GAO, Wei (Second Light Industrial Estate, Ciao Hing Road Dond Huang Sree, Panyu Guangdong 0, 51140, CN)
| CLAIMS 1. A self-oscillating half-bridge circuit device, comprising a switch element (Ql, Q2), a driving element (TIa, T2c, T2b) and a blocking capacitor (Cl), wherein: the switch element comprises a first transistor (Ql) and a second transistor (Q2) connected in series to form a half-bridge, and wherein the emitter of the first transistor (Ql) is coupled with the collector of the second transistor (Q2) , the collector of the first transistor (Ql) is coupled with a power supply (VDC) of the self-oscillating half-bridge circuit device, and the emitter of the second transistor (Q2) is coupled with a second output node (N) of the self-oscillating half-bridge circuit device; the driving element comprises a transformer with an air gap, which transformer with the air gap comprising a primary winding (TIa) , a first secondary winding (T2c) and a second secondary winding (T2b) , wherein the primary winding (TIa) has a dotted terminal coupled with a point (A) where the first transistor (Ql) and the second transistors (Q2) are connected, and the other terminal of the primary winding (TIa) is coupled with a terminal of the blocking capacitor (Cl); the first secondary winding (T2c) has a dotted terminal coupled with the base of the first transistor (Ql), and the other terminal of the first secondary winding (T2c) is coupled with the point (A) where the first transistor (Ql) and the second transistors (Q2) are connected; and the second secondary winding (T2b) has a dotted terminal coupled with the second output node (N) , and the other terminal of the second secondary winding (T2b) is coupled with the base of the second transistor (Q2); and the other terminal of the blocking capacitor (Cl) is coupled with a first output node (M) of the self-oscillating half-bridge circuit device. 2. The self-oscillating half-bridge circuit device according to claim 1, wherein the tolerance of the inductance of the transformer with the air gap is +/-3%. 3. The self-oscillating half-bridge circuit device according to claim 1 or 2, wherein the turn ratio of the primary winding (TIa) , the first secondary winding (T2c) and the second secondary winding (T2b) of the transformer with the air gap is 12:18:18, and the inductance of the transformer with the air gap is 8 μH. 4. A ballast comprising the self-oscillating half-bridge circuit device according to any one of claims 1 to 3, wherein a choke (Ll) is coupled between the other terminal of the primary winding (TIa) of the transformer with the air gap of the self-oscillating half-bridge circuit device and the blocking capacitor (Cl), and an igniting capacitor (C2) for a load of the ballast is coupled between the first output node (M) and the second output node (N) of the self-oscillating half-bridge circuit device. 5. An electronic transformer or an LED driving device comprising the self-oscillating half-bridge circuit device according to any one of claims 1 to 3. 6. A lamp comprising the ballast according to claim 4. |
Field of the Utility Model
[0001] The present utility model generally relates to the field of a transformer-driven oscillator circuit, and in particular to a transformer-driven self-oscillating half-bridge circuit and to a ballast and lamp using the self-oscillating half-bridge circuit .
Background of the Utility Model
[0002] A self-oscillating half-bridge circuit is widely used in application fields of lighting and the like. A toroidal transformer is used for a driving unit in the self-oscillating half-bridge circuit. Various parameters of the toroidal transformer have large tolerances, for example, the tolerance of the inductance of the toroidal transformer can be up to +/- 25%. This leads to an adverse influence upon the operating frequency of the self-oscillating half-bridge circuit driven by the transformer and makes it difficult to control the magnitude of the operating frequency within a certain range, resulting in a substantial variation in the operating frequency of a final product in which the self-oscillating half-bridge circuit is applied. For example, an application of such a self-oscillating half-bridge circuit in a ballast may result in poor consistency of the operating frequency of the produced ballast, and consequently a large number of ballasts which fail to satisfy a desired operating frequency range have to be rejected, which may result in a waste of considerable labor and money. Furthermore, another disadvantage of the toroidal transformer is poor ability of enduring magnetic saturation, and even a tiny direct-current component may cause the toroidal transformer to operate abnormally. It is well known that a transformer, a self-oscillating half-bridge circuit using a transformer and a ballast using a self-oscillating half-bridge circuit each are typically used in various power grids where various power consumption equipments are present. The consumption equipments may not be purely resistive and hence result in contamination of wave shapes in the power grids . Consequently, the magnetic core of the transformer may be caused to reach magnetic saturation to thereby generate interference of magnetic radiation. Such interference of magnetic radiation may influence operating performance of the self-oscillating half-bridge circuit driven by the toroidal transformer.
Summary of the Utility Model [0003] In view of the above problem present in the prior art, the present utility model proposes a self-oscillating half-bridge circuit device driven by a transformer with an air gap and a ballast and lamp including the self-oscillating half-bridge circuit device. [0004] According to an aspect of the utility model, there is provided a self-oscillating half-bridge circuit device including switch element, a driving element and a blocking capacitor, wherein: the switch element includes a first transistor and a second transistor connected in series to form a half-bridge, wherein the emitter of the first transistor is coupled with the collector of the second transistor, the collector of the first transistor is coupled with a power supply of the self-oscillating half-bridge circuit device, and the emitter of the second transistor is coupled with a second output node of the self-oscillating half-bridge circuit device; the driving element includes a transformer an air gap, which transformer with the air gap including a primary winding, a first secondary winding and a second secondary winding, wherein the primary winding has a dotted terminal coupled with a point where the first transistor and the second transistors are connected, and the other terminal of the primary winding is coupled with a terminal of the blocking capacitor; the first secondary winding has a dotted terminal coupled with the base of the first transistor, and the other terminal of the first secondary winding is coupled with the point where the first transistor and the second transistors are connected; and the second secondary winding has a dotted terminal coupled with the second output node, and the other terminal of the second secondary winding is coupled with the base of the second transistor; and the other terminal of the blocking capacitor is coupled with a first output node of the self-oscillating half-bridge circuit device.
[0005] The utility model further provides a ballast, an electronic transformer or an LED driving device including the above self-oscillating half-bridge circuit device and a lamp using the lamp.
[0006] The self-oscillating half-bridge circuit device driven by the transformer with the air gap according to the utility model can achieve the technical advantages of avoiding the drawback of a large tolerance of the inductance of the magnetic core in the toroidal transformer in the prior art and hence improving consistency of the operating frequency of the self-oscillating half-bridge circuit device, the efficiency of producing the self-oscillating half-bridge circuit device and reducing the waste. When the self-oscillating half-bridge circuit device according to the utility model is applied in the ballast, a temperature requirement of the ballast on the half-bridge circuit can be better satisfied to thereby bring an additional degree of freedom of designing the ballast.
Brief Description of the Drawings
[0007] The above and other objects, features and advantages of the utility model can be apparent from the descriptions of preferred embodiments of the utility model when taken in conjunction with the drawings throughout which identical functional components are denoted with identical reference numerals .
[0008] Fig.l illustrates a simplified circuit diagram of a ballast using a self-oscillating half-bridge circuit device according to an embodiment of the utitility model; and
[0009] Fig.2 illustrates a schematic diagram of comparison between current wave shapes of a ballast including a self-oscillating half-bridge circuit device driven by a toroidal transformer in the prior art and of the ballast including the self-oscillating half-bridge circuit device driven by a transformer with an air gap according to the embodiment of the utility model.
Detailed Description of the Utility Model [0010] Fig.l illustrates a simplified circuit diagram of a ballast using a self-oscillating half-bridge circuit device according to an embodiment of the utitility model. The self-oscillating half-bridge circuit device according to the embodiment of the utitility model includes a switch element, a driving element and a blocking capacitor. As illustrated in Fig.l, the switch element includes a first transistor Ql and a second transistor Q2 connected in series with the first transistor Ql, and the first transistor Ql and the second transistor Q2 form a half-bridge. The driving element is a transformer with an air gap Tl. The transformer with the air gap Tl includes a primary winding TIa, a first secondary winding T2c and a second secondary winding T2b. The primary winding TIa has a dotted terminal coupled with the point where the first and second transistors Ql and Q2 are connected, i.e., the middle node A of the half-bridge, and the other terminal of the primary winding TIa is coupled with a terminal of the blocking capacitor Cl. The first secondary winding T2c has a dotted terminal coupled with the base of the first transistor Ql via a first resistor Rl and is adapted to drive the first transistor Ql. The second secondary winding T2b has a dotted terminal coupled with a second output node N of the self-oscillating half-bridge circuit device (the ground in this embodiment) , and the other terminal of the second secondary winding T2b is coupled with the base of the second transistor Q2 via a second resistor R2. The second secondary winding T2b is adapted to drive the second transistor Q2. The collector of the first transistor Ql is coupled with a power supply of the self-oscillating half-bridge circuit device, and the power supply is a direct-correct power source VDC in this embodiment. The first and second transistors Rl and R2 referred to as base resistors are adapted to limit base currents of the first and second transistors Ql and Q2, respectively. The transistors Ql and Q2 may be BJT transistors, CMOS transistors, etc. Furthermore, the other terminal of the blocking capacitor Cl is coupled with a first output node M of the self-oscillating half-bridge circuit device, and the emitter of the second transistor Q2 is coupled with the second output node N of the self-oscillating half-bridge circuit device .
[0011] In the ballast of Fig.l, the load is a lamp, the inductor Ll is referred to as a choke is coupled between the primary winding TIa of the transformer with the air gap Tl and the blocking capacitor Cl. A capacitor C2 is referred to as an igniting capacitor and is connected in parallel with both terminals of the lamp. The inductor Ll and the capacitor C2 constitute a resonance circuit. The lamp may be a fluorescent lamp, an HID lamp, etc. Alternatively, the inductor Ll may be coupled between the capacitor Cl and the lamp as needed.
[0012] Although the dotted terminal of the primary winding TIa of the transformer with the air gap Tl acting as the driving transformer of the self-oscillating half-bridge circuit device is coupled with the middle node A of the half-bridge, the dotted terminal of the first secondary winding T2c is coupled with the base of the first transistor Ql, and the dotted terminal of the second secondary winding T2b is coupled with the emitter of the second transistor Q2 in the embodiment shown in Fig.l, in other embodiments, the respective circuit elements can be connected in other manners as needed in practice.
[0013] As mentioned above, the driving element used in the self-oscillating half-bridge circuit device according to the utility model is a transformer with an air gap instead of a toroidal transformer as used in the prior art. The inventors of the utility model have found from numerous experiments that, though the toroidal transformer w is used as a driving element for the self-oscillating half-bridge circuit device in the prior art, the substitution of the transformer with the air gap for the toroidal transformer could enable greatly improved consistency of the operating frequency of the resulting self-oscillating half-bridge circuit device while achieving operating performance of the self-oscillating half-bridge circuit device for which the toroidal transformer is used as a driving element in the prior art. The transformer with the air gap is a transformer with the air gap in the magnetic core thereof, and the inductance of the transformer with the air gap is determined mainly by the length of the air gap. The inventors of the utility model have learnt from the experiments that there is a determined relationship between the inductance of the driving transformer and the operating frequency of the self-oscillating half-bridge circuit device including the driving transformer. Therefore, a tolerance up to +/- 3% of the inductance of the transformer with the air gap can be achieved by adjusting the length of the air gap, which tolerance is far below that of the inductance of the toroidal transformer in the prior art, thereby improving substantially consistency of the operating frequency of the self-oscillating half-bridge circuit device. 014] Specifically, the usage of the transformer with the air gap to drive the self-oscillating half-bridge circuit device can enable the operating frequency of the self-oscillating half-bridge circuit device to be maintained within a certain range, that is, a reduced range over which the operating frequency varies can be obtained. Therefore, the proportion of the self-oscillating half-bridge circuit devices with their operating frequencies beyond the range can be reduced, with the result that the production efficiency is improved and the waste is reduced. Secondly, the usage of the transformer with the air gap can make the self-oscillating half-bridge circuit device have superior temperature stability to satisfy a temperature requirement of final equipments on components. Additionally, the transformer with the air gap used in the utility model has less demand for the material of the magnetic core as compared with that for the toroidal transformer in the prior art due to improved temperature and magnetic field stabilities resulting from the additional air gap. According to the utility model, relevant parameters of the circuit, such as the magnetic permeability, the inductance and the like, can be adjusted flexibly by adjusting the air gap of the transformer with the air gap during the design of the circuit, thereby bringing out a substantial degree of freedom of designing the circuit. Furthermore, the transformer with the air gap can prevent effectively magnetic saturation to thereby reduce interference of magnetic radiation to the self-oscillating half-bridge circuit device.
[0015] With regard to manufacturing the driving transformer Tl with the air gap as used in the utility model, consistency of inductance of the transformer with the air gap with that of the toroidal transformer can be achieved by increasing the numbers of turns of the respective windings of the transformer with the air gap proportionably relative to the toroidal transformer. For example, it is assumed that a conventional toroidal transformer has the inductance of 8 micro-henry (μH) and includes respective windings TIa, TIb and Tic, and the turn ratio of the windings TIa, TIb and Tie is 2:3:3. Then, a transformer with an air gap having the same inductance of 8 micro-henry can be achieved by selecting a magnetic core with an air gap and winding round the magnetic core three windings TIa, TIb and Tie, the turn ratio of which is 12:18:18.
[0016] Fig.2A and Fig.2B illustrate a schematic diagram of comparison between current wave shapes of a ballast including a self-oscillating half-bridge circuit device driven by the toroidal transformer in the prior art and of the ballast including the self-oscillating half-bridge circuit device driven by the transformer with the air gap according to the utility model. The wave shape diagrams are observed by a LeCroy oscillograph, for example. Fig.2A is the circuit wave shape diagram of the ballast including the self-oscillating half-bridge circuit device driven by the toroidal transformer, and Fig.2B is the circuit wave shape diagram of the ballast including the self-oscillating half-bridge circuit device driven by the transformer with the air gap according to the utility model. The respective current wave shapes illustrated in Fig.2A and Fig.2B are denoted with reference numerals 1-3 and l'-3' respectively in the comparison diagrams. Taking the specific circuit of the ballast in Fig.l as an example, the graphs 1 and 1' denote currents flowing through the middle node A of the half-bridge respectively, the graphs 2 and 2' denote currents flowing through the choke Ll respectively, and the graphs 3 and 3' denote currents flow through the driving winding T2b connected with the lower transistor Q2 respectively. Both inductances of the toroidal transformer and the transformer with the air gap as used are 8 μH, the diameter of the toroidal transformer is 10 mm, the turn ratio of respective windings thereof is 2:3:3, and the turn ratio of respective windings of the transformer with the air gap is 12:18:8. As can be apparent from the comparison diagrams illustrated in Fig.2A and Fig.2B, the ballast using the transformer with the air gap can result in the similar current wave shape to that of the ballast using the toroidal transformer. As can be apparent, the self-oscillating half-bridge circuit device according to the utility model can achieve the foregoing technical advantages while achieving other effects of the existing self-oscillating half-bridge circuit device driven by the toroidal transformer.017] Although the utility model has been described above by way of an example of the application in which the self-oscillating half-bridge circuit device driven by the transformer with the air gap is used in the ballast, those skilled in the art shall appreciate that the self-oscillating half-bridge circuit device according to the utility model can equally be applicable to an electronic transformer, an LED driving device, etc. The self-oscillating half-bridge circuit device can be connected with external circuits in various manners as needed in practical applications. Therefore, the electronic transformer, the LED driving device, etc., including the self-oscillating half-bridge circuit device driven by the transformer with the air gap according to the utility model shall be deemed as falling within the scope of the utility model . [0018] Furthermore, the ballast using the transformer with the air gap according to the utility model can be applied in a lamp including a fluorescent lamp, an HID lamp, etc. Therefore, the ballast including the self-oscillating half-bridge circuit device driven by the transformer with the air gap according to the utility model, the lamp including the ballast, etc., shall also be deemed as falling within the scope of the utility model .
[0019] It shall be noted here that the specific circuit connection mode, the types and parameters of the electronic elements, particularly the specific values of the inductances and the turn ratio of the windings of the transformer with the air gap, etc., as mentioned in the embodiments of the utility model are merely illustrative but not limitation to the utility model . [0020] Although the utility model has been disclosed above from the descriptions of the embodiments thereof, it shall be appreciated that those skilled in the art can make various modifications, adaptations or equivalents of the utility model without departing from the spirit and scope of the appended claims. These modifications, adaptations or equivalents shall also be deemed as being encompassed in the scope of the utility model .