---
# System prepended metadata

title: LED
tags: [ee, ' ee-part']

---

---
tags: ee, ee-part
title: LED
---
# `ee-led` LED

- drive with $330\Omega$ resistor to limit current
- an LED is a current-driven device: *think in current*  
  "Apply 2.2V constant-voltage to an LED, random result. Apply 20mA constant-current, predictable result." [:link:](https://electronics.stackexchange.com/q/339458)
- design for $I_F = 10 mA$ (?)  
  for higher temperatures the maximum $I_F$ drops rapidly!
  ![](https://i.imgur.com/Yx9Am5C.png =x200)
- "do not put a (low impedance) voltage source directly across a nonlinear element (such as an LED)!" 3:55
  {%youtube qqBU8-f8h2s %}


![](https://i.imgur.com/4eselT3.png)


### forward voltage drop $V_{F}$
- test condition (in datasheet) usually for $I_F = 20mA$
- can have a wide variation (e.g., +/-10%)  
![](https://i.imgur.com/eRDdman.png =x100)


![](https://i.imgur.com/pGiTqIh.png)

#### Elegoo LEDs
| color    | $V_F$ @ 20mA |  |
| -------- | --------  | -------- |
| red      | 2.10-2.18 |      |
| yellow   | 2.18-2.22 | kinda dimm |
| white    | 3.00-3.06 |      |
| blue     | 3.05-3.14 |      |
| green    | 3.18-3.24 |      |

(Values at room termperature. Vf drops slightly if LED warms up.)

### resistance $r$
$r = \frac{\Delta x}{\Delta y} = \frac{\Delta V}{\Delta I}$

Elegoo red LED:
- 2.01V @ 10mA
- 2.11V @ 20mA
- 2.19V @ 30mA

$r_1 = 0.1V/10mA = 0.1/0.01 = 10 \Omega$
$r_2 = 0.08V/10mA = 0.08/0.01 = 8 \Omega$

### equivalent circuit

![image alt](http://lednique.com/wp/wp-content/uploads/2017/11/LED-resistance-model.png =x300)  ![](http://lednique.com/wp/wp-content/uploads/2017/11/LED-equivalent-circuit.png)

### testing

## high-power LEDs for lighting

### testing with zener as dummy load
Zener 1N5334B [:link:](https://www.onsemi.com/pdf/datasheet/1n5333b-d.pdf)
- 3.6V @ 350mA
- 5W
- 2.5 $\Omega$ dynamic impedance (vs. ~1 $\Omega$ of LED)


### lamp
https://www.instructables.com/3-Watt-LED-Pail-Lamp/  
![](https://i.imgur.com/u5smpxI.png =x200)
- 3 1W-LEDs in series
- wall-wart + current-regualtor circuit = constant-current source
    - "White LEDs have a forward voltage of about 3.5V. For three LEDs, the forward voltage would be 10.5V, and the power supply should be 12V. If you are using old transformers, a 9V transformer may give you 12V when the current is low."

### simple constant-current circuit
original: https://www.instructables.com/Power-LED-s---simplest-light-with-constant-current/  
"redo": https://www.instructables.com/Simple-Power-LED-Constant-Current-Power-Supply-Dri/  
![](https://i.imgur.com/y1eTwXV.png =x200)
- R1: approximately 100k-ohm resistor (such as: Yageo CFR-25JB series)
- R3: current set resistor - see below
- Q1: small NPN transistor (such as: Fairchild 2N5088BU)
- Q2: large N-channel FET (such as: Fairchild FQP50N06L)
- wall-wart as power source

![](https://i.imgur.com/dbv6chs.png)  
https://www.circuitlab.com/circuit/wd55xkp5r42x/prj-led-cc_driver/

### resources

https://curiouscultivations.com/2020/03/31/match-an-led-to-a-driver/

https://electronics.stackexchange.com/questions/339458/led-forward-voltage-is-a-range-so-how-do-you-calculate-resistor-value
