Starting circuit and switch power source thereof
A technology of switching power supply and starting circuit, applied in electrical components, adjusting electrical variables, instruments, etc., can solve problems such as switching transistor degradation, and achieve the effects of reducing ripple, high stability, and small start-up time
Active Publication Date: 2009-11-04
FREMONT MICRO DEVICES SHENZHEN LTD
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Problems solved by technology
One of the disadvantages of this structure is that it is easy to cause the degradation of the switching transistor, because the switching transistor stops conduction by reverse biasing the base-emitter junction; another disadvantage of the above scheme is the need for high voltage withstand devices
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[0012] in figure 1 In the switching power supply shown, the input voltage applied at the voltage input terminal 101 is converted into the output voltage at the voltage output terminal 111. The terminals 101, 111 are coupled to a transformer 110 having a primary winding 110a and a secondary winding 110b. The drain terminal of the power FET 116 is connected to the primary winding 110a, and the source terminal is grounded through a resistor. The PWM control chip 115 controls the on or off of the power FET through the GDV drive terminal 113. The feedback loop 114 feeds back the output voltage at the terminal 111 to the PWM control chip 115, and the chip adjusts the duty cycle of the output signal of the GDV drive terminal according to this feedback signal to adjust the conduction state of the power FET. The DC input voltage at the terminal 101 charges the starting circuit capacitor 103 through a current-limiting resistor 102, and one end of the capacitor 103 is connected to the VCC t...
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The invention discloses a switching power supply and its start-up circuit, wherein the start-up circuit is used to supply power to a PWM control chip that controls the switching of a power field effect tube. The power supply of the PWM control chip ensures that the system has a relatively small start-up time; after successful start-up, in the normal working mode, a larger capacitor is connected in parallel with the start-up circuit capacitor through a switch to supply power for the PWM control chip, thereby It reduces the ripple of the power supply voltage when the switching power supply works normally, and improves the stability of the system. Using the switching power supply of the start-up circuit avoids the introduction of high-voltage devices into the PWM control chip, thereby reducing the process requirements for chip manufacturing, reducing the manufacturing cost of the PWM chip, and reducing power consumption while minimizing system start-up time.
Description
Technical field [0001] The present invention relates to the technical field of switching power supplies, in particular to a starting circuit for providing electric energy to a switching power supply controller and a switching power supply using the starting circuit. Background technique [0002] At present, the switching power supply circuit uses the PWM (short for pulse width modulation) control chip to control the turning on or off of the power FET. Many switching power supply systems require the integration of high-voltage devices in the PWM chip to form a startup circuit, thus Generate the lower bias voltage needed inside the chip. This not only puts forward requirements for the design of the chip, but more importantly, this solution requires the wafer factory to provide devices that can withstand fairly high voltages. But in fact, not every wafer manufacturer can meet the requirements, and high-voltage-resistant devices are often much higher in price than ordinary devices. U...
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IPC IPC(8): H02M3/28H02M3/335
Inventor 谷文浩石磊
Owner FREMONT MICRO DEVICES SHENZHEN LTD