Method of detecting switching power supply output current

Abstract

A method and apparatus for detecting output current in switching power supplies forgoes the need for any resistor or other components in series with the load. A method according to the invention includes the steps of inferring the peak current through the inductor as a function of input voltage and inductor charge time, and deriving the current available to the load based upon the flyback voltage during discharge of the inductor. Although a disclosed example is based upon a buck/boost topology, other converter topologies are anticipated. In terms of apparatus, in a switching power supply of the type wherein a switching device is used to charge an inductor that discharges to a load, the invention provides devices arranged for detecting output current without the need for a resistor or other component in series with the load. In the preferred embodiment, these devices include electrical components operative to generate a signal indicative of peak inductor current, and a switch for switching the signal to provide a waveform, the integral of which is proportional to peak inductor current multiplied by the duty cycle of the discharge of the inductor. Circuitry is further used for comparing the waveform to a fixed reference so as to output a signal indicative of load current.

I claim: 
     
       1. In a switching power supply of the type wherein a switching device is used to charge an inductor that discharges to a load, a method of detecting determining a magnitude of an output current without the need for a resistor or other component in series with the load, the said method comprising the steps of:
 inferring the a peak current through the said inductor as a function of input voltage and inductor charge time; and 
 deriving the a current available to the said load based upon the a flyback voltage produced by said inductor during discharge of the said inductor. 
 
     
     
       2. The method of  claim 1 , wherein said inductor forms part of a buck/boost topology. 
     
     
       3. In a switching power supply of the type wherein a switching device is used to charge an inductor that discharges to a load, an apparatus for detecting determining the magnitude of an output current without the need for a resistor or other component in series with the load, comprising:
 electrical components operative to generate a signal indicative of peak inductor current; 
 a switch for switching the signal to provide a waveform, the integral of which is proportional to peak inductor current multiplied by the duty cycle of the discharge of the inductor; and 
 circuitry for comparing the waveform to a fixed reference so as to output a signal indicative of load current. 
 
     
     
       4. Apparatus An apparatus for detecting determining the magnitude of an output current of a switching power supply without the need for a resistor or other component in series with the load, comprising:
 a switching device used to charge an inductor that discharges to a load in accordance with an input signal; 
 electrical components operative to generate a signal indicative of peak inductor current; 
 a switch for switching the signal to provide a waveform, the integral of which is proportional to peak inductor current multiplied by the duty cycle of the discharge of the inductor; and 
 circuitry for comparing the waveform to a fixed reference so as to output a signal indicative of load current. 
 
     
     
       5. The apparatus of  claim 4 , wherein the switching device and inductor form part of a buck/boost topology. 
     
     
       6. An apparatus for determining a magnitude of an output current through a load driven by a power supply, comprising:
 an inductive element included in the power supply;   a first circuit coupled to the inductive element and operable to determine a peak current through the inductive element as a function of a voltage across the inductive element and charge time of the inductive element; and   a second circuit coupled to the first circuit and operable to determine the magnitude of the output current based upon the peak current.   
     
     
       7. The apparatus of claim 6, wherein the inductive element comprises an inductor that forms part of a buck/boost topology. 
     
     
       8. The apparatus of claim 6, wherein the first circuit is operable to provide a signal indicative of the peak current through the inductive element. 
     
     
       9. The apparatus of claim 6, wherein the first circuit is further operable to switch the signal to provide a waveform the integral of which is proportional to the peak current multiplied by a duty cycle of a discharge time of the inductive element. 
     
     
       10. The apparatus of claim 6, wherein the second circuit is operable to compare the waveform to a fixed reference voltage to provide a signal indicative of the magnitude of the output current.