HIGH VOLTAGE SOURCE PROVIDING CONTINUOUSLY REGULATED OUTPUT VOLTAGE, PREFERABLY FOR SUPPLYING LOW-POWER ION AND ELECTRON BEAM MACHINING AND EVAPORATING APPARATUSES

Abstract: The invention relates to a stabilized high voltage source the output voltage of which may be regulated in wide range, whereby the adjusted output current is constant at variable load. The high voltage supply source comprises a high vol­ tage rectifier (NE) fed by a push-pull driving circuit (MH), a control circuit (V) supplying push-pull width modulated con­ trol signals of the driving circuit (MH) and an error signal processing circuit (H) working up the divided voltage and cur­ rent signals taken from the output of the high voltage source. The output signal of the error signal processing circuit (H) is applied to the control circuit (V) as a control signal. The supply voltage of auxiliary circuits of the supply source is provided by a stabilized low voltage supply unit.

Description: This invention relates to a stabilized high voltage source with output voltage regulated in wide range and constant output current at variable load. The high voltage source comprises a high voltage rectifier fed by a push-pull driving circuit, a control circuit supplying push-pull width modulated control signals of the driving circuit and an error signal processing circuit working up the divided voltage and current signals taken from the output of the high voltage source. The output signal of the error signal processing circuit is applied to the control circuit as a control signal. The supply voltage of auxiliary circuits of the supply source is provided by a stabilized low voltage supply unit. There are several solutions for forming high voltage supply sources, some of them provide regulated output voltage. The requirements of variable loads are met more conveniently by pulse width modulated push-pull switching operation supply sources providing well-regulated output voltage. These supply sources are built generally with low voltage outputs, so is e.g. the supply source of the firm LAMBDA described in Ferenczi, Ö. Switching mode supply sources, Chapter 2.2, Müszaki Könyvkiadó, Budapest, 1978. At this supply source the pus-pull inverter is driven with push-pull control signals through two NOR gates which distribute the width modulated signals. The width modulated signal is generated from the signal of a controlled oscillator by a controlled comparator. The comparator is controlled by a regulating and current limiting amplifier connected to DC output of the supply source. Distribution of signals is carried out by a bistable flip-flop driven by the same oscillator. The width modulated inverter is connected to output rectifier and filter providing output DC voltage, through a transofmer isolation. The layout of the output rectifier may be a range of solutions from the simple single-way rectifier to the voltage multiplying connection. In certain cases when the output transformer has multiple coil secondary side, the high voltage can be generated by additive voltage multiplier. At designing high voltage supply sources difficulties arise when several contradictory requirements should be met at the same time on the high voltage side. A compromise-like solution should meet the requirements as follows: stabilized high voltage output voltage variable in a wide range; constant output current adjustable independently of the output voltage; constant current and voltage at variable load; endurance of quick short circuits (caused by ion avalanche) without damage; minimum ripple. The known solutions do not comply with the above-described requirements, since the output filter should be eliminated in order to achieve suitable reactions in the case of quick variations which would result in inadmissible ripple and short circuit sensitivity. Keeping the output current and output voltage constant are also contradictionary requirements which can be carried out by suitable regulation in the case of suitable output impedance, that, however, needs an output RLC circuit. Using the known regulation circuit does not allow to adjust the output current independently of the variable but stabilized output voltage since that circuits are operable only when one or other constant is kept about level. Producing a circuit indispensable to comply with the above-described requirements contradicting to each other is based on the recognitions as follows: the contradictions with respect to the output filter can be resolved by transforming it to the primary side of the high voltage transformer and carrying it out on that side; the transformed filter must be designed that it may damp the oscillation in the driving circuit so that the high voltage side ripple may be decreased to minimum; a correlation must be ensured between the current and voltage of the high voltage output in an error sensing circuit so that the required constant level value thereof may be adjusted in the said circuit; the operation frequency of the inverter must be chosen so that it may be the same as the self-frequency of the primary circuit defined by the high voltage transformer. The present invention accordingly refers to a high voltage source providing continuously regulated output voltage, preferably for supplying low-power ion and electron beam machining and evapourating apparatuses, wherein said high voltage source comprises a control circuit, the control signal input of which is connected to signal output of an error signal processing circuit, a driving circuit, the control signal inputs of which are connected to push-pull control signal outputs of the control circuit. The driving circuit is coupled with a high voltage rectifier through a high voltage transformer having two push-pull primary windings, one of the high voltage output terminals of said rectifier is coupled through output voltage-sampling divider on the one hand with high voltage output terminal, on the other hand with voltage signal input of the error signal processing circuit. The other high voltage output terminal of the high voltage rectifier is coupled on the one hand through a high voltage capacitor with commoned ground potential point of the high voltage source, on the other hand with current signal input of the error signal processing circuit. Supply voltage terminals of circuit arrangement blocks are connected to a low voltage supply source, wherein ground points of said circuit arrangement blocks are connected to commoned ground potential terminal. The main point of the invention is that control inputs of the driving circuits each are connected to control inputs of controlled switches, respectively, the terminals of the controlled switches not connected to the ground potential are coupled with one end of each primary winding of the high voltage transformer, the other end of said each primary winding is coupled via secondary windings of transformers, respectively with supply voltage terminal of the low voltage supply source. One end of each primary winding of said transformers is commoned and connected to the ground point, each other end is coupled on the one hand via each diode with the supply voltage terminal, on the other hand via each series RC term with the ground point. The high voltage supply source according to the present invention may preferably designed so that control circuit comprises a free-running oscillator, a signal shaping unit and a gate control circuit connected in parallel to signal output of the free-running oscillator, a voltage controlled modulator and two AND-gates distributing the output signal, wherein the output of the signal shaping unit is connected to the signal carrier input of the modulator, the control outputs of the gate control circuit are connected to the inputs each of AND-gates. The other input of each AND-gate is connected to the output of the modulator and the modulating input of the modulator forms a control signal input for the control circuit. According to a preferred embodiment of the error signal processing circuit of the high voltage source, the current signal input is connected to the ground potential point through a current adjusting potentiometer whose sliding contact is connected to one input of a first error signal amplifier through a current limiting Zener diode. The other input of said error signal amplifier is connected to a reference voltage source, whereby the common point of the Zener diode and the input of the error signal amplifier is connected to the ground point through a resistor. The output of said error signal amplifier is connected also to the ground point through a voltage adjusting potentiometer, the sliding contact of which is connected to one input of another error signal amplifier, the other input of which forms the voltage signal input of the error signal processing circuit. The output of said another error signal amplifier is the signal output of said error signal processing circuit. This invention will be further explained with reference to drawings, wherein Fig. 1 shows a block diagram of a known pulse-width modulated push-pull switching operation supply source, Fig. 2 shows a schematic diagram of the supply source according to the invention. As it is shown in Fig. 1, in the known supply source, there is a low-voltage supply circuit 1 which provides supply voltages necessary for the operation of the apparatus (only high-current supply voltage connection of inverter 2 is indicated in said Figure). The inverter 2 of the supply source is controlled with push-pull pulse-width modulated signals distributed by NOR-gates 9 and 10 driven by bistable multivibrator 7. The pulse-width modulated control signals are generated by a voltage controlled pulse-width modulator 6 from the signal of an oscillator 8. Said signals are specified by the signals taken from the DC output 11 and a reference voltage source 13 and processed with an error amplifier 12. The inverter 2 controlled with the pulse-width modulated push-pull signals feeds a rectifier 4 through a transformer 3 ensuring galvanic isolation and voltage modification. The output signal of the said rectifier 4 is applied to the DC output 11 of the supply source through a smoothing and storing LC or LRC filter 5 and results in a smoothed d.c. current. The supply source according to the present invention as shown in Fig. 2 has in many respect a similar structure. Nevertheless, there are basic differences between the the known supply source and the new solution according to the present invention which may be summarized as follows: the layout of push-pull driving circuit MH fundamentally differs from that of the inverter 2 since the energy storing, the "filtering of output signals" and the damping of harmful oscillations are carried out in this part of the supply source; the filter 5 is eliminated at the output of high voltage rectifier NE corresponding to rectifier 4; the layout of error signal processing circuit H basically differs from the unit of the same purpose consisting of the error amplifier 12 and the reference voltage source 13 since the adjustment of the output high voltage is carried out by modifying a correlation between the constant reference signal and the feedback current and voltage signals, respectively rather than by changing the reference signal. In the high voltage supply source according to the invention, there is a control circuit V providing push-pull width modulated control signals for the driving circuit MH. There is a free-running oscillator 0 in the control circuit V, the output signals of which are applied on the one hand to the input of a gate control circuit KV, on the other hand to the carrier signal input of a voltage controlled modulator M via a shaping S, e.g. Schmitt-Trigger. The gate control circuit KV drives AND-gates K1 and K2 distributing the width modulated control signals, the other inputs of which the pulse-width modulated output signals of the modulator M are applied to. The outputs of AND-gates form the push-pull control signal output of the control circuit V, the control signal input of which is formed by the modulation input of modulator M. The output of the error signal processing circuit H is connected to the control signal input of the control circuit V. The voltage signal input of the error signal processing circuit H is connected to the earth via current adjusting potentiometer P1, the current signal input thereof is connected to one of the inputs of a second error signal amplifier HE2. The sliding contact of potentiometer P1 is connected to one of the inputs of a first error signal amplifier HE1 via current limiting Zener diode Z, the said input is connected to ground point via resistor R5. A reference voltage source UR is connected to the other input of the first error signal amplifier HE1, the output thereof is coupled with ground point via voltage adjusting potentiometer P2. The sliding contact of said potentiometer P2 is connected to the other input of the second error signal amplifier HE2 and the output thereof forms the signal output of the error signal processing circuit H. Width of square wave signals of the control circuit V is controlled by the voltage applied to the modulator M, and the output current and the output high voltage can be adjusted in the unit generating the said voltage by potentiometers P1 and P2, respectively, The Zener diode Z limits the magnitude of adjustable minimum current. Accordingly, in the output signal of the error signal processing circuit H, there will appear a correlation determined by the potentiometers P1 and P2 and threshold voltage of the Zener diode Z with respect to reference voltage. Since the error processing circuit H is connected to the high voltage output, the error signal arising from a modification of the adjusted values of output current and voltage by outer influences changes the control signals so that original state should be re-established with due reagrd to the lack of output filter and consequently the inductance thereof and with regard to that storing effect of the filter does not prevail and the control circuit operates extremely quickly. The push-pull control signals are applied to the control inputs of controlled switches VK1 and VK2 through driver amplifiers ME1 and ME2, respectively in the driving circuit MH. The controlled switches VK1 and VK2 connect each primarywinding of a high voltage transformer NTr to the ground potential point depending on the control. The other end of each primary winding of the high voltage transformer NTr is coupled through secondary winding of a transformer Tr1 and Tr2, respectively with supply voltage terminal U t of low voltage supply sources of the apparatus. One end of each primary winding of said transformers Tr1 and Tr2 is connected to the ground potential point, the other end of said primary winding is also connected to supply voltage terminal U t through diods D1 and D2, respectively. The said other end each is connected to ground potential point through series RC term consisting a resistor R1, R2 and a capacitor C1, C2, respectively. The push-pull width modulated control signals alternatively bring into operation the VK1 and VK2 controlled switches which alternatively connect one or other primary widing of the high voltage transformer NTr to the supply voltage via secondary widings of the transformers Tr1 and Tr2, respectively. At the instant of switch in, the secondary windings of transformers Tr1 and Tr2 prevent the front edge of the pulse from appearing on primary coil of the high voltage transformer NTr so that a high voltage pulse will not appear accross high voltage winding. Primary winding of the high voltage transformer NTr has a certain capacity in parallel therewith. That capacity start to charge via secondary coils of the transformers Tr1 and Tr2, respectively. Time of charge and hence the voltage is determined by the width of controlling square wave signal. A voltage of magnitude determined in this way will appear across the primary windings of high voltage transformer NTr. The magnitude of high voltage across secondary windings is determined in the same manner with respect to turn ratio. When controlled switches VK1 and VK2 turn off, the energy stored in the secondary windings of the transformers Tr1 and Tr2 will be fed back to the unregulated supply source via diodes D1 and D2, respectively. High frequency transients and oscillations are damped by series RC circuits connected to the unregulated supply source. The supply source may operate in a way described above if the frequency of the push-pull control signal equals the parallel self-frequency of the circuit containing the high voltage transformer. It may be seen that a time-variable change of primary current of the high voltage transformer NTr is determined by impedances of the circuit and length of control signal so that a saw-tooth voltage arises with an amplitude depending upon the control signal (from zero to the magnitude of unregulated supply voltage). Accordingly, the circuit arrangement ensures sufficient time to control system consisting of the error signal processing circuit H and the control circuit V for intervening. The secondary winding of the high voltage transformer supplies a high voltage rectifier NE of usual layout, e.g. a voltage-doubling rectifier. One output of the high voltage rectifier is coupled with high voltage terminal UN via a series limiting resistor R3. The voltage signal output of the error signal processing circuit H is connected via a resistor R4 to the same output terminal. Resistor R3 and R4 constitute a voltage sampling divider. The series resistor R3 limits short circuit current. The other output of the high voltage rectifier NE is connected to commoned ground point of the supply source through a condenser C3. The current signal input of error processing circuit H is connected the same output. The high voltage supply with circuit arrangement according to the invention has the advantageous property that the output current remains constant whereby the output high voltage is adjusted in a wide range and this advantage is achieved without changing dissipated power in the high voltage rectifier or in the driving circuit. At a realized supply source, the efficiency of conversion was about 80 % independently of the output power. The magnitude of output current remains practically constant at short circuit. Another advantage of the present solution is the small weight and size with respect to output power of the realized apparatus.

Claims: A high voltage source providing continuously regulated output voltage, preferably for supplying low-power ion and electron beam machining and evaporating apparatuses, wherein said voltage source comprises a control circuit (V) whose control signal input is connected to signal output of an error signal processing circuit (H), a driving circuit (MH) whose control signal inputs are connected to push-pull control signal outputs of said control circuit (V), said driving circuit (MH) is coupled with a high voltage rectifier (NE) via high voltage transformer (NTr) with two push-pull primary windings, one of the high voltage output terminals of said rectifier is coupled via output voltage-sampling divider (R3,R4) on the one hand with high voltage output terminal (U N ) of said high voltage source, on the other hand with voltage signal input of said error signal processing circuit (H), wherein the other high voltage output terminal of said rectifier is coupled on the one hand via a high voltage capacitor (C3) with a common ground potential point of said high voltage source, on the other hand with current signal input of said error signal processing circuit, and supply voltage terminals of circuit arrangement blocks are connected to a low voltage supply source, wherein ground points of said circuit arrangement blocks are connected to the common ground potential terminal, characterized in that the push-pull control signal inputs of said driving circuit (MH) each are connected preferably via driver amplifiers (ME1 and ME2) to the control inputs of controlled switches (VK1 and VK2), respectively, one terminal each of said controlled switches (VK1 and VK2) is connected to said ground point, the other terminal thereof is connected to one end of each primary winding of said high voltage transformer (NTr), the other end of said each primary winding is coupled via secondary windings of transformers (Tr1 and Tr2), respectively with supply voltage terminal (U t ) of said low voltage supply source, and one end of each primary winding of said transformers (Tr1, Tr2) is commoned and connected to said ground point, each other end thereof is coupled on the one hand via each diode (D1 and D2) with said supply voltage terminal (U t ) on the other hand via series RC term with said ground point. A high voltage source according to claim 1, characterized in that said current signal input of said error signal processing circuit (H) is connected to said ground point via a current adjusting potentiometer (P1) whose sliding contact is connected to one input of a first error signal amplifier (HE1) via a current limiting Zener diode (Z), the other input of said error signal amplifier (HE1) is connected to a reference voltage source (UR), whereby the common point of said Zener diode (Z) and the input of said error signal amplifier (HE1) is connected to said ground point via a resistor (R5), the output of said error signal amplifier is connected also to said ground point via a voltage adjusting potentiometer (P2), the sliding contact of which is connected to one input of an another error signal amplifier (HE2), the other input of which forms the voltage signal input of said error signal processing circuit (H) and the output of said another error signal amplifier (HE2) is the signal output of said error signal processing circuit.

Inventors: BARNA, ARPAD, BODI, ISTVAN
Applicants: MTA MUESZAKI FIZIKAI KUTATO INTEZETE
Application year: 1986
Main classification: H02M3
IPC codes: H02M3, H01J37