HIGH FREQUENCY SURGICAL GENERATOR COMPRISING AN ADDITIONAL TRANSFORMER

[0001] The invention relates to an HF surgical appliance having an HF generator and an additional transformer.

[0002] HF surgical appliances are known for a plurality of possible applications. With some of these possible applications, the load impedance lies between 0.1 and 1 kΩ, with other possible applications, the load impedance can be even lower. In particular, when a transurethral resection of the prostate (TUR) is to be performed with a bipolar instrument with a highly conductive irrigant fluid (NaCl 0.9%), the load impedance is only about 20Ω.

[0003] To be able to perform a load adaptation with a conventional HF surgical appliance, as shown in FIG. 4, a generator G is provided in the HF surgical appliance (indicated in FIG. 4 with a broken line); the generator G comprises an output transformer T₁ that supplies, via an inductance L₁ and a capacitance C₁, which together form a resonant circuit, output terminals 1, 2, on which the load resistor Z_L is suspended. With a high-resistance load, a first switch S1 is closed so that the entire secondary winding of the transformer T₁ is coupled to the load resistor Z_L via the resonant circuit. In the case of a low load impedance Z_L, only a part of the secondary winding of the transformer T₁ is coupled via the switch S2 to the load Z_L. In this case, although an improvement of the adaptation conditions of the impedances is ensured, the transformer T₁ has to be provided with a winding that has a larger wire cross section than the rest of the windings, or has an even larger overall wire cross section, to tap the switch S2. This is obviously a drawback. Furthermore, the adaptation of the resonant circuit, which has to take place in dependence on the generator frequency and the load Z_L, no longer takes place in one or the other switch position.

[0004] It is an object of the embodiments of the invention to provide an HF surgical appliance of the type discussed above in which adaptation to low loads is also enabled.

[0005] This object is achieved by an HF surgical appliance comprising an HF generator having an output circuit, which contains an output transformer, has an output impedance and comprises output terminals to which an HF surgical instrument for supplying a high-frequency current with a specific frequency into tissue for treating the same can be connected. An additional output circuit, which contains an additional transformer connected between the output circuit and the output terminals to reduce the output impedance is also provided.

[0006] The additional output circuit can either be embodied as an external additional appliance or mounted in the HF surgical appliance. This ensures, in a simple manner, that a conventional surgical appliance can be used for special purposes (with a low-resistance load) with a little amount of work.

[0007] Preferably, the additional transformer is embodied as an autotransformer so that the galvanic separation is provided by the transformer provided in the HF surgical appliances. This additional transformer comprises an asymmetric or, preferably, a symmetrical winding.

[0008] The additional transformer preferably has a small air gap, particularly no air gap. This enables the adaptation to be optimized. In addition, the additional transformer is preferably a low-scattering transformer. Moreover, the inductance of the additional transformer is preferably more than 1 mH.

[0009] The additional output circuit also comprises a capacitor between the additional transformer and the output terminals. It is preferable, however, that a resonant circuit having a resonant frequency above the specific frequency of the generator be provided. This further improves the adaptation to the load.

[0015] In the following description, the same reference numbers are used to refer to the same parts and parts with the same function.

[0016] FIG. 1 shows an HF surgical appliance that comprises a generator G comprising an output transformer T₁ and a resonant circuit L₁, C₁ as an output circuit. This arrangement is coupled to an additional transformer T₂ that has more turns in the primary winding than in the secondary winding. The additional transformer T₂ is connected, via another resonant circuit L₂, C₂, to output terminals 1, 2 to which a load Z_L is applied. The additional transformer T₂ reduces the internal resistance of the overall arrangement in such a way that a substantially adaptation to the load impedance Z_L takes place. The additional resonant circuit L₂, C₂ is designed so that adaptation, taking into account the output frequency of the generator G and the load Z_L, takes place.

[0017] The embodiment shown in FIG. 2 differs from that shown in FIG. 1 in that the additional transformer T₂ is embodied as an autotransformer. The embodiment in FIG. 3 differs from that shown in FIG. 2 in that this autotransformer T₂ has a symmetrical tap for coupling the load Z_L (via the resonant circuit L₂, C₂).