How IC power by battery work

W

Wong

Guest
Hi,
Some of the IC do have a pin (i.e. the name is "Vbat", or "VBAT")
for switching to battery source when the main supply is not available
on the IC. How is this work ?

If an IC does not have such a pin, can we still apply battery source
with just a few diodes (of course, there might be parts like capacitor
and resistor) to build our own circuit ? Typically the IC consumes
500mA and above.

Thousand thanks.
 
Wong wrote:
Hi,
Some of the IC do have a pin (i.e. the name is "Vbat", or "VBAT")
for switching to battery source when the main supply is not available
on the IC. How is this work ?

If an IC does not have such a pin, can we still apply battery source
with just a few diodes (of course, there might be parts like capacitor
and resistor) to build our own circuit ? Typically the IC consumes
500mA and above.

Thousand thanks.
Click to expand...
If you choose a Schottky-diode the battery voltage has to be 450mV higher
than the min. circuit spec.
A high-side switch can do with less loss(5-25mV), but requires an additional
comparator.

o------------+-----------o
|
BYV10 -
^
|+
battery ---
-
|
|
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

--
ciao Ban
Bordighera, Italy
 
On 29 Jun 2004 23:32:57 -0700, tatto0_2000@yahoo.com (Wong) wrote:

Hi,
Some of the IC do have a pin (i.e. the name is "Vbat", or "VBAT")
for switching to battery source when the main supply is not available
on the IC. How is this work ?

If an IC does not have such a pin, can we still apply battery source
with just a few diodes (of course, there might be parts like capacitor
and resistor) to build our own circuit ? Typically the IC consumes
500mA and above.

Thousand thanks.
Click to expand...
BATTERY SOURCE ------>|------+
+----------Device being powered
POWER SOURCE -------->|------+
 
"The Real Andy" <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply>
wrote in message news:srv4e0dprqrj6ip5c2ior38rn5t8m34vv3@4ax.com...
On 29 Jun 2004 23:32:57 -0700, tatto0_2000@yahoo.com (Wong) wrote:

Hi,
Some of the IC do have a pin (i.e. the name is "Vbat", or "VBAT")
for switching to battery source when the main supply is not available
on the IC. How is this work ?

If an IC does not have such a pin, can we still apply battery source
with just a few diodes (of course, there might be parts like capacitor
and resistor) to build our own circuit ? Typically the IC consumes
500mA and above.

Thousand thanks.

BATTERY SOURCE ------>|------+
+----------Device being powered
POWER SOURCE -------->|------+
While this will work, for most battery applications, the 'drop' associated
Click to expand...
with the diode is more than may be acceptable. Hence the switched terminal
in the IC versions, is normally connected via a FET, rather than simply
using a diode. Typically this gives a drop of perhaps 0.2v, against the 0.5v
from using a diode. Simple diode feeding, may be fine with battery voltages
like 9v, but more care is needed when dealing with systems operating off
perhaps 2.5v.

Best Wishes
 
On Wed, 30 Jun 2004 11:35:14 +0100, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk> wrote:

"The Real Andy" <.pearson@wayit_dot_com_dot_au_remove_the_obvious_to_reply
wrote in message news:srv4e0dprqrj6ip5c2ior38rn5t8m34vv3@4ax.com...
On 29 Jun 2004 23:32:57 -0700, tatto0_2000@yahoo.com (Wong) wrote:

Hi,
Some of the IC do have a pin (i.e. the name is "Vbat", or "VBAT")
for switching to battery source when the main supply is not available
on the IC. How is this work ?

If an IC does not have such a pin, can we still apply battery source
with just a few diodes (of course, there might be parts like capacitor
and resistor) to build our own circuit ? Typically the IC consumes
500mA and above.

Thousand thanks.

BATTERY SOURCE ------>|------+
+----------Device being powered
POWER SOURCE -------->|------+
While this will work, for most battery applications, the 'drop' associated
with the diode is more than may be acceptable. Hence the switched terminal
in the IC versions, is normally connected via a FET, rather than simply
using a diode. Typically this gives a drop of perhaps 0.2v, against the 0.5v
from using a diode. Simple diode feeding, may be fine with battery voltages
like 9v, but more care is needed when dealing with systems operating off
perhaps 2.5v.

Best Wishes
Click to expand...
Judging by the origonal post, i think the author is not capable of
anything more. You are correct however.
 
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