Charge pump for bus-powered device

Abstract

A charge pump can be used with a bus-powered device connected to a bus. The charge pump comprises a power connection from the bus carrying a DC power signal constrained to not exceed a given current limit and a given voltage limit, a DC-to-DC step-down voltage converter, a capacitor, and a DC-to-DC step-up voltage converter. The step-down converter has an input connected to the power connection and produces an intermediate signal having a voltage the same or less than the voltage of the power signal. The capacitor is connected to the output of the step-down converter. The step-up converter has an input connected to the output of the step-down converter and to the capacitor, and produces a final output signal having a voltage greater than the given voltage limit. The output of the step-up converter is connected to and provides DC power to the device.

1 . A charge pump for use with a bus-powered device connected to a bus, the charge pump comprising: 
 a power connection from the bus for receipt of a DC power signal constrained to not exceed a given current limit and a given voltage limit;    a DC-to-DC step-down voltage converter having an input and an output, the input connected to the power connection, the step-down voltage converter producing at its output an intermediate signal having a voltage the same or less than the voltage of the power signal;    a capacitor connected to the output of the step-down voltage converter; and    a DC-to-DC step-up voltage converter, having an input and an output, the input of the step-up voltage converter connected to the output of the step-down voltage converter and to the capacitor, the step-up voltage converter producing at its output a final output signal having a voltage greater than the given voltage limit, the output of the step-up voltage converter being connected to the bus-powered device and providing DC power to the device in the form of the final output signal.    
   
   
       2 . A charge pump according to  claim 1 , wherein the bus is a USB 2.0-compliant bus.  
   
   
       3 . A charge pump according to  claim 1 , wherein the bus is an IEEE 1394-compliant bus.  
   
   
       4 . A charge pump according to  claim 1 , wherein the device is a camera comprising an illumination source.  
   
   
       5 . A charge pump according to  claim 4 , wherein the illumination source is a strobe illumination source requiring approximately 200 mA of current at a voltage in the range from about 9 V to about 12 V for approximately 100 ms; wherein the given current limit is about 500 mA and the given voltage limit is about 5 V; wherein the intermediate signal produced by the step-down voltage converter has a current value of approximately 200 mA and a voltage of about 2 V; and wherein the capacitor has a capacitance value at least about 1 F.  
   
   
       6 . A bus-powered integrated camera connected to a bus, the camera comprising: 
 an imager connected to the bus and oriented to capture an image of an object to be imaged during an exposure time;    an illumination source oriented to supply light on the object to be imaged during the exposure time; and    a charge pump connected between the bus and the illumination source, wherein the charge pump comprises:    a power connection from the bus for receipt of a DC power signal constrained to not exceed a given current limit and a given voltage limit; 
 a DC-to-DC step-down voltage converter having an input and an output, the input connected to the power connection, the step-down voltage converter producing at its output an intermediate signal having a voltage the same or less than the voltage of the power signal;  
 a capacitor connected to the output of the step-down voltage converter; and  
 a DC-to-DC step-up voltage converter, having an input and an output, the input of the step-up voltage converter connected to the output of the step-down voltage converter and to the capacitor, the step-up voltage converter producing at its output a final output signal having a voltage greater than the given voltage limit, the output of the step-up voltage converter being connected to the bus-powered device and providing DC power to the device in the form of the final output signal.  
   
   
   
       7 . A camera according to  claim 6 , wherein the illumination source comprises a plurality of strings of LEDs, wherein each string comprises four LEDs.  
   
   
       8 . A camera according to  claim 7 , wherein the number of strings of LEDs is six, and the LEDs are arranged is a ring around the imager.  
   
   
       9 . A camera according to  claim 8 , wherein each LED string requires approximately 33 mA of current at a voltage in the range from about 9 V to about 12 V for the exposure time, which is approximately 100 ms; wherein the given current limit is about 500 mA and the given voltage limit is about 5 V; wherein the intermediate signal produced by the step-down voltage converter has a current value of approximately 200 mA and a voltage of about 2 V; and wherein the capacitor has a capacitance value at least about 1 F.  
   
   
       10 . A charge pump for use with a bus-powered device connected to a bus, the charge pump comprising: 
 a means for receiving a power signal from a bus;    a means for storing charge from the power signal;    a means for converting the power signal to a higher voltage, thereby resulting in a boost signal; and    a means for providing the boost power signal to a device connected to the bus for powering the device.    
   
   
       11 . A method comprising: 
 receiving a power signal from a bus;    storing charge from the power signal;    converting the power signal to a higher voltage, thereby resulting in a boost signal; and    providing the boost signal to a device connected to the bus for powering the device.    
   
   
       12 . A method according to  claim 11 , further comprising: 
 regulating the power signal to the same or a lower voltage before storing charge from the power signal, to facilitate the storing step.    
   
   
       13 . A method according to  claim 11 , wherein the bus is a USB 2.0-compliant bus.  
   
   
       14 . A method according to  claim 11 , wherein the bus is an IEEE 1394-compliant bus.  
   
   
       15 . A method according to  claim 11 , wherein the device is a camera comprising an illumination source.  
   
   
       16 . A method according to  claim 15 , wherein the illumination source comprises a plurality of strings of LEDs, wherein each string comprises four LEDs.  
   
   
       17 . A method according to  claim 15 , wherein the illumination source is a strobe illumination source requiring approximately 200 mA of current at a voltage in the range from about 9 V to about 12 V for approximately 100 ms; wherein the given current limit is about 500 mA and the given voltage limit is about 5 V; wherein the intermediate signal produced by the step-down voltage converter has a current value of approximately 200 mA and a voltage of about 2 V.  
   
   
       18 . A method according to  claim 11 , wherein the storing step comprises storing an amount of charge corresponding to at least about 1 Farad.