Calculating Voltage Ripple in a Full Wave Rectifier Circuit

[foobag]

http://img683.imageshack.us/img683/5329/unledtw.png

So its basically a power supply with a voltage regulator LM317T at the end.

The question asked to find the voltage ripple across the capacitor.

So I basically solved the peak voltage found which would be 12V * SQRT(2) = 17 volts.

and because of the diode bridge rectifier, 1.5 volt would be lost, so like 15.5 volts would go across the capacitor and eventually the LM317.

Now my question is how do I solve for the voltage ripple. I understand since this is a full wave rectifier, I should use 120 Hz instead of the 60Hz.

I found an equation as Vr = I / (2fC), where I is the current going into the capacitor? and another equation Vr = Vp / (R_load * C), where Vp is the peak voltage.

Could someone help me out and guide me through the problem?

 

[berkeman]

http://img683.imageshack.us/img683/5329/unledtw.png

So its basically a power supply with a voltage regulator LM317T at the end.

The question asked to find the voltage ripple across the capacitor.

So I basically solved the peak voltage found which would be 12V * SQRT(2) = 17 volts.

and because of the diode bridge rectifier, 1.5 volt would be lost, so like 15.5 volts would go across the capacitor and eventually the LM317.

Now my question is how do I solve for the voltage ripple. I understand since this is a full wave rectifier, I should use 120 Hz instead of the 60Hz.

I found an equation as Vr = I / (2fC), where I is the current going into the capacitor? and another equation Vr = Vp / (R_load * C), where Vp is the peak voltage.

Could someone help me out and guide me through the problem?

The higher the output current demand, the more droop you will get in the capacitor storage voltage each 120Hz cycle. Start with a sketch like the following, and figure out the voltages and currents. There will be no current into the capacitor from the rectifier when the cap voltage is higher than the input voltage (and account for the diode drop in there too).

http://macao.communications.museum/images/exhibits/2_16_0_12_eng.png

.

 

[foobag]

well so were my equations to solve for ripple close?

my understanding is I need to find the current running through the capacitor am I correct?