# Boost energy & power flow (i/p to o/p)

Discussion in 'General Electronics Chat' started by reggiereggie, Jun 2, 2008.

1. ### reggiereggie Thread Starter New Member

Jun 1, 2008
2
0
Hi all,

I am trying to understand the flow of energy an d thus power through a boost converter. I understand how the circuit works, but am a little confused on some concepts proposed by A.Presmans book switching power supply design second edition.

(For those of you with the book its the equation 1.13 on page 26 that I am not sure about)

The books is describing the power throughput of a discontinuous boost converter with an input full wave rectified line voltage of Vdc,

The equation that I am struggling with its meaning is:

Pdc=Vdc.(Ip/2)(Tr/T)

Pdc= power delivered to load during off time
Vdc= input voltage
Ip= average inductor current over Tr which equals Ip/2 during Tr
Tr= time for current in inductor to decay from peak to zero (reset time)
Tr/T = the duty factor of reset time

What I am struggling with is what it means. I thought a boost converter filled op the inductor during the fet on time and emptied the inductor during the fet off time. This equation seems to supply energy from the input during the fet off time because of the Vdc terms inclusion in this equation.

Does this equation state Pdc = average input voltage during tr. Average current during tr ? As
1) Input voltage during tr = Vdc(Tr/T) ?
2) Ip/2 = average inductor current during tr?

I know the current through the inductor during the fet off time is the input current and the load and capacitor current combined but the Vdc term is confusing me.

Can someone please explain the energy and power transfer for a discontinuous boost converter from input to output in words.