[SOLVED] Sugessions for 3.3v regulators

Please suggest some easily available 3.3v regulators

With LM317 you can make fixed 3.3V if you set fixed resistor
What is the input voltage?

You didn't specify input voltage and desired output current...
I have used MC33375 in the past, it is an LDO (37533 marking for 3.3V output). I don't know the availability in India.
https://www.onsemi.com/pub_link/Collateral/MC33375-D.PDF

Of course you can always use LM317 as rade908 suggested, I suppose it is available in your local supermarket!:grin:
LM317 pdf, LM317 description, LM317 datasheets, LM317 view ::: ALLDATASHEET :::

And this is a calculator for LM317 R2 resistor (R1 is supposed to be 240 Ohm).
**broken link removed**

For low current (<100mA) I find the LE33 from ST works very well and is inexpensive.

Brian

LM1117 , 800mA output in slim SOT223 package
**broken link removed**

Alex

My supply voltage is either 5v or 12v. I need around 200mA.

If you supply with 5V you must use LDO voltage regulator. Then you can't use LM317 because it's need 3 voltage difference from input to output to work good. If you supply with 12V you can use LM317, and you have this chip in TO220 package.
Do you need SMD component or thru holl component or it does not matter?

I'll stick with lm317 since i'm gonna use 12v. I have lm1117 but don't have tantalum SMD capacitors.

An 8.7V voltage drop is going to cause a hell of a lot of heat...

Hewitson his current is 200mA, and power is 8.7*200m=1.47W that is not a lot of heat

This website shows a simple voltage regulator using a transistor. It's okay for low power if the transistor is a large enough package, say TO-220.



The zener must be 3.3 + 0.6 = 3.9 V. This is a standard zener value.

Or else it can be obtained by using a stack of diodes. Or maybe just 2 led's.

If the regulation does not come out at exactly 3.3V then there are ways to 'bend' a zener value just a bit.

If you want to stick to LM317 that will be just fine for 12V input for light loads like yours 200ma.
Have a look at the image and formula to get desired voltage.

The formula for calculating the value of resistors is as follows.

Vout=1.25(1+R2/R1).
For your 3.3v the value for R1=240R, R2=394R.
394 ohm resistor is not a standard value.you can use a combination of 430 ohm and 4.7K in parallel to get nearest value.But an easy approach will be to use a variable resistor 500 ohm or 1K and adjust the output voltage to required value using a multimeter.

Your required current 200ma in this situation does not need active cooling or heatsink for the regulator.200ma max thats what your circuit will draw,otherwise Lm317 can supply much higher current say 1.5A but will require a heatsink of adequate size and active cooling.
If you have datsheet for LM317 you can find an application circuit of LM317 being used as current limiting regulator along with voltage regulator.Datasheet has all the details.

liteon said:

Your required current 200ma in this situation does not need active cooling or heatsink for the regulator

Click to expand...

With an input voltage of 12V, that would be 1.75W of dissipated power on the regulator. Are you suggesting that no heatsink is required?

Depends on what package the 317 is in. If it's the TO-3 version it will tolerate 1.75 W without a heatsink. Specs on the TO-3 LM317 say it will operate up to 150 Centigrade.

However if it's the TO-220 version then 1.75 W will make it too hot to touch (for me to touch anyway).

Quote from Wikipedia article as to TO-220:

"A TO-220 package that is not heatsinked typically dissipates around 1 watt (W), at a temperature 62.5C higher than the ambient temperature."

If no heatsink is used I think a TO-220 will get hot enough to go into protection mode. It won't destroy it, it will just shut down until it cools down enough to restore voltage again.

It was a typing mistake.I wrote
"Your required current 200ma in this situation does not need active cooling or heatsink for the regulator."

It should be " your required current of 200ma in this situation does not need active cooling for the heatsink"

TO-3 will not heat too much compared to TO-220 which will need some sort of heatsink to dissipate the heat and prevent a thermal shutdown.D2PAK versions are designed for moderate dissipation without heatsink as there is no metal tab and device is soldered to PCB which acts as heatsink.