JP2586862Y2 - Protection circuit in laser tube lighting power supply - Google Patents

Description

[Detailed description of the invention]

[0001]

Description of the Field of the Invention The present invention relates to a protection circuit for a DC / DC converter type laser tube lighting power supply.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a conventional protection circuit of this type. Reference numeral 1 denotes a DC power source such as a battery. When the start switch 2 is closed, a base current is supplied to the base of the switching element 4 via the starting resistor 6, and the switching element is turned on, and the high voltage generating transformer 3 is turned on. Assuming that the voltage E of the DC power supply 1 is applied to the primary winding 3-1 and the inductance of the primary winding 3-1 of the high-voltage generating transformer 3 is L3-1, a current of (E / L3-1) × t flows. The number of turns of the primary winding 3-1 of the high voltage generating transformer 3 is set to N3-1,
The number of windings of the feedback winding 3-2 is N3-2, and the number of windings of the feedback winding 3-2 is E.
× (N3-2 / N3-1) voltage is generated. This feedback winding 3
The voltage of -2 is applied to the base of the switching element.
Since the base current is supplied through the resistor 7, the switching element 4 keeps on. However, if the current amplification rate of the switching element is hfe, the base current × hfe <(E /
L3-1) .times.t, the switching element is turned off, and if the number of secondary windings is N3-3 on the secondary winding 3 (2) -3, the diode 11 is forward biased. Ex (N3-3
/ N3-1). When this voltage is applied to the laser tube and exceeds the trigger voltage Vt of FIGS. 2 and 4, the laser tube is turned on. If a stable current is not supplied to the laser tube when it is turned on, stable light may not be obtained or its life may be shortened. Therefore, the laser flowing through the current detecting resistor 9 inserted in series with the laser tube. The terminal voltage of the current detecting resistor 9 is detected by a Zener diode 12 so that the current becomes constant. If the laser current increases (decreases), the Zener diode turns on (off) and the transistor 5 Turns on (off), turns off (on) the switching element 4, and lowers (increases) the output voltage. In this way, the voltage applied to the laser tube is controlled. On the other hand, at the time of outgassing of the laser tube or disconnection of the wiring of the high-voltage circuit, no current flows through the laser tube and the current detection resistor 9, so that no terminal voltage is generated at the current detection resistor 9,
Therefore, the Zener diode 12 does not turn on, and the transistor 5 does not turn on. Therefore, the switching element 4 does not turn off and the high voltage is not controlled. There was a risk of causing a ground fault fire due to insulation breakdown.

[0003]

SUMMARY OF THE INVENTION In the prior art, an abnormally high voltage may be continuously generated due to a defect of a laser tube or the like, and there is a risk of causing an electric shock or a fire accident. An object of the present invention is to prevent an electric shock or a fire by providing a protection circuit for detecting an abnormally high voltage due to a failure of a laser tube and cutting off the output.

[0004]

FIG. 3 shows an embodiment of the present invention. FIG.
1, the same reference numerals as those in FIG. 1 represent the same parts. When the power supply operation start switch 48 is turned off and the current supply switch 2 is turned on between t0 and t1 in FIG. 4, the transistor 46 is turned off, so that the D flip (3) flip-flop IC
Since the set terminal S2 at 45 is at a high level "H" and the reset terminal R2 at a low level "L", the output Q2 is at "H", the transistor 47 is on and the switching element is off. As the analog switch 43 turns on, the output of the operational amplifier 40 becomes the Vref voltage. Vr
Since the ef voltage is set to the voltage of (Vc + Vd) / 2 in FIG. 4, the outputs of the operational amplifiers 41 and 42 are "L", and the set terminal S1 of the D flip-flop IC 44 is "L". The reset terminal R1 of the D flip-flop IC44 is reset by the differentiating circuit of the capacitor 34 and the resistor 28 when the power-on switch 2 is on, so that the output terminal Q1 becomes "L". Next, t1-t2
When the start signal switch 48 is turned on between the transistors, the transistor 46 is turned on, and the R of the D flip-flop IC 45 is turned on.
2 is "H", S2 is "L" and Q2 is "L". Therefore, the transistor 47 is turned off, the switching element is turned on, and the switching action causes the switching of the transformer 2.
When a predetermined high voltage is generated on the next side and exceeds the trigger voltage Vt shown in FIGS. 2 and 4, the laser tube is turned on. At this time, the voltage applied to the laser tube is divided by the voltage detection resistors 10 and 15,
Further, the signal is guided to an integration circuit of the operational amplifier 39 and the operational amplifier 40. The integration time constant is given by the product of the resistor 18 and the capacitor 33, and the voltage V divided by the voltage detection resistors 10 and 15 is
The integration operation is stopped at the point where a and the integrated output Vb of the operational amplifier 40 are balanced. The start of the integration operation is set by an analog switch 43 inserted in parallel with the capacitor 33. That is, if the analog switch 43 is on, the integral output is Vref = (VC + Vd) / 2 regardless of Va, and if the analog switch 43 is off, Vr = Vr + Vd.
Integration is performed up to Va value starting from ef. Next, when the start signal switch 48 is turned on, the DFF I
Since both Q1 and Q2 of C44 and 45 become "L", the analog switch 43 is turned off to start integration. If the integration time constant is appropriately selected, the high voltage generated when the laser tube is turned on is several milliseconds in a normal state, and slightly changes as shown in FIG. Just do it. The integrated voltage Vb is compared by comparators 41 and 42, and if it is within Vc and Vd, the laser tube is determined to be normal (4).

On the other hand, if it is assumed that a high voltage is continuously generated due to an abnormality in the laser tube or the like at t2, the high voltage is integrated as shown in FIG. 4b, and eventually exceeds the upper limit set value Vc. Then, the output of the comparator 41 becomes "H" and the D-FF
IC44S1 is set to "H", Q1 is latched to "H",
The transistor 47 is turned on, the switching element 4 is turned off, and the abnormally high voltage output is cut off to prevent an accident. At the same time, since Q1 of the D-FFIC 44 is "H" at the same time, the analog switch 43 is turned on to reset the integration circuit, and the apparatus enters a standby state for the next lighting.
To release the standby state and relight the laser tube, the start signal switch 48 is turned off once, and then turned on again.
That is, the details are as follows.
To “H” at the same time, and at the same time
The terminal also shifts from "L" to "H", the Q1 terminal of the IC 44 becomes "L", the transistor 47 is turned off, the switching element 4 is turned on, and the light is turned on again.

Next, as an example, when the output voltage is lowered for some reason, the output voltage is integrated as shown in FIG. H ”and Q1
Is also latched at "H", the transistor 47 is turned on, the switching element 4 is turned off and the output voltage is cut off to protect the laser tube and the power supply. In conclusion, by integrating the voltage Va obtained by dividing the voltage applied to the laser tube,
The high voltage generated during lighting is not judged to be abnormal,
Only continuous abnormal voltage can be determined to be abnormal based on the tube failure.

[0007]

As is clear from the above description, according to the present invention, in the laser tube lighting power supply device (5), when the gas load of the laser tube or the disconnection of the wiring of the high voltage circuit, which is the load, occurs. In this way, it is possible to prevent an electric shock accident and a fire caused by an abnormally high voltage.

[Brief description of the drawings]

FIG. 1 shows an example of a conventional laser tube lighting power supply device.

FIG. 2 Laser tube lighting trigger voltage waveform

FIG. 3 shows an embodiment of the present invention;

FIG. 4 is an operation waveform diagram based on one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC power supply 2 Power supply switch 3 High voltage generating transformer 4 Switching element 5 Transistor 6 Resistance 7 Resistance 8 Resistance 9 Resistance (for laser tube current detection) 10 Resistance (for voltage detection) 11 Rectifier diode 12 Zener diode C 13 Smoothing capacitor 14 Laser tube 15 Resistance (for voltage detection) (6) 16 Resistance 17 Resistance 18 Resistance 19 Resistance 20 Resistance 21 Resistance 22 Resistance 23 Resistance 24 Resistance 25 Resistance 26 Resistance 27 Resistance 28 Resistance 29 Resistance 30 Resistance REFERENCE SIGNS LIST 31 resistor 32 resistor 33 capacitor 34 capacitor 35 diode 36 diode 37 diode 38 diode 39 operational amplifier circuit 40 operational amplifier circuit 41 comparator circuit 42 comparator circuit 43 diode (7) 44 flip-flops Road 45 flip-flop circuit 46 transistor 47 transistor 48 Star - DOO signal switches

Claims (1)

(57) [Scope of request for utility model registration] 1. A DC / DC converter type laser tube in which a switching element is connected to the input winding of a transformer whose input winding side and output winding side are insulated, and a rectifying diode is connected to the output winding side. In the lighting power supply device, a control circuit of the power supply device incorporates a laser tube failure determination circuit,
The laser tube failure determination circuit includes a voltage dividing resistor and an integration circuit that detects a laser tube voltage, and first and second comparators that compare an output of the integration circuit with an upper limit setting and a lower limit setting value. Protection in a laser tube lighting power supply device, wherein an abnormally high voltage or an abnormally low voltage generated at the time of failure of the laser tube is detected based on one output of the first or second comparator and the power supply device is automatically stopped. circuit.