WO2021146980A1

WO2021146980A1 - Switch power source converter

Info

Publication number: WO2021146980A1
Application number: PCT/CN2020/073708
Authority: WO
Inventors: 严亮; 李鹏
Original assignee: Msj系统有限责任公司
Priority date: 2020-01-22
Filing date: 2020-01-22
Publication date: 2021-07-29

Abstract

The present invention relates to a switch power source converter, comprising: a transformer that includes a primary winding and a secondary winding, a power switch circuit and a voltage input circuit that are connected to the primary winding, a voltage output circuit connected to the secondary winding, an auxiliary winding coupled to the secondary winding, a control circuit connected to the power switch circuit, a current acquisition circuit connected to the control circuit and the power switch circuit, and a voltage sampling circuit connected to the auxiliary winding and the control circuit. The control circuit comprises: a timing unit used for acquiring a turn-off time of the power switch circuit to output a corresponding signal; a reference signal output unit connected to the current acquisition circuit; a drive unit connected to the timing unit and the reference signal output unit; and a sampling unit connected to the drive unit and the voltage sampling circuit. By means of the implementation of the present invention, the optimal sampling point sampling voltage of a feedback voltage can be acquired in real time in a switch period, and the scheme thereof is simple.

Description

Switching power converter

Technical field

The present invention relates to the technical field of power supplies, and more specifically, to a switching power supply converter, especially a flyback converter.

Background technique

The loop control of the traditional flyback converter directly detects the output voltage, generates feedback and compensation signals, and determines the duty cycle of the main power switch according to the compensation signal, thereby controlling the output, such as the output voltage. When electrical isolation is required between the input and output of the switching power supply, such as in the application of off-line converters, the feedback compensation circuit and the control circuit are often on both sides of the electrical isolation device, that is, one side is the input side (here called "primary side") ), the other side is the output side (here called "secondary side"). There is no direct common electrical connection between the primary and secondary sides, and isolation devices such as optocouplers are usually used to transmit signals. Isolation devices and their attached circuits increase the cost and size of the system. In many low-cost applications, primary-side detection methods are often used. This method is based on the principle of transformer coupling. When the primary side main switch is turned off and the output rectifier is turned on, the secondary winding of the transformer bears the output voltage. Due to the coupling between the auxiliary winding and the secondary winding, the voltage on the auxiliary winding and the secondary winding The winding voltage is proportional. Therefore, the control circuit on the primary side can indirectly detect the output voltage value by detecting the voltage on the auxiliary winding.

Based on Figure 7, where the input voltage Vin, S1 is the primary switch tube. The transformer Tx1 has a primary winding Np, a secondary winding Ns, and an auxiliary winding Na. D1 is the output rectifier tube, and its conduction voltage drop is Vf. The control circuit output signal DRV drives S1 to turn on and off. When S1 is turned on, the transformer receives and stores energy from the input Vin. When S1 is turned off, the transformer releases energy to the output. The power supply of the control circuit is provided by the auxiliary winding through the rectifier tube D2. The control circuit obtains output voltage information by detecting the signal from the auxiliary winding Na to FB. As shown in Figure 8, when the main switch tube drive signal DRV is turned off, the voltage detected by the auxiliary winding voltage can be expressed as

Among them: V _FB is the feedback signal; Vout is the output voltage; Vf is the conduction voltage drop of the output rectifier; Isec is the secondary side current of the transformer; Rsec is the equivalent resistance of the secondary side output circuit; Na is the number of turns of the auxiliary winding of the transformer; Ns Is the number of turns on the secondary side of the transformer. When the secondary side current drops to the minimum value, as shown in point A, Isec=0, Vf is also close to 0, and V _FB can feed back the output voltage Vout most accurately. So many methods have been proposed, the purpose is to sample the output voltage close to the A point.

In the US patent "US Patent no. 7,463,497 B2", two sampling and holding circuit channels are used to alternately detect the V _FB voltage. When a sudden change in the falling slope of _{V FB is detected, a stop signal is output.} The last sampling value of the V _FB voltage before the stop signal is used as the effective sampling voltage. This method is easy to implement, but requires two high-speed sampling and holding circuit channels, which is relatively expensive.

In the US patent "US Patent no. 6,956,750 B1", two variable voltage levels are used to track the position of the sudden change point of the _{V FB} slope, and the effective sampling voltage can be tracked and obtained through the relative position information of the _{two levels and V FB.} This method actively finds the location of the sampling point, but requires a complex digital control algorithm, which is costly.

Moreover, it is necessary to determine the sampling position of the next cycle based on the results of the previous cycle. When the signal voltage changes quickly, it cannot quickly keep up.

Summary of the invention

Aiming at the above-mentioned existing disadvantages of the prior art, the present invention provides a switching power supply converter.

The technical solution adopted by the present invention to solve its technical problems is to construct a switching power supply converter, including: a transformer including a primary winding and a secondary winding, a power switch circuit and a voltage input circuit connected to the primary winding, A voltage output circuit connected to the secondary winding, an auxiliary winding coupled to the secondary winding, and

A control circuit connected to the power switch circuit, a current acquisition circuit connected to the control circuit and the power switch circuit, and a voltage sampling circuit connected to the auxiliary winding and the control circuit;

The control circuit includes: a timing unit for obtaining the off time of the power switch circuit to output a corresponding signal;

A reference signal output unit that is connected to the current acquisition circuit to acquire a peak current or its equivalent peak voltage, and provides a reference signal according to the peak current or the equivalent peak voltage;

A drive unit connected to the timing unit and the reference signal output unit for generating a drive signal according to the output signal of the timing unit and the reference signal of the reference signal output unit;

A sampling unit connected to the driving unit and the voltage sampling circuit for receiving the driving signal for sampling to obtain the sampling voltage of the voltage sampling circuit and outputting an effective sampling voltage.

Preferably, the current acquisition circuit includes a current sampling circuit, the current sampling circuit includes a sampling resistor, the first end of the sampling resistor is respectively connected to the control circuit and the power switch circuit, and the second end of the sampling resistor Ground; or

The current acquisition circuit includes a current setting circuit, the current setting circuit includes an adjusting resistor, the first end of the adjusting resistor is respectively connected to the control circuit and the power switch circuit, and the second end of the adjusting resistor is grounded.

Preferably,

The timing unit includes: a current source, a charging unit and a reset unit;

The first end of the charging unit is respectively connected to the current source and the driving unit, and the second end of the charging unit is grounded;

The first end of the reset unit is connected to the first end of the charging unit, the second end of the reset unit is connected to the second end of the charging unit, and the third end of the reset unit is used to receive a reset signal So as to realize the discharge reset of the charging unit;

The reference signal output unit includes a peak holding unit and a first multiplier;

The first end of the peak holding unit is connected to the current acquisition circuit, the second end of the peak holding unit is connected to the first input end of the first multiplier, and the second input end of the first multiplier is input The first coefficient, wherein the first coefficient corresponds to the circuit parameter of the timing unit.

Preferably,

The charging unit includes a charging capacitor Cs, a first end of the charging capacitor Cs is connected to the current source, and a second end of the charging capacitor Cs is grounded;

The reference signal satisfies the following formula:

V _{ref_sample} = K _c1 R _is I _pk

Wherein, V _{ref_sample} is the reference signal, K _c1 is the first coefficient, R _is is the resistance value of the sampling resistor or the adjustment resistor, and I _pk is the peak current value;

And when the output voltage V _out of the voltage output circuit is a stable value, the first coefficient satisfies the following formula:

Wherein, L _m is the magnetizing inductance of the primary winding, n is an primary winding of the turns ratio of the secondary winding, V _out is the output voltage value of the voltage output circuit, I _s is a current source The current value, C _s is the capacitance value of the charging capacitor.

Preferably,

The current source is a voltage-controlled current source, the voltage-controlled input terminal of the voltage-controlled current source is connected to the output terminal of the sampling unit, and the output terminal of the voltage-controlled current source is connected to the charging unit;

The control circuit further includes a second multiplier, the first input of the second multiplier is connected to the sampling unit, and the second input of the second multiplier is input with a second coefficient;

And when the output voltage V _out of the voltage output circuit is a varying value, the first coefficient satisfies the following formula:

Wherein, K _i is the second coefficient, and K _v is the sampling ratio coefficient of the voltage sampling circuit.

Preferably,

The reset unit includes a switch tube S2, the control electrode of the switch tube S2 receives the reset signal, the first terminal source of the switch tube S2 is connected to the first terminal of the charging unit, and the switch tube S2 The second terminal is grounded. .

Preferably,

The timing unit includes: a clock source and a step counter;

The first end of the step counter is connected to the clock source, the second end of the step counter is connected to the drive unit, and the third end of the step counter is connected to receive a reset signal;

The reference signal output unit includes a peak holding unit, a first analog-to-digital conversion unit, and a third multiplier;

The first end of the peak holding unit is connected to the current acquisition circuit, the second end of the peak holding unit is connected to the first input end of the third multiplier via the first analog-to-digital conversion unit, and the first The third coefficient is input to the second input terminal of the three multiplier;

The reference signal satisfies the following formula:

V _{ref_sample} = K _c2 R _is I _pk

Wherein, V _{ref_sample} is the reference signal, K _c2 is the third coefficient, R _is is the resistance value of the sampling resistor or the adjustment resistor, and I _pk is the peak current value;

And when the output voltage V _out of the output circuit is a stable value, the third coefficient satisfies the following formula:

Where L _m is the magnetizing inductance of the primary winding, n is the turns ratio of the primary winding to the secondary winding, V _out is the output voltage value of the voltage output circuit, and T _CLK is the clock source Clock cycle.

Preferably,

The reference signal output unit further includes a divider and a second digital-to-analog conversion unit; the first input terminal of the divider is connected to the output terminal of the third multiplier, and the second input terminal of the divider passes through the The second digital-to-analog conversion unit is connected to the sampling unit,

And when the output voltage V _out of the voltage output circuit is a varying value, the third coefficient satisfies the following formula:

Wherein, K _v is the sampling ratio coefficient of the voltage sampling circuit.

Preferably,

The control circuit also includes an enabling unit connected to the driving unit, a PWM control unit connected to the enabling unit, a working drive of the PWM control unit, and a connection between the driving unit and the PWM control unit, A reset signal output unit for outputting the reset signal.

Preferably,

The reset signal output unit includes a latch, a first input end of the latch is connected to the driving unit, a second input end of the latch is connected to a PWM control unit, and an output end of the latch The reset signal is output.

Preferably,

The driving unit includes a comparator, the same direction input terminal of the comparator is connected to the timing unit, the reverse input terminal of the comparator is connected to the reference signal output unit, and the output terminal of the comparator is connected to the timing unit. Sampling unit.

A switching power converter implementing the present invention has the following beneficial effects: the optimal sampling point sampling voltage of the feedback voltage can be obtained in real time during the switching period, and the solution is simple.

Description of the drawings

The present invention will be further described below in conjunction with the accompanying drawings and embodiments. In the accompanying drawings:

Fig. 1 is a schematic structural diagram of an embodiment of a switching power converter of the present invention;

Figure 2 is a schematic circuit diagram of an embodiment of a switching power converter of the present invention;

Fig. 3 is a circuit schematic diagram of an embodiment of the control circuit in Fig. 1;

Fig. 4 is a schematic circuit diagram of another embodiment of the control circuit in Fig. 1;

FIG. 5 is a schematic circuit diagram of another embodiment of the control circuit in FIG. 1;

Fig. 6 is a schematic circuit diagram of another embodiment of the control circuit in Fig. 1;

Fig. 7 is a circuit schematic diagram of an existing flyback converter;

Fig. 8 is an explanatory diagram of feedback sampling in a flyback converter based on Fig. 7.

Detailed ways

In order to have a clearer understanding of the technical features, objectives and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in Figures 1 and 2, in an embodiment of a flyback converter of the present invention, it includes: a transformer including a primary winding 210 and a secondary winding 220, and a power switch circuit connected to the primary winding 210 40 and the voltage input circuit 10, the voltage output circuit 30 connected to the secondary winding 220, the auxiliary winding 70 coupled with the secondary winding 220, and

The control circuit 50 connected to the power switch circuit 40, the current acquisition circuit 61 connected to the control circuit 50 and the power switch circuit 40, and the voltage sampling circuit 62 connected to the auxiliary winding 70 and the control circuit 50;

The control circuit 50 includes: timing

units

510a, 510b for obtaining the off time of the power switch circuit 40 to output corresponding signals; connected to the current obtaining circuit 61 for obtaining the peak current or its equivalent peak voltage, and according to the peak current or The reference

signal output units

520a, 520b whose equivalent peak voltages provide reference signals; the

timing units

510a, 510b are connected with the reference

signal output units

520a, 520b, and the reference

signal output units

520a, 520b are connected to the output signals of the

timing units

510a, 510b. The reference signal of 520b generates the

driving unit

530a, 530b of the driving signal; connects the

driving unit

530a, 530b and the voltage sampling circuit 62 to receive the driving signal for sampling to obtain the sampling voltage of the voltage sampling circuit 62 and output the sampling of the effective

sampling voltage Units

540a, 540b; the control circuit 50 controls the work according to the effective sampling voltage.

Specifically, the flyback converter has the following basic relationships:

L _m I _pk = nV _out T _r

Among them, L _m is the magnetizing inductance of the primary winding 210 of the transformer; I _pk is the peak current value of the primary winding 210; n is the turns ratio of the primary winding 210 of the transformer to the secondary winding 220; V _out is the output voltage value ; T _r is the demagnetization time of the transformer, the output is oN time of the current, which is typically part of the power switching circuit at the time of off. T _r end point in time can be considered the ideal sampling point. For a certain design, the parameters L _m , n and the steady-state output voltage V _out are certain. Thus the target sample point T _r can be considered proportional to the winding peak current I _pk 210 with the primary side. That is, as long as the value of the current I _pk period is known, the target sample point T _r can be calculated and determined accordingly. In order to obtain the sampling voltage value of the sampling point, the driving

units

530a and 530b drive the

sampling units

540a and 540b to sample at this time point to obtain the sampling voltage of the voltage sampling circuit 62 at this time as the effective sampling voltage. In this sampling process, the voltage at the corresponding time point is obtained by sampling and holding. In order to obtain the time points when the driving

units

530a and 530b output the driving signals, the driving

units

530a and 530b are respectively connected to the

timing units

510a and 510b and the reference

signal output units

520a and 520b, wherein the

timing units

510a and 510b are set to be in each switching cycle After the main switch S1 is turned off, that is, when the transformer begins to demagnetize, the elapsed time of transformer demagnetization is recorded, and when the relationship between the elapsed time and the reference signal output of the reference

signal output units

520a, 520b meets the preset conditions, the drive The

units

530a and 530b start to output driving signals, and an ideal effective sampling voltage can be obtained at this time. I.e., the target sample point according to the time of the start of the transformer T _r after demagnetization is known, in order to perform a corresponding operation in a time period of the switching point, a reasonable

set timer unit

510a, 510b, and the reference

signal output unit

520a, 520b, so that each just to meet the relationship between the target sampling point in a preset relationship when T _r, thereby automatically given by the sampling circuit driving the target point Tr of the sample. According to the above described Meanwhile, after selecting a transformer T _r target sampling point acquiring winding peak current I _pk 210 related to the original circuit 61 acquires the current side, some of the time, the peak current may be equivalent to a peak voltage, That is, when setting the parameters of the reference

signal output units

520a and 520b, the peak current I _{pk of the} primary winding 210 needs to be considered at the same time. After obtaining the target sample point T _r the effective sampling voltage, the control circuit 50 may perform a corresponding operation based on the effective sampling voltage, for example, adjusting the duty cycle of the power switch 40 of the switching circuit.

Optionally, in an embodiment, the current acquisition circuit includes a current sampling circuit, the current sampling circuit includes a sampling resistor, and the first end of the sampling resistor is respectively connected to the control circuit and the power switch circuit, The second end of the sampling resistor is grounded; specifically, the peak current I _{pk of the} primary winding 210 can be obtained by a current sampling circuit, that is, it can be understood that the peak current I _pk can be obtained by a sampling resistor, for example, a current sampling resistor If the resistance value is R _is _{, the voltage value I pk} R _is sampled by the peak current of the sampling resistor is obtained to obtain the peak current I _pk .

In another embodiment, the current acquisition circuit includes a current setting circuit, the current setting circuit includes an adjusting resistor, and the first end of the adjusting resistor is respectively connected to the control circuit and the power switch circuit, and the adjusting resistor The second end of the resistor is grounded. Specifically, if the switching power converter adopts the peak current control mode, the voltage value I _pk R _is corresponding to the peak current is determined by the control amount of the peak current inside the control circuit. That is, the peak current is set by the current setting circuit inside the current acquisition circuit. After the peak current is set, the actual peak current is adjusted by the adjusting resistor. In this control mode circuit, the voltage value of the peak current also satisfies I _pk R _is , Where R _is is the resistance value of the adjustment resistor.

As shown in FIG. 3, in an embodiment, the timing unit 510a includes: a current source 511a, a charging unit 513a, and a reset unit 512a; the first end of the charging unit 513a is connected to the current source 511a and the driving unit 530a, and the charging unit 513a The second end of the reset unit 512a is connected to the ground; the first end of the reset unit 512a is connected to the first end of the charging unit 513a, the second end of the reset unit 512a is connected to the second end of the charging unit 513a, and the third end of the reset unit 512a is used to receive a reset The reference signal output unit 520a includes a peak holding unit 521a and a first multiplier 522a; the first end of the peak holding unit 521a is connected to the current acquisition circuit 61, and the second end of the peak holding unit 521a The first input terminal of the first multiplier 522a is connected, and the second input terminal of the first multiplier 522a inputs a first coefficient, wherein the first coefficient corresponds to the circuit parameter of the timing unit 510a. Specifically, the current source 511a in the control circuit 50 starts to work and charges the charging unit 513a. During the charging process of the charging unit 513a, its charging voltage increases with the charging process, and the charging voltage is input as the output voltage of the timing unit 510a a driving unit 530a, a drive unit 530a according to the charging voltage is compared with a reference signal from the reference signal output from the output unit 520a generates a drive signal when the relationship between them satisfy the preset condition, i.e. the time point corresponding to the target sampling point T _r. At the same time, the reset unit 512a can receive the reset signal to discharge the charging unit 513a, so that the charging unit 513a can restore the initial state, so that the same operation can be performed in the next switching cycle. The reference signal output unit 520a can obtain the peak current through the peak holding unit 521a, that is, it obtains the current of the current obtaining circuit 61 and obtains its peak value, and inputs the peak current as a sampled output to the first multiplier 522a. The other input terminal of 522a is used to output a fixed coefficient, that is, the first coefficient. The first coefficient is selected according to the circuit parameters of the timing unit 510a, and the corresponding relationship between the peak current and the timing unit 510a is established through the first multiplier 522a, so that timing unit 510a and the reference signal output unit 520a just to meet a predetermined relation when the target sample point T _r.

In an embodiment, the charging unit 513a includes a charging capacitor C _s , the first end of the charging capacitor C _s is connected to the current source 511 a, and _{the second end of the charging capacitor C s} is grounded; the reference signal satisfies the following formula:

V _{ref_sample} = K _c1 R _is I _pk

Wherein, V _{ref_sample} is the reference signal, K _c1 is the first coefficient, I _pk is the peak current value, and R _is is the resistance value of the sampling resistor or the adjustment resistor;

And when the output voltage V _out of the secondary winding 220 is a stable value, the first coefficient satisfies the following formula:

Among them, L _m is the excitation inductance of the primary winding 210, n is the turns ratio of the primary winding 210 to the secondary winding 220, V _out is the output voltage value of the voltage output circuit 30, I _s is the current value of the current source 511a, C _s is the capacitance value of the charging capacitor, and R _is is the resistance value of the sampling resistor or adjusting resistor. Specifically, the charging unit 513a may use a charging capacitor. After the reset signal reset is released, the charging capacitor starts to be charged. During the rising of the charging voltage, the relationship between the charging voltage of the charging capacitor and the reference signal satisfies the preset condition, and the driving unit 530a generates a driving signal. The setting of the first coefficient related to the reference signal can be set according to the parameters of the charging capacitor and the current source, that is _{, the setting of K c1} satisfies the above formula. I.e., a known value of the capacitor charging, the charging time of the charging capacitor is provided a charging capacitor charging, the charging voltage of the capacitor preset condition to satisfy the target charging voltage at the sample point T _r is the time of charging, i.e. the target sample when the charge voltage value set as a reference point signal T _r. Define T _sample as the charging time of the charging capacitor, and the charging voltage V _{s of the} charging capacitor satisfies the following formula:

Charging time T _sample set as a target sample point T _r, the charging voltage is obtained at point T _r is:

In order to set the driving unit 530a to trigger at this time point, V _{s1 is} set as the threshold value of the reference signal V _{ref_sample} , that is, V _{ref_sample} is set to satisfy the following formula:

In the above formula, L _m is the excitation inductance of the primary winding 210, n is the turns ratio of the primary winding 210 to the secondary winding 220, V _out is the output voltage of the voltage output circuit 30, which is a fixed value, and I _s is the current The current of the source 511a, C _s is the capacitance value of the charging capacitor, which are all known parameters after the circuit design, where I _pk is the peak current; it is a variable. According to the known parameters, a fixed coefficient K _{c1 is} obtained, and the obtained reference signal satisfies the following formula:

V _{ref_sample} = K _c1 R _is V _ipk

Therefore, the setting of the first coefficient K _c1 needs to satisfy the following formula:

Through the first multiplier 522, the variable I _pk R _is and the first coefficient K _c1 can be output from different input terminals, and the output terminal can obtain _{the reference signal that varies with the peak current I pk} , and obtain a reasonable target sampling point. T _r . Can also be understood, as long as the real-time according to I _pk value, multiplied by a fixed ratio K _c1 R _{_is} determined _V ref_sample, sampling points can be obtained in the demagnetization of the transformer T _sample time equals T _r, and thus to obtain accurate feedback Sampling point to obtain an effective sampling voltage.

As shown in FIG. 4, in one embodiment, the current source 511a is a voltage-controlled current source, the voltage-controlled input terminal of the voltage-controlled current source is connected to the output terminal of the sampling unit 540a, and the output terminal of the voltage-controlled current source is connected to the charging unit 513a. The control circuit 50 also includes a second multiplier 591a. The first input terminal of the second multiplier 591a is connected to the sampling unit 540a, and the second input terminal of the second multiplier 59a1 inputs the second coefficient; and the output voltage of the secondary winding 220 When V _out is a variable value, the first coefficient satisfies the following formula:

Among them, L _m is the excitation inductance of the primary winding 210, n is the turns ratio of the primary winding 210 to the secondary winding 220, C _s is the capacitance value of the charging capacitor, K _i is the second coefficient, and K _v is the output voltage sampling Scale factor. Specifically, during the operation of the system, the output V _out will change. In order to allow the sampling system to adapt to changes in output voltage, the current source 511a is set to the feedback voltage V _{fb_sample of} _{V out} , that is, the voltage-controlled current source controlled by the effective sampling voltage, that is, the voltage-controlled input terminal of the voltage-controlled current source is connected to the sampling unit 540a. The output terminal obtains the feedback voltage. Obtain real-time current source parameters according to the feedback voltage. The output voltage sampling output satisfies:

V _{fb_sample} = K _v V _out ;

Among them, K _v is the proportional coefficient of voltage sampling, which is determined according to the turns ratio of the voltage sampling circuit 62 and the transformer Na and Ns, that is, the turns ratio of the voltage sampling circuit 62 and the transformer Na and Ns is determined, and the sampling coefficient is also a fixed value. , V _{fb_sample} is the sampled value of the output voltage.

Specifically, through the second multiplier 591a, the current of the current source 511a satisfies:

I _s ＝K _i V _{fb_sample}

Among them, K _i is the second coefficient, and V _{fb_sample} is the output voltage sample value. When the output voltage V _out of the secondary winding 220 is a variable value, setting the first coefficient according to a fixed value can no longer obtain a reasonable value. At this point, according to the above formula, the reference signal can finally meet the following formula:

That is, at this time, the first coefficient input by the first multiplier 522a can satisfy:

This formula shows that in this circuit, as long as the real-time I _pk value is multiplied by a fixed ratio K _c1 R _is to determine V _{ref_sample} , and the current for charging and discharging the internal clock capacitor is based on the sampled value of the output voltage to K _i By changing the ratio, an accurate sampling point that adapts to the change of the output voltage can be obtained.

In one embodiment, the reset unit 512 includes a switch S2, the gate of the switch S2 is connected to the output terminal of the latch 580, the source of the switch S2 is connected to the first end of the charging unit 513, and the drain of the switch S2 Grounded. Specifically, the reset unit 512 adopts a switching tube S2. When the gate input high level, the switching tube S2 is turned on, and the charging unit 513 discharges and resets. When the gate input low level, the switching tube S2 is turned off, and the charging unit 513 enters a state to be charged. . The switch tube can be a MOS tube, a triode or other controllable switching devices.

As shown in FIG. 5, in an embodiment, the timing unit 510b includes: a clock source 511b and a step counter 512b; the first end of the step counter 512b is connected to the clock source 511b, and the second end of the step counter 512b is connected to the driving unit 530b, the third end of the step counter 512b is connected to receive a reset signal; the reference signal output unit 520b includes a peak holding unit 521b, a first analog-to-digital conversion unit 522b, and a third multiplier 523b; the first end of the peak holding unit 522b is connected In the current acquisition circuit 61, the second terminal of the peak holding unit 521b is connected to the first input terminal of the third multiplier 523b via the first analog-to-digital conversion unit 522b, and the second input terminal of the third multiplier 523b inputs the third coefficient; the reference signal Meet the following formula:

V _{ref_sample} = K _c2 R _is I _pk

Wherein, V _{ref_sample} is the reference signal, K _c2 is the third coefficient, R _is is the resistance value of the sampling resistor or the adjustment resistor, I _pk is the peak current value; and the output voltage V _out of the voltage output circuit 30 is a stable value When the third coefficient satisfies the following formula:

Where L _m is the magnetizing inductance of the primary winding 210, n is the turns ratio of the primary winding 210 to the secondary winding 220, V _out is the output voltage of the voltage output circuit 30, and T _CLK is the clock period of the clock source 511b.

Specifically, the flyback converter has the following basic relationships:

L _m I _pk = nV _out T _r

_{The peak current is} converted into a peak voltage I _pk R _is through a sampling resistor R is, and the digital value of the peak voltage is obtained through analog-to-digital (A/D) conversion, that is, the first analog-to-digital conversion unit 522b. In order to simplify the description, the calculation of analog-to-digital conversion is omitted and the corresponding analog voltage is used for calculation. The calculation result of the reference voltage is

V _{ref_sample} = K _c2 R _is I _pk

Define the coefficient here

Among them, T _clk is the period of the digital clock input by the counter.

Assuming that the count value is N _sample when the count result is equal to the corresponding value V _{ref_sample of the} reference voltage, then

N _sample = V _{ref_sample}

thus,

visible,

T _r position is just the position, that is, the sample count N _sample to the optimum sampling position.

As shown in FIG. 6, in an embodiment, the reference signal output unit 520b further includes a divider 525b and a second digital-to-analog conversion unit 524b; the first input terminal of the divider 525b is connected to the output terminal of the third multiplier 523b, and the division The second input terminal of the device 525b is connected to the sampling unit 540b via the second digital-to-analog conversion unit 524b, and when the output voltage V _out of the voltage output circuit is a varying value, the third coefficient satisfies the following formula:

Among them, K _v is the sampling coefficient of the voltage sampling circuit.

Specifically, the sampling ratio of the voltage sampling unit is K _v , that is, the _{sampling ratio of its sampling output V fb_sample} to the actual output voltage V _out is K _v , and the sampling output satisfies:

V _{fb_sample} = K _v V _out

After V _{fb_sample is converted} by the A/D modulus, that is, the second modulus conversion unit 524b, it is added to the calculation as a divisor as shown in the figure. In order to simplify the description, the calculation of analog-to-digital conversion is omitted and the corresponding analog voltage is used for calculation. Refer to the upper derivation process,

N _sample = V _{ref_sample}

inferred

That is, the sample count N _sample points to the optimum sampling time T _r of the position. K _c2 excludes the factor of output voltage V _out.

As shown in Figures 1-5, in one embodiment, the control circuit 50 further includes enabling

units

550a and 550b connected to the driving

units

530a and 530b,

PWM control units

560a and 560b connected to the enabling

units

550a and 550b, and connected to the PWM control The work driving of the

units

560a and 560b, and the connection of the driving

units

530a and 530b with the

PWM control units

560a and 560b, and the reset

signal output units

580a and 580b for outputting reset signals. Specifically, when the driving

units

530a, 530b trigger the output driving signal to obtain the effective sampling voltage, the enabling

unit

550a, 550b can use the effective sampling voltage to output the signal and generate a control signal to control the operation of the

PWM control unit

560a, 560b. At the same time, the PWM control unit 560 can output the control level and timing, and the reset

signal output units

580a and 580b can be controlled to output reset signals, so that the

timing units

510a and 510b are reset. It is also possible to output the trigger level through the driving

units

530a and 530b, so that the reset

signal output units

580a and 580b output reset signals to reset the

timing units

510a and 510b.

Further, the reset

signal output unit

580a, 580b includes a latch, the first input of the latch is connected to the

driving unit

530a, 530b, the second input of the latch is connected to the

PWM control unit

560a, 560b, the latch The output terminal outputs a reset signal. Specifically, the latch may adopt an SR latch, in which the

driving units

530a and 530b are connected to the S pin, and the

PWM control units

560a and 560b are connected to the R pin. At the same time, the

PWM control unit

560a, 560b can output the control level control work to drive 570a, 570b to output the control level or current to control the power switch circuit 40 to perform the switching operation.

In an embodiment, the driving

units

530a, 530b include comparators, the same direction input terminals of the comparators are connected to the

timing units

510a, 510b, the reverse input terminals of the comparators are connected to the reference

signal output units

520a, 520b, and the output terminals of the comparators are connected to the

timing units

510a and 510b. Connect the

sampling units

540a, 540b. Specifically, the driving

units

530a and 530b may include comparators, which compare the signals output by the

timing units

510a and 510b at the same direction input terminals with the reference signals input by the inverting input terminals, and the signals output by the

timing units

510a and 510b The relationship with the reference signal satisfies a preset condition, that is, when the signal output by the

timing unit

510a, 510b exceeds the reference signal, a high level is output, and the

sampling unit

540a, 540b is driven to obtain the corresponding sampling voltage, namely the feedback voltage.

It is understandable that the above examples only express the preferred embodiments of the present invention, and the descriptions are more specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention; it should be pointed out that for those of ordinary skill in the art In other words, without departing from the concept of the present invention, the above technical features can be freely combined, and several modifications and improvements can be made. These all belong to the scope of protection of the present invention; therefore, everything that follows the scope of the claims of the present invention All equivalent changes and modifications shall fall within the scope of the claims of the present invention.

Claims

A switching power converter, characterized by comprising: a transformer including a primary winding and a secondary winding, a power switch circuit and a voltage input circuit connected to the primary winding, and a voltage output circuit connected to the secondary winding , The auxiliary winding coupled with the secondary winding, and

A control circuit connected to the power switch circuit, a current acquisition circuit connected to the control circuit and the power switch circuit, and a voltage sampling circuit connected to the auxiliary winding and the control circuit;

The control circuit includes: a timing unit for obtaining the off time of the power switch circuit to output a corresponding signal;

A reference signal output unit that is connected to the current acquisition circuit to acquire a peak current or its equivalent peak voltage, and provides a reference signal according to the peak current or the equivalent peak voltage;

A drive unit connected to the timing unit and the reference signal output unit for generating a drive signal according to the output signal of the timing unit and the reference signal of the reference signal output unit;

A sampling unit connected to the driving unit and the voltage sampling circuit for receiving the driving signal for sampling to obtain the sampling voltage of the voltage sampling circuit and outputting an effective sampling voltage.
The switching power supply converter according to claim 1, wherein the current acquisition circuit includes a current sampling circuit, the current sampling circuit includes a sampling resistor, and the first end of the sampling resistor is respectively connected to the control circuit and In the power switch circuit, the second end of the sampling resistor is grounded; or

The current acquisition circuit includes a current setting circuit, the current setting circuit includes an adjusting resistor, the first end of the adjusting resistor is respectively connected to the control circuit and the power switch circuit, and the second end of the adjusting resistor is grounded.
The switching power converter according to claim 2, characterized in that,

The timing unit includes: a current source, a charging unit and a reset unit;

The first end of the charging unit is respectively connected to the current source and the driving unit, and the second end of the charging unit is grounded;

The first end of the reset unit is connected to the first end of the charging unit, the second end of the reset unit is connected to the second end of the charging unit, and the third end of the reset unit is used to receive a reset signal So as to realize the discharge reset of the charging unit;

The reference signal output unit includes a peak holding unit and a first multiplier;

The first end of the peak holding unit is connected to the current acquisition circuit, the second end of the peak holding unit is connected to the first input end of the first multiplier, and the second input end of the first multiplier is input The first coefficient, wherein the first coefficient corresponds to the circuit parameter of the timing unit.
The switching power converter according to claim 3, wherein the charging unit comprises a charging capacitor Cs, a first end of the charging capacitor Cs is connected to the current source, and a second end of the charging capacitor Cs is grounded ；

The reference signal satisfies the following formula:

V ref_sample = K c1 R is I pk

Wherein, V ref_sample is the reference signal, K c1 is the first coefficient, I pk is the peak current value, and R is is the resistance value of the sampling resistor or the adjustment resistor;

And when the output voltage V out of the voltage output circuit is a stable value, the first coefficient satisfies the following formula:

Wherein, L m is the magnetizing inductance of the primary winding, n is an primary winding of the turns ratio of the secondary winding, V out is the output voltage value of the voltage output circuit, I s is a current source The current value, C s is the capacitance value of the charging capacitor.
The switching power supply converter of claim 4, wherein the current source is a voltage-controlled current source, the voltage-controlled input terminal of the voltage-controlled current source is connected to the output terminal of the voltage sampling unit, and the voltage The output terminal of the controlled current source is connected to the charging unit;

The control circuit further includes a second multiplier, the first input of the second multiplier is connected to the sampling unit, and the second input of the second multiplier is input with a second coefficient;

And when the output voltage V out of the voltage output circuit is a varying value, the first coefficient satisfies the following formula:

Wherein, K i is the second coefficient, and K v is the sampling ratio coefficient of the voltage sampling circuit.
The switching power supply converter according to claim 3, wherein the reset unit comprises a switch tube S2, a control pole of the switch tube S2 receives the reset signal, and a first end of the switch tube S2 is connected to the The first end of the charging unit and the second end of the switch tube S2 are grounded.
The switching power converter according to claim 2, characterized in that,

The timing unit includes: a clock source and a step counter;

The first end of the step counter is connected to the clock source, the second end of the step counter is connected to the drive unit, and the third end of the step counter is connected to receive a reset signal;

The reference signal output unit includes a peak holding unit, a first analog-to-digital conversion unit, and a third multiplier;

The first end of the peak holding unit is connected to the current acquisition circuit, the second end of the peak holding unit is connected to the first input end of the third multiplier via the first analog-to-digital conversion unit, and the first The third coefficient is input to the second input terminal of the three multiplier;

The reference signal satisfies the following formula:

V ref_sample = K c2 R is I pk

Wherein, V ref_sample is the reference signal, K c2 is the third coefficient, R is is the resistance value of the sampling resistor or the adjustment resistor, and I pk is the peak current value;

And when the output voltage V out of the voltage output circuit is a stable value, the third coefficient satisfies the following formula:

Where L m is the magnetizing inductance of the primary winding, n is the turns ratio of the primary winding to the secondary winding, V out is the output voltage value of the output circuit, and T CLK is the clock of the clock source cycle.
The switching power supply converter according to claim 7, wherein the reference signal output unit further comprises a divider and a second digital-to-analog conversion unit; the first input terminal of the divider is connected to the third multiplier The second input of the divider is connected to the sampling unit via the second digital-to-analog conversion unit,

And when the output voltage V out of the voltage output circuit is a varying value, the third coefficient satisfies the following formula:

Wherein K v is the sampling ratio coefficient of the voltage sampling circuit.
The switching power converter according to claim 3 or 7, wherein the control circuit further comprises an enabling unit connected to the driving unit, a PWM control unit connected to the enabling unit, and a PWM control unit connected to the PWM control unit. Working drive of the unit, and a reset signal output unit that connects the drive unit and the PWM control unit to output the reset signal; and/or

The driving unit includes a comparator, the same direction input terminal of the comparator is connected to the timing unit, the reverse input terminal of the comparator is connected to the reference signal output unit, and the output terminal of the comparator is connected to the timing unit. Sampling unit.
The switching power supply converter according to claim 9, wherein the reset signal output unit comprises a latch, the first input terminal of the latch is connected to the driving unit, and the first input terminal of the latch is connected to the driving unit. The two input terminals are connected to the PWM control unit, and the output terminal of the latch outputs the reset signal.