Triac 101 - Page 1
Forum section: electronics / projects

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 09, 2023, 06:51:00 pm
content: I've never done this before.... I have a door bell solenoid... ok... four of them that I wish to turn on and off using a ESP32Literally years ago I came up with a little circuit...But now it's come to the time to populate the board and I'm no longer convinced!This is a one off and I've never used a Triac before so I am a bit worried.Does this look reasonable? AC voltage is 12V and control voltage is 3V3

author: Benta
author_rank: Super Contributor
timestamp: July 09, 2023, 06:59:49 pm
content: LED current is too low.MOC3021: 15 mAMOC3022: 10 mAMOC3023: 5 mAWhat's the purpose of R4?R3 looks low (depends on the triac).

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 10, 2023, 08:46:19 am
content: TBH I'm not sure where I got this from but it is currently baked into the PCB.I think R4 is to keep it stable off when the opto isn't active?For the LED side... 15mA is max for a MOC3021... I think typical is 8mA is typical but maybe R1 is a bit high.Does it matter which side the LOAD is applied?

author: Benta
author_rank: Super Contributor
timestamp: July 10, 2023, 11:07:47 am
content: R4 is unnecessary and will probably impair performance.I don't do designs using typical values, that's looking for trouble. But right now the LED is getting 6.5 mA.Load can be applied both sides.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 10, 2023, 08:07:56 pm
content: Quote from: Benta on July 10, 2023, 11:07:47 amNot quite.Wiki says thisBecause turn-ons are caused by internal capacitive currents flowing into the gate as a consequence of a high dv/dt, (i.e., rapid voltage change) a gate resistor or capacitor (or both in parallel) may be connected between the gate and MT1 to provide a low-impedance path to MT1 and further prevent false triggering. This, however, increases the required trigger current or adds latency due to capacitor charging. On the other hand, a resistor between the gate and MT1 helps draw leakage currents out of the device, thus improving the performance of the TRIAC at high temperature, where the maximum allowed dv/dt is lower. Values of resistors less than 1kΩ and capacitors of 100nF are generally suitable for this purpose, although the fine-tuning should be done on the particular device model.Renesas says thisFor high-sensitivity and low-current thyristors, it is generally recommended to insert a resistor of 1 kΩ between the gate and the cathode.

author: RoV
author_rank: Regular Contributor
timestamp: July 10, 2023, 08:20:38 pm
content: I would put a small snubber in parallel with the load, to limit dV/dt. 100 nF class X2 in series with 100 ohm are sufficient, because low energy is expected (the triac opens close to zero current).

author: Benta
author_rank: Super Contributor
timestamp: July 10, 2023, 10:09:20 pm
content: Quote from: PCB.Wiz on July 10, 2023, 08:07:56 pmWell, the Z0103 is hardly high-sensitivity. And there's a certain difference between 300 and 1k.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 10, 2023, 10:58:09 pm
content: Quote from: Benta on July 10, 2023, 10:09:20 pmThe supplier claims differentlyZ0103MN0Planar passivated very sensitive gate four quadrant triac• Very sensitive gate in four quadrantsGate trigger is 200uA~3mA

author: Benta
author_rank: Super Contributor
timestamp: July 10, 2023, 11:08:27 pm
content: Well, you're (as always) right. Feel better?

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 11, 2023, 12:33:11 am
content: Quote from: Benta on July 10, 2023, 11:08:27 pmMany people read these forums, over a long time, so it helps to have accurate information.

author: bostonman
author_rank: Super Contributor
timestamp: July 12, 2023, 02:28:59 am
content: FYI, this month (or issue) of Nuts and Volts has a multi part series on TRIACs.