i see. so i just consider 0V onwards as "on"? thanks, you've been so much of help.

now i'm left with only 2 doubts: i need to subtantiate why i'm not getting 6V and how i managed to calculate the reference voltage -8.57.

 

I just noticed a glitch in the forum software preventing your post appearing. If you notice this happen again post up a dummy post immediately after your first post and it will appear. Apologies for the digression.

Dave

 

Cherry,

A couple of things could have happened. First would be to confirm the input voltage and the output voltage under the specified load for that transformer. Then unload the transformer and see what the values are. That will tell if the light load of your circuit is influencing your readings.

You chose the neg 8.57 volt as your reference because it was the middle of your ripple levels. You could have choosen any voltage above the most positive portion of that ripple voltage, it depended on what duty cycle you were seeking.

On your simulation, change the reference and see what happens to the duty cycle ... maybe that will clear it up for you.

What is the model number of your transformer?

 

Cherry,

Attached is Tamura Corp's 3FL12 series transformers. Take notice of the electrical specifications. You will note up to a variance of 31% from no load to full load for this particular transformer. Your load on the transformer is light. I've seen a quote of +/- 2 volts from another manufacturer and even that will cause the 10 volts you see as within specifications. [6.3 x 1.414 = 8.9xxx].

The 10 volts on the secondary is only about 12% high for a 6.3V transformer. To find the specifications of your transformer, you'll need to look up that model number and get the manufacturer's specification.

 

http://www.allaboutcircuits.com/vol_2/chpt_9/index.html chapter 9 is the transformer chapter here.

http://www.allaboutcircuits.com/vol_2/chpt_9/6.html talks about voltage regulation when using transformers.