Author Topic: DIAC in a pinch replacement  (Read 8074 times)

0 Members and 1 Guest are viewing this topic.

Offline Waifian

  • Regular Contributor
  • *
  • Posts: 50
DIAC in a pinch replacement
« on: December 16, 2010, 10:21:57 pm »
Would anyone see a problem with replacing a DIAC rated at 30 volts with two Zener diodes back to back with the same rating or close to it? They should respond about the same I would guess, aside from the extra forward voltage drop.

This for an in a pinch repair of a CFL circuit.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 13824
  • Country: gb
  • 0999
Re: DIAC in a pinch replacement
« Reply #1 on: December 16, 2010, 10:25:19 pm »
No a zener diode is not the same as a DIAC.

A zener maintains a similar voltage across it as the current is varied. A DIAC behaves like a spark gap, once the firing voltage is exceeded, it conducts until the current drops below a certain level. A DIAC can be used to make a relaxation oscillator, a zener can't.
 

Offline mikeselectricstuff

  • Super Contributor
  • ***
  • Posts: 12105
  • Country: gb
    • Mike's Electric Stuff
Re: DIAC in a pinch replacement
« Reply #2 on: December 16, 2010, 11:14:51 pm »
pair of zeners plus a triac is probably closer.
Youtube channel:Taking wierd stuff apart. Very apart.
Mike's Electric Stuff: High voltage, vintage electronics etc.
Day Job: Mostly LEDs
 

Offline Waifian

  • Regular Contributor
  • *
  • Posts: 50
Re: DIAC in a pinch replacement
« Reply #3 on: December 16, 2010, 11:41:34 pm »
I see. I thought there may be a problem. Thanks for the quick response.
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 5951
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: DIAC in a pinch replacement
« Reply #4 on: December 17, 2010, 05:22:54 am »
If the diac is used in the startup circuit, you might be able to use small bipolar transistors instead. Connect the emitter to the more positive side, the collector to the more negative side, and do not connect the base. 2 or 3 of those in series would get you pretty close to the 30v level. Not sure how many cycles it would work for but I have made a pulse generator using that principle and it has worked fine over a few hours at a repetition rate of about 80Hz, so it should last the life of the bulb given it's only used once every startup.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline Zero999

  • Super Contributor
  • ***
  • Posts: 13824
  • Country: gb
  • 0999
Re: DIAC in a pinch replacement
« Reply #5 on: December 17, 2010, 08:08:05 pm »
pair of zeners plus a triac is probably closer.
The LM431 plus a bridge rectifier and a TRIAC will give an adjustable firing voltage from 3.7V to 37.2V, more complicated but more flexible.

Surely it's cheaper to just get a suitable DIAC though?

Is it a dimmable CFL ballast? DIACs are normally used to ensure the TRIAC fires reliably and symmetrically.
 

Offline Waifian

  • Regular Contributor
  • *
  • Posts: 50
Re: DIAC in a pinch replacement
« Reply #6 on: December 18, 2010, 02:19:06 pm »
I just ordered one. Cheap plus shipping. I was in the hopes of making something that would respond the same with parts I could find around. I appreciate the input.
I have never worked with diacs before so I ordered some extras to play around with them.

Also as a side note I can see a reason why Dave hates cats. They are always messing with what you are working on. Stealing parts to play with knocking things over when you aren't looking. That may be it's way of trying to help haha.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf