USB (Universal Serial Bus) is a de facto standard in every new personal computer and/or laptop. The proliferation of this standard results in the fact that new devices can be easily connected to a variety of laptops and PC's without much trouble. However, this doesn't come free. A USB 1.0-1.1 connection standard spells out that the maximum output voltage available for power devices is 5.0V.
A device that is becoming quite popular is that of a CCD Camera. Normal implementation of camera on a USB system is typically CMOS based. However, the pixel density and quality of the image of a CCD camera is typically many magnitudes better than that of CMOS. One problem of CCD is that it requires a relatively high voltage rail. A solution to this dilemma is shown in Figure 1.
The circuit is based on LM3500-16. The ability to boost up from a 5.0V source makes it ideal for powering a CCD Camera. RFB1 and RFB2 is set for an output voltage of 9.0V. The feedback voltage is 500mV. The desired equation is RFB1= RFB2(Vout/ 500mV-1) with Vout = 9V. Therefore, if we assume RFB2=1k Ohm, RFB1 must equal 17.0k Ohm. The LM3500-16's ability to maintain a steady output voltage over the entire input voltage range also makes it useful for providing 5V from a battery voltage such as L-ION. To set the output voltage to 5.0V, use the equation is RFB1= RFB2(Vout/500mV-1) with Vout = 5V. Therefore, if we assume RFB2=1k Ohm, RFB1 must equal 9k Ohm.
The LM3500-16 can also be connected up to LM4906 audio amplifier. Small ceramic input and output capacitors can be used on the LM3500-16 because of its high switching frequency (1 MHz). True isolation assures that no leakage will occur through from the power supply through the baseband I/O structure when the LM3500-16 is in shutdown mode.
Figure 1: Powering a CCD camera from a USB connection requires a driver and a few filter components.