Electric power conversion systems – Current conversion – Including automatic or integral protection means
Patent
1985-05-02
1986-07-29
Beha, Jr., William H.
Electric power conversion systems
Current conversion
Including automatic or integral protection means
315209R, 315244, 363132, H02M 75387
Patent
active
046033785
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an inverter circuit, comprising: direct-current supply transformer being connected to transistor base control circuits, capacitor and being connected across a point between transistors and a power source, and winding and the base control transformer's winding, connected to said secondary winding.
This type of inverter circuit is anticipated in U.S. Pat. No. 4,045,711. In that publication, the base current of transistors is controlled primarily by means of the secondary winding of a resonance circuit's inductive winding in a manner that a base current phase shifts forward relative to the collector current of a transistor, bringing of transistors into a conductive state being delayed so that the current of one transistor has had time to cut off despite the storage time. This eliminates the simultaneous conducting of transistors and power losses caused thereby.
Occurring in practice, however, are the following variation factors whose action is not compensated for by this prior art circuit:
1. The frequency and/or amplitude of a resonance circuit current may fluctuate considerably with varying load. As the frequency and/or amplitude increases, the hazard of simultaneous conducting of transistors increases. In order to prevent this, the leading of a transistor into a turned-off or non-conductive state should be made more effective or sped up, but this cannot be achieved by the prior art circuit switching.
2. The individual properties of transistors vary considerably. For example, the voltage drops occurring across different transistors with the same base current are unequal. When the voltage drop is minor, a transistor is deep in saturation and can be slowly led into a non-conductive state, in other words the "storage time" of a transistor will be long. The prior art circuit switching does not at all observe this individual variation of the properties of transistors, which is why transisotrs must be selected carefully if simultaneous conductivity of transistors is to be avoided.
An object of the invention is to provide an inverter circuit which includes a base current control circuit for observing both the state of a load and the state of a transistor.
This object is achieved by means of an inverter circuit of the invention whose characteristic features are set forth in the annexed claims.
One practical embodiment of the invention will now be described in more detail with reference made to the accompanying drawings, in which
FIG. 1 shows a circuit diagram of an inverter circuit of the invention applied as a ballast for a discharge lamp and
FIG. 2 shows a voltage division diagram of a base current control circuit, the respective voltages being indicated in FIG. 1 in the situation where transistor 1 is conductive.
Aside from a novel base control circuit, a corresponding inverter circuit and its operation has been disclosed in the Applicants' FI Patent specification No. 63147. However, the structure and operation of an inverter circuit will now be briefly explained. Across the direct-current terminals + and - are connected a filtering capacitor C as well as two in series connected transistors 1 and 2, geared in alternating phase operation by means of a base control transformer 3. Secondary windings 5 and 6 of said base control transformer 3 are connected to the bases of transistors 1 and 2 in a manner that the bases of each transistor receive opposite phase control voltages relative to each other. Thus, when one transistor is conductive the other is non-conductive and vice versa.
Across a point between transistors 1 and 2 and a power source is connected a load circuit, comprising an inductive winding 7 and capacitors 10 and 11 connected in series therewith, the current flowing through said capacitors alternately on successive half-cycles. Connected in series with a series resonance circuit provided by winding 7 and capacitors 10 and 11 is a connection in parallel consisting of a lamp 8 and an ignition capacitor 9. Resonance capacitors 10 and 11 are accompanied by stabilizing diodes
REFERENCES:
patent: 4045711 (1977-08-01), Pitel
patent: 4164014 (1979-08-01), Crowe et al.
patent: 4370600 (1983-01-01), Zansky
patent: 4392087 (1983-07-01), Zansky
patent: 4553070 (1985-11-01), Sairanen et al.
Beha Jr. William H.
OY Helvar
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