Advantage: Stability is good, load is answered fast. Output ripple is small.

 

Defect: Efficiency is low, input-output voltage is poor cannot too big. Laden cannot too big, at present the biggest LDO is 5A (but the limitative condition that should make sure the output of 5A still has a lot of)

 

DC/DC: Volts d.c. turns volts d.c. . Will strictly tell, LDO also is a kind of DC/DC, but at present DC/DC points to switch power source more. Have simple structure of a lot of kinds of develop, be like BUCK, BOOST.

 

Advantage: Efficiency is tall, input voltage range is wider.

 

Defect: Load is answered poorer than LDO, output ripple is bigger than LDO.

 

What is the distinction of DC/DC and LDO?

 

DC/DC converter is general by control chip, pole coil, diode, dynatron, capacitance is formed.

 

After DC/DC converter inputs voltage for change, effective output secures the voltage converter of voltage. DC/DC converter cent is 3 kinds: Converter of step up DC/DC, step-down DC/DC converter and rise step-down DC/DC converter. Can use 3 kinds of control according to demand. PWM control efficiency is tall have good output voltage ripple and noise. PFM control although be used for long, the advantage with bad news little report is had when small load especially. PFM control is practiced when PWM/PFM changeover small load, and automatic when heavy burden carries changeover is controlled to PWM. At present DC-DC converter applies extensively in the product such as camera of mobile phone, MP3, number, portable media player.

 

DC-DC (summarize a principle)

 

Actually interior is it is change of DC direct current source first AC of alternating current power source. It is circuit of concussion of a kind of self-excitation normally, the face needs the discrete element such as inductance beyond place.

 

Carry wave of repass integral filter in output next, return DC power source again. Because generate AC power source, so can very relaxed undertake step up follows step-down. Change twice, inevitable meeting produces loss, this is the how raises DC-DC efficiency question that everybody studies in effort.

 

Comparative:

 

1, DCtoDC includes Boost(step up) , Buck(step-down) , Boost/buck(rises / step-down) and oppose photograph construction, have the characteristic such as electric current of electric current of efficient, high output, small static state, as compositive spend rise, the periphery circuit of a lot of new-style DC-DC converter needs inductance and filter wave electric capacity only; But the output ripple of controller of this kinds of power source and switch noise bigger, cost is relative taller.

 

2, LDO: The outstanding advantage of low-pressure poor linear manostat is the cost that has minimum, the static electric current of lowermost noise and lowest. Its periphery parts of an apparatus is very few also, have 9 bypass electric capacity only normally. New-style LDO can reach the following target: Of electric current of static state of 30μV output noise, 60dBPSRR, 6μA and 100mV press difference.

 

LDO summarizes a principle:

 

The main reason that linear manostat can realize these character was adjusting a canal to use effect of field of P raceway groove to be in charge of at interior, is not the PNP transistor with linear normally medium manostat. The field effect canal of P raceway groove does not need drive of base electric current, reduced the source current of itself of parts of an apparatus greatly so; On the other hand, in the structure that uses PNP pipe, output ability to prevent PNP transistor to enter saturated condition to reduce, must make sure bigger input output presses difference; And effect of field of P raceway groove is in charge of press difference to be equal to output roughly electric current guides with its the product of electrify block, guide electrify block makes its press difference dinkily very low. When voltage and output voltage should be being inputted to be close to in the system, LDO is best choice, can achieve very tall efficiency. It is so in the application that changes voltage of lithium ion batteries the voltage that it is 3V choose LDO mostly, although batteries puts electric energy finally,measure 10% did not use, but LDO still can provide longer battery life in low noise structure.

 

No matter portable electron equipment is by communication town report passes rectification (or communicate adapter) hind power supply, or by accumulator group power supply, in working process, power source voltage will change inside very big range. For instance the voltage when enough electricity is batteries of monomer lithium ion 4.2V, the voltage after putting report is 2.3V, span is very big. The output voltage of all sorts of commutator suffers the effect that town report voltage changes not only, still suffer the effect of laden change. To make sure power supply tension is stable and constant, almost all electronic equipment use manostat power supply. Equipment of small-sized and accurate electron still asks power source is very clean (without ripple, without noise) , lest affect electronic facility,work normally. To satisfy the requirement of accurate electron equipment, answer to join linear manostat in the input end of power source, have wave of source noise filter in order to make sure power source tension is constant with implementation.

 

One, the fundamental of LDO

 

Low-pressure poor linear manostat (the basic circuit of LDO) is shown like graph 1-1 place, this circuit adjusts tubal VT by series connection (PNP transistor, note: In applying actually, here is commonly used is canal of effect of field of P raceway groove) , sampling resistor R1 and R2, compare amplifier A to comprise.

 

Graph 1-1 low pressure differs linear manostat basic circuit

 

Sampling voltage Uin is added in the inphase input end of comparator A, with add in the fiducial voltage Uref that inputs end instead (Uout*R2/ (R1+R2) ) compare, the.Uout=(U+-U-)*A after A of both amplifier of the classics that need a value magnifies notes A to be the multiple that compares amplifier, ) the pressing that controls series connection to move whole canal falls, stabilize output voltage thereby.

 

When output voltage Uout is reduced, the poor value of fiducial voltage Uref and sampling voltage Uin increases, the drive electric current that compares amplifier output increases, series connection adjusts tubal pressing to fall reduce, make output voltage elevatory thereby.

 

Contrary, if output the set value that voltage Uout needs more than, the van that compares amplifier output moves electric current to reduce, make output voltage drop small thereby. In power supply process, output voltage is corrective and successive undertake, settling time accepts the restriction that compares amplifier and rate of response of output transistor loop only.

 

Ought to explain, actual linear manostat still ought to have the function of a lot of other, for instance laden short circuit is protected, press too close, overheat closes, receive protection to wait instead, and series connection adjusts a canal to also can use MOSFET.

 

2, the main parameter of low-pressure poor linear manostat

 

1. Output voltage (OutputVoltage)

 

Outputting voltage is the parameter with the most important manostat of low-pressure poor linear, also be the parameter that the consideration answers above all when electronic equipment architect chooses manostat. Low-pressure poor linear manostat has fixed output voltage and adjustable output voltage two sort. Manostat of fixed output voltage is used more convenient, and because output voltage is course manufacturer delicate adjustment, manostat precision is very so tall. But the output voltage numerical value of its set all is worth for commonly used voltage, satisfy all applied requirements impossibly, but outside the change that accepts component numerical value will affect lasting accuracy.

 

2. Electric current of the biggest output (MaximumOutputCurrent)

 

The power of the equipment that use phone is different, the biggest electricity that requirement manostat exports is not identical also. Normally, the manostat cost with output bigger electric current is higher. To reduce cost, in the power supply system that forms in many manostat, the voltaic cost that should require according to departmental substation chooses proper manostat.

 

3. Input output voltage is poor (DropoutVoltage)

 

Inputting output voltage to differ is the parameter with the most important manostat of low-pressure poor linear. Below the condition that assures to output voltage to stabilize, this voltage presses difference lower, the performance of linear manostat is better. For instance, the low pressure of 5.0V differs linear manostat, want to input 5.5V voltage only, can make output voltage to stabilize in 5.0V.

 

4. Ground connection electric current (GroundPinCurrent)

 

IGND of ground connection circuit is to show series connection adjusts a canal to output electric current to be zero hour, input the manostat job electricity that power source provides. This electric current also calls static electric current sometimes, but when using PNP transistor to make series connection adjust tubal component, it is incorrect that this kind of habit makes a way. The ground connection electric current of idealer low-pressure poor manostat is very normally small.

 

5. Laden regulation (LoadRegulation)

 

Laden regulation can pass graph 2-1 and type 2-1 to define, the laden regulation of LDO is less, the ability that explains LDO restrains laden interference is stronger.

 

Graph 2-1OutputVoltage&OutputCurrent

 

 

In type

 

△ Vload— laden regulation

Imax—LDO is the biggest export electricity

When Vt— outputs electric current to be Imax, the output voltage of LDO

When Vo— outputs electric current to be 0.1mA, the output voltage of LDO

V— load current is △ respectively the outputs voltage difference when 0.1mA and Imax

 

6. Linear regulation (LineRegulation)

 

Linear regulation can pass graph 2-2 and type 2-2 to define, the linear regulation of LDO is less, input voltage change is jumped over to outputting voltage to affect small, the performance of LDO is better.

 

 

Graph 2-2OutputVoltage&InputVoltage

 

 

In type

 

△ Vline—LDO linear regulation

Vo—LDO name outputs voltage

Vmax—LDO is the biggest input voltage

△ V—LDO inputs Vo to output the difference of voltage maximum and the least value to Vmax”

 

7. Power source is restrained than (PSSR)

 

The input source of LDO often a lot of interference signal exist. PSRR mirrorred what LDO disturbs signal to these to control capacity.

 

3, the representative application of LDO

 

The representative application of low-pressure poor linear manostat is shown like graph 3-1 place. What graph 3-1(a) shows circuit is a kind of the commonnest AC/DC power source, after transformer of classics of voltage of alternating current source, commutation becomes the voltage of a need, volts d.c. turns into after commutate of this voltage classics. In this circuit, the action of low-pressure poor linear manostat is: When voltage of alternating current source or laden change stability outputs voltage, restrain ripple voltage, eliminate the communication noise that power source produces.

 

The working voltage of all sorts of accumulator changes inside certain limits. To make sure accumulator group output is constant voltage, ought to output termination to differ linear manostat into low pressure in batteries group normally, if pursue,3-1(b) place is shown. The power of low-pressure poor linear manostat is inferior, because this can prolong the service life of accumulator. In the meantime, because low pressure differs the output voltage of linear manostat and input voltage to be close to, when because this is close to discharge in accumulator,ending, still can assure to output voltage to stabilize.

 

Well-known, switch sex the efficiency of regulated power supply is very tall, but output ripple voltage is taller, noise is bigger, the performance such as voltage regulation is poorer also, be opposite especially when imitate circuit power supply, will produce bigger effect. In switch sex manostat output termination enters low pressure to differ linear manostat, if what graph 2-3(c) shows, can realize active filter wave, and the stabilized voltage precision that also can heighten output tension greatly, at the same time the efficiency of power source system also won’t be reduced apparently.

 

In certain applying, for instance radio communication equipment has power supply of one sufficient batteries only normally, but the different tension that each part circuit often uses mutual segregation, accordingly must by many manostat power supply. To save in all the n of batteries, when normally equipment does not work, hope low-pressure poor linear manostat works at Morpheus condition. For this, requirement linear manostat is had make can dominate end. The multichannel of power supply of accumulator of group having sheet is outputted and if what graph 3-1(d) shows,have the power supply system that opens control function.

 

Graph 3-1 low pressure differs linear manostat (LDO) representative application

 

DC-DC

 

Ought to can understand so: The means dc of DCDC changes (to) dc (the changeover that different direct current source is worth) , want to accord with this definition to be able to call DCDC converter only, include LDO. But prevailing view is change dc (to) the parts of an apparatus that dc realizes by switch means calls DCDC.

 

DC-DC converter includes step up, step-down, litre / step-down and turn over equal circuit. The advantage of DC-DC converter is efficiency tall, OK output big electric current, static state electric current is small. Along with compositive spend rise, a lot of new-style DC-DC converter need a few only outside receive inductor and filter wave capacitor. But, the output of controller of this kind of power source is pulsatile with switch noise bigger, cost is relative taller. In last few years, along with the development that writes semiconductor technology, the surface sticks the inductor of outfit, capacitor, and tall compositive the cost of chip of spent electric source control is reduced ceaselessly, volume is minorrer and minorrer. By at appeared to guide the MOSFET with electrify very small block can be outputted very high-power, do not need consequently external high-power FET. For example the input voltage to 3V, use the NFET on chip to be able to get the output of 5V/2A. Next, to in the application of small-power, can use cost low small-sized enclose. Additional, if switch frequency raises 1MHz, it is cost, OK to still can be reduced the inductor with use lesser dimension and capacitor. A little new parts of an apparatus or appliance still increases a lot of new functions, be like soft start, current limliting, PFM or PWM means choice.

 

As a whole, step up must choose DCDC, step-down, it is choice DCDC or LDO, should be in cost, efficiency, compare on noise and function.

 

LDO and DC/DC photograph compare:

 

Say from efficiency above all, the efficiency of DC/DC wants outclass LDO generally, this is decision of its job principle. Next, DC/DC has Boost, buck, boost/Buck, (Somebody also puts in ChargePump ‘s charge for this kind of) . And LDO falls only profiling.

 

Again, also be very important a bit, DC/DC brings about his because of the reason of its switch frequency power source noise is very big, far many bigger than LDO, everybody can pay close attention to PSRR this parameter. Should consider more sensitive imitate circuit time so, be about to sacrifice likely efficiency is those who assure power supply is pure and choice LDO.

 

Still have, the periphery parts of an apparatus that normally LDO place needs is simple, occupy an area small, and DC/DC can ask commonly inductance, diode, large electric capacity, some still can want MOSFET, especially Boost circuit, need considers the electric current of the biggest job of inductance, restore time of diode reversely, the ESR of large electric capacity is waited a moment, LDO is compared for the choice from periphery parts of an apparatus so complex, and occupy an area corresponding also conference is a lot of bigger.