Controlling apparatus for high frequency high voltage power source for corona discharge processing

• US 5,486,993 A
• Filed: 10/25/1993
• Issued: 01/23/1996
• Est. Priority Date: 10/26/1992
• Status: Expired due to Term

• Current Assignee: Kasuga Denki, Inc.
• Original Assignee: Kasuga Denki, Inc.
• Inventors: Sakurai, Yukihira, Ueda, Takehiko
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): NAPPI, ROBERT E
• Application Number:
  US08/140,549
• Time in Patent Office: 820 Days
• Field of Search: 363/132, 363/131, 363/98, 363/97
• US Class Current: 363/98
• CPC Class Codes: H02M 7/4815 Resonant converters H02M7/4811 and H02M7/4826 take precedence
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A controlling apparatus for a high frequency high voltage power source is disclosed which eliminates a switching loss of a high frequency invertor and allows adjustment of the output power to be performed continuously and accurately over a wide range. A resonance current of a resonance circuit of the high frequency high voltage power source is detected by current detection means, and a phase locked loop circuit locks itself with a frequency with which it coincides in phase with the resonance current to produce a synchronized pulse signal. From the pulse signal, a signal having a zero voltage outputting period of a preset duration is formed by a pulse density modulation circuit to change the pattern of a gate signal for switching semiconductor elements of a high frequency invertor to adjust the output power. An input voltage before a zero voltage outputting period is entered is stored into voltage storage means such as a sample and hold circuit so that the phase locked loop circuit may continue to lock with the same frequency also during the zero voltage outputting period.

Claims

1. A controlling apparatus for a high frequency high voltage power source for corona discharge processing of the type wherein an ac voltage from a commercial ac power supply is rectified into a dc voltage by a rectifier circuit and then converted into a voltage of a high frequency, comprising:

a high frequency invertor including a plurality of switching semiconductor elements connected in a bridge connection for converting the rectified voltage into a voltage of high frequency,

a high voltage transformer, having a discharge electrode for corona discharge processing, for boosting the voltage of high frequency and applying the boosted voltage to said discharge electrode, said high voltage transformer and at least said discharge electrode forming a resonance circuit with respect to said high frequency invertor, said controlling apparatus comprising;

current detection means for detecting a current flowing between said high frequency invertor and said high voltage transformer;

a phase locked loop circuit including a phase comparator and a voltage controlled oscillator for outputting a signal having a phase corresponding to the detection current of said current detection means and a frequency corresponding to a voltage of a signal output by said phase comparator;

a pulse density modulation circuit for inputting an output signal of said phase locked loop and thinning out the inputted output signal in accordance with an arbitrary instruction value to output a pulse signal synchronized with the inputted output signal and having a zero voltage outputting period of an arbitrary time length; and

a gate signal generation circuit for inputting the pulse signal from said pulse density modulation circuit and outputting a gate signal to said switching semiconductor elements of said high frequency invertor so that said resonance circuit may be put into and remain in a short-circuited condition within the zero voltage outputting period.

2. A controlling apparatus for a high frequency high voltage power source for corona discharge processing as claimed in claim 1, further comprising voltage storage means for storing an input voltage to said voltage controlled oscillator before the zero voltage outputting period is entered and inputting the thus stored voltage to said voltage controlled oscillator also during the zero voltage outputting period.

3. A controlling apparatus for a high frequency high voltage power source for corona discharge processing as claimed in claim 2, wherein said voltage storage means is a sample and hold circuit.

4. A controlling apparatus for a high frequency high voltage power source for corona discharge processing as claimed in claim 1, wherein each of said switching semi-conductor elements is a bipolar transistor of the insulated gate type.