element14 Community
element14 Community
    Register Log In
  • Site
  • Search
  • Log In Register
  • Members
    Members
    • Benefits of Membership
    • Achievement Levels
    • Members Area
    • Personal Blogs
    • Feedback and Support
    • What's New on element14
  • Learn
    Learn
    • Learning Center
    • eBooks
    • STEM Academy
    • Webinars, Training and Events
    • Learning Groups
  • Technologies
    Technologies
    • 3D Printing
    • FPGA
    • Industrial Automation
    • Internet of Things
    • Power & Energy
    • Sensors
    • Technology Groups
  • Challenges & Projects
    Challenges & Projects
    • Design Challenges
    • element14 presents
    • Project14
    • Arduino Projects
    • Raspberry Pi Projects
    • Project Groups
  • Products
    Products
    • Arduino
    • Dev Tools
    • Manufacturers
    • Raspberry Pi
    • RoadTests & Reviews
    • Avnet Boards Community
    • Product Groups
  • Store
    Store
    • Visit Your Store
    • Choose Another Store
      • Europe
      •  Austria (German)
      •  Belgium (Dutch, French)
      •  Bulgaria (Bulgarian)
      •  Czech Republic (Czech)
      •  Denmark (Danish)
      •  Estonia (Estonian)
      •  Finland (Finnish)
      •  France (French)
      •  Germany (German)
      •  Hungary (Hungarian)
      •  Ireland
      •  Israel
      •  Italy (Italian)
      •  Latvia (Latvian)
      •  
      •  Lithuania (Lithuanian)
      •  Netherlands (Dutch)
      •  Norway (Norwegian)
      •  Poland (Polish)
      •  Portugal (Portuguese)
      •  Romania (Romanian)
      •  Russia (Russian)
      •  Slovakia (Slovak)
      •  Slovenia (Slovenian)
      •  Spain (Spanish)
      •  Sweden (Swedish)
      •  Switzerland(German, French)
      •  Turkey (Turkish)
      •  United Kingdom
      • Asia Pacific
      •  Australia
      •  China
      •  Hong Kong
      •  India
      •  Korea (Korean)
      •  Malaysia
      •  New Zealand
      •  Philippines
      •  Singapore
      •  Taiwan
      •  Thailand (Thai)
      • Americas
      •  Brazil (Portuguese)
      •  Canada
      •  Mexico (Spanish)
      •  United States
      Can't find the country/region you're looking for? Visit our export site or find a local distributor.
  • Translate
  • Profile
Personal Blogs
  • Members
  • More
Personal Blogs
Legacy Personal Blogs LED Speed: Experimenting With a One-Transistor Current Source
  • Blog
  • Documents
  • Mentions
  • Sub-Groups
  • Tags
  • More
  • Cancel
  • New
Blog Post Actions
  • Subscribe by email
  • More
  • Cancel
  • Share
  • Subscribe by email
  • More
  • Cancel
Group Actions
  • Group RSS
  • More
  • Cancel
Engagement
  • Author Author: jc2048
  • Date Created: 26 Sep 2020 10:09 PM Date Created
  • Views 517 views
  • Likes 4 likes
  • Comments 0 comments
  • transistor
  • current source
  • breadboard
  • led
  • analogue
  • uno
  • arduino
Related
Recommended

LED Speed: Experimenting With a One-Transistor Current Source

jc2048
jc2048
26 Sep 2020

This is a very quick item to get me going again and back into the habit of blogging.

 

When Jan Cumps showed us a one-transistor current source in Simple Electronic Control Systems - Current Control with 1 transistor ,

I used it to drive an LED (see the comments to that blog). The current switched pretty quickly and I wondered how it would compare

to driving a simple resistor: just how fast can an LED be? Simple way to find out was to try it, so here's a shoot-out between a blue LED

and a resistor. The resistor has a very fast response and what we see for that will be mostly how the current source is performing.

Comparing the LED to the resistor's response will then allow us to see what the LED does.

 

This is the circuit. I've built Jan's circuit twice, with both current sources controlled by the same voltage derived from a UNO GPIO pin,

one driving a blue Nichia LED and the other a 100 Ohm resistor. The UNO is acting as a very 'cheap and cheerful' pulse generator.

 

 

image

 

Here it is on my carefully rebranded breadboard (the sticker is almost straight!)

 

image

 

Now for some waveforms (I did mention that this was going to be quick, didn't I?)

 

This is the voltage at the transistor bases [yellow] trace and the resulting LED current [blue] trace.

 

image

 

In this case, I've told the 'scope that channel 2 is a 'current probe' and I've dialled in an 'attenuation' value such that the voltage

across the 100R resistor, in series with the LED, is presented as the equivalent current. I'm now switching between 1.5mA and 6mA.

It's not as stable as before, perhaps because of the two transistors and the fast signals on an unsuitable breadboard, but it will do.

 

Here I'm now looking at the LED [blue] and the resistor [yellow] as the current ramps up and there really isn't much in it.

 

image

 

Here's the drop, and again there's very little in it.

 

image

 

Most of the behaviour we're seeing is actually that of the current source, and the LED runs current almost as fast as a resistor

does. Not the most precise experiment ever, but indicative and fairly good for the resources I'm throwing at it.

 

If you found this interesting and would like to see other blogs I've written, a list can be found here: jc2048 Blog Index

  • Sign in to reply
element14 Community

element14 is the first online community specifically for engineers. Connect with your peers and get expert answers to your questions.

  • Members
  • Learn
  • Technologies
  • Challenges & Projects
  • Products
  • Store
  • About Us
  • Feedback & Support
  • FAQs
  • Terms of Use
  • Privacy Policy
  • Legal and Copyright Notices
  • Sitemap
  • Cookies

An Avnet Company © 2023 Premier Farnell Limited. All Rights Reserved.

Premier Farnell Ltd, registered in England and Wales (no 00876412), registered office: Farnell House, Forge Lane, Leeds LS12 2NE.

ICP 备案号 10220084.

Follow element14

  • Facebook
  • Twitter
  • linkedin
  • YouTube