JP5177437B2 - Electron beam scanning power supply - Google Patents

Description

  The present invention relates to an electron beam scanning power supply device for driving a scanning coil for scanning an electron beam (electron beam) one-dimensionally or two-dimensionally.

  Electron beam scanning devices that scan one-dimensionally or two-dimensionally an electron beam with a small diameter are used in various devices such as an electron beam drawing device (electron beam exposure device), an electron beam evaporation device, and a scanning electron microscope. (See, for example, Patent Document 1). In many cases, scanning of an electron beam is performed by a magnetic field generated by a scanning coil, and a class B amplifier is generally used for a driving circuit that supplies a driving current to the scanning coil. However, the class B amplifier has a problem that power efficiency is not so good because most of the power input to the scanning coil is consumed by the transistors of the amplifier circuit.

  In order to solve such problems, conventionally, an electron beam scanning drive device using a high-frequency switching amplifier (so-called class D amplifier) is known (see Patent Document 2). This is roughly classified into a full bridge circuit system and a half bridge circuit system.

  FIG. 4 is a schematic configuration diagram of an inverter driving system circuit using a full bridge circuit. In FIG. 4, a current flowing through a scanning coil 23 for scanning an electron beam is detected by a current detector 22, and the error amplifier 10 outputs an error signal between the detection signal and an input signal for scanning control. This error signal is compared with a carrier signal such as a triangular wave or a sawtooth wave in the comparators 11 and 12, and a PWM (pulse width modulation) signal is output from each of the comparators 11 and 12. The full bridge circuit 17 connected between the DC power source 18 and GND (ground point) is composed of four power MOSFETs 171, 172, 173, 174. The PWM signal from the comparators 11, 12 is a non-inverting gate 13, 15 and the inverting gates 14 and 16 are supplied to the gate terminals of the power MOSFETs 171 to 174. The midpoint of the two bridge arms of the full bridge circuit 17 is connected to the scanning coil 23 via a high frequency smoothing reactor 19 and a capacitor 20.

  When the error signal from the error amplifier 10 is larger than the carrier signal, the comparator 12 outputs a PWM pulse having a level “1” and the comparator 11 having a level “0”. At this time, the power MOSFETs 172 and 173 are turned on, the power MOSFETs 171 and 174 are turned off, and a downward driving current flows through the scanning coil 23. On the other hand, when the error signal is smaller than the carrier signal, an upward drive current flows through the scanning coil 23.

  In general, a direct current detector (DCCT) using a Hall element is used as the current detector 22, but current detection accuracy by DCCT is relatively low. For this reason, it is difficult to stably perform electron beam scanning with high accuracy. Although it is conceivable to use a shunt resistor instead of DCCT to detect the current flowing in the scanning coil 23, in the case of the full bridge circuit as described above, both ends of the shunt resistor are in a state of floating with respect to GND. . Although the potential difference between both ends of the shunt resistor in such a state can be detected by the differential amplifier, the common-mode voltage cannot be removed even if the differential amplifier is used. Therefore, the current detection accuracy is still low, and it is difficult to perform stable electron beam scanning.

  In contrast, in the case of a half-bridge circuit, since the midpoint between the positive power supply voltage and the negative power supply voltage can be set to the ground potential, the current can be directly supplied by the shunt resistor, that is, without using a differential amplifier. Can be detected. Therefore, it is advantageous for improving the current detection accuracy. However, especially in the electron beam scanning apparatus for the above-described applications, complicated scanning is required, and not only a high-frequency current is allowed to flow through the scanning coil but also a DC current or a low-frequency current of about several Hz may be allowed to flow. When such a drive is performed, the energy stored in the high-frequency smoothing reactor is released to either the positive or negative bridge arm, and the voltage rises on that side and the balance of the bridge is lost. . As a result, the desired electron beam scanning may not be possible.

JP 2003-270390 A JP 2001-169138 A

  The present invention has been made in view of the above problems, and its main purpose is to superimpose a direct current on a high-frequency current flowing through a scanning coil, to drive at a low frequency, or to change an input power supply voltage. An object of the present invention is to provide an electron beam scanning power supply device capable of stable and highly accurate electron beam scanning even in the situation.

In order to solve the above problems, the present invention is connected between a positive electrode and a negative electrode of a DC power supply in order to supply a drive current to a scanning coil that scans an electron beam one-dimensionally or two-dimensionally. A half-bridge circuit including two switching elements in series, a scanning coil connected to a series connection point of the two switching elements via a reactor, and a resistor for detecting a current flowing through the scanning coil And a PWM drive circuit unit that generates a PWM signal for turning on and off the switching element of the half-bridge circuit according to a detection voltage by the resistor.
a) a pair of electrolytic capacitors provided between the positive electrode of the DC power source and the ground point, and between the ground point and the negative electrode of the DC power source;
b) The balance of the voltage across each of the pair of electrolytic capacitors is monitored, and when the voltage across the one electrolytic capacitor becomes larger than ½ of the DC power supply voltage, the current flowing out of the electrolytic capacitor is Energy transfer means having a current path flowing into the other electrolytic capacitor;
It is characterized by having.

  In the electron beam scanning power supply apparatus according to the present invention, in a steady operation state, the voltage across the electrolytic capacitors as a pair is maintained at VCC / 2 which is substantially half of the DC power supply voltage VCC, and the bridge arm of the half bridge circuit A power supply voltage of ± VCC / 2 is applied to both ends. As a result, the two switching elements of the half-bridge circuit operate in a balanced state. If the voltage across one of the paired electrolytic capacitors drops for some reason, the voltage across the other electrolytic capacitor rises by the reduced voltage. Then, the energy transfer means functions, and current is sent from the electrolytic capacitor on the side where the voltage at both ends is increased to the electrolytic capacitor on which the voltage is decreased. Due to this current flow, the latter electrolytic capacitor is charged to increase the voltage at both ends, and the voltage at both ends of the former electrolytic capacitor is decreased. As a result, the voltage across each electrolytic capacitor is quickly returned to VCC / 2.

In the electron beam scanning power supply device according to the present invention, as a specific aspect of the energy transfer means,
Two auxiliary switching elements in series connected between a positive electrode and a negative electrode of the DC power supply;
Two diodes in series connected between a positive electrode and a negative electrode of the DC power supply;
Drive signal generating means for supplying a drive signal for alternately turning on the two auxiliary switching elements;
The primary winding connected between the connection point of the two auxiliary switching elements and the grounding point, the same number of windings as the primary winding and the reverse polarity, and one end via the current limiting element A transformer having a secondary winding connected to a connection point of the two diodes and having the other end grounded;
It can be set as the structure containing.

  In this configuration, when the voltage across one electrolytic capacitor drops below VCC / 2 and the voltage across the other electrolytic capacitor rises above VCC / 2, the voltage across the capacitor increases through one auxiliary switching element that is turned on. Current flows from the electrolytic capacitor to the primary winding of the transformer. As a result, a reverse polarity voltage is generated in the secondary winding of the transformer, and current flows into the electrolytic capacitor whose voltage at both ends is low via a current limiting element such as a reactor and a diode. As a result, the voltage across each electrolytic capacitor is quickly returned to VCC / 2.

In the electron beam scanning power supply device according to the present invention, as another specific aspect of the energy transfer means,
The primary winding to which the voltage across one electrolytic capacitor is applied, the same number of windings as the primary winding and the reverse polarity, and the current is applied to the positive or negative electrode of the DC power source to which the other electrolytic capacitor is connected. A DC / DC converter including a transformer having a secondary winding connected to be supplied may be provided for each electrolytic capacitor.

  In this configuration, when the voltage across one electrolytic capacitor falls below VCC / 2 and the voltage across the other electrolytic capacitor rises above VCC / 2, the primary winding is connected to both ends of the electrolytic capacitor where the voltage across the capacitor has increased. The DC / DC converter including the transformed transformer functions, and a current flows from the secondary winding of the transformer to the electrolytic capacitor whose voltage at both ends is low. As a result, the voltage across each electrolytic capacitor is quickly returned to VCC / 2.

  According to the electron beam scanning power supply device according to the present invention, when a direct current is superimposed on a high frequency current passed through the scanning coil, when driven at a low frequency, when an input power supply voltage fluctuates, etc. Even when the balance between the positive and negative power supply voltages supplied to the bridge circuit is lost, it can be quickly restored to the original state. As a result, the supply of drive current to the scanning coil by the half bridge circuit is stabilized and the accuracy is improved, and the electron beam scanning can be performed stably and with high accuracy.

1 is a schematic configuration diagram of an electron beam scanning power supply device according to a first embodiment of the present invention. FIG. The schematic block diagram of the electron beam scanning power supply device by 2nd Example of this invention. FIG. 6 is a schematic waveform diagram for explaining the operation of the electron beam scanning power supply device according to the first and second embodiments of the present invention. 1 is a schematic configuration diagram of a conventional electron beam scanning power supply device.

[First embodiment]
Hereinafter, an electron beam scanning power supply according to a first embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram of an electron beam scanning power supply device according to the first embodiment. The same components as those of the conventional configuration already described are denoted by the same reference numerals and description thereof is omitted.

  In FIG. 1, the half bridge circuit 30 connected between the positive electrode and the negative electrode of the DC power supply 18 is constituted by two power MOSFETs 301 and 302, and the PWM signal from the comparator 11 is transmitted through the non-inverting gate 13 and the inverting gate 14 to the power MOSFET 301. , 302 are supplied to the gate terminals. A connection point P between the two power MOSFETs 301 and 302 is connected to one end of the scanning coil 23 via the high-frequency smoothing reactor 19, and between the other end of the scanning coil 23 and a ground point (hereinafter referred to as "GND"). Is provided with a shunt resistor 35 for current detection. A capacitor 20 is connected to the scanning coil 23 in parallel. A voltage signal corresponding to the coil current detected by the shunt resistor 35 is fed back to the error amplifier 10.

  A positive voltage side electrolytic capacitor 33 is connected between the positive electrode of the DC power supply 18 and GND, and a negative voltage side electrolytic capacitor 34 is connected between the GND and the negative electrode of the DC power supply 18. In addition, two power MOSFETs (auxiliary switching elements in the present invention) 40 and 41 are connected in series between the positive electrode and the negative electrode of the DC power supply 18, and a transformer 42 is connected between the connection point and GND. The primary winding L1 is connected. The secondary winding L2, which has the same number of windings as the primary winding L1 and has the opposite polarity, is also connected at one end to GND and the other end via the reactor 43, which is a current limiting element, to the positive and negative electrodes of the DC power supply 18. It is connected to the connection point of two diodes 44 and 45 connected in series between them.

  Pulse signals whose polarities are inverted are supplied from the pulse generator 46 to the gate terminals of the power MOSFETs 40 and 41, respectively. Strictly speaking, the pulse signals applied to the gate terminals of the power MOSFETs 40 and 41 are alternately “1” and the timing is adjusted so that the periods of “1” do not overlap. Therefore, the power MOSFETs 40 and 41 are controlled so that the other is always turned off while the other is turned on. The electrolytic capacitors 33 and 34, the diodes 44 and 45, the transformer 42, the reactor 43, the power MOSFETs 40 and 41, and the pulse generator 46 are used to quickly restore the bridge arm of the half bridge circuit 30 when the balance is lost. It has the function of.

  A characteristic operation of the electron beam scanning power supply device of the first embodiment will be described. The error signal from the error amplifier 10 is compared with a carrier signal that is, for example, a triangular wave in the comparator 11, and a PWM signal is output from the comparator 11. When the error signal is larger than the carrier signal, the comparator 11 outputs a PWM signal whose level is “0”, whereby the power MOSFET 301 is turned off and the power MOSFET 302 is turned on, and the upward drive current i 2 is supplied to the scanning coil 23. Flows. On the other hand, when the error signal is smaller than the carrier signal, the power MOSFET 301 is turned on, the power MOSFET 302 is turned off, and a downward driving current i1 flows through the scanning coil 23.

  In a state where the half bridge circuit 30 operates in a balanced manner, the voltage across each of the two electrolytic capacitors 33 and 34 is maintained at ½ of the DC power supply voltage VCC. For example, if VCC = 100 [V], both voltages are maintained at 50 [V]. As described above, the power MOSFETs 40 and 41 are alternately turned on. For example, when the power MOSFET 40 is turned on, the voltage across the positive voltage side electrolytic capacitor 33, that is, VCC / 2 is applied across the primary winding L 1 of the transformer 42. At this time, a voltage of -VCC / 2 is generated at both ends of the secondary winding L2 of the transformer 42 with respect to GND, but the end opposite to the end of the reactor 43 connected to the secondary winding L2 Since the potential between the part and GND is -VCC / 2, the current through the reactor 43 does not flow in any direction. That is, no current flows through the power MOSFET 40 in the on state. Similarly, when the power MOSFET 41 is turned on while the half bridge circuit 30 is operating in a balanced state, no current flows through the power MOSFET 41 in the on state.

  For example, as shown in FIG. 3A, when an input signal in which a DC voltage is superimposed on a scanning input signal is supplied, the pulse width of the PWM signal by the comparator 11 changes, and the balance of the bridge of the half bridge circuit 30 is changed. May collapse. Even in this case, since the DC power supply voltage VCC applied to the half-bridge circuit 30 is constant, the balance is lost as described above, and therefore, as shown in FIG. When the voltage at both ends decreases by ΔV from VCC / 2, the voltage at both ends of the negative voltage side electrolytic capacitor 34 increases by ΔV from VCC / 2 (the negative side terminal potential of the negative voltage side electrolytic capacitor 34 is − (VCC / 2− ΔV)).

  When the power MOSFET 41 is turned on, a voltage of (VCC / 2 + ΔV is applied to both ends of the primary winding L1 of the transformer 42, and the same voltage is generated at both ends of the secondary winding L2. Since the voltage at the end opposite to the ground end of the secondary winding L2 is VCC / 2 + ΔV, the voltage at the positive terminal of the positive voltage side electrolytic capacitor 33 is VCC / 2−ΔV. A potential difference of approximately 2 × ΔV is generated at both ends of the capacitor, and a current flows from the secondary winding L2 of the transformer 42 to the positive electrode side terminal of the positive voltage side electrolytic capacitor 33 via the reactor 43 and the diode 44. As a result, the voltage at both ends of the positive voltage side electrolytic capacitor 33 rises, and conversely, the voltage at both ends of the negative voltage side electrolytic capacitor 34 decreases. When the both-ends voltage reaches VCC / 2, the current flow through the reactor 43 and the diode 44 is stopped, so that the half-bridge circuit 30 returns to a balanced state.

  That is, when the voltage at both ends of the positive voltage side electrolytic capacitor 33 decreases and the voltage at both ends of the negative voltage side electrolytic capacitor 34 increases, the stored energy is transferred from the negative voltage side electrolytic capacitor 34 to the positive voltage side electrolytic capacitor 33 via the transformer 42. This causes the voltage across both electrolytic capacitors 33, 34 to be equal. When the voltage at both ends of the negative voltage side electrolytic capacitor 34 is lowered and the voltage at both ends of the positive voltage side electrolytic capacitor 33 is raised instead, the positive voltage is passed through the transformer 42 while the power MOSFET 40 is on. The stored energy is transferred from the side electrolytic capacitor 33 to the negative voltage side electrolytic capacitor 34, whereby the voltages at both ends of both electrolytic capacitors 33 and 34 become equal.

  As described above, in the electron beam scanning power supply device of the first embodiment, even when the balance of the half-bridge circuit 30 is lost due to various factors such as DC current superposition, low-frequency driving, or power supply voltage fluctuation, It is possible to implement such driving that quickly repairs it and allows an appropriate current to flow through the scanning coil 23. In particular, in the case of the configuration of this power supply device, feedback control is not performed to balance the voltages across the electrolytic capacitors 33 and 34, so there is no anxiety such as ringing associated with feedback control, and unnecessary power loss. Therefore, there is an advantage that efficiency is good.

[Second Embodiment]
Next, an electron beam scanning power supply device according to a second embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 2 is a schematic configuration diagram of an electron beam scanning power supply device according to the second embodiment. The same components as those of the conventional configuration and the first embodiment already described are denoted by the same reference numerals, and description thereof is omitted.

  In the electron beam scanning power supply device of the second embodiment, a positive voltage side electrolytic capacitor 33 is connected between the positive electrode of the DC power supply 18 and GND, and negative voltage side electrolysis is connected between the GND and the negative electrode of the DC power supply 18. The point that the capacitor 34 is connected is the same as in the first embodiment. When the balance of the bridge of the half-bridge circuit 30 is lost and the voltages at both ends of the electrolytic capacitors 33 and 34 change complementarily, the stored energy of the electrolytic capacitors 33 and 34 is moved to each other. The circuit configuration for this is different from that of the first embodiment.

  That is, in the second embodiment, the first DC / DC converter 31 is inserted between both ends of the positive voltage side electrolytic capacitor 33 and the negative electrode of the GND and the DC power supply 18. A second DC / DC converter 32 is interposed between both ends and the positive electrode and GND of the DC power supply 18. The first and second DC / DC converters 31 and 32 have the same configuration. For example, the first DC / DC converter 31 includes a transformer 312 and a switching winding connected in series to the primary winding of the transformer 312. MOSFET 311, a rectifying diode 313 connected in series to the secondary winding of the transformer 312, an output voltage after rectification via the diode 313, and a reference voltage of VCC / 2 by a built-in reference voltage source An error amplifier 314 that outputs an error, a PWM drive unit 315 that outputs a PWM signal having a pulse width corresponding to the output of the error amplifier 314, and a non-inverting gate 316 that supplies the PWM signal to the gate terminal of the MOSFET 311 are included.

  In FIG. 2, the transformers 312 and 322 are illustrated in a simplified manner. However, as shown in FIG. 1, this may include a current limiting element such as a reactor in addition to the transformer.

  The characteristic operation of the electron beam scanning power supply device of the second embodiment will be described. As in the first embodiment, when the half bridge circuit 30 is operating in a balanced manner, the voltage across the two electrolytic capacitors 33 and 34 is maintained at ½ of the DC power supply voltage VCC. At this time, the error detected by the error amplifiers 314 and 324 becomes almost zero, the outputs of the PWM drive units 315 and 325 become “0”, and the two MOSFETs 311 and 321 both remain off. As a result, neither the first and second DC / DC converters 31 and 32 operate, and energy transfer between the two electrolytic capacitors 33 and 34 does not occur.

  When the balance of the bridge of the half-bridge circuit 30 is lost and the voltage across the positive voltage side electrolytic capacitor 33 decreases by ΔV from VCC / 2 as shown in FIG. 3B, the voltage across the negative voltage side electrolytic capacitor 34 becomes Increased by ΔV from VCC / 2. Since the voltage across the positive voltage side electrolytic capacitor 33 is fed back to the error amplifier 324 of the second DC / DC converter 32, the error amplifier 324 calculates an error between (VCC / 2) -ΔV and the reference voltage VCC / 2. The PWM drive unit 325 outputs a PWM signal with a “1” pulse width expanded. The larger the ΔV, the wider the pulse width. As a result, the second DC / DC converter 32 operates, the MOSFET 322 is turned on while the PWM signal is “1”, and the current from the electrolytic capacitor 34 flows in the primary winding of the transformer 322. Accordingly, a current also flows through the secondary winding of the transformer 322, and this current flows into the positive voltage side electrolytic capacitor 33 through the diode 323, and the positive voltage side electrolytic capacitor 33 is charged. That is, by the operation of the second DC / DC converter 32, the stored energy is transferred from the negative voltage side electrolytic capacitor 34 to the positive voltage side electrolytic capacitor 33, so that the voltages at both ends of both electrolytic capacitors 33 and 34 become equal. . As a result, as in the first embodiment, the bridge arm of the half bridge circuit 30 is restored to a balanced state.

  Conversely, when the voltage at both ends of the negative voltage side electrolytic capacitor 34 decreases by ΔV from VCC / 2, and the voltage at both ends of the positive voltage side electrolytic capacitor 33 increases by ΔV from VCC / 2, the operation is completely opposite to the above. That is, by the operation of the first DC / DC converter 31, the stored energy is transferred from the positive voltage side electrolytic capacitor 33 to the negative voltage side electrolytic capacitor 34, so that the voltage across each of the electrolytic capacitors 33, 34 is Will be equal.

  As described above, even in the electron beam scanning power supply device of the second embodiment, even when the balance of the half-bridge circuit 30 is lost due to various factors such as DC current superposition, low-frequency driving, or power supply voltage fluctuation, It is possible to implement such driving that quickly repairs it and allows an appropriate current to flow through the scanning coil 23.

  In addition, the said Example is only an example of this invention, Even if it changes suitably, changes, or is added in the range of the meaning of this invention in points other than the above-mentioned description, it is included by the claim of this application. It is clear.

DESCRIPTION OF SYMBOLS 10 ... Error amplifier 11 ... Comparator 13 ... Non-inverting gate 14 ... Inverting gate 18 ... DC power supply 19 ... High frequency smoothing reactor 20 ... Capacitor 23 ... Scanning coil 30 ... Half bridge circuit 301, 302 ... Power MOSFET
31, 32 ... DC / DC converters 311, 321 ... MOSFETs
312, 322, transformers 313, 323, diodes 314, 324, error amplifiers 315, 325, PWM drive units 316, 326, non-inverting gate 33, positive voltage side electrolytic capacitor 34, negative voltage side electrolytic capacitor 35, shunt resistor 40, 41 ... Power MOSFET
42 ... Transformer 43 ... Reactors 44, 45 ... Diode 46 ... Pulse generator

Claims (3)

A half-bridge circuit including two switching elements connected in series between a positive electrode and a negative electrode of a DC power source for supplying a driving current to a scanning coil that scans an electron beam in a one-dimensional or two-dimensional manner; A scanning coil connected to a series connection point of the two switching elements via a reactor, a resistor for detecting a current flowing through the scanning coil, and the half bridge according to a detection voltage by the resistor In an electron beam scanning power supply device comprising: a PWM drive circuit unit that generates a PWM signal for turning on and off a switching element of a circuit;
a) a pair of electrolytic capacitors provided between the positive electrode of the DC power source and the ground point, and between the ground point and the negative electrode of the DC power source;
b) The balance of the voltage across each of the pair of electrolytic capacitors is monitored, and when the voltage across the one electrolytic capacitor becomes larger than ½ of the DC power supply voltage, the current flowing out of the electrolytic capacitor is Energy transfer means having a current path flowing into the other electrolytic capacitor;
An electron beam scanning power supply device comprising: The electron beam scanning power supply device according to claim 1, wherein the energy transfer means includes:
Two auxiliary switching elements in series connected between a positive electrode and a negative electrode of the DC power supply;
Two diodes in series connected between a positive electrode and a negative electrode of the DC power supply;
Drive signal generating means for supplying a drive signal for alternately turning on the two auxiliary switching elements;
The primary winding connected between the connection point of the two auxiliary switching elements and the grounding point, the same number of windings as the primary winding and the reverse polarity, and one end via the current limiting element A transformer having a secondary winding connected to a connection point of the two diodes and having the other end grounded;
An electron beam scanning power supply device comprising: The electron beam scanning power supply device according to claim 1, wherein the energy transfer means includes:
The primary winding to which the voltage across one electrolytic capacitor is applied, the same number of windings as the primary winding and the reverse polarity, and the current is applied to the positive or negative electrode of the DC power source to which the other electrolytic capacitor is connected. An electron beam scanning power supply apparatus comprising: a DC / DC converter including a transformer having a secondary winding connected to be supplied for each electrolytic capacitor.

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