GB2045013A - A DC/AC converter - Google Patents
A DC/AC converter Download PDFInfo
- Publication number
- GB2045013A GB2045013A GB8007196A GB8007196A GB2045013A GB 2045013 A GB2045013 A GB 2045013A GB 8007196 A GB8007196 A GB 8007196A GB 8007196 A GB8007196 A GB 8007196A GB 2045013 A GB2045013 A GB 2045013A
- Authority
- GB
- United Kingdom
- Prior art keywords
- transistor
- point
- circuit
- winding
- collector
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/538—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration
- H02M7/53803—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration with automatic control of output voltage or current
- H02M7/53806—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a push-pull configuration with automatic control of output voltage or current in a push-pull configuration of the parallel type
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
- Inverter Devices (AREA)
Abstract
The converter includes a transformer (T) whose primary winding is fed by a battery via two power transistors (Q1, Q2) controlled alternately by means of an oscillator circuit A. In order to prevent simultaneous conduction of the two power transistors (Q1, Q2) each power transistor has its base electrode connected to a point in a respective series circuit connected across the other transistor. Each series circuit consists of a diode (D1; D2), the emitter- collector path of a transistor (T2; T1) and a resistance (R3, R4; R1, R2). In order for, e.g. transistor (Q2) to be turned on, transistor (T2) must be conductive (output D of oscillator A) and transistor (Q1) must be fully switched off so that the collector potential of transistor (Q1) is sufficient to render transistor (Q2) conductive via transistor (T2). <IMAGE>
Description
SPECIFICATION
A DC/AC converter
The present invention relates to a DC/AC converter, in particular to one which converts DC into the form of uniform square-wave pulses. Such converters usually include a transformer with a source of electricity connected to its primary winding via two power transistors which are made to conduct alternately by an oscillator circuit which provides squarewave signals at a duty ratio of 1/2, phase shifted by a al radians with respect to each other and serving to render the power transistors conductive alternately.
In such a circuit, the instruction for one power transistor to become conductive must not arrive until the opposite transistor is effectively off. Otherwise, a period of simultaneous conductivity may destroy the transistor junctions by thermal stress, since a current peak occurs at the time of switching.
Now, a transistor does not turn off completely as soon as it is no longer biassed. When the base is used as the control electrode some collector current continues to flow for as long as there remains some charge stored on the base. It would obviously be possible to take such a delay into account by adjusting the oscillator circuit to have a duty ratio of less than 1/2, but the delay required is not the same for all transistors because of the usual dispersion in the properties of semiconductors.
Preferred embodiments of the present invention remedy these disadvantages and supress the current peaks at the time of switching, whatever the type and quality of the power transistors used may be.
The present invention provides a DC/AC converter which includes a transformer primary winding, a DC source whose first terminal is connected to the mid-point of said winding, a first power transistor one of whose junctions is connected between a first end of said winding and the second supply terminal, a second power transistor one of those junctions is connected between the second end of said winding and the second supply terminal, and an oscillator circuit which sends signals alternatively to the first power transistor and to the second power transistor respectively via a first output circuit and via a second output circuit to cause said power transistors to be in the conductive state or in the off state, wherein the first output of the oscillator circuit is connected to one electrode of a first transistor whose junction formed by the other two electrodes is in series in a circuit which is situated between the first end of said winding and the second terminal of the electricity source and which comprises : a first diode; said junction of the first transistor; and a first resistance, with the third electrode of the first power transistor being connected to a point on said first resistance; and wherein the second output of the oscillator circuit is connected to one electrode of a second transistor whose junction formed by the other two
electrodes is in series in a circuit which is situated
between the second end of said winding and the second terminal of the electricity source and which comprises : a second diode; said junction of the second transistor; and a second resistance; with the third electrode of the second power transistor being connected to a point of said second resistance.
In one advantageous embodiment, the power transistors are formed by pairs of Darlingtonconnected transistors.
The invention will be better understood from the following description of an embodiment with reference to the accompanying drawings in which Figure 1 is a circuit diagram of a converter in accordance with the invention;
Figure 2 is a circuit diagram of an oscillator circuit which can be used in the converter of Figure 1; and
Figure 3 is a waveform diagram of the phases at various points of the converter.
Figure 1 shows a transformer T having a primary winding with two ends P1 and P2 and a centre tap which is connected to the positive terminal B of a DC source, which may be a battery. The negative terminal of the DC source is connected to earth which therefore represents the second terminal of the DC source in the circuit diagram. The secondary winding S of the transformer is connected to a load.
The end P1 of the primary winding is connected to the collector of an NPN transistor T3 whose emitter is earthed. With a transistor T4, the transistor T3 forms a part of a Darlington pair Q1 which is equivalent to a first power transistor. The emitter of the transistor T4 is connected to earth via a resistor
R5 and a diode D3 is connected between earth and the end P1 of the primary winding.
Symmetrically, the end P2 of the primary winding is connected to the collector of an NPN transistor T6 which, with a transistor T5, forms a Darlington pair referenced Q2, the emitter of T6 being connected to earth. The emitter of the transistor T5 is connected to earth via a resistor R10. A diode D4 is connected between the end P2 of the primary winding and earth. The function of the diodes D3 and D4 is to pass the demagnetization current from the primary winding of the transformer T.
An oscillator circuit A represented by a rectangle emits square wave signals at C and D. The square wave signals have a duty ratio of 1/2 and are shifted with respect to each other by an angle of n. Point C is connected via a resistor R6 to the base of a PNP tra nsisto r T1 whose collector is connected to earth via two resistors R1 and R2 in series. The point common to R1 and R2 is connected to the base of the transistor T4 of the Darlington pair 01. Symmetrically, point D is connected to the base of a PNP trasistor
T2 via a resistor R9. The collector of the transistor T2 is connected to earth via two resistors R23 and R4 in series. The point common to these resistors is connected to the base of the transistor T5 of the
Darlington pair Q2.
The anode of a diode D1 is connected to point P1 and its cathode is connected to the emitter of the transistor T2. A resistor R8 is disposed between the emitter and the base of the transistor T2.
Symmetrically, the anode of a diode D2 is connected to point P2. Its cathode is connected to the emitter of the transistor T1. A resistor R7 is con
nected between the emitter and the base of the transistor Ti.
Before describing the operation of the circuit in accordance with the invention, Figure 2 will be rapidly described. Figure 2 shows a cheap and simple example of an astable oscillator circuit A.
The astable which constitutes the above circuit is constituted by two NPN transistors T7 and T8 whose emitters are connected to earth, two capacitors C1 and C2 and four resistors R11, R12, R13, R14. The base of the transistor T8 is connected to the capacitor C1 via a diode D8 and the base of the transistor T7 is connected to the capacitor C2 via a diode D7. The other plate of the capacitor C1 is connected via a diode D5 to the collector of the transistor T7 as well as to the point C of Figure 1.The other plate of the capacitor C2 is connected via a diode D6 to the collector of the transistor T8 as well as to the point D of Figure 1.
The point which is common to the capacitor C1 and to the diode D5 is connected to the positive terminal B of the DC source via the resistor R11 and the point which is common to the capacitor C1 and to the diode D8 is connected to the terminal B via the resistor R12. The point which is common to the capacitor C2 and to the diode D6 is connected to the terminal Bviathe resistor R14 and the point which is common to the capacitor C2 and to the diode D7 is connected to the terminal B by the resistor R13.
The diodes D7 and D8 for protecting the baseemitter junctions of the transistors T7 and T8, together with the diodes D5 and D6, provide rapid switching.
The astable operates conventionally. When the transistor T7 is conductive and the transistor T8 is off, the capacitor C1 charges via the resistor R12.
When the voltage on C1 becomes high enough, the transistorT8 is biased by its base and becomes conductive in its turn, thereby turning off the transistor T7.
The circuit in Figure 1 operates as follows, beginning at an instant when the Darlington pair Q1 is conductive and the Darlington pair 02 is off, in which case the collector potential of 02 is equal to 2U with respect to earth, where U is the supply voltage. The base of Q1 is biassed byg the circuit D2, T1, R1, R2.
The contrast, since the transistor Q1 is conductive, its collector is at zero potential with respect to earth and no current passes through the equivalent circuit D1, T2, R3, R4for biassing the Darlington pair 02, which is therefore in the off condition.
If point C now emits an instruction to turn off the
Darlington 1 and point D emits an instruction to saturate the pair 02, the transistor T1 turns off.
Although the "base" of Darlington pair Q1 is no longer biassed, some collector current continues to flow until all the charge stored on the "base" is completely removed. When finally the Darlington pairs is effectively turned off, its collector-earth potential rises to 2U. The transistor T2 whose base has already been biassed by the oscillator circuit becomes conductive only when the collector potential of Q1 reaches a high value. The circuit D1, T2, R3,
R4 then biasses the base of the Darlington pair02 which becomes conductive.
Figure 3 shows six waveform diagrams numbered 3a to 3fforvarious points of the circuit.
Diagrams 3a and 3b show the voltages Uc and UD respectively at C and D as a function of time.
Diagram 3c shows the current 1ci at the collector of the Darlington pair Q1 and diagram 3dshows the potential Ucl of the collector of the Darlington pair Qi as a function of time. Diagram 3e shows the current lo at the collector of the Darlington pair 02 and the diagram 3f shows the potential Uc2 of the collector of the Darlington pair Q2 as a function of time.
At the instant pl in diagram 3a the voltage Uc is at its maximum while at the corresponding point p2 -in diagram 3b the voltage is zero. The collector current of the pair Q1 is high, but its collector voltage is zero, as seen at p3 and at p4 in diagrams 3c and 3d. The collector current lC2 of the pair 02 is zero since 02 is turned off (point p5) but the voltage Uc2 at its collector is at its maximum (point p6).
At the point e1 the voltage drops to zero and the transistor T1 is off; however, the current 1ci is not interrupted at e3 and continues to rise up to f3, when it stops flowing. Whereas the voltage Ucl remained practically zero at e4, it rises at f4. At the same time the current 1C2 is established at the collector of the pair 02 as seen at f5 and the voltage Uc2 drop (point f6).
Likewise, atthe instant gl, although point C biasses the base of Tl,the Darlington pairs becomes conductive again only at the instant h5 and when the current lC2 is interrupted.
These diagrams show that the Darlington pairs Q1 and 02 are never conductive at the same time.
The relative values of R1 and R2 and of R3 must be chosen so that the above result is obtained. A few numerical values are given hereinafter by way of example.
The DC voltage between the terminal B and earth is, for example, 48 volts. The maximum voltage of the signals at C and D is consequently 48 volts in diagrams 3a and 3b. In diagrams brand 3f, the maximum voltage at the collectors of the pairs Q1 and Q2 reaches 96 volts. The collector currents of the
Darlington pairs Q1 and Q2 reach a maximum of 1A.
The values of the resistances R1 and R3 are 12 kQ each and those of the resistances R2 and R4 are 470Q each. Forthe Darlington pair Ql.for example, to become conductive the voltage at its base UB1 must reach about 1.2 volts. The collector voltage UC2 of 02 is related to U51 by the equation:
UD2 and UT1 being the voltages of the diodes D2 and of the emitter-collector junction of the transistor T1 respectively. The sum of these voltages is approximately 1 volt. The result of this is that for UB1 to reach the required value, the collector voltage of the pair 02 must reach about thirty volts. It is seen that the Darlington pair Q1 becomes conductive only when the pair Q2 is fully off.
The invention applies in particular to emergy power supply systems in which the DC voltage of a battery is to be transformed into a periodically varying voltage.
Claims (4)
1. A DC/AC converter which includes a transformer primary winding, a DC source whose first terminal is connected to the mid-point of said winding, a first power transistor one of whose junctions is connected between a first end of said winding and the second supply terminal, a second power transistor one of whose junctions is connected between the second end of said winding and the second supply terminal, and an oscillator circuit which sends signals alternately to the first power transistor and to the second power transistor respectively via a first output circuit and via a second output circuit to cause said power transistors to be in the conductive state or in the off state, wherein the first output of the oscillator circuit is connected to one electrode of a first transistor whose junction formed by the other two electrodes is in series in a circuit which is situated between the first end of said winding and the second terminal of the electricity source and which comprises : a first diode; said junction of the first transistor; and a first resistance, with the third electrode of the first power transistor being connected to a point on said first resistance; and wherein the second output of the oscillator circuit is connected to one electrode of a second transistor whose junction formed by the other two electrodes is in series in a circuit which is situated between the second end of said winding and the second terminal of the electricity source and which comprises : a second diode; said junction of the second transistor; and a second resistance, with the third electrode of the second power transistor being connected to a point of said second resistance.
2. A converter according to claim 1, wherein each of the power transistors is constituted by a
Darlington-connected pair of transistors.
3. A converter according to claim 1 or 2, wherein said junctions of the various transistors are emittercollector junctions.
4. A DCjAC converter substantialy as herein described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7907257A FR2452198A1 (en) | 1979-03-22 | 1979-03-22 | DIRECT CURRENT CONVERTER DEVICE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2045013A true GB2045013A (en) | 1980-10-22 |
Family
ID=9223448
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8007196A Withdrawn GB2045013A (en) | 1979-03-22 | 1980-03-03 | A DC/AC converter |
Country Status (4)
| Country | Link |
|---|---|
| DE (1) | DE3010160A1 (en) |
| ES (1) | ES489795A1 (en) |
| FR (1) | FR2452198A1 (en) |
| GB (1) | GB2045013A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2543756A1 (en) * | 1983-03-31 | 1984-10-05 | Dubuis Jean Charles | Method and device intended for converting the voltage from a DC voltage source |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3411067A (en) * | 1966-03-14 | 1968-11-12 | Bunker Ramo | Transformer connected amplifier circuits including means for minimizing unbalanced transformer currents |
| US3490027A (en) * | 1967-12-05 | 1970-01-13 | Ibm | Transistor converter amplifier circuit |
| FR2345847A1 (en) * | 1976-02-10 | 1977-10-21 | Fontaine Ets Pierre | Transistor DC:AC convertor - uses two transistors and transformer connected to form push:pull circuit |
-
1979
- 1979-03-22 FR FR7907257A patent/FR2452198A1/en not_active Withdrawn
-
1980
- 1980-03-03 GB GB8007196A patent/GB2045013A/en not_active Withdrawn
- 1980-03-17 DE DE19803010160 patent/DE3010160A1/en not_active Withdrawn
- 1980-03-21 ES ES489795A patent/ES489795A1/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2543756A1 (en) * | 1983-03-31 | 1984-10-05 | Dubuis Jean Charles | Method and device intended for converting the voltage from a DC voltage source |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3010160A1 (en) | 1980-10-02 |
| FR2452198A1 (en) | 1980-10-17 |
| ES489795A1 (en) | 1980-09-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |