Thanks everyone for helping me out, everyone's idea was great but since I did not want to use any other voltage regulator as it would it take extra space and increase to cost so I would go with #14 idea of @dl324 but i would like help @eetech00 to help me able to view it in bar graph mode and brief a bit more about what he was saying in #16
Thanks everyone for the insights

 

Hello all ones again,
I tried the circuit first on simulation first what i did was used 10k and 50k resistance in series which divided my voltage to one by sixth hence 25.2V/6=4.2 and 18V/6=3 and connected this to signal pin, hence a supply of 3v to 4.2v on signal pin

Then for 200uA to the Leds I needed to use a resistance 1.25V/200uA = 6250 ohm, so i calculated by parallel resistance formula with 12k resistance of internal resistance of LM3914 IC , on calculation I got it ~13k which i connected between High Resistance Reference pin and Low Resistance Pin and finally to get a Voltage of 3V on Rlow reference pin i calculated 200uA from Led and 75uA from Radjust pin = 275uA and then for 3V on Resistance low Reference pin, R=3V/275uA=10909ohm

it worked perfect in simulation but when i try it in hardware it creates a problem
1- I tried to provide variable voltage with help of a potentiometer the voltage drop is quite variable like at max everything is fine but when i turn potentiometer a bit less it shows like 18 volt between pot and ground but as soon as I remove supply from ic the voltage on voltmeter jumpes to 22.4 why is this happening?
2-The first lits up only at 21V approx

Why is this happening can anyone suggest where I am going wrong, many people suggested to use a linear regulator, I open for that too.

 

Hi flip,
Show how you connected the pot to the Input on the actual ciciuit
E

 

 

Hi flip,
You should not have pot wiper providing the power to the LM3914 and LED's
E

 

@ericgibbs that is for my convivence of providing variable voltage from 18v to 25.2v and should i know why

 

Hello,

I would use a voltage regulator of 12 or 15 Volts for the LM and the leds.
The absolute maximum voltage for the LM is 25 Volts. (Read the datasheet)
That will provide a more stable result.



Bertus

 

that is for my convivence of providing variable voltage from 18v to 25.2v and should i know why

Hi flip,
Because your full circuit when powered from the pot wiper will give incorrect results.
This plot show what you should get from the pot and divider.
E

 

Hello,

Next to the voltage regulator, do the following:
Vary the battery voltage in the simulation in stead of RV1.
Connect R3 direct to the battery.

Bertus

 

Be certain to provide the local bypass capacitors, 0.1 mfd, for the voltage regulator, at the regulator, or you may have oscillations. ANDuse the much smaller regulator LM78L12 if space really matters. The 78L12 is I do not understand MUCH SMALLER than the LM7812.

 

Hello,

@MisterBill2 , You are correct about the capacitors on the regulator.
I have some doubts about the LM78L12.
When the LM3914 is in bar mode, there will be a higher current drawn when all leds are on.
There will be no issue when used in dot mode.

Bertus

 

Thanks everyone for helping me out, everyone's idea was great but since I did not want to use any other voltage regulator as it would it take extra space and increase to cost so I would go with #14 idea of @dl324 but i would like help @eetech00 to help me able to view it in bar graph mode and brief a bit more about what he was saying in #16
Thanks everyone for the insights

Hi
You already have written you have no space for a regulator, so...

What I am implying in #16 is.....If you want to use "bar mode" then you have two choices:
1. use a voltage regulator, and the bar graph display of your choice.
2. Use a voltage divider, and keep the LED load under 10mA.

Item 1 requires a regulator, that you have already written you don't want to use because of space limitations.

Item 2 requires a bar graph display that draws under 10mA when all LEDs are lighted.
This will require a small dropping resistor as part of the divider to avoid using resistors that are physically too large (maybe 1W or greater).
If you can accept using large resistors, then not using a regulator because of size becomes questionable because either solution requires space.

So....unless you can find an ultra low current bar graph for Item 2, or can accept using a regulator, then bar mode isn't a viable option.

Please confirm your design choice(s).

 

Hi
You already have written you have no space for a regulator, so...

What I am implying in #16 is.....If you want to use "bar mode" then you have two choices:
1. use a voltage regulator, and the bar graph display of your choice.
2. Use a voltage divider, and keep the LED load under 10mA.

Item 1 requires a regulator, that you have already written you don't want to use because of space limitations.

Item 2 requires a bar graph display that draws under 10mA when all LEDs are lighted.
This will require a small dropping resistor as part of the divider to avoid using resistors that are physically too large (maybe 1W or greater).
If you can accept using large resistors, then not using a regulator because of size becomes questionable because either solution requires space.

So....unless you can find an ultra low current bar graph for Item 2, or can accept using a regulator, then bar mode isn't a viable option.

Please confirm your design choice(s).

since usage of voltage regulator becomes a mandotory thing as my led consume 20ma, therefore suggest me with use of voltage regulator and also do suggest me some small voltage regulators

 

my led consume 20ma

That's the rating for a typical LED, but high-brightness types can generate a significant light at a much lower current.

 

Hello,

There is a way to set the led current on the LM3914 between 3 and 30 mA:

Bertus

 

Hi flip,
Because your full circuit when powered from the pot wiper will give incorrect results.
This plot show what you should get from the pot and divider.
E

So can you suggest me how to make a variable voltage using a fixed voltage battery and an potentiometer.

 

Hi flip,
Check my post #45
Post #48 shows the voltage plots.
E

 

Hi flip,
Have you considered an inline voltage regulator module, located say near the battery.?
eg: 2 wires from the battery to a regulator module and 3 wires from the reg module to the LM3914 module


E

 

OK, that regulator is now an MC78L12, with an input range of 14 to 35 volts, max current of 100mA, in a TO92 package, the same as small signal transistors. Certainly there is room for that. Then you will have a well regulated supply voltage and the circuit will work.

 

Hi,
25v -12v = 13v at 0.1A = 1.3Watts
Check wattage of LM78L12

E