CN111082666B

CN111082666B - Switching power supply converter

Info

Publication number: CN111082666B
Application number: CN202010073787.XA
Authority: CN
Inventors: 严亮; 李鹏
Original assignee: Msj Systems LLC
Current assignee: Msj Systems LLC
Priority date: 2020-01-22
Filing date: 2020-01-22
Publication date: 2022-04-01
Anticipated expiration: 2040-01-22
Also published as: CN111082666A

Abstract

The invention relates to a switching power converter, comprising: the transformer comprises a primary winding, a secondary winding, a power switch circuit, a voltage input circuit, a voltage output circuit, an auxiliary winding, a control circuit, a current acquisition circuit and a voltage sampling circuit, wherein the power switch circuit and the voltage input circuit are connected with the primary winding; the control circuit includes: the timing unit is used for acquiring the 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 driving unit connecting the timing unit and the reference signal output unit; and the sampling unit is connected with the driving unit and the voltage sampling circuit. The invention can obtain the optimal sampling point sampling voltage of the feedback voltage in real time in the switching period, and has simple scheme.

Description

Switching power supply converter

Technical Field

The invention relates to the technical field of power supplies, in particular to a switching power supply converter, and particularly relates to a flyback converter.

Background

The loop control of a conventional flyback converter directly detects an output voltage, generates a feedback and compensation signal, and determines a duty ratio of a main power switch according to the compensation signal, thereby controlling an output quantity, such as the output voltage. When electrical isolation is required between the input and output of a switching power supply, such as in an off-line converter, the feedback compensation circuit and the control circuit are often on both sides of the electrical isolation device, i.e., on one side, the input side (referred to herein as the "primary side") and on the other side, the output side (referred to herein as the "secondary side"). There is no direct common electrical connection between the primary and secondary sides, and isolation devices such as optocouplers are typically used to transmit signals. The isolation device and its accompanying circuitry add cost and size to the system and the primary side detection method is often used in many low cost applications. According to the method, according to the transformer coupling principle, when a primary side main switch is turned off and an output rectifier tube is turned on, a secondary side winding of a transformer bears output voltage, and due to the coupling of the secondary side winding and the auxiliary winding, the voltage on the auxiliary winding is proportional to the voltage of the secondary side winding. Thus, the control circuit on the primary side can indirectly detect the value of the output voltage by detecting the voltage across the auxiliary winding.

Based on fig. 7, where the input voltage Vin, S1 is the primary side main switching tube. The transformer Tx1 has a primary winding Np, a secondary winding Ns, and an auxiliary winding Na. D1 is an output rectifier with a conduction voltage drop of Vf. The control circuit output signal DRV drives S1 on and off. When S1 is turned on, the transformer accepts and stores energy from the input Vin. When S1 turns off, the transformer releases energy to the output. The control circuit power is supplied by the auxiliary winding through a rectifier D2. The control circuit obtains output voltage information by detecting a signal of the auxiliary winding Na to FB. As shown in FIG. 8, the voltage detected by the auxiliary winding voltage after the main switch tube driving signal DRV is turned off can be expressed as

Wherein: v_FBIs a feedback signal; vout is the output voltage; vf is the conduction voltage drop of the output rectifier tube; isec is the secondary side current of the transformer; the Rsec is the equivalent resistance of the secondary output line; na is the number of turns of the auxiliary winding of the transformer; ns is the number of secondary turns of the transformer. When the secondary side current is reduced to the minimum value, as shown in the point A, Isec is equal to 0, Vf is also close to 0, V_FBThe output voltage Vout can be fed back most accurately. Many methods have therefore been proposed to sample the output voltage near the a point location.

U.S. Pat. No.7,463,497B 2 uses 2 sample and hold circuit channels to alternately detect V_FBA voltage. When V is detected_FBIs suddenly changed, a stop signal is output. V_FBThe method that the last sampling value of the voltage before the stop signal is used as the effective sampling voltage is easy to realize, but 2 high-speed sampling and holding circuit channels are needed, and the cost is high.

U.S. Pat. No.6,956,750B 1 uses 2 variable voltage levels to track V_FBPosition of slope discontinuity through 2 levels and V_FBCan track and obtain the effective sampling voltage. The method actively finds the position of the sampling point, but a complex digital control algorithm is needed, and the cost is high.

And the sampling position of the next period needs to be determined according to the result of the previous period, and the sampling position cannot be quickly followed when the signal voltage changes quickly.

Disclosure of Invention

The present invention addresses the above-identified deficiencies of the prior art by providing a switching power converter.

The technical scheme adopted by the invention for solving the technical problems is as follows: a switching power supply converter is constructed including: a transformer including a primary winding and a secondary winding, a power switching 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

the control circuit is connected with the power switch circuit, the current acquisition circuit is connected with the control circuit and the power switch circuit, and the voltage sampling circuit is connected with the auxiliary winding and the control circuit;

the control circuit includes: the timing unit is used for acquiring the turn-off time of the power switch circuit to output a corresponding signal;

a reference signal output unit connected to the current acquisition circuit to acquire a peak current or an equivalent peak voltage thereof and provide a reference signal according to the peak current or the equivalent peak voltage;

the driving unit is connected with the timing unit and the reference signal output unit and used for generating a driving signal according to the output signal of the timing unit and the reference signal of the reference signal output unit;

and the sampling unit is connected with the driving unit and the voltage sampling circuit and used for receiving the driving signal to sample so as to obtain the sampling voltage of the voltage sampling circuit and output effective sampling voltage.

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

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

Preferably, the first and second electrodes are formed of a metal,

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

the first end of the charging unit is respectively connected with 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 with the first end of the charging unit, the second end of the reset unit is connected with the second end of the charging unit, and the third end of the reset unit is used for receiving a reset signal to realize discharging reset of the charging unit;

the reference signal output unit includes a peak hold unit and a first multiplier;

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

Preferably, the first and second electrodes are formed of a metal,

the charging unit comprises a charging capacitor Cs, a first end of the charging capacitor Cs is connected with 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_c1R_isI_pk

wherein, V_{ref_sample}For the reference signal, K_c1Is said first coefficient, R_isFor sampling the resistance value of the resistor or of the regulating resistor, I_pkIs the peak current value;

and at the output voltage V of the voltage output circuit_outAt a stable value, the first coefficient satisfies the following equation:

wherein L is_mIs the primary sideThe excitation inductance of the winding, n is the turn ratio of the primary winding to the secondary winding, V_outIs the output voltage value of the voltage output circuit, I_sIs the current value of a current source, C_sIs the capacitance value of the charging capacitor.

Preferably, the first and second electrodes are formed of a metal,

the current source is a voltage-controlled current source, the voltage-controlled input end of the voltage-controlled current source is connected with the output end of the sampling unit, and the output end of the voltage-controlled current source is connected with the charging unit;

the control circuit further comprises a second multiplier, wherein a first input end of the second multiplier is connected with the sampling unit, and a second input end of the second multiplier inputs a second coefficient;

and at the output voltage V of the voltage output circuit_outThe first coefficient satisfies the following equation for a variation value:

wherein, K_iIs the second coefficient, K_vIs the sampling proportionality coefficient of the voltage sampling circuit.

Preferably, the first and second electrodes are formed of a metal,

the reset unit comprises a switch tube S2, a control electrode of the switch tube S2 receives the reset signal, a source electrode of a first end of the switch tube S2 is connected with a first end of the charging unit, and a second end electrode of the switch tube S2 is grounded. .

Preferably, the first and second electrodes are formed of a metal,

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

the first end of the step counter is connected with the clock source, the second end of the step counter is connected with the driving unit, and the third end of the step counter is connected with a reset signal;

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

a first end of the peak holding unit is connected with the current acquisition circuit, a second end of the peak holding unit is connected with a first input end of the third multiplier through the first analog-to-digital conversion unit, and a second input end of the third multiplier inputs a third coefficient;

the reference signal satisfies the following formula:

V_{ref_sample}＝K_c2R_isI_pk

wherein, V_{ref_sample}For the reference signal, K_c2Is said third coefficient, R_isIs the resistance value of the sampling resistor or the regulating resistor, I_pkIs the peak current value;

and at the output voltage V of the output circuit_outThe third coefficient satisfies the following formula when the third coefficient is a stable value:

wherein L is_mIs the excitation inductance of the primary winding, n is the turn ratio of the primary winding to the secondary winding, V_outIs the output voltage value, T, of the voltage output circuit_CLKIs the clock period of the clock source.

Preferably, the first and second electrodes are formed of a metal,

the reference signal output unit further comprises a divider and a second digital-to-analog conversion unit; a first input end of the divider is connected with an output end of the third multiplier, a second input end of the divider is connected with the sampling unit through the second digital-to-analog conversion unit,

and at the output voltage V of the voltage output circuit_outThe third coefficient satisfies the following formula when the third coefficient is a variation value:

wherein, K_vIs the sampling proportionality coefficient of the voltage sampling circuit.

Preferably, the first and second electrodes are formed of a metal,

the control circuit further comprises an enabling unit connected with the driving unit, a PWM control unit connected with the enabling unit, a work drive connected with the PWM control unit, and a reset signal output unit connected with the driving unit, the PWM control unit and used for outputting the reset signal.

Preferably, the first and second electrodes are formed of a metal,

the reset signal output unit comprises a latch, a first input end of the latch is connected with the driving unit, a second input end of the latch is connected with the PWM control unit, and an output end of the latch outputs the reset signal.

Preferably, the first and second electrodes are formed of a metal,

the driving unit comprises a comparator, the equidirectional input end of the comparator is connected with the timing unit, the reverse input end of the comparator is connected with the reference signal output unit, and the output end of the comparator is connected with the sampling unit.

The switching power supply converter has the following beneficial effects: the optimal sampling point sampling voltage of the feedback voltage can be obtained in real time in a switching period, and the scheme is simple.

Drawings

The invention will be further described with reference to the accompanying drawings and examples, in which:

fig. 1 is a schematic structural diagram of an embodiment of a switching power converter according to the invention;

FIG. 2 is a circuit schematic of an embodiment of a switching power converter of the present invention;

FIG. 3 is a circuit schematic of one embodiment of the control circuit of FIG. 1;

FIG. 4 is a circuit schematic of another embodiment of the control circuit of FIG. 1;

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

FIG. 6 is a circuit schematic of another embodiment of the control circuit of FIG. 1;

fig. 7 is a schematic diagram of a flyback converter circuit of the prior art;

fig. 8 is an explanatory diagram of feedback sampling in the flyback converter based on fig. 7.

Detailed Description

For a more clear understanding of the technical features, objects and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

As shown in fig. 1 and fig. 2, in an embodiment of a flyback converter of the present invention, the flyback converter includes: a transformer comprising a primary winding 210 and a secondary winding 220, a power switching circuit 40 and a voltage input circuit 10 coupled to the primary winding 210, a voltage output circuit 30 coupled to the secondary winding 220, an auxiliary winding 70 coupled to the secondary winding 220, and

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

the control circuit 50 includes: a

timing unit

510a, 510b for acquiring the off time of the power switch circuit 40 to output corresponding signals; a reference

signal output unit

520a, 520b connected to the current acquisition circuit 61 for acquiring the peak current or its equivalent peak voltage and providing a reference signal according to the peak current or its equivalent peak voltage; a

driving unit

530a, 530b connected to the

timing unit

510a, 510b and the reference

signal output unit

520a, 520b, for generating a driving signal according to the output signal of the

timing unit

510a, 510b and the reference signal of the reference

signal output unit

520a, 520 b; the

sampling units

540a and 540b are connected with the driving

units

530a and 530b and the voltage sampling circuit 62, and are used for receiving the driving signals to sample so as to obtain the sampling voltage of the voltage sampling circuit 62 and output effective sampling voltage; the control circuit 50 controls the operation according to the effective sampling voltage.

Specifically, the flyback converter has the following basic relationship:

L_mI_pk＝nV_outT_r

wherein L is_mThe excitation inductance of the primary winding 210 of the transformer; i is_pkThe peak current value of the primary winding 210; n is the primary winding 210 to the secondary winding 220 of the transformerThe turn ratio; v_outIs the output voltage value; t is_rThe demagnetization time of the transformer is also the on-time of the output current, which is usually a fraction of the time that the power switching circuit is off. T is_rThe point in time of the end can be considered as the ideal sampling point. For a given design, the parameter L_mN and the steady-state output voltage V_outIs determined. Thus the target sampling point T_rThe peak current I of the primary winding 210 can be considered_pkIs in direct proportion. That is, as long as I of the current cycle_pkThe value is known, the target sampling point T_rThe determination may be calculated 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 the time point, so as to obtain the sampling voltage of the voltage sampling circuit 62 at this time as an effective sampling voltage. The sampling process acquires the voltage of the corresponding time point through 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 configured to count the time elapsed for the transformer to demagnetize after the main switch S1 is turned off, that is, the transformer starts to demagnetize, and when the relationship between the elapsed time and the reference signal output of the reference

signal output units

520a and 520b satisfies a preset condition, the driving

units

530a and 530b start to output the driving signals, and at this time, the ideal effective sampling voltage can be obtained. Namely, according to the time of the target sampling point, the transformer begins to demagnetize after T_rIt is known that, in order to perform the corresponding operation at the time point in one switching cycle, the

timing units

510a, 510b and the reference

signal output units

520a, 520b are properly arranged so that the relationship therebetween is just at the target sampling point T_rThe preset relationship is satisfied, so that the sampling drive at the target sampling point Tr is automatically given by the circuit. Meanwhile, according to the above description, after the transformer is selected, the target sampling point T is obtained_rWith the peak current I of the primary winding 210 obtained by the current obtaining circuit 61_pkIn correlation, the peak current may be equivalent to the peak voltage at some time, i.e. at the reference signal inputWhen setting the parameters of the

units

520a, 520b, the peak current I of the primary winding 210 needs to be considered_pk. When a target sampling point T is obtained_rAfter the effective sampling voltage, the control circuit 50 may perform corresponding operations according to the effective sampling voltage, for example, adjust a switching duty ratio of the power switching circuit 40.

Optionally, in an embodiment, the current obtaining circuit includes a current sampling circuit, the current sampling circuit includes a sampling resistor, a first end of the sampling resistor is connected to the control circuit and the power switch circuit, respectively, and a second end of the sampling resistor is grounded; specifically, the peak current I of the primary winding 210_pkMay be obtained by a current sampling circuit, i.e. the peak current I may be understood_pkCan be obtained by a sampling resistor, e.g. a current sampling resistor with a resistance value of R_isObtaining the voltage value I of the peak current sample of the sampling resistor_pkR_isThe peak current I can be obtained_pk。

In another embodiment, the current obtaining circuit includes a current setting circuit, the current setting circuit includes an adjusting resistor, a first end of the adjusting resistor is connected to the control circuit and the power switch circuit, respectively, and a second end of the adjusting resistor is grounded. Specifically, if the switching power supply converter adopts the peak current control mode, the voltage value I corresponding to the peak current_pkR_isIs determined by the amount of control of the peak current within the control circuit. That is, the peak current is set by a current setting circuit inside the current acquisition circuit, and after the peak current is set, the actual peak current is adjusted by an adjusting resistor, and in this control mode circuit, the voltage value of the peak current also satisfies I_pkR_isWherein R is_isTo adjust the resistance value of the resistor.

As shown in fig. 3, in one embodiment, the timing unit 510a includes: a current source 511a, a charging unit 513a, and a reset unit 512 a; a first terminal of the charging unit 513a is connected to the current source 511a and the driving unit 530a, respectively, and a second terminal of the charging unit 513a is grounded; the first terminal of the reset unit 512a is connected to the chargerA first terminal of the electrical unit 513a, a second terminal of the reset unit 512a is connected to the second terminal of the charging unit 513a, a third terminal of the reset unit 512a is configured to receive a reset signal to implement a discharging reset on the charging unit 513a, and the reference signal output unit 520a includes a peak holding unit 521a and a first multiplier 522 a; a first terminal of the peak hold unit 521a is connected to the current obtaining circuit 61, a second terminal of the peak hold unit 521a is connected to a first input terminal of the first multiplier 522a, and a first coefficient is input to a second input terminal of the first multiplier 522a, where the first coefficient corresponds to a circuit parameter of the timing unit 510 a. Specifically, the current source 511a in the control circuit 50 starts to operate and charges the charging unit 513a, during the charging process of the charging unit 513a, the charging voltage increases along with the charging process, the charging voltage is input to the driving unit 530a as the output voltage of the timing unit 510a, the driving unit 530a compares the charging voltage with the reference signal output by the reference signal output unit 520a, and generates the driving signal when the relationship between the charging voltage and the reference signal satisfies the preset condition, that is, the time point corresponds to the target sampling point T_r. Meanwhile, the charging unit 513a can be discharged by the reset unit 512a receiving a reset signal, so that the charging unit 513a restores the initial state to perform the same operation in the next switching cycle. The reference signal output unit 520a may obtain the peak current through the peak holding unit 521a, that is, it obtains the current of the current obtaining circuit 61 and obtains the peak value thereof, and inputs the peak current as the sampling output to the first multiplier 522a, the other input terminal of the first multiplier 522a is used to output a fixed coefficient, that is, a first coefficient, which is selected according to the circuit parameters of the timing unit 510a, so as to establish the corresponding relationship between the peak current and the timing unit 510a through the first multiplier 522a, so that the timing unit 510a and the reference signal output unit 520a are just at the target sampling point T_rThe predetermined relationship is satisfied.

In one embodiment, the charging unit 513a includes a charging capacitor C_sCharging capacitor C_sIs connected with a current source 511a and a charging capacitor C_sThe second terminal of (1) is grounded; the reference signal satisfies the following formula:

V_{ref_sample}＝K_c1R_isI_pk

wherein, V_{ref_sample}As a reference signal, K_c1Is a first coefficient, I_pkIs the peak current value, R_isThe resistance value is a sampling resistance or a regulating resistance;

and the output voltage V at the secondary winding 220_outAt a stable value, the first coefficient satisfies the following equation:

wherein L is_mIs the excitation inductance of the primary winding 210, n is the turn ratio of the primary winding 210 to the secondary winding 220, V_outIs the output voltage value, I, of the voltage output circuit 30_sIs the current value of the current source 511a, C_sTo charge the capacitance value of the capacitor, R_isThe resistance value of the sampling resistor or the adjusting resistor. Specifically, the charging unit 513a may employ a charging capacitor. After the reset signal reset is released, the charging capacitor starts to be charged, and the relationship between the charging voltage of the charging capacitor and the reference signal during the rising process of the charging voltage meets the preset condition, so that the driving unit 530a generates the driving signal. The setting of the first coefficient related to the reference signal may be set in dependence on the parameters of the charging capacitor and the current source, i.e. K_c1Satisfies the above formula. Namely, the capacitance value of the charging capacitor is known, and the target sampling point T is set in the charging process of the charging capacitor according to the charging time of the charging capacitor_rThe charging voltage value is a preset condition to be met by the charging voltage of the charging capacitor, namely a target sampling point T_rThe charging voltage value at the time is set as the reference signal. Definition of T_sampleFor charging time of the charging capacitor, charging voltage V of the charging capacitor_SThe following formula is satisfied:

setting the charging time T_sampleAs a target sampling point T_rThen is obtained at T_rThe charging voltage at the point is:

to set the drive unit 530a to trigger at this point in time, V is set_s1Set as a reference signal V_{ref_sample}Of the threshold value, i.e. setting V_{ref_sample}The following formula is satisfied:

in the above formula, L_mIs the excitation inductance of the primary winding 210, n is the turn ratio of the primary winding 210 to the secondary winding 220, V_outThe output voltage of the voltage output circuit 30 is a fixed value, I_sIs a current source 511a current, C_sThe capacitance value of the charge capacitor is a known parameter after the circuit is designed, wherein I_pkIs the peak current; which are variables. Obtaining a fixed coefficient K according to the known parameters_c1And obtaining a reference signal satisfying the following formula:

V_{ref_sample}＝K_c1R_isV_ipk

thus the first coefficient K_c1The setting of (c) should satisfy the following formula:

the variable I can be converted by the first multiplier 522_pkR_isAnd a first coefficient K_c1Respectively output from different input terminals, the output terminal thereof can obtain the current I following the peak value_pkObtaining reasonable target sampling point T by the changed reference signal_r. It is also understood that I is the only real-time basis_pkValue, multiplied by a fixed ratio K_c1R_isTo determine V_{ref_sample}Then a sampling point T can be obtained_sampleEqual to demagnetization of the transformerTime T_rAnd thus, an accurate feedback sampling point is obtained so as to obtain an effective sampling voltage.

As shown in fig. 4, in an embodiment, the current source 511a is a voltage-controlled current source, a voltage-controlled input terminal of the voltage-controlled current source is connected to an output terminal of the sampling unit 540a, and an output terminal of the voltage-controlled current source is connected to the charging unit 513 a. The control circuit 50 further comprises a second multiplier 591a, a first input terminal of the second multiplier 591a is connected to the sampling unit 540a, and a second input terminal of the second multiplier 59a1 inputs the second coefficient; and the output voltage V at the secondary winding 220_outThe first coefficient satisfies the following equation for a variation value:

wherein L is_mIs the excitation inductance of the primary winding 210, n is the turn ratio of the primary winding 210 to the secondary winding 220, C_sTo charge the capacitance value of the capacitor, K_iIs the second coefficient, K_vThe scaling factor is sampled for the output voltage. Specifically, during the system operation, the output V_outA change will occur. In order to allow the sampling system to adapt to output voltage variations, the current source 511a is set to be V_outIs fed back to the voltage source V_{fb_sample}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 output terminal of the sampling unit 540a, so as to obtain the feedback voltage. And acquiring real-time current source parameters according to the feedback voltage. The output voltage sampling output satisfies:

V_{fb_sample}＝K_vV_out；

wherein, K_vIs a proportionality coefficient of voltage sampling, which is determined according to the turn ratio of the voltage sampling circuit 62 and the transformers Na and Ns, i.e. the turn ratio of the voltage sampling circuit 62 and the transformers Na and Ns, and is also a fixed value, V_{fb_sample}Is the output voltage sample value.

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

I_S＝K_iV_{fb_sample}

wherein, K_iIs the second coefficient, V_{fb_sample}Is the output voltage sample value. Output voltage V at secondary winding 220_outIn order to change the value, the first coefficient is set to a fixed value, and a reasonable value is not obtained. At this time, according to the above formula, the reference signal can be finally obtained to satisfy the following formula:

that is, the first coefficient input by the first multiplier 522a at this time may satisfy:

this formula shows that under this circuit, only according to the real-time I_pkValue, multiplied by a fixed ratio K_c1R_isTo determine V_{ref_sample}And the current charged and discharged by the internal clock capacitor is measured by K according to the sampling value of the output voltage_iThe accurate sampling point adapting to the change of the output voltage can be obtained by the change of the proportion.

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

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

V_{ref_sample}＝K_c2R_isI_pk

wherein, V_{ref_sample}As a reference signal, K_c2Is the third coefficient, R_isFor sampling the resistance value of the resistor or said regulating resistor, I_pkIs the peak current value; and at the output voltage V of the voltage output circuit 30_outThe third coefficient satisfies the following equation at a stable value:

wherein L is_mIs the excitation inductance of the primary winding 210, n is the turn ratio of the primary winding 210 to the secondary winding 220, V_outIs the output voltage, T, of the voltage output circuit 30_CLKThe clock period of clock source 511 b.

Specifically, the flyback converter has the following basic relationship:

L_mI_pk＝nV_outT_r

the peak current passes through a sampling resistor R_isIs converted into peak voltage I_pkR_isThe digital quantity of the peak voltage is obtained by analog-to-digital (a/D) conversion, i.e., the first analog-to-digital conversion unit 522 b. For simplifying the description, if the calculation of the 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_c2R_isI_pk

The coefficients are defined here

Wherein T is_clkIs the period of the digital clock at the input of the counter.

Suppose that when the counting result is equal to the corresponding value V of the reference voltage_{ref_sample}A timer value of N_sampleThen there is

N_sample＝V_{ref_sample}

In this way,

as can be seen,

is exactly at T_rThat is to say the sampling counts to N_sampleIs the optimal 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 524 b; the first input terminal of the divider 525b is connected to the output terminal of the third multiplier 523b, the second input terminal of the divider 525b is connected to the sampling unit 540b via the second DAC unit 524b, and the output voltage V of the voltage output circuit is_outThe third coefficient satisfies the following equation:

wherein, K_vIs the sampling coefficient of the voltage sampling circuit.

Specifically, the sampling proportion is K according to the voltage sampling unit_vI.e. its sampled output V_{fb_sample}For actual output voltage V_outHas a sampling ratio of K_vAnd the sampling output meets the following conditions:

V_{fb_sample}＝K_vV_out

V_{fb_sample}through A/D modulus, i.e. second modulusAfter conversion by the conversion unit 524b, the divisor is added to the calculation as shown. For simplicity of explanation, the calculation of analog-to-digital conversion is omitted and the corresponding analog voltage is used for calculation, referring to the upper derivation process,

N_sample＝V_{ref_sample}

to obtain

That is to say the samples count to N_sampleIs the optimal sampling position T_rThe time point of (a). K_c2Excludes the output voltage V_outOf (c) is determined.

As shown in fig. 1 to 5, in an embodiment, the control circuit 50 further includes an enable

unit

550a, 550b connected to the

driving unit

530a, 530b, a

PWM control unit

560a, 560b connected to the enable

unit

550a, 550b, a reset

signal output unit

580a, 580b connected to the

driving unit

530a, 530b and the

PWM control unit

560a, 560b for outputting a reset signal. Specifically, when the driving

units

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

units

550a and 550b may output the signal by using the effective sampling voltage, and generate the control signal to control the

PWM control units

560a and 560b to operate. Meanwhile, the reset

signal output units

580a, 580b may be controlled to output reset signals by the PWM control unit 560 outputting control levels and timings such that the

timing units

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

units

530a, 530b such that the reset

signal output units

580a, 580b output a reset signal to reset the

timing units

510a, 510 b.

Further, the reset

signal output units

580a, 580b include latches, first input terminals of the latches are connected to the driving

units

530a, 530b, second input terminals of the latches are connected to the

PWM control units

560a, 560b, and output terminals of the latches output the reset signal. Specifically, the latch may adopt an SR latch, in which the

driving units

530a and 530b are connected to S pins thereof, and the

PWM control units

560a and 560b are connected to R pins thereof. Meanwhile, the

PWM control units

560a and 560b may output control levels to control the

operation drivers

570a and 570b to output control levels or currents to control the power switching circuit 40 to perform switching operations.

In one embodiment, the driving

units

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

timing units

510a and 510b, the opposite-direction input terminals of which are connected to the reference

signal output units

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

sampling units

540a and 540 b. Specifically, the driving

units

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

timing units

510a and 510b at the inputs in the same direction with reference signals input at the inputs in the opposite direction, and output a high level when the relationship between the signals output by the

timing units

510a and 510b and the reference signals meets a preset condition, that is, the signals output by the

timing units

510a and 510b exceed the reference signals, and drive the

sampling units

540a and 540b to obtain corresponding sampling voltages, that is, feedback voltages.

It is to be understood that the foregoing examples, while indicating the preferred embodiments of the invention, are given by way of illustration and description, and are not to be construed as limiting the scope of the invention; it should be noted that, for those skilled in the art, the above technical features can be freely combined, and several changes and modifications can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention; therefore, all equivalent changes and modifications made within the scope of the claims of the present invention should be covered by the claims of the present invention.

Claims

1. A switching power converter, comprising: a transformer including a primary winding and a secondary winding, a power switching 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

the sampling unit is connected with the driving unit and the voltage sampling circuit and used for receiving the driving signal to carry out sampling so as to obtain the sampling voltage of the voltage sampling circuit and output effective sampling voltage;

the control circuit further comprises an enabling unit connected with the driving unit, a PWM control unit connected with the enabling unit, a work drive connected with the PWM control unit, and a reset signal output unit connected with the driving unit and the PWM control unit and used for outputting a reset signal, wherein the reset signal is used for resetting the timing unit;

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

the first end of the reset unit is connected with the first end of the charging unit, the second end of the reset unit is connected with the second end of the charging unit, and the third end of the reset unit is used for receiving the reset signal to realize discharging reset of the charging unit;

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

the current source is a voltage-controlled current source, a voltage-controlled input end of the voltage-controlled current source is connected with an output end of the voltage sampling circuit, and an output end of the voltage-controlled current source is connected with the charging unit;

wherein, K_c1Is said first coefficient, K_iIs said second coefficient, K_vIs the sampling proportionality coefficient, R, of the voltage sampling circuit_isIs a resistance value, L, of the current acquisition circuit_mIs the excitation inductance of the primary winding, C_sAnd n is the turn ratio of the primary winding to the secondary winding.

2. The switching power converter according to claim 1, wherein the current obtaining circuit comprises a current sampling circuit, the current sampling circuit comprises a sampling resistor, a first end of the sampling resistor is connected to the control circuit and the power switch circuit, respectively, and a second end of the sampling resistor is grounded; or

3. The switching power converter according to claim 2, 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_c1R_isI_pk

wherein, V_{ref_sample}For the reference signal, I_pkIs the peak current value; r_isThe resistance value of the sampling resistor or the adjusting resistor is obtained;

wherein, V_outIs the output voltage value of the voltage output circuit, I_sIs the current value of the current source.

4. The switching power converter according to claim 3, wherein the reset unit comprises a switch tube S2, a control electrode of the switch tube S2 receives the reset signal, a first terminal of the switch tube S2 is connected to the first terminal of the charging unit, and a second terminal of the switch tube S2 is grounded.