CN101540555A - Power supply and bootstrap circuit thereof - Google Patents

Abstract

The invention discloses a power supply and a bootstrap circuit thereof. The bootstrap circuit comprises a transistor, a first capacitor, a first impedance and a voltage stabilizing circuit. The collector and emitter of the transistor are respectively used as the input end and the output end of the bootstrap circuit. One end of the first capacitor is coupled to the collector of the transistor. One end of the first impedance is coupled to the other end of the first capacitor. The voltage stabilizing circuit is coupled with the other end of the first impedance and the base electrode of the transistor and is used for clamping the voltage of the base electrode at a preset potential.

Description

Power supply and its bootstrap circuit

technical field

The present invention relates to a power supply and its bootstrap circuit, and more particularly to a power supply with low power consumption and a bootstrap circuit that only consumes power during startup.

Background technique

As the energy crisis is approaching, the awareness of environmental protection has gradually risen. In recent years, the US government has proposed energy-saving standards such as 80Plus and Energy Star (Energy Star), in order to regulate the energy consumption of electronic products. The above-mentioned energy-saving standards have been applied to computer systems, which limit the power consumption of the computer system in a standby state to be below 3W. In the computer system, the conversion efficiency of the power supply (Power Supply) is generally only 60% to 70%, causing a lot of electrical energy to be converted into heat energy and lost in the air, making the power supply the main energy-consuming component in the computer system One of them, therefore, the above-mentioned power consumption limitation poses a serious challenge to the existing design method of the power supply.

For now, although the power supply has adopted quasi-resonant technology and synchronous rectification technology to improve efficiency, there are still many auxiliary circuits that do not provide a good solution to the power loss (Power Loss), as shown in Figure 1. Of. FIG. 1 is a circuit diagram of a power supply with a traditional bootstrap circuit (Bootstrap Circuit). In FIG. 1 , the resistor 102 and the capacitor 104 constitute a traditional bootstrap circuit. The capacitance of the capacitor 104 of the bootstrap circuit must be large enough to provide enough power to the pulse width modulation (Pulse Width Modulation, PWM) control circuit 106, and the resistance of the resistor 102 must also be large enough to avoid surges Current (InrushCurrent) through resistor 102 destroys the element. The problem with this power supply is that although the PWM control circuit 106 consumes only a few tenths of a watt of power when driving the MOS transistor 108, the resistor 102 still consumes a large amount of power after the power supply is turned on, making it difficult for the computer system to operate. Meet the aforementioned energy-saving standards.

Contents of the invention

The present invention provides a bootstrap circuit, which can be applied to a power supply, and the bootstrap circuit only consumes power during the start-up process of the power supply.

The invention provides a power supply whose power consumption is smaller than that of the traditional power supply.

The present invention proposes a bootstrap circuit, which includes a transistor, a first capacitor, a first impedance and a voltage stabilizing circuit. The collector and emitter of the transistor serve as the input and output of the bootstrap circuit respectively. One end of the first capacitor is coupled to the collector of the transistor, and one end of the first impedance is coupled to the other end of the first capacitor. The voltage stabilizing circuit is coupled to the other end of the first impedance and the base of the transistor for clamping the voltage of the base at a preset potential.

The present invention provides a power supply, which includes a bridge rectifier, a first capacitor, a transformer, a switch, a first diode, a second capacitor, a pulse width modulation control circuit and a bootstrap circuit. The bridge rectifier has two AC input terminals, a positive power output terminal and a negative power output terminal. One end of the first capacitor is coupled to the positive output end of the power supply, and the other end is coupled to the negative output end of the power supply and the common potential. The transformer has a primary coil and a secondary coil, and one end of the primary coil is coupled to the positive output terminal of the power supply. The switch has a first end, a second end and a control end, and the first end of the switch is coupled to the other end of the primary coil, and the second end of the switch is coupled to a common potential. The anode of the first diode is coupled to one end of the secondary coil. One end of the second capacitor is coupled to the cathode of the first diode, and the other end is coupled to the other end of the secondary coil and the common potential. The input end of the pulse width modulation control circuit is coupled to the cathode of the first diode, and the output end is coupled to the control end of the switch. The bootstrap circuit is coupled between the positive output terminal of the power supply and the input terminal of the pulse width modulation control circuit. When the output terminal of the power supply generates a power supply voltage, the bootstrap circuit provides a starting voltage to the input terminal of the pulse width modulation control circuit. Closes itself after a predetermined time.

In an embodiment of the present invention, the bootstrap circuit in the above-mentioned power supply adopts the above-mentioned bootstrap circuit structure.

The bootstrap circuit of the present invention is composed of a transistor, a capacitor, an impedance and a voltage stabilizing circuit, wherein the capacitor and the impedance are used to generate a time constant. When the voltage at the input terminal of the bootstrap circuit changes instantaneously, this capacitor can couple the instantaneous voltage to the base of the transistor through the impedance to quickly turn on the transistor, so that the emitter of the transistor can generate a start-up voltage; and when the bootstrap circuit passes through the above When the steady state is reached after a time constant, the capacitor is turned off and the transistor is turned off, further allowing the bootstrap circuit to turn itself off without consuming power. In addition, the power supply of the present invention can adopt the above-mentioned bootstrap circuit architecture. Since the bootstrap circuit only consumes power during the start-up process of the power supply, the power supply of the present invention consumes less power in standby , so that its power consumption is smaller than that of traditional power supplies. Accordingly, the computer system using the power supply or the bootstrap circuit of the present invention can easily meet the specifications of energy-saving standards such as 80Plus and Energy Star.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a circuit diagram of a power supply with a conventional bootstrap circuit.

FIG. 2 is a circuit diagram of a power supply and its bootstrap circuit according to an embodiment of the invention.

Detailed ways

FIG. 2 is a circuit diagram of a power supply and its bootstrap circuit according to an embodiment of the invention. The power supply includes a bridge rectifier (Bridge Rectifier) 202, a capacitor 204, a transformer T1, a switch 210, a diode 212, a capacitor 214, a pulse width modulation (Pulse Width Modulation, PWM) control circuit 216 and a bootstrap circuit 218. The bridge rectifier 202 has AC input terminals 202-1 and 202-2, and a positive power output terminal 202-3 and a negative power output terminal 202-4. One end of the capacitor 204 is coupled to the power output positive end 202-3, and the other end is coupled to the power output negative end 202-4 and the common potential GND. The transformer T1 has a primary coil 206 and a secondary coil 208 , and one end of the primary coil 206 is coupled to the power output positive terminal 202 - 3 . The switch 210 has a first terminal, a second terminal and a control terminal, and the first terminal is coupled to the other terminal of the primary side coil 206 , and the second terminal is coupled to the common potential GND.

An anode of the diode 212 is coupled to one terminal of the secondary coil 208 . One end of the capacitor 214 is coupled to the cathode of the diode 212 , and the other end is coupled to the other end of the secondary coil 208 and the common potential GND. The two terminals of the capacitor 214 are used to generate the output VOUT of the power supply. The PWM control circuit 216 has an input terminal VDD, an output terminal OUT and a ground terminal VGND, and the input terminal VDD is coupled to the cathode of the diode 212 , and the output terminal OUT is coupled to the control terminal of the switch 210 . The bootstrap circuit 218 is coupled between the positive output terminal 202-3 of the power supply and the input terminal VDD of the pulse width modulation control circuit 216. When the output terminal 202-3 of the power supply generates the supply voltage VREC, the bootstrap circuit 218 provides the start-up voltage VAUX to The input terminal VDD of the pulse width modulation control circuit 216 is automatically turned off after a predetermined time.

In this example, the bootstrap circuit 218 includes a capacitor 220 , impedances 222 and 224 , a transistor 226 , diodes 228 and 230 , and a voltage regulator circuit 232 . The collector of the transistor 226 is coupled to the power output positive terminal 202 - 3 through the impedance 224 , and the emitter is coupled to the input terminal VDD of the PWM control circuit 216 for outputting the start-up voltage VAUX. One end of the capacitor 220 is coupled to the power output positive end 202 - 3 and the impedance 224 , and the other end is coupled to the voltage regulator circuit 232 through the impedance 222 . The anode of the diode 230 is coupled to the common potential GND, and the cathode is coupled to the impedance 222 . The anode of the diode 228 is coupled to the regulator circuit 232 , and the cathode is coupled to the base of the transistor 236 . The voltage stabilizing circuit 232 is coupled to the impedance 222 and the anode of the diode 228 for clamping the voltage of the anode at a predetermined potential.

The voltage stabilizing circuit 232 includes impedances 234 and 236 , and also includes a shunt regulator 238 . One end of the impedance 234 is coupled to the impedance 222 and the anode of the diode 228 , and the impedance 236 is coupled between the other end of the impedance 234 and the common potential GND. The shunt regulator 238 has an anode terminal, a cathode terminal and a reference terminal, the cathode terminal is coupled to the anode of the diode 228, the anode terminal is coupled to the common potential GND, and the reference terminal is coupled to the other end of the impedance 234, and the shunt regulator 238 determines the voltage between its anode terminal and cathode terminal according to the voltage of its reference terminal. In this example, the switch 210 can be realized by a Metal Oxide Semiconductor Transistor (MOS Transistor), the impedances 222, 224, 234 and 236 can be realized by resistors, and the transistor 226 can be realized by an NPN power transistor ( PowerTransistor) to achieve.

When the AC input terminals 202-1 and 202-2 of the bridge rectifier 202 receive AC power, they will start to convert AC to DC, so that the power output positive terminal 202-3 and the power output negative terminal 202- 4 Output pulsating DC, the polarity of this DC power supply has been marked in the figure, + means positive, - means negative. At this time, because the voltage VREC of the positive output terminal 202-3 of the power supply changes instantaneously, the capacitor 220 can couple the voltage to the phase coupling point with the impedance 222, and then conduct the high voltage to the The base of the transistor 226 further allows the transistor 226 to be turned on quickly. In this way, the transistor 226 can quickly generate the start-up voltage VAUX at its emitter, and output it to the input terminal VDD of the pulse width modulation control circuit 216, so that the pulse width modulation control circuit 216 starts to work and drives the switch 210, This in turn causes the transformer T1 to start operating.

After the transformer T1 starts to operate, the power required by the PWM control circuit 216 can be transmitted through the diode 212 , and the capacitor 214 can be used to keep the power stable. As for the bootstrap circuit 218, since its capacitor 220 and impedance 222 are used to set a time constant, that is, the operating time of the bootstrap circuit 218, when the capacitor 220 is charged for a period of time and presents a steady state, the capacitor 220 is disconnected ( open) to turn off the transistor 226, further allowing the bootstrap circuit 218 to turn itself off without consuming power. That is to say, when the power supply is turned on, the bootstrap circuit 218 is responsible for making the transformer T1 start to operate, and after the transformer T1 starts to operate to generate the power required by the PWM control circuit 216, the bootstrap circuit 218 is automatically turned off. . It can be seen that the bootstrap circuit 218 only consumes power during the start-up process of the power supply, so that the power consumption of the power supply is less in the standby state, and the power consumption thereof is lower than that of the traditional power supply. Small.

In addition, in the above-mentioned bootstrap circuit 218, the voltage stabilizing circuit 232 can not only clamp the voltage of the anode of the diode 228 at a preset potential to protect the transistor 226 from being damaged by the instantaneous large voltage, but also the user can Adjust the ratio of the impedances 234 and 236 to determine the value of the start-up voltage VAUX. In addition, the diode 230 is used to protect other components from negative voltage, and the impedance 224 is used as a current limiting resistor to make the transistor 226 operate in a safe operation area (Save Operation Area, SOA). In the bootstrap circuit 218, the impedance 224, the diodes 228 and 230 are all unnecessary components, and users can also decide whether to use them according to the actual needs of the design.

In summary, the bootstrap circuit of the present invention is composed of a transistor, a capacitor, an impedance and a voltage stabilizing circuit, wherein the capacitor and the impedance are used to generate a time constant. When the voltage at the input terminal of the bootstrap circuit changes instantaneously, this capacitor can couple the instantaneous voltage to the base of the transistor through the impedance to quickly turn on the transistor, so that the emitter of the transistor can generate a start-up voltage; and when the bootstrap circuit passes through the above When the steady state is reached after a time constant, the capacitor is turned off and the transistor is turned off, further allowing the bootstrap circuit to turn itself off without consuming power. In addition, the power supply of the present invention can adopt the above-mentioned bootstrap circuit architecture. Since the bootstrap circuit only consumes power during the start-up process of the power supply, the power supply of the present invention consumes less power in standby , so that its power consumption is smaller than that of traditional power supplies. Accordingly, the computer system using the power supply or the bootstrap circuit of the present invention can easily meet the specifications of energy-saving standards such as 80Plus and Energy Star.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention, and anyone with ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the claims.

Claims (11)

1. A bootstrap circuit comprising: a transistor, the collector and the emitter of which serve as the input and output of the bootstrap circuit respectively; a first capacitor, one end of which is coupled to the collector of the transistor; a first impedance, one end of which is coupled to the other end of the first capacitor; and A voltage stabilizing circuit, coupled to the other end of the first impedance and the base of the transistor, is used to clamp the voltage of the base at a preset potential. 2. The bootstrap circuit according to claim 1, wherein the voltage stabilizing circuit comprises: a second impedance, one end of which is coupled to the other end of the first impedance and the base of the transistor; a third impedance coupled between the other end of the second impedance and a common potential; and A shunt voltage regulator has an anode terminal, a cathode terminal and a reference terminal, the cathode terminal is coupled to the base of the transistor, the anode terminal is coupled to the common potential, and the reference terminal is coupled to the other end of the second impedance, and The shunt regulator determines the voltage between its anode terminal and cathode terminal according to the voltage of its reference terminal. 3. The bootstrap circuit according to claim 1, further comprising a second impedance, the second impedance is coupled between the collector of the transistor and the first capacitor, and the second impedance and The phase coupling of the first capacitor serves as the input terminal of the bootstrap circuit. 4. The bootstrap circuit according to claim 1, further comprising a first diode, the anode of the first diode is coupled to the common potential, and the cathode is coupled to the first impedance another side. 5. The bootstrap circuit according to claim 1, further comprising a first diode, the anode of the first diode is coupled to the regulator circuit, and the cathode of the first diode then coupled to the base of the transistor. 6. A power supply, comprising: A bridge rectifier with two AC input terminals, a positive power output terminal and a negative power output terminal; A first capacitor, one end of which is coupled to the positive output end of the power supply, and the other end is coupled to the negative output end of the power supply and a common potential; A transformer has a primary side coil and a secondary side coil, one end of the primary side coil is coupled to the positive output terminal of the power supply; A switch has a first end, a second end and a control end, the first end of the switch is coupled to the other end of the primary side coil, and the second end of the switch is coupled to the common potential; a first diode, the anode of which is coupled to one end of the secondary coil; a second capacitor, one end of which is coupled to the cathode of the first diode, and the other end is coupled to the other end of the secondary coil and the common potential; a pulse width modulation control circuit, its input terminal is coupled to the cathode of the first diode, and its output terminal is coupled to the control terminal of the switch; and A bootstrap circuit, coupled between the positive output terminal of the power supply and the input terminal of the pulse width modulation control circuit, when the output terminal of the power supply generates a power supply voltage, the bootstrap circuit provides a start-up voltage to the pulse width modulation The input terminal of the control circuit, and automatically shut down after a predetermined time. 7. The power supply according to claim 6, wherein the bootstrap circuit comprises: a transistor, the collector of which is coupled to the positive output terminal of the power supply, and the emitter is coupled to the input terminal of the pulse width modulation control circuit for outputting the start-up voltage; a third capacitor, one end of which is coupled to the collector of the transistor; a first impedance, one end of which is coupled to the other end of the third capacitor; and A voltage stabilizing circuit is coupled to the other end of the first impedance and the base of the transistor for clamping the voltage of the base at a preset potential. 8. The power supply according to claim 7, wherein the voltage stabilizing circuit comprises: a second impedance, one end of which is coupled to the other end of the first impedance and the base of the transistor; a third impedance coupled between the other end of the second impedance and the common potential; and A shunt voltage regulator has an anode terminal, a cathode terminal and a reference terminal, the cathode terminal is coupled to the base of the transistor, the anode terminal is coupled to the common potential, and the reference terminal is coupled to the other end of the second impedance, and The shunt regulator determines the voltage between its anode terminal and cathode terminal according to the voltage of its reference terminal. 9. The power supply as claimed in claim 7, wherein the bootstrap circuit further comprises a second impedance coupled between the collector of the transistor and the positive output terminal of the power supply. 10. The power supply according to claim 7, wherein the bootstrap circuit further comprises a second diode, the anode of the second diode is coupled to the common potential, and the cathode is coupled to the the other end of the first impedance. 11. The power supply according to claim 7, wherein the bootstrap circuit further comprises a second diode, the anode of the second diode is coupled to the regulator circuit, and the second two The cathode of the transistor is coupled to the base of the transistor.

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