Connecting a Voltage Regulators - TL750L05CLP

[Aria]

Hi all,

I'm pretty new to circuit designs and am trying to use a TL750L05CLP
voltage regulator by Texas Instruments in my circuit which takes 6V as
input and should regulate the output at 5V. I can't find any app notes
in the datasheet for this regulator so I connected it the way I thought
I should and the output seems to go up and down as the input changes
which totally defeats the point of a regulator. The schematic I am
using can be seen at http://www.unibooks.ca/schematic-VR.gif and the
datasheet for this model can be found at
http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/TL750L,TL751L%20Series.pdf

What am I doing wrong? How is this supposed to be connected?


Thanks in advance,
Aria

 

[scada]

"Aria" <akashefi@interchange.ubc.ca> wrote in message
news:1124991821.193472.124510@g49g2000cwa.googlegroups.com...

Hi all,

I'm pretty new to circuit designs and am trying to use a TL750L05CLP
voltage regulator by Texas Instruments in my circuit which takes 6V as
input and should regulate the output at 5V. I can't find any app notes
in the datasheet for this regulator so I connected it the way I thought
I should and the output seems to go up and down as the input changes
which totally defeats the point of a regulator. The schematic I am
using can be seen at http://www.unibooks.ca/schematic-VR.gif and the
datasheet for this model can be found at

http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/TL750L,TL751L%20Series.pdf

What am I doing wrong? How is this supposed to be connected?


Thanks in advance,
Aria

Your connection is correct, although you may need to add an input bypass
capacitor, or - and an output electrolytic capacitor depending upon your
circuit.
6 volts is not much "overhead" (1 volt!) for this voltage regulator. That
is, the regulator needs a few volts above the regulated voltage to maintain
regulation. Although the datasheet does say that a minimum of 6V is required
, I suspect that when you place your load onto the 5V reg output, the input
is going somewhat lower than 6V. How much current does your load (device)
require? Can you use a higher voltage as the input to the regulator? If you
describe in some detail your project, we can better advise you.

 

[ehsjr]

Aria wrote:

Hi all,

I'm pretty new to circuit designs and am trying to use a TL750L05CLP
voltage regulator by Texas Instruments in my circuit which takes 6V as
input and should regulate the output at 5V. I can't find any app notes
in the datasheet for this regulator so I connected it the way I thought
I should and the output seems to go up and down as the input changes
which totally defeats the point of a regulator. The schematic I am
using can be seen at http://www.unibooks.ca/schematic-VR.gif and the
datasheet for this model can be found at
http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/TL750L,TL751L%20Series.pdf

What am I doing wrong? How is this supposed to be connected?


Thanks in advance,
Aria

You say the output seems to go up and down as the input
changes. The lowest input voltage you can use is 6 volts.
The maximum current you can draw from the output is 150 mA.
So, what is the load resistance? It *must* be greater than
33 ohms. (I'd recommend using a 100 ohm resistor.) And, when
you talk about the input changing, do you have specifics?
Finally, you need a 10uf tantalum capacitor from output to
ground to match the scant information on the datasheet. You
could probably use a low ESR aluminum electrolytic instead.

Ed

 

[ehsjr]

Aria wrote:

Hi all,

I'm pretty new to circuit designs and am trying to use a TL750L05CLP
voltage regulator by Texas Instruments in my circuit which takes 6V as
input and should regulate the output at 5V. I can't find any app notes
in the datasheet for this regulator so I connected it the way I thought
I should and the output seems to go up and down as the input changes
which totally defeats the point of a regulator. The schematic I am
using can be seen at http://www.unibooks.ca/schematic-VR.gif and the
datasheet for this model can be found at
http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/TL750L,TL751L%20Series.pdf

What am I doing wrong? How is this supposed to be connected?


Thanks in advance,
Aria

Ooops - meant to mention one more thing: you must
have a load on the regulator. If you are measuring
v out without a load you won't get decent regulation.

Ed

 

[Aria]

Hi guys,

Thanks for the help. After I posted this message, I added a 3.3 uF
capacitor between the output and the ground and this seems to have
stablized the output to 4.9 volts. I would really like to have a 5 volt
output so I tried a .47 uF cap and the output seems to change as you
put more load on it (not good). So, I looked for a 1 uF cap but couldnt
find one. Would using a 1 uF cap bring my output voltage to 5 volts?

The input can't be higher than 6 volts (4 AAA batteries) so do you
think I should switch to a different regulator? someone mentioned
LM2936 regulator, what do you think? worth the trouble of changing
regulators?

I also had a .01uF cap from the input to the ground but this seems to
make no difference in the output voltage, should it?

Thanks,
Aria

 

[Aria]

hi again,

here's the new schematic http://www.unibooks.ca/schematic-VR_rev2.gif
if anyone's interested.

 

[Andy]

Hello Aria,

Aria wrote:

Hi guys,

Thanks for the help. After I posted this message, I added a 3.3 uF
capacitor between the output and the ground and this seems to have
stablized the output to 4.9 volts. I would really like to have a 5 volt
output

You need to define what output voltage is acceptable, under which load.
No regulator part will be specified to provide 5.0V *exactly*. The
precision of the regulation is specified in the datasheet and need to be
compatible with your requirements.

so I tried a .47 uF cap and the output seems to change as you
put more load on it (not good). So, I looked for a 1 uF cap but couldnt
find one. Would using a 1 uF cap bring my output voltage to 5 volts?

In the normal operation, the bigger the value of the capacitor the less
the output voltage will vary with the changing input voltage and the
load. But this will not shift much the average value - which you are
probably measuring.

The input can't be higher than 6 volts (4 AAA batteries)

This is not a very efficient use of the batteries' capacity - much of
their capacity will still be there when their total output voltage will
drop to 5V+ voltage_regulator_dropout or below. And you won't have
enough voltage at all if the accumulators are used.

so do you
think I should switch to a different regulator? someone mentioned
LM2936 regulator, what do you think? worth the trouble of changing
regulators?

You should either increase the number of batteries, or use a switching
regulator which can upconvert - but the latter option would probably be
too much a challenge given your current knowledge of circuit design.

I also had a .01uF cap from the input to the ground but this seems to
make no difference in the output voltage, should it?

Thanks,
Aria

-- Andy

 

[Meindert Sprang]

"Aria" <akashefi@interchange.ubc.ca> wrote in message
news:1124991821.193472.124510@g49g2000cwa.googlegroups.com...

Hi all,

I'm pretty new to circuit designs and am trying to use a TL750L05CLP
voltage regulator by Texas Instruments in my circuit which takes 6V as
input and should regulate the output at 5V. I can't find any app notes
in the datasheet for this regulator so I connected it the way I thought
I should and the output seems to go up and down as the input changes
which totally defeats the point of a regulator. The schematic I am
using can be seen at http://www.unibooks.ca/schematic-VR.gif and the
datasheet for this model can be found at

http://rocky.digikey.com/WebLib/Texas%20Instruments/Web%20data/TL750L,TL751L%20Series.pdf

What am I doing wrong? How is this supposed to be connected?

This regulator needs a 10uF decoupling capacitor at the output to be stable.

Meindert

 

[Aria]

Thanks Meindert. Just for my future reference, how do you know? does it
say that somewhere in the datasheet?

 

[John Popelish]

Aria wrote:

Thanks Meindert. Just for my future reference, how do you know? does it
say that somewhere in the datasheet?

Low drop out regulators are especially picky about the output

capacitor. Take a look at figure 4 on the data sheet. It shows how
much resistance must be *in series with* the output capacitor to keep
the regulator stable versus load current, when using a 10 uF
capacitor. The acceptable series resistance for 15 mA to 150 MA (note
the bottom scale change from 5 mA per division to 40 mA per division,
indicated by bold versus thin vertical lines) must fall in a 16 to one
range of .024 to .4 ohms. Most people don't even know that capacitors
have internal resistance. For load current below 15 ma, the
resistance can be higher. Other values of output capacitance would
have a different set of limits for series resistance, and since they
don't give you the other curves, most people will just use 10 uF.
Production designs usually require a full temperature check and
guarantees on capacitor internal resistance if the thing must work.

If doing a through hole design, I usually use a stacked film capacitor
(that has a very low internal resistance) and add a resistor in
series, so I know what the situation is. Quite often, a 1uF stacked
film in series with something like 0.22 ohms and that paralleled by an
aluminum electrolytic of 10 to 22 uF will work fine, at least at room
temperature.

If doing an SMT design, I might use a 10 uF ceramic like Digikey #
PCC2326C 10 uF, 25 V 1206 size X5R type low series resistance
capacitor (a couple milliohms), with a series 0.22 or 0.33 ohm resistor.

Either set needs to be very close to the regulator output and common pins.

 

[ehsjr]

Aria wrote:

Hi guys,

Thanks for the help. After I posted this message, I added a 3.3 uF
capacitor between the output and the ground and this seems to have
stablized the output to 4.9 volts. I would really like to have a 5 volt
output so I tried a .47 uF cap and the output seems to change as you
put more load on it (not good). So, I looked for a 1 uF cap but couldnt
find one. Would using a 1 uF cap bring my output voltage to 5 volts?

The input can't be higher than 6 volts (4 AAA batteries) so do you
think I should switch to a different regulator? someone mentioned
LM2936 regulator, what do you think? worth the trouble of changing
regulators?

I also had a .01uF cap from the input to the ground but this seems to
make no difference in the output voltage, should it?

Thanks,
Aria

You need a completley different chip and circuit if the input
source you have must be 4 AAA cells. Something like a TL499
would give you good regulation at 5V output with a 100 mA draw
as the batteries faded down from 6V to below 3 volts. If
current consumption is lower, it can provide 5 volts as the
batteries fade even further. The maximum current it can provide
is 100 mA. If your load is under 100 mA, this, or an equivalent,
is the chip and ciruit to use.

See the datasheet at:
http://pdf.alldatasheet.co.kr/datasheet-pdf/view/28824/TI/TL499.html

Ed

 

[Meindert Sprang]

"Aria" <akashefi@interchange.ubc.ca> wrote in message
news:1125008189.349963.231830@o13g2000cwo.googlegroups.com...

Thanks Meindert. Just for my future reference, how do you know? does it
say that somewhere in the datasheet?

From personal experience. I designed a battery operated device, which ran an
80c51 micro from a 9V battery and used a TL750L05 to get 5V for the micro. I
first had 1u before and after the regulator and saw the 5V really being a
sawtooth-like voltage, oscillating between 2 and 6V. I then replaced the
output capacitor with a 10u one, which solved the problem.

But as other have pointed out, running this from 4 cells at 6V won't give
you much operating time, since 6V is the minimum input voltage. There are
better linear regulators available which work with only 150mV voltage drop.

Meindert