TWI463801B - Zero current detector for a power supplier and method thereof - Google Patents

Description

Zero current detector and method for power supply

The present invention relates to a zero current detector and method for a power supply, and more particularly to a zero current detector and method using capacitive coupling.

In some applications, zero current detection is a very important technique. Zero current detection techniques are typically used in a quasi-resonant mode of flyback, boost or buck systems to stabilize the output current or achieve some protection. 1 shows a conventional flyback power supply having a zero current detection function, wherein the control integrated circuit 10 controls a switch M1 connected in series with the primary winding Lp of the transformer T1 to convert the input voltage Vin into an output voltage Vo. When the secondary side current Is supplied to the output terminal Vo falls to zero, a high frequency signal is generated on the auxiliary coil La of the transformer T1 via the resistor Rzcd to the pin ZCD of the control integrated circuit 10, and the integrated circuit 10 is controlled to thereby trigger zero. The current signal Szcd stabilizes the output current or achieves some protection.

2 shows a timing chart of the signal of FIG. 1. At time t1, the pin GD of the control integrated circuit 10 is sent to a signal of a high level to turn on the switch M1, so that the primary side current Ip starts to rise, at the switch. During the opening of M1, the signal Vaux on the auxiliary coil La is equal to (-Vin) × Nf / Np, where Np is the number of turns of the primary side coil Lp, and Nf is the number of turns of the auxiliary coil La. At time t2, the signal on the pin GD of the control integrated circuit 10 is turned to a low level to turn off the switch M1, at which time the secondary side current Is on the secondary side coil Ls starts to decrease from the peak value. During the closing of the switch M1, the signal Vaux on the auxiliary coil La is equal to Vo × Nf / Ns, where Ns is the number of turns of the secondary side coil Ls. At time t3, the secondary side current Is drops to zero, causing a high frequency oscillation of the voltage on the secondary side coil Ls, thereby generating a high frequency signal 12 on the auxiliary coil La, and detecting the integrated circuit 10 detecting the foot. When the high frequency signal 12 appears on the bit ZCD, the zero current signal Szcd is triggered. However, conventional zero current detection methods require additional pins to implement, which increases cost.

Therefore, an apparatus and method for realizing zero current detection using a multi-function pin is a problem.

One of the objects of the present invention is to provide a zero current detector and method for a power supply.

One of the objects of the present invention is to provide a zero current detector and method for reducing the number of pins.

According to the present invention, a zero current detector of a power supply includes a sensing circuit, a capacitor, and a control integrated circuit that generates a high frequency signal when a current supplied to an output of the power supply drops to zero. The capacitor couples the AC component of the high frequency signal to the pin of the control integrated circuit to cause the control integrated circuit to trigger the zero current detection signal. Since the capacitor can prevent the voltage level of the pin from being affected by the low frequency signal and the DC component outputted by the sensing circuit, the pin can also be used to implement functions other than zero current detection to reduce the number of pins.

According to the present invention, a zero current detecting method for a power supply device includes generating a high frequency signal when a current supplied to an output terminal of the power supply source drops to zero, and coupling an alternating current component of the high frequency signal to a control by a capacitor The pin of the integrated circuit is such that the control integrated circuit triggers a zero current signal.

3 shows a first embodiment of the zero current detector 20 of the present invention. In the flyback power supply of FIG. 3, the resistors R1 and R2 divide the input voltage Vin to generate a voltage Vind associated with the input voltage Vin to the control product. The pin MULT of the body circuit 10 controls the integrated circuit 10 to obtain input voltage information based on the voltage Vind of the pin MULT. Figure 4 shows a timing diagram of the signals in Figure 3. Referring to FIG. 3 and FIG. 4, the zero current detector 20 includes a capacitor Czcd, a control integrated circuit 10, and an auxiliary coil La of the transformer T1. The auxiliary coil La is used as a sensing circuit for detecting the secondary current Is, and the capacitor Czcd is connected. Between the pin MULT of the control integrated circuit 10 and the auxiliary coil La, the capacitor Czcd blocks the low frequency signal and the DC component of the auxiliary coil La from being input to the pin MULT, so the zero current detector 20 does not affect the voltage of the pin MULT. The Vind level, the control integrated circuit 10 can obtain the correct input voltage information according to the voltage Vind. When the secondary side current Is drops to zero, as indicated by time t4, the auxiliary coil La generates a high frequency signal 12, and the capacitor Czcd couples the alternating current component of the high frequency signal 12 to the pin MULT, causing a drop surge in the voltage Vind. When the voltage Vind is lower than the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd to achieve zero current detection. In the control integrated circuit 10, the comparator voltage comparison Vind and the preset value Vpre can be used to trigger the zero current signal Szcd. As can be seen from FIG. 4, at the moment when the switch M1 is turned on, the auxiliary coil La also generates a high-frequency signal to make the voltage Vind lower than the preset value Vpre, as shown by time t5, so that some mechanisms are designed to prevent mistakes in the control integrated circuit 10. The zero current signal Szcd is triggered, for example, the control integrated circuit 10 can only trigger the zero current signal Szcd during the off period of the switch M1, or shield the incorrect zero current signal Szcd with the mask signal.

FIG. 5 shows a second embodiment of the zero current detector 20 of the present invention, which includes the capacitor Czcd and the control integrated circuit 10 as in the circuit of FIG. 3, but uses the primary side coil Lp of the transformer T1 as a sensing circuit to detect The secondary side current Is, the capacitor Czcd is connected between the pin MULT and the primary side coil Lp, and the capacitor Czcd blocks the low frequency signal on the primary side coil Lp and the DC component input to the pin MULT, so the zero current detector 20 does not affect The level of the voltage Vind of the pin MULT, the control integrated circuit 10 can obtain the correct input voltage information according to the voltage Vind. 6 shows a timing chart of the signal of FIG. 5. As shown by time t6, when the secondary side current Is drops to zero, the primary side coil Lp generates a high frequency signal 12, and the capacitance Czcd couples the alternating current component of the high frequency signal 12 to The pin MULT causes the voltage Vind to have a falling spurt. When the voltage Vind is lower than the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd to achieve zero current detection.

7 shows a third embodiment of the zero current detector 20 of the present invention, which includes the capacitor Czcd and the control integrated circuit 10 as well as the circuit of FIG. 3, but uses the secondary side coil LS of the transformer T1 as a sensing circuit to detect The secondary side current Is is measured, the capacitor Czcd is connected between the pin MULT and the secondary side coil Ls, and the capacitor Czcd blocks the low frequency signal and the DC component of the secondary side coil Ls from being input to the pin MULT, so the zero current detector 20 does not affect the level of the voltage Vind of the pin MULT, and the control integrated circuit 10 can obtain the correct input voltage information according to the voltage Vind. 8 is a timing chart showing the signal of FIG. 7. As shown by time t7, when the secondary side current Is drops to zero, the high frequency signal 12 is generated on the secondary side coil Ls, and the capacitance Czcd is the alternating current component of the high frequency signal 12. Coupling to the pin MULT causes the voltage Vind to have a falling spurt. When the voltage Vind is lower than the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd to achieve zero current detection.

9 shows a fourth embodiment of the zero current detector 20 of the present invention. In the boost power supply of FIG. 9, the control integrated circuit 10 controls the switch M1 connected in series with the inductor L1 to charge and discharge the inductor L1. The input voltage Vin is converted into an output voltage Vo, and the resistors R1 and R2 divide the input voltage Vin to generate a voltage Vind to the pin MULT of the control integrated circuit 10, so that the control integrated circuit 10 can obtain the input voltage information. The zero current detector 20 of FIG. 9 includes a capacitor Czcd, a control integrated circuit 10 and an auxiliary coil La. The auxiliary coil La is used as a sensing circuit for detecting the current IL of the inductor L1. The capacitor Czcd is connected to the control integrated circuit 10. Between the pin MULT and the auxiliary coil La, the capacitor Czcd blocks the low frequency signal and the DC component of the auxiliary coil La from being input to the pin MULT, so the zero current detector 20 does not affect the level of the voltage Vind of the pin MULT, and the control product The body circuit 10 can obtain correct input voltage information based on the voltage Vind. Figure 10 is a timing diagram of the signal of Figure 9, wherein the waveform 22 is the current through the switch M1, and the waveform 24 is the current through the diode D1. When the control integrated circuit 10 turns on the switch M1, as shown by time t8, the inductance The current IL flows to the ground through the switch M1 and the resistor Rcs. At this time, the inductor L1 is charged, and the current IL starts to rise, as shown by the waveform 22. When the control integrated circuit 10 turns off the switch M1, as shown by time t9, the current IL of the inductor flows through the diode D1 to the output terminal Vo, and at this time, the inductor L1 is discharged, and the current IL starts to decrease, as shown by the waveform 24. When the current IL drops to zero, as indicated by time t10, the auxiliary coil La generates a high frequency signal 12, and the capacitor Czcd couples the alternating current component of the high frequency signal 12 to the pin MULT, causing the voltage Vind to appear a falling glitch at the voltage Vind Below the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd for zero current detection.

11 shows a fifth embodiment of the zero current detector 20 of the present invention. In the buck power supply of FIG. 11, the control integrated circuit 10 controls the switch M1 to charge and discharge the inductor L1, thereby converting the input voltage Vin. For the output voltage Vo, the resistors R1 and R2 divide the input voltage Vin to generate a voltage Vind to the pin MULT of the control integrated circuit 10, so that the control integrated circuit 10 can obtain the input voltage information. The zero current detector 20 of FIG. 11 includes a capacitor Czcd, a control integrated circuit 10 and an auxiliary coil La. The auxiliary coil La is used as a sensing circuit for detecting the current IL of the inductor L1, and the capacitor Czcd is connected to the control integrated circuit 10. Between the pin MULT and the auxiliary coil La, the capacitor Czcd blocks the low frequency signal and the DC component of the auxiliary coil La from being input to the pin MULT, so the zero current detector 20 does not affect the level of the voltage Vind of the pin MULT, and the control product The body circuit 10 can obtain correct input voltage information based on the voltage Vind. Figure 12 is a timing diagram of the signal of Figure 11, wherein waveform 26 is the current through switch M1, and waveform 28 is the current through diode D1. When control integrated circuit 10 turns on switch M1, as shown at time t11, the inductor The current IL flows to the ground through the switch M1 and the resistor Rcs. At this time, the inductor L1 is charged, and the current IL starts to rise, as shown by the waveform 26. When the integrated circuit 10 is controlled to turn off the switch M1, as shown by time t12, the current IL of the inductor flows through the diode D1 to the output terminal Vo, at which time the inductor L1 is discharged and the current IL begins to decrease, as shown by the waveform 28. When the current IL drops to zero, as indicated by time t13, the auxiliary coil La generates a high frequency signal 12, and the capacitor Czcd couples the alternating current component of the high frequency signal 12 to the pin MULT, causing the voltage Vind to appear a falling glitch at the voltage Vind Below the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd for zero current detection.

In the foregoing embodiment, the zero current detector 20 is implemented by using the MULT pin for detecting the input voltage information, thereby reducing the number of pins. In addition to the pin MULT, the zero current detector 20 of the present invention can also use pins of other functions, such as the pin CS for detecting the current of the switch M1. A sixth embodiment of the zero current detector 20 of the present invention is shown in FIG. 13. In the flyback power supply of FIG. 13, when the switch M1 is turned on, the primary side current Ip is generated by the resistor Rcs in series with the switch M1. The voltage Vcs is controlled to the pin CS of the integrated circuit 10, and the control integrated circuit 10 can determine the value of the primary side current Ip passing through the switch M1 based on the voltage Vcs. Fig. 14 is a timing chart showing the signal of Fig. 13, in which the waveform 30 is the primary side current Ip and the waveform 32 is the secondary side current Is. 13 and FIG. 14, the zero current detector 20 of FIG. 13 includes the capacitor Czcd, the control integrated circuit 10, and the auxiliary coil La of the transformer T1, but the capacitor Czcd is connected to the control integrated circuit 10 as well. Between the pin CS and the auxiliary coil La, since the capacitor Czcd blocks the low frequency signal of the auxiliary coil La and the DC component is input to the pin CS, the zero current detector 20 does not affect the level of the voltage Vcs of the pin CS, and controls The integrated circuit 10 can determine the value of the primary side current Ip based on the voltage Vcs. When the secondary side current Is drops to zero, as indicated by time t14, the auxiliary coil La generates a high frequency signal 12, and the capacitor Czcd couples the alternating current component of the high frequency signal 12 to the pin CS, causing a drop surge in the voltage Vcs. When the voltage Vcs is lower than the preset value Vpre, the control integrated circuit 10 triggers the zero current signal Szcd to achieve zero current detection. As can be seen from FIG. 14, at the moment when the switch M1 is turned on, the auxiliary coil La also generates a high frequency signal such that the voltage Vcs is lower than the preset value Vpre, as shown at time t15, in order to avoid false triggering of the zero current signal Szcd, the embodiment of this embodiment The control integrated circuit 10 provides a comparison result of the masking signal ZCD_Mask at the moment when the switch M1 is turned on, and the masking voltage Vcs is compared with the preset value Vpre. Similarly, in the zero current detector 20 shown in FIG. 5, FIG. 7, FIG. 9 and FIG. 11, one end of the capacitor Czcd connection pin MULT can also be changed to be connected to the pin CS.

The zero current detector 20 of the present invention may also not share the pin position with other functions, that is, the pin connected to the capacitor Czcd has only a zero current detecting function.

10. . . Control integrated circuit

12. . . High frequency signal

20. . . Zero current detector

twenty two. . . Current through switch M1

twenty four. . . Current through diode D1

26. . . Current through switch M1

28. . . Current through diode D1

30. . . Primary current Ip

32. . . Secondary current Is

Figure 1 shows a conventional flyback power supply with zero current detection;

Figure 2 shows a timing diagram of the signal of Figure 1;

Figure 3 shows a first embodiment of the zero current detector of the present invention;

Figure 4 shows a timing diagram of the signals in Figure 3;

Figure 5 shows a second embodiment of the zero current detector of the present invention;

Figure 6 shows a timing diagram of the signals in Figure 5;

Figure 7 shows a third embodiment of the zero current detector of the present invention;

Figure 8 shows a timing diagram of the signals in Figure 7;

Figure 9 shows a fourth embodiment of the zero current detector of the present invention;

Figure 10 is a timing chart showing the signal of Figure 9;

Figure 11 shows a fifth embodiment of the zero current detector of the present invention;

Figure 12 shows a timing diagram of the signals in Figure 11;

Figure 13 shows a sixth embodiment of the zero current detector of the present invention;

Figure 14 shows a timing diagram of the signals in Figure 13.

10. . . Control integrated circuit

20. . . Zero current detector

Claims (20)

A zero current detector of a power supply, the power supply comprising a transformer for converting an input voltage into an output voltage, the zero current detector comprising: a control integrated circuit having a pin; a sensing circuit Sensing the secondary side current of the transformer, generating a high frequency signal when the secondary side current drops to zero; and a capacitor connected between the pin and the sensing circuit to couple the alternating current component of the high frequency signal To the pin, so that the control integrated circuit triggers a zero current signal. The zero current detector of claim 1, wherein the control integrated circuit detects the input voltage by the pin. The zero current detector of claim 1, wherein the control integrated circuit detects the primary current of the transformer by the pin. The zero current detector of claim 1, wherein the control integrated circuit triggers the zero current signal when the voltage of the pin is lower than a preset value. The zero current detector of claim 1, wherein the sensing circuit comprises a primary side coil, a secondary side coil or an auxiliary coil of the transformer that generates the high frequency signal when the secondary side current drops to zero. A zero current detector of a power supply, the power supply comprising an inductor and a switch connected to the inductor, wherein the switch is switched to convert an input voltage into an output voltage, the zero current detector comprising: a control integrated circuit Having a pin; a sensing circuit for sensing a current of the inductor, generating a high frequency signal when the current drops to zero; and a capacitor connected between the pin and the sensing circuit, the high frequency An alternating component of the signal is coupled to the pin such that the control integrated circuit triggers a zero current signal. The zero current detector of claim 6, wherein the control integrated circuit detects the input voltage by the pin. The zero current detector of claim 6, wherein the control integrated circuit detects the current passing through the switch by the pin. The zero current detector of claim 6, wherein the control integrated circuit triggers the zero current signal when the voltage of the pin is lower than a predetermined value. A zero current detector as claimed in claim 6, wherein the sensing circuit includes an auxiliary coil that senses the current to generate the high frequency signal. A zero current detecting method for a power supply, the power supply comprising a transformer for converting an input voltage into an output voltage, the zero current detecting method comprising the steps of: (A) sensing a secondary current of the transformer, Generating a high frequency signal when the secondary side current drops to zero; and (B) coupling the alternating current component of the high frequency signal to a pin of the control integrated circuit by a capacitor to cause the control integrated circuit to trigger a zero current signal. The zero current detecting method of claim 11, wherein the step A comprises generating the high frequency signal by connecting a primary side coil, a secondary side coil or an auxiliary coil of the transformer. The zero current detecting method of claim 11, wherein the step B comprises coupling the high frequency signal to the pin for detecting the input voltage. The zero current detecting method of claim 11, wherein the step B comprises coupling the high frequency signal to the pin for detecting a primary side current of the transformer. The zero current detecting method of claim 11, wherein the step B comprises triggering the zero current signal when the voltage of the pin is lower than a preset value. A zero current detecting method for a power supply, the power supply comprising an inductor and a switch connected to the inductor, wherein the switch is switched to convert an input voltage into an output voltage, and the zero current detecting method comprises the following steps: controlling a product a body circuit having a pin; (A) sensing a current of the inductor, generating a high frequency signal when the current drops to zero; and (B) coupling an alternating component of the high frequency signal to the control integrated body by a capacitor The pin of the circuit is such that the control integrated circuit triggers a zero current signal. The zero current detecting method of claim 16, wherein the step A comprises sensing the current by the auxiliary coil to generate the high frequency signal. The zero current detecting method of claim 16, wherein the step B comprises coupling the high frequency signal to the pin for detecting the input voltage. The zero current detecting method of claim 16, wherein the step B comprises coupling the high frequency signal to the pin for detecting the current of the switch. The zero current detecting method of claim 16, wherein the step B comprises triggering the zero current signal when the voltage of the pin is lower than a preset value.