Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Working with the MCR100-8 thyristor

Working with the MCR100-8 thyristor

Working with the MCR100-8 thyristor

I'm trying to make a phase control-like dimmer with this thyristor (I've attached a schematic candidate)

Maybe I'm reading the datasheet* wrongly, but I see many hard-to-swallow values, like 0.8V for the MAXIMUM gate voltage, and 300uA (MICRO AMPERES) for the current

To achieve a low output voltage (my intention) I need to trigger this SCR on the very beginning of the pulse. Not before, not after

First, I thought of putting a DIAC on the gate, but 30V of breaking voltage is apparently an insane value.

A ZENER is now the option, but the lowest existing is 3V3, which is still above the MAX voltage

It is my understanding that one of these components IS necessary to prevent misfire by noise, but apparently the gate doesn't like it

Could someone help me on this ?



RE: Working with the MCR100-8 thyristor

0.8V is the max voltage (of any randomly-chosen part) necessary... to turn on the gate.

Dan - Owner

RE: Working with the MCR100-8 thyristor

Let me see if I got it: more than 0.8 will work, but is unnecessary. Is that correct ?

So, question two: where do I see the maximun allowed/tolerable gate current and voltage, then ?

RE: Working with the MCR100-8 thyristor


Randomly pick a part out of the parts bin. Part 'A' may turn on with any voltage higher than 0.5V, part 'V' may not turn on until you've applied at least 0.7V, etc. The spec says all parts in the bin are guaranteed to be "on" when you've applied 0.8V or more, but some parts may require less.

The spec does not say applying a gate voltage higher than 0.8V is wrong. But perhaps the issue is you're looking at this at a voltage-controlled device, whereas the proper view is as a current-controlled device.

The gate requires a minimum current to turn the device on... once you hit that minimum current, the device is on and the voltage at the gate is merely a by-product of the resistance in the gate to that current. Think of it like you're powering an LED... give it the current it wants and the voltage across the LED sets itself.

Dan - Owner

RE: Working with the MCR100-8 thyristor

Datasheet 101:

In datasheets you'll always see several sections.

One is "Maximum Ratings". This part lists which currents/voltages/temperature/power etc. you should not exceed, as it will damage the device.

The other parts define the electrical performance of the part, for instance under what conditions the SCR will turn on. In this case: at a gate current larger than 200 microamps and at a gate voltage larger than 0.8 V, the SCR is guaranteed to turn on.

On the other hand, "Maximum Ratings" also tells you that average gate power should be no higher than 10 mW.

Right, take it from there. It's a simple calculation.



RE: Working with the MCR100-8 thyristor

Thank you both for the attention and the very comprehensive answers

That's all that I needed

Observation.: I tought leds had no resistance, therefore appliying current would not build any voltage

Thank you both again

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close