PDA

View Full Version : DC to DC Regulator



Rama
11-07-2007, 10:14 AM
Hi
I am a commerce guy so please pardon my ignorance in electronics and posting a silly question.
For one of the school projects, my relative is making a mobile robot.
He has a LCD which requires 12V, 5A, 60 W. He has a battery pack which is giving 19V,0-6A.
Now we did some basic research and found out that there needs to be a DC to DC regulator in between the LCD and Battery pack.
Does someone know a good shop in Chennai or other places who can custom make this regulator or sell readymade?

Thanks for your time.
Rama

rao
11-07-2007, 12:27 PM
Use LM1084IT-12 voltage regulator, not sure of availability in Chennai, but try at your local electrical/electronics store.. and then follow the link


http://www.elecfree.com/electronic/12v-5a-power-supply-regulator-with-lm1084it-12/

Rao

MohitM
11-07-2007, 01:48 PM
Rama:
Are you sure the LCD takes in 5A with a 12V supply? That's a bit too much. Or have you included the motor load in this figure? I also don't think the LCD would like 12V. Most I've seen are 5V or 3.3V and lower.

Rao:
That's a step down of of 19V-12V = 7V... 7V x 5A = 35W. The LM1084IT-12 will have to be mounted on an ice-block to keep it from smoking. :-)

Rama
11-07-2007, 02:46 PM
Thank you Rao and Mohit.
Mohit- It is indeed the same voltage as I have specified.
The brochure of this LCD talks about 12V,5A,60W. I am getting slightly apprehensive now after reading your post whether it is the right LCD?
Is it really that abnormal?

MohitM
11-07-2007, 03:25 PM
Is it really that abnormal?
Yup! Even if you are a commerce guy, this should make sense - Although we're comparing two vastly different products, to give you an idea; an LG 20" LCD monitor consumes about 45W of energy...
http://www.lge.com/products/model/detail/l204wt.jhtml

I'm sure the LCD your relative has isn't anywhere even close.

Rama
11-07-2007, 03:35 PM
Believe me Mohit. A commerce guy will not know the difference :)

Look at the following link:-
http://www.screentouchlcd.com/index.php?option=com_content&task=view&id=23&Itemid=45#specs

In the sleep mode, the LCD takes 5 W but in the normal mode it is 34.5W.
So is 34.5 W a correct measure of such a small LCD?

MohitM
11-07-2007, 04:51 PM
So is 34.5 W a correct measure of such a small LCD?
I haven't looked very closely at your example. But maybe the touchscreen uses some energy, and maybe the backlighting consumes a lot.

Anyway, it would be a more meaningful conversation if you can do the research on the LCD that your relative has, find out its part/model number and then let us know, be able to assist you. I seriously doubt if s/he has something that uses up 60W.

firoz
11-07-2007, 06:40 PM
in our office projects,we use PLC's for which the rated amp is only 500ma(constant drawing).mostly thy are 16C 8lines.

its just display right.so there is no way an LCD draw so much current.

docel
11-07-2007, 07:53 PM
Rama!
First of all, WE are not gods to 'see' what your relative has.
Second, even if we do see, it is difficult to believe:arrow: what in heaven is he using ( and you asking meaningless questions on his behalf...) a 12v5A60W LCD for a SCHOOL mobile project...... 8O 8O

That IS a ridiculous project :P

Now , i suggest this:
1. Find a webcam and take a close shot pic and post it here.
2. Tell us ordinary folks WHY are you using such a ridiculous 12v5A60W LCD in a Mobile Robot.
3. Ask your relative to join us and convince us about his Project.

Other wise, all of us busy guys art wasting our time trying to get some relevant facts from you.

It has taken 5 posts for you to tell us about the TouchScreen LCD
:!: :!:

debu
11-07-2007, 10:23 PM
@Rama: Seems to me like your relative is using the FBT-0651OTEAR module. The reason the power consumption is so high is due to the use of the resistive touch screen sensor, in contrast to the more widely used capacitive sensors. These resistive sensor based touchscreens are generally used for MMI/HMI (Man Machine Interface or Human Machine Interface) applications along with PLC's in industrail machinery, where:

1) Power consumtion is not much of an issue.
2) 12v Signals are provided.

Capacitive sensor based touch screens are used in PDA's and alike where power consumption is an issue, and hence they are generally based on 1.8v/3.3v/5v signals and consume far less power.

As for, your question that you asked, I take it that you would be requiring two things, 1) A method to drive the LCD with your existing microcontroller signals which are based on 3.3v/5v, and 2) A method for converting the battery 19v to the required 12v high current, which is used to power the LCD. I dont think you require an IC for either of the two tasks, nor do I think there would be one available.

The simplest way of accomplishing the first task would be to make a transistor driving circuit, using an NPN (Try BC548B) to boost the signal voltage to 12V. Remember to use a resistor to source the current from the uC. A simple google will provide you with countless circuit diagrams. (or PM me).

The second task, would involve the use of a linear regulator (step down kind). I would have suggested a 7812, except for the high current requirement, so we go into the world of MOSFET's, a n-channel IRF 540 based circuit (again google), would suffice up till 10Amps. You would obviously have to use a supporting zener, resistor(s) and capacitor(s) in order to limit the voltage to 12v.

I hope that all this information would not be too overwhelming for you, I wrote it hoping your relative would be able to read it and derive some help from it.

Regards,

Debu

MohitM
11-07-2007, 11:37 PM
Methinks this thread is heading nowhere. If its a school project like he says it is, I don't think a touchscreen LCD is doable. Secondly, he should chuck the 19V battery pack and get a 12V one instead. That should be cheaper than getting a DC-DC converter custom built (or even readymade).

rao
11-08-2007, 02:19 PM
sorry Mohit.. and thanks for correcting me.. My fault.. didnt read throught the part details carefully enough :D

Rao