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Home > Industry Information > The top ten principles of DC/DC conversion circuit design
First, we should understand the classification of DC/DC power and DC/DC conversion circuit.
The DC/DC power supply circuit is also called DC/DC conversion circuit. The main function is to perform input/output voltage conversion.Different application areas have different laws, such as PC, commonly used 12V, 5V, 3.3V, commonly used 5V and 15V of simulated circuits, and 3.3V commonly used in digital circuit.The current FPGA and DSPs also use voltage below 2V, such as 1.8V, 1.5V, 1.2V, etc., which are also called secondary power in the communication system.
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DC/DC conversion circuit is mainly divided into the following three categories:
(1) Stabilization of voltage diode voltage voltage voltage circuit
(2) Linear (simulation) stabilization circuit
(3) Switching voltage voltage circuit
Zina diode is the simplest design plan.The stabilized circuit structure is simple, but the load capacity is poor and the output power is small.When choosing a Qina diode, you can estimate as follows:
(1) Uz=Vout；
(2) Izmax=(1.5-3)ILmax
(3) Input voltage = (2-3) output voltage
The circuit structure is simple and can inhibit the disturbance of the input voltage. However, due to the large operating current and output voltage of the stabilizer, it cannot be adjusted at the same time. Therefore, the circuit is suitable for the occasion that does not require the output voltage to be adjusted. The load current is small. The requirements are required.not tall.
Qina diode regulator circuit diagram
In another form of the voltage voltage circuit, some chips have higher requirements for power voltage, such as the reference voltage of the AD DA chip, etc. At this time, some commonly used voltage reference chips such as TL431, MC1403, Ref02, etc.
TL431 is the most commonly used benchmark chip, and the three -ends with good thermal stability can be adjusted.Its output voltage can be arbitrarily set to VREF (2.5V) and 36V through two resistors.Several reference voltage source chip circuits are similar.
Ad DA conversion module
Candidate stabilization power supply circuit Knowledge: Candidate stabilizer is a type of DC voltage voltage. In fact, the DC power supply method commonly used before the three -ends stabilizer appeared.Before the appearance of the three -terminal stabilizer appears, there are usually OP amplifiers and regulatory diode composition of the composition of the wrong circuit.
Commonly used design schemes for linear (simulation) integrated voltage voltage circuit.
The design of the linear voltage voltage circuit is mainly based on the three -terminal integrated regulator.There are two main types of three -terminal regulator:
One type of output voltage is fixed, called a fixed output three -ends.There are 78 series (positive power supply) and 79 series (negative power supply) of the products commonly used in the three -terminal regulator.The output voltage is represented by the last two digits in the specific model, respectively, 5V, 6V, 8V, 9V, 12V, 15V, 18V, 24V and other grades.The output current is distinguished from the letters after 78 (or 79), L represents 0.1A, M represents 0.5A, and the letterless representation is 1.5A.For example, Table 78L05, 5V is 0.1A.
Another output voltage is a adjustable linear regulator, which is called the adjustable output three ends.This chip represents LM317 (positive output) and LM337 (negative output) series.The difference between the large input/output limit is 40V, the output voltage is 1.2V-35V (-1.2V-35V), the output current is 0.5-1.5A, the voltage between the output and the adjustment end is 1.25V, the adjustment end of the static current currentFor 50UA.
These two basic principles are the same, and both use series stabilization circuit.In the linear integrated regulator, because the three -ends have only three leaders, they have the advantages of less peripheral components, convenient use, stable performance, and low price, so they are widely used.
Linear series stabilizer
DC/DC switching voltage voltage circuit design scheme.The above DC/DC transformation circuits are all connected feedback regulatory circuits.
Under this way of working, the stabilization tube in the integrated regulator is operated linearly.Therefore, when the load current is large, the loss is relatively large, that is, the conversion efficiency is not high.Therefore, the power circuit of the integrated voltage regulator is not very high, generally only 2-3W.This design scheme is only applicable to small -power power supply circuits.
The DC/DC conversion circuit is used to design the switching power chip, which has high conversion efficiency and is suitable for larger power circuits.At present, it has been widely used, and is divided into non -isolation power supply circuits and isolation.Of course, the basic topology of the switching power supply has antihypertensive, voltage voltage, lifting voltage and anti -excitement, positive, bridge changes, etc.
Candidate feedback stabilizer
Non -isolation DC/DC switch and switch IC chip design scheme.The DC/DC switch integrated circuit chip, which is used in principle similar to LM317.Take L4960 as an example.
They generally use a 50Hz power transformer for AC-AC transformation, and then move down ~ 220V switching power supply integration conversion chip.5V, increased to 40V, a large output current 2.5A (can also be connected to high -power switching tube expansion), and has perfect protection functions, such as overcurrent protection and overheating protection.
Although the use of L4960 is similar to LM317, the efficiency of the switching power supply L4960 is different from the efficiency of linear power supply LM317.L4960 large output power can reach 100W (PMAX = 40V*2.5A = 100W), but it consumes up to 7W at most, so the volume of the radiator is small and it is easy to make.Similar to L4960 is L296, which is the same as L4960, but the large output current can reach 4A, more protection functions, and different packaging forms.There are many chips, such as the LM2576 series, TPS54350, LTC3770, etc.Generally, manufacturers will provide detailed instructions and typical circuits for reference when using these chips.
Switch stabilizer
The design scheme of the circuit design scheme of the isolation DC/DC switching power module, the commonly used isolation DC/DC transformation is mainly divided into three categories:
1. Anti -fiery transformation
Anti -graval converter schematic diagram
2. Positive transformation
Positive stimulus change device
3. Single -ended anti -excitement
Our common single -ended anti -fixing DC/DC conversion circuit, which is also a lot of control chip models.The typical representative of the control chip is the UC3842 series.This controller is a high -performance frequency frequency current controller, which is mainly used to isolate AC/DC and DC/DC conversion circuits.
The main application principle is: the circuit consists of the main circuit, control circuit, starting circuit and feedback circuit.The main circuit adopts a single -ended anti -fixing topology structure, which consists of a voltage -chop circuit and a evolved isolation transformer.The circuit has a simple structure, high efficiency, and wide input voltage range.The control circuit is the core of the entire switching power supply.
This circuit adopts the second ring control of the peak current, that is, the peak current feedback control is added to the voltage closed -loop control system.The power of transformers and MOS tubes in this scheme can be great.Compared with the previous design schemes, the circuit structure is complicated, the component parameters are difficult to determine, and the development cost is high.Therefore, when this solution is needed, you can choose the DC/DC isolation module with relatively cheap prices on the market.
The DC/DC switch integrated power module scheme, many microprocessors and digital signal processors (DSP) need the kernel power and input/output (I/O) power supply, they must be sorted during startup.
Designers must consider the relative voltage and timing of kernel and I/O voltage sources during power -on and power -off operations to meet the manufacturer's performance specifications.If there is no correct power sorting, a lock or over -current consumption may occur, which may cause microprocessor, programming logic device (PLD), on -site programming door array (FPGA) or I/O ports supporting device./O port or memory, for example, because the data converter is damaged.
In order to ensure that the I/O load is not driven before the kernel voltage is correct, the kernel power and I/O power supply are required.
Now there are professional power module companies to customize some special switching power modules, mainly for DC/DC power modules, with small size, high power density, high conversion efficiency, less fever, long average failure working time, good reliability, except for conventional conventionalOutside of electrical performance indicators, the cost is lower and more performance.
These modules combine most or all components required to implement the plug -in solution, and can replace up to 40 different components.This simplifies the integration and speeds up the design speed, while reducing the power management part of the circuit board space.In addition to conventional electrical indicators, the cost is lower and the performance is higher.
Simplified PAL device
The most traditional and common non -isolated DC/DC power module is still a single -column direct -inserted (SIP) package.These open framework solutions have indeed made progress in reducing design complexity.However, the easiest way is to use standard packaging elements on the printing circuit board.
Select the precautions for the DC/DC power conversion scheme.You need to pay attention to three points:
1. The voltage voltage circuit cannot be used for power supply, and can only be powered on chips without power supply.
2. The linear voltage voltage voltage circuit structure is simple, but the conversion efficiency is low, and it can only be used for low -power voltage voltage power.
3. The switch -type voltage voltage voltage circuit with high conversion efficiency can be applied to high -power occasions, but its limitations are that the circuit structure is relatively complicated (especially high -power circuits), which is not conducive to miniaturization.
Based on the above ten principles, we can choose the appropriate design solution according to actual needs during the design process.
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