RU82390U1 - HIGH-VOLTAGE PULSE MODULATOR WITH NANOSECOND FRONT FOR CONTROL OF ELECTRO-OPTICAL SHUTTERS IN THE VIEW OF POCKSEL CELL - Google Patents

Abstract

1. A high-voltage pulse modulator with a nanosecond front for controlling electro-optical gates in the form of a Pockels cell, containing a high-voltage power supply, shunted by a capacitor, connected to two series-connected semiconductor switches with galvanically isolated control circuits, a clock generator supplied to the control circuit, a discharge resistor connected parallel to the semiconductor switch connected to the minus of the source, and the electro-optical shutter, the first output to which is connected to a common point of semiconductor switches, characterized in that, in order to expand the functionality of the modulator, a second controllable high-voltage source shunted by a capacitor is inserted into it, the positive terminal of the second source being connected to the second terminal of the gate, and the negative terminals of both sources being connected to a common by bus. ! 2. The high-voltage pulse modulator according to claim 1, characterized in that, in order to reduce the voltage of the first source, both semiconductor switches are replaced by a Marx generator, in each stage of which the capacitor is connected to two series-connected switches with a control circuit, and the switch connected to minus capacitor, is shunted by the resistor, and a diode is connected to the key connected to the plus of the capacitor, the cathode of which is connected to the plus of the capacitor in the next stage, with the common point of the keys in the previous the cade is connected to the minus of the capacitor in the next stage, and the common point of the keys in the last stage is connected to the first output of the shutter, the second output of which is connected�

Description

The invention relates to the field of high-voltage pulse technology and is intended to control electro-optical shutters in the form of a Pockels cell. It can be used as a part of a solid-state laser operating in the Q-switching mode.

Description of analogues

Known semiconductor generator of nanosecond pulses based on a drift diode with a sharp recovery (DDRV) (Letters in ZhTF, 1983, vol. 9, issue 7, p. 435). It contains DDRV 1, a reverse current driver 2, connected in parallel to the DDRV and connected by a positive terminal to the DDRV cathode, a load circuit 3, connected in parallel to the DDRV, and a direct current driver 4, connected to the negative terminal to the cathode of the DDRV, and positive to the anode of the LDRV through LC- filter 5 (figure 1).

When the direct current driver is turned on through the DDRV, a short forward current pulse occurs, which leads to the accumulation of an excess charge of minority carriers in the DDRV base, which is localized in the region immediately adjacent to the boundary of the pn junction. After turning on the reverse current driver, the extraction of minority carriers from the base into the emitter of the DDDR occurs. As a result, the accumulated charge of minority carriers in the base disappears completely, which is accompanied by a sharp increase in the reverse voltage at the DDRV and the same fast switching of the current to the load.

The disadvantages of the considered generator: the lack of commercially available diodes with a sharp recovery; short duration of the current pulse in the load (of the order of several nanoseconds); inefficient use of the direct current driver and the inability to implement the “switch-off” mode, in which there is a high voltage level in the pause between pulses at the load (gate), and low voltage during pulse formation.

Known generator of nanosecond pulses (RF patent No.2009611 from 03/15/1994), containing a drift diode with a sharp recovery of 6; a reverse current circuit 7 connected in parallel to the DDRV and consisting of series-connected

a capacitor 8, an inductor 9 and a switch 10, wherein the switch is connected to the cathode of the DRRV, and the capacitor is shunted by the diode 11 connected by the anode to the anode of the LDS; a direct current circuit 12 connected in parallel to the switch 10, and consisting of a series-connected capacitor 13, an inductor 14 and its own switch 15; load circuit 3 connected in parallel to the DDRV; and a charge circuit 16 connected in parallel with a capacitor in a direct current circuit (FIG. 2).

When the switch is turned on in the direct current circuit, the capacitor of this circuit is discharged through the inductances of the forward and reverse current circuits, the capacitor of the reverse current circuit and the DRRV, forming a short forward current pulse through the DRRV. In this case, a thin layer of an excess charge of minority carriers is formed in the DDRV base in the region adjacent to the boundary of the pn junction. After the capacitor is charged in the reverse current circuit to the amplitude value of the voltage, the switch is turned on in the reverse current circuit, which leads to the passage through the DDRV of a short reverse current pulse with a large amplitude. Due to the extraction of minority carriers from the base into the emitter of the DDRV, the excess charge layer is depleted, which leads to a sharp increase in the voltage on the DTCS and the same fast switching of the current to the load. Subsequently, all the energy stored in the inductor and the capacitor of the reverse current circuit is transferred to the load through a shunt diode, which prevents the capacitor from overcharging in the reverse current circuit. Due to this, the efficiency of the generator and its efficiency are increased.

The disadvantages of the considered generator: the lack of commercially available diodes with a sharp recovery; short duration of the current pulse in the load; the inability to implement the switch-off mode.

Prototype description

A known fast high-voltage modulator circuit (US patent No. 5,594,378 dated January 14, 1997) comprising a high-voltage power supply 17 connected by a minus to a common bus; the first semiconductor switch, consisting of series-connected MOS transistors 18-22, the drain of the upper transistor connected to the plus of the power source, and the source of the lower transistor through a resistor 23 with the first output of the load (gate) 55; a second semiconductor switch, consisting of series-connected MOS transistors 24 - 28, the drain of the upper transistor connected via a resistor 29 to the first output of the load 55, and the source of the lower transistor with a common bus; voltage limiters connected in parallel

each transistor in the first and second keys 30 - 49; shunt transistors connected in parallel to the gate-source circuits of each transistor in the first key 50 - 54; a load connection circuit 55 connected by a second terminal to a common bus;

a discharge resistor 56 connected in parallel with the load and galvanically isolated control circuits of each transistor 57 - 66, performing synchronized switching of both keys by a pulse from the control circuit 67-69 (figure 3).

The scheme works as follows.

When a pulse is applied from the control circuit 67 (drive circuit) to turn on 68 (on pulse), all the series-connected MOS transistors of the first key 18-22 are turned on simultaneously. In this case, a positive voltage pulse is formed in the load with an amplitude almost equal to the voltage of the high-voltage source 17. Simultaneously with the removal of the pulse 68 (on pulse) from the control circuit in the gate circuit of all shunt transistors of the first switch 50-54 and all the transistors of the second switch connected in series 24-28, a pulse is sent to turn off 69 (off pulse). The transistors of the first key 18-22 are turned off quickly and the transistors of the second key 24-28 are turned on as quickly. Since the second switch actually shunts the load, the voltage on the load quickly resets. After that, the pulse to turn off 69 (off pulse) is removed. A zero value of the voltage at the load is maintained until the next pulse is applied to turn on 68 (on pulse) due to the resistor 56 connected in parallel with the load. Thus, in relation to electro-optical shutters, this circuit implements the “switch-on” mode. Voltage limiters connected in parallel to all series-connected transistors of the first and second switches 30 to 49 protect the transistors from overvoltages that occur when the keys are turned on and off. Resistors 23, 29, connected in series with both keys, protect them from through currents at the time of turning off the first and turning on the second key.

The disadvantages of this scheme are the short duration of the direct current and the inability to implement the switch-off mode. This invention is the closest analogue of the invention, i.e. is a prototype.

As follows from the analysis, in none of the considered circuits, as well as in other circuits known to us, both control modes of electro-optical shutters cannot be implemented: “switch-on” and “switch-off”. In the first of them, in the interval between pulses, when the shutter is closed, it is kept low

voltage (close to zero). To open the shutter, a high-voltage voltage pulse (several kilovolts) with a nanosecond front is formed on it. In the “switch-off” mode, on the contrary, in the pause between pulses with the shutter closed, it maintains a high voltage level (several kilovolts), and to open the shutter the voltage on it is reset to almost zero in a few nanoseconds. Creating a universal modulator capable of working in both modes without changing the circuit is an urgent task. In this case, it becomes possible to equip both types of existing shutters with one modulator.

Another urgent task, which cannot be solved within the framework of the existing circuitry, is the possibility of compensation by the electric method of a violation of gate alignment in a laser operating in the Q-switching mode. A violation of the gate alignment can occur either as a result of heating the Pockels cell, or due to mechanical displacements of the components of the optical scheme. To compensate for the violation of the adjustment of the shutter, it is necessary to apply a constant bias voltage to it, the value of which lies within one kilovolt.

The third task to be solved in the proposed modulator is the possibility of implementing a mode in which the voltage drop across the gate at the time of opening is higher than the amplitude of the constant blocking voltage. This mode ensures the operation of the electro-optical shutter with maximum contrast.

Finally, due to the inclusion of the second source, when the shutter is in the “switch-on” mode, the shutter can be constantly opened, which is used to align the laser in the free-running mode.

The aim of the invention is the creation of a universal high-voltage modulator, which implements two control modes "switch-on" and "switch-off", it is possible to compensate for misalignment of the laser by supplying an additional bias voltage to the gate; a mode is implemented in which the voltage drop across the gate at the moment of opening is higher than the amplitude of the constant locking voltage due to the supply of an additional bias voltage to the gate; a mode is implemented in which the shutter operating in the "switch-on" mode is constantly open due to the supply of a constant bias voltage to it.

In other words, expanding the functionality of existing modulators. This goal is achieved by connecting a second high-voltage controlled source to the modulator circuit. The block diagram of the proposed modulator is presented in figure 4.

The modulator contains a high-voltage power supply 70, shunted by a capacitor 71, connected by a positive clamp to the semiconductor switches 72 and 73 connected in series with galvanically isolated control circuits 74 and 75, a clock generator 76 for on and off, respectively applied to control circuits 74 and 75, a discharge resistor 77 connected in parallel with the semiconductor switch 73, an electro-optical shutter 78, one output of which 81 is connected to a common point of the semiconductor switches 72 and 73, and d the other 82 - with the plus of a controlled source 79, shunted by the capacitor 80. In this case, both sources are connected to the common bus with their negative terminals.

Consider the operation of the circuit in the "switch-on" mode. In the initial state, both switches 72 and 73 are open, the voltage of the source 79 is set to zero. Since the output 81 of the gate 78 through the resistor 77 is connected to a common bus, the voltage at the gate in the initial state and in the pause between pulses is zero. When the on-pulse pulse is supplied from the generator 76, a control voltage pulse is generated in the control circuit 74, which turns on the semiconductor switch 72. A voltage pulse is generated on the gate 78, the amplitude of which is almost equal to the voltage of the high-voltage source 70. After a time interval equal to the set pulse duration, the on-pulse is removed and the sync-pulse is turned off at the same time. The control circuit 74 turns off the semiconductor switch 72, and the control circuit 75 turns on the semiconductor switch 73. A quick discharge occurs through the gate capacitance switch 73 to zero voltage and the circuit returns to its original state. Subsequently, as clock pulses arrive, the described process repeats.

Consider the operation of the modulator in the switch-off mode. In the initial state, both switches 72 and 73 are open, the voltage of the source 79 is set equal to the voltage of the source 70. Since, thanks to the resistor 77, the common bus potential is maintained at the gate terminal 81, the gate voltage in the initial state of the circuit is equal to the voltage of the source 79. When when a pulse from the generator 76 is turned on (on pulse) from the control circuit 74, the semiconductor switch 72 is turned on. In this case, the output potential of the gate 81 of the gate 78 jumps up to the source voltage 70, and the gate voltage, respectively significantly reduced to zero. After a time interval equal to the set pulse duration, the on-pulse sync pulse is removed and the off-pulse sync pulse is simultaneously applied. Co control circuit 74 shuts off the semiconductor

the key 72, and from the control circuit 75 - the simultaneous inclusion of a semiconductor key 73. The shutter capacity is quickly charged through the key 73 to the voltage of the source 79 and the circuit returns to its original state. Subsequently, as the clock pulses arrive, the considered process is repeated.

To compensate for misalignment of the gate, operating in the Q-switching mode, a constant bias voltage of the required value is supplied from the source 79 to the gate terminal 82.

To implement a mode in which the voltage drop across the gate at the time of opening is higher than the amplitude of the constant blocking voltage, the voltage level of the source 70 is set higher than the voltage of the source 79.

To implement a mode in which the shutter operating in the "switch-on" mode is constantly open, the corresponding voltage value of the source 79 is set.

It should be noted that the source 79 operates on a capacitive load (Pockels cell), so the average output current of the source 79 usually does not exceed fractions of a microampere.

To reduce the voltage of the source 70, the semiconductor switches 72, 73 can be replaced by a Marx generator (Fig. 5), in each stage of which the capacitor is connected to two switches connected in series with a control circuit, the switch connected to the minus of the capacitor is shunted by a resistor, and to the switch connected to the capacitor plus, the anode is connected to a diode, the cathode of which is connected to the capacitor plus in the next stage, while the common point of the keys in the previous stage is connected to the minus of the capacitor in the next stage, and bschaya point in the last stage of keys connected to the first gate terminal, a second terminal of which is connected to the positive second source; the plus of the first source is connected to the plus of the capacitor in the first stage, and the minuses of both sources are connected to a common bus.

Claims (2)

1. A high-voltage pulse modulator with a nanosecond front for controlling electro-optical gates in the form of a Pockels cell, containing a high-voltage power supply, shunted by a capacitor, connected to two series-connected semiconductor switches with galvanically isolated control circuits, a clock generator supplied to the control circuit, a discharge resistor connected parallel to the semiconductor switch connected to the minus of the source, and the electro-optical shutter, the first output to which is connected to a common point of semiconductor switches, characterized in that, in order to expand the functionality of the modulator, a second controllable high-voltage source shunted by a capacitor is inserted into it, the positive terminal of the second source being connected to the second terminal of the gate, and the negative terminals of both sources being connected to a common by bus. 2. The high-voltage pulse modulator according to claim 1, characterized in that, in order to reduce the voltage of the first source, both semiconductor switches are replaced by a Marx generator, in each stage of which the capacitor is connected to two series-connected switches with a control circuit, and the switch connected to minus capacitor, is shunted by the resistor, and a diode is connected to the key connected to the plus of the capacitor, the cathode of which is connected to the plus of the capacitor in the next stage, while the common point of the keys is in the previous the cade is connected to the minus of the capacitor in the next stage, and the common point of the keys in the last stage is connected to the first output of the shutter, the second output of which is connected to the plus of the second source; the plus of the first source is connected to the plus of the capacitor in the first stage, and the minuses of both sources are connected to a common bus.