A constant current control system for a large leakage inductor primary-side feedback flyback converter

Abstract

The present invention discloses a constant current control system for a large leakage inductance primary feedback flyback converter, which relates to the technical field of switching power supplies. The system includes a main topology circuit and a control circuit that forms a closed loop with the main topology circuit. The structure of the clamp circuit is adjusted in the main topology circuit, and the current sampling resistor voltage on the input side of the main topology circuit is used as the first input signal of the control circuit. The peak current, average current and conduction time of the primary winding are calculated in combination with the voltage signal. The voltage division value of the auxiliary winding is used as the second input signal of the control circuit to obtain the demagnetization time of the transformer. The average current of the diode in the output circuit is calculated in combination with the above-calculated parameters and the switching cycle. The system takes into account the energy loss caused by the primary leakage inductance to the charging stage of the clamp circuit, so that a high-precision constant output current can be achieved in a flyback converter with a large leakage inductance.

Description

Technical Field

[0001] The invention relates to the technical field of switch power supply, in particular to a constant current control system of a large leakage inductance primary side feedback flyback converter. Background Art

[0002] With the development of technology, switching power supplies are widely used in small and medium power applications. Isolated switching power supplies can achieve electrical isolation between input and output, and have the characteristics of safe isolation and high reliability. Flyback converters have the advantages of simple structure, high reliability and low cost, and are widely used in small and medium power consumer electronics. Among them, the flyback converter based on primary side feedback technology has a simpler circuit structure than the traditional flyback converter based on secondary side feedback technology, and does not require the use of nonlinear devices such as optocouplers, and its reliability, life and integration can be further improved.

[0003] The current method for primary feedback flyback converter to achieve output constant current is mainly to control the output diode current to be constant. The main idea is: calculate the average current of the primary winding of the transformer in the conduction stage through relevant methods, and obtain the average current of the output winding in the demagnetization stage according to the principle that the ratio between the primary winding current of the transformer and the output winding current is equal to the ratio of the number of turns of the primary winding and the secondary winding; finally, the average current of the output diode is obtained based on the average current in the demagnetization stage, the length of the demagnetization stage and the switching cycle, and the load current is constant by keeping the average current constant. At present, this method can be used in both discontinuous current mode and continuous current mode, and can obtain good output voltage accuracy.

[0004] However, the current primary feedback constant current control method ignores the effect of transformer leakage inductance on output current accuracy. When the leakage inductance is significant, the ratio of the average current of the primary winding to the average current of the output winding will be lower than the turns ratio of the primary winding to the secondary winding of the transformer. If the existing primary feedback constant current control method is used, the actual output current will be lower than the target reference current. In order to solve this problem, a special winding method is usually used to reduce the transformer leakage inductance and increase the clamping resistance value to increase the clamping capacitor voltage. However, the special winding method will increase the difficulty and cost of winding the transformer, and the clamping voltage of the clamping circuit is high, and the drain voltage of the switch tube increases, resulting in an increased breakdown risk. Summary of the invention

[0005] In view of the above problems and technical requirements, the inventors have proposed a constant current control system for a large leakage inductance primary-side feedback flyback converter, which simplifies circuit control and improves output current accuracy.

[0006] The technical solution of the present invention is as follows:

[0007] A constant current control system of a large leakage inductance primary-side feedback flyback converter, comprising a main topology circuit and a control circuit forming a closed loop with the main topology circuit;

[0008] The main topology circuit includes the primary and secondary windings of the transformer, a switch tube, an auxiliary winding, a clamping circuit and an output circuit; the primary winding is located on the input side, its same-name end is connected to the positive end of the DC voltage, its opposite-name end is connected to the drain end of the switch tube, and the source end of the switch tube is connected to the input side ground end through a current sampling resistor; the clamping circuit includes a clamping diode and a clamping capacitor and a clamping resistor in parallel, the positive electrode of the clamping diode is connected to the drain end of the switch tube, the negative electrode of the clamping diode is connected to the positive electrode of the clamping capacitor, and the negative electrode of the clamping capacitor is connected to the source end of the switch tube; the secondary winding is located on the output side, and the secondary winding is connected to the output circuit; the auxiliary winding is located on the input side, and the two ends of the auxiliary winding are connected in series with a voltage divider resistor, and the same-name end of the auxiliary winding is connected to the input side ground end;

[0009] The voltage of the current sampling resistor is used as the first input signal of the control circuit. The peak current, average current and conduction time of the clamping diode of the primary winding are calculated in combination with the voltage signal. The voltage division value of the auxiliary winding is used as the second input signal of the control circuit to obtain the demagnetization time of the transformer. The average current of the diode in the output circuit is calculated in combination with the peak current, average current of the primary winding, conduction time of the clamping diode, demagnetization time and switching period of the transformer.

[0010] Its further technical solution is that the control circuit is located on the input side, and includes a primary current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM drive module; the in-phase input end of the primary current detection module receives a first input signal, and the inverting input end receives a voltage signal provided by the PID calculation module; the output end of the primary current detection module is connected to the input end of the output current calculation module; the primary current detection module is used to calculate the peak current, average current and conduction time of the primary winding based on the comparison result of the current sampling resistor voltage and the voltage signal and the switch tube drive signal; the input end of the demagnetization time detection module receives a second input signal, the output end of the demagnetization time detection module is connected to the input end of the output current calculation module, and the demagnetization time detection module is used to obtain the demagnetization time of the transformer in the current mode based on the comparison result of the auxiliary winding demagnetization value and zero and the switch tube drive signal; the output current calculation module is connected to the PWM drive module through the PID calculation module, the output current calculation module is used to calculate the average current of the diode in the output circuit, and the PWM drive module outputs the drive signal of the switch tube as the output signal of the control circuit, which is connected to the gate end of the switch tube.

[0011] A further technical solution thereof is that the primary side current detection module includes a first comparator, a second comparator, and a primary side current calculation unit. The non-inverting input terminals of the first comparator and the second comparator serve as the non-inverting input terminal of the primary side current detection module to receive the first input signal v p , the inverting input terminal of the first comparator serves as the inverting input terminal of the primary side current detection module to receive the first voltage signal V pp , the inverting input terminal of the second comparator serves as the inverting input terminal of the primary side current detection module to receive the second voltage signal V pm , and V pm = k * V pp , where 0 < k < 1; when v p > V pp , the first comparator outputs a high level, otherwise it outputs a low level; when v p > V pm , the second comparator outputs a high level, otherwise it outputs a low level; the output terminals of the first comparator and the second comparator and the switch tube drive signal are connected to the input terminal of the primary side current calculation unit, and the output terminal of the primary side current calculation unit serves as the output terminal of the primary side current detection module to output the calculated peak current I p max , average current I pav and the conduction time T c of the clamping diode;

[0012] When the switch tube drive signal is at a high level, obtain the time length t1 when the output results of the first comparator and the second comparator are both at a low level, and obtain the time length t2 when the output result of the first comparator is at a low level and the output result of the second comparator is at a high level; when the switch tube drive signal is at a low level, obtain the time length t3 when the output results of the first comparator and the second comparator are both at a high level, and obtain the time length t4 when the output result of the first comparator is at a low level and the output result of the second comparator is at a high level, and substitute them into the corresponding calculation formulas to obtain the values of I p max , I pav and T c , and the expressions are respectively:

[0013]

[0014]

[0015]

[0016] Among them, R p is the resistance value of the current sampling resistor.

[0017] A further technical solution is that the demagnetization time detection module includes a third comparator and a demagnetization time calculation unit, and the in-phase input end of the third comparator serves as the input end of the demagnetization time detection module to receive the second input signal v FB , the inverting input terminal of the third comparator is set to zero potential, when v FB >0, the third comparator outputs a high level, otherwise it outputs a low level; the output end of the third comparator and the switch tube driving signal are connected to the input end of the demagnetization time calculation unit, and the output end of the demagnetization time calculation unit is used as the output end of the demagnetization time detection module to output the demagnetization time of the transformer in the current mode;

[0018] In the demagnetization time calculation unit, a state variable of the transformer in a switching cycle is defined based on the output result of the third comparator and the switch tube driving signal, and the working mode of the transformer is determined according to the change of the state variable, and the state variable includes a low-level state, a first-level state, a second-level state and a third-level state from low to high; when in the continuous current mode, the time length of the first-level state is obtained as the demagnetization time in this mode, and when in the discontinuous current mode, the time length T of the first-level state is obtained respectively. r_temp and the duration of the second level state t valley , based on [T r_temp -(t valley / 2)] as the demagnetization time in this mode.

[0019] A further technical solution is that the input signal of the output current calculation module also includes the switching cycle provided by the PID calculation module, and the output signal of the output current calculation module is the average current of the diode in the output circuit of the current cycle, expressed as:

[0020]

[0021] Among them, n ps is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding, I p max is the peak current of the primary winding, I pav is the average current of the primary winding, T c is the conduction time of the clamping diode, T r is the demagnetization time of the transformer in the current mode, T s is the current switching cycle.

[0022] Its further technical solution is that the input signal of the PID calculation module is the average current of the diode in the output circuit, and the output signal of the PID calculation module is the first voltage signal, the second voltage signal and the switching cycle obtained by error calculation and PID compensation algorithm. The average current of the diode in the output circuit is controlled to be equal to the target reference current to be achieved, so as to achieve constant output current; wherein, the first voltage signal and the second voltage signal are transmitted to the inverting input terminal of the primary current detection module, and the switching cycle is transmitted to the PWM drive module.

[0023] Its further technical solution is that the input signal of the PWM drive module includes the switching cycle provided by the PID calculation module, the comparison result of the current sampling resistor voltage provided by the primary current detection module and the first voltage signal, and the output signal of the PWM drive module is the drive signal of the switch tube, which is expressed as: the drive signal is set to a high level and the switch tube is turned on every switching cycle, and when the comparison result changes from low to high, the drive signal is set to a low level and the switch tube is turned off.

[0024] A further technical solution is to define a state variable of the transformer in a switching cycle based on the output result of the third comparator and the switch tube drive signal, and determine the working mode of the transformer according to the change of the state variable, including:

[0025] When the switch tube driving signal is at a high level, the state variable is at a low level;

[0026] When the switch tube driving signal is at a low level, if the output result of the third comparator changes from a low level to a high level, the state variable switches to the first level state; if the state variable is at the first level state, and the output result of the third comparator changes from a high level to a low level, the state variable switches to the second level state; if the state variable is at the second level state, and the output result of the third comparator changes from a low level to a high level, the state variable switches to the third level state;

[0027] When the state variable switches only between the low level state and the first level state, the transformer operates in a continuous current mode; when the state variable switches between four level states, the transformer operates in a discontinuous current mode.

[0028] The beneficial technical effects of the present invention are:

[0029] The system reduces the circuit complexity by adjusting the clamping circuit structure of the primary feedback flyback converter, and the current flowing into the clamping circuit is obtained by the low-voltage current sampling resistor voltage, and there is no need to perform high-voltage current or voltage sampling on the traditional clamping circuit, which greatly reduces the difficulty of current sampling in the clamping circuit; by performing voltage discrimination on the primary sampling resistor voltage, the peak current, average current and conduction time of the primary winding and the clamping diode are obtained, and the demagnetization time of the auxiliary winding is obtained by performing voltage discrimination on the voltage division value of the auxiliary winding, and the accurate value of the average current of the output diode is obtained by comprehensive calculation, that is, the constant current control based on a simple peripheral circuit and calculation method can well eliminate the calculation error caused by large leakage inductance, and can still obtain good output current accuracy under large leakage inductance conditions; the system can be applicable to isolated or non-isolated switching power supply circuit structures, and has the advantages of versatility, reusability and portability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of a constant current control system of a large leakage inductance primary-side feedback flyback converter provided in the present application.

[0031] Figure 2 It is a schematic diagram of the working waveform of the primary current detection module provided in this application.

[0032] Figure 3 It is a schematic diagram of the relevant variable waveforms of the demagnetization time detection module provided in the present application; Figure (a) is the relevant variable waveform of the intermittent current mode, and Figure (b) is the relevant variable waveform of the continuous current mode.

[0033] Figure 4 It is a schematic diagram related to the calculation method of the average current of the output circuit diode for the output current calculation module provided by the present application; Figure (a) is a schematic diagram of the calculation method in the discontinuous current mode, and Figure (b) is a schematic diagram of the calculation method in the continuous current mode.

[0034] Figure 5 It is a schematic diagram related to the calculation method of the average current of the output diode of the traditional primary-side feedback flyback converter; Figure (a) is a schematic diagram of the calculation method in the discontinuous current mode, and Figure (b) is a schematic diagram of the calculation method in the continuous current mode. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0036] This embodiment provides a constant current control system for a large leakage inductance primary feedback flyback converter. Compared with a traditional primary feedback flyback converter, an auxiliary winding is added on the input side, and the structure of the input side clamping circuit is adjusted. On the basis of simplifying the circuit control, a certain calculation method is combined to improve the accuracy of the average current of the output diode. The specific structure of this constant current control system for a large leakage inductance primary feedback flyback converter will be described in detail below.

[0037] like Figure 1 As shown in FIG. 1 , the system includes a main topology circuit and a control circuit forming a closed loop with the main topology circuit. The main topology circuit includes the primary and secondary windings of the transformer, the switch tube M p , Auxiliary winding W a , clamping circuit and output circuit. Primary winding W p Located on the input side, its same-name end is connected to the positive end of the DC voltage V in , the negative end of the DC voltage is grounded, the primary winding W p The opposite end is connected to the switch tube M p The drain end of the switch tube M p The source end passes through a small resistance current sampling resistor R p Connect to the input side ground. The clamping circuit includes a clamping diode D c , Clamping capacitor C c and clamp resistor R c , clamping diode D c The positive pole of the switch tube M p The drain terminal of the clamping diode D c The negative terminal of the clamp capacitor C c The positive electrode of the clamp capacitor C c The negative pole of the switch tube M is connected p The source end, clamp capacitor C c and clamp resistor R c Parallel. Secondary winding W s Located on the output side, the output circuit includes an output diode D1 and a parallel output capacitor C L and load R L , secondary winding W s The opposite end is connected to the positive electrode of the output diode D1, and the negative electrode of the output diode D1 is connected to the output capacitor C L The positive terminal of the output capacitor C L The negative pole and secondary winding W s The same-name terminals of the auxiliary winding W are connected to the output ground terminal. a Located on the input side, the auxiliary winding W a The two ends of the current sampling resistor are connected in series with the voltage divider resistors R1 and R2, and their same-name terminals are connected to the input side ground terminal. p As the first input signal of the control circuit, the auxiliary winding W a The voltage divider value VFB The second input signal of the control circuit is connected to the control circuit and is used to calculate the average current of the output diode D1.

[0038] In this embodiment, by making the above-mentioned adjustment to the clamp circuit structure, not only the circuit complexity is reduced, but also the current flowing into the clamp circuit is obtained by the easily accessible low-voltage end current sampling resistor voltage, and there is no need to sample the current or voltage at the high-voltage end of the traditional clamp circuit, which greatly reduces the difficulty of current sampling in the clamp circuit.

[0039] The control circuit is located on the input side, including a primary current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM drive module. Among them, the in-phase input end of the primary current detection module receives the first input signal, the inverting input end receives the voltage signal provided by the PID calculation module, the output end of the primary current detection module is connected to the input end of the output current calculation module, and the primary current detection module is used to calculate the current based on the current sampling resistor voltage v p The comparison result with the voltage signal and the switch tube drive signal is used to calculate the peak current, average current and conduction time of the primary winding. The input end of the demagnetization time detection module receives the second input signal, and the output end of the demagnetization time detection module is connected to the input end of the output current calculation module. The demagnetization time detection module is used to calculate the demagnetization time based on the auxiliary winding voltage V FB The comparison result with zero and the switch tube drive signal are used to obtain the demagnetization time of the transformer in the current mode. The output current calculation module is connected to the PWM drive module through the PID calculation module. The output current calculation module is used to calculate the average current of the output diode D1. The PWM drive module outputs the switch tube drive signal as the output signal of the control circuit and connects the switch tube gate end of the main topology circuit.

[0040] The system can effectively eliminate the calculation error caused by large leakage inductance based on simple peripheral circuits and calculation methods, and can still obtain good output current accuracy for the flyback converter with large leakage inductance, overcoming the problem of low actual output current in traditional solutions. Therefore, it has the advantages of low cost, simple control and high accuracy. The most fundamental reason for this advantage is that the present invention combines structural adjustment with simplified control. The specific structure and principle of each module will be introduced in detail below.

[0041] 1) Primary current detection module, whose input signal includes primary current sampling signal v p , voltage signal V pp and V pm , and the switch tube drive signal duty; the output signal includes the comparison result S comp1 , S comp1 The peak current I is transmitted to the PWM drive module to achieve peak current control, including the peak current Ip max and the average current I pav and the conduction time T of the clamping diode c , and these three signals are transmitted to the output current calculation module to calculate the accurate output current.

[0042] Specifically, this module includes a first comparator, a second comparator, and a primary current calculation unit. The non-inverting input terminals of the first comparator and the second comparator serve as the non-inverting input terminals of the primary current detection module to receive the first input signal v p , and the inverting input terminal of the first comparator serves as the inverting input terminal of the primary current detection module to receive the first voltage signal V pp , and the inverting input terminal of the second comparator serves as the inverting input terminal of the primary current detection module to receive the second voltage signal V pm , and V pm = k * V pp , where 0 < k < 1; when v p > V pp , the first comparator outputs a high level, otherwise it outputs a low level; when v p > V pm , the second comparator outputs a high level, otherwise it outputs a low level. The output terminals of the first comparator and the second comparator and the switch tube drive signal duty are connected to the input terminal of the primary current calculation unit, and the output terminal of the primary current calculation unit serves as the output terminal of the primary current detection module to output the calculated peak current I p max , average current I pav and the conduction time T of the clamping diode c .

[0043] Figure 2 is the working waveform of the primary current detection module in the continuous current mode (CCM), including the waveforms of the switch tube drive signal duty, v p , V pp , V pm , and the comparison results S comp1 , S comp2 . After duty is set to "1", after the turn-on delay t d , the switch tube turns on, and v p linearly rises from V pmin to its peak value V pmax . The calculation methods of relevant time variables are as follows: when the switch tube drive signal is at a high level "1", obtain the time length when the output results of the first comparator and the second comparator are both at a low level, denoted as t1; obtain the time length when the output result of the first comparator is at a low level and the output result of the second comparator is at a high level, that is, the time when v p rises from V pm to V ppWhen the switch tube driving signal is at a low level "0", the time length during which the output results of the first comparator and the second comparator are both at a high level is obtained, which is recorded as t3, which is the switch tube turn-off delay t d ; Get the length of time when the output result of the first comparator is low and the output result of the second comparator is high, that is, v p From V pp Down to V pm The length of time is recorded as t4.

[0044] Assuming that the turn-on delay and turn-off delay of the switch tube are equal, v p From V pmin Linearly rise to V pm The time length is t1-t d , which is t1-t3. Considering v p The slope of the rise k p is constant, so k is calculated p 、V pmin 、V pmax The value of is shown as follows:

[0045]

[0046]

[0047]

[0048] Based on V pmax With V pmin , and further calculate the peak current I of the primary current during the on-state phase of the switch tube p max With the average current I pav (That is, the primary current corresponding to the midpoint of the switch conduction phase) is shown in the following formula. pm Generally, it is between V pmax With V pmin The value between is usually taken as V mentioned above. pm = k*V pp , or V pm You can also take V pmax With V pmin The current calculation method of discontinuous current mode (DCM) is the same as that of CCM, so it will not be repeated here.

[0049]

[0050]

[0051] Considering v p The slope of the decrease is constant, based on V pmaxWith V pp The conduction time T of the clamping diode is calculated c As shown in Equation (6), considering that the actual t3 << t2 in Equation (2) (t3 is the turn-off delay of the switching transistor, which is generally very small), so V pp and V pmax (V pmax = I pmax * R p ) are approximately equal, then Equation (6) is further simplified to obtain Equation (7).

[0052]

[0053]

[0054] 2) The demagnetization time detection module, whose input signals include the auxiliary winding voltage division value v FB , 0V, and the switching transistor drive signal duty; the output signal is the demagnetization time T r of the transformer in the current mode, which represents the conduction time of the output diode D1, that is, the time length when the output diode current i d is greater than zero.

[0055] Specifically, this module includes a third comparator and a demagnetization time calculation unit. The non-inverting input terminal of the third comparator serves as the input terminal of the demagnetization time detection module to receive the second input signal v FB , and the inverting input terminal of the third comparator is set to zero potential. When v FB > 0, the third comparator outputs a high level, otherwise it outputs a low level. The output terminal of the third comparator and the switching transistor drive signal duty are connected to the input terminal of the demagnetization time calculation unit, and the output terminal of the demagnetization time calculation unit serves as the output terminal of the demagnetization time detection module to output the demagnetization time T r of the transformer in the current mode.

[0056] In the demagnetization time calculation unit, based on the output result S comp3 of the third comparator and the switching transistor drive signal duty, a state variable enable of the transformer in a switching cycle is defined, and the working mode of the transformer is determined according to the change of the state variable enable. The state variable enable includes a low level state "0", a first level state "1", a second level state "2", and a third level state "3" from low to high. Figure 3 is the waveform diagram of the demagnetization time detection module calculating the demagnetization time T FB based on duty, v r . The figure respectively shows the waveforms of duty, v FB , i d , S comp3 and enable. As Figure 3 As shown in (a) and (b), when the switch tube drive signal duty is at a high level, the state variable is at a low level state "0". When the switch tube drive signal duty is at a low level, if the output result S of the third comparator is comp3 When the state variable is in the first level state "1", and the output result S of the third comparator is comp3 When the state variable is in the second level state "2", and the output result S of the third comparator is comp3 When it changes from low to high level, the state variable switches to the third level state "3". The above state switching conditions are shown in Table 1.

[0057] Table 1. State variable switching conditions

[0058]

[0059] When the state variable enable switches between the four levels, the transformer operates in DCM, such as Figure 3 (a) As shown; In this mode, the time length T of the first level state "1" is obtained respectively. r_temp and the duration t of the second level state "2" valley , based on [T r_temp -(t valley / 2)] as the demagnetization time T in this mode r When the state variable enable switches only between the low level state "0" and the first level state "1", the transformer operates in CCM, such as Figure 3 (b) As shown; In this mode, the time length of the first level state "1" is obtained as the demagnetization time in this mode, that is, T r =T r_temp .

[0060] 3) Output current calculation module, whose input signal includes the peak current I of the primary winding p max , average current I pav , the conduction time of the clamping diode T c and the demagnetization time T in the current mode r , and the switching period T provided by the PID calculation module s ; The output signal is the average current I of the diode in the output circuit in the current cycle d1 .

[0061] Figure 4 After obtaining the above parameters, the average current of the output diode I d1 Schematic diagram of the calculation method, showing the primary winding current i p, excitation current i m and the output diode current i d The waveform of p As shown by the solid line, during the switch tube conduction stage i p Linear increase, at this time i m with i p Coincidence, i d is equal to zero; at i d When i is greater than zero, m Greater than i p .i d Proportional to i m with i p The difference is expressed as: d =n ps (i m -i p ), where n ps It is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding.

[0062] Figure 4 (a) is the relevant schematic diagram under DCM. The average current of the output diode D1 can be described as i d The average value of the integration over time is denoted as I d1 , and I d1 is proportional to the shaded area in the figure. m and i p In T r The average value after time integration is calculated, i m The integral over time can be expressed by I pav 、T r and T s Get, I p The integral over time can be expressed by I pmax 、T c and T s get. Figure 4 (b) is a schematic diagram of the calculation method under CCM. The calculation formula for the average current of the output diode D1 is consistent with that of DCM, which is expressed as:

[0063]

[0064] Figure 5 (a) and (b) are the design ideas of the traditional primary feedback flyback converter constant current control in two modes. The figure shows the primary winding current i p , excitation current i m and the output diode current i d The waveform is shown in Figure 2. Here, it is assumed that after the switch tube is turned off, the current of the primary winding of the transformer is immediately transferred to the output winding, that is, the charging stage of the clamping circuit by the primary leakage inductance is not considered. cThe energy loss caused by c =0. The average current of the output diode at this time is recorded as I d2 , and I d2 It is proportional to the area of ​​the shaded part in the figure, and the calculation formula is shown in formula (9). Compared with formula (8), it can be seen that the I calculated by the traditional scheme is d2 Than the actual value I d1 Therefore, when the leakage inductance is large and T c When the actual output current is significantly higher than I d2 When the solution proposed in this application is adopted, the deviation of the output current introduced by the large leakage inductance can be corrected.

[0065]

[0066] 4) PID calculation module, whose input signal is the average current I of the diode in the output circuit d1 The output signal is the first voltage signal V calculated by error calculation and PID compensation algorithm. pp , the second voltage signal V pm and the switching period T s , by controlling the average current I of the diode in the output circuit d1 Equal to the target reference current I REF , to achieve constant output current. Among them, the first voltage signal V pp , the second voltage signal V pm Transmitted to the inverting input terminal of the primary current detection module, the switching period T s Passed to the PWM driver module.

[0067] 5) PWM drive module, whose input signal includes the switching period T provided by the PID calculation module s , the comparison result S of the current sampling resistor voltage provided by the primary current detection module and the first voltage signal comp1 The output signal is the driving signal duty of the switch tube, and the waveform is expressed as: the time length of each switching cycle T s Set the drive signal to high level "1", turn on the switch tube, and when the comparison result S comp1 When it changes from low to high level, the drive signal is set to low level "0" and the switch tube is turned off to achieve peak current control.

[0068] In this embodiment, the peak current, average current and conduction time of the primary winding are obtained by voltage discrimination of the primary sampling resistor voltage, the demagnetization time of the auxiliary winding is obtained by voltage discrimination of the voltage division value, and the accurate value of the average current of the output diode is obtained by comprehensive calculation. The system is applicable to isolated or non-isolated switching power supply circuit structures, and has the advantages of versatility, reusability and portability.

[0069] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A constant current control system of a large leakage inductance primary side feedback flyback converter, characterized in that: It includes a main topology circuit and a control circuit forming a closed loop therewith; The main topology circuit includes a transformer primary and secondary windings, a switch tube, an auxiliary winding, a clamping circuit and an output circuit; the primary winding is located on the input side, its same-name end is connected to the positive end of the DC voltage, and its opposite-name end is connected to the drain end of the switch tube, and the source end of the switch tube is connected to the input side ground end through a current sampling resistor; the clamping circuit includes a clamping diode and a clamping capacitor and a clamping resistor in parallel, the positive electrode of the clamping diode is connected to the drain end of the switch tube, the negative electrode of the clamping diode is connected to the positive electrode of the clamping capacitor, and the negative electrode of the clamping capacitor is connected to the source end of the switch tube; the secondary winding is located on the output side, and the secondary winding is connected to the output circuit; the auxiliary winding is located on the input side, and the two ends of the auxiliary winding are connected in series with a voltage divider resistor, and the same-name end of the auxiliary winding is connected to the input side ground end; The voltage of the current sampling resistor is used as the first input signal of the control circuit, and the peak current, average current and conduction time of the clamping diode of the primary winding are calculated in combination with the voltage signal, and the voltage division value of the auxiliary winding is used as the second input signal of the control circuit to obtain the demagnetization time of the transformer, and the average current of the diode in the output circuit is calculated in combination with the peak current, average current of the primary winding, conduction time of the clamping diode, demagnetization time and switching period of the transformer; The control circuit is located at the input side, and includes a primary current detection module, a demagnetization time detection module, an output current calculation module, a PID calculation module and a PWM drive module; The non-inverting input terminal of the primary current detection module receives the first input signal, and the inverting input terminal receives the voltage signal provided by the PID calculation module. The output terminal of the primary current detection module is connected to the input terminal of the output current calculation module. The primary current detection module is used to calculate the peak current, average current and conduction time of the primary winding based on the comparison result between the current sampling resistor voltage and the voltage signal and the switch tube drive signal; The input end of the demagnetization time detection module receives the second input signal, the output end of the demagnetization time detection module is connected to the input end of the output current calculation module, and the demagnetization time detection module is used to obtain the demagnetization time of the transformer in the current mode based on the comparison result between the auxiliary winding demagnetization value and zero and the switch tube drive signal; the output current calculation module is connected to the PWM drive module through the PID calculation module, and the output current calculation module is used to calculate the average current of the diode in the output circuit, and the PWM drive module outputs the drive signal of the switch tube as the output signal of the control circuit, and is connected to the gate end of the switch tube.

2. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 1 is characterized in that: The primary side current detection module includes a first comparator, a second comparator and a primary side current calculation unit. The non-inverting input terminals of the first comparator and the second comparator serve as the non-inverting input terminal of the primary side current detection module to receive a first input signal v p , the inverting input terminal of the first comparator serves as the inverting input terminal of the primary side current detection module to receive a first voltage signal V pp , the inverting input terminal of the second comparator serves as the inverting input terminal of the primary side current detection module to receive a second voltage signal V pm , and V pm = k * V pp , where 0 < k < 1; when v p > V pp , the first comparator outputs a high level, otherwise outputs a low level; when v p > V pm , the second comparator outputs a high level, otherwise outputs a low level; the output terminals of the first comparator and the second comparator and the switch tube drive signal are connected to the input terminal of the primary side current calculation unit, and the output terminal of the primary side current calculation unit serves as the output terminal of the primary side current detection module to output the calculated peak current I pmax , average current I pav and the conduction time T c of the clamping diode; When the switch tube driving signal is at a high level, the time length t1 during which the output results of the first comparator and the second comparator are both at a low level is obtained, and the time length t2 during which the output result of the first comparator is at a low level and the output result of the second comparator is at a high level is obtained; when the switch tube driving signal is at a low level, the time length t3 during which the output results of the first comparator and the second comparator are both at a high level is obtained, and the time length t4 during which the output result of the first comparator is at a low level and the output result of the second comparator is at a high level is obtained, and the corresponding calculation formula is substituted to obtain I pmax ,I pav and T c The values ​​of are: Among them, R p is the resistance value of the current sampling resistor.

3. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 1, characterized in that: The demagnetization time detection module includes a third comparator and a demagnetization time calculation unit. The in-phase input terminal of the third comparator serves as the input terminal of the demagnetization time detection module to receive the second input signal v FB , the inverting input terminal of the third comparator is set to zero potential, when v FB >0, the third comparator outputs a high level, otherwise it outputs a low level; the output end of the third comparator and the switch tube driving signal are connected to the input end of the demagnetization time calculation unit, and the output end of the demagnetization time calculation unit is used as the output end of the demagnetization time detection module to output the demagnetization time of the transformer in the current mode; In the demagnetization time calculation unit, a state variable of the transformer in a switching cycle is defined based on the output result of the third comparator and the switch tube drive signal, and the working mode of the transformer is determined according to the change of the state variable, and the state variable includes a low-level state, a first-level state, a second-level state and a third-level state from low to high; when in the continuous current mode, the time length of the first-level state is obtained as the demagnetization time in this mode, and when in the discontinuous current mode, the time length T of the first-level state is respectively obtained. r_temp and the duration of the second level state t valley , based on [T r_temp -(t valley / 2)] as the demagnetization time in this mode.

4. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 1, characterized in that: The input signal of the output current calculation module also includes the switching cycle provided by the PID calculation module. The output signal of the output current calculation module is the average current of the diode in the output circuit in the current cycle, expressed as: Among them, n ps is the ratio of the number of turns of the primary winding to the number of turns of the secondary winding, I pmax is the peak current of the primary winding, I pav is the average current of the primary winding, T c is the conduction time of the clamping diode, T r is the demagnetization time of the transformer in the current mode, T s is the current switching cycle.

5. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 1, characterized in that: The input signal of the PID calculation module is the average current of the diode in the output circuit, and the output signal of the PID calculation module is the first voltage signal, the second voltage signal and the switching cycle obtained by error calculation and PID compensation algorithm. The average current of the diode in the output circuit is controlled to be equal to the target reference current to be achieved, so as to achieve constant output current; wherein, the first voltage signal and the second voltage signal are transmitted to the inverting input terminal of the primary current detection module, and the switching cycle is transmitted to the PWM drive module.

6. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 1, characterized in that: The input signal of the PWM driving module includes the switching cycle provided by the PID calculation module, the comparison result of the current sampling resistor voltage provided by the primary current detection module and the first voltage signal, and the output signal of the PWM driving module is the driving signal of the switching tube, which is expressed as: the driving signal is set to a high level and the switching tube is turned on every switching cycle; when the comparison result changes from low to high, the driving signal is set to a low level and the switching tube is turned off.

7. The constant current control system of the large leakage inductance primary side feedback flyback converter according to claim 3, characterized in that: Defining a state variable of the transformer in a switching cycle based on the output result of the third comparator and the switch tube driving signal, and determining the working mode of the transformer according to the change of the state variable, includes: When the switch tube driving signal is at a high level, the state variable is at a low level; When the switch tube driving signal is at a low level, if the output result of the third comparator changes from a low level to a high level, the state variable is switched to a first level state; if the state variable is at the first level state and the output result of the third comparator changes from a high level to a low level, the state variable is switched to a second level state; if the state variable is at the second level state and the output result of the third comparator changes from a low level to a high level, the state variable is switched to a third level state; When the state variable switches only between the low level state and the first level state, the transformer operates in a continuous current mode; when the state variable switches between four level states, the transformer operates in a discontinuous current mode.

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