The advantages and disadvantages of LDO, switching power supply DC

Source: Internet
Author: User

The typical Ldo power supply itself consumes (vin-vout) *iout, so the larger the two, the greater the power consumption and the lower the efficiency.

LDO, switching power supply DC's advantages and disadvantages (2008-11-06-22:40:23) Reprint Tags: power supply talk low dropout linear regulator, so the name thought, for linear regulator, can only be used in buck applications. That is, the output voltage must be less than the input voltage. Advantages: Good stability, fast load response. Output Ripple Small disadvantage: low efficiency, the input and output voltage difference can not be too large. The load can not be too large, the current largest ldo is 5A (but to ensure that the output of 5 a There are many restrictions) DC-dc: D.C. voltage to DC voltage. In strict terms, the Ldo is also a one-DC, but the current DC-to multi-point switching power supply. It has many topological structures, such as buck,boost. etc... Advantages: High efficiency, wide input voltage range. Cons: Load response is worse than Ldo and output ripple is larger than Ldo. Ldo is the meaning of low-voltage drop (LDO) linear regulator with lower cost, low noise and small quiescent current, these are its outstanding advantages. It requires only a few external components, usually requiring only one or two bypass capacitors. The new Ldo linear regulator achieves the following indicators: Output noise 30ΜV,PSRR is 60dB, quiescent current 6μa, voltage drop is only 100mV. The performance of an LDO linear regulator can be achieved at this level mainly because the regulator is using a P-channel MOSFET, whereas a common linear regulator uses a PNP transistor. The P-channel MOSFET is voltage-driven and does not require current, so it greatly reduces the current consumed by the device itself; On the other hand, in a circuit that uses a PNP transistor, the voltage drop between the input and output is not too low to prevent the PNP transistor from entering saturation and reducing the output capability , and the voltage drop on the P-channel MOSFET is roughly equal to the product of the output current and the on-resistance. The voltage drop on the MOSFET is very low because the on-resistance of the MOSFETs is very small. If the input voltage and output voltage is very close, it is best to choose the Ldo regulator, can achieve a high efficiency. So, most of the applications that convert lithium-ion battery voltages to 3V output voltages are LDO regulators. Although 10% of the battery's energy is not in use, the Ldo regulator is still able to keep the battery working longer and with less noise. If the input voltage and output voltage is not very close, it is necessary to consider switching type of DCDC, should be from the above principle can be known that the Ldo input current is basically equal to the output current, if the pressure drop is too large, the energy consumption on the Ldo is too high, inefficient. DC-to converters include boost, buck, liter/buck, and anti-equivalence circuitry. The advantages of a DC-to converter are high efficiency, large current output, and low quiescent current. With the increase in integration, many new-DC converters require only a few external inductors and filter capacitors. However, the output pulsation and switching noise of this kind of power controller are higher and the cost is relatively high. In general, it is important to choose DCD for boostC, Buck, is the choice of DCDC or Ldo, to be compared in cost, efficiency, noise and performance.   Power supply is an indispensable component of all kinds of electronic equipment, its performance is directly related to the technical indicators of electronic equipment and the ability to work safely and reliably and its advantages and disadvantages. Power supply is an indispensable component of various electronic equipment, its performance is directly related to the technical indicators of electronic equipment and can work safely and reliably.   The current commonly used DC power supply and switching power supply two major categories, due to switching power supply internal key components work in the high-frequency switch state, the energy consumption is very low, switching power supply efficiency up to 80%~90%, more than the normal linear regulator power supply, has become the mainstream of voltage supply products. 2 Switch-stabilized power supply structure diagram (1) To draw a switch-stabilized power supply schematic diagram and equivalent principle block diagram, it is composed of full-wave rectifier, switch Tube VI, excitation signal, continuous current diode VD, energy storage inductor and filter capacitance C. In fact, the core part of the switching voltage supply is a DC transformer. Here we explain the DC converters and inverters as follows. Inverter, which is a device that converts DC to AC. Inverters are commonly used in backup power supplies that are made up of levels or batteries. DC converter, which is a device that converts DC into AC and then converts AC into DC. This kind of device is widely used in switching regulated power supply.   A DC converter can transform a DC supply voltage into a variety of DC supply voltages with different polarity and values. 3 Advantages and disadvantages of switching regulator power supply 3.1 The advantages of switching power supply are low power consumption, high efficiency. In the switch-stabilized power supply circuit in figure (1), the transistor V in excitation signal excitation, it alternately work on the on-off and cut-off conduction switch state, the conversion speed, the frequency is generally about 50kHz, in some technologically advanced countries, can achieve hundreds of or nearly 1000kHz.   This makes the switching transistor V power consumption is very small, power efficiency can be greatly improved, its efficiency can reach 80%. Small size, light weight. It is clear from the schematic diagram of the switch-stabilized power supply that there is no cumbersome frequency transformer. Since the dissipation power on the adjustment tube V is greatly reduced, a larger heat sink is omitted.   Because of these two reasons, the switching regulator power supply is small in volume and light in weight. Wide voltage regulation range. The output voltage from the switching voltage supply is regulated by the duty ratio of the excitation signal, and the change of the input signal voltage can be compensated by frequency modulation or width adjustment, so that it can still guarantee a stable output voltage when the power frequency grid voltage changes greatly. So the switching power supply voltage regulator range is very wide, stable effect is very good. In addition, there are two ways to change the duty ratio: pulse width modulation type and frequency modulation type. In this way, the switching regulator power supply not only has the advantages of wide voltage regulation range, but also more methods to achieve voltage regulation, designers can according to the actual application requirements, flexible selection of variousType of switching regulator power supply. The efficiency of filtering is greatly improved, which greatly reduces the capacity and volume of the filter capacitance. Switching voltage Regulator power supply operating frequency is basically working at 50kHz, is a linear regulated power supply of 1000 times times, which makes the filtering efficiency of the rectification is almost 1000 times times higher. Is the use of half-wave rectifier after the addition of capacitor filtering, efficiency has also increased 500 times times.   At the same ripple output voltage, when switching power supply is used, the capacity of the filter capacitance is only the 1/5001/1000 of the filter capacitance in the linear regulated power supply. The circuit form is flexible and diverse.   For example, there are self-excited and he-type, have wide-width and FM type, there are single-ended and double-ended, etc., designers can play a variety of types of circuit features, design to meet the different applications of switching voltage regulator power supply. 3.2 The disadvantage of switching power supply is the disadvantage of switching regulator power supply is that there are serious switching interference. Switching regulator power supply, the Power regulator switch transistor v operating in the switch state, it produces the AC voltage and current through the circuit of other components to produce peak interference harmonic vibration interference, these interference if not take certain measures to suppress, eliminate and shielding, it will seriously affect the normal work of the machine.   In addition, because the switching regulator power supply oscillator does not have the isolation of the frequency transformer, these disturbances will be strung into the power-frequency grid, so that other nearby electronic instruments, equipment and household appliances are seriously disturbed. At present, due to the domestic microelectronics technology, blocking container parts production technology and magnetic materials technology and some technologically advanced countries still have a certain gap, so the cost can not be further reduced, but also affect the further improvement of reliability. Therefore, in China's electronic instruments and electromechanical integration instruments, switching power supply can not be widely used and widespread. Especially for the non-power transformer switching voltage supply in the high-voltage electrolytic capacitors, high-back-pressure switch tube, switching transformer core materials and other devices, in China is still in the research, development stage. In some technologically advanced countries, although the switch-stabilized power supply has a certain development, but in practical applications there are still some problems, not very satisfactory. This exposes another disadvantage of switching power supply, which is the complex circuit structure, high failure rate, maintenance trouble. For this, if the designers and manufacturers do not give full attention, it will directly affect the application of switching voltage regulator power supply. Nowadays, the main reason of popularization and application of switching regulator power supply is that it is difficult to make technology, repair trouble and high cost 4 Ldo introduction The Ldo is a micropower low dropout linear regulator that typically has very low own noise and a high power supply rejection ratio of PSRR (   Powersupplyrejectionratio). The structure of Ldo low dropout linear regulator (2) mainly includes starting circuit, constant current source bias unit, enable circuit, adjustment element, reference source, error amplifier, feedback resistor network and protection circuit. The basic principle of work is this: system power, if the footAt high level, the circuit starts, the constant current source circuit to provide bias for the entire circuit, the reference source voltage quickly established, the output with the input is rising, when the output is about to reach the specified value, the output feedback voltage from the feedback network is close to the reference voltage value, At this time, the error amplifier to the output feedback voltage and the reference voltage between the small error signal amplification, and then by the adjustment tube amplification to the output, thereby forming a negative feedback, to ensure that the output voltage stability in the specified value, similarly if the input voltage changes or output current changes, this closed loop will keep the output voltage unchanged, namely: vout= ( R1+R2)/r2xvref The actual low-dropout linear regulator also features other functions such as short-load protection, overvoltage shutdown, thermal shutdown, and reverse-connect protection.

LDO, the advantages and disadvantages of switching power supply DC

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