FR2718260A1 - High impedance power source. - Google Patents

Abstract

Current source power supply, comprising a current mirror circuit (Q1, Q2) having a high input impedance and also having a current passing in first and second channels through it, as well as a part for controlling the passage of the current, current reference means (Z3) adapted to establish a connection between the output part of the first current channel and an output of the current source power supply, current detection means (R6) adapted to establish a connection between the output part of the second current path and the output of the current source power supply, a feedback circuit (Q4) connecting the current flow control part of the current mirror circuit to both first and second current paths, wherein the feedback circuit regulates the current in the current sensing means so that the total voltage drop on the c sensing means and the reaction circuit is adapted to the voltage drop on the current reference means.

Description

HIGH IMPEDANCE POWER SOURCE

  The present invention relates to electrical power supplies

  rcues, and in particular a food source of

  zourant suitable for use in a communication network

two-wire munr.ication.

  By way of example only, the invention is presented in the context of a control system for a building,

  which uses a two-wire communication medium

  1O ment used to transmit power to con-

  tzriors located remotely in the system. The system of

  control includes many transmitting devices-

  receivers with low energy consumption, connected in parallel via the communication and power support with two wires, although other supports are suitable for the application of the invention described. The

  Figure 1 describes a basic design of such a network.

  Each device in the control system is

  adapted and arranged for exchanging signals via

  diary of the two-wire support, while also being

  suitable for receiving power from a power supply

- central ion.

  Pairs of wires used in this configuration

  Typically have the wires twisted together to equal

  release the electromagnetic interaction between themselves and

  other neighboring wires, and are available shielded or not

  bi-ncdes. However, other combined communication media

  catisn and food may include other confi-

  gura.ons of conductors adjusted or adapted to conduct a feed current from the power supply to the remote transceiver devices, and

control signals.

  The effective input impedance of all the devices when "listening" to a communication message is preferably considerably greater than the impedance of

  effective output of the transmitting part of each device

  - positive. However, since all the devices on the network are powered by the same pair of wires, the

  4ceo :: cn of the communication signal is affected negative-

  if the feed input imoedance of the device is low compared to the effective impedance of the part

% ceprc e of the device.

  2nd reference, the network therefore requires for the dis-

  posi-_ L a a: imentation having an extremely high input impedance at the frequencies used by the communication signal, while still being able to provide

  has the power needed to power each device.

  This allows as many devices as possible to be connected simultaneously to the power supply and

signal communication.

  By way of example only, functional requirements

  typical of a power source intended for

  powering networked devices may be the following

  values: Maximum voltage (in transient state): Vmax = 65 V Minimum operating voltage: Vmin = 6 V Current regulation range: 5 mA <I supply. <35 mA mpedance on the communication frequency range: Z input> 50 kOhms Communication frequency range: 3 kHz <Fcom <20 kHz

  An alternative is to use an induc-

  in series with the input of the power supply, in order to obtain

  high impedance at communication frequencies

  C desired, while still allowing the device to receive

  see the power from the wires. However, to get

  the required impedance, the inductor must have a

  inductance of approximately 5 Henry. Characteristically

  ri-st-ique, this inductance value is only available when using an inductor with a large number of windings

  around a magnetic core, which is typically encom-

  brant et -eu economic if there is a large number of avail-

  remote control devices on the network.

  Its necessary supplies to provide a source

  Do not zour = nt constant can include sources of cost

  semiconductor rant using either junction-field transistors (JFET) operating above the squeeze eur ension, or bipolar transistors in "mirror" conflcuration, designed to use the voltage of i $ base of bipolar transistors so as to defy the

  collector current, or any functioning linear transistor

  working with a negative feedback loop that tries to

chase the current.

  However, it is also known that sources of

  rant using JFET transistors operating above

  of the pinch voltage are typically

  that, limited by device parameters. Impediments

  typical JFET dances, for devices intended to operate in this mode, are less than 25 kOhms for

a current of 4.7 mA.

  Transistors (bipolar or field effect) which

  are used to regulate the current in response to a circ

  reaction cooked, depend on circuit response time

  controller to present appropriate performance.

  The use of such a circuit in high voltage applications such as those described in the embodiment of the invention is unnecessarily complicated by

  the use of a variety of amplifier-based circuits

  operational factors in addition to the supply circuit to

constant current.

  Another current source technique which uses linear bipolar integrated circuits is the mirror of

  current. A typical current mirror circuit is shown

  feel in figure 2. The slow input current is "efiéchi" in the output part of the circuit, so that, if the imoedance of the circuit is appropriate, an identical current will pass in the collectors of the two transistors Q1 and Q2 . In the current mirror zircuit shown in Figure 2, ent. causes a current to flow

  in the base of transistor Q1, thus allowing a

  rant of collector to pass in the same transistor. The curant. resulting therefore through the transmitter of Q1 and creates a voltage drop from the base to the transmitter, equal to -s, which is connected (logarithmically) to the current Ient. As the transistor Q2 has its base connected in parallel to the base of the transistor Q1, it has the same base-emitter voltage and, therefore, allows the same current to pass through its emitter from the power supply connected to its collector. In a circuit with discrete components forming a current mirror, it is necessary to introduce resistors in series with the emitters of the transistors, so that the effects of temperature and of a detuning of the parameters

  are less pronounced. Transmitter resistances

  29 also kill a simple way to calibrate if necessary

the output current.

  Integrated circuit versions of a current mirror

  use various known techniques to obtain the

  constant and regulated rant necessary, but in the case of a network comprising a plurality of spaced devices the

  along a support with two wires conducting current of ali-

  mentaton and signal carrier, the requirements of high

  voltage that are needed make a solution in circ

  built-in more difficult current, not to say

immoraficable.

  Thus, one aspect of the present invention is to provide

  provide a constant current source that uses a combination

  new birth of a current mirror principle and a negative feedback loop in order to obtain the regulation of

  current required, which still has an impedance of

  very high at the frequencies used to communicate control signals. The invention overcomes the problems that

  these circuit techniques comprise in themselves.

  In a broad aspect of the invention, a current source power supply includes:

  a current mirror circuit having an impedance

  high entry dance and also having a massaging current in first and second channels, as well as a control oartze for the passage of the current,

  current reference means suitable for

  blir a connection between the output part of said pre-

  first current path in said mirror circuit

  current and an output of said power supply source

  rant, current detection means suitable for establishing a connection between the output part of said second current path in said current mirror circuit and said output of said current source supply,

  a feedback circuit connecting the com- part

  current flow from said mirror circuit

  running on both the first and second lane

  rant, wherein the feedback circuit regulates the current in the current sensing means so that the total voltage drop across the current sensing means and the feedback circuit is adapted to the drop

  voltage on the current reference means.

  In another aspect of the invention of a diet

  current source, the current mirror includes two transa

  weak signal sistors having their base terminals connected together and their collectors connected to a

common voltage source.

  In another aspect of the invention of a diet

  current source, the current reference means

  take a voltage reference to Zener diode and a re-

  sistance to convert the measured current into a voltage at

  for comparison with the reference voltage.

  Another aspect relates to a voltage source power supply according to any one of the preceding aspects, in

  = current! e Dredetermined input impedance of said ali-

  mentat on current source is greater than 50 Ohms.

  A particular embodiment of the invention will now be described in detail with reference to the figures.

  annexed on which it is illustrated.

  i This embodiment serves as an illustration and is not

not imitative for the invention.

  Figure _ shows a plurality of control devices interconnected by a pair of wires which form a current network topology; : 5 Figure 2 is a circuit of a prior art current mirror; and Figure 3 shows a current source circuit according to

  an embodiment of the invention.

  A wide variety of information systems,

  2J control and management using two-wire power and communication supports has been developed for

  such a wide variety of systems used in buildings

  residential and commercial and industrial areas-

  the. Pairs of conductors are easily laid and

  routed to new or existing buildings and similar

  overlapping type connections can be made

  at any point along the pair of conductors. The topo-

  basic logie of such a network is described schematically in figure i. Wires 10 and 12 constitute a support

  for the communication of signals, from or to the devices

  sitfs 14, 16, 18 and 20, which can be distributed as needed over the entire length of wires 10 and 12. It is preferable that there is a maximum length of wire along

  where a device can be placed, and this aspect of the invention will be described later in the specification.

  A suitable current source supply circuit which overcomes the problems of the prior art, includes a

  zircuit using both the principle of the color mirror

  rant and a negative feedback loop. The current of ali-

  but we can be regulated while an input impedance

  adequate to the communication frequencies used

  sees. _a Figure 3 describes an embodiment of such a current source supply circuit, wherein R2 i0 is a high value resistor which delivers sufficient current to the base Q4 to put it in conduction, after cuoi the reaction to through transistor Q1 will maintain the

proper operation.

  A low voltage Zener diode (3.3 V), Z3, is used

  to establish a reference voltage and current and

  is an example of reference current means. A cir-

  cooked separately it produces a low current reference

  could also fulfill this circuit function.

  The transistor Q4 is a summing element and is part of the reaction circuit of the current supply which delivers the basic current to the two transistors Q1 and Q2, causing the flow of current in each of the two collectors thereof. Q1 and Q2, in this configuration with respect to each other, constitute an example of means forming a current mirror. Voltage drop

  appears on resistance R6 in response to the current coming from

  from transistor Q2, a resistor being an example of

current detection means.

  The transistor Q4 regulates the current I2 so that the voltage drop on the resistor R6, plus the base-emitter voltage 7E of the transistor Q4, corresponds to the drop

Zener voltage of Z3.

  it should be emphasized that it is preferable, but not critical

  tick, that the temperature zoefficient of the base-emitter voltage VE of the transistor Q4 is approximately identical for the Zener diode Z3, so that the coagulated current is not negatively affected by a variation in temperature.

  An optional CL capacitor is used in the circuit.

  _cuit to bring stability to frequencies of

high functioning.

  e current t passing through the Zener diode Z3 is regulated, and is of the order of 5 mA for the required current range

  by th network. This guarantees stability and reproducibility.

  iO0 biLity of the characteristics of the Zener diode.

  The transistor Q3 can be optionally included for deli-

  check additional current at higher voltage

  than that of the current source output terminal.

  Resistors R2, R3 and R4 are preferably included to compensate for errors caused by parameters and temperature characteristics at variance between the discrete transistors used in this embodiment, namely Q1 and Q2. Resistor R5 performs a function

  similar if the additional transistor Q3, with its capa-

  city of additional current transport, is used.

  In addition, circuits as described above can be added to deliver even more current

  in order to adapt to a particular application of the

  vention. Resistor R6 is a current detection means used to predetermine the required regulation current, and the current delivered must be generated by a separate circuit.

  The total impedance of the current source at the frequencies

  Communication frequencies, typically in the 3 kHz range <Fcom <20 kHz, is determined to a large extent by certain component parameters. The transistors Q1, Q2, and Q3 may preferably be components BC856 / BC556, which have been specially chosen for

  their parameters h, and can therefore provide performan-

  those of consistent and predictable speed. The transistor Q4 operates with a very low collector current and therefore does not appreciably affect the output impedance of the

Power source.

  The previous description presents a version with

  discrete posanrs of a constant current power supply

  so much. However, it is within the capabilities of a person specialized in the subject matter to produce a circuit having the same functionality in the form of an integrated circuit or of a hybrid surface mounting. The principles of the circuit are the same, but the shape of the electronic parts is modified to adapt to production considerations

in large series.

  LI should be noted that the invention uses both a principle of current mirror and a negative feedback loop to obtain the desired circuit response for

  a current source suitable for the application described.

  However, subject matter experts will understand that

  the invention is not limited in its use to the ap-

  described, and that the invention is not limited either, from the point of view of the particular components and

  configurations described here, in its pre-

  Brother. It should be noted that various modifications can be made without departing from the principles of the invention, and the invention should therefore be considered to include all

  changes within this framework.

Claims (11)

CLAIMS Current source power supply, comprising: a current mirror circuit having a high input impedance and also having a current flowing therein in first and second channels, as well as a control circuit for the current passaae , these current reference means adapted to establish a connection between the output part of said first current path in said current mirror circuit and an output of said current source power supply, current detection means suitable for establishing a connection between the output portion of said second current path in said current mirror circuit and said output of said current source power supply, a feedback circuit connecting the control portion of the current flow of said circuit forming a current mirror in both the first and second current paths, in which the feedback circuit regulates the current in the mo current detection yen so that the total voltage drop on the current detection means and the reaction circuit is adapted to the voltage drop on the current reference means.   2. Power supply according to the claim   tion _, in which the current mirror comprises two weak signal transistors having their basic terminals connected together and their collectors connected to a common voltage source.   3. Power supply according to the claim   tion i, in which the current reference means comprise a Zener diode voltage reference and a resistor for converting the measured current into a voltage   for comparison with the reference voltage.   4. Power supply according to the claims   1, 2 and 3, wherein said feedback circuit comprises a weak signal transistor having a collector connected to the base terminals of said current mirror circuit, a transmitter connects to the junction of the second sourcing channel of said mirror circuit of current and   said current detection means, and a connected base   tee at the junction of the first current path of said current mirror circuit and said means of ! 0 current reference.   5. Power supply according to the claim   tion 4, wherein said weak signal transistor of the reaction circuit is actuated with a low current of   collector while maintaining the impe-   input dance of said current source power supply.   6. Power supply according to the claim   tion 5, wherein said weak signal transistor of   feedback circuit is of the npn type.   7. Power supply according to the claim   tion 2, wherein said weak signal transistors are paired transistors.   8. Power supply according to the claim   tion 2, wherein said weak signal transistors are npn type transistors.   9. Power supply according to the claim   tion 7, wherein said weak signal transistors   have their transmitters connected via resis-   tances in series with said common voltage source, so as to adapt the parameters and characteristics of   temperature of said weak signal transistors.   i0. Power supply according to the claim   is there 7, wherein said weak signal transistors are chosen on the basis of their gain characteristics, so as to provide an impedance characteristic   predetermined high input.   11. Power supply according to the claim   tion 1, before means forming a capacitor in parallel with said current reference means for stabilizing   in frequency said power source supply.   Power supply according to the claim   tion L, having at least one additional current transport channel supplied by current amplifier means connected to said voltage source means and to said constant voltage output, having a current flow control part connected to said control part of the current flow from said current mirror circuit, so that the current delivered by said additional current transport channel is added to the current   total delivered by said current source power supply.   13. Voltage source supply according to any one   as in the preceding claims, in which the impe-   predetermined input dance of said source supply   current is greater than 50 Ohms.   14. Two-wire communication system having a power source according to any one of previous claims.