voltage drop from 555 / 556

L

Lyle

Guest
I'm playing with designing an IR tracking system using IR LED's flashed from
a 556. I want to run it off of a 9 v battery and was trying to calculate
the right resistor for high output but I can't find specs for output voltage
drop under load. I may just have to manually graph it out but by chance,
does anyone know what kind of voltage drop below Vcc I can expect out of a
555 or 556 at 100 - 150 mA max load?
thanks
Lyle
 
Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
Click to expand...
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be as high
as 2V worst case. You can see the 4 lower diagrams on page 3 which refer to
a supply voltage of 5V, 10V and 15V. These are the typical values, the max
values are specd for 15V only on page2.
--
ciao Ban
Bordighera, Italy
 
On Fri, 3 Jun 2005 09:52:46 -0400, the renowned "Lyle"
<walshlgNOSPAM@knology.NOSPAM.net> wrote:

I'm playing with designing an IR tracking system using IR LED's flashed from
a 556. I want to run it off of a 9 v battery and was trying to calculate
the right resistor for high output but I can't find specs for output voltage
drop under load. I may just have to manually graph it out but by chance,
does anyone know what kind of voltage drop below Vcc I can expect out of a
555 or 556 at 100 - 150 mA max load?
thanks
Lyle
Click to expand...
If you read the data sheet, it says Voh for sourcing 100mA on a 15V
supply, 13.3V typical, 12.75V minimum. At 200mA, 12.5V typical.

So, one guess would be 1.7V drop at 100mA and 2.1V at 150mA. Assuming
you're talking about the bipolar type. Be sure to bypass the battery
well.

If you use a transistor such as a 2N4401 wth 15mA of base drive, the
drop will likely be less than a couple hundred mV.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de>
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be as high
as 2V worst case. You can see the 4 lower diagrams on page 3 which refer to
a supply voltage of 5V, 10V and 15V. These are the typical values, the max
values are specd for 15V only on page2.
Click to expand...
I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Build it, try it...

Sometimes we get so bogged down in designing things on paper and in
software that we forget that occasionally the best method is just to
get the old breadboard out and try it!

Mike
 
Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).
Click to expand...
Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
--
ciao Ban
Bordighera, Italy
 
Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).
Click to expand...
Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
--
ciao Ban
Bordighera, Italy
 
Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).
Click to expand...
Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
--
ciao Ban
Bordighera, Italy
 
Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).
Click to expand...
Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
--
ciao Ban
Bordighera, Italy
 
Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).
Click to expand...
Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
--
ciao Ban
Bordighera, Italy
 
On Fri, 03 Jun 2005 16:49:20 GMT, the renowned "Ban" <bansuri@web.de>
wrote:

Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).


Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
Click to expand...
Typical values @25°C:

Source Sink 2N4401 ZTX1051A
NE555 NE555 Ib=Ic/10 Ib=Ic/100
1mA 1.3V 0.015V 0.006V 0.05V
10mA 1.4V 0.1V 0.005V 0.05V
100mA 1.6V 1.5V 0.1V 0.05V
200mA 2.5V 2.5V 0.15V 0.06V




Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
thanks all! gives me a good place to start and I'll bread board it and test
from there.
thanks
Lyle



"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:ig41a1hulkee74h7q4r3cjgb8v359126an@4ax.com...
On Fri, 03 Jun 2005 16:49:20 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Spehro Pefhany wrote:
On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:

Lyle wrote:
I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle
http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).


Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.

Typical values @25°C:

Source Sink 2N4401 ZTX1051A
NE555 NE555 Ib=Ic/10 Ib=Ic/100
1mA 1.3V 0.015V 0.006V 0.05V
10mA 1.4V 0.1V 0.005V 0.05V
100mA 1.6V 1.5V 0.1V 0.05V
200mA 2.5V 2.5V 0.15V 0.06V




Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com
Click to expand...
 
LOL, yup, I just wanted to get a good starting idea as I'm trying to get as
much out of the IR LED's as is reasonable but their voltage drop is about
half that of a standard LED so its easy to fry them, very easy.
Lyle


"MSC" <spam@spam.com> wrote in message
news:9e01a19itkqtotjsgct7k88u47par5no1v@4ax.com...
Build it, try it...

Sometimes we get so bogged down in designing things on paper and in
software that we forget that occasionally the best method is just to
get the old breadboard out and try it!

Mike
Click to expand...
 
Ban wrote:
Spehro Pefhany wrote:

On Fri, 03 Jun 2005 14:08:40 GMT, the renowned "Ban" <bansuri@web.de
wrote:


Lyle wrote:

I'm playing with designing an IR tracking system using IR LED's
flashed from a 556. I want to run it off of a 9 v battery and was
trying to calculate the right resistor for high output but I can't
find specs for output voltage drop under load. I may just have to
manually graph it out but by chance, does anyone know what kind of
voltage drop below Vcc I can expect out of a 555 or 556 at 100 - 150
mA max load? thanks
Lyle

http://www.national.com/ds.cgi/LM/LM555.pdf
page 2,3
with 9V the droop will be typical around 1V with 100mA, but can be
as high as 2V worst case. You can see the 4 lower diagrams on page 3
which refer to a supply voltage of 5V, 10V and 15V. These are the
typical values, the max values are specd for 15V only on page2.

I assume he's talking about sourcing current, rather than sinking,
since he mentions "voltage drop below Vcc", but I could be wroing
(sic).



Well, the droop is pretty symmetrical sourcing or sinking, even if the
graphics and the tables are not giving the same values.
Click to expand...
gesundheit!
 
I see it now, thanks for pointing it out. What do you mean bypass the
battery well? I was just going to use the output from the 556 in this
version until I need higher currents, do I need a transistor driver? (I'm
just a hobbyist)
Lyle


If you read the data sheet, it says Voh for sourcing 100mA on a 15V
supply, 13.3V typical, 12.75V minimum. At 200mA, 12.5V typical.

So, one guess would be 1.7V drop at 100mA and 2.1V at 150mA. Assuming
you're talking about the bipolar type. Be sure to bypass the battery
well.

If you use a transistor such as a 2N4401 wth 15mA of base drive, the
drop will likely be less than a couple hundred mV.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers:
http://www.trexon.com
Embedded software/hardware/analog Info for designers:
http://www.speff.com
Click to expand...
 
On Fri, 3 Jun 2005 17:27:24 -0400, the renowned "Lyle"
<walshlgNOSPAM@knology.NOSPAM.net> wrote:

I see it now, thanks for pointing it out. What do you mean bypass the
battery well? I was just going to use the output from the 556 in this
version until I need higher currents, do I need a transistor driver? (I'm
just a hobbyist)
Lyle

The battery will have some internal resistance. It will get worse as
Click to expand...
the battery runs down. You should put a capacitor across the battery
that will supply most of the current *during* your high-pulse with
little droop. The battery can recharge the capacitor between pulses.

For example, suppose you wanted to pulse at 150mA for 1msec and 200mV
of drop was considered okay.

You'd need C = 0.15A * 0.001 sec/0.2V = 750uF (use 1,000uF/10V).
Put 0.1uF ceramic in parallel.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
 
Lyle wrote:

LOL, yup, I just wanted to get a good starting idea as I'm trying to get as
much out of the IR LED's as is reasonable but their voltage drop is about
half that of a standard LED so its easy to fry them, very easy.
Click to expand...
That's why you use a series resistor. To set the current. The variation in Vf
for the diode ( or the margin in Voh for the 556 ) will make very little
difference to the current.

Best not to design right on the edge anyway.

Graham
 
Lyle wrote:

I see it now, thanks for pointing it out. What do you mean bypass the
battery well?
Click to expand...
Put a big capacitor across it ! The current drawn by the IR led(s) will see the
full battery impedance otherwise and the supply volts will sag.

I was just going to use the output from the 556 in this
version until I need higher currents, do I need a transistor driver? (I'm
just a hobbyist)
Click to expand...
A transistor driven by the 556 would give a better saturation voltage. On a 9V
supply that's not really a big issue. A bipolar transistor would also 'waste'
the base current thus reducing battery life.

Graham
 
Lyle wrote:
LOL, yup, I just wanted to get a good starting idea as I'm trying to get as
much out of the IR LED's as is reasonable but their voltage drop is about
half that of a standard LED so its easy to fry them, very easy.
Lyle


"MSC" <spam@spam.com> wrote in message
news:9e01a19itkqtotjsgct7k88u47par5no1v@4ax.com...

Build it, try it...

Sometimes we get so bogged down in designing things on paper and in
software that we forget that occasionally the best method is just to
get the old breadboard out and try it!

Mike
Click to expand...
Do you have the data sheet for IRLED you're using? Some of them can
really take a wallop, go ohmic, and develop 5V drop. But you need the
datasheet to determine maximum current, maximum permissible pulse width,
and allowable average power, as well as heat sinking techniques using
short leads to large traces/planes. 9V Type N are not particularly
famous for high capacity, and in alkaline will spend most of their
useful life in the 7.2-8.5V range, so that the resistor drop method is
not the best way to drive the LED.
 
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