Self-oscillating driver with soft start circuit

Abstract

A method for providing a soft start operation for a transistor driver circuit, comprising providing a saw tooth waveform from an oscillator at a given frequency; comparing the saw tooth waveform to a reference value; and modifying the saw tooth waveform as a result of the comparison to produce pulses of increased length when the reference value is below a value of the saw tooth waveform.

1 . A method for providing a soft start operation for a transistor driver circuit, comprising: 
 providing a saw tooth waveform from an oscillator at a given frequency;    comparing the saw tooth waveform to a reference value; and    modifying the saw tooth waveform as a result of the comparison to produce pulses of increased length when the reference value is below a value of the saw tooth waveform.    
   
   
       2 . The method according to  claim 1 , further comprising supplying the pulses to a driver circuit for driving the transistor.  
   
   
       3 . A driver circuit for driving a transistor, comprising: 
 an oscillator circuit for producing an oscillation signal;    a driver circuit for receiving the oscillation signal and producing an output signal suitable for operating the transistor; and    an overcurrent detection circuit for detecting an overcurrent condition and operable to disable the oscillation signal or the driver circuit for a predetermined period of time to recover from the overcurrent condition.    
   
   
       4 . A soft start circuit for increasing a pulse length delivered to a transistor driver, comprising: 
 a comparator having an input coupled to a saw tooth waveform to provide a varying comparison operation;    a reference value coupled to another input of the comparator for comparison against the saw tooth waveform.    
   
   
       5 . An output of the comparator operable on a pulse train derived from the saw tooth waveform to vary a pulse width when the reference value is less than a value of the saw tooth waveform.  
   
   
       6 . The circuit according to  claim 5 , wherein the reference value is derived from a voltage on a capacitor.  
   
   
       7 . The circuit according to  claim 5 , wherein the reference value is variable.  
   
   
       8 . The circuit according to  claim 6 , wherein the voltage across the capacitor varies to provide a variable comparison with the saw tooth waveform.