Switching Power Supplies A - Z

Chapter 2

time

time

B

PK

B

PP

B

PK

B

AC

B

DC

I

PP

I

PK

B

DC

I

DC

B

DC

I

PK

I

DC

B

AC

I

AC

∆B

∆B

NA

L

I

B

NA

L

=

====≡

Current

∆I

∆I

B

I

B-field

B ∝ I

Proportionality Constant is:

NA

L

(symbolically)

Figure 2-13: B and I Can Be Usually Considered to Be

Proportional to Each Other

their average values, their ac values, their dc values, and so on. The constant of

proportionality is equal to

L

NA

(Proportionality constant linking B and I)

where N is the number of turns and A the actual geometrical cross-sectional area of the core

(its center limb usually, or simply the ‘effective area’ A

e

given in the datasheet of the core).

Worked Example (5) — When Not to Increase the Number of Turns

Note that the voltage-independent ...