LDO or Switching power supplier?

[crenyen]

The voltage conversions exist in most circuits including digital and analog circuits.
Gererally, there are two major kind of converters. One is LDO and the other Switching power supplier.
When design circuits, I always encounter which one I should use and.
Can anyone tell me how to select power convertes between them?

 

[sunking]

it depond on your system requirement.
LDO can only drop to a lower voltage than supply voltage, but it is simple.
Switching can not only down voltage, but also up voltage.
Another is switching is high efficiency than LDO

 

[sefton]

Also switching is cheaper than LDO for high power, but more expensive for low power, and switching can generate RFI which can be a problem in certain RF applications.

 

[Davood Amerion]

Hi;
when in your circuit (Vi-Vo) ~ (1-2)Volts it is better to use LDO.
and if (Vi-Vo) is much higher its beter to use Switching type.

Regards
Davood Amerion

 

[Rayengine]

Audio applications are also sensitive to noise application. Switching regulator are hard to control noise especially in large variation in loading.

 

[Kral]

crenyen,
LDO (Low Drop Out voltage) regulators are linear series regulators that are designed to operate at small input-output voltage differentials. They share the advantages of other linear regulators:
~ Low Noise
~ Good frequency response
~ Excellent line and load regulation.
By applying an unregulated input that is just above the (Output voltage + Dropout Voltage) spec , you can keep the dissipation of the regulator reasonably low. However, you must be very careful to design the power supply so that under worst case (low line voltage, low filter capacitance, low input frequency) that the dropout voltage spec is met. If you do this, then the dissipation under worst case high unregulated voltage conditions, the dissipation may be excessive.
.
Switching regulators, as a rule have:
~ Worse Regulation
~ Higher Noise
~ Lower dissipation
.
Regards,
Kral

 

[crenyen]

Presently, I am designing a VOIP ADSL router and the power plan is as follow.
12V for VOIP
5V for USB and ADSL.
The power form adapter is 12V.
To prevent serious EMI issue, my idea is that I down conver 12V to 9V by an LDO and then down converter 9V to 5V by another two LDOs.
Is my design suitable?
Can anyone recommend the suitable power IC?

 

[sefton]

It depends on the current you require on the 5V. If the current is not too high, you can use a linear regulator like the 7805. You don't need to use a LDO. If the current is high then you will have to use a switching supply or otherwise a big heatsink with a linear regulator. If you choose a linear device then multiply the current by 7 (12 - 5) to get the watts dissipated and check the specifications of the device.

 

[zenisle]

LDO is like PR

 

[crenyen]

What is different between LDO and linear regular?

 

[sefton]

A LDO is a linear regulator. For a linear regulator, the input voltage has to be at least a few volts higher than the output for it to function. With an LDO the input still must be higher than the output, but requires less "extra" volts than a regular linear regulator. You can think of an LDO as a high quality linear regulator.