Power supply with limited power protection and associated control method

Abstract

A power supply with power limit protection and a related control method. The power supply includes a transformer, a current sensing resistor, a bus switch and a power transfer controller. The transformer has a primary winding and a secondary winding on the secondary side for AC isolation between the primary side and the secondary side. The current sensing resistor is used to sense the bus current outputted by the power supply and to provide a current sensing signal. The bus switch is connected between the secondary winding and a bus voltage and is used to cut off the electrical connection between the transformer and the bus voltage. The power transfer controller controls the opening and closing of the bus switch according to the current sensing signal and a power sensing signal on the secondary side. The power transfer controller provides a power threshold according to the bus voltage. When the current sensing signal exceeds the current threshold or the power sensing signal exceeds the power threshold, the power transfer controller closes the bus switch to stop the power supply from providing power to the bus to stop the output of the voltage and current to achieve the power limit protection.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to power limit protection of a power supply, and more particularly to power limit protection triggered from a related detection signal at the secondary side of a transformer and a bus of the power supply and related control method. BACKGROUND

[0002] An AC to DC power supply converts AC mains to DC power that meets the output specification. The most basic function of a power supply is to accurately output the specified voltage and current.

[0003] Regulations also require power supplies to meet many safety specifications. For example, to prevent fires caused by power supplies outputting too much power, the international safety standard IEC 60950 defines limited power source (LPS) requirements that require a power supply to meet the maximum allowable current and power under all operating conditions.

[0004] The output current of a power supply can be sensed by a current sense resistor that generates a current sense signal. When the current sense signal reflects that the output current is continuously exceeding the LPS requirements or any maximum rated current specified by a safety standard, a power controller in the power supply can terminate power conversion to prevent a fire or accident, achieving power limit protection.

[0005] However, if the current sense resistor is not functioning properly, for example, because it has become a short circuit for unknown reasons, the current sense signal cannot reflect the output current. Without other proper overcurrent or power limit protection mechanisms, the power supply can not be able to meet the safety specification requirements. SUMMARY

[0006] Embodiments of the present application provide a power supply that converts an input voltage at a primary side to a bus voltage at a secondary side. The power supply includes a transformer, a current detection resistor, a bus switch, and a power transfer controller. The transformer has a primary winding and a secondary winding that electrically isolates the primary side from the secondary side. The current detection resistor detects a bus current output by the power supply and provides a current detection signal. The bus switch is connected between the secondary winding and the bus voltage and can cut off an electrical connection between the transformer and the bus voltage. The power transfer controller controls the bus switch according to the current detection signal and a power detection signal at the secondary side. The power transfer controller provides a power threshold according to the bus voltage. When the current detection signal exceeds a current threshold or the power detection signal exceeds the power threshold, the power transfer controller turns off the bus switch to stop the power supply from providing power to the bus to stop voltage or current output, thereby achieving power limiting protection.

[0007] Embodiments of the present application provide a control method for a power supply that converts an AC input voltage at a primary side to a bus voltage at a secondary side. The control method includes detecting a bus current output by the power supply to provide a current detection signal, providing a power detection signal at the secondary side, providing a power threshold according to the bus voltage, and stopping power supply to the bus and voltage or current output when the current detection signal exceeds a current threshold or the power detection signal exceeds the power threshold, thereby achieving power limiting protection. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 A power supply 10 implemented according to embodiments of the present application is shown.

[0009] Figure 2 An example of a power transfer controller 108a is shown.

[0010] Figure 3 A control method M01 for the power supply 10 is shown.

[0011] Figure 4 A power supply 20 implemented according to embodiments of the present application is shown.

[0012] Figure 5 An example of a power transfer controller 109a is shown.

[0013] SYMBOL DESCRIPTION

[0014] 10, 20 power supply

[0015] 28 intermediate power ground

[0016] 101 input

[0017] 102 transformer

[0018] 104 power supply controller

[0019] 106 synchronous rectification circuit

[0020] 108, 108a, 109, 109a power transfer controller

[0021] 110 duty cycle detection circuit

[0022] 112 optocoupler

[0023] 114 USB Type-C connector

[0024] 118, 118a current sense resistor

[0025] 120, 120a current sensing device

[0026] 123 power switch

[0027] 124 bus switch

[0028] 130 current limiting resistor

[0029] 132 feedback resistor

[0030] 1062 synchronous rectification controller

[0031] 1064 detection resistor

[0032] 1068 rectification switch

[0033] 1082 current feedback loop

[0034] 1086, 1092, 1094 digital to analog converter

[0035] 1088, 1096, 1105, 1107 analog to digital converter

[0036] 1090 voltage feedback loop

[0037] 1098 microprocessor

[0038] 1100, 1101 NMOS transistor

[0039] 1102 diode

[0040] 1104, 1106 resistor

[0041] 1108 capacitor

[0042] 1400 microprocessor

[0043] 1402, 1404, 1410 analog-to-digital converter

[0044] 1406 auxiliary current detection circuit

[0045] 1408 cross voltage detection circuit

[0046] CB bus power capacitor

[0047] CC1, CC2, DP, DN connection port

[0048] CM intermediate power capacitor

[0049] CR power capacitor

[0050] DRVSR drive signal

[0051] DTDET variation signal

[0052] GND bus ground

[0053] GNDSR relatively low voltage

[0054] IBUS bus current

[0055] IN input voltage

[0056] IREF reference signal

[0057] ISEN, ISEN2 current detection signal

[0058] ISET set current

[0059] LP primary side winding

[0060] LS secondary side winding

[0061] M01 control method

[0062] N_CTL control signal

[0063] OPTO drive voltage

[0064] PRCT power detection signal

[0065] PRM primary side

[0066] S01, S02, S03, S04 step

[0067] SEC secondary side

[0068] S FB feedback signal

[0069] VBUS bus voltage

[0070] VCC intermediate voltage

[0071] VCCSR Relative High Voltage

[0072] VSENS detection signal

[0073] VSET sets the voltage. Detailed Implementation

[0074] In this specification, some identical symbols are used to represent elements having the same or similar structure, function, or principle, which can be inferred by those skilled in the art based on the teachings of this specification. For the sake of brevity, elements with the same symbols will not be repeated.

[0075] According to some embodiments of the present invention, a power supply has an AC-isolated primary side and a secondary side. The power supply converts an AC input voltage on the primary side into a bus voltage on the secondary side, which serves as an output voltage source. On the secondary side, a current-sensing resistor is used to detect a bus current and generate a current-sensing signal. A power transmission controller on the secondary side performs overcurrent or power limiting protection based on the current-sensing signal and a power-sensing signal. The power-sensing signal on the secondary side is associated with a synchronous rectifier controller located in the power supply, another current-sensing resistor for detecting the bus current, an optocoupler providing a feedback signal to the primary side, or a channel voltage across a bus switch controlling the bus current. In some embodiments, the synchronous rectifier controller has two voltage terminals and a driving terminal. The two voltage terminals provide an operating voltage for the synchronous rectifier controller, and the driving terminal controls a rectifier switch. The power-sensing signal is generated based on either the two voltage terminals or the driving terminal.

[0076] Because the power detection signal is located on the secondary side, it can accurately reflect the magnitude of the bus current, thus providing more accurate overcurrent or power limiting protection.

[0077] Figure 1 The power supply 10 implemented according to the present invention can be used to convert the input voltage IN (relative to the input ground 101 of the primary side PRM) to the bus voltage VBUS (relative to the bus ground GND of the secondary side SEC) to supply power to the load connected to the USB Type-C connector 114. In one embodiment, the input voltage IN can be a DC voltage rectified from AC mains power, while the bus voltage VBUS, relative to the bus ground GND of the secondary side SEC, can be between 3.3V and 21V to provide the USB Type-C related voltage.

[0078] The power supply 10 has, but is not limited to, a transformer 102, a power controller 104, a synchronous rectification circuit 106, a bus switch 124, an intermediate power supply capacitor CM, a bus power supply capacitor CB, a current sensing device 120, a current limiting resistor 130, a photo coupler 112, a feedback resistor 132, a duty cycle detection circuit 110, and a power delivery controller 108.

[0079] At the primary side PRM, the power controller 104 varies the inductive current flowing through the primary winding LP of the transformer 102 by switching the power switch 123. Through inductive induction, an induced voltage / current is generated at the secondary winding LS, which is rectified by the synchronous rectification circuit 106 to generate the intermediate power ground 28 and the intermediate voltage VCC. At the secondary side SRM, the bus voltage VBUS is generated at the bus ground GND by the bus switch 124. Figure 1 In an embodiment according to the present application, the synchronous rectification circuit 106 is located between the intermediate voltage VCC and the secondary winding LS, but the present application is not limited thereto. In an embodiment according to the present application, the intermediate voltage VCC is directly connected to the secondary winding LS, and the synchronous rectification circuit 106 is located between the intermediate power ground 28 and the secondary winding LS.

[0080] The current sensing device 120 includes a current sensing resistor 118 connected between the bus ground GND and the intermediate power ground 28, which can be used to sense the bus current IBUS from the bus ground GND to generate a current sensing signal ISEN.

[0081] The intermediate power supply capacitor CM and the bus power supply capacitor CB are respectively used to stabilize the intermediate voltage VCC (with respect to the intermediate power ground 28) and the bus voltage VBUS (with respect to the bus ground GND). The intermediate voltage VCC and the bus voltage VBUS can be regarded as two voltage power supplies.

[0082] The photo coupler 112 and the current limiting resistor 130 are connected in series between the intermediate voltage VCC and the power delivery controller 108.

[0083] The power delivery controller 108 can know through the connection ports CC1, CC2, DP, DN of the USB Type-C connector 114 what the bus voltage VBUS (relative to the bus ground GND) should be or the condition of the bus current IBUS flowing through the current sense resistor 118 at the moment, and control the intermediate voltage VCC and the bus switch 124 accordingly. For example, assume that the power delivery controller 108 knows that the bus voltage VBUS should be maintained at 5V and the bus current IBUS should not exceed 2A at the moment, and the relevant voltage and current values will be different according to different fast charging protocols. Therefore, the power delivery controller 108 detects the intermediate voltage VCC and the current sense signal ISEN, and controls the current flowing through the optocoupler 112 accordingly; the optocoupler 112 thus provides a feedback signal S FB to the power supply controller 104 on the primary side PRM; according to the feedback signal S FB , the power supply controller 104 maintains or changes the duty cycle of the power switch 123 to control the power transmitted to the secondary side SEC, thereby controlling the intermediate voltage VCC and the bus current IBUS. For example, when the intermediate voltage VCC is about 5V, which meets the current demand of the load connected to the USB Type-C connector 114, the power delivery controller 108 turns on the bus switch 124 through the control signal N_CTL, so that the bus voltage VBUS and the intermediate voltage VCC are about electrically shorted, and the load connected to the USB Type-C connector 114 is powered.

[0084] The synchronous rectification circuit 106 includes a rectification switch 1068, a synchronous rectification controller 1062, a power supply capacitor CR, and a detection resistor 1064. The power supply capacitor CR has two voltage terminals connected to the synchronous rectification controller 1062, respectively having a relatively high voltage VCCSR and a relatively low voltage GNDSR, to provide an operating voltage for the synchronous rectification controller 1062. The synchronous rectification controller 1062 detects a channel cross voltage of the rectification switch 1068 through the detection resistor 1064, that is, the voltage difference between the synchronous rectification ground GNDSR and the intermediate voltage VCC, and provides a drive signal DRVSR on the drive end to control the rectification switch 1068 accordingly. The synchronous rectification controller 1062 is configured to implement synchronous rectification, that is, when the channel cross voltage is greater than zero, the rectification switch 1068 is turned on; when the channel cross voltage is less than zero, the rectification switch 1068 is turned off.

[0085] The duty cycle detection circuit 110 is electrically connected between the synchronous rectifier circuit 106 and the power transmission controller 108. The duty cycle detection circuit 110 can generate a power detection signal PRCT based on a fluctuation signal DTDET at an input terminal of the synchronous rectifier circuit 106, which the power transmission controller 108 uses to provide power limiting protection. In one embodiment, the fluctuation signal DTDET can be one of the relative high voltage VCCSR, relative low voltage GNDSR, or drive signal DRVSR in the synchronous rectifier circuit 10. Simply put, the fluctuation signal DTDET on the secondary side SEC can change with the switching of the power switch 123 located on the primary side PRM, and can carry information about the duty cycle of the rectifier switch 1068. Therefore, the power detection signal PRCT generated by the duty cycle detection circuit 110 can be associated with the duty cycle of the rectifier switch 1068, allowing the power transmission controller 108 to determine whether to trigger power limiting protection.

[0086] exist Figure 1 In this circuit, the duty cycle detection circuit 110 provides rectification and low-pass filtering functions to generate a power detection signal PRCT. The duty cycle detection circuit 110 includes a diode 1102, resistors 1104 and 1106, and a capacitor 1108. Diode 1102 provides rectification, which can roughly detect the duty cycle of the rectifier switch 1068. Resistors 1104, 1106, and capacitor 1108 form a low-pass filter, generating a roughly stable power detection signal PRCT, which can be correlated with the duty cycle of the rectifier switch 1068. Diode 1102 and the low-pass filter are connected in series between the input of the synchronous rectification circuit 106 and the power transmission controller 108. Under a certain bus voltage VBUS, the duty cycle of the rectifier switch 1068 can approximately correspond to the bus current IBUS. Therefore, the power detection signal PRCT can serve as another indicator of the bus current IBUS.

[0087] Figure 2 For example, a power transmission controller 108a is shown, which includes a current feedback loop 1082, a voltage feedback loop 1090, NMOS transistors 1100 and 1101, digital-to-analog converters (DACs) 1086, 1092, and 1094, analog-to-digital converters (ADCs) 1088, 1096, 1105, and 1107, and a microprocessor (MCU) 1098. The current feedback loop 1082 amplifies the current detection signal ISEN and the reference signal IREF (from...). Figure 1The difference between the approximately equal to the intermediate power supply ground 28) and the set current ISET provided by the microprocessor 1098 through the DAC 1086 is compared to control the NMOS transistor 1100, which drives the optocoupler 112. The amplified result of this difference is also transmitted to the microprocessor 1098 through the ADC 1105. The current feedback loop 1082 and the microprocessor 1098 are configured to make the bus current IBUS not higher than a corresponding current value corresponding to the set current ISET. The set current ISET can be set according to the current bus voltage VBUS, or according to the signals from the connection ports CC1, CC2, DP, DN. Similarly, the voltage feedback loop 1090 scales the intermediate voltage VCC to generate a detection signal VSENS, which is compared with the set voltage VSET provided by the microprocessor 1098 through the DAC 1092 to control the NMOS transistor 1101. The voltage feedback loop 1090 and the microprocessor 1098 are configured to make the intermediate voltage VCC not higher than a corresponding voltage value corresponding to the set voltage VSET. The set voltage VSET can be set according to the signals from the connection ports CC1, CC2, DP, DN.

[0088] The microprocessor 1098 can know the approximate current value of the current bus IBUS through the ADC 1105, and the voltage values of the current bus voltage VBUS and the intermediate voltage VCC through the ADCs 1096 and 1107, respectively. In other words, the microprocessor 1098 can know the current bus voltage VBUS, the intermediate voltage VCC, and the current bus current IBUS. The microprocessor 1098 can also know the power detection signal PRCT through the ADC 1088.

[0089] Figure 3A control method M01 for the power supply 10 is shown. In step S01, the duty cycle detection circuit 110 detects one of the relative high voltage VCCSR, the relative low voltage GNDSR, or the drive signal DRVSR, and generates a power detection signal PRCT accordingly. In step S02, the power delivery controller 108a provides a power threshold based on the present bus voltage VBUS obtained from the ADC 1096, or a target value of the bus voltage VBUS obtained through the connection ports CC1, CC2, DP, DN. For example, the power delivery controller 108a can have a look-up table written in firmware to define the correspondence between the bus voltage VBUS and the power threshold. In step S03, the power delivery controller 108a monitors both the current detection signal ISEN and the power detection signal PRCT. In step S04, once the bus current IBUS causes the current detection signal ISEN to exceed a corresponding current value of the set current ISET, or causes the power detection signal PRCT to exceed the power threshold in step S02, and such condition is maintained for a predetermined time, the power delivery controller 108a implements current-limited or power-limited protection to force the bus switch 124 off through the DAC 1094.

[0090] If the present bus voltage VBUS is an output voltage value, for example, it is found through experiments that the power detection signal PRCT is approximately equal to a measured value when the power supply 10 outputs a power approximately equal to a limited power source (LPS) requirement. Therefore, a look-up table is written in firmware in the power delivery controller 108a to record the relationship between the bus voltage VBUS and the power detection signal PRCT based on the output voltage value and the measured value.

[0091] In normal operation, the power-limited protection provided by the power detection signal PRCT and the current detection signal ISEN can prevent the power delivery controller 108a from implementing the power-limited protection even if one of them fails. For example, if the current detection resistor 118 in the current detection circuit 116 is shorted to cause the current detection signal ISEN to incorrectly reflect the real bus current IBUS, the power detection signal PRCT can still reflect the real output power of the power supply 10 to provide the power-limited protection. Figure 1

[0092] Figure 4 ​The power supply 20 implemented according to the present invention can be used to convert the input voltage IN (relative to the input ground 101 of the primary side PRM) located on the primary side PRM into the bus voltage VBUS (relative to the bus ground GND of the secondary side SEC) located on the secondary side SEC, so as to supply power to the load connected to the USB type C connector 114. Figure 4 Power supply 20 and Figure 1 The similarities or differences between the power supply 10 and the power supply 10 can be learned from the previous teachings and will not be repeated here.

[0093] and Figure 1 The power supply is different for 10 different types. Figure 4 The power supply 20 does not have a duty cycle detection circuit 110, but it does have a current detection device 120a and a power transmission controller 109. The current detection device 120a has, but is not limited to, current detection resistors 118 and 118a, used to detect the bus current IBUS from the bus ground GND, and thereby provide current detection signals ISEN and ISEN2 and a reference signal IREF to the power transmission controller 109. The current detection signals ISEN and ISEN2 can be a first current detection signal and a second current detection signal, respectively.

[0094] Figure 5 For example, the power transmission controller 109a can be applied to... Figure 4 Power supply 20. Figure 5 The power transmission controller 109a and Figure 2 The similarities or differences between the power transmission controller 108a and the previous teachings are known and will not be repeated here.

[0095] and Figure 2 The power transmission controller 108a is different. Figure 5 The power transmission controller 109a has a microprocessor 1400, ADCs 1402, 1404, and 1410, an auxiliary current detection circuit 1406, and an inter-voltage detection circuit 1408.

[0096] The auxiliary current detection circuit 1406 amplifies the difference between the current detection signal ISEN2 and the current detection signal ISEN, and provides it to the microprocessor 1400 via the ADC 1404. The current detection signal ISEN2 can be used as a power detection signal and provided to the power transmission controller 109a to implement power limiting protection. In one embodiment, Figure 4The current sense resistors 118, 118a have approximately the same resistance value, so theoretically the difference between the current sense signal ISEN2 and the current sense signal ISEN should be the same as the difference between the current sense signal ISEN and the reference signal IREF. The power delivery controller 109a is configured to trigger the power limit protection and keep the bus switch 124 off when the difference between the output of the ADC 1404 (which represents the difference between the current sense signal ISEN2 and the current sense signal ISEN) and the output of the ADC 1105 (which represents the difference between the current sense signal ISEN and the reference signal IREF) exceeds a predetermined value.

[0097] The cross voltage detection circuit 1408 amplifies the difference between the intermediate voltage VCC and the bus current IBUS and provides the output to the microprocessor 1400 through the ADC 1402. The difference between the intermediate voltage VCC and the bus current IBUS is equal to the channel cross voltage of the bus switch 124. The microprocessor 1400 can set a power threshold based on the bus voltage VBUS and a lookup table stored in the firmware. When the output of the ADC 1402 indicates that the channel cross voltage exceeds the power threshold, the microprocessor 1400 triggers the power limit protection and keeps the bus switch 124 off.

[0098] The ADC 1410 converts the drive voltage OPTO at one end of the optocoupler 112 to a digital form and provides the output to the microprocessor 1400. When the output of the optocoupler 112 indicates that the drive voltage OPTO is below a power threshold, it can mean that the bus current IBUS is too high. The microprocessor 1400 triggers the power limit protection and keeps the bus switch 124 off. The power threshold can be set based on the bus voltage VBUS and a lookup table stored in the firmware.

[0099] In normal operation, Figure 4 Any one of the current sense signal ISEN, the current sense signal ISEN2, the channel cross voltage of the bus switch 124 (which is equal to the difference between the intermediate voltage VCC and the bus current IBUS), and the drive voltage OPTO can be used as a signal to trigger the power limit protection. When the current sense resistor 118 is shorted and causes the current sense signal ISEN to incorrectly reflect the actual bus current IBUS, the current sense signal ISEN2, the difference between the intermediate voltage VCC and the bus current IBUS, and the drive voltage OPTO can still provide the power limit protection.

[0100] The above descriptions are only the preferred embodiments of the present application, and any equivalent changes and modifications made according to the claims of the present application should be covered by the scope of the present application.

Claims

1. A power supply converting an input voltage at a primary side to a bus voltage at a secondary side, comprising: a transformer having a primary winding and a secondary winding electrically isolating the primary side from the secondary side; a current sense resistor for sensing a bus current outputted from the power supply to provide a current sense signal; a bus switch connected between the secondary winding and the bus voltage to cut off an electrical connection between the transformer and the bus voltage; a power transfer controller for controlling the bus switch according to the current sense signal and a power sense signal at the secondary side, wherein the power transfer controller provides a power threshold according to the bus voltage, and when the current sense signal exceeds a current threshold or the power sense signal exceeds the power threshold, the power transfer controller turns off the bus switch and stops providing power to the bus to stop voltage or current output to achieve power limiting protection; a synchronous rectification circuit comprising: a rectification switch connected to the secondary winding; a synchronous rectification controller for providing a driving signal to the rectification switch to control the rectification switch; and a power supply capacitor having two voltage terminals with a relatively high voltage and a relatively low voltage to provide operating voltages for the synchronous rectification controller; and a duty cycle detection circuit having an input terminal receiving one of the driving signal, the relatively high voltage and the relatively low voltage to provide the power sense signal to the power transfer controller.

2. The power supply of claim 1, wherein, The duty cycle detection circuit provides rectification and low pass filtering to generate the power sense signal, and wherein the duty cycle detection circuit comprises a diode and a low pass filter connected in series between the input terminal and the power transfer controller.

3. The power supply of claim 1, further comprising: an intermediate voltage electrically connected to the bus voltage through the bus switch; and an opto-coupler electrically connected between the intermediate voltage and the power transfer controller to provide a feedback signal to the primary side; wherein the opto-coupler provides a driving voltage as the power sense signal.

4. The power supply of claim 1, wherein, The current sense resistor is a first current sense resistor, and the power supply comprises: a current sensing device comprising the first current sense resistor and a second current sense resistor both for sensing the bus current to correspondingly provide a first current sense signal and a second current sense signal; wherein the second current sense signal is used as the power sense signal.

5. The power supply of claim 1, wherein, The power transfer controller detects a channel voltage across the bus switch as the power sense signal.

6. A control method for a power supply converting an input voltage at a primary side to a bus voltage at a secondary side, comprising: sensing a bus current outputted from the power supply to provide a current sense signal; providing a power threshold according to the bus voltage; providing a power sense signal at the secondary side; and when the current sense signal exceeds a current threshold or the power sense signal exceeds the power threshold, stopping providing power to the bus to stop voltage or current output to achieve power limiting protection. ​ The power supply includes a transformer, a synchronous rectification circuit, a duty cycle detection circuit, and a power transfer controller. The transformer includes a primary winding and a secondary winding. The synchronous rectification circuit is connected between the bus voltage and the secondary winding. The method includes: The duty cycle detection circuit provides the power detection signal to the power transfer controller based on one of a drive signal in the synchronous rectification circuit, a relatively high voltage, and a relatively low voltage.

7. The control method of claim 6, further comprising: detecting a bus current provided by the bus voltage to provide a first current detection signal and a second current detection signal, each representative of the bus current; wherein the first current detection signal is the current detection signal and the second current detection signal is the power detection signal.

8. The control method of claim 6, the power supply includes an optocoupler providing a feedback signal to the primary side, the control method comprising: generating the power detection signal based on the optocoupler.

Images