The circuit shows one
way of obtaining a voltage of 90V from a 1.5V battery supply. The LT1073
switching regulator from Linear Technology (http://www.linear-tech.com)
operates in boost mode and can work with an input voltage as low as 1.0
V. The switching transistor, which is hidden behind connections SW1 and
SW2, briefly takes one end of choke L1 to ground. A magnetic field
builds up in the choke, which collapses when the transistor stops
conducting: this produces a current in diode D1 which charges C3. The
diode cascade comprising D1, D2, D3, C2, C3 and C4 multiplies the output
voltage of the regulator by four, the pumping of C2 causing the voltage
developed across C4 via C3, D2 and D3 to rise.
Finally, the regulator control loop is closed via the potential
divider (10 MΩ and 24 kΩ). These resistors should be 1 % tolerance metal
film types. With the given component values, fast diodes with a reverse
voltage of 200 V (for example type MUR120 from On Semiconductor http://www.onsemi.com) and a choke such as the Coilcraft DO1608C-154 (http://www.coilcraft.com) an output voltage of 90 V will be obtained. The output of the circuit can deliver a few milliamps of current.