DE102007004391B3 - Driver circuit for driving of electro-optical elements, particularly pockel cells, has compensation circuit that is attached at H-bridge in order to stabilize dropping voltage at element, where compensation circuit has auxiliary condenser - Google Patents

Abstract

The driver circuit has a H-bridge (4), where a switch (S1) is arranged in a main path (1) for switching the element. A compensation circuit is attached at the H-bridge in order to stabilize dropping voltage (U-pc) at the element. The compensation circuit has an auxiliary condenser and an auxiliary switch for switching on and off the auxiliary condenser.

Description

State of the art

The The invention relates to a driver for switching components, in particular Pockels cells, according to the preamble of claim 1

Driver circuits, which are referred to herein as fast voltage switches, capable of injecting a device in very short periods of time and turn off. The switching cycles can be in the range of a few nanoseconds lie. Such drivers are used in particular for laser applications used with Pockels cells.

A typical application is z. B. the removal of material of a substrate by laser. For this purpose must ultrashort laser pulses are generated with high energy. The laser beam is about this coupled a Pockels cell into an optical amplifier (resonator), goes through this until the needed Energy is reached, and is then decoupled again. there it is necessary, the Pockelszelle short term - d. H. with a duration of a few nanoseconds - turn on, so that the Laser pulse is coupled into the resonator, and the Pockels cell switch off shortly after a specified round trip time to to decouple the laser pulse again.

1 shows a known driver circuit for Pockels cells, as shown for example in the FR-A-1 490 953 is described. The driver includes an H-bridge 4 with a first main path 1 , a second main path 2 and a cross path 3 in which the Pockels cell 5 is arranged. The H bridge 4 is connected to a supply voltage V. In the two main paths 1 . 2 there is a respective switch S1, S2, which is used to turn on or off the Pockels cell 5 serves. In series with the switches S1, S2, a resistor R1 or R2 is arranged in each case. The resistors R1, R2 are also referred to as reloading resistors. The switches S1, S2 each have parasitic capacitances C1, C2, which are indicated here in dashed lines parallel to the switches S1, S2. The Pockels cell 5 is connected to the nodes V1 and V2 between the resistor R1 and the switch S1 and R2 and S2, respectively.

In the off state, both switches S1, S2 are open, as shown in the figure. Both node voltages V1, V2 are then at the supply potential V. The at the Pockels cell 5 decreasing voltage U _pc is thus equal to zero.

At time t0, the first switch S1 is closed (see associated timing diagram S1). As a result, the voltage applied to the node V1 falls against the reference potential (in this case ground) and the Pockels cell voltage U _pc rises against the value V. The closing of the first switch S1 also has an influence on the node voltage V2, which is initially pulled slightly downwards (see associated time diagram V2) and then rises again with the resistance value R2 against the supply voltage V. Consequently, the Pockels cell voltage U _{pc is} not constant during the switch-on phase T1 and also does not quite reach the desired setpoint V. At time t1, the switch S2 is then closed. As a result, the node potential V2 falls to the reference potential (ground) and the Pockels cell voltage U _pc is degraded. The switch-on phase T1 is completed at the time t2.

From time t2, the two switches S1 and S2 are opened again. In the following recharge phase T2, the two nodes V1, V2 are pulled via the associated resistors R1, R2 against the supply potential V. In the recharging phase T2, it is important that both node potentials V1, V2 are led upward as symmetrically as possible. Otherwise arise at the Pockels cell 5 small non-zero voltages leading to an unwanted state change of the Pockels cell 5 lead and thus affect the application. Such unwanted stresses can only be with an absolutely symmetrical formation of the left and right main path 1 respectively. 2 be prevented, which can never be achieved in practice, in particular due to manufacturing tolerances of the components in the rule.

From the US 3,910,679 is a driver circuit for driving in particular of electro-optical components, such. B. Pockels cells known, which is designed as H-bridge. The H-bridge comprises two main paths, each with a switch and a transverse path in which the component is arranged. To stabilize the voltage dropping across the component capacitors C _A and C _B are also provided, which act as a kind of compensation circuit.

From the DE 102 51 888 A1 is another driver circuit for Pockels cells known, which is constructed as H-bridge circuit. In each case, two switches are arranged in the two main paths of the H-bridge, by means of which the driver voltage is switched on and off.

Pockels cells in the optical amplifier z. B. react to even the smallest voltage changes and change their optical behavior accordingly. The fluctuation of the Pockels cell voltage U _pc or its deviation from the desired setpoint V or 0V can thus function as the Pockels cell 5 or the amplifier significantly affect.

Disclosure of the invention

It Thus, the object of the present invention is a driver circuit to create, by means of a possible exact and continuous switch-on or switch-off signal at switching times can be generated in the nanosecond range and below.

Is solved this task according to the invention by the features specified in claim 1. Further embodiments The invention are the subject of subclaims.

One essential aspect of the invention is that of the component falling voltage during stabilize the switch-on using an auxiliary capacitor and keep it constant. The auxiliary capacitor is an auxiliary switch assigned, by means of which the auxiliary capacitor in certain switching phases can be switched on or off. This can cause fluctuations in the component voltage avoided and the accuracy of the application significantly improved become. Furthermore the circuit works very low loss. The auxiliary switch can with respect to the Auxiliary capacitor arranged either supply side or ground side be.

According to one preferred embodiment of Invention is the auxiliary capacitor to the terminal node of the device interconnected in the second main path.

According to one first embodiment the invention is the auxiliary capacitor with that supply potential connected, of which also the H-bridge is supplied. In this case, the capacity of the auxiliary capacitor is preferable the same size as the capacity of the driven device (eg a Pockels cell). When switching of the first switch, this results in a balancing effect - the node voltage at node V2 on the one hand over the capacity of the device down and on the other hand via the auxiliary capacitor upwards pulled - the causes the voltage drop across the device to remain constant and the desired one Setpoint V has.

According to one second embodiment The invention is the auxiliary capacitor with an auxiliary supply voltage connected, which is larger as the supply voltage of the H-bridge. This allows the auxiliary capacitor chosen smaller to achieve the same compensation effect as above has been described. This has the advantage that during a switching process the switch S2 less charge must be reloaded and switching thus can run faster.

By A variation of the auxiliary supply voltage may also cause variations in the device decreasing voltage decreases or drifts this voltage be prevented. The higher one Auxiliary supply voltage can, for example, by means of a known Voltage amplifier, such as As a Marks generator can be generated.

Next the auxiliary capacitor and the auxiliary switch is preferably also an auxiliary resistance provided. A connection of the auxiliary resistance is preferably with the auxiliary capacitor and the auxiliary switch connected. The auxiliary resistor, depending on the embodiment, either the supply side or relative to the mass side be arranged of the auxiliary capacitor.

Of the Auxiliary switch is preferably synchronously and in the same direction with the switched first switch. That is, the auxiliary switch is simultaneously with the first switch in the same state (open or closed).

According to one third embodiment The invention is at least one of the reload resistors Assigned switch, by means of which the reload resistance or can be switched off. This can significantly reduce the power dissipation of the driver be reduced.

Of the associated Switch of the recharging resistor is preferably synchronous, but switched in the opposite direction to the first switch. That is, if the first switch is closed, the other switch is opened and vice versa.

the Auxiliary resistance is preferably also associated with a switch, which is switched synchronously, but in opposite directions to the first switch.

According to one fourth embodiment The invention can parallel to the driven device, a diode be switched, which prevents in the regeneration phase the two node voltages of the device increase unevenly and thus a voltage drop over the component is created. The course of the two node tensions V1, V2 in the recharging phase can also be artificial, z. B. by an unbalanced Training of the resistors the two main paths, to be manipulated. In the extreme case can do it completely on the recharging resistor in a main path, in particular in the first Main path, be waived. This imbalance is caused by the diode balanced again, as it prevents one of the potentials rises faster than the other.

According to one special embodiment of the Invention, the first diode can also be replaced by a switch become.

Between the second terminal node of the device (in the second main path) and the supply voltage V can also be connected to a second diode be. The second diode prevents the node voltage V2 in the Case of overcompensation through the auxiliary capacitor via the supply voltage V increases.

According to one fifth embodiment the invention, a first control circuit is provided, the driven on the Component voltage drops and during a control phase, in particular at least in the recharging phase, the component voltage on one fixed value. For example, the first control loop a differential amplifier include the voltage dropping across the driven component receives. When a voltage drop occurs, the first control loop modulates the switch of the first reload resistor and thus ensures that the voltage drop across the component in the recharge phase is the same Zero remains.

optional It is also possible to provide a second control circuit which determines the voltage difference between the supply voltage and the second connection node measures the driven component and ensures that the voltage on node V2 does not exceed the supply voltage (protection against overcompensation). Because of the small pulse durations of a few nanoseconds, the voltage difference preferably sampled and from this the recharging voltage for the following Pulse calculated.

in the Trap of high-voltage drivers, with voltages of several kV are the switches and possibly also the diodes of the driver preferably as a series connection of a plurality of transistors or diodes realized. Each component thus sees only a part of the total voltage and will not be overloaded.

Brief description of the drawings

The Invention will be exemplified below with reference to the accompanying drawings explained in more detail. It demonstrate:

1 a circuit diagram of a known Pockels cell driver with associated timing diagrams;

2 a circuit diagram of a Pockels cell driver with compensation circuit according to a first embodiment of the invention;

3 a circuit diagram of a Pockels cell driver with compensation circuit according to a second embodiment of the invention;

4 a circuit diagram of a Pockels cell driver with compensation circuit according to a third embodiment of the invention;

5a a circuit diagram of a Pockels cell driver with compensation circuit and diodes according to a fourth embodiment of the invention;

5b a circuit diagram of a Pockels cell driver with compensation circuit according to a fifth embodiment of the invention;

6 a circuit diagram of a Pockels cell driver with compensation circuit and controllers according to a sixth embodiment of the invention; and

7 a circuit diagram of a Pockels cell driver with compensation circuit and regulators according to the embodiment of 2 but in a mirrored arrangement.

Embodiments of the invention

Regarding the explanation of 1 Reference is made to the introduction to the description.

2 shows the circuit diagram of a Pockels cell driver with a compensation circuit 5 according to a first embodiment of the invention. The Pockels cell driver comprises in a known manner an H-bridge arrangement 4 to drive a Pockels cell 5 , as well as a compensation circuit, denoted overall by the reference numeral 6 is designated. The H bridge 4 includes a first main path 1 , a second main path 2 and a cross path 3 in which the Pockels cell 5 is arranged. The H bridge 4 is connected to a supply voltage V. Every main path 1 . 2 comprises a resistor R1 or R2 connected to the supply potential V (recharging resistors) and a switch S1 or S2 connected to a reference potential (here ground). The Pockels cell 5 is in each case connected to a center node V1 or V2.

By switching the switches S1, S2, which are usually formed as transistors, the Pockels cell 5 switched on and off. The timing diagram shown in the figure below shows a switching cycle in which the Pockels cell 5 once switched on and off again. The duration of such a switching cycle is usually in the nanosecond range or below.

In the initial state (before time t0) Both switches S1, S2 are open, as shown in the figure. At the two nodes V1, V2, the potential V is applied. At time t0, the first switch S1 is closed, whereby the potential V1 falls against the reference potential. The at the Pockelszelle 5 decreasing voltage U _pc thus increases against the value V on.

As at the beginning regarding 1 has already been mentioned, the potential V2 is also influenced by switching on the switch S1, since charge via the Pockels cell 5 flows to node V1. To prevent the drop of the potential V2, here is a compensation circuit 6 provided with an auxiliary capacitor Ch, a Hilsschalter Sh and an auxiliary resistor Rh.

Of the Auxiliary capacitor Ch is connected to node V2 and via the Auxiliary switch Sh connected to the supply potential V. The auxiliary resistance Rh is at a node Vh between the auxiliary capacitor Ch and the Auxiliary switch Sh connected and switched against the reference potential.

The auxiliary switch Sh is now closed simultaneously with the switch S1 (see signal Sh). By closing the first switch S1, although the node potential V2 continues to be pulled down, at the same time it is pulled upwards via the auxiliary capacitor Ch. This results in a compensation effect, which causes the voltage at node V2 remains stable. This is clearly visible on the curve V2. Thus, the Pockels cell voltage U _pc remains stable at the value V. A complete compensation of the voltage V2 is achieved here when the capacity of the auxiliary capacitor Ch equal to the capacity of the Pockels cell 5 is selected.

To a period t1 then the second switch S2 is closed, whereby also the potential at node V2 falls to ground (s. Curve V2). Once it is ensured that the potential at node V2 has reached the final value and both node voltages V1, V2 the same Have value, the two main switches S1, S2 are opened. The Switch-on phase T1 is now completed and the recharging phase begins T2.

From time t2, the two nodes V1, V2 are recharged via the resistors R1 and R2, respectively, until the supply potential V is reached (see diagrams V1, V2). If the H bridge 4 and in particular the resistors R1, R2 are designed symmetrically, the voltages V1, V2 are synchronous with V, so that over the Pockels cell 5 no voltage drops.

The switching edges of the signal U _pc , especially the first edge (t0), are passed through the compensation circuit 5 hardly affected, since the switch S1 only the own parasitic capacitance C1 and the capacity of the Pockels cell 5 has to reload. The switch S2 must have its own parasitic capacitance C2 as well as the relatively small capacities of the Pockels cell 5 and the auxiliary capacitor Ch reload.

3 shows a second embodiment of a Pockels cell driver with one opposite 2 slightly modified compensation circuit 6 , The compensation circuit 6 Also includes an auxiliary capacitor Ch, the auxiliary switch Sh and the auxiliary resistor Rh. In contrast to 2 is the compensation circuit 5 However, not connected to the supply voltage V, but with an auxiliary supply potential Vh, which is higher than the voltage V. This makes it possible to choose a smaller auxiliary capacitance Ch and thus to achieve faster switching edges.

For a complete compensation of the node potential V2, it is only necessary that the following relationship: Q = U · C = constant preserved. When the auxiliary supply potential Vh is increased by the factor k, that is to say Vh = k * V, the capacitance Ch must be selected smaller by the factor k than in 2 ,

The Auxiliary supply potential Vh can be either by means of a separate Voltage source provided or z. B. from the supply voltage V self-generated. In the latter case, for example, a known voltage multiplier, such. A Marks generator be used.

During the switch-on phase T1, the auxiliary supply voltage Vh can also be slightly varied in order to influence the node voltage V2 as desired. This can be done either as part of a control or regulation. This can be done at the Pockels cell 5 decreasing voltage U _pc can be set exactly to a desired value.

4 shows a third embodiment of a Pockels cell driver with compensation circuit 6 , In this embodiment, the recharging resistors R1, R2 are kept relatively small to shorten the recharging phases T2. However, small reload resistors R1, R2 have the disadvantage that in the closed state, the switch S1 or S2, the electrical power loss is relatively high. In the first main path 1 Therefore, an additional switch S _{R1 is} provided, by means of which the node V1 can be disconnected from the supply potential V. The switch S _R1 is switched synchronously, but in the opposite sense to the first switch S1 (see associated time diagram) agramm). That is, the switch S _R1 is opened when the switch S1 is closed and vice versa.

In addition, an additional switch S _{Rh is} arranged in the path of the auxiliary resistor Rh, by means of which the node Vh can be disconnected from the reference potential when the auxiliary switch Sh is closed. The switch S _Rh is in turn switched synchronously and in opposite directions to the switch Sh.

5a shows a Pockels cell driver constructed similarly as in FIG 4 but includes two additional diodes D1 and D2.

In this embodiment, the resistors R1 and R2 are not identical, but R1 <R2. This artificially ensures that the voltage at the node V1 in the recharging phase T2 rises faster than at the node V2. The node voltages V1 and V2, however, via the diode D1, which are parallel to the Pockels cell 5 switched, balanced, so no voltage U _pc at the Pockels cell 5 drops.

The Diode D2 is between node V2 and the supply potential V switched and serves to bridge the voltage V2 to the supply potential V limit.

Drift and tolerances of the electrical components can influence the recharging behavior and thus the voltage profile at the nodes V1 and V2 in the recharging phase. In order to achieve the most symmetrical increase of the voltages V1, V2, the capacitance of the auxiliary capacitor Ch is chosen to be slightly larger than that of the Pockels cell 5 (Overcompensation). In this case, the diode D2 prevents the voltage at the node V2 from growing above the voltage V.

The Diodes D1 and D2 can either integrated individually or jointly in the circuit.

5b shows an alternative embodiment 5a in which instead of the diode D1, a switch S _{pc is} provided. The switch S _pc is preferably closed in the recharging phase T2 and ensures a balance of the node voltages V1, V2. This prevents a voltage U _pc at the Pockels cell in the recharging phase T2 5 drops. In this case, it would also be conceivable to dispense completely with the resistor R1 and possibly also with the switch S _R1 .

6 shows another embodiment of a Pockels cell driver with two control loops 7 . 8th , The first control loop 7 Measure those over the Pockels cell 5 decreasing voltage and ensures that the Pockelszellen voltage U _pc in the Nachladephase remains about zero, even if the balance between the nodes V1 and V2 is slightly disturbed. The actual controller is the reference numeral 9 characterized. The Pockels cell voltage U _pc is from a differential amplifier 10 tapped. The actuator of the control forms the switch S _R1 , which is modulated in dependence on the height of the Pockelszellen voltage U _pc .

The second controller 8th Measures and samples the voltage difference between the nodes V2 and V and ensures that the voltage at which the auxiliary capacitor Ch is charged, the supply potential V is tracked. The voltage difference is preferably sampled in this case because of the small pulse durations of a few ns, and from this the required recharging voltage for the following pulses is calculated and set. The actuator of the control forms a controllable voltage source 13 which is arranged in the path of the auxiliary resistor Rh.

The Regulation is more complex than the circuits described above, but none are with parasitic capacities used additional elements needed. The regulator arrangement is thus very fast and energy saving.

7 shows an embodiment of the invention similar 2 in which the individual components R, S are mirrored with respect to a horizontal axis.

In contrast to 2 Here are the switches S1, S2 connected to the supply potential V and the resistors R1, R2 connected to the reference potential. In the compensation circuit 6 the resistor Rh is connected to the supply potential V and the auxiliary switch Sh is connected to the reference potential. The circuit is operated in the same way as in 2 ,

The circuits of 3 to 6 could also be arranged mirrored. On a separate presentation is omitted here.

Claims (16)

Driver circuit for driving, in particular, electro-optical components ( 5 ), such. B. Pockels cells, with an H-bridge ( 4 ) - one in a first main path ( 1 ) arranged first switch (S1) for switching on the device ( 5 ), - one in a second main path ( 2 ) arranged second switch (S2) for switching off the device ( 5 ), and - that in a cross path ( 3 ) arranged component ( 5 ), characterized in that at the H-bridge ( 4 ) a compensation circuit ( 6 ) is connected to the device ( 5 ) stabilizing voltage drop (U _pc ), wherein the compensation circuit ( 6 ) comprises an auxiliary capacitor (Ch) and an auxiliary switch (Sh), by means of which the auxiliary capacitor (Ch) can be switched on and off. Driver circuit according to claim 1, characterized in that the auxiliary capacitor (Ch) with a node (V2) in the second main path ( 2 ) of the H-bridge ( 4 ) is interconnected Driver circuit according to Claim 1 or 2, characterized in that the capacitance of the auxiliary capacitor (Ch) is approximately equal to that of the component ( 5 ) corresponds. Driver circuit according to one of the preceding claims, characterized in that a connection (Vh) of the auxiliary capacitor (Ch) connected to the auxiliary switch (Sh) and an auxiliary resistor (Rh) is. Driver circuit according to one of the preceding claims, characterized characterized in that the auxiliary switch (Sh) synchronously and in the same direction is switched with the first switch (S1). Driver circuit according to one of the preceding claims, characterized in that the first and second switches (S1, S2) each with a node (V1, V2) of the component ( 5 ) are interconnected. Driver circuit according to one of the preceding claims, characterized in that the auxiliary capacitor (Ch) is connected to an auxiliary supply voltage (Vh), which is greater than the supply voltage (V) of the H-bridge ( 4 ). Driver circuit according to claim 7, characterized in that the auxiliary supply voltage (Vh) after switching on the first switch (S1) is varied in order to the on the component ( 5 ) to keep falling voltage (U _pc ) constant. Driver circuit according to one of the preceding claims, characterized in that at least in one of the main paths ( 1 . 2 ) a resistor (R1, R2) is provided. Driver circuit according to Claim 9, characterized in that the resistors (R1, R2) of the main paths ( 1 . 2 ) are different in size. Driver circuit according to one of the preceding claims, characterized in that in at least one of the main paths ( 1 . 2 ) an additional switch (S _R1 ) is provided, by means of which the main path ( 1 . 2 ) can be switched off. Driver circuit according to claim 11, characterized in that the at least one switch (S _R1 ) is switched synchronously, but in opposite directions to the first switch (S1). Driver circuit according to one of the preceding claims, characterized in that parallel to the component ( 5 ) a first diode (D1) or a switch (Spc) is connected. Driver circuit according to one of the preceding claims, characterized in that between a node (V2) of the device ( 5 ) and the supply voltage (V) of the H-bridge ( 4 ) a second diode (D2) is connected. Driver circuit according to one of the preceding claims, characterized in that a first regulator ( 7 ) provided on the component ( 5 ) voltage decreases (U _pc ) and during a recharging phase (T2) regulates the voltage (U _pc ) to a predetermined value. Driver circuit according to one of the preceding claims, characterized in that a second control circuit ( 8th ) is provided, which determines the voltage difference between the supply voltage (V) and one at a node (V2) of the component ( 5 ) voltage applied (V2) and leads to the supply voltage (V).