small 3.3V power supply required

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Mithun_K_Das

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I nee a very precious 3.3V DC power supply. I tried with LM317 but output voltage is not preciously regulated to run a bluetooth module. As the module is highly costly so I can't take the risk. Also, the power supply should be small enough to fix in a 2*2*1 inch box.
Need help in this case.

I/P: 5V-12V DC
O/P power 5-10W, 3.3V


MKDas
 

You say that you have tried with LM317 which can provide a max of 1.5A and then you specify you output requirment as 5-10W @3.3v so you need 2-3A.
If this is the case then try with LM350 (3A) or LM338 (5A)

Alex
 

Hi Dear,
You can use LM1085 or LM1086.
I think it i so easy to use and suitable for your application.
BR
Alireza
 

I think it would be better to use a switching regulator. You can use a switching regulator chip or you can use a PWM chip and a buck stage (maybe it won't be cost effective, but depends on target price). Or you could use the linear regulators suggested above.

Hope this helps.
Tahmid.
 
Yes,
If you are concerened about heat dessipation of Regulator in relativehigh out put current, It is so better to apply high efficiency switching buck regulators such LM2676.
BR
Alireza
 

georgz, I used fixed resistors in this case. although according to my calculation

alexan_e, I used LM317 just to control the voltage and a transistor (BD135) is used to control the current. But voltage was not fixed. when load reduces the voltage increases up to 3.9V for some moments. This will definitely damage my bluetooth module. So I need something else.

Tahmid, SMPS will take larger space and EMI may create problem in the Transmitter. So SMPS can't be used here.

alirez.m.f, I've no idea about LM1085 or LM1086 or LM2676. But I'll think about it.
 

You can use the other two regulators I have mentioned in my previous post

LM350 is like an LM317 but for 3A
and LM338 is the same but for 5A

Alex
 
Tahmid, SMPS will take larger space
Click to expand...
Not necessarily. The circuit employing LM2576 should be quite small. If you look at diagram 1 in the datasheet, you just need 3 external components. Since you won't need as large a heatsink for LM2576 as you will for LM317, you might find that the circuit is instead smaller.
and EMI may create problem in the Transmitter. So SMPS can't be used here.
Click to expand...
Not sure about this, but I doubt the EMI problem will be too great that it will create erroneous transmission. Look at cell-phone chargers. You can plug them into your phone and still talk or use bluetooth. The charger is most likely going to be SMPS and there's no problem.

However, if you still feel, there's gonna be a problem, you should use LM350 or LM338 as suggested by Alex. Here's the datasheets:
http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS009061.PDF
http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS009060.PDF

Hope this helps.
Tahmid.
 

use a pot with the 317 as suggested in the datasheet, I have been using this device for ages now. I don't see why it should not work for you.
 

It's going to cost more, but it depends how much is the limit for this circuit. An advantage as I pointed out is that, it's going to get less hot. However, cost is likely to be more. If cost is the primary issue, linear regulator would be better.
 

I suggest you LMZ12003TZ-ADJ
Please, read this: **broken link removed**
It is a switch regulator with an integrated inductor.
Max output current is 3A, it will satisfy your requirements.
 

LMZ12003TZ it is SMD. I need SIL/DIL ic.


Tahmid, can you ensure me that LM2576 is available in our market (Patuatoli / Nababpur?) and probable rate of LM2576?

---------- Post added at 08:08 ---------- Previous post was at 08:04 ----------

arbj, as the load is varying and inductive too, for LM317 output voltage giving a small overshoot of 3.9V at the time of load disconnection. As a bluetooth module is always connected with this so it can be damage. So I can not take the risk of being damage of this 89$ module.
 
Last edited:

I'm not exactly sure about LM2576, but I remember buying the LM2575 for around 25 Taka (almost a year back), but if I remember correctly, the good quality LM317 is around 15 to 20 Taka. Since today is holiday, I can't contact any vendor, so you have to wait till tomorrow.

Hope this helps.
Tahmid.
 

I think your problem is not 3.3V stabilizator but their dynamic parameter. In other words changing BT module consuption between receiving mode and transmitting mode. Due this companies manufacture special power supllies for transceivers.

Anyway BT modue for 889USD...oooops!
Ok what is the maximum current consuption of this module in tx mode and rx mode?
 

bohumilfulin, BT is not the main load. But I need to drive a stepper motor to change a sensor position. This is the problem. when motor is turned off a overshoot is created. And the BT is transmitting and receiving in each 0.5 sec gap. I'll check the circuit with LM2575 or 2576. if it work well then it can be used. But as our local market is off today so I can not give any feedback ans for that.
 

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