Why is the output current of a boost switching regulator lower than the regulator\s rated current?
The current ratings for boost switching regulators like the LM2585 SIMPLE SWITCHER are for the peak switch current, not the output current. The switch current is dependent both on the output current and the amount of boost in voltage that is required in the design. So for designs which require a large increase in voltage, the switch current is much greater than the output current. Energy must be conserved by the following equation: Pout = Pin x Efficiency or Iin = (Vout x Iout)/(Vin x Efficiency) which is approximately = Iswitch For an example, let Vin=12V and Vout=48V at 0.5A. If we assume 85% efficiency, then the peak switch current rating will need to be at least: Iswitch = (48 * 0.5)/(12 * 0.85) = 2.4A (choose device with at least 3A rating) Higher load current or greater boosting ratios will require proportionally higher switch ratings. To determine appropriate solutions for your boost regulator design, use the online design tool WEBENCH Power Designer.
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