AU3515201A

AU3515201A - Method of regulating a voltage in an electronic circuit and electronic circuit for carrying out the method

Info

Publication number: AU3515201A
Application number: AU35152/01A
Authority: AU
Inventors: Henry Fluhrer
Original assignee: Diehl AKO Stiftung and Co KG
Current assignee: Diehl AKO Stiftung and Co KG
Priority date: 2000-05-12
Filing date: 2001-04-11
Publication date: 2001-11-15
Anticipated expiration: 2021-04-11
Also published as: ES2238358T3; DE50105511D1; EP1154344A1; AU778884B2; DE10023347A1; EP1154344B1; ZA200103835B

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

TO BE COMPLETED BY APPLICANT Name of Applicant: Actual Inventor: Address for Service: Invention Title: DIEHL AKO STIFTUNG CO. KG Henry Fluhrer CALLINAN LAWRIE, 711 High Street, Kew, Victoria 3101, Australia METHOD OF REGULATING A VOLTAGE IN AN ELECTRONIC CIRCUIT AND ELECTRONIC CIRCUIT FOR CARRYING OUT THE

METHOD

The following statement is a full description of this invention, including the best method of performing it known to me:- 10/04/01,TDI 1940.CS,1 la- Diehl AKO Stiftung Co.KG, D-88239 Wangen Method of regulating a voltage in an electronic circuit and electronic circuit for carrying out the method The invention concerns a method of regulating a voltage in an electronic circuit as set forth in the classifying portion of claim 1, an electronic circuit for carrying out the method, and use of an electronic circuit for carrying out the method.

Capacitor mains supply portions are increasingly used for electronic circuits (in particular small or inexpensive circuits), instead of the transformers which were earlier the conventional practice. The capacitor mains supply portions essentially comprise a resistor, a capacitor, a full- *o°wave rectifier and a charging capacitor, wherein the resistor and the capacitor are connected in series and are connected to an input of the fullooo.oi wave rectifier while the charging capacitor is connected to the two outputs of the full-wave rectifier. Such a capacitor mains supply portion delivers a i" constant direct current which with a stable mains supply voltage arises •I :oessentially out of the capacitance of the capacitor. The voltage which occurs at the outputs of the full-wave rectifier and thus the loads connected to the ooo 25 capacitor mains supply portion depends on the dc resistance of the load in oooo• Saccordance with the formula U R x I.

A major problem with such capacitor mains supply portions is the fact that, by virtue of mains supply voltage fluctuations and component tolerances, the constant current delivered by the capacitor mains supply portion is subjected to large tolerances which in part are over 50%. That naturally means that the voltage which is dropped at the connected loads also involves the same large tolerances. Therefore, in the case of conventional capacitor mains supply portions, measures are additionally necessary for voltage stabilisation purposes, for example in the form of a stabilisation circuit, voltage limitation or a voltage regulator.

2 Based on that state of the art, the object of the invention is to provide a method and an electronic circuit for carrying out the method, with which the voltage which is dropped across a load connected to the capacitor mains supply portion can be easily regulated without major additional circuitry expenditure.

That object is attained by a method having the features of claim 1 and an electronic circuit as set forth in one or more of the appendant claims. The other claims recite embodiments and developments of the invention.

The basic concept of the invention is that the voltage which is dropped across a load connected to a constant current source such as for example a capacitor mains supply portion is reduced as a mean in respect of time if the load is short-circuited at least intermittently or cyclically by way of a parallel current branch with a lower or negligibly low resistance.

S 15 If that parallel current branch is opened and closed cyclically by way of a switch disposed therein, then the mean value in respect of time of the voltage at the load can be set within certain limits by way of the ratio of the switch-on time to the switch-off time of that switch (duty factor). In that .case an increase in the duty factor (prolonging the switch-on time in relation to the switch-off time) causes a reduction in the voltage and a reduction in the duty factor (shortening the switch-on time in relation to the switch-off time) causes an increase in the voltage.

In that way, in the event of the function of the load not being required, the voltage applied to the load can be reduced by an increase in the duty factor, with the consequence that the electrical power consumption of the circuit is reduced as although the current flow generated by the constant current source remains constant, the voltage drop in the circuit is however reduced. In that way, in the case of apparatuses with a constant current source, in which a constant current always flows but the function of the load is not required on an on-going basis, it is possible to achieve a considerable saving in terms of electrical energy.

If a vacuum fluorescence display element (VFD) is used as the load, in which the heating means is connected in series with an electronic switch and is actuated cyclically by way thereof, the current branch which contains the heating means and the switch can be considered as the current branch which is parallel in relation to the load, in which case then the tube-like arrangement of the VFD with cathode and anode is to be considered as the actual (high-resistance) load. In that case the voltage occurring at the 'tube' of the VFD can be regulated directly by way of the duty factor of the heating actuation means. That is already an attractive proposition in particular for the simple reason that no further components which are not already necessary for normal operation of the VFD are required for that purpose in the electronic circuit.

A development of the invention provides that the voltage applied to the load or a partial voltage which is correlated with that voltage is fed to a •control element for controlling the cyclic procedure and is detected thereby, ".'and that the control element compares the detected voltage to a target or 15 reference voltage which is stored in a memory and increases or reduces the duty factor of the switch depending on whether the detected voltage is higher or lower than the reference voltage.

The feed of the voltage applied to the load, to the control element, can be implemented directly if the control element has a suitable input, or also by way of a voltage divider, wherein in the latter case the control element is fed with a partial voltage which is smaller (in quantitative terms) but which is in a fixed relationship with the voltage which is dropped at the Sload. If the control element itself is connected directly to the voltage applied to the load, a further feed line is no longer necessary as the voltage is in fact already fed by way of the power supply line. In that case however it is necessary to ensure that on the one hand the control element remains fully operational even when the applied voltage is variable and that on the other hand the control element is supplied with a reference voltage by way of a voltage standard so that measurement of the voltage applied to the load is possible by comparison of the supplied voltage with that reference voltage.

The advantage of the invention is that regulation of the voltage in an electronic circuit with a constant current source is possible, without involving major circuitry expenditure, and indeed even entirely without circuitry expenditure in the case of the VFD with the heating means which is already actuated by way of an electronic switch. That therefore eliminates the complication and expenditure in the form of a voltage regulator, a stabilisation circuit or a voltage limiting means, which would otherwise be required if there were fluctuations in mains supply voltage or component tolerances. In addition, the method according to the invention makes it possible in a simple manner to implement a power saving mode in order to reduce the power consumption of the circuit when the function of the load is not required.

The invention will be described in greater detail hereinafter by means of two embodiments. In the drawings: Figure 1 is a basiccircuit diagram showing the principle of an electronic circuit for carrying out the method according to the invention, Figure 2a shows a variation in respect of time of switch actuation and 15 the voltage applied to the load, Figure 2b shows a further variation in respect of time as shown in Figure 2a with another duty factor, Figure 3 shows a basic circuit diagram of an alternative embodiment, and Figure 3a shows a basic circuit diagram without capacitor mains supply portion in accordance with a variant of the embodiments of Figure 3.

An electronic circuit 1 has a capacitor mains supply portion 2 as a constant current source. It comprises a resistor R1, a capacitor C1, a fullwave rectifier 3, a charging capacitor C2 and a Zener diode Z1. The capacitor mains supply portion 2 is connected by terminals 4 and 4a to the mains supply voltage while the output of the full-wave rectifier 3 is earthed. The charging capacitor C2 serves to smooth the variation in respect of time of the voltage at the outputs of the full-wave rectifier 3, and the Zener diode C1 limits that voltage upwardly in order to protect components connected to the capacitor mains supply portion 2 from overvoltage.

The load connected to the capacitor mains supply portion 2 is symbolically indicated in the form of the resistor R2 in Figure 1. Besides the load R2, a microcontroller 6 is connected to the outputs and of the fullwave rectifier 3 and thus the capacitor mains supply portion 2, by way of a voltage regulator 5. The voltage regulator 5 which is also connected to the outputs of the capacitor mains supply portion 2 provides that the microcontroller 6 is always supplied with the 5V voltage which it requires.

The load R2 can be any conceivable kind of electrical loads. In a particularly advantageous configuration of the embodiment according to the invention, the load R2 is formed by a light emitting display element (LEDdisplay) or a liquid crystal display element (LCD). Both the LED-display and also the LCD are actuated by the microcontroller this is not shown for the sake of clarity of the drawing in which respect the microcontroller, depending on the respective requirements involved, connects various lighting segments of the LED-display or the LCD to the power supply, and separates others therefrom.

In addition the microcontroller 6 switches a transistor T1 which is 15 connected as an electronic switch into a current branch 7 which in turn extends parallel to the load R2. When the transistor T1 is caused to conduct and therefore the current branch 7 is connected into circuit, the load R2 and therewith also the charging capacitor C2 are short-circuited. The charging capacitor C2 is discharged by way of the current branch 7 and the voltage U applied to the load R2 collapses. If in contrast the transistor T1 is oo:° switched off again, the capacitor C2 is charged up again and the voltage U

C

rises.

The microcontroller 6 actuates the transistor T1 cyclically, The tlll•: variation in respect of time of that actuation and the resulting value for the voltage U is shown in Figure 2a. At the time tl the transistor T1 is caused to conduct, that is to say the current branch 7 is connected into circuit. As explained above the voltage U falls until at time t2 the transistor T1 is switched into the non-conducting condition, thatis to say it is switched off.

Thereupon the voltage U rises slowly again until at the time t3 the transistor T1 is caused to conduct once again, that is to say it is switched on, whereupon the voltage U falls again until at time t4 the transistor T1 is switched off again.

Due to the current branch 7 being cyclically switched on and off by way of the transistor T1, a time mean value is afforded for the voltage U, smoothed by the charging capacitor C2, the mean value corresponding to the following formula: U (I x R) D In that formula I is the constant current supplied by the capacitor mains supply portion 2, R is the ohmic resistance of the load R2 and D is the ratio of switch-on and switch-off times (duty factor) of the transistor T1. The constant current I is determined by the mains supply voltage and the dimensioning of the resistor R1 and in particular the capacitor C1. The illustrated embodiment is assumed to involve a current I of 10 mA and a resistance R of the load R2 of 100 ohms. The duty factor D can be seen from Figure 2a as D (t2 tl)/(t3 tl) 1/20, which gives a mean voltage of U 10 mA x 100 ohm x 20 20 V.

oFigure 2b shows a situation in which the transistor T1 is caused to f conduct, that is to say switched on, for twice as long as in the case shown in Figure 2a. Here the duty factor is D (t2' tl)/(t3 tl) 2/20 1/10.

.o Accordingly this gives a mean value in respect of the voltage U of U mA x 100 ohms x 10 10 V. The variation in the voltage curve around that mean value of 10 V is greater in Figure 2b than in Figure 2a as here the charging capacitor C2 is discharged for longer and therefore the voltage U collapses to a greater extent. It will be appreciated that this voltage collapse in Figure 2b like also that in Figure 2a is shown on a greatly exaggerated scale for the sake of enhanced clarity.

It can be seen from Figures 2a and 2b that the voltage U which is o:o. applied to the load R2 on average in respect of time can be adjusted within relatively wide ranges by virtue of a variation in the duty factor D. In that way it is possible for the voltage U to be set precisely to a desired value, even if for example the constant current I supplied by the capacitor mains supply portion 2 is not precisely known or fluctuates by virtue of component tolerances within a product series. For that purpose, the value of the voltage U, which is just prevailing, must be measured, the measured voltage value must be compared to the desired or reference value of the voltage U, and correspondingly the duty factor of actuation of the transistor T1 must be varied, depending on whether the prevailing voltage is excessively high or excessively low.

7 In the embodiment shown in Figure 1 the prevailing voltage U is measured in such a way that connected in parallel with the load R2 is a voltage divider comprising a series circuit of resistors R3 and R4 whose divider tapping 8 is connected to the microcontroller 6. In that way the microcontroller 6 can measure the partial voltage UT which occurs at the resistor R4 and which is directly correlated with the voltage U, and compare it for example with a stored partial voltage reference value which would occur when the reference voltage is present at the load R2.

If the function of the load R2 is not required, it is further possible with a suitable duty factor D to reduce the voltage U to such an extent that the microcontroller 6 is just still operational. In that case the current which is always supplied constant by the capacitor mains supply portion flows away by way of a comparatively slight voltage difference so that only a comparatively low level of electrical power is also consumed. That is of S 15 great advantage from the point of view of energy saving, in relation to apparatuses which are admittedly continually connected to the mains supply voltage but in which the function of individual or given loads is not continuously required.

Figure 3 shows a second embodiment of the invention in which the oo..

load used is a vacuum fluorescence display element (VFD) 9 having an anode 10 and a cathode 11, wherein the cathode 11 serves at the same time as a heating means 12. In this case, the path from the anode 11 to the cathode 10 is to be viewed as the actual high-resistance load. The l heating means 12 is connected in series with the transistor T1 into the current branch The microcontroller 6 is connected directly to the voltage U, which is only possible if it is operable with variable voltages.

The microcontroller 6 cyclically switches the transistor T1 in accordance with the diagram showing the variation in respect of time in Figure 2a. During the conducting times, that is to say the switch-on times, of the transistor T1, current flows through the heating wires of the heating means 12 whereby they are greatly heated. Even during the time in which the transistor T1 is switched off, that heating effect is adequate to sufficiently liberate electrons from the anode 11, which are then accelerated to the cathode 10. It should be noted here that actuation of the 8 various lighting segments of the VFD is also effected by way of the microcontroller 6, but is not shown in Figure 3 for the sake of clarity.

The microcontroller 6 is also connected to a voltage standard 13 which supplies a fixed reference voltage. That fixed reference voltage is necessary so that the controller 6 can ascertain the actual value of the voltage U from the voltage at its voltage supply inputs, and thereupon, as described above, can set the voltage U to a desired reference value.

It will be appreciated that it is also possible for the microcontroller 6 in the embodiment shown in Figure 3 to be connected to the voltage U by way of a voltage regulator 5 and for detection of the value of the voltage U, as also in the first embodiment, to be effected by way of measurement of a partial voltage UT occurring at a voltage divider. This variation in the abovementioned embodiment is shown in Figure 3a. It will be appreciated also that likewise in the embodiment shown in Figure 1 the microcontroller can 15 be connected directly to the voltage U, as shown in Figure 3. It is also :conceivable that the microcontroller is connected to the voltage U by way of °eea voltage regulator 5, but for measurement of the voltage U is connected directly thereto.

.eee°i Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof .eeeei

Claims

1. A method of regulating a voltage U in an electronic circuit (1) comprising a constant current source (preferably a capacitor mains supply portion with resistor capacitor rectifier and charging capacitor a control element preferably in the form of a microcontroller, and at least one load (R2) having a first ohmic resistance and applied to the voltage U, characterised in that the load (R2) is short- circuited intermittently or cyclically by way of a parallel current branch (7) having a second ohmic resistance which is less than the first, by means of an electronic switch (T1) which is actuated by the control element wherein to reduce the voltage U on average in respect of time the ratio of the switch-on time to the switch-off time (duty factor) of the switch (T1) in the short-circuiting current branch is increased and to increase the voltage U the duty factor of the switch (T1) is reduced. o 2. A method according to claim 1 characterised in that to reduce the electrical power consumption of the electronic circuit when the function of the load (R2) is not required the voltage U is reduced on average in respect of time by increasing the duty factor of the switch (T1) in the short- circuiting current branch by means of the control element

3. A method according to claim 1 or claim 2 characterised in that ooo* when using a vacuum fluorescence display element (VFD) as the loBad, wherein the heating means (12) of the VFD is connected in series with the electronic switch (T1) which is cyclically actuated by the control element the duty factor of actuation of the heating means is increased or reduced by way of the switch (T1) by the control element to reduce or increase respectively the voltage U on average in respect of time.

4. A method according to one of claims 1 to 3 characterised in that the voltage U or a partial voltage UT correlated therewith is fed to the control element and detected thereby, that the control element compares the detected voltage UE to a reference voltage Us stored in a memory, and increases or reduces the duty factor of the switch (T1) depending on whether the detected voltage UE is higher or lower than the reference voltage Us. An electronic circuit for carrying out the method according to claim 1 or claim 2, which has a constant current source (preferably a capacitor mains supply portion with resistor capacitor rectifier and charging capacitor a control element which is preferably in the form of a microcontroller, and at least one load (R2) having a first ohmic resistance and applied to the voltage U, characterised in that provided in parallel with the load (R2) is a current branch having a second ohmic resistance which is lower than the first, wherein said current S.i branch is closable by way of a switch (T1) actuable by the control element preferably a transistor.

6. An electronic circuit according to claim 5 characterised in that connected in parallel with the load (R2) is a voltage divider adapted to tap off the voltage U and having a divider tapping which is connected to a terminal of the control element and at which the partial voltage UT can be tapped off. 0% An electronic circuit for carrying out the method according to claim 4 when appendant to claim 3, wherein the circuit has a constant current 0••°03 source (preferably a capacitor mains supply portion with resistor (R1), capacitor rectifier and charging capacitor a control element which is preferably in the form of a microcontroller, and as the load applied to the voltage U a vacuum fluorescence display element (VFD) wherein the heating means (12) of the VFD is cyclically actuable by the control element by way of an electronic switch preferably a transistor, characterised in that connected in parallel with the VFD is a voltage divider adapted to tap off the voltage U and having a divider tapping which is connected to a terminal of the control element and at which the partial voltage UT can be tapped off. 11

8. An electronic circuit according to claim 5 or claim 6 characterised in that the control element is connected to the voltage U and at the same time is connected to a component (13) supplying a reference voltage UR.

9. Use of an electronic circuit which has a constant current source (preferably a capacitor mains supply portion with resistor (R1), capacitor rectifier and charging capacitor a control element which is preferably in the form of a microcontroller, and as the load applied to the voltage U a vacuum fluorescence display element (VFD) wherein the heating means (12) of the VFD is cyclically actuable by the control element by way of an electronic switch preferably a .transistor, for carrying out the method according to claim 3. clai 10. An electronic circuit for carrying out the method according to claim 1 or claim 2 characterised in that S* the constant current source is in the form of a capacitor mains supply portion having a full-wave rectifier to one input of which is applied the one terminal of the mains voltage by way of a series circuit of a resistor (R1) and a capacitor (C1) and to the other input of which is applied the other terminal (4a) of the mains voltage, and to the two outputs of which is connected a parallel circuit of a charging capacitor (C2) and a Zener diode (Z1) connected in the reverse direction, the one output of the full-wave rectifier is earthed, connected to the outputs of the full-wave rectifier as a load (R2) there are also a light emitting diode display element (LED-display) or a liquid crystal display element (LCD) and a voltage regulating element a voltage supply input of a microcontroller is connected to the output of the voltage regulating element and the other voltage supply input is earthed, and in addition connected to the outputs of the full-wave rectifier is a current branch which has a transistor switch (T1) connected to the microcontroller and controlled thereby and which can be opened and closed by the transistor switch.

11. An electronic circuit for carrying out the method according to claim 3 characterised in that the constant current source is in the form of a capacitor mains supply portion having a full-wave rectifier to one input of which is applied the one terminal of the mains voltage by way of a series circuit of a resistor (R1) and a capacitor (C1) and to the other input of which is applied the other terminal (4a) of the mains voltage, and to the two outputs of which is connected a parallel circuit of a charging capacitor (C2) and a Zener diode (Zl) connected in the reverse direction, the one output of the full-wave rectifier is earthed, connected to the outputs of the full-wave rectifier as a load there are also a vacuum fluorescence display element (VFD) and a voltage regulating element the one voltage supply input of a microcontroller is connected to the output of the voltage regulating element and the other voltage S. SO supply input is earthed, and in addition connected to the outputs of the full-wave rectifier is a current branch which has a series circuit of the heating means (12) of the VFD and a transistor switch (T1) connected to the microcontroller and controlled thereby for opening and closing the current branch sees*:

12. An electronic circuit according to claim 10 or claim 11- for carrying out the method according to claim 4 characterised in that connected to the outputs of the full-wave rectifier as a voltage divider is a series circuit of two resistors (R3, R4) or series and/or parallel circuits of resistors, wherein the divider tapping of the voltage divider is connected to a measuring input of the microcontroller Datedthis 11 th day of April, 2001. DIEHL AKO STIFTUNG CO. KG By their Patent Attorneys: CALLINAN LAWRIE