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Power is an indispensable part of a variety of electronic devices, its performance is directly related to the technical indicators of electronic equipment and can work safely and reliably. As the key components of the switching power supply work in high-frequency switching state, low power consumption, high conversion rate, and the volume and weight of only 20% to 30% of linear power, so it has become the mainstream of power supply products.
First, the composition of the switching power supply
Switching power supply from the main circuit, control circuit, detection circuit, auxiliary power of the four major components
1, the main circuit
Impact Current Limiting: Limits the inrush current on the input side of the instantaneous power supply.
Input filter: its role is to filter the existence of clutter grid and impede the local clutter generated feedback back to the grid.
Rectification and filtering: The AC power grid rectifier directly smoother DC.
Inverter: The rectified DC into high-frequency AC, which is the core of high-frequency switching power supply.
Output rectification and filtering: According to the load needs to provide a stable and reliable DC power supply.
2, control circuit
On the one hand, sampling from the output, compared with the set value, and then to control the inverter, change its pulse width or pulse frequency, so that the output stability, on the other hand, according to the test circuit data provided by the protection circuit identification provide Control circuit of the power for a variety of protective measures.
3, the detection circuit
Provide protection circuit is running in a variety of parameters and a variety of instrumentation data.
4, auxiliary power supply
Power software (remote) to start, to protect the circuit and control circuit (PWM and other chips) work power supply.
Second, the working principle of switching power supply
Switching power supply is the use of power semiconductor devices as a switching element, through the periodic on-off switch, the switching element to control the duty cycle to adjust the output voltage. The switching elements are repeatedly turned on and off at certain time intervals. When the switch is off, the input power source Vi supplies power to the load RL through the switch S and the filter circuit. When the switch S is turned off, the energy storage device (L1, C2, diode D circuit) to the load RL released when the switch is turned on the energy stored so that the load to obtain a continuous and stable energy.
VO = TON / T * Vi
VO is the average voltage across the load
TON is the switch on time each time
T is the switch on-off duty cycle
It can be seen from the formula, change the switch on-time and duty cycle ratio, the average voltage between VO will also change, therefore, with the load and the input power supply voltage changes automatically adjust the ratio of TON and T to maintain the output voltage VO change. Changing the on-time TON and the duty cycle ratio changes the duty cycle of the pulse, a technique called Time Ration Control (abbreviated TRC).
According to TRC control principle, there are three ways:
1, Pulse Width Modulation (Pulse With Modulation, abbreviated as PWM): the switching cycle is constant, by changing the pulse width to change the duty cycle.
2, Pulse Frequency Modulation (abbreviated as PFM): The constant on-pulse width changes the duty cycle by changing the switching frequency.
3, mixed modulation: on-pulse width and switching frequency are not fixed, each can change the way it is a mixture of the above two methods.
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