Hello. I am designing a fully controllable rectifier bridge using 4 SCR Thyristors. I use an Arduino Nano to detect Zero Crossing and provide the ability to the user to select the firing angle. The user can select the firing angle via a rotary encoder and a small 16x2 lcd displays that current angle. The code is fully tested and I manage to get smooth triggering from 3 to 175 degrees (tested with my oscilloscope). And now comes my problem. I am trying to build the triggering circuit using MOC3021 as opto-isolator.
In the schematic I have omitted the rest of the MOC3021. +5V is a logic HIGH from Arduino. I think I understand how to trigger Thyristor 1 and 2 (marked D1, D2) but when it comes to D3 and D4 I can't realise how to connect the opto isolator since I can't understand the potential difference. Is it right to say that almost all voltage will be dropped on the load (connected between TP1 and TP2) except for that small voltage drop on the Thyristor when it's on? If so, should I use a resistor like R2?

Thanks in advance.

 

hi tk,
Why do you think it is necessary to phase control the two upper SCR's.?

Analyse the two possible current paths thru the bridge and you should be able show that only the two lower SCR's are required, the upper two could be regular diodes.

E

 

hi tk,
Why do you think it is necessary to phase control the two upper SCR's.?

Analyse the two possible current paths thru the bridge and you should be able show that only the two lower SCR's are required, the upper two could be regular diodes.

E

Hey there ericgibbs, thanks for your answer. That is an option but that would not be a fully controllable rectifier bridge.

I think I found my answer, I will try tonight to simulate it on my breadboard and write back.

 

That is an option but that would not be a fully controllable rectifier bridge.

It would fully control the output from the rectifier.

 

I agree with Eric and Albert.
It's completely redundant to control more than two SCR's.

 

There are many applications where 4 quadrant is used instead of 2 quadrant, drive manufacturers use 4 quadrant for reversing and dynamic braking.
Max.

 

A four quadrant bridge rectifier?

 

A four quadrant bridge rectifier?

The original servo drive, but mostly 3ph SCR bridge.

KB Drive
The KBMG Series of DC Drives are rated for 1/100 to 2 horsepower motors.* This chassis ultra-compact, full-wave regenerative drive is capable of operating DC PM or Shunt motors in a bidirectional mode. Its 4-quadrant operation provides forward and reverse torque in both speed directions. A 5k ohm potentiometer is included.
Max.

 

hi tk,
This LTSpice shows your circuit operating as a full bridge rectifier.
I have chosen values to suit the sim, you should compute your own circuit values.

E

EDIT:
Sim now corrected;

 

hi tk,
This LTSpice shows your circuit operating as a full bridge rectifier.
I have chosen values to suit the sim, you should compute your own circuit values.

E

Thanks to everyone for answering.
Extra thanks Eric for your trouble, I will simulate it on my breadboard. Unfortunately Weekends are full because of my regular job, so I think I 'll give a try at Monday.