# Step down voltage from power unit

#### circuitbuild72

Joined Oct 1, 2022
12
Hi all !

I’m new to this and am building a circuit board for a battery power pack. The output is 5V and I want to use it with both 5V & 3.2V lights. Is there a way to reduce the power output to 3.2v without adding another output which has a resistor (internal to the power pack) or adding a resistor into the 3.2v light (external to the power pack)?

#### ericgibbs

Joined Jan 29, 2010
18,835
hi c72,
Welcome to AAC.
How much current for the 5v and 3.2V do you need .?
E

#### circuitbuild72

Joined Oct 1, 2022
12
Thanks for the reply @ericgibbs !

I’m using some LEDs which draw 0.02 A at 5V and some which draw the same at 3.2 V

The power pack is 1A & 5V output.

As I understand it this means the 5V / 0.02A LED’s powered by 5V / 1A power pack meansI can run up to 50 LED’s at full brightness.

I’m looking at an resistor attached to the cable for the 3.2V LED’s to step down voltage. This is as far as I’ve got, I’m a little lost in terms of if that resistor is the right way to go and how many LED’s it would power!

#### ericgibbs

Joined Jan 29, 2010
18,835
hi c7,
Usually with LED's the current has to be controlled, typically by using a series resistor.
eg: say your LED is White, which has a typical forward voltage of 3.2v.

So from a 5Vdc supply, if you wanted 20mA through the LED, that would require that 5V-3.2V at 20mA be dropped across the resistor.
ie 1.8V/0.02A = 90 Ohms,, a 100 Ohm resistor be OK.

Note, each LED will require its own dropping resistor.

E

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#### circuitbuild72

Joined Oct 1, 2022
12
hi c72,
Welcome to AAC.
How much current for the 5v and 3.2V do you need .?
E
Thanks @ericgibbs very helpful. I can’t add resistor to each LED as I’m doing for off the shelf led strips and (long story!) can’t just replace with another type.
Is there no way to drop down the voltage to the entire set of these LED’s between the power and the LED’s?
Many thanks again

#### AlbertHall

Joined Jun 4, 2014
12,346
Which LEDs are you using (type or link)?

#### circuitbuild72

Joined Oct 1, 2022
12
Hi @AlbertHall I’m using 3.2v / 0.02A leds and 5V / 0.02A leds - I can use as many / few as I need to get full brightness.

#### circuitbuild72

Joined Oct 1, 2022
12

#### ericgibbs

Joined Jan 29, 2010
18,835
hi,
What colour and how many LED's on the 3.2V strip.?
E

#### circuitbuild72

Joined Oct 1, 2022
12

#### djsfantasi

Joined Apr 11, 2010
9,160

#### circuitbuild72

Joined Oct 1, 2022
12
@djsfantasi thanks - they are commercial so I’ll get this info and post when I do.

#### Danko

Joined Nov 22, 2017
1,834
Use this driver and get 20 mA for up to 10 white LEDs.
V_IN can be 3.2 V or 5 V, does not matter.

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#### circuitbuild72

Joined Oct 1, 2022
12

#### circuitbuild72

Joined Oct 1, 2022
12

#### Danko

Joined Nov 22, 2017
1,834

#### Papabravo

Joined Feb 24, 2006
21,225
No, I had, but now have not.
Maintaining a website has quantifiable economic and other costs. One needs a reason to bear those costs. I'd be curious to know how other people who do have websites manage those costs.

#### Danko

Joined Nov 22, 2017
1,834
Maintaining a website has quantifiable economic and other costs. One needs a reason to bear those costs. I'd be curious to know how other people who do have websites manage those costs.
My main reason was to keep resume published.
Cost: $17 per year. #### Papabravo Joined Feb 24, 2006 21,225 My main reason was to keep resume published. Cost:$17 per year.
That is actually pretty reasonable. I don't know if you have retired, but that would explain why it is no longer of use to have a place for that resume. I too have abandoned my website, my blog, and my LinkedIn account since I retired in 2014. I have less than zero interest in being contacted for those purposes ever again.