Ldo and Buck Buck regulator comparison

Ldo and Buck Buck regulator comparison

In the control system with MCU/DSP/FPGA design, the low-voltage input stage (generally under 12V), the output 5v/3.3v/1.8v/1.5v/1.2v circuit, the common power chip is the buck (buck type) switching regulator and Ldo (low dropout) linear regulator. These two power chips in the application, have their own advantages and disadvantages, in the circuit design, it is necessary to use according to the actual choice.
One, Ldo and Buck Buck regulator comparison
1, when the input voltage is high voltage (generally >5v time), and the input and output pressure difference is very large, the need to choose the buck switching regulator, in this case, the use of switching power supply chip, high efficiency, low calorific value; If the linear regulator is used, the input and output pressure differential is too large, this part of the power is consumed, The result is low efficiency and huge heat dissipation, which requires an additional large heatsink. Ldo linear regulators are preferred when the input voltage is below 5V, which is characterized by low cost and the use of switching regulator chips without regard to cost and high requirements.
2, when the output current of the board level output is >1a, it is advisable to use buck switching regulator, this kind of chip model is very many, here do not enumerate; When the output power is below 1A, the best choice of Ldo chip, using switching regulator on some waste resources, hehe.
3, Buck switching regulator output ripple and voltage regulator is not as good as the Ldo, so like MCU/DSP/FPGA and other core power (1.2V, 1.5V, 2.5V, etc.) will generally choose the Ldo, this can see more TI's power management chip manual, There are many recommended models for different processors in the chip. In addition, when the input voltage is high or the input/output voltage differential pressure is large, and the output current is large, the "Buck+ldo" scheme can be used. This scheme is easy to implement on the General Control Board, and the cost is not very high.
4, from the complexity of the circuit design: Buck switching regulator circuit to use external inductance, large volume, some also use external MOS tube, circuit design and commissioning takes a certain amount of time, unless it is a mature design prior to accumulation, and the Ldo circuit is simple, its peripheral circuit requires only a few filter capacitors.
5, Buck switching regulator is more efficient than the Ldo, the thermal temperature characteristic is better than the Ldo, in the circuit design, when the need for high output voltage accuracy, the LDO must be implemented.
Summary: Only combine the two to get a stable, is considered to be the perfect power circuit.
Second, Ldo and Buck Buck Regulator application considerations
1. What are the most common causes of LDO oscillations? is the output capacitor!
A, ESR is too high. Tantalum capacitors with poor quality have high ESR and generally use imported devices as much as possible. Aluminum electrolytic capacitors will have high ESR at low temperatures, and tantalum capacitors are generally used.
B, ESR is too low. In the circuit, it is best to choose a well-known brand of SMD devices.
2, causing the buck switching voltage regulator chip fever Serious One reason: is inductance.
We know that the choice of inductors depends on the load resistance, operating frequency, output voltage (duty ratio) work efficiency to determine, not the larger or smaller the better. At present, some of the purchase of SMD Inductor is prone to the capacity and the identity of the situation, resulting in a serious chip heating, the solution is to use a straight-plug cylindrical inductor.

Third, power supply design sharing



The first figure is a Lp3965-adj Ldo power supply design, and you can see that a large ground plane is designed to be used as a radiator in the circuit.


The second figure is a LM2596 buck switch power supply design, you can find that the switching power supply chip area of only 1/2, the loss is greatly reduced, which means that the switching power supply can
withstands higher thermal resistance and reduces the area of heat dissipation.

Turn:

The Ldo is a low dropout regulator, which means a lower dropout linear regulator, compared to a conventional linear regulator. Conventional linear regulators, such as the 78XX series of chips, require an input voltage higher than the output voltage

2v~3v above, otherwise it will not work properly. However, in some cases, such conditions are obviously too harsh, such as 5v to 3.3v, the input and output of the pressure difference is only 1.7v, obviously is not satisfied with the conditions. In response to this situation, only the

The Ldo class is a power conversion chip.

Ldo linear Buck Chip:

The principle is equivalent to a resistor voltage divider to achieve buck, energy loss, the lower voltage converted into heat, buck pressure and load current, the more obvious the chip heat. This kind of chip packaging is relatively large, easy to heat dissipation.

Voltage/DC Buck chip:

In the process of pressure reduction, the energy loss is relatively small, the chip fever is not obvious. Small chip package, can achieve PWM digital control

Ldo and Buck Buck regulator comparison