Problem with forward average current in a diode

[Lucifre]

I am trying to design a 1 Amp power supply, it is going to use center tapped transformer, i need to choose the diode with correct characteristics for a full wave rectifier. I have problem with Ifav or forward average current during conduction. The formula given in the book(microelectronic circuits by sedra and smith) is
Iav = Il(1+π(2vp/vr)^.5) or whatever its(i don't have the book in front of me) the problem with that is the current comes out to be ridiculously high like 17 amps or even more, now the diode with ifav of 17 amps would be about the size of my thumb and i can't have that, besides i don't think they make them. Maybe they are refering to different diode characteristic? or maybe they don't know practical information about diodes commonly used. the output of the fw rectifier is going to be filtered and regulated via voltage regulator.

 

[flatulent]

Re: Diode question

Select your diode with the manufacturer's data sheet. They will tell you the average and the peak current it will reliably pass.

 

[throwaway18]

Diode question

In practise 3amp diodes will be fine.

the diode with ifav of 17 amps would be about the size of my thumb and i can't have that, besides i don't think they make them

20amp rectifer diodes are a euro each in small quantitys from any electronic component supplier.

 

[IanP]

Re: Diode question

For centre tap configuration Idc=Iac (average) ..
Pretty common diode in these applications is 1N400X: 1N4002, 1N4003 .. with average rectified forward current of 1A (peak current of ≈50A) **broken link removed**
Regards,
IanP

 

[nandu_r]

Re: Diode question

This may happen when you forward bias the diode with a very high voltage .
Check your load(it should not take more than 1A, according to ur spec)
Use a series resistor to control current , (ofcource it will dissipate lot of power)

 

[Lucifre]

Re: Diode question

I finally have been enilighted....., the formula which i gave needs to be multiplied by percent of time that diode conducts. Now the results look reasonable compared to the data sheets. By the way sedra and smith didn't mention it in their third edition, ( i personally would not reccomend this book)