Power supply

Abstract

An embodiment of the present invention provides a power supply, which includes a transformer, a rectifying switch, a secondary-side synchronous rectification controller, and two diodes. The transformer has a primary winding, a secondary winding, and a sensing winding, which are inductively coupled to each other. The rectifying switch is connected in series with the secondary winding between two output power lines. The secondary-side synchronous rectification controller is connected to two ends of the sensing winding and controls the rectifying switch according to two terminal signals at the two ends. The two diodes are connected in series back-to-back between the two ends.

Description

Technical Field

[0001] The present invention generally relates to a control method and a controller for synchronous rectification of a power supply. Background Art

[0002] In addition to requiring accurate output voltage or output current, power conversion efficiency is often one of the specifications that the industry cares very much about.

[0003] A traditional flyback switching power supply uses a transformer to separate the primary side and the secondary side. By switching a power switch, the voltage across the primary winding on the primary side changes. Due to inductive coupling, an AC component is generated across the secondary winding, which can supply a load located on the secondary side after being rectified.

[0004] For rectification on the secondary side, the simplest way is to use a rectifier diode. However, the forward voltage required for the rectifier diode to turn on makes the rectifier diode a component that constantly consumes energy. In order to reduce or eliminate the energy consumption of the rectifier diode and increase the power conversion efficiency, the industry has developed a rectifier switch to replace the rectifier diode. However, how to turn on and off the rectifier switch at the correct time not only affects the power conversion efficiency but also relates to the safety considerations of the power supply, which is often the goal that circuit designers of each company strive to improve. Summary of the Invention

[0005] An embodiment of the present invention provides a power supply, including a transformer, a rectifier switch, a secondary side synchronous rectification controller, and two diodes. The transformer has a primary winding, a secondary winding, and a sensing winding, which are inductively coupled to each other. The rectifier switch is connected in series with the secondary winding between two output power lines. The secondary side synchronous rectification controller is connected to two ends of the sensing winding and controls the rectifier switch according to two end signals on the two ends. The two diodes are connected in series back-to-back between the two ends.

[0006] An embodiment of the present invention provides a power supply, which includes a transformer, a power switch, a rectifier switch, and a secondary synchronous rectification controller. The transformer has a primary winding and a secondary winding, which are inductively coupled to each other. The power switch is connected in series with the primary winding between two input power lines. The rectifier switch is connected in series with the secondary winding between two output power lines. An output voltage is located on one of the two output power lines. The secondary synchronous rectification controller is connected to the rectifier switch and controls the rectifier switch. A dead time is located after the rectifier switch is turned off and before the power switch is turned on. The secondary synchronous rectification controller is configured to detect the output voltage to adjust the dead time. Description of the Drawings

[0007] Figure 1 Shows a flyback switch-mode power supply 10 with synchronous rectification implemented according to the present invention.

[0008] Figure 2 Shows Figure 1 some signal waveforms in.

[0009] Figure 3 Shows Figure 1 the secondary synchronous rectification controller 20 in.

[0010] Figure 4 Shows Figure 3 some signal waveforms in.

[0011] Figure 5 Shows a flyback switch-mode power supply 100 with synchronous rectification implemented according to the present invention.

[0012] List of Reference Numerals

[0013] 10, 100 Flyback Switch-Mode Power Supply

[0014] 12 Secondary-Side Controller

[0015] 14 Primary-Side Controller

[0016] 16 Load

[0017] 17 Output Capacitor

[0018] 18 Transformer

[0019] 20 Secondary Synchronous Rectification Controller

[0020] 26 Input Ground Wire

[0021] 28 Output Ground Wire

[0022] 42, 44, 62 Comparator

[0023] 45 Adder

[0024] 46 Discharge time timer

[0025] 47 Updating device

[0026] 50 Recording capacitor

[0027] 52 Capacitor

[0028] 56 Voltage-to-current converter

[0029] 60 Logic circuit

[0030] 77, 88 Resistor

[0031] 112 Secondary-side controller

[0032] 120 Operational amplifier

[0033] dV Voltage difference

[0034] DB1, DB2 Body diode

[0035] E11 Signal falling edge

[0036] E22 Signal rising edge

[0037] E21 Signal falling edge

[0038] IN Input power line

[0039] I BIAS Bias current

[0040] I PRI 、I SEC Winding current

[0041] I RD Current

[0042] IS Current source

[0043] LA Detection winding

[0044] LP Primary winding

[0045] LS Secondary-side winding

[0046] NMP Power switch

[0047] NMS Rectifying switch

[0048] NS1, NS2 Switch

[0049] OUT Output power line

[0050] S FLBK PWM signal

[0051] S INI Start signal

[0052] S- NB Signal

[0053] S SWD1 、S SWD2 Terminal signal

[0054] S SYN Control signal

[0055] S UPD Pulse

[0056] SWD1 and SWD2 endpoints

[0057] t0, t1, t 01 、t 02 、t 03 、t 04 、t 05 Time point

[0058] T D1 、T D2 、T DD Dead time

[0059] T DIS Discharge time

[0060] V DS Channel voltage

[0061] V OUT Output voltage

[0062] V QUESS Estimated signal

[0063] V RAISED Voltage

[0064] V REAL Triangular wave signal

[0065] V WD2 Voltage Specific implementation mode

[0066] In this specification, there are some identical symbols, which represent components with the same or similar structures, functions, and principles, and can be inferred by those skilled in the art based on the teachings of this specification. For the sake of the simplicity of the specification, the components with the same symbols will not be restated.

[0067] Figure 1Disclosed is a flyback switching power supply 10 with synchronous rectification implemented according to the present invention, having a transformer 18, a primary controller 14, a secondary controller 12, a power switch NMP, a rectification switch NMS, and an output capacitor 17.

[0068] The transformer 18 includes a primary winding LP, a secondary winding LS, and a sensing winding LA that are mutually inductively coupled. In an embodiment, the transformer 18 may also have other windings on the primary or secondary side. The primary winding LP on the primary side is connected in series with the power switch NMP between the input power line IN and the input ground line 26. The primary controller 14 on the primary side provides a PWM signal S FLBK , which controls the power switch NMP. Controlling the power switch NMP to turn on and off changes the winding current I PRI , enabling the transformer 18 to store and release energy.

[0069] The secondary winding LS on the secondary side is connected in series with the rectification switch NMS between the output power line OUT and the output ground line 28. The secondary controller 12 provides a control signal S SYN , which controls the rectification switch NMS, and it is desired that when the transformer 18 releases energy and the winding current I SEC is positive, the rectification switch NMS can be turned on in a timely manner to provide a low-impedance current path to charge the output capacitor 17. In other words, when the channel voltage V DS of the rectification switch NMS is negative, the rectification switch NMS should be turned on; conversely, when the channel voltage V DS of the rectification switch NMS is positive, the rectification switch NMS should be turned off.

[0070] The output voltage V OUT on the output power line OUT can supply electrical energy to the load 16. For example, the load 16 is a rechargeable battery.

[0071] The secondary controller 12 can be a single-chip integrated circuit, having two switches NS1 and NS2, and a secondary synchronous rectification controller 20. The switches NS1 and NS2 are connected in series between the endpoints SWD1 and SWD2 of the sensing winding LA. As Figure 1 shown, two body diodes DB1 and DB2 in the switches NS1 and NS2 are connected in series back-to-back between the endpoints SWD1 and SWD2, and the connection point between the body diodes DB1 and DB2 is connected to the output ground line 28. There are terminal signals S SWD1 and S SWD2 respectively on the endpoints SWD1 and SWD2.

[0072] In an embodiment, the secondary synchronous rectification controller 20 is based on the terminal signals SSWD1 With S SWD2 , to generate a control signal S SYN , to control the rectifying switch NMS. That is to say, the secondary side synchronous rectification controller 20 is based on the terminal signals S SWD1 and S SWD2 , to determine the switching timing of the rectifying switch NMS.

[0073] Figure 2 Display Figure 1 Some signal waveforms in. The PWM signal S FLBK has a rising edge at the time point t 01 , starts to turn on the power switch NMP, and also starts a switching cycle. When the power switch NMP is on, the control signal S SYN is maintained at logically "0", turning off the rectifying switch NMS; the terminal signal S SWD1 reflects the input voltage V IN , depending on the turns ratio of the visual sensing winding LA to the main winding LP; the terminal signal S SWD2 is approximately 0V of the output ground wire 28.

[0074] At the time point t 02 , the PWM signal S FLBK changes from logically "1" to "0", starts to turn off the power switch NMP, and the transformer 18 starts to release energy. Therefore, the terminal signal S SWD1 generates a signal falling edge E11 approximately at the time point t 02 , and the terminal signal S SWD2 generates a signal rising edge E22. When the transformer 18 releases energy, the terminal signal S SWD2 is approximately the voltage V WD2 , reflecting the output voltage V OUT ; and the terminal signal S SWD1 is approximately 0V of the output ground wire 28.

[0075] In response to the signal falling edge E11, the secondary side synchronous rectification controller 20 starts to turn on the rectifying switch NMS at the time point t D1 after the dead time T 03 , as shown by the control signal S Figure 2 in. In another embodiment, the secondary side synchronous rectification controller 20 starts to turn on the rectifying switch NMS in response to the signal rising edge E22 at the time point t SYN . 03 Start to turn on the rectifying switch NMS.

[0076] In one embodiment, the on-time length of the rectifying switch NMS is determined by the discharge time T SWD2 when the terminal signal S is greater than 0V in the previous switching cycle DISDetermined by the terminal signal S in the previous switching cycle SWD2 According to the signal falling edge E21 of SWD2 , the secondary side synchronous rectification controller 20 starts to turn off the rectification switch NMS at time point t 04 How the secondary side synchronous rectification controller 20 determines to turn off the rectification switch NMS at time point t will be explained in detail later 04 Turn off the rectification switch NMS

[0077] At time point t 05 That is, at time point t 04 After delaying the dead time T D2 The PWM signal S FLBK Has another signal rising edge and starts a new switching cycle

[0078] Figure 2 The dead time T marked in D2 Is located between time point t 04 And time point t - 05 The dead time T DD Belongs to a part of the dead time T D2 And is also located between time point t 04 And time point t - 05 But specifically refers to the period from time point t 04 To the discharge time T DIS Ends

[0079] In an embodiment, the secondary side synchronous rectification controller 20 controls the time length of the dead time T DD According to the signal falling edge E21 in the previous switching cycle. Moreover, the secondary side synchronous rectification controller 20 can make the time length of the dead time T DD Approach a default length TEXP with each switching cycle. The secondary side synchronous rectification controller 20 detects the output voltage V OUT To set the default length TEXP. The secondary side synchronous rectification controller 20 controls the dead time T DD Which is equivalent to controlling the dead time T D2

[0080] Figure 3 Shown Figure 1 The secondary side synchronous rectification controller 20 in Figure 4 Shown Figure 3 Some signal waveforms in

[0081] Taiwan Patent Certificate No. I555320 teaches an adaptively synchronous rectification controller for reference to further understand​Figure 3 The operation of the secondary - side synchronous rectification controller 20 in. For the sake of brevity, Figure 3 The similarities and differences between the secondary - side synchronous rectification controller 20 and the Taiwan patent certificate number I555320 may not be explained again.

[0082] Comparator 42 detects the falling edge of the terminal signal S Figure 4 at the time point t0 in, and through the start signal S SWD1 and the control signal S INI , at the time point t1 after the dead - time T SYN , turns on the rectification switch NMS. D1

[0083] Comparator 44 detects whether the terminal signal S SWD2 is positive, and accordingly generates the signal S - NB . When the signal S - NB is logically "1", it is defined as the discharge time T DIS . When the discharge time T DIS ends, the signal S - NB changes to logically "0" and provides the pulse S UPD , as Figure 4 shown.

[0084] The discharge - time timer 46 uses the current source IS and the capacitor 52 to generate a triangular - wave signal V REAL to time the duration of the current discharge time T DIS . When the discharge time T DIS ends, the triangular - wave signal V REAL represents the length of the current discharge time T DIS . The pulse S UPD can trigger the update device 47 to update the estimated signal V REAL on the record capacitor 50 with the triangular - wave signal V QUESS . Therefore, it can be understood that the estimated signal V QUESS will more and more represent the true length of the discharge time T DIS as each switching cycle passes. As Figure 4 shown, each time the pulse S UPD passes, the estimated signal V QUESS gets closer to the triangular - wave signal V REAL .

[0085] The secondary - side synchronous rectification controller 20 is designed to close the rectification switch NMS in advance before the end of the discharge time T DIS , and the dead - time T DIS from when the rectification switch NMS is closed until the end of the discharge time T DD, will approach a default length TEXP with each switching cycle.

[0086] The adder 45 has a voltage-to-current converter 56, a resistor 77, and an operational amplifier 120. The adder 45 makes the voltage V RAISED equal to the sum of the triangular wave signal V REAL and the voltage difference dV. In one embodiment, the voltage-to-current converter 56 provides a current I OUT according to the output voltage V RD . For example, I RD = K * V OUT , where K is a constant. In another embodiment, the voltage-to-current converter 56 provides a current I WD2 according to the voltage V RD , and the voltage V WD2 can be obtained by sampling the sampling result of the sampling terminal signal S SWD2 at an appropriate time. Through a simple circuit analysis of the adder 45 in Figure 3 , it can be known that V RAISED = V REAL + dV = V REAL + I RD * R 77 = V REAL + K * V OUT * R 77 , where R 77 is the resistance value of the resistor 77. It can be known that the voltage difference dV = K * V OUT * R 77 .

[0087] The comparator 62 and the logic circuit 60 can be regarded as a switch controller. When the voltage V RAISED is approximately higher than the estimated signal V QUESS , the rectification switch NMS is turned off. In the steady state, the estimated signal V QUESS will get closer and closer to the length of the actual discharge time T DIS with each switching cycle passing. The voltage V RAISED is higher than the triangular wave signal V REAL by a voltage difference dV. Therefore, the secondary side synchronous rectification controller 20 is equivalent to being designed to make, in the steady state, after the rectification switch NMS is turned off, the discharge time T REAL ends after the default length TEXP of the triangular wave signal V DIS climbs the voltage difference dV more. So, the preset length TEXP = dV * C 52 / I IS , where C 52 is the capacitance value of the capacitor 52 in Figure 3 , and I ISis the current value of the current source IS. After arrangement, TEXP = V OUT *R 77 *C 52 / I IS . In other words, as each switching cycle passes, the estimated signal V QUESS will get closer and closer to the true discharge time T DIS , and the dead time T DD will get closer and closer to the preset length TEXP, as shown in Figure 4 . The secondary side synchronous rectification controller 20 sets the default length TEXP according to the output voltage V OUT , and the preset length TEXP increases as the output voltage V OUT increases. In another embodiment, the secondary side synchronous rectification controller 20 sets the preset length TEXP according to a sampling result of the voltage V WD2 and the terminal signal S SWD2 . The voltage V WD2 is equal to the result of the secondary side synchronous rectification controller 20 detecting the output voltage V OUT through the sense winding.

[0088] Using the terminal signals S SWD1 and S SWD2 of the sense winding LA to control the rectifying switch NMS has some advantages. For example, the secondary side controller 12 does not need to directly contact the secondary side winding LS, and it is possible to use a low-voltage semiconductor process for manufacturing. At the moment when the main winding LP just turns off, there are often very high voltage surges at both ends of the secondary side winding LS. Therefore, integrated circuits in contact with the secondary side winding LS often require high voltage tolerance and have to use expensive high-voltage semiconductor processes. For the secondary side controller 12, even if the rated value range of the output voltage V OUT is from 3V to 21V, as long as an appropriate turns ratio is designed, the maximum voltage value of the terminal signals S SWD1 and S SWD2 can be limited to a low enough range, so it is possible to use a relatively inexpensive low-voltage semiconductor process to manufacture the secondary side controller 12.

[0089] In one embodiment, the secondary side synchronous rectification controller 20 can turn on the switches NS1 and NS2 at an appropriate time to short-circuit the two endpoints SWD1 and SWD2. When the two endpoints SWD1 and SWD2 are short-circuited, the primary side controller 14 fixedly turns off the power switch NMP, delaying the start of the next switching cycle. When the switches NS1 and NS2 change from on to off and the two endpoints SWD1 and SWD2 are no longer short-circuited, the primary side controller 14 can use the PWM signal S FLBK, provide a pulse with a fixed pulse width to briefly turn on the power switch NMP and start a switching cycle. In other words, the secondary side synchronous rectification controller 20 can be a secondary side controller that controls the start of a switching cycle by controlling the switches NS1 and NS2.

[0090] Although the secondary side synchronous rectification controller 20 uses the terminal signals S SWD1 and S SWD2 of the detection winding LA to control the rectification switch NMS, the present invention is not limited thereto. Figure 5 Discloses a flyback switching power supply 100 implementing synchronous rectification according to the present invention, which is the same as or similar to the flyback switching power supply 10 in Figure 1 , and can be known according to the previous teachings on the flyback switching power supply 10, and will not be repeated here.

[0091] The secondary side controller 112 in the flyback switching power supply 100 detects the channel voltage V through the resistor 88 DS , and it is expected that when the channel voltage V DS is negative, the rectification switch NMS is turned on. To prevent short-circuit penetration, there is a dead time T between the start of the power switch NMP turning off and the start of the rectification switch NMS turning on D1 , and there is a dead time T between the start of the rectification switch NMS turning off and the start of the power switch NMP turning on D2 . However, to prevent the problem of poor conversion efficiency caused by the rectification switch NMS turning off too late, the secondary side controller 112 can detect the output voltage V OUT , and accordingly provide a bias current I when the rectification switch NMS is turned on BIAS . The bias current I BIAS flows through the resistor 88. The larger the output voltage V OUT , the larger the bias current I BIAS , and the rectification switch NMS can be turned off earlier, thereby controlling and adjusting the time length of the dead time T D2 .

[0092] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A power supply, comprising: A transformer having a primary winding, a secondary winding, and a sensing winding that are inductively coupled to each other; A rectifying switch connected in series with the secondary winding between two output power lines; A secondary side synchronous rectification controller connected to two ends of the sensing winding and controlling the rectifying switch according to two end signals on the two ends; Two diodes connected in series back-to-back between the two ends; and A power switch connected in series with the primary winding between two input power lines; Wherein the two end signals are a first end signal and a second end signal respectively, a dead time is located after the rectifying switch is turned off and before the power switch is turned on, and the secondary side synchronous rectification controller is configured to control the dead time according to a first signal falling edge of the second end signal.

2. The power supply according to claim 1, wherein, The secondary side synchronous rectification controller turns on the rectifying switch according to a first signal falling edge of the first end signal or a first signal rising edge of the second end signal.

3. The power supply according to claim 1, wherein, The secondary side synchronous rectification controller is configured to make the dead time approach a default length with each switching cycle.

4. The power supply according to claim 3, wherein, The secondary side synchronous rectification controller sets the default length according to an output voltage on one of the two output power lines or a sampling result of one of the two end signals.

5. The power supply according to claim 1, further comprising: Two switches connected in series between the two ends; Among them, The secondary side synchronous rectification controller controls the two switches to short-circuit the two ends.

6. A power supply, comprising: A transformer having a primary winding, a secondary winding, and a sensing winding that are inductively coupled to each other; A power switch connected in series with the primary winding between two input power lines; A rectifying switch connected in series with the secondary winding between two output power lines, and an output voltage is on one of the two output power lines; and A secondary side synchronous rectification controller connected to two ends of the sensing winding and controlling the rectifying switch according to two end signals on the two ends; Among them, A dead time is located after the rectifying switch is turned off and before the power switch is turned on, and the secondary side synchronous rectification controller is configured to detect the output voltage to adjust the dead time, and Wherein the two end signals are a first end signal and a second end signal respectively, and the secondary side synchronous rectification controller is configured to control the dead time according to a first signal falling edge of the second end signal.

7. The power supply according to claim 6, wherein, The secondary side synchronous rectification controller is configured to make the dead time approach a default length with each switching cycle, and the secondary side synchronous rectification controller detects the output voltage to set the default length.

8. The power supply according to claim 6, wherein, The secondary side synchronous rectification controller detects the output voltage through the sensing winding to control the time length of the dead time.

9. The power supply according to claim 8, wherein, The power supply further includes two diodes connected in series back-to-back between the two ends.

10. The power supply according to claim 9, wherein, The secondary side synchronous rectification controller turns on the rectifying switch according to a first signal falling edge of the first end signal or a first signal rising edge of the second end signal.

11. The power supply according to claim 6, wherein, The secondary side synchronous rectification controller is connected to the secondary side winding through a resistor, and the secondary side synchronous rectification controller provides a bias current flowing through the resistor according to the output voltage.

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