Boost

Used for: Stepping a voltage up in value with high efficiency

Literature references

Pros:

  • Steps input up to any value
  • Simple circuit
  • Easy Low-side gate drive for main switch
  • Switch voltage limited to Vout + spike

Cons:

  • High output ripple - can be > output DC current so need large low ESR output caps
  • Step-up in voltage only
  • Inherently not-immune to short circuits
Boost

Basics:

  • SW1 and SW2 are alternately on and off at high frequency
  • SW1 and SW2 are never both on together
  • Vout = Vin/(1- D) where D is the switching duty cycle (0 -1)
  • Input ripple current is low, set by inductor L
  • Output ripple current is high and is sunk into C2
  • SW2 can be a diode - the action of SW1 turning off automatically forward biases the diode causing it to conduct. Action of SW1 turning on reverse biases the diode causing it to block current

CONTROL LOOP PARAMETERS

boost params

Vramp = amplitude of sawtooth ramp    

Ri = Rsense x Current gain eg. Rsense x 100 for 100:1 sense transformer
Optimum slope compensation assumed in each case
D = Duty cycle
f = operating frequency