Working with the MCR100-8 thyristor 3

[LucasBS]

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 ?


*Datasheet:

http://www.onsemi.com/pub_link/Collateral/MCR100-D.PDF

Schematic:

 

[MacGyverS2000]

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

Dan - Owner

http://www.Hi-TecDesigns.com

 

[LucasBS]

Good.
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 ?

 

[MacGyverS2000]

Incorrect.

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

http://www.Hi-TecDesigns.com

 

[benta]

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.

Cheers,

Benta.

 

[LucasBS]

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

 

[MacGyverS2000]

EVERYTHING has resistance, even superconductors...

Dan - Owner

http://www.Hi-TecDesigns.com