problem while selecting regulator

I got stucked at selecting regulator for control circuitory. I saw there are three methods as Low dropout regulator, Linear regulators and switching regulators.
So which are reliable and which parameter to study while selecting regulators rather than input and output voltage.

ep.hobbyiest said:

I got stucked at selecting regulator for control circuitory. I saw there are three methods as Low dropout regulator, Linear regulators and switching regulators.
So which are reliable and which parameter to study while selecting regulators rather than input and output voltage.

Click to expand...

Linear regulators are simply transistor circuits integrated on one chip. Most of them are offered to regulate output voltage when input voltage or the load current vary. Linear regulators dissipate power and need heat sinks. Some are fixed (e.g. 7805...7815 series), others are adjustable (LM317T), some offer a good voltage regulation even with only 1...3 V higher source voltage (low-drop types).
To reduce heat dissipation, there are new switching regulators which utilize pulsed operation to achieve regulated output. They come in many versions but as they switch relatively high power, they generate a lot of interference, often in RF range >1 MHz. Their output voltage is rippled, so they are not recommended to be used with sensitive loads like oscillators.
To begin, I would recommend to start with the common LM317T adjustable regulator. Read the specifications and recommendations for use, and attach a large heat sink if you feed a load with up to 1 A.
With some basic experience you can then try a switching regulator from a wide selection of types. Read carefully the specifications and be ready to fight the interference and ripple if you need to handle sensitive loads.

this depends on the input voltage and required output voltage difference and size of the system , if the difference between input voltage and required output voltage is lesser then 5V then i would recommend to go for linear regulator, if it is higher i would go for smps, because at higher difference power desssipation across the regulator increases, which creates extra energy loss, but for smps size and time requirment is bit little more, you have to check input voltage range and output , then the current of the system then proper inductor capacitor and resistance selection to get required output.

LDO and normal regulator have nearly same pros and cons.

hope that would help

Hi,

First you need to decide the spcifications for your regulator.

Input and output voltage is not enough.
Current, input voltage range, output voltage ripple, power dissipation, budget, size, part count, EMI, and others are to think of.

Low droput are linear regulators especially designed for low droput voltage. Often they are used as post regulators for switching regulators.

Besides of low power dissipation the benifit for switching regulators is that they can generate a higher output voltage than the input voltage (boost converters) also there are types that can handle both higher and lower input voltage than the output voltage (sepic converters).
To get satisfying results a switching regulateor is more complicated to design. A proper layout, grond plane and intelligent routing is necessary. But with a good layout you can keep EMI low and use it in almost any application.
I use it in applications with very sensitive analog measurement where i measure in the pA range and also use oscillators in the same application.

So if you see a benifit in your application dont be worried and give the smps a try and make your own experience. Yes experience...before designing a smps read the datasheets carefully and go through some application notes. On www.linear.com you will find a lot of helpful information. Also a selection guide to choose the right device.

Klaus

Some of my projects are powered from a 9V battery that drops to 6V during its life.
An ordinary 7805, 78L05 or LM317 needs an input voltage of at least 7V. So they fail when the battery still has plenty of power remaining.
Therefore I use a low dropout 5V regulator that still works perfectly when its input voltage has dropped to 5.4V.

Apart from being more complicated in layout design switch regulators require more board space (due to input output capacitors-inductors) than linear regulators so keep that in mind also. Most of regulator suppliers also offer now tools that help you design your system and perform simple simulations like https://www.analog.com/en/power-management/products/pmp_ADIsimPower_DesignCenter/fca.html from Analog devices which is rather cool and easy to use.

Thank you for giving suggestion.
I want to regulate +5v and +12v Volt from 36v power supply. Actually i need three of the range. i m using 5, 12 and 36 volt too.
so to convert from 36v to 5v i am thinking this option.

Hi,

From 36V to 5V calls for a switching regulator.
With every about 33mA you dissipate 1W in a linear regulator. With switching regulators it is about nothing.
It depend on current if it is useful witv 12V.

The most voltage drop is from 36V to 12 V. Maybe it makes sense to step down from 36 to 12V an then with a linear regulator from 12 to 5V.

About board space... I designed a 1.5A step down in the same size as a horizontal mounted TO220, capacitors included.
No heatsink required. If you all mechanical parts take into account like heatsink, screw, washer, thermal compound.. a switcing solution may be cheaper than a linear solution.

Klaus

KlausST said:

About board space... I designed a 1.5A step down in the same size as a horizontal mounted TO220, capacitors included.
No heatsink required. If you all mechanical parts take into account like heatsink, screw, washer, thermal compound.. a switcing solution may be cheaper than a linear solution.

Klaus

Click to expand...

That's true: I just bought **broken link removed**. Adjustable from 30V down to 1.2V, up to 3A, size 45 (L) * 20 (W) * 14 (H) mm (with potentiometer): .

BTW: Here is a nice search/selector tool for DC-DC converter IC's.

I bought some small AC-DC wall-wart adapters with a switching adjustable voltage regulator from 3V to 36V at 15W maximum. They are preset for 5V at 2A. They costed $1.75 each. They were name-brand and made to power a dial-up modem (remember dial-up?). I haven't cut one open to peek inside yet.
They probably have a trimpot to adjust the voltage and another trimpot to adjust the current limit.

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This is a test post to see if the lower tails on the letters on the bottom line of my text are extended normally and to have the "Did you find this post helpful?, +Give Points and Add Contact" text.
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EDIT: Maybe the tails are fixed but the "Helped Me?" box and "Add Points" text are still missing.

Audioguru said:

EDIT: Maybe the tails are fixed but the "Helped Me?" box and "Add Points" text are still missing.

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You never see these texts in your own posts.