Hello all ,
I have this circuit that supposed to light a specific led when varDC/DC is 20V
And another led when varDC/DC is 15V and so on ..
My question is , why do I have to add the mosfet and the voltage divider at the exit of the comparator (the red mark)??

it seems to me that I can connect the output of the comparator directly to the led with a resistor ,
When the output is low ('0') led will light on , and when its ('1') led will shutdown ,
so I can save the extra resistors and the mosfet , what am I missing ?
Thanks

 

The output from the comparators is a high signal when the input voltage reaches the reference, The FETs invert that signal to turn on the LEDs. I agree, using FETs is complete overkill. If you switch the + and - inputs to the comparators, you could connect the led with its sreies resistor directly between the comparator output and Vjack.

 

But keep in mind that this Comparitor can only sink around ~10mA.
If You want very bright LEDs, the FETs are necessary.

What is "V-Jack" ????
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You could use an LM3914 LED bar graph display IC.

 

The output from the comparators is a high signal when the input voltage reaches the reference, The FETs invert that signal to turn on the LEDs. I agree, using FETs is complete overkill. If you switch the + and - inputs to the comparators, you could connect the led with its sreies resistor directly between the comparator output and Vjack.

Thank you for clarifying the fact that the FET invert the signal , and that is indeed possible to connect it directly to the comparator

 

But keep in mind that this Comparitor can only sink around ~10mA.
If You want very bright LEDs, the FETs are necessary.

What is "V-Jack" ????
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That's and excellent comment, maybe that's the reason they added the FET's(because its not enough current to light the led very bright) .
This is a typ c ,VBUS led detection , VBUS can be 5v,9v,15v,20v , V-Jack that's another voltage for the VCONN connection (that's for the active cable in PowerDelivery TYPE c circuit (its usually 5V) .
so they use that for those led as well.

BTW can you tell me what's the parameter in the Data sheet that told you this comparator sinks only 10mA ??
is it the IO max?

 

You could use an LM3914 LED bar graph display IC.

WOW I have looked on a lot of options (including zenner diodes , and other stuff ) , but this IC is by far the best option .
Thank you for telling me such an IC exist , I will defently use that kind of IC )
I have another 2 question regarding this IC :
1. it has a reference analog pin , but I have seen it being connected to a variable resistor , why ? is this variable resistor mandatory ?
2. LM3914 in none stock everywhere , do you know of another IC that is in stock ?

 

If Vjack is only 5V (per post #6) those blue LEDs must be extremely efficient, given that they each have a 249k series resistor! Something doesn't seem right.

 

WOW I have looked on a lot of options (including zenner diodes , and other stuff ) , but this IC is by far the best option .
Thank you for telling me such an IC exist , I will defently use that kind of IC )
I have another 2 question regarding this IC :
1. it has a reference analog pin , but I have seen it being connected to a variable resistor , why ? is this variable resistor mandatory ?
2. LM3914 in none stock everywhere , do you know of another IC that is in stock ?

Jameco in USA is showing stock.
https://www.jameco.com/z/LM3914N-1-...Dot-Bar-Display-Driver-10-Segment_300003.html

You can use a variable resistor to set the range at which the LEDs turn on.

 

I know LM3914s work over a range of voltages, but can they be set up to light their LEDs only on specific voltages?

I mean without additional circuitry.

IE: VBUS can be 5v,9v,15v,20v.

 

Jameco in USA is showing stock.
https://www.jameco.com/z/LM3914N-1-...Dot-Bar-Display-Driver-10-Segment_300003.html

You can use a variable resistor to set the range at which the LEDs turn on.

I am seeking for the none DIP package, can you that anywhere ?

 

If You don't mind creating an account with Texas Instruments,
You can order directly from them ........
This is the SMD part .........
https://www.ti.com/product/LM3914/part-details/LM3914V/NOPB
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I know LM3914s work over a range of voltages, but can they be set up to light their LEDs only on specific voltages?

I mean without additional circuitry.

IE: VBUS can be 5v,9v,15v,20v.

The LM3914 divides the voltage range between the two inputs into ten bands, and while the reference is adjustable the voltage interval is not.

 

If you divide down the input voltage of the LM3914 then the LEDs can light in sequence: 5V, 10V, 15V, 20V, 25V, 30V, 35V, 40V, 45V and 50V.
Use only 4 outputs if you want.

 

There are also P-DIP packaged arrays of 10-LEDs that make a great Bar-Graph-Meter.
https://www.digikey.com/en/products/detail/liteon/LTA-1000G/153278
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@lampel Do you intend to dim the LED's? As LED's exhibit a very exponential characteristic light curve.

 

The LM3914 allows setting all 10 LED Currents evenly with a single Resistor.
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