Quasi-resonance circuit trough voltage detection method

Abstract

The invention discloses a quasi-resonance circuit trough voltage detection method, which comprises the following steps: step 1, when an auxiliary side voltage VFB passes through a first actual comparison point A, a first switch is switched on, a second switch is switched off, a charging capacitor is charged, the initial voltage of the capacitor is zero, and the charging current is I; when it is detected that the VFB passes a second actual comparison point B, the first switch is switched off, the second switch is switched on, charging of the charging capacitor is stopped, the charging capacitor starts discharging, the discharging current is 2I, and discharging is performed to zero voltage; 2, discharging the charging capacitor to zero voltage, compensating for 2 alpha-beta time, and at the moment, sending out a valley bottom detection signal; alpha is the delay between the zero point of the zero-crossing comparator and the actual comparison point, and beta is the internal delay of the zero-crossing comparator. The lowest point of the resonance voltage can be detected to conduct the switch.

Description

Technical Field

[0001] The invention relates to a method for detecting the lowest point of a switch voltage of a flyback switching power supply, and in particular to a method for detecting a valley voltage of a quasi-resonance circuit. Background Art

[0002] Figure 1 This is the flyback circuit structure diagram. Figure 2 This is the electrical signal waveform diagram when the flyback circuit is working. Ip is the primary inductor current, Is is the secondary inductor current, V DS is the voltage across the drain and source of switch Q1, Vg is the signal that controls the conduction of switch Q1, and the auxiliary side voltage is added to lead out V FB , the voltage VFB is equal to the drain-source voltage V DS .like Figure 2 Medium time period T off As shown in the waveform, when the demagnetization time T demag After the switch Q1 ends, the voltage V DS It will not immediately become 0, but will enter the dead zone T off , that is, when the primary inductor current Ip and the secondary inductor current Is are both zero, the primary inductor Lp and the parasitic capacitance C of Q1 D Resonance will occur, resulting in a voltage V across Q1 DS resonance, which will lead to certain switching losses, which are particularly obvious at high frequencies. DS When the resonance reaches the lowest voltage point, the MOS switch tube Q1 is turned on. At this time, the switching loss is minimal, effectively reducing the switching loss.

[0003] Detect V DS The resonance valley method is: when resonance starts, since the resonance signal is a sine wave, V is detected twice. FB Zero crossing is 1 / 2 of the resonance period, and delaying the above resonance process by a quarter of a period is V FB The voltage is at its lowest point, and a valley detection signal is output. The difficulty of the detection method is how to accurately obtain the time size of T / 4. The following are several methods provided by existing technologies.

[0004] The first detection method is to add a fixed delay T after the switch voltage resonates to zero. delay , after a delay of T delay After that, the valley detection signal is output and the switch is turned on through the subsequent logic circuit. delay ,When the switching circuit operates at high frequency, the resonant period changes greatly, so the accuracy of this method is very low.

[0005] The second detection method is to charge the capacitor to obtain T / 4. Figure 3As shown, when the secondary current drops to 0 and the resonance starts, the first capacitor C1 is charged. When the switch voltage is detected to be zero, the charging of the first capacitor is stopped, and the second capacitor C2 is charged with the same current, and the two capacitance values ​​are equal. The voltages of the two capacitors are respectively input to the positive and negative input terminals of the comparator. When the voltage on the second capacitor is equal to the voltage on the first capacitor, the valley detection signal is output through the comparator. This method can solve the problem of the first method that the resonance period changes greatly when the circuit works at high frequency. If the resonance period is relatively large, the delay time will also become larger. If the resonance period is relatively small, the delay time will also become smaller.

[0006] The third type of detection method is to obtain T / 4 by charging and discharging the capacitor. When the secondary current drops to 0 and the resonance begins, the capacitor starts to charge from zero voltage. When the switch voltage is detected to be zero, the charging of the capacitor stops. At this time, the capacitor is discharged with the same current as the charging current (using a current mirror to make the charging and discharging currents the same). When the capacitor is discharged to zero voltage, a valley detection signal is output. This method can solve the problem of the first type of method that the resonance period changes greatly when the circuit works at high frequency.

[0007] The second and third detection methods mentioned above do not take into account the deviation caused by non-ideal factors. First, due to the limitation of the common-mode input range of the comparator, the actual comparison point cannot reach the zero point, which will cause a deviation in the detection of the zero point. Second, the comparator will also produce a delay. These two factors will cause the final output valley detection signal to be inaccurate, especially when the resonant frequency is relatively high, the deviation is particularly obvious. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for detecting valley voltage of a quasi-resonant circuit. The present invention can detect the lowest point of the resonant voltage to turn on the switch.

[0009] The technical solutions to the above problems are as follows: A quasi-resonant circuit valley voltage detection method includes a first constant current source, a second constant current source, a charging capacitor, a first switch, and a second switch, wherein one end of the first constant current source is connected to one end of the first switch, the other end of the first switch is connected to one end of the charging capacitor, the other end of the charging capacitor is connected to the other end of the first constant current source, one end of the charging capacitor is also connected to one end of the second switch, the other end of the second switch is connected to one end of the second constant current source, and the other end of the second constant current source is connected to the other end of the charging capacitor, the first constant current source, the first switch, and the charging capacitor form a charging circuit, the second constant current source, the second switch, and the charging capacitor form a discharging circuit, and the charging and discharging circuits of the charging capacitor are used to make the valley voltage detection according to the following steps: Step 1: When the auxiliary side voltage V FBWhen the first actual comparison point A is passed, the first switch is closed and the second switch is opened, and the charging capacitor starts to be charged. The initial voltage of the capacitor is zero and the charging current is I. When it is detected that VFB passes the second actual comparison point B, the first switch is opened and the second switch is closed, and the charging capacitor stops being charged. The charging capacitor starts to discharge, and the discharge current is 2I, and it discharges to zero voltage. Step 2, the charging capacitor is discharged to zero voltage, and then compensated for 2α-β time, at which time a valley detection signal is issued; α is the delay between the zero point of the zero-crossing comparator and the actual comparison point, and β is the internal delay of the zero-crossing comparator.

[0010] Furthermore, the α and β are obtained by testing the zero-crossing comparator, the zero-crossing comparator inputs a sinusoidal signal, the sinusoidal signal is compared with the first actual comparison point A and the first actual comparison point B to obtain the zero-crossing comparator flip point, and α+β and α-β are obtained through testing, thereby obtaining the values ​​of α and β.

[0011] Furthermore, it also includes a comparator and a delay circuit, the non-inverting input terminal of the comparator is connected to one end of the charging capacitor, the delay circuit includes a third switch tube and a fourth switch tube, the first ends of the third switch tube and the fourth switch tube are connected to the output end of the comparator, the second end of the third switch tube is used to connect to the power supply, the third end of the third switch tube is connected to the second end of the fourth switch tube, the third end of the fourth switch tube is grounded, and the connection between the third end of the third switch tube and the second end of the fourth switch tube is the output end of the delay circuit.

[0012] Furthermore, the delay circuit also includes a capacitor, one end of the capacitor is connected to the connection between the third end of the third switch tube and the second end of the fourth switch tube, and the other end of the capacitor is grounded.

[0013] The technical effects of the present invention are: The present invention adopts compensation to eliminate the error caused by the delay of the zero-crossing comparator and the comparison point of the zero-crossing comparator, and can accurately detect the lowest point of the resonant voltage and turn on the switch tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the schematic diagram of the flyback circuit.

[0015] Figure 2 It is the waveform diagram of the flyback circuit in each time state.

[0016] Figure 3 The schematic diagram of the second type of detection method is background technology.

[0017] Figure 4 This is a schematic diagram of the principle of obtaining valley voltage by charging and discharging a capacitor according to the present invention.

[0018] Figure 5 It is the principle diagram of the delay time compensation circuit of the present invention.

[0019] Figure 6 A schematic diagram for obtaining delay parameters α and β.

[0020] Figure 7 This is the waveform diagram of delay time compensation.

[0021] Figure 8 This is a delay time compensation analysis diagram. DETAILED DESCRIPTION

[0022] like Figures 4 to 8 As shown, a quasi-resonant circuit valley voltage detection method of the present invention includes a first constant current source I1, a second constant current source I2, a charging capacitor C, a first switch S1, and a second switch S2, wherein one end of the first constant current source I1 is connected to one end of the first switch S1, the other end of the first switch S1 is connected to one end of the charging capacitor C, the other end of the charging capacitor C is connected to the other end of the first constant current source I1, one end of the charging capacitor C is also connected to one end of the second switch S2, the other end of the second switch S2 is connected to one end of the second constant current source I2, the other end of the second constant current source I2 is connected to the other end of the charging capacitor C, the first constant current source I1, the first switch S1, and the charging capacitor C constitute a charging circuit, and the second constant current source I2, the second switch S2, and the charging capacitor C constitute a discharge circuit.

[0023] The charging and discharging circuit of the charging capacitor C is used to detect the valley voltage in the following steps: Step 1: When the auxiliary side voltage V FB When the first actual comparison point A is passed, the first switch S1 is closed, the second switch S2 is opened, and the charging capacitor C starts to be charged, the initial voltage of the capacitor is zero, and the charging current is I; when it is detected that VFB passes the second actual comparison point B, the first switch S1 is opened, the second switch S2 is closed, and the charging capacitor C stops being charged, and the charging capacitor C starts to discharge, the discharge current is 2I, and discharges to zero voltage; Step 2, the charging capacitor C is discharged to zero voltage, and then compensated for the time of 2α-β, at which time a valley detection signal is issued; α is the delay between the zero point of the zero-crossing comparator and the actual comparison point, and β is the internal delay of the zero-crossing comparator.

[0024] The α and β are obtained by testing the zero-crossing comparator. The zero-crossing comparator inputs a sinusoidal signal, and the sinusoidal signal is compared with the first actual comparison point A and the first actual comparison point B to obtain the zero-crossing comparator flip point. After testing, α+β and α-β are obtained, and then the values ​​of α and β are obtained.

[0025] It also includes a comparator COMP and a delay circuit. The non-inverting input terminal of the comparator COMP is connected to one end of the charging capacitor C. The delay circuit includes a third switch tube S3 and a fourth switch tube S4. The first ends of the third switch tube S3 and the fourth switch tube S4 are connected to the output end of the comparator COMP. The second end of the third switch tube S3 is used to connect to a power supply. The third end of the third switch tube S3 is connected to the second end of the fourth switch tube S4. The third end of the fourth switch tube S4 is grounded. The connection between the third end of the third switch tube S3 and the second end of the fourth switch tube S4 is the output end of the delay circuit.

[0026] The delay circuit further includes a capacitor C0, one end of the capacitor C0 is connected to the connection point between the third end of the third switch tube S3 and the second end of the fourth switch tube S4, and the other end of the capacitor C0 is grounded.

[0027] The voltage on the charging capacitor C is input from the non-inverting input terminal of the comparator COMP to the comparator COMP. The inverting input terminal of the comparator COMP is used to input the comparison voltage K. The output V c is the uncompensated switching signal, V c After the delay circuit is completed, the valley conduction signal V is output. D ,control Figure 1 The switch tube Q1 in.

[0028] The principle of the present invention is: 1. Obtain the auxiliary side voltage V through the zero-crossing comparator FB The time between the two zero points during resonance is T / 2. FB The voltage is drawn through the zero-crossing comparator, and the time between two zero-crossings is T / 2.

[0029] like Figure 4 As shown, the first constant current source I1 is connected to the two electrodes of the charging capacitor C through the first switch S1 to form a charging circuit; the two electrodes of the charging capacitor C are connected to the second constant current source I2 through the second switch S2 to form a discharging circuit. FB When the first zero point is passed, the first switch S1 is closed to start charging the charging capacitor C. The initial voltage of the charging capacitor C is zero and the charging current is I. FB When it reaches zero again, the first switch S1 is turned off to stop charging the charging capacitor C, and the second switch S2 is turned on to start discharging the charging capacitor C. The discharge current is 2I and the voltage is discharged to zero. Since it is the same charging capacitor C, but the current is doubled, the discharge time is 1 / 2 of the charging time, that is, T / 4, and a valley detection signal is issued at this time.

[0030] 2. Determine the compensation time of the zero-crossing comparator delay The comparison point of the zero-crossing comparator cannot reach the zero point, so the valley detection signal sent out after a delay of T / 4 after the zero point is finally detected is not the real valley. In order to improve the accuracy of valley detection, this delay time needs to be compensated.

[0031] like Figure 8 As shown in the figure, the reaction time difference of the zero-crossing comparator to the waveform: Assuming that the delay between the zero point and the actual comparison point is α, the internal delay of the op amp is β, and the actual charging time of the charging capacitor C is (T / 2-2α); the last quarter of the waveform is the discharge time, and the real bottom of the waveform is the (T / 4+α-β) time period after the discharge is turned on. From the perspective of the charging capacitor discharge stage: because the charging capacitor C has insufficient charging time, the discharge of the charging capacitor C ends early. It can be deduced that the discharge time is only (T / 2-2α) / 2, which is one period α less than the actual T / 4. At the same time, from Figure 8 It can be seen that the discharge starting point is before zero crossing (α-β), which should be compensated. Therefore, the time required to compensate for 2α-β is the real valley.

[0032] The examples described above are only some embodiments of the present invention, rather than all of them. Based on the examples in the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention.

Claims

1. A quasi-resonant circuit valley voltage detection method, comprising a first constant current source (I1), a second constant current source (I2), a charging capacitor (C), a first switch (S1), and a second switch (S2), wherein one end of the first constant current source (I1) is connected to one end of the first switch (S1), the other end of the first switch (S1) is connected to one end of the charging capacitor (C), the other end of the charging capacitor (C) is connected to the other end of the first constant current source (I1), one end of the charging capacitor (C) is also connected to one end of the second switch (S2), the other end of the second switch (S2) is connected to one end of the second constant current source (I2), the other end of the second constant current source (I2) is connected to the other end of the charging capacitor (C), the first constant current source (I1), the first switch (S1), and the charging capacitor (C) form a charging circuit, and the second constant current source (I2), the second switch (S2), and the charging capacitor (C) form a discharging circuit, characterized in that: The charging and discharging circuit of the charging capacitor (C) is used to detect the valley voltage in the following steps: Step 1: When the auxiliary side voltage V FB When the voltage VFB passes the first actual comparison point A, the first switch (S1) is closed and the second switch (S2) is opened, and the charging capacitor (C) starts to be charged, the initial voltage of the capacitor is zero, and the charging current is I; when it is detected that VFB passes the second actual comparison point B, the first switch (S1) is opened and the second switch (S2) is closed, and the charging capacitor (C) stops being charged, and the charging capacitor (C) starts to discharge, and the discharge current is 2I, and discharges to zero voltage; Step 2: The charging capacitor (C) is discharged to zero voltage, and then compensated for 2α-β time, at which time a valley detection signal is issued; α is the delay between the zero point of the zero-crossing comparator and the actual comparison point, and β is the internal delay of the zero-crossing comparator.

2. A quasi-resonant circuit valley voltage detection method according to claim 1, characterized in that: The α and β are obtained by testing the zero-crossing comparator. The zero-crossing comparator inputs a sinusoidal signal, and the sinusoidal signal is compared with the first actual comparison point A and the first actual comparison point B to obtain the zero-crossing comparator flip point. After testing, α+β and α-β are obtained, and then the values ​​of α and β are obtained.

3. The method for detecting valley voltage of a quasi-resonant circuit according to claim 1, characterized in that: The invention also includes a comparator (COMP) and a delay circuit, wherein the in-phase input terminal of the comparator (COMP) is connected to one end of the charging capacitor (C), and the delay circuit includes a third switch tube (S3) and a fourth switch tube (S4), wherein the first ends of the third switch tube (S3) and the fourth switch tube (S4) are connected to the output end of the comparator (COMP), the second end of the third switch tube (S3) is used to connect to a power supply, the third end of the third switch tube (S3) is connected to the second end of the fourth switch tube (S4), the third end of the fourth switch tube (S4) is grounded, and the connection between the third end of the third switch tube (S3) and the second end of the fourth switch tube (S4) is the output end of the delay circuit.

4. A method for detecting valley voltage of a quasi-resonant circuit according to claim 3, characterized in that: The delay circuit further comprises a capacitor (C0), one end of the capacitor (C0) is connected to the connection point between the third end of the third switch tube (S3) and the second end of the fourth switch tube (S4), and the other end of the capacitor (C0) is grounded.

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