# Single Phase Controlled Rectifier with µcontroller

#### iceman11

Joined May 4, 2007
39
hey ppl, nice to see you all again.

i need help with the following design please...any hints, tip, ideas, schematics etc will be appreciated

"Desing and build a thyristor based controlled rectifier. AC supply 230:15V, 45VA transformer, DC supply controllable from 5v to 15v via 8 -bit serial command from a pc. up to 2A with overload /short circuit protection. Ripple no more than 0.25Vrms."

thanks in advance ppl. shout out to all who know me!!!

#### hgmjr

Joined Jan 28, 2005
9,029
If this is a classroom assignment then it would be best if you made the initial effort to put forward a circuit diagram of the design.

You can start with a sketch of the major circuit blocks that will be needed. Following that, you can start putting the components needed into each of these blocks to accomplish the finished design.

You should research your course material (e.g. textbook, course handouts, etc.) and "google" search the Internet to find examples of "thyristor based controlled rectifiers". This will get you started.

Once you have undergone this research and have a sketch of the circuit then post it here so that the members can comment.

Good Luck,
hgmjr

PS. Here is just one quick Link to a basic explanation of thyristor phase control. There are many others to be found on the Internet.

#### iceman11

Joined May 4, 2007
39
yo, thanks hgmjr.

i did some research on the net, and was wondering if you think it is better to do a fully controlled or semi controlled configuration??

i have also attached a diagram of what i think the setup should be like,
the microcontroller code to select the trigger angles for the thyristors to fire at is also confusing

thanks again hgmjr for all your never failing help

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#### hgmjr

Joined Jan 28, 2005
9,029
yo, thanks hgmjr.

i did some research on the net, and was wondering if you think it is better to do a fully controlled or semi controlled configuration??
Greetings iceman11,

I assume by your phrase "fully controlled or semi controlled configuration", you are referring to full-wave or half-wave rectification.

The design constraint of 0.25 volts of ripple max makes it most likely that full-wave rectification would give you the best shot at meeting that design goal particularly as you have to deliver an output power of 30 Watts (15V times 2A).
i have also attached a diagram of what i think the setup should be like,
the microcontroller code to select the trigger angles for the thyristors to fire at is also confusing
Maybe you could start by listing the functions that will need to be performed by the circuit to provide the microcontroller with the information it needs to carry out the phase angle control.

One function you will need is a zero crossing detector circuit. Another function you will need is an output voltage monitoring circuit that will provide the micro with a continuous reading of the output voltage. These are a couple of things to consider in your design.

How much detail are you required to provide in your design? Are you required to build and demonstrate that your design meets the specifications you have been given?

hgmjr

#### iceman11

Joined May 4, 2007
39
heya,
yea it is required that we demonstrate the design, and we will be marked on how well it meets the systems requirements.

our prof also told us that we should use optically coupled transistors etc?

i think the difficult thing would actually be writing the controller code, and also he was very vague about what the serial communication will be used for - i was thinknig that maybe the user would give a desired av.voltage o/p to the pc....maybe thats what he meant?

i have completed the Multisim simulation model....i wonder if you would prefer to see the schematics or must i attach the actual file so you can run the simulation or your pc??

thanks again, hgmjr!!!

#### hgmjr

Joined Jan 28, 2005
9,029
A pdf formatted file of the schematic should be sufficient.

hgmjr

#### iceman11

Joined May 4, 2007
39
hey,

i have attached a schematic of the circuit we plan to use. the resistor and cap values are not the final ones we plan on using. we used them just for simulation purposes.

do you know of any method to calculate the resistor and cap values that we are supposed to use here??

also, i have no idea how to simulate using the SCR's. since we have to send in a gate pulse for the thing to work, i decided to use a function gen. however how do i connect the gate terminals to the function gen??

the attachments are also here, PS i dont have PDF creator..so i saved as .GIF and .doc formats

thanks a lot hgmjr....

Best Regards,

iceman11
3rd year electrical engineering
University of KwaZulu-Natal
South Africa

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#### hgmjr

Joined Jan 28, 2005
9,029
You have the very basic design for the AC to DC full-wave bridge composed of the thyristors. That's a good start.

In the schematic, do you have a purpose in mind for R2 (56R)? Since the design is required to deliver 2 Amps, this resistor will be a problem in the final design if it is allowed to be in series with the load.

How do you think your instructor expected you to use the optically coupled transistors?

When do you need to have the design completed and ready to build up for the demonstration?

hgmjr

#### iceman11

Joined May 4, 2007
39
How do you think your instructor expected you to use the optically coupled transistors?

When do you need to have the design completed and ready to build up for the demonstration?

hgmjr
well, the opto coupled trans are for the zero crossing detector..we managed to get his working i.e producing a continuous square wave.

PCB submission is due on wednesday so the schematic has to be compelted and working in multisim b4 then.

do you have any ideas on how to effectivley calc the Resistors, and cap vals??? so as to adhere to systems specs?

are the SCR's connected to the func gen correctly??

best regards

#### hgmjr

Joined Jan 28, 2005
9,029
Sounds like you have a basic understanding of what is needed. I too would have used the opto-coupled transistors as the basis for the zero-crosing detection.

Sorry to be so negative but unless you plan to work from now until the time to turn in the assignment I don't hold out much hope for you complete the assignment by this Wednesday.

Good Luck,
hgmjr