1, AC/DC and DC/DC
AC/DC is one type of switching power supply. This type of power supply is also called a primary power supply – AC is alternating current and DC is direct current. After high voltage rectification and filtering, a DC high voltage is obtained for DC/DC The converter obtains one or several stable DC voltages at the output end, and the power ranges from several watts to several kilowatts. Productsare used in different occasions.
AC/DCPower Management Chip Conversion is to convert AC into DC. The power flow can be bidirectional. The flow from the power supply to the load is called “rectification”, and the flow of power from the load back to the power supply is called “active inversion”.
The input of the AC/DC converter is 50/60Hz alternating current, which must be rectified and filtered, so a relatively large filter capacitor is essential. At the same time, due to the restrictions of safety standards (such as UL, CCEE, etc.) and EMC directives (such as IEC, FCC, CSA), AC input EMC filtering must be added on the side and components that comply with safety standards must be used, which limits the miniaturization of the AC/DC power supply.
DC/DC power supply refers to a power supply that converts DC into DC. From this definition, DCDC in a broad sense means that as long as it is converted from DC to DC, it is called DCDC, LDO (Low dropoutLinear regulator) The chip should also be a DC/DC power supply. However, the conventional definition is: Generally, a power supply that only converts DC to DC, and this conversion method is achieved through switching, is called a DC/DC power supply. (In the first picture, DC/DC in a narrow sense)
2. Linear power supply and switching power supply
The adjustment tube of the linear power supply works in an amplified state, so it generates a lot of heat and has low efficiency (related to the voltage drop), and a bulky heat sink is required. When realizing AC/DC, a similarly large power frequency transformer is also required. When multiple sets of voltage outputs are to be produced, the transformer will be even larger.
The regulating tube of the switching power supply works in saturation and cut-off states, so it generates less heat and has high efficiency. AC/DC power supplies eliminate the need for bulky transformers. However, a large ripple (50mVat5Voutputtypical) will be superimposed on the DC output of the switching power supply. A voltage regulator should be connected in parallel at the output end< a i=3>Diode can be improved. In addition, since the switching tube will produce a large peak pulse interference when working, it is also necessary to connect magnetic beads in series in the circuit to improve it. Relatively speaking, the linear power supply does not have the above defects, and its ripple can be made very small (below 5mV).
Switching power supplies can be implemented through different topologies, including buck, boost, and buck-boost. Linear power supplies can only achieve voltage reduction.
Power supplies are divided into two categories: ordinary power supplies and special power supplies.
Ordinary power supply
It can also be subdivided into: PC power supply, rectified power supply, customized power supply, heating power supply, welding power supply/arc power supply, electroplating power supply, switching power supply, inverter power supply, voltage regulating power supply, transformer power supply. parameter, power adapter, other ordinary power supply, inverter power supply, power supply, power operating power supply, led power supply, linear power supply, power supply controller/network power supply, module power supply, variable frequency power supply, UPS power supply, EPS emergency power supply , purified power supply, communications, DC regulated power supply, DC/DC power supply,
Special power supply
Special power supplies can be subdivided into: shore power supply, security power supply, high voltage power supply, medical power supply, military power supply, aerospace power supply, laser photoelectric source, Other special power supplies.
The so-called special is mainly because the technical index requirements for measuring power supplies are different from commonly used power supplies. The main reasons are that the output voltage is particularly high, the outputcurrent is particularly large, or the The requirements for stability, dynamic response and ripple are particularly high, or the voltage or current output by the power supply is required to be pulse or other requirements.
4. Isolated power supply and non-isolated power supply
When designing a power circuit for an embedded system or selecting a finished power module, one of the important issues to consider is whether to use an isolated or non-isolated power solution. . Before discussing, let us first understand the concepts of isolation and non-isolation, and the main characteristics of the two.
The concept of power isolation and non-isolation
The isolation and non-isolation of power supplies are mainly for switching power supplies. The more common views in the industry are:
There is no direct electrical connection between the input circuit and the output circuit of the power supply. The input and output are in an insulated high-resistance state and there is no current circuit.
Non-isolated power supply
There is a direct current loop between the input and the output, for example, there is a common ground between the input and the output.
The schematic diagram of the isolated power supply is shown in the figure.
a/Flyback transformer working principle b/Voltage and current waveform in DCM mode
Applications of isolated and non-isolated power supplies
By understanding the advantages and disadvantages of isolated and non-isolated power supplies, we can know that they each have their own advantages. For some commonly usedembeddedpower supplies Choose, we can make accurate judgments:
In order to improve the anti-interference performance and ensure reliability, the power supply of the front stage of the system generally uses an isolated power supply.
For power supply to IC or some circuits in the circuit board, non-isolated solutions are preferred based on cost performance and volume.
In occasions where safety is required, such as AC-DC power supply from the mains or medical power supply, in order to ensure personal safety, an isolated power supply must be used. In some cases, a reinforced isolation power supply must be used.
For the power supply of remote industrial communication, in order to effectively reduce the impact of ground potential difference and wire coupling interference, an isolated power supply is generally used to supply power to each communication node separately.
For situations where battery power is used and battery life is stringent, non-isolated power supply is used.
Advantages and disadvantages of isolated power supply and non-isolated power supply
Isolated power supply :High safety factor, low conversion efficiency.
non-isolated power supply :High conversion efficiency, poor anti-interference ability.