Full Wave Rectifier with Diode Bridge

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Starting a new thread to try to keep things cleaner.

Ok, I'll start drawing a circuit with a diode bridge. Then we will discuss it...

In the first screen I have just built a circuit to see the diode voltage drop.
We can see it by the difference existing between the peak of the Vin curve and the peak of the Vout curve...

Please, correct me if I'm wrong!
 

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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
What I'm doing next is to place a resistor between Vout and the ground and increase the resistor value...

I can see that the diode Vdrop decreases, meaning that the drop of 2*0.7 is changing to something like 2*0.66 or 2*0.62 or so.

Why does this happens?
 

THE_RB

Joined Feb 11, 2008
5,438
Have a look through the datasheet for the 1N4001 diode. (1N400x series).

There are some charts there that might give you an idea. :)
 

Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
I have this in standard.dio

Rich (BB code):
.MODEL 1N4001 D(IS=2.55E-9 RS=0.042 N=1.75 TT=5.76E-6 CJO=1.85E-11 VJ=0.75 M=0.333 BV=50 IBV=1E-5 )
So I think it's VJ=0.75 that should give me the Vdrop...
 

ericgibbs

Joined Jan 29, 2010
18,766
hi Psy,
Recall the earlier posts on the other thread of yours, when we LTS plotted the effect on the diode charging current when using different values of C1 smoothing capacitor.

E
 

ericgibbs

Joined Jan 29, 2010
18,766
I have this in standard.dio

Rich (BB code):
.MODEL 1N4001 D(IS=2.55E-9 RS=0.042 N=1.75 TT=5.76E-6 CJO=1.85E-11 VJ=0.75 M=0.333 BV=50 IBV=1E-5 )
So I think it's VJ=0.75 that should give me the Vdrop...
hi,
This is a clip from the 1N4001 datasheet, study the curve of I inst versus V forward diode drop.

What do you make the diode current to be at say Vfwd of 0.75V.???

EDIT:
Added a diode pdf for you to read.
 

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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
That graph looks like to have a logarithmic scale at Y-axis... So, I would say that until around 0.7V~0.8V the current goes up to 0.1A. Then in only 0.4V, the current goes up to 10A...

This is what we say to be the Vf, I guess... Is where the current as a considerable increase for a small amount of voltage!
 

ericgibbs

Joined Jan 29, 2010
18,766
Did you look back at the diode current plots in the other thread.?

As a rough guide we assume a Vfwd of 0.7V for a general purpose silicon rectifier.

This image shows the I/V curve for a silicon diode.

Whats the next step in your experiment.?
 

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Thread Starter

PsySc0rpi0n

Joined Mar 4, 2014
1,755
Yes, I know...

We also assume that value of 0.7V for silicon diodes, but the definition in standard.dio says vf=0.75. When we have a rectifier with a bridge of diodes, that will produce a 1.5V rather than 1.4V as we should have assuming 0.7V
 
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