CIRCUIT ARRANGEMENT

Abstract: The invention relates to a circuit arrangement for supplying a lamp (La) with a high-frequency current, provided with a DC-AC converter which comprises a bridge circuit provided with bipolar switches (51, 52), a control transformer (Lprim, SEC1, SEC2, P1, P2, Z1, Z3) for rendering the switches conducting and non-conducting, and a ballast coil (Lb, Z2). The control transformer and the ballast coil are integrated into one component in such a manner that the magnetic material surrounded by the secondary windings (SEC1, SEC2) of the control transformer becomes saturated during each high-frequency cycle, whereas the ballast coil does not become saturated. The control of the switches with low power losses and the ballast function are thus effectively realized by means of one component.

Description: Circuit arrangement. The invention relates to a circuit arrangement for supplying a load by means of a high-frequency current, provided with a DC-AC converter comprising a first input terminal and a second input terminal for connection to a supply voltage source, - a series arrangement of a first and a second switching element, a first end of said series arrangement being coupled to the first input terminal and a second end being coupled to the second input terminal, a load branch which shunts one of the switching elements and which is provided with: - connection terminals for holding the lamp, a control transformer which comprises a first closed magnetic loop of magnetizable material around which a primary winding, a first secondary winding coupled to the first switching element, and a second secondary winding coupled to the second switching element are provided, - inductive means provided with a magnetizable core having two ends and with at least a winding Lb which is provided around the magnetizable core between the two ends in series with the primary winding of the control transformer. The invention also relates to an inductive component and to a compact lamp. A circuit arrangement as mentioned in the first paragraph is known from US 5,434,480. The known circuit arrangement is widely used for supplying low-pressure mercury discharge lamps. These are often so-called compact fluorescent lamps with the supply circuit integrated in the lamp. Such compact fluorescent lamps have a high luminous efficacy and are very widely used in locations where traditionally incandescent lamps were used. A disadvantage of the known circuit arrangement is that it consists of a comparatively large number of components. Owing to this large number of components of the circuit arrangement, it is comparatively complicated to assemble the circuit arrangement and to integrate it in the compact fluorescent lamp. The invention has for its object to provide a circuit arrangement which consists of a comparatively small number of components. According to the invention, a circuit arrangement as mentioned in the opening paragraph is for this purpose characterized in that the ends of the magnetizable core are connected to the first closed magnetic loop by means of a magnetizable material such that the two secondary windings are provided around a part of the first closed magnetic loop in which the fluxes generated by the winding Lb and the primary winding reinforce one another during operation of the circuit arrangement. Since the total flux is maximal in that part of the first closed magnetic loop that is surrounded by the secondary windings, that part can saturate while the remaining part of the first magnetic loop and the magnetizable core do not saturate. This saturation is highly desirable for rendering the switching elements non-conducting comparatively quickly, more in particular if the switching elements of the circuit arrangement are bipolar transistors. A comparatively small power dissipation in the switching elements is achieved in that these switching elements are rendered non-conducting comparatively quickly. This comparatively small power dissipation gives the switching elements a comparatively long useful life. The control transformer and the inductive means have been integrated into one inductive component in a circuit arrangement according to the invention. The process of assembling a circuit arrangement according to the invention and its integration in a compact lamp are comparatively simple as a result of this. The inductive means may comprise a ballast coil. Such a comparatively simple construction of the circuit arrangement is suitable for applications in which the supply voltage with which the circuit arrangement is supplied has a comparatively high amplitude, while the operating voltage of the lamp is comparatively low. If the supply voltage with which the circuit arrangement is supplied as a comparatively low amplitude and/or the operating voltage of the lamp is comparatively high, it may be desirable to use inductive means which comprise a transformer. In such an embodiment of a circuit arrangement according to the invention, the winding Lb forms a primary winding of this transformer. The connection terminals for holding a lamp are coupled to a secondary winding of the transformer. The magnetizable core may be provided with an air gap. It is achieved thereby that the magnetic flux in the magnetizable core is comparatively small even for a comparatively strong current through the winding Lb, so that the magnetizable core cannot reach the saturated state and the inductive means operate in the desired manner. A comparatively simple, and thus comparatively inexpensive manner of jointly forming the first closed magnetic loop and the magnetizable core is by means of two E-cores. A circuit arrangement according to the invention is highly suitable for use in the electronic ballast of a compact lamp, more in particular a compact low-pressure mercury lamp comprising - a light source provided with a lamp vessel which is closed in a gastight manner and which transmits visible light, a housing which is fastened to the light source and is provided with a lamp cap, an electronic ballast which is electrically connected to the light source so as to supply this light source and which is accommodated in a space surrounded by the housing. Embodiments of the invention will be explained in detail with reference to a drawing, in which Fig. 1 shows an embodiment of an inductive component according to the invention; Fig. 2 shows an embodiment of a circuit arrangement according to the invention which comprises an inductive component as shown in Fig. 1 with a lamp connected to it; and Fig. 3 shows an embodiment of a compact lamp according to the invention. In Fig. 1, M is a structure of magnetizable material formed by means of two E-cores. The structure consists of two parallel legs PI and P2 which are interconnected by transverse legs Zl, Z2 and Z3. Lprim, SEC1 and SEC2 are a primary winding and a first and a second secondary winding of a control transformer, respectively. These windings are provided around the transverse leg Zl. The transverse leg Zl forms a first closed magnetic loop together with leg PI, leg P2, and transverse leg Z3. The first closed magnetic loop together with the windings Lprim, SEC1 and SEC2 forms a control transformer. The transverse leg Z2 forms a magnetizable core. Lb is a winding which in this embodiment forms a ballast coil together with the transverse leg Z2. Ls is an air gap in the transverse leg Z2. The first E-core comprises the leg PI and half of each of the transverse legs Zl , Z2 and Z3. The second E-core comprises the leg P2 and half of each of the transverse legs Zl , Z2 and Z3. RV1 is a plane which intersects the transverse leg Z3 perpendicularly and in which the first and the second E-core touch one another. RV2 is a plane which intersects the transverse leg Zl perpendicularly and in which the first and the second E-core touch one another. In Fig. 2, Kl and K2 are a first and a second input terminal, respectively, for connection to a supply voltage source. Kl is connected to K2 by means of a series arrangement of a first switching element SI and a second switching element S2. The switching elements in this embodiment are formed by bipolar transistors. The switching element SI is shunted by a diode Dl, and the switching element S2 is shunted by a diode D2. The switching element S2 is shunted by a load branch which is formed in this embodiment by a series arrangement of the primary winding Lprim, the winding Lb, the connection terminals K3 and K4 for holding a lamp, and a capacitor Cl . A low-pressure mercury discharge lamp La is connected to the connection terminals K3 and K4 and is shunted by a capacitor C2. Respective ends of the secondary winding SEC1 are connected to the base and to the emitter of the switching element SI . Respective ends of the secondary winding SEC2 are connected to the base and to the emitter of the switching element S2. The operation of the magnetic component shown in Fig. 1 and of the circuit arrangement shown in Fig. 2 is as follows. When the input terminals Kl and K2 are connected to a DC voltage source, the secondary windings SEC1 and SEC2 will render the switching elements SI and S2 alternately conducting and non-conducting with high frequency. As a result of this, a high-frequency AC current flows through the load branch and the lamp La is supplied thereby. This high-frequency AC current causes a first flux in the structure M via the winding Lb. This first flux is present both in the second closed magnetic loop, formed by the transverse leg Zl together with the transverse leg Z2 and those portions of the legs PI and P2 which are situated between the transverse legs Zl and Z2, and in a third closed magnetic loop formed by the transverse leg Z3 together with the transverse leg Z2 and the portions of the legs PI and P2 which are present between the transverse legs Z2 and Z3. The first flux is comparatively small owing to the presence of the air gap Ls in the second and in the third closed magnetic loop. The high-frequency AC current flowing in the load branch also causes a second flux, which is present in the first closed magnetic loop and in the second closed magnetic loop, via the primary winding Lprim of the control transformer. The portion of the second flux which is present in the second closed magnetic loop, however, is comparatively small on account of the presence of the air gap Ls. The total second flux, however, is comparatively great because the first closed magnetic loop does not have an air gap. The first and the second flux reinforce one another in transverse leg Zl and transverse leg Z2, and cancel one another out partly in transverse leg Z3. Since the total flux, which is equal to the sum of the first flux and the second flux, reaches its highest value in the transverse leg Zl, the latter can enter the saturated state whereas the transverse leg Z2 and the transverse leg Z3 do not become saturated. The voltages which are present between ends of the secondary windings SEC1 and SEC2 drop comparatively quickly as a result of the saturation of the transverse leg Zl. This achieves that the switching elements SI and S2 become nonconducting comparatively quickly, so that comparatively little power is dissipated in the switching elements. At the same time, the ballast coil formed by the transverse leg Z2 and the winding Lb continues operating in the desired manner because the transverse leg Z2 does not become saturated, thanks to the air gap. In Fig. 3, reference numeral 8 denotes a portion of a lamp vessel which is sealed in a gastight manner and which transmits visible light. A wall 6 of a housing is connected to the lamp vessel 8 and is provided with a lamp cap 3, while a circuit arrangement B according to the invention is present in a space 7 enclosed by the housing. The circuit arrangement is diagrammatically indicated as consisting of components P and Cl to C4. Connection wires 9 extend between the circuit arrangement and electrodes (not shown) in the lamp vessel. E denotes connection wires between the circuit arrangement and the electrical contacts 1 and 2 arranged on the lamp cap. Since the winding Lb and the primary winding of the control transformer are connected in series, both pass the same current during operation of the circuit arrangement. The flux induced in the first closed magnetic loop by the primary winding, however, is considerably greater than the flux induced by the winding Lb, if the first closed magnetic loop does not comprise an air gap.

Claims: CLAIMS: 1. A circuit arrangement for supplying a load by means of a high-frequency current, provided with a DC-AC converter comprising a first input terminal and a second input terminal for connection to a supply voltage source, - a series arrangement of a first and a second switching element, a first end of said series arrangement being coupled to the first input terminal and a second end being coupled to the second input terminal, a load branch which shunts one of the switching elements and which is provided with: - connection terminals for holding the lamp, a control transformer which comprises a first closed magnetic loop of magnetizable material around which a primary winding, a first secondary winding coupled to the first switching element, and a second secondary winding coupled to the second switching element are provided, - inductive means provided with a magnetizable core having two ends and with at least a winding Lb which is provided around the magnetizable core between the two ends in series with the primary winding of the control transformer, characterized in that the ends of the magnetizable core are connected to the first closed magnetic loop by means of a magnetizable material such that the two secondary windings are provided around a part of the first closed magnetic loop in which the fluxes generated by the winding Lb and the primary winding reinforce one another during operation of the circuit arrangement. 2. A circuit arrangement as claimed in claim 1, wherein the inductive means comprise a ballast coil. 3. A circuit arrangement as claimed in claim 1, wherein the inductive means comprise a transformer, and the winding Lb forms a primary winding of said transformer. 4. A circuit arrangement as claimed in any one or several of the preceding claims, wherein the magnetizable core is provided with an air gap. 5. A circuit arrangement as claimed in any one or several of the preceding claims, wherein the first closed magnetic loop and the magnetizable core are formed by two E-cores. 6. An inductive component for use in a circuit arrangement as claimed in any one or several of the preceding claims, comprising a control transformer which comprises a first closed magnetic loop of magnetizable material around which a primary winding and two secondary windings are provided, inductive means provided with a magnetizable core having two ends and with at least a winding Lb which is provided around the magnetizable core between the two ends in series with the primary winding of the control transformer, characterized in that the ends of the magnetizable core are connected to the first closed magnetic loop by means of a magnetizable material such that the winding Lb, the primary winding, and the two secondary windings are provided around a second closed magnetic loop which is formed by the magnetizable core and part of the first closed magnetic loop and in which the fluxes generated by the winding Lb and the primary winding reinforce one another when said windings conduct a current. 7. A compact lamp comprising a light source provided with a lamp vessel which is closed in a gastight manner and which transmits visible light, a housing which is fastened to the light source and is provided with a lamp cap, an electronic ballast which is electrically connected to the light source so as to supply this light source and which is accommodated in a space enclosed by the housing, characterized in that the electronic ballast comprises a circuit arrangement as claimed in claim 1, 2, 3, 4 or 5. 8. A compact lamp as claimed in claim 7, wherein the light source is a low-pressure mercury discharge lamp.

Inventors: LAROS PETRUS CORNELIS JOHANNES, REESINK KOEN DANIEL, LAROS, PETRUS, CORNELIS, JOHANNES, REESINK, KOEN, DANIEL
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1998
Main classification: H05B41
IPC codes: H05B41