A CONVERTOR, A POWER SUPPLY, AND A BATTERY CHARGER

Abstract: A convertor which can suitably be used, for example, in a charger device for rechargeable batteries has an input and a load output, the convertor comprises a resonant transducer means provided with a transducer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, and a transducer control means coupled between the input of the convertor and the transducer input, which transducer control means is a controllable transducer control means. Such a convertor can be flexibly outlined and embodied so as to be suitable for the intended use. In particular the output rectifier circuit shows a variety of possible embodiments.

Description: A convertor, a power supply, and a battery charger. The present invention relates to a convertor having an input and a load output, the convertor comprising a resonant transducer means provided with a transducer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, and a transducer control means coupled between the input of the convertor and the transducer input. The present invention also relates to a power supply and a battery charger which are provided with a convertor. Such a convertor is known from DE-C-33 00 669 which discloses a convertor applied in a DC current power supply. The known convertor comprises a resonant transducer means in the form of a resonant piezo-electric transformer whose input impedance is connected to a transducer control means in the form of a self-oscillating pulse providing means which provides pulses at a pulse rate which is equal to the resonant frequency of the resonant transducer means. An input convertor AC voltage is rectified and stabilised and then fed to the resonant transducer means through the self-oscillating pulse providing means. The transducer output of the resonant transducer means is connected to the output rectifier circuit and a voltage stabiliser circuit to provide a high performance output power at the load output of the convertor which is virtually independent of the open or short circuit state of the load. In particular, the known convertor provides an alternately operated parallel arrangement of two piezo-electric transducer means for enhancing the availability of the output power on the load means. A disadvantage of the known convertor is that its flexibility in terms of variability and arrangement of the convertor as a whole and the output rectifier circuit in particular is limited. Therefore, it is an object of the present invention to provide a convertor whose embodiment and properties can be easily adapted to a practically required range of applications. To achieve this, the convertor according to the invention is characterised in that the transducer control means is a controllable transducer control means. The convertor according to the invention has the advantage that by using controllable transducer control means, the stability and the statistical spread of the properties of the convertor are enhanced because they are no longer largely dependent on the input impedance of the piezoelectric transducer means, which input impedance shows a great statistical spread in practice. Furthermore, it is determined that variations which are important in practical applications of the convertor according to the invention are very easy to implement. In particular, the convertor according to the invention can be easily made suitable, in a variety of possible embodiments, for application, for example, in a fast battery charger. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: Fig. 1 shows a first embodiment of the convertor according to the invention, Fig. 2 shows a general outline of the convertor of fig. 1 applied in a battery charger of a power supply, Fig. 3 shows a second embodiment of the convertor of figs 1 and 2, Figs. 4, 5, 6 and 7 show possible embodiments of an output rectifier circuit for application in the convertor of figs 1 and 2, Fig. 8 shows interrelated diagrams of voltages and voltage ratios applying to the embodiment of fig 6, Figs. 9, 10, and 11 show further possible embodiments of relevant parts of the convertor according to the invention, and Fig. 12 shows an equivalent circuit of a piezo electric transducer. Fig. 1 shows an outline of a first embodiment of a convertor 1. The convertor 1 has an input 2 and a load output 3. The convertor 1 comprises an input rectifier circuit 4, whereto a voltage stabilising capacitor 5 is connected. The convertor 1 further comprises a resonant transducer means 6 provided with a transducer input 7 and a transducer output 8 coupled to the load output 3 by means of an output rectifier circuit 9. A transducer control means 10 included in the convertor 1 is coupled between the input 2 of the convertor and the transducer input 7. The transducer control means 10 is controllable via a control input 11, which is connected to a series arrangement of current doublers Ql and Q2, which are also referred to as current mirrors. The output rectifier circuit 9 can supply a control signal to a control input/output 12 thereof and comprises a parallel arrangement of current doublers Q3 and Q4. The various diodes connected in parallel to Ql, Q2, Q3 and Q4 only allow substantial voltages to be present across these diodes if the diodes do not conduct current. The output rectifier circuit 9 is connected through a smoothing coil pair LI and L2 to a stabilising capacitor CO connected to the load output 3 of the convertor 1. The convertor comprises an LC circuit Lr, Cr coupled between the transducer control means 10 and the resonant transducer means 6. Fig. 2 shows a possible loop configuration in a general outline of the convertor 1 applied in a battery charger, wherein a battery 13 is connected to the load output 3. Apart from a driver 14, a loop filter 15 is connected between control output 12 and control input 11. An alternative to the LC circuit is shown wherein an additional capacitor Cs is connected in parallel to the resonant transducer means. In general, the resonant transducer means may be embodied as a resonant miniature transformer means 6, such as a well-known planar transformer realized by lithographic patterning for example, on a multilayer printed circuit board, also known as a switched mode power supply, but a piezo-electric transducer can be applied as well. A piezoelectric transducer or piezo coupler is used in DE-C-33 00 669 mentioned hereinabove. For the sake of completeness, an equivalent circuit for such a piezo-electric transducer which can suitably be incorporated in any of the embodiments described herein, is shown in figure 12. The operation of the convertor 1 is such that after rectifying and stabilising an AC signal on input 2, control input 11 is controlled such that in a resonant rate ranging mostly between 50 KHz and 250 KHz, a mainly pulse shaped signal is applied to the resonant transducer means 6 and that the pulse shaped signal on transducer output 8 is again rectified by the active output rectifier circuit 9 and then DC stabilised and fed to the load, which can be any device capable of receiving the output power provided, such as a capacitor or the battery 13. As the convertor 1 is capable of outputting large amounts of current, the load could also be constructed as a high power or high current load, such as a high power capacitor or a traction battery. In such an application of the convertor 1, safety means could be limited to a minimum, while the volume occupied by said converter is also limited to a minimum. Fig. 3 shows a rather detailed connection scheme wherein the control signal on input 11 is derived from the resonant transducer means 6 by means of an additional transducer coupling 14 therein. After some basic thresholding executed by means of operational amplifiers OP1 and OP2, optocoupling in optocoupler 15 for optimal isolation between input 2 and output 3, integration in integrator 16 and manipulation in block 17, a control signal δ is applied to control input 11 to control the rate to allow it to correspond with the resonance frequency of the transducer means 6. Dependent on, for example, the requirements imposed by the type of load 13, several embodiments of the output rectifier circuit 9 can be realised. Figs. 4, 5, 6 and 7, as well as 9, 10 and 11 show examples thereof. The embodiment of fig. 4 shows a self-driven current doubler configuration of Ql and Q2. In this example, input/output 12 is crosswise connected to transducer output 8 to be self-driven. Again, either Ql or Q2 block the RF frequency pulses to the smoothing coils LI and L2. Another embodiment of the output rectifier circuit 9, wherein the resonant transducer means 6 has a central shunt or tap 18 is shown in figure 5. The central shunt 18 is connected to just one coil Lo. The circuit 9 now functions as a self-driven full wave synchronous rectifier. Self-driven half-wave synchronous rectifier circuits are also shown in figures 6 and 7. The embodiment of fig. 6 needs no central shunt, whereas in the embodiment of fig. 7, two separate resonant transducers 6-1 and 6-2 are used. The voltages in figure 6, denoted Vi, Vp, Vs, Vr, Uo and Udc (see fig. 3) are also shown in fig. 8 to illustrate, by way of example, the functioning of this embodiment of circuit 9. Assuming that IL, : n s is the transducer transformation ratio and δ = T H : T, then the calculated values of the upper and lower peak values of the denoted voltages are as indicated in Fig. 8. For δ = 112, the DC load voltage Uo reaches it maximum value of (n s /4*n p ) Udc. Figure 9 shows an embodiment which has a very small number of separate components realising a very efficient voltage transformation in miniature planar technology as described above, the transformation ratio being 4:1. Still further self-driven embodiments, in particular, of the output rectifier circuit 9 are outlined in figures 10 and 11. For accurate control of the input/output 12 of the rectifier circuit 9, these resonant transducer means 6 are each provided with an additional transducer coupling 14 with central tap 18, or with separate additional couplings 14-1 and 14-2 for self-driving the active rectifier circuits 9 in a way described hereinabove.

Claims: CLAIMS: 1. Convertor having an input and a load output, the convertor comprising a resonant transducer means provided with a transducer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, and a transducer control means coupled between the input of the convertor and the transducer input, characterised in that the transducer control means is a controllable transducer control means. 2. Convertor according to claim 1, characterised in that the controllable transducer control means is provided with a control input coupled to the resonant transducer means for inputting a control signal containing a measure of the resonance frequency of the resonant transducer means. 3. Convertor according to claim 1 or 2, characterised in that the convertor comprises an LC circuit coupled between the transducer control means and the resonant transducer means. 4. Convertor according to claim 1, 2 or 3, characterised in that the resonant transducer means is embodied as a resonant miniature transformer means. 5. Convertor according to claim 1, 2, 3 or 4, characterised in that the resonant transducer means is a planar resonant transducer means. 6. Convertor according to claim 1, 2, 3 or 4, characterised in that the resonant transducer means is a piezo-electric resonant transducer means. 7. Convertor according to any of the preceding claims referring to claim 2, characterised in that the output rectifier circuit comprises one or more current doublers having a control output coupled to the control input of the transducer control means. 8. Convertor according to claim 7, characterised in that the convertor comprises a loop filter connected between the control output of the output rectifier circuit and the control input of the transducer control means. 9. Convertor according to claim 7 or 8, characterised in that the at least one current doubler is embodied as a self-driven current doubler. 10. Convertor according to one of claims 1-9, characterised in that the output rectifier circuit is embodied as a synchronous rectifier. 11. Convertor according to claim 10, characterised in that the synchronous rectifier is a half-wave or full-wave rectifier. 12. Power supply provided with a convertor according to one of the claims 1- 11, the convertor comprising a resonant transducer means provided with a transducer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, and a transducer control means coupled between the input of the convertor and the transducer input, characterised in that the transducer control means is a controllable transducer control means. 13. Battery charger, characterised in that the battery charger is provided with a convertor according to one of the claims 1-11, and in that the convertor comprises a resonant transducer means provided with a transducer input and a transducer output coupled to the load output, an output rectifier circuit coupled to the load output, and a transducer control means coupled between the input of the convertor and the transducer input, which transducer control means is a controllable transducer control means.

Inventors: VAN LERBERGHE STEVEN JAN WILLE, VAN LERBERGHE, STEVEN, JAN, WILLEM
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 1998
Main classification: H02M3
IPC codes: H02J7, H02M3