Switching power supply is used by circuit control switch for high-speed Road through and closing. The direct current into high frequency AC provided to the transformer substation, resulting in the need of one or more sets voltage! Switch to high-frequency alternating current is due to Huawei's high-frequency AC transformer circuit in the transformer efficiency is much higher than 50Hz. Switch transformer can do so little, but work is not very hot! Low cost. If you do not become the 50Hz high-frequency switching power supply that does not make sense
Switching power supply can be divided into two separate and non-isolated, isolation-type transformers must be a switch, rather than isolation may not have.
Switching power supply works are:
1. AC power input into DC by the rectifier;
2. By high-frequency PWM (pulse width modulation) signal control switch, the DC added that the primary switch on the transformer;
3,. Switch induces high-frequency transformer secondary voltage, the rectifier filter supply load;
4. Output in part through some of the circuit back to the control circuit to control PWM duty cycle to achieve stable output purposes.
AC power input generally flow through Ecuador ring or something, brown-line interference filters also filter out the interference power on the grid;
The same in power, the higher the switching frequency, the smaller size of the transformer switch, but switch the higher requirements;
Switch can have multiple secondary transformer winding or a winding with multiple taps to get the required output;
General should also increase the number of protection circuits, such as no-load, short circuit protection, switching power supply or may be destroyed
ATX power supply major components:
EMI filter circuit: EMI filter circuit outside the main role is to filter out high frequency pulses on the power grid disturbance, but also serve to reduce switching power supply itself outside electromagnetic interference, generally in the high-quality power supply EMI filter circuit poles.
An EMI circuit: AC power outlet is a welding power supply EMI filter circuit, which is a separate circuit board, is after the AC input circuit through the first set, the choke and the capacitor formed by the low through the network to filter out high frequency power line clutter and interference signals in phase, while the interference signals within the power shield, which form anti-electromagnetic interference power first line of defense.
2 EMI circuit: electricity into the power supply fuse board after the first pass, and then again through the inductance and capacitance of the second high-frequency EMI filter circuit in order to fully clutter, and then through the high-voltage current-limiting resistor into the rectification filter circuit . Fuse in the power device short-circuit power is too big or when the internal fuse to protect the power components, while the current limiting resistor with metal oxide component, to limit instantaneous high-current, reducing the power of the internal components of the current impact.
Bridge rectifier and high-pressure filtering: EMI filtered through electricity, through the full bridge rectifier and capacitor filter into a high voltage DC after. The AC input into a pulsed DC, there are two forms, one is four diode full bridge is to package together, one is composed of four discrete diode bridge rectifier circuit, the same effect, the effect is the same .
In general, there should be two full-bridge near the tall barrel or more components, that is, High Voltage Capacitors, its role is to filter the pulsating DC output AC components and relatively smooth DC. High Voltage Capacitors for use with the switch circuit is closely related to power supply capacity is often in the past when the focus of evaluation, but in fact it is the power capacity and power nothing, but increase its power capacity will decrease ripple interference, improve the quality of power supply current output.
PFC circuit: PFC circuit is called power factor correction or compensation circuit, the higher the power factor, the greater energy efficiency.
PFC circuit now has two methods for a Passive PFC, also known as passive PFC, one is active-type PFC, also known as active PFC. Passive PFC inductor through a frequency to compensate for the exchange of fundamental input current and voltage phase, forcing the same current and voltage phase, passive PFC less efficient, generally only 65% -70%, and workers used frequency inductance was big and bulky, but low cost, there are still many ATX power supply in this way. Active PFC is composed of electronic components, small size, light weight, through a dedicated IC to adjust the phase current waveform and efficiency greatly increased, more than 95%, but because of high cost, usually only in advanced applications to see.
Switching transistor and switching transformers: switching power supply is switch the name suggests the core of the word. Switching transistor and the switch is a switching power supply transformer core components, or by self-excited oscillation to switch his work in saturation, cut-off (that and off) state to the switch transformer windings on the Deputy High voltage is induced, then rectified, filtered and regulated DC voltage after the output of all kinds. Switching transistor and the switch is the ATX power supply transformer core components, its quality directly affects the power of good and bad, and life, especially in switching transistor, work in high back pressure condition, there is not enough protection circuit, it is easy to breakdown burned. Switch the power directly determines the quality of stability, it is also the main heating element power supply, open the main power is to see the two transistors on the heat sink is the switch.
Affect performance of high frequency switching transformer efficiency include ferrite, core cross-sectional area of the size and the magnetic gap width, the small cross-sectional area prone to magnetic saturation of transformer can not output large power, all winding turns directly affect the output voltage, usually is not possible to grasp these parameters, it can not accurately judge how much of the output transformer to power in the end, only through e-Fu Zai Ji Celiang to know, In addition, the switch transformer output side, despite all of them some of the output is used in the same winding, such as +3.3 VDC and +5 VDC is the case, so when +3.3 VDC maximum output current can not be output when the + 5VDC large current, so we can not supply all the output power of a simple accumulation.
In addition to the main transformer, the power supply in general, there should be two small transformers, one of which will switch control signal amplification circuit to drive the switch to work, but also can switch the work area and high-voltage integrated circuits for the work area of low pressure physical isolation. The other is a completely independent small switching power supply, which is what we call the standby circuit, the output voltage to power the main circuit power supply, while the output side through the +5 V StandBy wake-up function to the board to achieve.
Low voltage rectifier circuit: after high-frequency pulse after the beginning of voltage step-down transformer to use the same diode and rectifier and filter capacitor, just at this time when the work of rectifying the high frequency, you must use a fast recovery Schottky Rectifiers ordinary rectifier diodes can hardly carry any, and the rectifier of capacitor used can not have too much impedance, or which can not filter out high frequency AC components, so choose the capacity not only to large capacitance, but also have lower The AC resistance for the job can also see the huge volume of 1,2 months with a core of the inductor coil, and filter capacitor filter with high frequency communication components, ensure that output pure DC.
As the needs of low-voltage rectifier side output large current, rectifier diodes also produce a lot of heat, in front of these diodes and the switch requires a separate heat sink for heat, power in the other heat sink is that these components are fixed. The output from these devices is the variety of different voltage output current up.
Regulators and protection circuits: voltage regulator is usually the output from the power supply output voltage sampling of some of the standard voltage for voltage and compares the difference amplified to drive through switch transistor to regulate the switch duty cycle to achieve the voltage stability. The role of protection circuit by detecting the end of the output voltage or current changes, when the output end of a short circuit, over voltage, over current, overload, undervoltage until the phenomenon, the protection circuit action, cut off switch control of the excitation signal to switch stop oscillator, output voltage and current is zero, has protective effects.