THE STEP-UP SWITCHING REGULATOR

Figure 18 shows the basic circuit for a step-up switching

regulator. In this circuit Q1 is used as a switch to alternately

apply V

and energy is drawn from V

biased and I

Q1 opens, t

where D1 turns ON. The output current is now supplied

through L1, D1 to the load and any charge lost from C

o

during t

regulator, the current through L1 has a DC component plus

some

∆I

∆I

I

ON and OFF times.

Since

∆I

∆I

and neglecting V

The above equation shows the relationship between V

and duty cycle.

In calculating input current I

tor’s DC current, assume first 100% efficiency:

for

η = 100%, P

00865023

FIGURE 18. Basic Step-Up Switching Regulator

00865024

FIGURE 19. Relation of Switch Timing to Inductor Current in Step-Up Regulator

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