Re: 5V @ 3.5A for automotive - best way?
- From: "Brian Ellis" <XXbellis350@xxxxxxxxxxx>
- Date: Tue, 2 Jan 2007 23:26:30 -0600
<ferrari.secret.santa@xxxxxxxxx> wrote in message
news:1167757609.733221.4530@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm trying to make a little project work here... trying to use seven
5x7 dot-matrix displays to make a little "digital readout" that I can
display text on based on feedback from various things in a car (like
temperature, etc).
The 5x7 displays are of course multiplexed and have a 1/10th drive
current of 100ma. I am using shift registers to control the state of
each row, then sequentially updating the rows to produce the display.
That's all fine.
Problem is, given 7 rows, 35 dots per row, at 100mA per dot, that's a
potential max current of 3.5A! The duty cycle doesn't help me because
I drive the rows one after another, so if all elements were on, there's
a potential 3.5A constant current requirement, thats a lot.
Can anyone suggest solutions for getting such a drive current from a
12V automotive source? The problem is, I do not want the display to
flicker in brightness when the vehicle is started, so I really want to
use a regulated source, also if I just ran the segments off the 12V,
the power dissipation in the resistors becomes huge and I am trying to
keep this small. I have looked at the 1084 regulator which can do 5A
with up to 30V input, but this is a linear regulator.
I am a bit of a noob when it comes to circuit design, but am I correct
in believing the power dissipation of the regulator is the voltage drop
from Vi to Vo times the current? If so, and if you assume 13.8V in,
then that's around 30 watts which seems to be a ton. I have used
switchers in the past but the problem is the cost and number of
additional components (board space is tight).
Am I missing some obvious answer that would solve my problems here?
Would you guys go a different route in this design other than a
traditional linear or switching regulator, and if so, what would you
use?
Thanks!
CJ
Try something like this, http://www.fncwired.com/12to5VoltExample/
You can get the parts at Digikey. Very reasonable prices.
Brian Ellis
.
- References:
- 5V @ 3.5A for automotive - best way?
- From: ferrari . secret . santa
- 5V @ 3.5A for automotive - best way?
- Prev by Date: Re: Getting Hysterical over the Hysteretic Buck Controller
- Next by Date: Re: How to sample multiple signals at the same time with ADC?
- Previous by thread: Re: 5V @ 3.5A for automotive - best way?
- Next by thread: Anode and Cathode confusion?
- Index(es):
Relevant Pages
|
Loading
