Many hardware designers do not have the correct understanding and use DC / DC converters. The following small packs have organized some particularly useful articles as welfare to everyone!
First, correctly understand DC / DC converter
The DC / DC converter is a voltage converter that effectively outputs a fixed voltage after the input voltage. The DC / DC converter is divided into three categories: boost DC / DC converter, buck type DC / DC converter, and lifting-type DC / DC converter. Three types of control can be used depending on the requirements. PWM control is high efficiency and has good output voltage ribbed and noise. Even the PFM control has the advantage of consuming small power consumption when used for a long time. PWM / PFM Converted Small loads Implement PFM control, and automatically switches to PWM control when the load is loaded. At present, the DC-DC converter is widely used in mobile phones, MP3, digital cameras, portable media players and more. A chopper circuit is belonging to the circuit type classification.
Second, DC / DC converter circuit design principle
DC-DC is DC-DC transform, generally boost, buck (BUCK type). The output current of the buck DC / DC converter is large, mostly hundreds of mA to several security, so applicable to the case where the output current is large. The basic working principle circuit of the buck DC / DC converter is shown below. VT1 is a switch tube. When VT1 is turned on, the input voltage Vi is powered to the load RL through the inductance L1, and at present, it is also charged to the capacitor C2. In this process, the capacitance C2 and the inductance L1 are stored in the inductance L1. When VT1 is closed, the energy stored in the inductance L1 is continuously powered, and when the output voltage is lowered, the energy in the capacitor C2 also discharges to the RL, and the output voltage is maintained. The diode Vd1 is a seventh diode to constitute a circuit circuit. The output voltage Vo is partially pressurized by the voltage divider composed of R1 and R2, and the signal of the output voltage is fed back to the control circuit, and the control circuit is controlled by the control circuit, and the output voltage remains unchanged.
DC / DC converter basic working principle
Third, DC-DC circuit design should consider the following conditions:
1. The externally input supply voltage range, the size of the output current.
2. The voltage, current, and system of the DC-DC output are maximum.
Fourth, the main points to consider using the PWM IC:
1. The maximum input voltage of the PWM IC.
2. The frequency of the PWM switch is related to the efficiency of the system. There is a certain impact on the choice of energy storage inductance and capacitance.
3. The maximum rated current and its rated power of the MOS tube, if the DC-DC IC comes with MOS, only the rated current of the IC output is required.
4. MOS switch voltage VGS size and maximum load voltage.
Five, inductive, diode, capacitance selection
1. Inspiration: Size is mainly determined by the switching frequency, the size will affect power ripple; rated current, internal resistance of inductors is determined by system power consumption.
2. Diodes: Schottky diode is usually used. When selecting the filter reverse voltage, forward current, in general, the reverse voltage is twice the input power supply voltage, and the forward current is twice the output current.
3. Capacitor: The choice of capacitance is based on the frequency of the switch, the requirements of system ripple and the output voltage requirements. The equivalent resistance inside the capacity and the capacitor determines the size of the ripple (of course, and inductance).
6. How to get a relatively small power ripple, relatively small interference on the system, and relatively stable and reliable DC-DC circuitry, the principle of the above circuit is required to modify:
1. Input section: The power input needs to be added to the inductance capacitor filter. OBJECTIVE: Because the MOS tube switches and inductance changes in an instantaneous fluctuations, especially when the power consumption fluctuation is large, the effect is more obvious.
2. Output section:
(1) Assuming that 100uf selected by C2 is correct, we want to get a smaller ripple, can change the 100UF capacitance to the capacitance of two 47uF (based on the same type of capacitance); if the 100UF capacitor uses aluminum electrolysis, A 10uF magnetic capacitor or tantalum capacitance can be added based on the original basis.
(2) Adding a capacitor and a capacitor to the original power supply to obtain a smaller power supply for the output.
In summary, the DC-DC converter is powered by various circuits in the entire system. Only the skill of the DC / DC converter circuit design is to consider all the factors to consider, in order to improve the overall performance of the system, reach the performance of the performance effects of each circuit.
Our other product:
