JPS5598881A - Method of driving piezoelectric transformer - Google Patents

Abstract

PURPOSE: To stabilize the output of a piezoelectric transformer in a high voltage power supply using the transformer by the negative feedback of pulse width control type.

CONSTITUTION: An oscillating transformer 7 is driven in push-pull state by a drive circuit 8 and transistors 9, 10 to thus drive a piezoelectric transformer 6. The drive current of the transformer 6 is detected by inserting a series resistor 16. The drive voltage is displaced at its phase at 90° with a capacitor 17 and a resistor 18 inserted across both ends of the transformer 7 to set the voltage in phase with the current. Thus, the current is converted to a voltage by a phase detector 15. Then, the frequency is counted at a voltage controlled oscillator 14. The sectified output voltage V₀ of the transformer 6 is compared by a comparator 11 with standard voltage E, and also compared with the voltage of the oscillator by a comparator 13. Thus, the pulse output corresponding to the error level is applied to the drive circuit 8. When the output voltage V₀ is lowered, the drive pulse width of the transformer 7 is increased to thereby raise the voltage of the fundamental component of the oscillated frequency at the secondary side of the transformer 7. Thus, the drive current of the transformer 6 is increased to thereby increase the output. Accordingly, the output of the transformer is stabilized with respect to the load variation.

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