Switched Mode Power Supply Having Variable Minimum Switching Frequency

Abstract

In a switched mode power supply (SMPS) that regulates an output voltage in response to load conditions by switching an inductor circuit between a supply voltage and ground at a switching frequency, under light loading conditions, the switching frequency of the SMPS is reduced down to a variable minimum switching frequency sufficiently high to avoid audible noise generation.

1 . A method of operating a switched mode power supply, comprising:
 regulating an output voltage in response to load conditions by switching an inductor circuit between a supply voltage and ground at a switching frequency;   under light loading conditions, reducing the switching frequency down to a variable minimum switching frequency sufficiently high to avoid audible noise generation.   
   
   
       2 . The method of  claim 1  further comprising tuning the minimum switching frequency for each application in which the switched mode power supply is deployed. 
   
   
       3 . The method of  claim 1  wherein the variable minimum switching frequency is established by a resistance value applied to a timer circuit in the switched mode power supply. 
   
   
       4 . The method of  claim 3  further comprising varying the resistance value for one or more applications including the switched mode power supply to establish the minimum switching frequency sufficiently high to avoid audible noise generation by circuits in that application. 
   
   
       5 . The method of  claim 4  further comprising applying a corresponding fixed resistance value to a plurality of the applications including the switched mode power supply.