EP0191032A1

EP0191032A1 - Capacitive transformer

Info

Publication number: EP0191032A1
Application number: EP85903363A
Authority: EP
Inventors: Giacinto Allevi
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-08-23
Filing date: 1985-07-16
Publication date: 1986-08-20
Also published as: WO1986001653A1; IT1180809B; IT8412588A0

Abstract

Transformateur capacitif de tension, pouvant fournir un courant continu basse tension par conversion du courant alternatif du réseau. Le transformateur se compose d'un circuit diviseur (H ou Q) pourvu de condensateurs (C) et de diodes (D), permettant la charge et la décharge en parallèle desdits condensateurs (C); ce diviseur est mis en service par un circuit commutateur (S.A,B) qui relie le diviseur (H ou Q) alternativement à l'alimentation en tension (Vi) et à la charge (Vo). Il est en outre possible de séparer l'appareil du courant alternatif du réseau en doublant le commutateur sur les deux pôles, aussi bien à l'entrée qu'à la sortie. Tout cela se traduit pratiquement par une amplification négative de la tension et une amplification positive du courant. La réalisation la plus simple se rapportant à l'invention est un auto-transformateur capacitif de tension, limité à un diviseur par deux (H2).Capacitive voltage transformer, which can provide low voltage direct current by converting the alternating current from the network. The transformer consists of a divider circuit (H or Q) provided with capacitors (C) and diodes (D), allowing the parallel charging and discharging of said capacitors (C); this divider is put into service by a switch circuit (S.A,B) which connects the divider (H or Q) alternately to the voltage supply (Vi) and to the load (Vo). It is also possible to separate the device from the alternating current of the network by doubling the switch on both poles, both at the input and at the output. All this practically results in a negative voltage amplification and a positive current amplification. The simplest embodiment relating to the invention is a capacitive voltage auto-transformer, limited to a divider by two (H2).

Description

"CA ACITIVE TRANSFORMER"

This invention is concerned with a voltage capa- citive transformer, the basic feature of wich is the possibility of obtaining sub-multiples of a given input

5. voltage., without employing inductive transformers, and with the possibility of severance of load from the A.C. (alternating current) mains .

- According to the present condition of technics, to obtain a reduced D.G. (direct current) tension from 10. a given alternating voltage, an inductive transformer is usually employed, in addiction to rectifying diodes and levelling capacitors.

This method presents substantially the draw - back that the inductive transformer is bulky, heavy and 15. expensive.. Moreover, in TV use - or for professional ^• Oscilloscopes - noxious effects of scattering magnetic fields must be considered,

A further known method to reduce voltage without the

inductive transformer is the use of ohmic-drop resistors at hight dissipation, which consequently allow a very

small efficiency.

At present, and especially for TV use, the switchin system is employed. But this method doesn't allow for re

5. markable voltage drops, because of the dissipation limits imposed by switching transistors, and is anyway unecon£ ical regarding used components wich cannot be. exploited at the best of their potentiality.

On the contrary, capacitive multipliers are a_l

10. ready well known, like the symmetrical doubler of Latour or the asymmetric doubler of Schenkel; and the latter, repeatedly connected in series, is able to obtain a vol¬ tage equal to the original but multiplied for a fixed integral factor; this circuit is utilized for instance

15. in E.H.T.-generators for anodic supply voltage of C.R.T.s in actual TV sets.

Nevertheless, while the multiplier has already been well known for many years, its complementary - the capacitive divider - has never been realized or conceived.

20 Moreover, the methods hitherto considered don't separate the appliance from the A.C. mains, and yet some times this severance is an indispensable condition, either

for personal safegard (elektrocardiographes, encephalogra

phes. etc.)or for a correct working of supplied circuits (computers and peripherical units, mycrosolderers for

I.C.s, etc.); finally, multipliers can work only with

A.C. supply.

The main aim of the present invention is to provide

5. a circuit which reduces voltage, and which would be compact, light and economical, and which would allow a complete range of transformations: not only increasing the voltage -as it is already known - but also, above all, in decrea- sing it.

10. A further aim of the present invention is to obtain this negative booster (in voltage) by transferring the power to the greatest efficiency, with ayield near 100%. Another aim of the invention is to eliminate the damaging scattering magnetic fields.

15. Yet another aim of the present invention is to allow large voltage drops, and the use of the economical S.C.R.s, with simple fittings.

A possible aim of the present invention is to provide a circuit wich allows for the total separation of

20. the appliance from the power supply.

All the aforesaid objectives have been carried out by the means of a capacitive transformer, according to the present invention, composed of a voltage divider, made up of capacitors and diodes connected in such a way

25. as to allow a serial-charge and a parallel-discharge of the same capacitors, through an electronic alternating

switch,obtaining in this way an auto- ransformer, which has an efficiency near 100%.

The possible aim- of procuring a capacitive tran-

5. sformer with a distinct separation of the appliance from the mains is obtained by putting into action the switches on both the poles, in input and output as well ..

Indeed, according to the present invention,. the transformer provides performances analogous to the behavior

10. of the inductive transformers,- but with the clear advantage of being smaller and weighing and costing less.

It can also be operative with a D.C. input; it has a greater.efficiency, it- can produce wide ranges in voltage; it doesn't have scattering magnetic fields, and

15. it is in a position to totally separate the appliance from the mains.

To arrive at the aforesaid aims, the capacitive transformer is made up of an electronic circuit wich is put into action by switching the connections,, according

20. to the present invention, and comprising: a) a basic unit, also called "adder stage", which is com posed of three diodes placed in series to forme a bipole, leaving two connections free; a divider by one (=capacitor) can be connected to each of these respectively and achie-

25. ving in this way a divider by two. If a divider by two is connected to either one

or both of the free connections, a multiple divider is

achieved, be it a divider by three or four.

If a multiple divider is connected with either

5. one or both of them, a division with a superior deno i nator is obtained. b) an electronic circuit with switching connections, also obtainable with the use of discrete elements (transistors,, mes-fets, S.C.R.s, power-diodes, etc.),which connects a_l

10 . ternatively the divider to the power supply and to the appliance.

As an alternative to the aforesaid divider "a)", which works by means of a sum of denominators, .likewise an iterative voltage divider by "N" can be obtained, con

15. necting a capacitor with a basic unit, in such a way as

to form an iterative cell, wich is thus composed of three diodes and a capacitor. A divider by "N" is obtained con necting "N-1" iterative cells in cascades, and closing the free ends on either one of both poles: directly, if a

20. capacitor is already present; otherwise with an adjunctive de-coupling capacitor. The above divider by "N" must al. ways be put into action by the electronic circuit with switching connections as explained in "b)". The total number of necessary capacitors is "N"; this re_

25. suits from the sum of the de-coupling capacitor plus "N-1" capacitors contained in the "N-1" iterative cells .The mi¬

nimum number of necessary diodes is N =3(N-1) .It is possi¬ ble,moreover,to connect two divider groups in cascades ob tained as described above,whether they be sum dividers or

5. iterative dividers,and obtaining in this way a division by higher factors,since it operates by multiplying denomi¬ nators. The capacitive transformers described are all aut£ transformers. If one wishes to separate totally the appli¬ ance from the power supply,the switching circuit must in-

10. elude two double electronic switches working in opposition of phases,on both the poles,be it input or o.utput,contro]L led bya squared wave frequency generator,which canbe_.also obtained by squaring the^'wave of the A.C. mains.

When working with a divider by the product of de-

15. nominators,obviously a single frequency generator will be sufficient to control both the stages,and the successive dividers can be made up of capacitive autotransformers ac cording to the present invention.

The versatility of the described circuits is made

20. evident by the possibility of obtaining D.C. voltages ha¬ ving a continuous or alternative input supply.

For a best illustration of the invention, the fo_l lowing drawings are appended by mere way of illustration. In the drawings:

25. Fig.l represents the well-known diagram of the working of the charge and discharge of a capacitor;

Fig.2 is the schematic diagram of a synchronous total separator according to the present invention;

Fig.3 illustrates a basic unit or "adder" stage;

5. Fig.4 is the plan of a capacitive auto-transformer divider by two, according to the invention;

Fig.5 indicates the diagram of a multiple divider by a sum of denominators;

Fig.6 shows an example of a divider by three; 10. Fig.7 illustrates the diagram of a divider by "N" with iterative cells;

Fig.8 is the complete diagram of a capacitive tran sformer;

Fig.9 is a block diagram of -a divider by.a product: 15. of denominators.

Referring to Fig.l, is shown the mechanism of a capacitor's charging and discharging process, and how in the same way the principle of the separator has been de e loped. 20 The switch S in position A charges the capacitor

C at the input voltage V. ; in position B discharges the same on the resistor R which represents the load.

Fig.2 represents a synchronous separator circuit M, with double electronic switches S.A and S.B, controlled

25. by a square wave frequency generator G.f; all this allows for the perfect separation between the input V. and the output V .

V. is a D.C. voltage, obtained in any way, as for instance that of the mains at 50 or 60 p.p.s., rectified

5. and levelled.

Regarding the frequency generator G.f, one can also use the mains frequency, by previously squaring; and eventually using an optocoupler for the control.

As for the switching components, up to around 100

10. Watt, line output and/or video transistors and also S.C.R.s for T.V. can be used.

Since the output voltage is approximate to that of the input, we will establish that the capacitor C should be called "divider by one".

15. Fig.3 Illustrates a basic unit E, or adder stage, which is composed of three diodes D₁ , D_, D-., placed in

series to form a bipole with two free connections land 2.

In the square in Fig.4, a divider by two H- is shown, as the present invention requires; this is made up

20. of a basic unit. E: two dividers by one are connected to the aforesaid free connections 1 and 2, these being two capacitors C. and C„.^' Throughout the charging, the switch S is in position A, the diodes D₁ and D_ are put into interdiction, and as a result, the capacitors C. and C_

25. are placed in series through the diode D„. When the discharge occurs, with the switch S in position

B, the diodes D₁ and D-, become conductors, they render the

capacitors in parallel, and bring the diode D-, into the interdiction.

5. In Fig.5 a basic unit E is shown, so that a multi_¬ ple divider H may be produced; which is, in effect, a reproduction of the divider by two H_ , as in Fig.4, where instead of the capacitors C, and G-,, two divider sets H' and H" have been placed and ringed; these can be dividers ^"10 by one (capacitors C. or G-,) or by two (H-,), generating dividers by three or four, in a first phase. These last ones, in their turn, can be added in pairs, putting them in the places H' and H" of the^' circuit in Fig.5, deriving dividers by five, six, seven and eight; carrying on this

15. way, multiple dividers with superior denominators can be obtained.

Fig.6 is an example of a divider by three H„, obtained by substituting in the set in Fig.5 a divider by two in the place H", and a divider by one, that is a capa

20. citor C. , in the place H'.

The maximum transference of power is realized when 0 =0 =0..; but, to obtain more economical dividers, diffe¬ rent values in the dividers by two may also be used,limited to small amounts of power (less than 10 Watt for all of

25. them), but with the possibility of obtaining fractional dividers .

In the aforesaid adder system, the diodes which

forme the groups H' and H" result in serial disposition with regard to the diodes of adder stage E, thus raising

5. the power loss because of the voltage drop, which is a round 1 Volt for every diode. Furthermore, a few diodes from the adder stage are bridged by a current which is the sum of the single component set.Indeed, on examination of the example in Fig.6, it will be noted that the diode

10. D- is bridged by C_, and C 's current of discharge.

This fact could be a drawback in the case of strong cur¬ rents or very low voltage outputs.

To avoid such drawbacks, an iterative divider of voltage Q has been studied, as will be seen in Fig.7.

15. This is made up of the iterative cells K, one of which has been emphasised in the diagram, for clarity's sake.

The iterative cell K .Is made up of a basic unit E, with three diodes D₁ , D-,, D„, but in addition a capacitor

20. is joined to either one of the free connections 3 or 4 : which can be identified -with reference to the diagram- for the second connection , with capacitors from C' to C' ; whilst, for the first connection, they can be identified from G' to C' , . 1 N-1

25. Thus the iterative cell introduces two free con- neetions again, one by means of a capacitor and the other without, in a position to be connected with the analogous

adjacent cells, arranged in a cascade.

The circuit is closed with a capacitor (C' or C'

5. respectively) which is connected either with the first free connection 1 of the first cell K₁ , or with the second free connection N of the last cell K-. ₁.

Therefore, to obtain a divider of tension by N, a divider by one (that is a capacitor, whether C' or C')is 10. connected with a number N-1 of iterative cells K, which are arranged in a cascade, arriving at a total of N capa citors .

The total number of necessary components can be determined by looking at Fig.7, in which one can deduce 15. the number of capacitors N =N, while the number of diodes must be N =3(N-1) .

This configuration has the characteristic that the discharge current of every capacitor bridges a maxi¬ mum of two diode, and every diode is bridged by the current 20. of a single capacitor; this fact is an advantage for low voltages and strong currents.

Incidentally it is noted that the divider by two EL in Fig.4 follows at the same time the diagram of the divider by sum and that of the iterative divider. 25. A complete capacitive voltage transformer T, which can separate input from output, is obtained by placing a

group H or Q, assembled in whatever way, instead of C ( as shown in Fig.2); this complete capacitive transformer is shown in Fig.8. This circuit has an output voltage V . 5. which is, generally speaking, a fraction of the input V..

Regarding the group H or Q, formed with N capacS

tors all having the same value, we have anyway V =V./N.

The aforesaid V is a pulsating voltage, for .in¬

stance like the one found after the diodes bridge in a 10. conventional power supply; it must be consecutively level, led and stabilized in the usual way. ^•

It can be seen that the rectifier, in a capaciti ve transformer according to the invention,precedes the group H or Q while, in the case of conventional power 15. supplies, it follows the inductive transformer: this allows for the use of two simple diodes like the first separator (S.A),when using themains frequency,thus including the function of the rectifier as well.

A low tension power supply is obtained with the 20. capa_itive voltage transformer as described, usually be¬ tween 5 to 50 Vol s, converting it from the alternating mains voltage, which is normally 220 Volts, without nota¬ ble power loss and without using any inductive transformer.

The maximum deliverable current depends upon which 25. electronic components are used, and on the order of 10 or 15 Amperes, or more ; last, special components are not

necessary.

In Fig.9 a block-diagram is shown, as an example of a capacitive transformer with dividers by the product

5. of denominators.

The first block T_ represents a capacitive tran¬ sformer divider by three; the second block is a simple divider by four H,, followed by a single switch S.B con¬ trolled in its turn by the frequency generator G.f inclu

10. ded in T .

With this said capacitive transformer, with divi¬

der by product, an overall division of tension is obtained which is equal to the product of both the dividers: 3 x 4 = 12.

15. Regarding the groups E, H, K, Q, the order in which their components are represented is unimportant, inasmuch as the speculars diagrams are electrically iden tical to those shown in the figures.

Claims

C L A I M S

1. A capacitive voltage transformer, controlled

by a switching electronic circuit, comprising: a) a unit of base , or "adder stage" (E), which consists 5. of three diodes (D. , D_, D_) placed in series to forme a bipole, with two free connections (1, 2) to which we can connect:

- a divider by one, or capacitor (C_.,C_) respectively to each free connection (1, 2), to form a divider by two (EL);

10. or in addition:

- a divider by two (EL) can be connected to one or both of the above connections (1,2) to obtain a multiple divider (H) by three or four; or

- a multiple divider (H) can be connected to one or both 15. of the aforesaid connections, to obtain a division with a superior denominator;

b) a switching electronic circuit (S.A,B) which connects alternatively the divider (H) to the power supply (V.) and to the appliance (V ) .

20.

2. A capacitive voltage transformer, according to the claim 1, comprising: a) a unit of base (E), composed of three diodes (D* ,D',D') placed in series to form a bipole, with two free connec¬ tions (3,4) ;

25. b) a capacitor (C',...,C' or C' ...,C') connected to a free connection (3 or 4) of the unit of base (E), and which forms an iterative cell (K) ;

c) a capacitor (C' or C' ) connected with the first free connection (1) of the first iterative cell (K.), or with

5. the second free connection (N) of the last iterative cell (K^ ) ; whereby if the capacitors are N, a voltage divider is obtained composed of a divider by one (capacitor C' or C') connected in cascade with N-1 iterative cells (K) ; d) a switching electronic circuit (S.A,B) wich connects 10. the divider by N alternatively with the power supply (V.)

« or with the appliance (V ) . o

3. A buffer stage (M), which separates the applian ce (V ) from the mains or the power supply (V.), by the means of a switching electronic circuit, comprising two

15. double electronic switches (S.A and S.B) working In opp£ sition of phase between input and output, and placed on both the poles too, controlled by a sqare-waves frequency generator (G.f).

4. A buffer stage according to claim 3, in which 20. the. frequency generator (G.f) can be obtained by squaring the wave of the alternating mains voltage.

5. A voltage capacitive transformer, according to claim 1 or 2, in which the switching electronic circuit (S.A,B) is comprised of a buffer stage (M) according to

25. claim 3 and eventually claim 4.

6. A capacitive tension transformer according to

claims 1 and/or 2,in which the single dividers (H or Q) are connected in cascades, to obtain the product of the denominators .

7. A capacitive tension transformer according to all that has been described and illustrated in the present specification and in the enclosed diagrams.