FR2558655A1 - CONTINUOUS CURRENT-CONTINUOUS CURRENT CONVERTER - Google Patents

Abstract

THE CONVERTER ACCORDING TO THE INVENTION INCLUDES CONVERSION ELECTRONICS 30, A TRANSFORMER T1 FOLLOWED BY A FILTER 42, 43 AND A REACTION ASSEMBLY CONSISTING OF A TRANSISTOR 50 AND A T2 TRANSFORMER.

Description

CONTINUOUS CURRENT-CONTINUOUS CURRENT CONVERTER

  The invention generally relates to direct current direct current converters, and more particularly

their precise regulation.

  A dc to dc converter is used to provide a constant dc voltage to supply power or operating potential to a charging device. The output of a pulse generator or pulse generator feeds the primary winding of a transformer, the secondary voltage thereof being rectified and filtered, and the output voltage being determined by the coefficient of use of the pulse generator and by the transformation ratio or ratio between the number

of transformer turns.

  In order to obtain a continuous output voltage cons-

  aunt, we use a kind of reaction assembly to modify the coefficient of use for the case where the

  output voltage would deviate from its desired value.

  Normally, part of the output voltage directly supplies the pulse generator for the function of

  reaction which is to maintain a constant output voltage.

  There are however many cases in which, for various reasons, the load side of the transformer must absolutely be isolated from the input side of the transformer. These reasons include, for example, preventing circulating currents that could destroy components, preventing unwanted fields that could create health risks, or even bilateral isolation

noises.

  In cases where the isolation between the output and the input must absolutely be maintained, the feedback circuit does not constitute a direct connection. The montages at

  isolated reactions include the use of optocouplers

  to transfer the feedback signal from the output side to the input side, or other outputs that require some additional energy to operate. These electrical fixtures tend to be temperature sensitive and more or less non-linear, resulting in regulation

less than accurate.

  The main objective of the present invention is to provide a converter of the type described in which the output is isolated from the input by a circuit which requires no external energy, which uses a minimum number of

  components, and that is extremely linear.

  Accordingly, there is provided an apparatus which has a circuit for generating a waveform

  pulse whose coefficient of use is variable.

  This pulse waveform signal is applied to the primary winding of a transformer, the secondary winding of which is rectified and filtered to supply a load device via an output. A transistor means is mounted across the output and is connected and cut in response to the pulse signal from the secondary winding. Means electrically isolated from this transistor means and excited by its conduction and non-conduction is provided to generate a reaction signal indicative of the DC output voltage. This reaction signal is sampled, or its peak is detected, and is applied back to the circuit to adjust its coefficient of use.

  if the output voltage deviates from its desired value.

  Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a simplified diagram showing a typical DC-DC converter according to the prior art ; Figure 2 is an assembly diagram showing an embodiment of the present invention; FIG. 3 represents a variant of the circuit of FIG. 2 allowing a more precise reaction control; -3- Figure 4 is an assembly diagram showing

  another embodiment of the invention; and -

  Figure 5 shows yet another form of

realization of the invention.

  The DC to DC converter of

  Figure 1 includes an electrical circuit such as an

  conversion tronic 10 which can operate to generate a signal with a pulse waveform, the coefficient of use of which can be varied. This signal is applied to the primary winding of a transformer 12 to decrease or increase the voltage depending on the ratio between the number of turns of the transformer. The secondary winding of the transformer is connected to a rectifier circuit 14 which transforms the pulse and bidirectional waveform of the secondary winding into a unidirectional pulse waveform which is filtered by a filter 16 and which is supplied to an output. 18 in the form of a DC voltage

  constant intended to supply a load.

  A part of the output voltage is sampled by a feedback circuit 20 which supplies a feedback signal to the conversion electronics 10 to adjust the utilization coefficient if the output voltage deviates from a desired predetermined value. As already mentioned, a direct feedback connection is unacceptable in cases where electrical isolation is imperative. An improved isolation reaction arrangement which overcomes the disadvantages of prior art arrangements is shown in the

  Figure 2, to which we will now refer.

  In Fig. 2, an electrical circuit in the form of conversion electronics 30 can operate to provide an output signal in a two-way pulse waveform. Such circuits are well known to those skilled in the art and are commercially available. The circuit 30 of FIG. 2 comprises a reaction connection 31 making it possible to adjust the coefficient of use of the output waveform, and a connection 32 for return or earth.

  The pulse and bidirectional waveform signal

  tional is applied to the primary winding 34 of a transformer T1 having a secondary winding 35 with central tap whose ends are connected to a rectifier circuit composed of diodes 38 and 39 which can operate

  to transform the pulse and bidirectional waveform

  tional secondary winding in a pulse wave and unidirectional which is filtered by a filter device comprising an inductor 42 and a

  capacitor 43. The unidirectional DC voltage results

  aunt is available at output terminals 46 and 47 for

  connection to a charging device.

  The isolated reaction assembly comprises a transistor means which, in its simplest form, comprises a bipolar transistor 50 having a first electrode or emitter electrode 51, connected to the output terminal 47, a second electrode or collector electrode 52, and a third electrode or control electrode (base) 53. The electrode of

  control is connected to the secondary winding 35 of the trans-

  formatter via a resistor 54 chosen so that the transistor 50 goes from a cut or non-conductive state to a well saturated or conductive state

  of the pulse waveform of the secondary winding.

  The primary winding 58 of a transformer T2 is mounted in the collector circuit of the transistor 50 between the collector electrode 52 and the output terminal 46 and is excited by the cut-off connection of the transistor 50 and of the output voltage. This operation produces a voltage in the secondary winding 59 of the transformer T2, the magnitude of which depends

  of the ratio between the number of turns of the transformer.

  A diode 60 is provided in the circuit between the electrodes 51 and 53 in order to prevent damage to the base-emitter junction of the transistor 50 during the negative parts

  of the base control waveform.

  The magnitude of the voltage in the secondary winding

  Daire 59 is sampled by a detector such as a peak detector, an example of which includes a resistor 62, a diode 63 and a capacitor 64. The feedback signal, the peak of which has been detected, which appears at the junction of the diode 63 and capacitor 64 is then applied to the conversion electronics 30 by connection 31 to vary the coefficient of use of its output signal if the output voltage at terminals 46 and 47 deviates from a value predetermined. A resistor 66, connected in circuit between the reaction connection 31 and the return connection 32, together with the input impedance at the reaction connection 31, regulates the damping constant

of the peak detector.

  The voltage drop across the diode 63 is about 0.6 volts, varying from about 0.25 volts on the usual temperature extremes, and if we make sure that the ratio between the number of turns of the transformer T2 is large enough, the resulting voltage is much greater than the voltage variation across the diode 63 so as to minimize any linearity defect and

  to remove the need for temperature compensation.

  An even more precise control circuit can be produced in accordance with FIG. 3, which reproduces a part of FIG. 2 and has the same numerical references. But in the assembly of FIG. 3, an additional diode 63 ′ is included in the return line and is supplied by a bias current through a resistor 68 connected to a source of potential V +, the voltage drop at the terminals of the diode 63 'being added to the output of the peak detector and being equal to the voltage drop at

  diode 63 terminals so as to ensure compensation.

  FIG. 4 represents another embodiment of the invention in which the transistor takes the form of a field effect transistor (FET) while the transistor 50 of FIG. 2 is a bipolar transistor. The PET 70 has first and second electrodes 71 and 72 which are connected between the output terminals 47, 46 and further comprises a control electrode 73 which is connected directly to the secondary winding 35 of the transformer so as to switch the FET between its conductive state and its non-conductive state. An advantage of FET is that no base current, and therefore no excitation energy,

is not necessary.

  Due to the presence of the FET connection and of the resistor 76, the current which passes through the circuit of the FET, when it is conductive, is proportional to the output voltage. This current is detected by a current transformer 78 which also provides electrical isolation, and the

  current transformer output is used to generate

  on the reaction signal. This can be done for example using an operational amplifier which can operate to provide an output voltage proportional to the peak of the current supplied by the current transformer 78. Or

  well, and as just shown in figure 4, a resis-

  Tance 80 is mounted in circuit to create a voltage proportional to the intensity of the current supplied by the current transformer. This voltage, the magnitude of which is proportional to the output voltage and which is switched on and off by the operation of the FET 70, is detected by the peak detector circuit comprising a resistor 82, a diode 83 and a capacitor 84, which can operate to provide a feedback signal to connection 31, as well as

has already described it.

  Figure 5 is similar to Figure 2 but shown

  feels another detector that can be used in the reaction setup. This detector 86 is a demodulator

  synchronous which samples the voltage of the second winding

  daire 59 when it is at its maximum and maintains it until - 7 the next sampling. The frequency of the conversion electronics is used, via connections 87 and 88, so that the detector operates in synchronism with the waveform coupled by the feedback transformer T2. The use of the synchronous demodulator, which is a well-known circuit commercially available in the form of an integrated circuit "chip", is capable of allowing a

  wider bandwidth than the detectors already described.

  Consequently, a DC-DC converter has been described which provides the required isolation.

  between the output and input sides of the converted transformer

  and which allows stabilized and precise regulation of the output voltage with a minimum number of components without

  require no auxiliary power source.

Claims (9)

  1. DC-DC converter comprising a transformer having a primary winding and a secondary winding; an electrical circuit connected to said primary winding and operable to provide it with a pulse waveform signal; a rectifier circuit connected to said secondary winding and   capable of operating to provide a uniform signal   directional with pulse waveform in response to said signal applied to said primary winding; a converter output for connection to a charging device; filtering means operable to filter the output signal from said rectifier circuit and to give said output signal a nominally constant DC voltage; transistor means having a first electrode, a second electrode and a control electrode, said first and second electrodes being connected to said output and said control electrode being connected to said secondary winding so as to make said transistor means conductive or non-conductive ; means electrically isolated from said transistor means and excited by said conduction and non-conduction thereof to provide a feedback signal indicative of the DC output voltage; means for detecting said feedback signal; and means for applying said detected signal to said electrical circuit to control the output signal   impulse which is provided by it.   2. Converter according to claim 1, characterized in that said electrical circuit is of a type capable of varying the coefficient of use of its pulse waveform output signal, and said feedback signal is used to make vary said coefficient of use. 3. Converter according to claim 1 or 2, characterized in that it comprises a second transformer having a primary winding and a secondary winding, the primary winding of said second transformer being mounted in series with said first electrode, and said detection means being connected to the secondary winding of said second transformer. 4. Converter according to any one of   claims 1, 2 or 3, characterized in that said means   transistor is a bipolar transistor, the control electrode of said bipolar transformer being connected via a resistor to said secondary winding   of the transformer mentioned first.   5. Converter according to any one of   claims 1, 2, 3 or 4, characterized in that said   detection means is a peak detector.   6. Converter according to any one of   claims 1, 2, 3 or 4, characterized in that said   detection means is a synchronous demodulator.   7. Converter according to claim 1 or 2, characterized in that said transistor means is a field effect transistor whose control electrode is directly connected to said secondary winding * 8. Converter according to claim T, characterized in that it comprises a current transformer capable of operating so as to detect the current which passes through said field effect transistor when it is conductive, current which is proportional to said direct voltage , and means using said current to generate said signal of reaction.   9. Converter-according to claim 8, characterized in that said means of use comprises a resistor mounted across the terminals of said current transformer for   provide a corresponding voltage signal.