AU604391B2

AU604391B2 - High voltage power supply

Info

Publication number: AU604391B2
Application number: AU27418/88A
Authority: AU
Inventors: Christos Christoforidis; Peter Wedd
Original assignee: EMAIL WESTINGHOUSE Pty Ltd
Current assignee: EMAIL WESTINGHOUSE PTY Ltd
Priority date: 1988-01-08
Filing date: 1988-12-22
Publication date: 1990-12-13
Anticipated expiration: 2008-12-22
Also published as: AU2741888A

Description

,3A HN A LlA, LE PATENTS ACT 1952 COMPLETE SPECIFICATION (ORIGINAL)

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FOR OFFICE USE6 0 4 j Form Short Title: Int. CI: Application Number: Lodged: PI 6225 8th January 1988 T~i ocurnezit contains the Ii L r1v2'dne.~tS made under1 Sec tion 49 and is correct f'or rinting~ *69mplete Specification-Lodged: a r Accepted: *:ofI Lapsed: 44*6 Published: 04 **Priority: so r 0 Related Art: Na~pe of Applicant: 0 Adlress of Applicant: 0.0 TO BE COMPLETED BY APPLICANT EMAIL WESTINGHOUSE PTY. LIMITED Joynton Avenue, Waterloo, N.S.W.,

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Actual Inventor: Address for Service: HALFORD AND MAXWELL, Patent and Trade Mark Attorneys, 49-51 York Street, SYDNEY, 2000 Complete Specification for the invention entitled: "HIGH VOLTAGE POWER SUPPLY" The following statement is a full description of this invention, Including the best method of performing it known to us:- S 0 0 4 4*7 22!-1 12 a jl iiSi e i a :jS~i ru

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CCt The present invention relates to a high voltage power supply suitable for use with electrostatic filters.

Prior art high voltage supplies suffer from poor load and/or power supply regulation and are bulky. The applicant's own prior art power supply uses a mains frequency transformer followed by a magnetic amplifier with feedback. This supply provides feedback to match the output to the load conditions but is heavy and bulky in requiring the use of iron-core transformers.

Another type of prior art supply uses a leakage reluctance transformer similar to that used to power fluorescent tubes or high-pressure sodium vapour lamps for the high voltage transformer. However, this type of supply is designed to work with a constant load and is therefore not efficient when used with a load which varies with time.

Another type of power supply uses tuned circuits resonant at the mains frequency. This provides a large output while using simple components but suffers from poor regulation. The transformers since they are being used at mains frequency are bulky. A further type of high voltage power supply uses a transformer at the mains frequency followed by voltage doubler circuit using rectifiers and capacitors. Again this type of supply is not well regulated and suffers from output voltage drop as the load demand increases. It does not well regulate supply voltage fluctuations.

Yet another type of high voltage power supply is the flyback converter as used to develop the anode supply for the image tube in the domestic television receiver. This type of supply uses the flyback signal at a frequency of approximately 15 KHz to generate

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44 t -3high frequency pulses to the primary of a transformer.

This type of supply has poor load and supply regulation and relies on the pre-existence of a 15 KHz signal.

Electrostatic filters are subject to varying power supply requirements as the dust load of the filter changes. The above-mentioned types of power supply would each suffer from some disadvantages if used with electrostatic filters.

It is an object of the invention to overcome or substantially ameliorate these disadvantages in the prior art types of high voltage power supplies.

In accordance with the present invention there is disclosed a high voltage power supply for use with electrostatic filters including pulse generator means for producing a waveform having a variable duty cycle, voltage multiplier means for increasing the voltag(- of said waveform, and means to regulate the voltage and/or current of the output of said voltage multiplier means wherein said output of said voltage multiplier means provides the output of said high voltage power supply, the pulse generator means includes an oscillator operating at supersonic frequencies of the order of 20-30 KHz, while the voltage multiplier means includes a transformer connected on its secondary side to a voltage multiplier circuit. Preferably the multiplier circuit comprises a plurality of capacitors and rectifiers in parallel and the transformer is an air gap ferrite core type. The regulating means preferably includes feedback means providing voltage and/or current feedback, and pulse width modulation means for controlling the pulse generator means to vary the duty cycle of said waveform in response to said feedback 9.

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r IC e 10 4 I 1 #1 It I t I I I ii I 1 II In this manner an efficient, regulated and less bulky high voltage power supply is provided in improvement over the above-mentioned prior art devices.

A preferred embodiment of the invention will now be described with respect to the drawings in which: Figure 1 is a block circuit diagram of the high voltage power supply according to the present invention; Figure 2 is an expanded circuit diagram of the power supply for the invention as shown in Figure 1; Figure 3 is an expanded circuit diagram of the PWM and output circuitry of the invention as shown in Figure 1; Figure 4 is an expanded circuit diagram of the voltage regulator circuitry of the invention as shown in Figure 1; Figure 5 is expanded circuit diagram of the voltage multiplier circuitry of the invention as shown in Figure 1; and Figure 6 is an expanded circuit diagram of the alarm circuitry for the invention as shown in Figure 1.

As shown in Figure 1 the high voltage power supply can be divided into several separate blocks. The voltage multiplier 10 is supplied with the output 11 from pulse width modulator (PWM) circuitry 12. The PWM circuitry is controlled by stop/start line 13 and slow start line 14 from the alarm circuitry 15. The PWM St td 10

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5r 5: 1 I e S 455 C I' circuitry 12 is also supplied by a reference voltage Vc by line 16 from the voltage regulator circuitry 17 which in turn is provided with a feed back signal voltage Vs from the voltage multiplier 10 via line 18.

The alarm circuitry 15 is supplied by a feedback current signal Is from the voltage multiplier via line 19. This signal Is is used to monitor the output of the voltage multiplier 10 and to indicate and control the occurrence of any abnormal performance.

The high voltage power supply is supplied from the mains by the power supply circuitry 20. The power supply circuitry 20, provides as shown in Figure 2 a regulated supply of +12 volts DC and an unregulated +300 volts output. The power supply circuitry employs standard circuitry to supply these voltages.

The variable resistor 21 (VDR 1) is a voltage dependent resistor which safeguards the input power to the high voltage side of the power supply.

The pulse width modulator circuitry 12 as shown in Figure 3 supplies the multiplier 10 with a pulse width modulated output signal. U4, a NE5560 switched mode power regulator circuit, includes an oscillator operating at supersonic frequencies in the 20-30 KHz frequency range, and is provided with a control voltage Vc via the network comprising the resistors R21, R29, and the capacitor C9. The circuit U4 is supplied by the power supply with +12 volts at pin 1 and in addition is provided with a stop/start facility by line 13 and a slow start from line 14 via the network of capacitor C13 and resistances R23 and R24.

The output of the voltage regulator U4 drives the gate of the P-channel JFET transistor Q1 which controls the primary 23 of the output transformer 22 and the associated network on the primary side comprising diodes D9 to D13, resistances R31 and R32 and Su

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i; i- i -6capacitor C17. The primary 23 of the output transformer 22 is supplied with the +300 volt output of the power supply 20. Transformer 22 is preferably an air gap transformer with a ferrite core (a type well known in the art of switched mode power supplies) for improved linearity. The JFET Q1 is normally "on".

A signal from pin 14 of the switched mode power regulator U4 turns Q1 "off" thereby interrupting the 4 supply to the primary 23 of the transformer 22 to generate an output from the secondary 24 of the transformer 22 to be fed to the voltage multiplier 4,o4 ^O The voltage regulator circuitry 17 as shown in Figure o. o 4 comprises a voltage regulator U2 which is supplied with a feedback voltage Vs by line 18 from the voltage multiplier. This feedback voltage Vs is fed via the network of resistance R9 and capacitor C4 to the variable resistor VR1 providing the input to the gain control operational amplifier Ul. The variable resistor VR1 enables the output of the high voltage power supply to be varied by changing the feedback voltage Vs. The output of the voltage regulator U2 supplies the control voltage Vc at line 16 to the PWM circuitry 12 via the opto-isolator U3. U3 provides 4 0 25 the necessary voltage isolation between the voltage multiplier 10 and the PWM circuitry 12. This is necessary as the ground indicated in Figure 3 for the PWM circuitry is floating.

.30 The alarm circuitry is shown in Figure 6. A feed back current Is is fed via line 19 from the voltage multiplier 10 to the network comprising the capacitor C1 and resistor R2 to the input of an operational amplifier 29,1/4 of quad op.amp. Ul, acting as a current to voltage amplifier. The output of the operational amplifier 29 feeds the pair of operational PLLA amplifiers 30 and 31 acting as a window comparator.

*4,6i S 10 aaur 94 M ar 400 AI a 0 0 00 a ar 04 *4 25 6 a -7- The output of the operational amplifiers 30 and 31 is summed at the junction 33 to provide an alarm signal gated by the opto-isolator U4. The output of the opto-isolator U4 can be used to operate an external alarm with relay LIA or can be used to drive via timer U6 the stop/start line 13. The output of the 555 timer U6 also provides a slow start signal via the line 14.

In broad terms, the alarm circuitry operates as follows. If the output of operational amplifier 29 is between the voltages at pins 5 and 9 of U1 set by the resistor ladder of R5, R6 and R7 the output of operational amplifiers 30 and 31 will be at ground potential. When the output voltage is below the voltage set at pin 5 the output of op. amp. 31 will be at the supply voltage so that U6 via opto-isolator U4 will initiate a "start". When this voltage rises above that set at pin 9 then U6 will initiate a "stop" signal.

The secondary 24 of the transformer 22 via line 11 of the PWM circuit 12 is applied to the capacitor-diode network of the voltage multiplier 10 to provide an output of 6.5 Kvk as shown in Figure The feedback voltage Vs via line 18 and the feed back current Is via line 19 enable the output of the voltage multiplier 10 to be regulated and monitored for any alarm conditions. This provides an improved high voltage power supply which can adjust to the demands made on the voltage multiplier 10 by a load.

Though the invention has been described with respect to a specific embodiment thereof it is to be understood that the invention is not restricted thereto. That is, other integrated circuits can be -t -8used to define the module which comprise the units of the present invention. Also the alarm circuits can be used to not only control the operation of a power supply but can be used to signal to some remote point the indication of an alarm state. Though the power supply has been shown as operated from a mains supply the high voltage power supply can also be operated from other than a mains supply, for example from an inverter circuit operating from a battery supply.

Any other electrical supply which provides the necessary low voltage DC for the operation of the 4 circuits and the high voltage DC for the operation of the multiplier can be used.

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Claims

1. A high voltage power for use with electrostatic filters including: pulse generator means producing a wave form having a variable duty cycle, voltage multiplier means for increasing the voltage of said wcve form, 'tt" means to regulate the voltage and/or current of the .a*t output of said voltage multiplier meansvwherein said output of said voltage multiplier means provides the output of said high voltage power supply, at wherein said pulse generator means includes an oscillator operating at supersonic frequencies of the order of 20-30 KHz, and i4t c t t said voltage multiplier means includes a transformer connected on a secondary side to a plurality of voltage doubler circuits.

2. A high voltage power supply as claimed in claim 1 wherein each of said voltage doubler circuits comprises a plurality of capacitors and rectifiers in parallel.

3. A high voltage power supply as claimed in claim 2 Swherein said regulating means includes feedback means for providing voltage and/or current feedback and pulse width modulation means for controlling said pulse generator means to vary the duty cycle of said wave form in response to said feedback means. Z^TIA.

4. A high voltage power supply as claimed in any one I li-- of the previous claims further including means for determining an unsafe condition of said output as indicated by said feedback voltage or current, means for signalling the existence of said unsafe condition and means dependant on said unsafe condition for controlling said output.

A high voltage power supply as claimed in claim 4 wherein said means for controlling said output includes first comparator means and second comparator means -n r 4 -r m4wosnc, wherein said first S: comparator means compares the output of said voltage multiplier means with a first set value and wherein said second comparator means compares said output of said voltage multiplier means with a second set value, said first set value being less than said second set value, whereby said output being less than said first set value turning said power supply on, and said output being greater than said second set value turning said power supply off.

6. A high voltage power supply substantially as hereinbefore described with reference to and as shown in the accompanying drawings. S• Dated this 31st day of July 1990 EMAIL WESTINGHOUSE PTY. LIMITED Patent Attorneys for the Applicant: FIALFORD CO. <'olyq L K, Vl u MIS tl L- :ii i r