JP2953178B2 - High voltage switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high voltage switch constituting a pulse generation circuit for a pulse laser or the like.

[0002]

2. Description of the Related Art In the following description, a circuit of a copper vapor laser using a high voltage switch will be described. 1 and 2 show a pulse generator of a copper vapor laser described in, for example, JP-A-3-226114, in which 1 is a high-voltage power supply, 2 is a charging reactor, 3 is a charging diode,
Is a capacitor, 5 is a peaking capacitor, 6 is a laser discharge tube, 7 is a charging resistor, 8 is a high voltage switch, 9 is a snubber circuit, 10 is a trigger circuit, 11 is inductance of circuit wiring, 12 is a snubber diode, and 13 is a snubber diode. A snubber capacitor, 14 is a snubber resistor, and 15 is an FET.

Next, the operation will be described. The high voltage generated by the high voltage power supply 1 passes through the charging reactor 2, the charging diode 3, and the charging resistor 7, and charges the discharging capacitor 4 with the high voltage. The trigger signal generated by the trigger circuit 10 constitutes the high voltage switch 8
When input to T15, the high voltage switch 8 is turned on, and the voltage stored in the discharge capacitor 4 is supplied to the laser discharge tube 6 through the inductance 11 of the circuit wiring to obtain laser oscillation. The above operation is repeated at several kHz. The copper vapor laser is a pulsed laser and generally has a laser discharge tube 6.
The steeper the current flowing inside, the higher the laser efficiency. Therefore, it is necessary that the inductance 11 and the like of the circuit wiring be as small as possible (about 300 nH). The peaking capacitor 5 is provided to eliminate the rounding of the current flowing through the laser discharge tube 6 due to the inductance 11 of the circuit wiring. The snubber circuit 9
If the conduction timing of a specific parallel stage of the FET 15 connected in series is delayed, an overvoltage is applied to that stage and F
This is provided to prevent the ET 15 from being destroyed. FIG. 2 shows details of the snubber circuit 9.
If the conduction timing is delayed, the snubber diode 1
2, the circuit current is bypassed to the snubber capacitor 13. By making the snubber capacitor 13 sufficiently large, the voltage rise due to the inflow of is can be reduced, and the FE
T15 can be protected from overvoltage. The electric charge that has flowed into the snubber capacitor 13 is released during the rest period of the repetition cycle. Note that the timing delay is caused by the trigger circuit 10.
It is caused by the variation of the wiring in the inside and the variation of the components.

[0004]

Since the high-voltage switch used for the conventional copper vapor laser is constructed as described above, if the timing delay of a particular parallel stage repeatedly occurs, the high-voltage switch during the repetition period is inactive. In addition, the electric charge flowing into the snubber capacitor 13 cannot be completely discharged, so that the voltage of the snubber capacitor 13 increases, and the original function of the snubber deteriorates.

The present invention has been made in order to solve the above-mentioned problems. Even if the timing delay of a specific parallel stage occurs repeatedly, the voltage of the snubber capacitor 13 does not rise abnormally, and An object is to obtain a high-voltage switch capable of maintaining its original function.

[0006]

According to the high voltage switch of the present invention, the inductance of the switch circuit is L ₁ , the switching time of the high voltage switch is t _on , and the maximum value of variation in the conduction timing of a plurality of semiconductors is τ _c. When the number of series semiconductors is k and the switching repetition frequency is f, the size of the snubber resistor is 6L ₁ · t _on / (τ _c ³ f (k
-1)).

[0007]

In the high voltage switch according to the present invention,
Since the size of the snubber resistance is smaller than 6L ₁ · t _on / (τ _c ³ f (k-1)), the charge flowing into the snubber capacitor due to the timing delay can be sufficiently released during the rest period of the repetition period.

[0008]

[Embodiment 1] Hereinafter, the limiting condition of the snubber resistor 14 will be described. High voltage switch 8
Assume that the FETs 15 are connected in k stages in series.
FIG. 3 shows an equivalent circuit when the timing of a specific parallel stage is delayed. Vd is the voltage stored in the discharging capacitor 4, 13a is a parallel-stage snubber capacitor with a delayed timing, and the capacitance is Cs. When the discharge capacitor 4 is charged with Vd, it is assumed that the voltage is uniformly distributed to both ends of the k series FETs 15. At this time, the current i flowing into the snubber capacitor 13a at the time of switching of the high voltage switch 8 (assuming that the voltage of the FET 15 other than the specific stage monotonously decreases as shown in FIG. 4 during the switching time t _on ). ( _t ) is as follows.

[0009]

(Equation 1)

Therefore, if the time of the timing delay is τc, the amount of charge flowing into the snubber capacitor 13 up to τc is

[0011]

(Equation 2)

## EQU1 ## In order to discharge the inflowing charge during the rest period of the repetition cycle,

[0013]

(Equation 3)

## EQU1 ## Therefore, by obtaining the tolerance of Rc expand the second term of the left side _{Rc <6L 1 · t on /} (τ c 3 f (k-1)) and becomes. In other words, as shown in FIG. 5, even if the charge that flows in at τc is released during a period of about 1 / f and the voltage of the snubber capacitor 13a is reduced to Vd / k, even if the timing delay occurs repeatedly, The voltage of the snubber capacitor 13 does not exceed Vd / k, and the snubber function can be reliably maintained. If the electric charge flowing into the snubber capacitor 13a cannot be released during the idle period, the voltage gradually increases as shown by the dotted line in FIG. 5, and the snubber function decreases.

[0015]

As described above, according to the present invention, the size of the snubber resistance is made smaller than 6L ₁ · t _on / (τ _c ³ f (k-1)), so that the timing delay occurs repeatedly. However, there is an effect that the voltage of the snubber capacitor does not abnormally increase, a stable snubber function can be maintained, and a highly reliable high-voltage switch can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a pulse generation circuit for a pulse laser.

FIG. 2 is a circuit diagram showing a snubber circuit of a high-voltage switch.

FIG. 3 is a circuit diagram showing an equivalent circuit at the time of timing delay.

FIG. 4 is a characteristic diagram showing switching characteristics of the FET.

FIG. 5 is an explanatory diagram illustrating the operation of the high-voltage switch according to one embodiment of the present invention.

[Explanation of symbols]

 8 High voltage switch 9 Snubber circuit 10 Trigger circuit 11 Inductance of circuit wiring 12 Snubber diode 13 Snubber capacitor 14 Snubber resistor 15 FET

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01S 3/097-3/0977 H02M 9/04 H03K 3/57

Claims (1)

(57) [Claims] 1. A semiconductor device comprising: a plurality of semiconductors connected in series; a series circuit of a diode and a capacitor connected in parallel to both ends of each semiconductor; and a resistor connected in parallel to both ends of the capacitor. In a high voltage switch that conducts all at once by an external trigger signal, L ₁ is the inductance of the switch circuit, t _on is the switching time of the high voltage switch, and τ _c is the maximum value of the variation in the conduction timing of the plurality of semiconductors. , K is the series number of the semiconductor and f is the switching repetition frequency, the magnitude of the resistor is smaller than 6L ₁ · t _on / (τ _c ³ f (k-1)). High voltage switch.