DE102010002231A1 - Method for generating voltage pulse to specific range, involves loading output capacitors over inductor, adjusting level of voltage pulse, and addressing pockels cell with voltage pulse, where pulse level is provided in specific range - Google Patents

Abstract

The method involves loading output capacitors (16-19) over an inductor (L). A level of a voltage pulse is adjusted, where the pulse level is less than 2 percent, and is varied. A pockels cell (11) is addressed with the voltage pulse via switch-on time of semiconductor switches (12-15) e.g. bipolar transistors, voltage of a direct voltage supply (25) and/or a transmission ratio of a transmitter. Energy in the inductors is stored, where the stored energy is reloaded in the capacitors or the switches. Rising and/or falling edges of the pulse comprise a slope greater than 40 volts per nanosecond. An independent claim is also included for a circuit for supplying pockels cell with a voltage pulse comprising semiconductor switches switched in series.

Description

The invention relates to a method for generating a voltage pulse> 500 V with constant voltage, as well as a circuit, in particular for carrying out the method.

For certain applications, for example for controlling a Pockels cell, very high voltage pulses, in particular in the range> 500 V, more often even in the range> 3000 V, must be generated. While these voltage pulses are applied to the Pockels cell, their voltage should be as constant as possible. In addition, steep edges of the voltage pulse are desirable. So far, so-called Pockels cell switch were used to drive Pockels cells, which are very complex and expensive. As a rule, the high voltage to be applied to the Pockels cell was generated by a voltage source and, if necessary, applied to the Pockels cell via a switch.

A circuit for generating a high-voltage pulse having an inductance, a switch and a capacitor arranged in parallel with the switch, which is charged via the inductance, is known from US Pat JP 02-197 269 A , of the JP 02-304 991 A and the US 5,881,082 known.

The DE 10 2006 060 417 A1 discloses a system for generating a voltage pulse with a pulse generator, wherein a plurality of cells are each provided with a controllable semiconductor switch and a capacitor for generating a voltage pulse by series connection and / or parallel connection of the capacitors by means of the semiconductor switches.

The US 6,184,662 B1 discloses a pulsed power supply in which a series circuit of capacitor, inductance and another parallel circuit of a coil and a resistor is provided parallel to a switch.

From the DE 103 56 648 A1 an electronic Pockelszellentreiber with a high voltage switch is known, wherein the high voltage switch has at least two provided with one input and one output bridges.

The object of the present invention is to provide a method or a circuit which is suitable for generating a voltage pulse of> 500 V with as constant a voltage as possible and steep edges.

This object is achieved according to the invention by a method having the features of claim 1. This method has the advantage that a voltage at the level of the voltage pulse does not have to be constantly provided, but that, for example, a DC voltage source having a voltage between 40 V and 90 V. is sufficient to produce a very high voltage pulse. The inductance charges the output capacitance of at least one semiconductor switch. As a result, a high voltage drops in the capacity. Once the capacitance is charged, a backflow of charge into the inductor and thus a discharge of the capacitance across the inductor is prevented. This ensures that the voltage at the output capacitance remains constant during the duration of the voltage pulse.

The height of the voltage pulse is set. The voltage pulse can thus be adapted to the respective application.

Advantageously, the height of the voltage pulse over the turn-on of the semiconductor switch can be adjusted. In particular, it can be provided that the inductance is arranged in series with the semiconductor switch. By turning on the semiconductor switch, a current can flow into the inductor, so that energy is stored in the inductor. The longer the semiconductor switch is turned on, the more energy can be stored in the coil and the higher the voltage across the output capacitance of the semiconductor switch when the switch is opened.

Furthermore, it can be provided that the height of the voltage pulse is set via the number of series-connected semiconductor switches. If all the same semiconductor switches are used, the output voltage, or the magnitude of the voltage pulse, can be scaled as desired.

According to a variant of the method it can be provided that the height of the voltage pulse is adjusted by the voltage of a DC voltage supply and / or the transmission ratio of a transformer. This procedure is particularly suitable when the inductance is the secondary winding of a transformer and the primary winding of the transformer can be connected to a DC voltage supply.

It is particularly preferred if the height of the voltage pulse after settling varies by less than 10%, preferably less than 5%, particularly preferably less than 2%. If the voltage of the voltage pulse varies less than these tolerances, the magnitude of the voltage is considered constant in the sense of the invention. With the method according to the invention, it is possible in a simple manner to generate a voltage pulse of constant height, which is suitable for operating a Pockels cell.

Further advantages result if the rising and / or the falling edge of the voltage pulse has a slope> 40 V / ns.

In a particularly preferred embodiment of the method can be provided that the voltage pulse is terminated by the at least one semiconductor switch is turned on. This means that the end of the voltage pulse is not initiated and determined by characteristics of the components of the circuit, but that actively the end of the voltage pulse can be initiated by means of the semiconductor switch. Thus, the length of the voltage pulse is definable and adjustable.

According to a variant of the method, it can be provided that the voltage pulse is terminated in stages, by at least two series-connected semiconductor switches being turned on successively. Thus, the output capacitances of the semiconductor switches are discharged sequentially. The discharge takes place via internal resistors of the semiconductor switch.

First, the energy can be stored in the inductor and then the stored energy can be reloaded into one or more output capacitances of the semiconductor switch (s). As previously described, this procedure can be used to set the energy stored in the inductance, which is then made available to the output capacitances. Thus, the height of the voltage pulse can be adjusted particularly easily. However, current must first be fed into the inductance before the voltage pulse can be generated. The generation of the voltage pulse can therefore be associated with a time delay.

Particular advantages arise when a Pockels cell is driven by the voltage pulse.

In the context of the invention, in addition, a circuit, in particular for carrying out the method according to the invention, with the features of claim 10. Such a circuit has the advantage that it can be constructed very inexpensively. Besides, it is relatively easy. The circuit can be made so small that it may be accommodated in a laser. In this respect, the circuit is particularly suitable for supplying Pockels cells with a voltage pulse. In particular, voltage pulses of more than 500 V, in particular up to 20 kV can be generated with the circuit.

It is particularly preferred if a plurality of semiconductor switches are connected in series. This reduces the output capacitance of the circuit on the one hand and on the other hand can thereby generate a higher voltage pulse.

In one embodiment it can be provided that the semiconductor switches are assigned the same inductance supplying the respective output capacitance. This means that the inductance and the semiconductor switches are connected in series.

In a further development it can be provided that the inductances are secondary windings or secondary winding sections of a transformer. Through the use of transformers galvanic isolation can take place. The secondary winding sections can be formed by the secondary winding of the transformer having a plurality of taps.

In particular, in this context, so if each semiconductor switch is assigned its own inductance, it is advantageous if each semiconductor switch is associated with its own backflow preventer. Thus, it can be reliably prevented for each semiconductor switch that this is unintentionally discharged via a current flow back to the inductor.

Particular advantages arise when the one or more backflow preventer comprises at least one diode, in particular a SiC diode, or a switch. Both diodes and (semiconductor) switches should be designed to have only very small reverse recovery charges. The junction capacitance can be reduced if several diodes or (semiconductor) switches are connected in series. It can thereby be achieved that the capacity of the non-return valve is smaller than the output capacity of the circuit.

If this condition is met, backflow of charge into the inductor can be reliably prevented.

In one embodiment, at least one transformer can be provided, to whose primary winding a switch is connected in series. By this measure, the flow of current can be controlled in the transformer.

The primary winding and the secondary winding of the transformer can be arranged in the same direction or in opposite directions. In an opposing arrangement of the primary winding and the secondary winding, the coil can first be charged and then the energy is transferred from the coil to the output capacitance. In the same direction winding can be done with power to the primary winding immediately charging the output capacitance across the secondary winding.

It is particularly preferred if a switch is provided, via which one or more semiconductor switches can be switched on and off simultaneously (conductive and non-conductive switchable). This can ensure that the voltage pulse is generated with a large slope. For example, the switch can drive drive transformers, which are connected to the control terminals of the semiconductor switches.

As already mentioned, it is advantageous if the circuit has a DC voltage supply. The voltage provided by the DC voltage supply can be significantly less than the amplitude or the height of the voltage pulse to be generated.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

Preferred embodiments of the invention are shown schematically in the drawing and are explained below with reference to the figures of the drawing. Show it:

1a a first embodiment of a circuit according to the invention;

1b a diagram for explaining the operation of the circuit according to 1a ;

2 B a second embodiment of a erfindungnsgemäßen circuit;

2 B a diagram for explaining the operation of the circuit according to 2a ;

3a a third embodiment of a circuit according to the invention;

3b a diagram for explaining the operation of the circuit according to 3a ;

4a a voltage pulse recorded with a meter;

4b the rising and the falling edge of the voltage pulse of the 4a in greater temporal resolution.

The circuit 10 according to 1a serves to generate a voltage pulse for driving a Pockels cell 11 with the capacity approx. The circuit 10 In the exemplary embodiment, there are four series-connected semiconductor switches 12 . 13 . 14 . 15 on, each having an output capacity 16 to 19 exhibit. With the capacities 16 to 19 These are internal capacities of the semiconductor switches 12 to 15 , They do not represent separate components.

The semiconductor switches 12 to 15 may be formed as shown as bipolar transistors, as field effect transistors, in particular MOSFETs, or the like. The output capacitance of the semiconductor switches 12 to 15 is in each case 80 pF, for example. Due to the series connection of the capacities 16 to 19 This means that the output capacitance of the series connection of the semiconductor switches 12 to 15 20 pF. This capacity is connected in parallel with the capacitance Ca, which is 5 pF, for example. The total output capacitance of the circuit is therefore about 25 pF.

A trained in the embodiment as a transistor switch T1 is connected to the semiconductor switches 12 to 15 assigned Ansteuerübertragern 20 to 23 connected. The switch T1 in turn has a drive transformer 24 on, and can thus be controlled for example by a function generator. When the switch T1 is turned on, the semiconductor switches automatically become simultaneously as well 12 to 15 switched on. This means that a current through the semiconductor switch 12 to 15 can flow. In particular, flows due to the DC power supply 25 that have a capacitor 26 includes, a current through the inductance L, the backflow preventer 27 and the semiconductor switches 12 to 15 ,

This is also from the 1b seen. At time t1, the switch T1 and thus the semiconductor switches 12 to 15 switched on. At the same time, the current iL increases linearly in the inductance L, which is due to the straight line 30 is indicated. After a predetermined time, for example one microsecond, the switch T1 is switched off again (falling edge 31 ). This means that practically suddenly stored in the inductance L energy in the capacity 16 to 19 is transferred and the current iL breaks, which is due to the falling edge 32 is indicated. At the same time, the voltage U _Ca at the capacitance Ca jumps to a significant value, which is due to the edge 33 is indicated. This voltage is kept constant, see straight line 34 , This is because the capacities 16 to 19 because of the backflow preventer 27 can not be unloaded. The backflow preventer 27 is in the embodiment of four series-connected diodes 35 to 28 , in particular SiC diodes, formed. The prevention of the discharge of the output capacities is in particular caused by the capacity of the non-return valve 27 is less than the output capacitance of the circuit 10 ,

The tension, see straight line 34 , is held constant until the switch T1 and thus the semiconductor switches 12 to 15 be switched back on (turned on). At the same time, the voltage U _Ca abruptly drops to 0 and at the same time the current iL again begins to increase linearly. In this embodiment, the voltage pulse occurs 40 with a delay to turn on the switch T1 or the semiconductor switch 12 to 15 one thing by the arrow 41 is indicated. This may be desirable only in some applications.

From the 1b It can be seen that the magnitude of the current in the inductance iL of the turn-on of the semiconductor switches 12 to 15 depends. This also means that it is the height of the voltage pulse 40 depends. About the duty cycle of the semiconductor switch 12 to 15 can thus also the height of the voltage pulse 40 be set.

The semiconductor switches 12 to 15 For example, they may be designed so that a voltage of 800 V drops across each semiconductor switch. In the exemplary embodiment, therefore, a maximum voltage pulse of 3,200 V could be generated. This means that also about the number of semiconductor switches used 12 to 15 the height of the voltage pulse can be influenced. From the description of 1a and 1b It is also clear that the voltage level from pulse to pulse over the duty cycle of the semiconductor switches 12 to 15 is adjustable. By choosing the switch-off of the semiconductor switch 12 to 15 In addition, the pulse duration can be set. Because of the output capacities 16 to 19 the semiconductor switch 12 to 15 can be used, the circuit can be built particularly inexpensive, since no additional components for the capacity are needed.

In the embodiment of a circuit 100 according to 2a again is a DC power supply 25 intended. At this is a transformer 101 connected, wherein the primary winding LP is connected in series with the switch T1. To the secondary windings 102 . 103 . 104 . 105 are the semiconductor switches 12 to 15 connected, being between the output capacities 16 to 19 the semiconductor switch 12 to 15 Backflow preventer 106 . 107 . 108 . 109 are connected, which are designed as diodes. The secondary windings 102 to 105 are arranged in opposite directions to the primary winding LP. The secondary windings may be separate coils or secondary winding sections formed by tapping a secondary winding.

The control terminals of the semiconductor switches 12 to 15 are each with Ansteuerübertragern 20 to 23 connected, which are controlled by the switch T2. Parallel to the series connection of the output capacities 16 to 19 is again the Pockels cell 11 switched with their capacity Ca.

The switch T1 can in turn be turned on at time t1, which is due to the rising edge 110 in the 2 B is indicated. This means that a current can flow into the primary winding LP. With increasing duty cycle of the transistor T1, the current in the primary winding LP of the transformer increases 101 , This is due to the rising straight 101 shown. Because of the opposite winding of the secondary windings 102 to 105 and the arrangement of the form of a diode backflow preventer 106 to 109 (Secondary winding side with its anode), a current flow is prevented on the secondary side, while the switch T1 is turned on.

The switch T1 is turned off, due to the falling edge 112 is shown, then the current iLP, which flows into the primary winding LP, abruptly drops, which is due to the falling edge 113 is shown. At the same time it will be in the transformer 101 stored energy in the capacities 16 to 19 transhipped. This too occurs abruptly, so that a sudden increase in the voltage U _Ca over the capacitance Ca takes place. This is due to the rising edge 114 indicated.

The backflow preventers 106 to 109 prevent a discharge of capacity 16 to 19 over the secondary windings 102 to 105 , This means that the voltage U _Ca remains constant, reflecting the line 115 is indicated. The length of the voltage pulse 116 is determined by the switch T2. This is about Ansteuerübertrager 117 . 118 . 119 . 120 with the control terminals of the semiconductor switches 12 to 15 connected. Accordingly, if the switch T2 is turned on, so are the semiconductor switches simultaneously 12 to 15 turned on, so that the capacity 16 to 19 discharged suddenly. This leads to the falling edge 121 , For this purpose, the switch T2 must only be switched on for a short time, as indicated by the switch-on pulse 122 lets recognize. By the arrow 123 is implied that the voltage pulse 116 is generated with a delay after switching on the switch T1.

In particular, the voltage pulse is 116 only when the switch T1 is turned off again, that is not turned on. The end of the voltage pulse 116 However, it occurs immediately when switching on the switch T2. This is by the arrow 124 implied, which expresses that the flanks 125 . 121 almost simultaneously. In contrast to the previous embodiment, the switch T1 is therefore only for charging the primary winding LP and thus the secondary windings 102 to 105 and for the beginning of the voltage pulse 116 responsible. The end can be initiated independently of the switch T1 by the switch T2.

In the 3a is a circuit 200 shown, in turn, a DC power supply 25 having. The switch T1 is in turn in series with the primary winding LP of a transformer 201 connected. The secondary windings 202 . 203 . 204 . 205 of the transformer 201 are arranged in the same direction to the primary winding LP. To the secondary windings 202 to 205 are designed as diodes backflow preventer 206 . 207 . 208 . 209 Solid state switch 12 to 15 with internal capacities 16 to 19 , at the same time the output capacitances of the respective semiconductor switches 12 to 15 represent, connected. The capacities 16 to 19 are connected in series. Parallel to this again is the capacity Ca of the Pockels cell 11 connected.

Is in the embodiment of 3a the switch T1 is turned on, so again flows a current in the primary winding LP of the transformer 201 , Because of the co-directional winding of the secondary windings 202 to 205 and the circuit of the backflow preventer 206 to 209 with their anode semiconductor switch side, the capacitances 16 to 19 immediately charged. This is in the 3b illustrated. Again at time t1, the transistor T1 is turned on. However, switching on is pulse-like. In particular, the switch T1 can only be switched on for about 20 ns. This leads to a "needle-shaped" current 211 in the primary winding LP. This power is sufficient to the capacity 16 to 19 charge, so that suddenly the voltage pulse 212 is produced. In particular, the rising edge 213 and the rising edge 214 almost at the same time, something by the arrow 215 is indicated. The voltage (height) of the voltage pulse 212 is constant as long as it is available. In particular, prevent the backflow preventer 206 to 209 , which are also designed as diodes, a discharge of capacity 16 to 19 over the secondary windings 202 to 205 , In this case, the capacitances of the diodes are preferably lower than the capacitances 16 to 19 ,

As in the previous embodiment, a switch T2 is provided, via which the semiconductor switches 12 to 15 are controllable. If the switch T2 is turned on (rising edge 216 ) are also the semiconductor switches 12 to 15 switched on. This can increase the capacity 16 to 19 via the internal resistances of the semiconductor switches 12 to 15 discharged. This happens abruptly, so that the voltage pulse 212 abruptly ended. This is due to the falling edge 217 indicated. The simultaneity is through the arrow 218 indicated.

The 4a shows a recorded trace. In particular, a voltage pulse 300 with a very steep rising edge 301 and a steep falling flank 302 shown. It is on the horizontal line 303 to recognize that the voltage of the voltage pulse 300 is very constant.

In the 4b is the rising flank 301 shown with a stronger temporal resolution. It can be seen that a slope> 40 V / ns can be achieved with the circuits according to the invention. At the point 304 is to detect a small overshoot, which with the blocking charge of the diodes of the backflow preventer in the 1a hangs together. After settling, however, the voltage is very constant. This can be seen in particular by the dashed line 305 recognize the end of the voltage pulse 300 represents. The steepness of the flank 302 is similar to the rising edge 301 only with opposite sign.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 02-197269A [0003]
• JP 02-304991 A [0003]
• US 5881082 [0003]
• DE 102006060417 A1 [0004]
• US 6184662 B1 [0005]
• DE 10356648 A1 [0006]

Claims (21)

Method for generating a voltage pulse ( 40 . 116 . 305 )> 500 V with constant voltage, in which an inductance (L, 102 - 105 . 202 - 205 ) a capacity ( 16 - 19 ) and unloading the capacity ( 16 - 19 ) via the inductance (L, 102 - 105 . 202 - 205 ), characterized in that as capacity ( 16 - 19 ) the output capacity ( 16 - 19 ) at least one semiconductor device ( 12 - 15 ) and the magnitude of the voltage pulse ( 40 . 116 . 305 ), whereby a Pockels cell ( 11 ) with the voltage pulse ( 40 . 116 . 305 ) is driven. Method according to claim 1, characterized in that the height of the voltage pulse ( 40 . 116 . 305 ) over the turn-on time of the semiconductor switch ( 12 - 15 ) is set. Method according to claim 1 or 2, characterized in that the height of the voltage pulse ( 40 . 116 . 305 ) via the number of series-connected semiconductor switches ( 12 - 15 ) is set. Method according to one of claims 1 to 3, characterized in that the height of the voltage pulse ( 40 . 116 . 305 ) by the voltage of a DC power supply ( 25 ) and / or the gear ratio of a transformer ( 101 . 102 ) is set. Method according to one of the preceding claims, characterized in that the height of the voltage pulse ( 40 . 116 . 305 ) varies after settling by less than 10%, preferably less than 5%, more preferably less than 2%. Method according to one of the preceding claims, characterized in that the rising and / or the falling edge ( 33 . 114 . 121 . 214 . 217 . 301 . 302 ) of the voltage pulse ( 40 . 116 305 ) has a slope> 40 V / ns. Method according to one of the preceding claims, characterized in that the voltage pulse ( 40 . 116 . 305 ) is terminated by the at least one semiconductor switch ( 12 - 15 ) is turned on. Method according to one of the preceding claims, characterized in that the voltage pulse ( 40 . 116 . 305 ) is terminated in stages by at least two series-connected semiconductor switches ( 12 - 15 ) are turned on successively. Method according to one of the preceding claims, characterized in that initially energy in the inductance (L, 102 - 105 ) and then the stored energy in one or more output capacities ( 16 - 19 ) of the semiconductor switch (s) ( 12 - 15 ) is transhipped. Circuit ( 10 . 100 . 200 ), in particular for carrying out the method according to one of the preceding claims, with at least one inductance (L, 102 - 105 . 202 - 205 ) and at least one in series with the inductor (L, 102 - 105 . 202 - 205 ) switched semiconductor switch ( 12 - 15 ) with an output capacity ( 16 - 19 ), as well as between inductance ( 1 . 102 - 105 . 202 - 205 ) and semiconductor switches ( 12 - 15 ) arranged backflow preventer ( 27 . 106 - 109 ; 206 - 209 ), where the circuit ( 10 . 100 . 200 ) a Pockels cell ( 11 ) connected. Circuit according to Claim 10, characterized in that a plurality of semiconductor switches ( 12 - 15 ) are connected in series. Circuit according to Claim 10 or 11, characterized in that the semiconductor switches ( 12 - 15 ) the same the respective output capacity ( 16 - 19 ) is associated with feeding inductance (L). Circuit according to Claim 10 or 11, characterized in that each semiconductor switch ( 12 - 15 ) own the respective output capacity ( 16 - 19 ) feeding inductance ( 102 - 105 . 202 - 205 ) assigned. Circuit according to Claim 13, characterized in that the inductances ( 102 - 105 . 202 - 205 ) Secondary windings or secondary winding sections of a transformer ( 101 . 201 ) are. Circuit according to one of the preceding claims 10 to 14, characterized in that each semiconductor switch ( 12 - 15 ) its own backflow preventer ( 106 - 109 . 206 - 209 ) assigned. Circuit according to one of the preceding claims 10 to 15, characterized in that the one or more backflow preventer (s) ( 27 . 106 - 109 . 206 - 209 ) at least one diode ( 35 - 38 ), in particular a SiC diode, or a switch. Circuit according to one of the preceding claims 10 to 16, characterized in that the capacity of the non-return valve ( 27 . 106 - 109 . 206 - 209 ) is smaller than the output capacitance of the circuit ( 10 . 100 . 200 ). Circuit according to one of the preceding claims 10 to 17, characterized in that at least one transformer ( 101 . 201 ), to whose primary winding (LP) a switch (T1) is connected in series. Circuit according to Claim 18, characterized in that the primary winding (LP) and the secondary winding ( 102 - 105 . 202 - 205 ) are arranged in the same direction or in opposite directions. Circuit according to one of the preceding claims 10 to 19, characterized in that a switch (T1, T2) is provided, via which one or more semiconductor switches ( 12 - 15 ) are switched on and off simultaneously. Circuit according to one of the preceding claims 10 to 20, characterized in that a DC voltage supply ( 25 ) is provided.

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