TWI678605B - Power adaptor - Google Patents

Abstract

The invention provides a power adapter, which includes a transformer, a power switch, a control circuit, and a current detection circuit. The transformer includes a primary winding, a secondary winding, and an auxiliary winding. A transformer is used to convert an input voltage into an output voltage. The first end of the power switch is coupled to the primary winding. The control circuit is coupled to the second end of the power switch and is used to generate a switch control signal to control the operation of the power switch. The current detection circuit is coupled to the third terminal of the power switch, and is used for sensing the current detection voltage according to the first voltage and the reference voltage related to the auxiliary winding to provide the control circuit.

Description

Power Adapter

The invention refers to a power adapter, especially a power adapter that can effectively improve the overall output power.

With the development of technology, there are more and more types of electronic products, such as mobile communication devices, notebook computers, personal assistants, multimedia players, etc. These electronic products need to use power adapters to connect high-voltage AC power or DC The power supply is converted into a stable DC power supply that meets the needs, and is used as a power source for charging or normal operation. Furthermore, in order to realize power supply for various electric devices, the Universal Serial Bus Power Delivery (USB PD) standard has proposed different output voltage specifications. For example, the power adapter can provide output voltages of at least 5 volts, 9 volts, 15 volts, and 20 volts.

In order to ensure the normal and stable operation of the power adapter, an automatic protection mechanism is usually used to stop the operation of the power adapter when conditions such as overcurrent, overvoltage, overpower, overload, short circuit, etc. occur, to prevent internal components or related equipment from being damaged. damage. For example, please refer to FIG. 1, which is a schematic diagram of a conventional power adapter 1. The power adapter 1 includes a transformer 10, a control circuit 12, a power switch SW1, and a resistor R1. The transformer 10 can convert an input voltage VI into an output voltage VO. The transformer 10 includes a primary winding NP, a secondary winding NS, and an auxiliary winding NA. The control circuit 12 senses the current of the primary winding NP through the current detection voltage generated by the resistor R1 to perform over current protection. When the current detection voltage reaches a certain value, the power switch SW1 is turned off or the power adapter is used to prevent the output current from being too large and causing damage. However, from another From a perspective, the over-current protection mechanism will limit the maximum power output of the power adapter and cannot maximize the output energy. Therefore, it is necessary to improve the conventional technology.

Therefore, the main object of the present invention is to provide a power adapter capable of effectively improving the overall output power.

The invention discloses a power adapter including: a transformer including a primary winding, a secondary winding, and an auxiliary winding for converting an input voltage into an output voltage; a power switch, one of the power switches. One end is coupled to the primary winding; a control circuit is coupled to a second end of the power switch to generate a switch control signal to control the operation of the power switch; and a current detection circuit is coupled to Connected to a third terminal of the power switch for sensing a current detection voltage according to a first voltage and a reference voltage related to the auxiliary winding to provide the current to the control circuit.

1, 2‧‧‧ power adapter

10, 20‧‧‧ transformer

12, 22‧‧‧ control circuit

24‧‧‧Current detection circuit

242‧‧‧ Comparator

244‧‧‧Driver

26‧‧‧Regulator

C1, C2, CO‧‧‧ capacitors

CS, GD, GND, Vcc‧‧‧ pins

D1, D2, DO‧‧‧diodes

GND1‧‧‧First ground

GND2‧‧‧Second ground

ICS‧‧‧Primary winding current

Load‧‧‧Load

NA‧‧‧Auxiliary winding

NP‧‧‧Primary winding

NS‧‧‧Secondary winding

Q1‧‧‧Transistor

R1, R2, R3‧‧‧ resistance

S1‧‧‧Control signal

S2‧‧‧Drive signal

SW1‧‧‧Power Switch

SW2‧‧‧Auxiliary switch

VC1, VC2‧‧‧Capacitor voltage

VCC‧‧‧ Power supply voltage

VCS‧‧‧Current detection voltage

VI‧‧‧Input voltage

VO‧‧‧Output voltage

VNA‧‧‧Auxiliary winding voltage

VR‧‧‧ Reference Voltage

ZD‧‧‧Zina Diode

Figure 1 is a schematic diagram of a traditional power adapter.

FIG. 2 is a schematic diagram of a power adapter according to an embodiment of the present invention.

Certain terms are used in the description and the scope of subsequent patent applications to refer to specific elements. It should be understood by those with ordinary knowledge in the art that hardware manufacturers may use different names to refer to the same component. The scope of this specification and subsequent patent applications is not based on differences in names. The way to distinguish components is to use the functional differences of components as a criterion for distinguishing. "Inclusion" mentioned throughout the specification and the scope of subsequent patent applications is an open-ended term and should be interpreted as "including but not limited to." In addition, the term "coupling" includes any direct and indirect means of electrical connection. Therefore, if a first device is described as being coupled to a second device, it means that the first device can be electrically connected directly to the second device or indirectly electrically connected to the second device through other devices or connection means.

Please refer to FIG. 2, which is a schematic diagram of a power adapter 2 according to an embodiment of the present invention. The power adapter 2 is used to provide an output voltage VO to a load Load. Among them, the load Load can be any electronic product that requires power, and the output voltage VO can be used as a source of power for charging or normal operation of the electronic product. The power supply device 2 includes a transformer 20, a control circuit 22, a current detection circuit 24, a voltage stabilization circuit 26, a power switch SW1, a capacitor CO, and a diode DO. The transformer 20 can convert an input voltage VI into an output voltage VO. The transformer 20 includes a primary winding NP, a secondary winding NS, and an auxiliary winding NA. A first terminal of the primary winding NP receives the input voltage VI, and a second terminal of the primary winding NP is coupled to the power switch SW1. The first end of the secondary winding NS is coupled to the diode DO, and the second end of the secondary winding NS is coupled to a second ground GND2. A first terminal of the auxiliary winding NA is coupled to the voltage stabilization circuit 26, and a second terminal of the auxiliary winding NA is coupled to the first ground GND1. The anode of the diode DO is coupled to the first end of the secondary winding, and the cathode of the diode DO is coupled to the capacitor CO and the load Load. A first terminal of the capacitor CO is coupled to the cathode of the diode DO and a load Load, and a second terminal of the capacitor CO is coupled to a second ground GND2.

A first terminal of the power switch SW1 is coupled to a second terminal of the primary winding NP. The second terminal of the power switch SW1 is coupled to the control circuit 22 for receiving a control signal S1. The third terminal of the power switch SW1 is coupled to the current detection circuit 24. The power switch SW1 can control the first according to the potential of the control signal S1. The signal transmission path between the terminal and the third terminal is in a conducting state (short circuit) or a non-conducting state (open circuit). The power switch SW1 may be a power transistor. For example, the power switch SW1 can be a metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), a bipolar junction transistor (BJT), or other components with similar functions, but not This is the limit. When the power switch SW1 is turned on, the primary winding current ICS flows through the primary winding NP and the power switch SW1, and the primary winding NP stores energy. At this time, the output voltage VO is generated by the capacitor CO to supply power to the load Load. When the power switch SW1 is not turned on, the energy stored in the primary winding NP will be transferred to the secondary winding NS to supply power to the capacitor CO.

The control circuit 22 is coupled to the power switch SW1, the current detection circuit 24, and the voltage stabilization circuit 26. The control circuit 22 includes pins GD, CS, Vcc, and GND. The control circuit 22 can receive a power voltage VCC through the pin Vcc and perform related operations accordingly. The control circuit 22 is used to generate a switch control signal S1 to control the operation of the power switch SW1. For example, the control circuit 22 may generate a switch control signal S1 according to a current detection voltage VCS to control the operation of the power switch SW1. In one embodiment, when the current detection voltage VCS is greater than a first threshold value, the control circuit 22 may generate a switch control signal S1 according to the current detection voltage VCS to control the power switch SW1 to switch to a non-conductive state. In another embodiment, when the current detection voltage VCS is greater than a second threshold, the control circuit 22 may control the power adapter 2 to shut down according to the current detection voltage VCS.

The current detection circuit 24 is coupled to the third terminal of the power switch SW1 and the control circuit 22. The current detection circuit 24 can sense the current detection voltage VCS according to a first voltage related to the auxiliary winding NA and a reference voltage VR. In detail, the current detection circuit 24 includes a comparator 242, a driver 244, an auxiliary switch SW2, and resistors R1, R2. The first terminal of the resistor R1 is coupled to the third terminal of the power switch SW1, and the second terminal of the resistor R1 is coupled to the first ground GND1. The first terminal of the resistor R2 is coupled to The third terminal of the power switch SW1 and the second terminal of the resistor R2 are coupled to the first terminal of the auxiliary switch SW2. The comparator 242 includes a first input terminal, a second input terminal and an output terminal. The comparator 242 of the current detection circuit 24 can compare the signals received by the first input terminal and the second input terminal to generate a comparison signal. The comparison signal may be a voltage signal or a current signal, but is not limited thereto. A first input terminal of the comparator 242 is used to receive a first voltage related to one of the auxiliary windings NA. In an embodiment, as shown in FIG. 2, the first input terminal of the comparator 242 is coupled to the voltage stabilization circuit 26 to receive a capacitor voltage VC1 related to the auxiliary winding NA. In this case, the aforementioned first voltage related to the auxiliary winding NA is the capacitor voltage VC1. In another embodiment, the first input terminal of the comparator 242 may receive the auxiliary winding voltage VNA of the auxiliary winding NA or other voltage signals related to the auxiliary winding NA, that is, the aforementioned first voltage about the auxiliary winding NA. It can also be the auxiliary winding voltage VNA of the auxiliary winding NA or other voltage signals related to the auxiliary winding NA. Further, the second input terminal of the comparator 242 is used to receive a reference voltage VR, and the output terminal of the comparator 242 is used to output a comparison signal. The driver 244 is coupled to the output terminal of the comparator 242, and is used for receiving a comparison signal and generating a driving signal S2 to the auxiliary switch SW2 accordingly. The first terminal of the auxiliary switch SW2 is coupled to the second terminal of the resistor R2, and the second terminal of the auxiliary switch SW2 is coupled to the driver 244 for receiving the driving signal S2. The third terminal of the auxiliary switch SW2 is coupled to the first ground GND1.

When the voltage of the first input terminal (non-inverting terminal) of the comparator 242 (ie, the first voltage related to the auxiliary winding NA) is less than or equal to the voltage of the second input terminal (ie, the reference voltage VR), the comparator 242 generates a comparison signal to the driver 244. The driver 244 generates a driving signal S2 to the auxiliary switch SW2 according to the comparison signal. In this case, the auxiliary switch SW2 is in a non-conducting state in response to the driving signal S2. In other words, when the first voltage of the auxiliary winding NA is less than or equal to the reference voltage VR, the comparator 242 outputs a corresponding comparison signal to the driver 244, so that the driver 244 generates a corresponding driving signal S2 to the auxiliary switch SW2 to control. The auxiliary switch SW2 is in a non-conducting state. In this case, since the auxiliary switch SW2 is in a non-conducting state, the resistor R2 is in an open state. Therefore, it is coupled to the switch SW1 and the first The total resistance of the load resistor between ground GND1 is the resistance of resistor R1.

When the voltage at the first input terminal (non-inverting terminal) of the comparator 242 (that is, the first voltage about the auxiliary winding NA) is greater than the voltage at the second input terminal (that is, the reference voltage VR), the comparator 242 generates and outputs Compare signal to driver 244. The driver 244 generates a driving signal S2 to the auxiliary switch SW2 according to the comparison signal. In this case, the auxiliary switch SW2 is in a conducting state in response to the driving signal S2. In other words, when the first voltage of the auxiliary winding NA is greater than the reference voltage VR, the comparator 242 outputs a corresponding comparison signal to the driver 244, so that the driver 244 generates a corresponding driving signal S2 to the auxiliary switch SW2 to control the auxiliary switch. SW2 is on. In this case, since the auxiliary switch SW2 is in an on state, the resistor R2 is in a short-circuit state. Therefore, the total resistance value of the load resistance coupled between the switch SW1 and the first ground GND1 is a parallel resistance value after the resistance R1 and the resistance R2 are connected in parallel. Since the equivalent resistance of the resistors in parallel will be smaller than the resistance values of the respective resistors, the total resistance value of the load resistor coupled between the switch SW1 and the first ground GND1 will be changed compared to the resistance value of the resistor R1. Small (resistance value of resistor R1 and resistor R2 in parallel <resistance value of resistor R1), this will allow a larger primary winding current ICS to reach the trigger voltage of overcurrent protection and can effectively improve the power adapter 2 overall power output energy.

The voltage stabilizing circuit 26 is coupled to the auxiliary winding NA and the control circuit 22, and is configured to generate a power supply voltage VCC to the control circuit 22 and a capacitor voltage VC1 to the current detection circuit 24 according to the auxiliary winding voltage VNA of the auxiliary winding NA. As shown in FIG. 2, the voltage stabilization circuit 26 includes diodes D1 and D2, capacitors C1 and C2, a Zener diode ZD, a transistor Q1, and a resistor R3. The anode of the diode D1 is coupled to the first terminal of the auxiliary winding NA, and the cathode of the diode D1 is coupled to the capacitor C1, the transistor Q1, the resistor R3 and the first input terminal of the comparator 242. The first terminal of the capacitor C1 is coupled to the cathode of the diode D1 and the first input terminal of the comparator 242, and the second terminal of the capacitor C1 is coupled to the first ground GND1, where the capacitor voltage VC1 is electrical A voltage across one of the capacitors C1, and the capacitor voltage VC1 is related to the auxiliary winding voltage VNA of one of the auxiliary windings NA. The first terminal of the resistor R3 is coupled to the cathode of the diode D1, the first terminal of the capacitor C1 and the first input terminal of the comparator 242, and the second terminal of the resistor R3 is coupled to the Zener diode ZD. The cathode of the Zener diode ZD is coupled to the second terminal of the resistor R3 and the transistor Q1, and the anode of the Zener diode ZD is coupled to the first ground GND1. The first terminal of transistor Q1 is coupled to the anode of diode D2, the second terminal of transistor Q1 is coupled to the cathode of zener diode ZD and the second terminal of resistor R3, and the third terminal of transistor Q1 Coupled to the cathode of diode D1, the first terminal of resistor R3, and the first input terminal of comparator 242. The anode of the diode D2 is coupled to the first terminal of the transistor Q1, and the cathode of the diode D2 is coupled to the pin Vcc of the control circuit 22. The first terminal of the capacitor C2 is coupled to the cathode of the diode D2 and the pin Vcc of the control circuit 22 to output a power voltage VCC to the control circuit 22, and the second terminal of the capacitor C2 is coupled to the first ground GND1.

In one embodiment, the comparator 242 compares the capacitor voltage VC1 received at the first input terminal with the reference voltage VR received at the second input terminal to determine whether the auxiliary switch SW2 is on or off. Assume that the turns ratio of the primary winding NP, the secondary winding NS, and the auxiliary winding NA is 35: 5: 15. The maximum power supply voltage that the control circuit 22 can withstand is 40 volts. The second input terminal of the comparator 242 is coupled to a certain voltage source to receive a reference voltage VR, wherein the reference voltage VR is 40 volts. When the output voltage VO is 5 volts or 9 volts, the auxiliary winding voltage VNA of the auxiliary winding NA is between 15 volts and 27 volts and the capacitor voltage VC1 is between 15 volts and 27 volts. At this time, the Zener diode ZD has not yet collapsed, and the maximum value of the capacitor voltage VC2 of the capacitor C2 is equal to the maximum value of the power supply voltage VCC. And get: VC2 = VCC = 27 Volts-forward bias of diode D1-forward bias of transistor Q1 VBE-forward bias of diode D2 = 27 volts-0.7 volts-0.7 volts-0.7 Volts = 24.9 Volts (1)

It can be known from the formula (1) that the maximum value of the power supply voltage VCC is 24.9 volts without exceeding the power supply voltage value that the control circuit 22 can withstand. In other words, the voltage stabilization circuit 26 does achieve the purpose of voltage stabilization. Further, since the capacitor voltage VC1 is between 15 volts and 27 volts and the reference voltage VR is 40 volts, the voltage at the first input terminal (15 volts to 27 volts) of the comparator 242 is smaller than the voltage at the second input terminal. (40 volts), the comparator 242 generates and outputs a low voltage level comparison signal to the driver 244. The driver 244 generates a low-level driving signal S2 to the auxiliary switch SW2 according to the comparison signal of the low-voltage level. In this case, the auxiliary switch SW2 is in a non-conducting state in response to the low-level driving signal S2. In this case, since the auxiliary switch SW2 is in a non-conducting state, the resistor R2 is in an open state. Therefore, the total resistance value of the load resistor coupled between the switch SW1 and the first ground GND1 is the resistance value of the resistor R1.

When the output voltage VO is 15 volts or 20 volts, the auxiliary winding voltage VNA of the auxiliary winding NA is between 45 volts and 60 volts and the capacitor voltage VC1 is between 45 volts and 60 volts. At this time, the Zener diode ZD collapsed and turned on and the voltage of the Zener diode ZD was maintained at 30 volts. In this case, the maximum value of the capacitor voltage VC2 of the capacitor C2 is equal to the maximum value of the power supply voltage VCC. The maximum value of the capacitor voltage VC2 of the capacitor C2 and the maximum value of the power supply voltage VCC can be obtained according to the following formula: VC2 = VCC = 30 volts-forward bias of transistor Q1 VBE-forward bias of diode D2 = 30 volts-0.7 volts-0.7 volts = 28.6 volts (2)

It can be known from the formula (2) that the maximum value of the power supply voltage VCC is 28.6 volts without exceeding the value of the power supply voltage that the control circuit 22 can withstand. Therefore, the voltage stabilization circuit 26 does achieve the purpose of voltage stabilization. Furthermore, since the capacitor voltage VC1 is between 45 volts and 60 volts and the reference voltage VR is 40 volts, the voltage (45 volts to 60 volts) of the first input terminal (non-inverting terminal) of the comparator 242 is greater than The voltage (40 volts) of the second input terminal (inverting terminal), the comparator 242 generates and outputs a comparison signal of a high voltage level to the driver 器 244. The driver 244 generates a high-level driving signal S2 to the auxiliary switch SW2 according to the comparison signal of the high-voltage level. In this case, the auxiliary switch SW2 is in a conducting state according to the high-level driving signal S2. Since the auxiliary switch SW2 is in a conducting state and the resistor R2 is in a short-circuit state, the total resistance value of the load resistor coupled between the switch SW1 and the first ground GND1 is a parallel resistance value after the resistor R1 and the resistor R2 are connected in parallel. Since the equivalent resistance of the resistors in parallel will be less than the resistance value of each resistance, in this way, the primary winding current ICS will allow a larger primary winding current ICS to reach the trigger voltage of the overcurrent protection and be effective. Increase the overall output energy of the power adapter 2.

In summary, the embodiments of the present invention can effectively adjust the sensing current tolerance value according to different output voltages without affecting the overcurrent protection, and can effectively improve the overall output power of the power supply. The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the scope of patent application of the present invention shall fall within the scope of the present invention.

Claims (7)

A power adapter includes: a transformer including a primary winding, a secondary winding, and an auxiliary winding for converting an input voltage into an output voltage; a power switch, a first end of which is coupled to a power switch Connected to the primary winding; a control circuit coupled to a second end of the power switch for generating a switch control signal to control the operation of the power switch; and a current detection circuit coupled to the A third terminal of a power switch is used to sense a current detection voltage to provide to the control circuit according to a first voltage and a reference voltage related to the auxiliary winding. The current detection circuit includes: a first A resistor, a first terminal of the first resistor is coupled to the third terminal of the power switch, and a second terminal of the first resistor is coupled to a first ground; a second resistor, the second resistor A first terminal is coupled to the third terminal of the power switch; an auxiliary switch, a first terminal of the auxiliary switch is coupled to a second terminal of the second resistor, and a second terminal of the auxiliary switch Used to receive a driver A third terminal of the auxiliary switch is coupled to the first ground; a comparator includes a first input terminal, a second input terminal, and an output terminal for comparing the first input terminal with the first input terminal. The signals received by the two input terminals generate a comparison signal, wherein the first input terminal is used for receiving the first voltage related to the auxiliary winding, the second input terminal is used for receiving the reference voltage, and the output terminal is used for To output the comparison signal; and a driver coupled to the output terminal of the comparator for generating the driving signal according to the comparison signal. The power adapter according to item 1 of the scope of patent application, wherein when the first voltage of the auxiliary winding is smaller than the reference voltage, the comparator generates and outputs the comparison signal, and the driver generates the driving signal to The auxiliary switch and the auxiliary switch are in a non-conducting state due to a driving signal. The power adapter according to item 1 of the scope of patent application, wherein when the first voltage on the auxiliary winding is greater than the reference voltage, the comparator generates and outputs the comparison signal, and the driver generates the driving signal to The auxiliary switch and the auxiliary switch are in a conducting state in response to a driving signal. The power adapter according to item 1 of the patent application, wherein the first voltage of the auxiliary winding is an auxiliary winding voltage of the auxiliary winding. The power adapter according to item 1 of the scope of the patent application, further comprising: a voltage stabilizing circuit coupled to the auxiliary winding and the control circuit, for generating a power supply voltage to The control circuit and the first voltage related to the auxiliary winding are generated to the current detection circuit. The power adapter according to item 5 of the scope of patent application, wherein the voltage stabilizing circuit includes: a first diode, an anode of the first diode is coupled to a first end of the auxiliary winding, and A cathode of the first diode is coupled to the current detection circuit; a first capacitor, a first end of the first capacitor is coupled to the cathode of the first diode and the current detection circuit And a second terminal of one of the first capacitors is coupled to the first ground, wherein the first voltage about the auxiliary winding is a voltage across the first capacitor; a third resistor, the third resistor A first terminal is coupled to the cathode of the first diode; a zener diode, one of the zener diodes is coupled to a second terminal of a third resistor, and the zener diode An anode of an electrode body is coupled to the first ground; a transistor includes a first terminal, a second terminal, and a third terminal, and the second terminal of the transistor is coupled to the Zener diode. The cathode, the third end of the transistor is coupled to the cathode of the first diode; a second diode, the second diode An anode is coupled to the first terminal of the transistor, and a cathode of the second diode is coupled to the control circuit; and a second capacitor, a first terminal of the second capacitor is coupled to the The cathode of the second diode and the control circuit, and a second terminal of the second capacitor is coupled to the first ground. The power adapter according to item 1 of the scope of patent application, further comprising: a third diode, an anode of the third diode is coupled to the secondary winding; and a third capacitor, the A first terminal of a third capacitor is coupled to a cathode of the third diode, and a second terminal of the third capacitor is coupled to a second ground.