GB2163911A - Stabilized DC to DC/AC converter - Google Patents

Abstract

In the primary circuit of a dc-to-dc converter or (dc-to-ac converter by omitting 41-46), transistor switching units are associated with two primary windings 33, 34, of a transformer 30. The transistor switching units each control the flow of current through an associated winding. The first transistor 20 is activated by apparatus 10 that alternatively applies and removes activation signals to the transistor and consequently allows conduction through the transistor and the associated winding. The second transistor 21 receives activation signals from a third primary winding 32 and causes conduction of current through the associated primary transformer winding. The activation signal from the third winding, causing the second transistor to be conductive, is the result of interruption of current in the first primary transformer winding. The activation signals produced by the third primary transformer winding is removed when the first transistor is activated and current flows in the first primary winding. <IMAGE>

Description

SPECIFICATION Stabilized dc to dc/ac converter This invention relates generally to dc-to-dc and dc-to-ac converters and more particularly to converters that utilize current switches to activate primary coils of the transformer involved in the conversion.

It is known in the related art to activate periodically current switches such as silicon controlled rectifiers, in primary transformer windings to produce a voltage (and current flow) of alternating phase in the secondary windings. When current requirements are not excessive, it is known in the art to increase the frequency at which the converters can function.

Higher frequencies permit physically smaller components to be employed, such as capacitors. However, as higher frequencies are utilized, other effects become important. For example, it is known in the artto utilize a common oscillator to control conduction through two switches (and through transformer windings associated with each switch). To prevent simultaneous conduction by the two switches that can result in excessive energy dissipation, an inverter element can be coupled between the oscillator and one of the transistors. As the frequency is increased, the delay of the inverter element can result in undesirable simultaneous conduction by the two switches.

It is an object of the present invention to provide an improved converter for converting a dc signal to an ac signal.

It is another object of the present invention to provide two transistors for alternatively introducing current into two primary windings.

It is a more particular object of the present invention to provide switches for alternatively introducing current into primary coils of a transformer, the apparatus of the invention preventing simultaneous conduction of the two switches.

It is yet another particular object of the present invention to provide a third coil in the primary winding configuration of a transformer, the third winding controlling conduction of current through one of two transistor switching circuits and thus controlling conduction of current to an associated transformer winding.

It is still another particular object of the present invention to provide two transistor switching units, alternatively applying current to two primary windings of a transformer and wherein the two switching units are not simultaneously conducting.

The aforementioned and other objects of the present invention are accomplished by a transformer having three windings in the primary coii configuration. The first two primary windings alternatively introduce current of opposite phase into the transformer. The control of current through each of the two windings is accomplished by a transistor switching unit associated with each winding. Conduction of a first transistor switching unit, and consequently conduction through an associated primary winding, is accomplished by a device for periodically applying and removing an actuation signal to the control element (gate) of the transistor switching unit.The conduction of the second transistor switching unit and consequently the conduction of current through an associated second winding is controlled by a voltage generated in a third winding and applied to the control element (gate) of the second transistor switching unit. The voltage in the third winding has the correct phase to permit conduction in the second transistor switching unit upon interruption of the current in the first primary winding. The two transistors cannot be simultaneously conducting.

The invention will now be described further, by way of example only, with reference to the accompanying drawings in which: Figure lisa schematic diagram of a dye to dc converter according to the instant invention; and Figure 2 is a timing diagram illustrating the control voltages in the instant invention.

Referring now to Figure 1, terminals 5 and 6 are the voltage input terminals for a dc voltage, terminal 5 being coupled to a positive input voltage and terminal 6 being coupled to a negative (relative to terminal 5) input voltage. Terminal 5 is coupled through capacitor 14 to terminal 6, is coupled to one terminal of resistor 11 and is coupled to a terminal coupled to each position of the two principal primary windings 33 and 34. The second terminal of resistor 11 is coupled to terminals 14, 4, 5 and 6 of a (4047B) multivibrator 10 and through capacitor 15to input terminal 6. Terminal 3 of multivibrator 10 is coupled through resistor 14 to terminal 2 of multivibrator 10 and through capacitor 13 to terminal of multivibrator 10. Terminals 7,8,9 and 12 of multivibrator 10 are coupled to input terminal 6.Input terminal 6 is coupled to a source terminal of MOS transistor 20, to a source terminal of MOS transistor 21 and through a first primary winding 32 of transformer 30 to a gate terminal of transistor 21, the standard polarity of the first primary winding 32 being coupled to the gate terminal. The drain terminal of transistor 21 is coupled through a second primary winding 33 to the intermediate terminal 31, the standard polarity of the second primary winding 33 being coupled to the intermediate terminal. The gate terminal of transistor 20 is coupled to terminal 11 of multivibrator 10, while the drain terminal of transistor 20 is coupled through third primary winding 34 of transformer 20 to the intermediate terminal 31, the standard polarity of the third primary transformer winding being coupled to the drain terminal of transistor 20.The output terminals of the voltages produced in the secondarywindings of the transformer 30 are 51, 52 and 53. Output terminal 51 is the positive terminal, output terminal 52 is the common terminal and output terminal 53 is the negative terminal. Output terminal 52 is coupled through capacitor 45 to terminal 51, through capacitor 46 to terminal 53 and is coupled to transformer 30 secondary windings 37 and 38 at terminal 39. The standard polarity of the secondary winding 38 is associated with terminal 39.

The second terminal of secondary transformer winding 38 is coupled to a cathode terminal of diode 44 and an anode terminal of diode 42. The second terminal of secondary winding 37, the standard polarity terminal, is coupled to an anode of diode 41 and a cathode of diode 43. The anode of diode 41 and the anode of diode 42 are coupled to terminal 51, while the cathode of diode 44 and the cathode of diode 43 are coupled to terminal 53. Because the converter is designed to operate at a relatively high frequency,transformer30 is shielded. Typical values for the elements are 6.8k ohms for resistor 11 and resistor 14;22pf for capacitor 13, .01 uF for capacitor 15 and .33 uFfor capacitor 14. Typical operating parameters are 600 Khz frequency and 15 volt input voltage.

Referring to Figure 2, idealized waveforms for the current conducted through transistors 20 and 21 under no-load conditions as shown along with the idealized waveforms for gate voltages controlling the associated transistors. The gate voltage of transistor 20 can alternate, in a typical mode of operation from 0 to 6v, while gate voltage of transistor 21 will vary from -6v to +6v.

Referring once again to Figure 1, the multivibrator 10 is configured to act as an oscillator for applying a signal from terminal 11 to the gate of transistor 20 for a predetermined period of time. The oscillator then removes the signal activating transistor 20, generally, for the same period of time. During the period of activation of transistor 20, current flows through the primary winding 34 from terminal 5 to terminal 6.As currentflowsthrough primarywinding 34, a voltage is induced in primary winding 32.

The polarity of the induced voltage in winding 32 maintains transistor 21 in a non-conducting state.

When the activation signal is removed from the gate of transistor 20 and the transistor is placed in a non-conducting state, the current in the primary winding is interrupted and a reverse electromotive force is generated causing a change in polarity of the signal applied to the gate of transistor 21. This change in polarity causes transistor 21 to become conducting. Current then flows through winding 33, causing a change in the current flow in the secondary windings and maintaining the conducting state of transistor 21 through the voltage induced in winding 32. Transistor 21 remains in a conducting state until the activation signal is applied to transistor 20, and the flow of current through primary winding 34 induces a voltage in winding 32 causing transistor 21 to be placed in a non-conducting state.

Thus it will be seen that conduction through transistor 21 is determined by non-conduction through transistor 20 andsimukaneous actuation of the two transistors cannot occur.

Elements 41,42,43 and 44 provide full wave rectification of the transformer signal to provide a dc output across terminals 51 and 53. It will be clear that dc to ac conversion can be performed by removing the rectifying elements.

The invention can function in a mannerthat maintains a zero magneticflux in the transformer core. This phenomenon will result in an equalization of the duty cycles of each transistor for small excursions from equal transistor duty cycles. As a result of any small imbalance in the duty cycle, flux will accumulate in the transformer core and will result in a change of the on-set of conduction in the transistors.

The above description is included to illustrate the invention and the operation of the preferred embodimentand is notmeantto limitthescopeofthe invention. The scope of the invention is to be limited only by the following claims.

Claims (22)

1. A dc to dc/ac converter comprising a transformer, said transformer having a first primary winding, a second primary winding and a third primary winding; a first transistor coupled to said first primary winding for controlling of conduction of current through said first winding during a first portion of a cycle; signal means for activating said first transistor; and a second transistor coupled to said second winding, said second transistor controlling conduction of current therethrough, said second transistor being coupled to said third winding, said third winding causing said second transistor to be conducting during a second portion of said cycle.

2. The dc to dc/ac converter of claim 1 wherein said transistors are complementary metal oxide semiconductor elements and said third winding is coupled between a gate and a source of said second transistor.

3. The dc to dc/ac converter of claims 1 and 2 wherein said third winding is coupled directly between a gate and a source of said second transistor.

4. The dc to dc/ac converter of claims 1, 2 and 3 wherein said signal means is a multivibrator.

5. The dye to dc/ac converter of claims 1,2,3 and 4 wherein said transformer provides a high frequency ac output at the terminals of the secondary windings.

6. The dye to dc/ac converter of claims 1,2,3,4 and 5 wherein said f st portion 7 of said second cycle portion cycle have an equilibrium relationship.

7. An apparatus for converting dc voltage to ac voltage comprising: transformer means having a first, a second and a control primary winding, and a secondary winding; first switching means coupled to said first primary winding for periodically producing conduction of current through said first primary winding; and second switching means coupled to said second primary winding and to said control winding for production conduction of current through said second primary winding when said first switching means is not conducting current.

8. The voltage converter apparatus of claim 7 wherein said first switching means includes an oscillator and a first transistor.

9. The voltage converter apparatus of claims 7 and 8 wherein said second switching means includes a second transistor, conduction of current through said second transistor controlled by voltage from said control winding coupled to a control element of said second transistor.

10. The voltage converter apparatus of claims 7, 8 and 9 wherein voltage at terminals of said secondary winding is high frequency ac voltage.

11. The voltage converter apparatus of claims 7, 8,9 and 10 wherein a period for conduction by said first switching means and a period for conduction by said second switching means reach an equilibrium condition.

12. The method for converting a dc voltage to an ac voltage comprising the steps of: activating a first switch causing current to flow through a first primary winding of a transformer during a first portion of a cycle; deactivating said first switch at an end of said first cycle portion; said deactivation causing a control signal to be generated in a control primary winding of said transformer; and activating a second switch with said control signal causing a conduction of current in a second primary winding of said transformer.

13. An apparatus for converting a dc voltage to an acvoltage comprising: transformer means including a first, a second and a control primary winding; first switching means coupled to a said first primary winding for establishing magnetic flux in a core of such transformer means; and second switching means coupled to said second primary winding for establishing a flux in said transformer core, wherein said control primary winding activates said second switching means in response to predetermined core flux condition.

14. The dcto ac converter apparatus of claim 13 wherein said first switching means includes a first transistor coupled in series between said dc voltage and said first primary winding.

15. The de to ac converter apparatus of claim 13 and 14 wherein said second switching means includes a second transistor coupled between said second primary winding and said dc voltage, wherein a control element of said second transistor is coupled to said control primary winding of said transformer means.

16. The dc to ac converter apparatus of claims 13, 14 and 15 wherein said first and said second switching means are activated for approximately equal periods of a cycle, wherein said core magnetic flux equalizes said cycle periods.

17. The dc to ac converter apparatus of claims 13, 14, 15 and 16 wherein said transformer core magnetic flux establishes an equilibrium condition for periods of operation by said first switching means and said second switching means.

18. Apparatus for converting a de voltage to an ac voltage comprising: transformer means; first switching means for applying current to said transformer during a first period of a cycle; second switching means for applying current to said transformer during a second period of said cycle; and control means for activating said second switching means when said first switching means is deactivated.

19. The dye to ac converter apparatus of claim 18 wherein said first cycle period and said second cycle period have an equilibrium condition.

20. A dc to dc/ac converter substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

21. Apparatus for converting dc voltage to ac voltage substantially as herein before described with reference to Figures 1 and 2 of the accompanying drawings.

22. A method for converting a dc voltage to an ac voltage substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.