Hello everyone,
I'm new to electronics. I am making a low-power indicator that can set any value below 18V. Here is a schematic that I use from learnelectronics on YouTube:
I want one LED D4 bright when the power is under the set point, so is there any way that I can remove the LED D1, or replace it with other components? It would be better if it consumed less power. Thank you guys so much.

 

Hope to get you guys advice!!

 

Replace D1 with a 2 volt zener diode.

 

D1 can be removed completely.

R-7 should be changed to a ~2K Resistor,
unless You really want the absolute maximum brightness from the LED,
( ~20ma may be too much Current over long periods for maximum dependability from the LED ).

On standby, the Circuit will only pull roughly as much as the LED, ( ~10ma with a 2K R-7 Resistor ).

If You want seriously low Standby-Power-consumption,
the Circuit will have to be slightly more complex.

Are You willing to have any additional Components for lower Standby-Current ?
.
.
.

 

Here's a circuit that uses a TLV431 voltage reference so its voltage setting is quite stable with temperature
It generates a constant-current through the LED when the voltage goes below the set point, so the LED current stays low and does not change significantly with the supply voltage.

The constant current is approximately 0.6V divided by R4.
That gives about 2mA of LED current here for R4=300Ω, which should be sufficiently bright with a high-brightness type LED.

The LED goes ON when the voltage at the TLV431 REF input goes below 1.24V nominal.

When the LED is off, the battery load is no lower than 25kΩ..

The simulation shows a voltage adjust range of about 4V to 19V for a U2 pot adjustment of 0 to 100%.

 

Replace D1 with a 2 volt zener diode.

I just simulated it and it works perfectly, but a 2-voltage zener is not common so I can't buy it to test soon.

 

D1 can be removed completely.

R-7 should be changed to a ~2K Resistor,
unless You really want the absolute maximum brightness from the LED,
( ~20ma may be too much Current over long periods for maximum dependability from the LED ).

On standby, the Circuit will only pull roughly as much as the LED, ( ~10ma with a 2K R-7 Resistor ).

If You want seriously low Standby-Power-consumption,
the Circuit will have to be slightly more complex.

Are You willing to have any additional Components for lower Standby-Current ?
.
.
.

Yeah, of course, I really want to know. I try to remove the D1 and change the R7 to 2k, but it seems doesn't work.

 

Here's a circuit that uses a TLV431 voltage reference so its voltage setting is quite stable with temperature
It generates a constant-current through the LED when the voltage goes below the set point, so the LED current stays low and does not change significantly with the supply voltage.

The constant current is approximately 0.6V divided by R4.
That gives about 2mA of LED current here for R4=300Ω, which should be sufficiently bright with a high-brightness type LED.

The LED goes ON when the voltage the the TLV431 REF input goes below 1.24V nominal.

When the LED is off, the battery load is no lower than 25kΩ..

The simulation shows a voltage adjust range of about 4V to 19V for a U2 pot adjustment of 0 to 100%.

This looks great, I will give it a try. Thank you~

 

I just simulated it and it works perfectly, but a 2-voltage zener is not common so I can't buy it to test soon.

Three 1N4148 diodes in series will be appx 2 volts.

 

Three 1N4148 diodes in series will be appx 2 volts.

Oh, I got your idea. You're so great. It works now!!

 

Here's a circuit that uses a TLV431 voltage reference so its voltage setting is quite stable with temperature
It generates a constant-current through the LED when the voltage goes below the set point, so the LED current stays low and does not change significantly with the supply voltage.

The constant current is approximately 0.6V divided by R4.
That gives about 2mA of LED current here for R4=300Ω, which should be sufficiently bright with a high-brightness type LED.

The LED goes ON when the voltage at the TLV431 REF input goes below 1.24V nominal.

When the LED is off, the battery load is no lower than 25kΩ..

The simulation shows a voltage adjust range of about 4V to 19V for a U2 pot adjustment of 0 to 100%.

What is the value of the trimpot? I had a check on the components and see that I can't buy TLV431 now, they only have TL431. As I searched, it seems that the TL431 has a higher current min and max than the TLV431. What can I use to replace it?

 

What is the value of the trimpot? I

250kΩ,

I can't buy TLV431 now, they only have TL431

Who is "they".
Where can you purchase parts?

What can I use to replace it?

Don't offhand know of a replacement.