T 0955/91 04-02-1993

1. Procedural matters - Admissibility of the Appellant's late-filed requests

This appeal was characterised by a large number of alternative auxiliary requests filed by the Appellant at a very late stage in the appeal proceedings, both shortly before and during the oral proceedings, such auxiliary requests being in respect of claims defining different combinations of technical features, as set out in paragraph III above.

As mentioned in paragraph VIII (a) above the Respondent Siemens AG objected to this conduct as being unfair and apparently deliberate (since the same thing had occurred before the Opposition Division), and said that be was tired of such abuse of procedure. The Board has considerable sympathy with such Respondent in this respect, although it accepts the Appellant's explanation that such numerous requests were not made deliberately in order to complicate the procedure, but were made in response to arguments from the Respondents.

Attention is drawn once again to Decision T 95/83 (OJ EPO 1985, 75), which has been constantly followed by the Boards of Appeal, and whose headnote states:

"If an applicant for a patent or a patentee desires to submit amendments to the description, claims or drawings of a European patent application or a European Patent in the course of appeal proceedings, this should be done at the earliest possible moment (OJ EPO 6/1981, 176; 8/1984, 376). It is only in the most exceptional circumstances, where there is some clear justification both for the amendment and for its late submission, that it is likely that an amendment not submitted in good time before oral proceedings will be considered on its merits in those proceedings by a Board of Appeal."

Similarly in Decision T 153/85 (OJ EPO 1988, 1), the Board of Appeal stated that "When deciding on an appeal during oral proceedings, a Board may justifiably refuse to consider alternative claims which have been filed at a very late stage, for example during the oral proceedings, if such alternative claims are not clearly allowable.".

In the Board's view it is a misconception of the nature of opposition procedure, in particular opposition appeal procedure, to think that the Patentee can continue to file alternative sets of claims in response to an Opponent's attacks upon the patentee's previous requests, right up to and even during oral proceedings. In the present case the European patent application was filed in January 1983, and the application was granted in 1988. The documents on which the opposition was based were filed in July and August 1989, and remained the most relevant documents throughout the opposition proceedings including the appeal stage. Further documents cited and introduced during the course of the proceedings were of a subsidiary nature. The Patentee has had a long time in which to decide upon the form of the claims which be wishes to defend as satisfying the requirement of inventive step. The oral hearing in an opposition appeal is intended to be the very final stage in the opposition procedure, and the point in time at which the decision to maintain or to revoke the patent is taken. It is crucial that such oral hearing and the procedure immediately leading up to it is conducted in a manner which is fair to both sides (the Patentee and the Opponent(s)), and in a manner which allows the Board to make its decision in fair and proper circumstances.

For the reasons set out in paragraphs 2.1 to 2.7 and 3.1 to 3.4 below, the claim sets D to G filed on 21 January 1993 immediately prior to the oral hearing, and the claim set D' filed during the oral hearing on 4 February 1993, are not clearly allowable (Decision T 153/85), in that they do not clearly meet the requirements of Article 56 EPC. Such claim sets are therefore inadmissible.

Similarly, the unformulated proposals for amendment of claim set D' which were made during the oral proceedings on 4 February 1993 are inadmissible.

On the other hand, for the reasons set out in paragraph 3.5 claim set H filed on 21 January 1993 is clearly allowable, and is therefore admitted into the proceedings.

2. Inventive step of Claims 1 of claim sets A to F

2.1. Claims 1 of claim sets A and D add to the subject-matter of Claim 1 as granted in the specification of the patent under appeal the "loose coupling" feature defined in paragraph III, Claim 1 of claim set D' additionally the "constant voltage" feature. Claims 1 of claim sets B and E add to the subject-matter of granted Claim 1 the features of granted Claim 2 - i.e. the "E-core" feature - and correspond to the first auxiliary request before the Opposition Division. Claims 1 of claim sets C and F add to the subject-matter of granted Claim 1 as well the "loose coupling" and the "E-core" features. Due to this close technical interrelationship the question of inventive step underlying one of the main claims of claim sets A to F is examined in common:

2.2. From the nearest prior art according to document D4 it is known in the wording of Claims 1 of claim sets A, B, C, D, D', E and F:

"A high frequency (see D4, Claim 1, 10 KHz to 30 KHz) electronic ballast for gas discharge lamps comprising a controlled oscillator (D4, Fig. 5; 7, 8, 5; page 9, paragraph 1) providing two ... high frequency outputs (Fig. 5, "Ansteuerung"), which are variable in frequency under at least one control input (7, 8; page 14, lines 18 to 20) to said oscillator (5), said ... outputs inputting to drive means (3 in Fig. 5 and P1 in Fig. 4), which, in turn, provides an input to an inverter (2 in Fig. 4), the output of said inverter being a source to a "circuit element" (Dr in Fig. 2) which enables the inverter to directly drive a gas discharge lamp (L in Fig. 2), said controlled oscillator and driver means being adapted to be supplied from a low DC voltage source (+15V in Fig. 5) and said inverter being adapted to be supplied from a high DC voltage source (+300V in Fig. 4), wherein ... control is provided by said at least one control input to the oscillator to vary the frequency of the oscillator and thereby vary the light output of the gas discharge lamp (page 8, lines 5 to 9; page 9, lines 1 to 3)."

2.3. Starting from the prior art disclosed in document D4, the objective technical problem underlying the patent under appeal with regard to claim sets A, C, D, D' and F is to provide a ballast wherein the circuit element, enabling the inverter to directly drive a gas discharge lamp, prevents additional energy losses in a choke and allows to strike a discharge lamp at its minimum dimmed level in the same way as at its full light level with little difference in striking time; see the description of the patent under appeal column 8, lines 8 to 10; column 9, lines 19, 20; and column 8, line 59, to column 9, line 1.

The problem of striking a discharge lamp is observable in practice. Also, a reduction of power consumption is a generally known problem in the art of gas discharge lamps. Thus, the formulation of the objective problem does not contribute to an inventive step underlying the subject- matter of the claims.

2.4. Having regard to claims sets A and D this problem is solved in that:

the circuit element "is a transformer, which has primary and secondary windings disposed such that loose coupling is obtained between the primary and secondary windings".

Such a circuit element is known from document D5; see 3 in Fig. 1 and page 2, lines 9 and 10. A skilled person derives from document D5, Claim 5, the "overshoot" properties of such loose coupling, also used in the patent under appeal for enabling a start at each dimming level, and from D5, page 1, lines 20-24, the advantage of eliminating the need for an additional choke, resulting from the loose coupling. Therefore, it is obvious for a skilled person to make analogous use of the transformer disclosed in document D5 for replacing the choke Tr in the ballast disclosed in document D4. In the Board's view, no technical difficulties are encountered on adapting the output of inverter 2 in Fig. 4 of document D4 to the input of transformer 3 of document D5. The ballast embodied in Figures 5 and 4 of document D4 represent already an open loop control circuit; see paragraph VII(a) and IX(a). Only when the brightness level is set via control input 7, feedback control via element 6 and 8 gets effective to maintain the manually set brightness level. An analogous additional feedback is also foreseen in an embodiment of the patent under appeal; see column 3, lines 5 to 9. Hence, a skilled person would have no technical prejudice that the unstability of the open loop ballast disclosed in document D4 prevents its use in dimming.

No particular frequency limits are defined in the claims or description of the patent under appeal. Thus, control input 7 of document D4 would automatically function as "dimming" control as claimed after inputting the output of inverter 4 of document D4 into the input of transformer 3 of document D5, the brightness variation of which is explicitly termed as "dimming" (see the title of D5).

Also the subject-matter of Claim 1 of claim sets A, C, D, D' and F results in a permanent overshoot repetitively produced with each pulse; see Fig. 6c with the corresponding description. For this reason the Appellant's argument in paragraph VII(d) is not relevant.

In order to find out that the outputs of oscillator 5 in Fig. 5 of document D4 should be "complementary" ones as claimed, a skilled person only needs to fill out an informational gap in this document by his general knowledge; see also paragraph IX(a).

For the reasons stated above, the Board regards the subject-matter of Claims 1 of claim sets A and D to be the result of an analogous use of the loose coupled transformer disclosed in document D5 in the technically close situation of the ballast disclosed in document D4 followed by routine adaptations. Therefore, Claims 1 of claim sets A and D are considered to lack an inventive step within the meaning of Article 56 EPC.

2.5. The feature added by the wording of Claim 1 of claim set D' to that of Claim 1 of claim set D: "so that there is no significant change in the voltage applied to the gas discharge lamp at any dimming level" is disclosed in the patent under appeal, column 8, lines 48 to 63, as a mere logical consequence of the use of a transformer. In the Board's view, a skilled person expects an unchanged secondary voltage as a generally known advantage which is automatically realised in the analogous use of the transformer disclosed in document D5 in the ballast of document D4.

2.6. Claims 1 of claim sets B and E specify mainly that in the ballast of document D4 (see paragraph 2.2 above):

the circuit element "is an E-core transformer with primary and secondary windings disposed on opposite ends of the centre leg".

E-core transformers are generally known to be leakage transformers with a variable range of the spread self- inductance (see for instance document D13, page 132) and thus per se, do not necessarily have the sufficient leakage to solve the objective problem as stated in paragraph 2.3 above. For this reason, the general claiming of an E-core transformer can only be attributed the function of a "circuit element which enables the inverter to directly drive a gas discharge lamp". Hence, the replacement of choke Tr in the ballast disclosed in document D4 by an E-core transformer such as disclosed in document D13 reduces to an obvious exchange of well-known equivalents. It belongs to the special knowledge of the skilled person that E-cores can be realised without iron shunts of ferrite, function in the high frequency region up to 1 MHz and are excellent for pulse transformers; see for instance document D22, page 262, lines 3 to 13 which is introduced into the proceedings according to Article 114(1) EPC. For these reasons the Appellant cannot be followed in his opinion according to paragraph VII(b), and Claims 1 of claim sets B and E are regarded not to satisfy Art. 56 EPC.

An interpretation of Claims 1 of claim sets B and E on the basis of Article 69 EPC would lead to the subject-matter of Claims 1 of claim sets C and F.

2.7. Having regard to claim sets C and F the objective problem defined in paragraph 2.3 above is solved in the identical way as indicated with regard to claim sets A and D in paragraph 2.4 above, i.e. by a loose coupled transformer such as disclosed in document D5 and by specifying additionally that such transformer shall be

"an E-core transformer, which has primary and secondary windings disposed on opposite ends of the centre leg."

Continuing the reasoning in paragraph 2.4 above, the remaining issue of an inventive step underlying the subject-matter of the main claims of claim sets C and F reduces to the question whether it would be obvious to realise the generally disclosed transformer 3 document D5 with an E-core and the claimed winding arrangement on its centre leg.

In particular, in view of the Appellant's arguments according to paragraph VII the Board introduces late-filed document D22 into the proceedings as relevant for the decision to be taken. Document D22 discloses an E-core transformer particularly designed for use in the high frequency range (page 262, line 12). Moreover, a skilled person derives from D22, page 262, paragraph 4, that the leakage inductance is a function of the volume of the air between the windings, each having in the side by side arrangement the shape of a flat disk as also schematically indicated in Fig. 9-10(b) on page 263. In the Board's view, on the basis of such guidance a skilled person is able to dispose the primary and secondary windings "on opposite ends of the centre leg" in such a way that the E- core transformer according to Fig. 9-10(b) is able to exercise the functions of transformer 3 disclosed in document D5.

For these reasons, document D5 provides a hint to a skilled person to replace choke Tr in the ballast disclosed in document D4 by the E-core transformer disclosed in document D22. Therefore, Claims 1 of claim sets C and F are considered to lack an inventive step within the meaning of Article 56 EPC.

3. Inventive step of Claim 1 of claim set G and H

3.1. Claim 1 of claim set G comprises the subject-matter of granted claims 1, 3 and 4 and corresponds to the third (and last) auxiliary request before the Opposition Division.

3.2. From the nearest prior art disclosed in document D4 it is known in the wording of Claims 1 of claim sets G and H

"A high frequency ballast for gas discharge lamps comprising a controlled oscillator (7,8,5 in Fig. 5) providing two high frequency outputs which are variable in frequency under at least one control input (7,8) to said oscillator (5), whereby a dimming control can be achieved (see paragraph 2.4 for details), said outputs inputting to driver means (3 in Fig. 5, P1 in Fig. 4) which, in turn, provides an input to an inverter (2 in Fig. 4), the output of said inverter being a source to a choke (Tr in Fig. 2) which enables the inverter to directly drive a gas discharge lamp (L in Fig. 2), said controlled oscillator and driver means being adapted to be supplied from a low DC voltage source (+15V in Fig. 5) and said inverter being adapted to be supplied from a high DC voltage source (+300V in Fig. 4), said driver means comprising a push- pull transistor circuit (TD1, TD2 in Fig. 5) which is transformer (TR1 in Figures 5 and 4) coupled to said inverter."

3.3. The fact that the oscillator outputs are "complementary" results from an obvious filling of a gap in the information of document D4. The alternative use of a transformer instead of a choke for enabling the inverter to directly drive a gas discharge lamp represents an obvious exchange of known equivalents; see paragraph 2.6 above for details. Thus, the objective problem underlying Claims 1 of claims sets G and H reduces to protecting the conventional ballast against damage from simultaneously conducting push-pull transistors at mains voltage drops; see the description of the patent under appeal, column 3, lines 20 to 23. In the Board's view, a skilled person is able to recognise that such "power down" events lead to simultaneously conducting push and pull transistors of the conventional driver circuit. Hence, the formulation of the objective problem is obvious to a skilled person.

3.4. Solving this problem in that - according to the remaining wording of Claim 1 of claim set G -

the driver means "is controlled by a safe-guard circuit, characterised in that said safe-guard circuit deactivates the push-pull transistor circuit when the mains voltage drops below a predetermined level due to line voltage variation or power up and power down of said ballast"

in the Board's view has to be regarded as the obvious result of a skilled person's logical thinking within his normal routine activities. Moreover, the claimed general principle of a deactivation of a failing component in the driver-inverter circuit for a gas discharge lamp is known from document D1, in particular column 11, lines 37 to 45; see also paragraph IX(d) above.

For these reasons, the subject-matter of Claim 1 of claim set G lacks an inventive step within the meaning of Article 56 EPC.

3.5. The objective problem defined in paragraph 3.3 above is solved -according to the wording of Claim 1 of claim set H - in addition to the solution in Claim 1 of claim set G, in that:

the safeguard circuit "comprises a low voltage sensor coupled via a transistor to the emitters of said push-pull transistors and to the ground of the low voltage rail".

The use of such means in a fail-safe system is nowhere mentioned in any one of the cited documents and, in the Board's view, involves an inventive step. It is to be noted that neither Respondent raised the objection of lack of inventive step and submitted any arguments in support of such an objection in respect of the particular solution claimed in Claim 1 of claim set H.

3.6. For the reasons stated above, in the Board's judgment the subject-matter of Claim 1 of claim set H involves an inventive step within the meaning of Article 56 EPC.

4. Hence, it follows that Claim 1 of claim set H is allowable. Dependent Claims 2 to 4 of claim set H concern particular embodiments of the apparatus according to Claim 1 and are likewise allowable.