Answers.Body: <p>My speed regulator is clearly labeled as being 9-12V AC. I have an official 12VAC transformer.</p>
  
  <p><img src="https://i.sstatic.net/xUBe9.jpg" alt="controller back"></p>
  
  <p>I was curious about the internals of this device, so I opened it up:</p>
  
  <p><img src="https://i.sstatic.net/os9st.jpg" alt="pcb top"></p>
  
  <p><img src="https://i.sstatic.net/0ga88.jpg" alt="pcb bottom"></p>
  
  <p>The circuit begins with 4 diodes in standard <a href="https://en.wikipedia.org/wiki/Bridge_rectifier" rel="nofollow noreferrer">bridge rectifier</a> configuration. This converts the AC input into a rippled DC voltage. The large capacitor (2200uF, 25V) then cleans up the ripples. There is also an <a href="https://en.wikipedia.org/wiki/LM317" rel="nofollow noreferrer">LM317</a> adjustable voltage regulator configured to output various voltages depending on the dial setting.</p>
  
  <p>This means that the input can be 9-12 voltes AC or DC because the rectifier simply passes DC current.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2014-02-24T15:13:32.260Z
Answers.LastActivityDate: 2014-03-04T21:05:22.433Z
Answers.LastEditDate: 2014-03-04T21:05:22.433Z
Answers.UserDisplayName: jncraton
Body: <p>I wanted to buy a transformer for the <a href="http://www.bricklink.com/catalogItem.asp?P=2868b" rel="nofollow">speed regulator</a>, so based on <a href="http://www.bricklink.com/catalogItemPic.asp?P=70931" rel="nofollow">this image</a>, I bought a transformer with 12V DC output. It works.</p>
  
  <p>However, discussing this with a fellow AFOL, he pointed out that his (original from LEGO) transformer has a 10V AC output, as seen in <a href="http://brickowl.com/catalog/lego-transformer-for-9-volt-products-with-120-volt-input-45541" rel="nofollow">this image</a>.</p>
  
  <p>So... which one is correct? Or they both work? Or there are different versions of the speed regulator with different input requirements?</p>
  
Tags: <power-functions><electronics><9v>
Title: What is the correct input voltage for the 9v Lego train speed regulator?
UserDisplayName: Conrado
ThreadText: # What is the correct input voltage for the 9v Lego train speed regulator?
  
  (Asked by: username_0 on 2014-02-24)
  
  I wanted to buy a transformer for the [speed regulator](http://www.bricklink.com/catalogItem.asp?P=2868b), so based on [this image](http://www.bricklink.com/catalogItemPic.asp?P=70931), I bought a transformer with 12V DC output. It works.
  
  However, discussing this with a fellow AFOL, he pointed out that his (original from LEGO) transformer has a 10V AC output, as seen in [this image](http://brickowl.com/catalog/lego-transformer-for-9-volt-products-with-120-volt-input-45541).
  
  So... which one is correct? Or they both work? Or there are different versions of the speed regulator with different input requirements?
  
  **Tags:** power-functions, electronics, 9v
  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_1 on 2014-02-24. Score: 3 | Accepted answer
  
  My speed regulator is clearly labeled as being 9-12V AC. I have an official 12VAC transformer.
  
  ![controller back](https://i.sstatic.net/xUBe9.jpg)
  
  I was curious about the internals of this device, so I opened it up:
  
  ![pcb top](https://i.sstatic.net/os9st.jpg)
  
  ![pcb bottom](https://i.sstatic.net/0ga88.jpg)
  
  The circuit begins with 4 diodes in standard [bridge rectifier](https://en.wikipedia.org/wiki/Bridge_rectifier) configuration. This converts the AC input into a rippled DC voltage. The large capacitor (2200uF, 25V) then cleans up the ripples. There is also an [LM317](https://en.wikipedia.org/wiki/LM317) adjustable voltage regulator configured to output various voltages depending on the dial setting.
  
  This means that the input can be 9-12 voltes AC or DC because the rectifier simply passes DC current.
  
  
  ---
  
  