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Measuring DIACs (and other thyristors)[edit]

How can I measure the diac and thyristor?

The standard method is to use a curve tracer, a specific kind of electronic test equipment that looks like an oscilloscope but can apply a variable, bipolar voltage to the device under test and measures the resulting current. Curve tracers can also apply base (trigger) bias and display how that affects the resulting change in the V-I curves.
You can kludge up a minimalist curve tracer using an ordinary oscilloscope, an isolation transformer, and a load resistor.
Atlant 23:53, 8 August 2005 (UTC)

A DIAC is not "two Zeners"[edit]

I'm not a registered user, so I'm not going to edit the article, but I wanted to point out that this statement: "It is similar to two Shockley or Zener diodes connected in inverse parallel." is blatantly false. Zener diodes have a point where they become virtually straight lines on the VI curve, but lack the negative resistance zone that a DIAC has. A DIAC acts a lot more like a trigger tube - once the voltage reaches the "trigger" point, the effective voltage across it suddenly drops to a very low value, and current will flow appropriately. Only when the current falls off does the voltage drop go back up. —The preceding unsigned comment was added by (talkcontribs) .

Your point is correct. And you needn't feel shy about editing the article just because you haven't registered yet. But I'll make your suggested edits.
Atlant 16:39, 15 May 2006 (UTC)
Note that it says "similar", not the same. It's a metaphor for those more familiar with Zener diodes.
The Lightning Stalker (talk) 07:18, 11 May 2009 (UTC)

can u simplify the explanation??[edit]

i am a fresher and wanted ta kno abt diac... the explanation is quite hard to understand..—Preceding unsigned comment added by (talkcontribs)

a diac, its just a 2-way diode that will only conduct electricity (including AC, or oscillating current) when the breakdown voltage is exceeded. XU-engineer 18:49, 26 July 2007 (UTC)

The DB3 and BR100 are three layer NPN devices that do not latch. Please see I-V plot for DB3 —Preceding unsigned comment added by (talkcontribs)

There is also plot of correct V-A characteristics on commons, but description is in Slovakian: Image:Vachdiak.png -- 15:00, 16 October 2007 (UTC)

Let's say there's a capacitor you want to charge to a certain voltage and then dump the energy into something, lather, rinse, repeat. The DIAC/SIDAC can do that automatically for you. The capacitor charges to the breakover voltage and then it turns on like a switch and does some work. The Lightning Stalker (talk) 08:33, 11 May 2009 (UTC)


According to data sheets in the reference section this article contains several errors:

  • DIAC doesn't have holding current (no latching)
  • DIAC V-A diagram is wrong


  • trisil is not similar to DIAC
  • SIDAC is not electrically equivalent to DIAC

-- (talk) 07:39, 29 August 2008 (UTC)

SIDACs and DIACs are the same for all intents and purposes.
The Lightning Stalker (talk) 07:23, 11 May 2009 (UTC)

DIAC has same function as MOV.[edit]

The DIAC article makes no mention of MOV or surge supression. It appears from my investigation of 2 separate SMPS's (Switch Mode Power Supply) that a DIAC or Silicon Bilateral Voltage Triggered Switch is performing the same function to a MOV (Metal Oxide Varistor) or VDR (Voltage Dependant Resistor). In my case both power supplies have either two 150 Volt DIAC's or MOV's situated after the bridge rectifier, between the main DC filter capacitors from 0 volts and positive rail and 0 volts and negative rail. I don't have a login thus can't edit the article. Please add a 'See also' heading. —Preceding unsigned comment added by (talk) 07:54, 7 December 2008 (UTC)

You don't need to login to edit. Just go ahead and do it. —Preceding unsigned comment added by (talk) 17:03, 5 January 2009 (UTC)

A DIAC does not have the the same function as an MOV.

An MOV does not "switch" or go to a low impedance state upon reaching a threshold voltage. A MOV is like a SAD. The voltage across an MOV increases with increasing current passing like a SAD. However, an SAD is described to clamp voltage flatter than an MOV, the increase of voltage with an increase in current is greater for a MOV than a SAD. Simply, a DIAC has an "on state" voltage independent of the current when "on". —Preceding unsigned comment added by (talk) 21:45, 21 April 2009 (UTC)

Unfortunately, they do not function the same and are not interchangeable. I've tried using an MOV in place of a DIAC or SIDAC and they don't work because there is no sharp decrease in resistance. It gradually falls off toward the voltage rating. I don't believe they latch either. The resistance depends mostly on the voltage across it. —Preceding unsigned comment added by The Lightning Stalker (talkcontribs) 07:34, 11 May 2009 (UTC)

Silicon Bilateral Switch (SBS) and Silicon Unilateral Switch (SUS)[edit]

I see these terms for these components from time to time. Are they just another term for DIAC and SIDAC? The Dutch Wikipedia has an article describing them. The SBS characteristic are similar to the DIAC, but with a lower gate voltage trigger level. Perhaps these parts are obsolete. New stock is still easily found at distributors. At any rate, Silicon Bilateral Switch is found easily and often enough in English web sites that I think there should at least be a redirect from Silicon Bilateral Switch and Silicon Unilateral Switch to one of the thyristor articles. For device examples look up 2N4991 (SBS) and 2N4990 (SUS). --NoahSpurrier (talk) 19:32, 26 September 2014 (UTC)