Linear regulated power supplies have been popular in low power applications due to their simplicity and low cost. This linear regulated power supply requires only a small number of components and is easier to design and manufacture than the switching power supply SMPS (Switch Mode POWER Supply). However, linear power supplies have gradually been replaced in recent years for two reasons: First, many linear power supplies are bundled as external power supplies (EPS) for products such as PDAs, cordless phones, and cell phones. Today's EPS must comply with strict new energy-saving standards, and such standards almost exclude linear power supplies, because linear power supplies often fail to meet standards for efficiency and no-load power consumption; second, most advanced low-power SMPSs are at cost. And simplicity is comparable to linear power. This article will explore the shortcomings of low-power SMPS in the initial application phase, and discuss a feasible method to help design engineers design products that meet the new EPS energy-saving standards in terms of cost-effectiveness, while reducing design time and simplifying design work. .
Self-oscillation flyback converter. RCC (Ring Choke Converter) is widely used in small and medium power conversion applications because of its simple circuit topology, electrical isolation from the input voltage, and no need for output filter inductors. It can efficiently provide multiple sets of DC output and wide voltage rise and fall range. Converters that are typically used with power supplies below 50 W. It is widely used in mobile phone chargers and notebook adapters. The RCC adopts a driving method opposite to the PWM type converter. The switching of the switch does not require a special trigger circuit, and is completely completed by the inside of the circuit. This converter has its unique advantages, that is, the circuit is simple and has a high cost performance. However, if the RCC circuit is composed of discrete components, the number of typical circuit components is actually more than 50, so designing an integrated RCC power supply device has become a trend.
Firstly, the circuit principle is analyzed and designed in detail, and the circuit simulation is carried out by computer simulation. Secondly, the RCC device was applied to the charger for actual testing, which was verified with the theoretical values, and then analyzed the device test results and the problems that need to be further solved. Finally, the conclusion is given.
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1 RCC device application circuit
A typical RCC circuit requires about 50 discrete components, which is difficult to design and debug, and the reliability is not high enough. In order to solve this problem, an RCC integrated device is designed. Figure 1 is a typical application circuit. As can be seen from the figure, there are only 8 discrete components on the input side of the discrete device and 2 discrete components on the output side. If the triode 13001, diode VD2 and capacitor C4 are packaged into the device, the number of discrete components will be reduced to 7. Integration will be the most compact RCC circuit. The rectification and filtering circuit of the application circuit is composed of a diode VD5 and a capacitor C5; the converter adopts a double-winding flyback converter, the power tube is selected as the model 13001, and the starting circuit is composed of a resistor R6 and a capacitor C6 connected in series, and the flyback switching power supply The pin FB of the integrated circuit is connected to the secondary coil of the converter, the pin SW is connected to the emitter of the power tube 13001, the collector of the power tube 13001 is connected to the main coil, and the pin VCC and the positive electrode of the capacitor C6 are connected. Connected, pin GND is grounded.
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The 85-220 V AC input passes through VD5 and C5 first, and the waveform is converted from AC to a DC voltage with a large ripple. Since the voltage of the capacitor C6 is OV at power-on, the output tube of the pin SW is turned off, and the power supply passes. Resistor R6 charges capacitor C6. When capacitor C6 is charged to the startup voltage of the flyback switching power supply IC, the flyback switching power supply IC starts to work normally, its internal oscillator starts to start, and SW outputs a large duty cycle switch. The signal is used to control the output power tube 13001 so that the power tube 13001 is also turned on and off. When the power tube 13001 is turned on, the voltage of the collector of the power tube 13001 is a low voltage, so that the voltage of the output and the pin FB are sensed through the transformer. For the negative voltage, when the 13001 is turned off, since the current of the inductor cannot be abrupt, a kickback voltage is generated on the main coil of the power tube 13001, and the output coil and the auxiliary coil of the transformer are coupled with a positive voltage, and the output rectifier diode VD7 is outputted. On, the capacitors C6 and C8 are charged. When the power tube 13001 is turned on once, the coupling voltage on the output coil and the auxiliary coil is a negative voltage, and the capacitors C6 and C8 are on the capacitor. Operating Current Operating voltage can be maintained and the output load current flyback switching power supply integrated circuit. In this cycle, the system can continue to work; the voltage control at the output is controlled by the overvoltage protection voltage inside the flyback switching power supply integrated circuit. When the output load decreases, the voltage of VCC rises to the overvoltage point, and the flyback switch The power IC will internally turn off the SW. At this time, the power tube 13001 will not turn on until the VCC voltage is discharged below the overvoltage point, and the SW will be turned on, so that the flyback switching power supply IC will enter the intermittent mode of operation ( Working in a few cycles, several cycles do not work), the working frequency will be reduced. The output voltage can be maintained at a constant value.
2 internal structure of the RCC device
Figure 2 is a schematic diagram of the internal structure of the RCC. The flyback switching power supply integrated circuit includes an oscillator, a small duty cycle generating circuit, a duty ratio selecting circuit, and a blanking circuit. The oscillator is connected to the small duty cycle generating circuit, the oscillator and the small duty cycle generating circuit are respectively connected to the duty ratio selecting circuit, the duty ratio selecting circuit is connected to the blanking circuit, and the undervoltage lockout (UVLO) is The starting circuit of the whole flyback switching power supply integrated circuit controls the starting and shutting down of the flyback switching power supply integrated circuit, the protection circuit is connected with the output driving tube VMO, the blanking circuit also controls the output driving tube VMO, and the diode VD8 is directly connected. The pin FB and the pin VCC, and the capacitor on the periphery of the flyback switching power supply integrated circuit (ie, C6 in FIG. 1) constitute a rectifying and filtering circuit.
Self-oscillation flyback converter. RCC (Ring Choke Converter) is widely used in small and medium power conversion applications because of its simple circuit topology, electrical isolation from the input voltage, and no need for output filter inductors. It can efficiently provide multiple sets of DC output and wide voltage rise and fall range. Converters that are typically used with power supplies below 50 W. It is widely used in mobile phone chargers and notebook adapters. The RCC adopts a driving method opposite to the PWM type converter. The switching of the switch does not require a special trigger circuit, and is completely completed by the inside of the circuit. This converter has its unique advantages, that is, the circuit is simple and has a high cost performance. However, if the RCC circuit is composed of discrete components, the number of typical circuit components is actually more than 50, so designing an integrated RCC power supply device has become a trend.
Firstly, the circuit principle is analyzed and designed in detail, and the circuit simulation is carried out by computer simulation. Secondly, the RCC device was applied to the charger for actual testing, which was verified with the theoretical values, and then analyzed the device test results and the problems that need to be further solved. Finally, the conclusion is given.
1 RCC device application circuit
A typical RCC circuit requires about 50 discrete components, which is difficult to design and debug, and the reliability is not high enough. In order to solve this problem, an RCC integrated device is designed. Figure 1 is a typical application circuit. As can be seen from the figure, there are only 8 discrete components on the input side of the discrete device and 2 discrete components on the output side. If the triode 13001, diode VD2 and capacitor C4 are packaged into the device, the number of discrete components will be reduced to 7. Integration will be the most compact RCC circuit. The rectification and filtering circuit of the application circuit is composed of a diode VD5 and a capacitor C5; the converter adopts a double-winding flyback converter, the power tube is selected as the model 13001, and the starting circuit is composed of a resistor R6 and a capacitor C6 connected in series, and the flyback switching power supply The pin FB of the integrated circuit is connected to the secondary coil of the converter, the pin SW is connected to the emitter of the power tube 13001, the collector of the power tube 13001 is connected to the main coil, and the pin VCC and the positive electrode of the capacitor C6 are connected. Connected, pin GND is grounded.
The 85-220 V AC input passes through VD5 and C5 first, and the waveform is converted from AC to a DC voltage with a large ripple. Since the voltage of the capacitor C6 is OV at power-on, the output tube of the pin SW is turned off, and the power supply passes. Resistor R6 charges capacitor C6. When capacitor C6 is charged to the startup voltage of the flyback switching power supply IC, the flyback switching power supply IC starts to work normally, its internal oscillator starts to start, and SW outputs a large duty cycle switch. The signal is used to control the output power tube 13001 so that the power tube 13001 is also turned on and off. When the power tube 13001 is turned on, the voltage of the collector of the power tube 13001 is a low voltage, so that the voltage of the output and the pin FB are sensed through the transformer. For the negative voltage, when the 13001 is turned off, since the current of the inductor cannot be abrupt, a kickback voltage is generated on the main coil of the power tube 13001, and the output coil and the auxiliary coil of the transformer are coupled with a positive voltage, and the output rectifier diode VD7 is outputted. On, the capacitors C6 and C8 are charged. When the power tube 13001 is turned on once, the coupling voltage on the output coil and the auxiliary coil is a negative voltage, and the capacitors C6 and C8 are on the capacitor. Operating Current Operating voltage can be maintained and the output load current flyback switching power supply integrated circuit. In this cycle, the system can continue to work; the voltage control at the output is controlled by the overvoltage protection voltage inside the flyback switching power supply integrated circuit. When the output load decreases, the voltage of VCC rises to the overvoltage point, and the flyback switch The power IC will internally turn off the SW. At this time, the power tube 13001 will not turn on until the VCC voltage is discharged below the overvoltage point, and the SW will be turned on, so that the flyback switching power supply IC will enter the intermittent mode of operation ( Working in a few cycles, several cycles do not work), the working frequency will be reduced. The output voltage can be maintained at a constant value.
2 internal structure of the RCC device
Figure 2 is a schematic diagram of the internal structure of the RCC. The flyback switching power supply integrated circuit includes an oscillator, a small duty cycle generating circuit, a duty ratio selecting circuit, and a blanking circuit. The oscillator is connected to the small duty cycle generating circuit, the oscillator and the small duty cycle generating circuit are respectively connected to the duty ratio selecting circuit, the duty ratio selecting circuit is connected to the blanking circuit, and the undervoltage lockout (UVLO) is The starting circuit of the whole flyback switching power supply integrated circuit controls the starting and shutting down of the flyback switching power supply integrated circuit, the protection circuit is connected with the output driving tube VMO, the blanking circuit also controls the output driving tube VMO, and the diode VD8 is directly connected. The pin FB and the pin VCC, and the capacitor on the periphery of the flyback switching power supply integrated circuit (ie, C6 in FIG. 1) constitute a rectifying and filtering circuit.
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