Triggering TRIAC via DC

When energized, the optocoupler output is shorting the gate to MT1. This holds the TRIAC in the off state.

See page 3 of this datasheet for the correct connections:



ak

Where is the DC supply for U2’s photo transistor side?
Don’t tell me it is V2. That supplies the LED side only.
The circuit as drawn will always be off.

schmitt trigger ok, as I see there is not connection for the transistor base, It looks really strange.

But event if completelly remove triggering from the base it still continue to producing the current acroos R2.

Have you seen the scale? It is microamps.
Leakage currents.

anso-engineer said:

Hello, I am trying to simulate TRIAC and see strange results. So here is my questions:
1. Why I got on R2 node current as sinusoidal during the whole simulation time?
2. Why I have those values? drive zone online vs carx street

View attachment 148800

Click to expand...

Hello! It sounds like your TRIAC simulation might be conducting continuously or triggering unexpectedly. Could you check your gate trigger conditions and confirm the TRIAC’s holding current behavior in your setup?

Triacs leak from output capacitance and Early effects

Using DC to trigger a TRIAC requires careful gate control to avoid latching issues. A microcontroller like the advertising link removed - moderator known for its precise control capabilities, could help in designing a reliable triggering circuit for better efficiency.

WestonTate said:

Using DC to trigger a TRIAC requires careful gate control to avoid latching issues. A microcontroller like the MCF52223CAF80, known for its precise control capabilities, could help in designing a reliable triggering circuit for better efficiency.

Click to expand...

What particular "precise control capabilities" about that microcontroller make it better for this task than a generic microcontroller?

updated

WestonTate said:

A microcontroller like the MCF52223CAF80,

Click to expand...

32 bit processor
80 MHz clock
128 K program storage
32 K data storage
6 serial I/O protocols
17 (estimated) internal peripherals
144 pin package
*** NO complete datasheet ***

1. The thread question is about simulation results using Linear Tech SPICE. Please post a link to an LTS model for this part.

2. Exactly how much overkill does it take to turn on a light bulb?

ak

AnalogKid said:

32 bit processor
80 MHz clock
128 K program storage
32 K data storage
6 serial I/O protocols
17 (estimated) internal peripherals
144 pin package
*** NO complete datasheet ***

1. The thread question is about simulation results using Linear Tech SPICE. Please post a link to an LTS model for this part.

2. Exactly how much overkill does it take to turn on a light bulb

Click to expand...

Considering he's a new member, and only made one dubious post including an advertising link, he's looking rather like a spammer - so I've removed the link.

It seems your Triac demo has failed with 0.4 mA leakage current at 5 Hz sine wave ( every 200 ms).

This is exactly what you may expect with from your voltage source using 220V peak (not rms) 5 Hz.



Look at other examples in LTspice or ask your favorite AI search engine for clues where/how to use LTspice. I prefer https://x.com/i/grok to LTspice's internal help link.

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from Grok3
I can’t directly show you an LTspice simulation since I can’t generate or display images, simulations, or GUIs like LTspice itself. However, I can guide you step-by-step to create a TRIAC demo in LTspice yourself! Here’s a simple setup to demonstrate a TRIAC in action, controlling an AC load:

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TRIAC Demo in LTspice: Step-by-Step Guide
What You’ll Simulate

• A TRIAC switching an AC load (e.g., a lamp or resistor) with a basic gate trigger circuit.
• This will show how the TRIAC conducts in both halves of an AC cycle when triggered.

Steps to Build the Circuit

1. Open LTspice:
   • Launch LTspice on your computer (download it from the official site if you don’t have it).
2. Place Components:
   • TRIAC: LTspice doesn’t have a built-in TRIAC model, but you can approximate it using a generic TRIAC model from a library or define one. For simplicity, we’ll use a substitute approach later if needed.
     • Go to Component (shortcut: F2), search for “TRIAC” or use a specific model like Q6015L5 if you’ve added a TRIAC library. If unavailable, we’ll model it with switches or a SPICE directive.
   • AC Voltage Source: Add a voltage source (sine wave for AC).
   • Resistor (Load): Add a resistor (e.g., 100 ohms) as the load.
   • Gate Trigger Circuit: Add a pulse voltage source (for triggering) and a resistor (e.g., 1k ohm) to the gate.
3. Wire the Circuit:
   • Connect the AC source (e.g., 120V RMS, 60 Hz) in series with the load resistor and the TRIAC’s main terminals (MT1 and MT2).
   • Connect the gate trigger pulse source (e.g., 5V pulse) through the gate resistor to the TRIAC’s gate and MT1.
4. Set Up the TRIAC Model (if needed):
   • If you don’t have a TRIAC component, you can use this basic SPICE subcircuit for a generic TRIAC: