DUAL VOLTAGE ILLUMINATION POWER SUPPLY
Original Publication Date: 1984-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
Figure I shows a dual voltage power supply circuit 8 for energizing a flash lamp 10. Power supply 12 charges high voltage capacitor 14 to at least half of the energy required for lamp 10. Power supply 16 charges a lower voltage capacitor 18 to the remaining energy level. SCR 20 is used to quench capacitor 18 when the required flash lamp energy is reached. Assuming 1250 volts to be the operating limit of SCR 20, then capacitor 18 will be charged to no greater than 1250 volts. Assuming equal energy storage in the two capacitors and assuming that capacitor 14 is limited to 2500 volts, then capacitor 18 would be required to have four times the capacitance of capacitor 14. Rectifier 22 keeps the higher voltage from charging capacitor 18 beyond the lower voltage but allows capacitor 18 to deliver its energy once the voltage on capacitor 14 reaches the voltage on capacitor 18. When SCR 20 is turned on, it dumps the remainder of the energy stored in capacitor 18. The energy left in capacitor 14 cannot be quenched because of the blocking action of rectifier 22. If the residual voltage left on capacitor 14 introduces too much of an exposure error that cannot be compensated for by the timing of the quench then a second SCR can be introduced that will remove the excess voltage left on capacitor 14. Figure 2 shows this added SCR 24. For this particular example, both SCRs would be required to block 1250 volts prior to the triggering of the flash lamp. However, at quench time, when at least one half of the stored energy would have been delivered to the lamp, SCR 24 would have zero volts across it since the voltage on capacitor 14 would have decreased to that on capacitor 18. Using the same power assumptions, the voltage on the two capacitors would be at 1118 volts when half of the energy has been dissipated, so SCR 20 would have less than I1 18 volts across it at quench time.