another way to generate a sine half-wave reference module with a constant amplitude; referring to Figure 6, the sine half-wave reference module Vref includes a divider, a transistor Q _b1 , a resistor R _b1 , a resistor R _b2 , a resistor R _b3 , a capacitor C _b1 , Mirror current source I and mirror current source II; one end of the resistor R _b1 is connected to the high-level output end of the flyback LED driver input rectifier _B1 , the other end of the resistor R _b1 is connected to the collector and base of the transistor Q _b1 , and the transistor Q The emitter of _b1 is grounded, the collector and base of transistor Q _b1 are connected to the input terminals of mirror current source I and mirror current source II respectively, the output of mirror current source I is connected to one end of resistor R _b2 , one end of capacitor C _b1 and The divisor end B of the divider is connected, the other end of the resistor R _b2 is grounded to the other end of the capacitor C _b1 , the output of the mirror current source II is connected to one end of the resistor R _b3 and the dividend end A of the divider; the transistor Q _b1 and the resistor R _b1 is used to convert the sinusoidal half-wave voltage signal output by the flyback LED driver input rectifier _B1 into a current signal; the mirror current module I obtains a sinusoidal half-wave current signal proportional to the current flowing through the R _b1 branch, and passes through the resistor Capacitance network R _b2 and C _b1 obtain a DC voltage signal proportional to the amplitude of the input AC voltage of the flyback LED driver, which is connected to the dividend terminal B of the divider; mirror current module II obtains a current proportional to the current flowing through the R _b1 branch The sinusoidal half-wave current signal is converted into a voltage signal by the resistor R _b3 , and sent to the divisor terminal A of the divider; the two signals are divided (A/B) in the divider, and the amplitude is generated at the output terminal of the divider A sinusoidal half-wave voltage reference signal that is constant and has the same frequency and phase as the output voltage waveform of the input rectifier. The current mirror module can be composed of metal oxide semiconductor field effect transistors or bipolar transistors, which belongs to the known technology.

The utility model can be applied to isolated output, and can also be applied to non-isolated output. Fig. 7 is a schematic diagram of the main circuit connection between the utility model and a non-isolated buck-boost circuit; wherein, the specific implementation of each module can refer to Fig. 2, and the specific implementation shown in Fig. 4 to Fig. 6 example.

The specific modules included in the utility model, such as the peak current sampling and holding circuit 100, the secondary current analog module 200 and the sine half-wave signal reference generation circuit, etc., can be implemented in various ways by those skilled in the art without violating its spirit. way, or through various combinations to form different specific embodiments, which will not be described in detail here.

No matter how detailed the above description is, there are many ways to implement the utility model, and what is described in the description is only a specific implementation example of the utility model. All equivalent transformations or modifications made according to the spirit of the utility model shall fall within the protection scope of the utility model.

Claims (10)

1. A constant current control device for the primary side of an LED driver, including a peak sampling and holding module, a secondary side current simulation module, an average current loop, a sawtooth wave generation module, a comparison module, an inductor current zero-crossing detection module, a driving pulse generation module and a driver module, characterized in that: The output terminal of the peak sample and hold module is connected to the input terminal of the secondary current analog module, the output terminal of the secondary current analog module is connected to the input terminal of the average current loop, the output terminal of the average current loop is connected to an input terminal of the comparison module, and the output terminal of the comparison module is The other input terminal is connected to the output terminal of the sawtooth wave generating module, the output terminal of the comparison module is connected to one input terminal of the driving pulse generating module, the other input terminal of the driving pulse generating module is connected to the output terminal of the inductor current zero-crossing detection module, and the driving pulse The output terminal of the generating module is connected to the driving module; The average current loop includes an input resistor _R22 , a compensation network, a voltage reference Vref and an operational amplifier, the output of the secondary current analog module is connected to the negative terminal input of the operational amplifier in the average current loop through the resistor _R22 , and the positive input of the operational amplifier is The terminal input is connected to the voltage reference Vref, one end of the compensation network is connected to the negative terminal input of the operational amplifier, and the other end of the compensation network is connected to the output terminal of the operational amplifier; The sawtooth wave generation module includes a DC voltage source V _DD , a DC current source I _DC , a capacitor C ₃₃ and a switch S ₃₃ , the input terminal of the DC current source I _DC is connected to the DC voltage source V _DD , and the output terminal is connected to the capacitor C ₃₃ One end of the capacitor C33 and one end of the switch _S33 are used as the output end of the sawtooth wave generation module; the other end of the capacitor _C33 is connected to the other end of the switch _S33 and then grounded, and the control end of the switch _S33 is connected to the inverting output of the drive generation module end The comparison module includes a first comparator _U1 , the negative terminal input of the first comparator _U1 is connected to the output terminal of the average current loop, and the positive terminal input of the first comparator _U1 is connected to the output of the sawtooth wave generation module; The inductance current zero-crossing detection module includes a second comparator _U2 and a delay module, the negative terminal input of the second comparator _U2 is connected to the opposite end of the auxiliary winding of the flyback LED driver transformer, and the positive terminal of _U2 The input is grounded; one end of the delay module is connected to the output end of the second comparator _U2 , and the other end of the delay module is used as the output end of the inductor current zero-crossing detection module; Described driving pulse generation module adopts RS flip-flop, the R foot of RS flip-flop connects the output end of comparison module, the S foot of RS flip-flop connects the output end of inductor current zero-crossing detection module, the output of driving pulse generation module is driven The module is sent to the gate of the primary switch tube _Q1 of the flyback LED driver, and the output of the driving pulse generation module is also used as the control signal of the switch _S11 in the secondary current simulation module. 2. A kind of LED driver primary side constant current control device according to claim 1, it is characterized in that: described secondary side current simulation module comprises resistance R ₁₁ and switch S ₁₁ ; One end of resistance R ₁₁ is connected with peak value sampling and holding The output end of the module, the other end of the resistor R ₁₁ is connected to one end of the switch S ₁₁ and used as the output end of the secondary current simulation module, the other end of the switch S ₁₁ is grounded, and the control end of the switch S ₁₁ is connected to the positive phase output of the drive generation module Terminal Q. 3. A LED driver primary side constant current control device according to claim 1, characterized in that: said secondary side current simulation module includes a resistor R ₁₁ , a switch S ₁₁ and an inverter U ₁₁ , and the resistor R ₁₁ One end of the resistor R11 is connected to the output end of the peak sampling and holding module, the other end of the resistor _R11 is connected to one end of the switch _S11 as the output end of the secondary current analog module, the other end of the switch _S11 is grounded, and the control end of the switch _S11 is connected to the reverse The output terminal of the phaser U ₁₁ , the input terminal of the inverter U ₁₁ is connected to the inverting output terminal of the drive pulse generation module

4. A LED driver primary side constant current control device according to claim 1, characterized in that: said secondary side current simulation module includes a switch S ₄₄ , a switch S ₅₅ and an inverter U ₂₂ , the switch S ₅₅ One end of the switch S55 is connected to the output end of the peak sampling and holding circuit, the other end of the switch _S55 is connected to one end of the switch _S44 as the output end of the secondary current analog module circuit, the other end of the switch _S44 is grounded, and the switch _S44 controls the terminal The control signal of the positive-phase output terminal Q of the driving pulse generating module, S ₅₅ is obtained by inverting the positive-phase output terminal Q of the driving pulse generating module through the inverter _U22 . 5. A LED driver primary side constant current control device according to claim 1, characterized in that: said secondary side current simulation module includes a switch _S44 and a switch _S55 , and one end of the switch _S55 is connected to peak value sampling and holding At the output end of the circuit, the other end of the switch _S55 is connected to one end of the switch _S44 as the output end of the secondary current analog module circuit, the other end of the switch _S44 is grounded, and the control terminal of the switch _S44 is connected to the positive side of the drive pulse generation module. The phase output terminal Q, the control terminal of the switch _S55 is connected to the inverting output terminal of the drive pulse generation module

6. A LED driver primary side constant current control device according to claim 1, characterized in that: said secondary side current simulation module includes a switch _S66 and a resistor _R66 , and one end of the switch _S66 is connected to peak value sampling and holding The output end of the circuit, the other end of the switch _S66 and one end of the resistor _R66 are used as the output end of the secondary current analog module circuit, the other end of the resistor _R66 is grounded, and the control end of the switch _S66 is directly connected to the drive pulse generation module The inverting output of

7. A LED driver primary side constant current control device according to claim 1, characterized in that: said secondary side current simulation module includes a switch S ₆₆ , a resistor R ₆₆ and an inverter U ₃₃ , the switch S ₆₆ One end of the switch S66 is connected to the output end of the peak sampling and holding circuit, the other end of the switch _S66 is connected to one end of the resistor _R66 as the output end of the secondary current analog module circuit, the other end of the resistor _R66 is grounded, and the control signal of the switch _S66 It is obtained by inverting the positive phase output terminal Q of the driving pulse generating module through the inverter _U33 . 8. The LED driver primary side constant current control device according to claim 1, characterized in that: said voltage reference Vref adopts a DC voltage source. 9. A LED driver primary side constant current control device according to claim 1, characterized in that: said voltage reference Vref comprises a divider, resistor R _a1 , resistor R _a2 , resistor R _a3 , resistor R _a4 and One end of the capacitor C _a1 and R _a1 is connected to the high-level output end of the flyback LED driver input rectifier _B1 , and the other end is connected to one end of the parallel branch of the resistor R _a3 and the capacitor C _a1 , and then connected to the divisor end B of the divider. The other end of the parallel connection of resistor R _a3 and capacitor C _a1 is grounded, one end of resistor R _a2 and one end of resistor R _a4 are connected to the dividend terminal A of the divider, and the other end of resistor R _a2 is connected to the flyback LED driver input rectifier B ₁ High level output terminal, the other end of the resistor R _a4 is grounded. 10. A LED driver primary side constant current control device according to claim 1, characterized in that: said voltage reference Vref comprises a divider, transistor Q _b1 , resistor R _b1 , resistor R _b2 , resistor R _b3 , Capacitor C _b1 , the first mirror current source and the second mirror current source, one end of the resistor R _b1 is connected to the high-level output end of the flyback LED driver input rectifier _B1 , and the other end of the resistor R _b1 is connected to the collector of the transistor Q _b1 and The base, the emitter of the triode Q _b1 is grounded; the collector and the base of the triode Q _b1 are respectively connected to the input terminals of the first mirror current source and the second mirror current source, and the output terminal of the first mirror current source is connected to the resistor R _b2 One end, one end of the capacitor C _b1 , and the divisor end B of the divider are connected, and the other end of the resistor R _b2 is connected to the other end of the capacitor C _b1 ; the output end of the second mirror current source is connected to one end of the resistor R _b3 , and the dividend of the divider Terminal A is connected; the other end of resistor R _b3 is grounded.

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