GB2026739A - Voltage regulation - Google Patents

Voltage regulation Download PDF

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Publication number
GB2026739A
GB2026739A GB7924512A GB7924512A GB2026739A GB 2026739 A GB2026739 A GB 2026739A GB 7924512 A GB7924512 A GB 7924512A GB 7924512 A GB7924512 A GB 7924512A GB 2026739 A GB2026739 A GB 2026739A
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GB
United Kingdom
Prior art keywords
circuit
voltage
power source
reference voltage
battery
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.)
Granted
Application number
GB7924512A
Other versions
GB2026739B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Seiko Instruments Inc
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Seiko Instruments Inc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Seiko Instruments Inc filed Critical Seiko Instruments Inc
Publication of GB2026739A publication Critical patent/GB2026739A/en
Application granted granted Critical
Publication of GB2026739B publication Critical patent/GB2026739B/en
Expired legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G04—HOROLOGY
    • G04G—ELECTRONIC TIME-PIECES
    • G04G19/00—Electric power supply circuits specially adapted for use in electronic time-pieces
    • G04G19/02—Conversion or regulation of current or voltage
    • G04G19/06—Regulation
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromechanical Clocks (AREA)
  • Electric Clocks (AREA)

Abstract

A voltage regulator for an electronic timepiece comprises a MOS transistor, a reference voltage generating circuit 14 to receive the voltage A from a battery and to produce a reference voltage at C which is less than the battery voltage, a control circuit 12 (a switching MOS transistor) which also receives the battery voltage, and a comparator circuit 13 which compares the reference voltage with the output voltage of the control circuit. The comparator output is connected to the control circuit 12 so that the regulator output voltage is substantially independent of fluctuations of battery voltage. Due to the negative temperature coefficient of the MOS transistors in the circuit 14, a liquid crystal display fed from the regulator will produce a good contrast display over a broad temperature range. <IMAGE>

Description

SPECIFICATION Power source circuit This invention relates to power source circuits for example for electronic timepieces.
Nowadays, quartz crystal electronic timepieces are highly accurate timekeeping devices, such timepieces being either analog or digital. It is now desired to produce a multifunctional electronic timepiece which has a long battery life. With respect to a long battery life of an electronic timepiece, one method is to attain lower power dissipation of an oscillator circuit and another method is to use a solar cell which charges a secondary cell at high efficiency. Moreover, power consumption can be reduced using multiplex driving or time sharing technology in order to display many different forms of data in the limited display area of a liquid crystal display device, to achieve multifunctional digital electronic timepiece.
In conventional electronic timepieces the battery voltage is fed to electronic circuitry including an oscillator circuit, a frequency divider circuit, an operation and control circuit, and a driving circuit. Variation of battery voltage affects the functioning of the electronic timepiece and, in particular, causes variation of the osciliating frequency of the oscillator circuit which leads to instability of the timekeeping accuracy and may even cause the oscillator circuit to stop and variation of the battery voltage will also lower the contrast of the liquid crystal display device.
According to one aspect of the present invention there is provided a power source circuit comprising: a reference voltage generating circuit connected to receive a battery voltage and to produce a reference voltage which is less than the battery voltage; a control circuit connected to receive the battery voltage; and a comparator circuit for comparing the reference voltage with the output voltage of the control circuit, the output signal of the comparator circuit being connected to the control circuit to control operation thereof so that the output voltage of the control circuit is substantially constant and substantially independent of fluctuations of the battery voltage.
Preferably the reference voltage generating circuit has negative temperature characteristics.
In the preferred embodiment the reference voltage generating circuit comprises a plurality of MOS transistors connected in series so that the reference voltage is equal or substantially equal to the sum of the threshold voltages of said MOS transistors.
A latching circuit may be provided for storing the output signal of the comparator circuit.
A control circuit may include time constant means.
According to a further aspect of the present invention there is provided an electronic timepiece including timekeeping circuitry and a power source circuit as recited above arranged to drive the timekeeping circuitry.
Preferably the power source circuit is fabricated on a single integrated circuit chip with the timekeeping circuitry.
The invention is illustrated, merely by way of example, in the accompanying drawings, in which: Figure 1 is a block diagram of an electronic timepiece according to the present invention; Figure 2 is a block diagram of a power source circuit according to the present invention; Figure 3(a) is a circuit diagram of the power source circuit of Figure 2; Figure 3(b) is a circuit diagram of an energising circuit of the power source circuit of Figure 3(a); Figure 4 is a circuit diagram of a comparator of the power source circuit of Figure 3(a); Figures 5(a) and 5(b) illustrate, by voltage waveforms and a timing chart, the operation of the comparator of Figure 4; Figure 6 shows the temperature characteristics of a liquid crystal display device of the electronic timepiece of Figure 1; and Figure 7 shows the temperature characteristics of the power source circuit of Figure 3(a).
Figure 1 illustrates a digital electronic timepiece according to the present invention. A battery 1 is connected to a power source circuit 2 forming part of an integrated circuit 11. The power source circuit 2 according to the present invention produces an output voltage below the voltage of the battery 1 and applies the voltage to an oscillator circuit 3, a frequency divider circuit 4, an operational or counter circuit 5, a decoder circuit 6, a booster circuit 8, and a control circuit 10. A relatively high frequency oscillating circuit from the oscillator circuit 3 is fed to the divider circuit and is frequency divider to produce a relatively low frequency signal. The low frequency signal is fed to the counter circuit 5 and the latter counts time and produces a counting signal which is fed to the decoder circuit 6 where it is converted into a display signal.A driving circuit 7, which receives the display signal, causes a liquid crystal display device 9 to display time information. The control circuit 10 produces a control signal for controlling the counter circuit 5 and the driving circuit 7. The boosting circuit 8 steps up two or three times the output voltage of the power source circuit 2 and the resulting boosted voltage is used as a driving voltage to the driving circuit 7.
Figure 2 shows the construction of the power source circuit 2. The voltage of the battery 1 is fed to an input terminal A of the power source circuit 2. The power source circuit 2 consists of a control circuit 12, a reference voltage generating circuit 14 and a comparator circuit 1 3. The output voltage of the reference voltage generating circuit 1 4 is fed to the comparator 1 3.The output voltage of the control circuit 1 2 is also fed to the comparator 1 3. The output voltage of the reference voltage generating circuit 1 4 is thus compared with the output voltage of the control circuit 1 2 by the comparator 1 3. The output signal of the comparator 13 serves as a control signal so that the output voltage of the control circuit 1 2 becomes equal or substantially equal to the output voltage of the reference voltage generating circuit 14. Accordingly, the output voltage of the control circuit 1 2 produces a power source voltage which is substantially equal to the output voltage of the reference generating circuit but independent or substantially independent of the variation of the battery voltage.The reference voltage generating circuit may consist of elements having the same negative temperature characteristics as other electronic circuit eiements of the electronic timepiece.
Figure 3(a) is a circuit diagram of the power source circuit 2. The terminal A of the reference voltage generating circuit 14 is connected to the source of a P channel MOS transistor 23 and a resistor 32 is connected to the drain thereof. One terminal of the resistor 32 is connected in series with N channel MOS transistors 24, 25, 26. The source of the transistor 26 is grounded. The gate terminal of each of the transistors 24,25,26 is connected with its drain. The drain of the transistor 24 is connected to capacitor 31 through an N channel MOS transistor 27. The control circuit 12 includes a P channel MOS transistor 28 whose drain is grounded via a resistor 29 and a capacitor 30. The source of the transistor 28 is connected to the input terminal A.An output terminal C of the reference voltage generating circuit and an output terminal B of the control circuit 1 2 are connected to the comparator 1 3. An output terminal D of the comparator 13 is connected to the drain of the transistor 28. The output of an energising circuit 20 and a sample pulse q) are fed to inputs of a NOR circuit 21. The output of the NOR circuit 21 is applied to the gate of the transistor 23 and the input terminal of an inverter 22. The output of the inverter 22 is applied to the gate of the transistor 27.
Next, the operation of the power source circuit 2 will be described. The transistors 23, 27 are switched to the ON state when the sampling pulse is applied to the NOR circuit 21. The capacitor 31 is charged to a voltage of 3Vth (1.41 V) existing between the drain of the transistor 24 and ground since the transistors 24, 25, 26 operate in the saturation region, if the threshold voltage Vth of each of the transistors 24, 25, 26 is 0.47V. The voltage at the terminal C of the capacitor 31 is held as the reference voltage since the transistors 23, 27 are switched to the OFF state. The transistor 28 is switched to the ON state since the output signal at the terminal D of the comparator 1 3 becomes logic "0" (ground) when the voltage at the terminal B of the control circuit 12 is lower than that at the terminal C.A voltage Eo at the terminal B is given by Eo = Eie-'CR where Ei is the input voltage, C is the capacity of the capacitor 30 and R is the resistance of the resistor 29. The transistor 28 is switched to the OFF state since the voltage at the terminal D of the comparator 13 becomes logic "1" when Eo > 3Vth. The voltage at the terminal D falls with discharge of the capacitor 30 with a time constant T=CR. The output at the terminal D of the comparator 13 becomes logic "0" when the voltage at the terminal B is below the voltage at the terminal C. Accordingly, the transistor 28 is switched to the ON state. The operation described above is repeated when the next sampling pulse appears.
Consequently, the output voltage at the terminal B becomes substantially equal to the voltage of the terminal C of the reference voltage generating circuit 14.
The sampling pulse is an intermittent pulse signal which causes the transistor 23 to switch to the ON state intermittently to reduce current dissipation.
The transistor 27 executes a switching action to cut the discharging path. Therefore, the power source circuit 2 has relatively low power consumption as a result of providing the sampling pulse so that the voltage at the terminal C is not below or above the reference voltage. The energising circuit 20 is used to create stable operation of the power source circuit and determines the initial state of the power source circuit. Namely, the energising circuit 20 generates a one shot pulse compulsorily on energisation and applies it to the NOR circuit 21.
Thus, for example, when the battery 1 is inserted into the electronic timepiece, the energising circuil 20 creates a one shot pulse compulsorily so that the capacitor 31 holds the reference voltage and the transistor 28 is switched to the ON state for operating the power source circuit. The energising circuit 20 may be a differential circuit using a capacitor 50 and a resistor 51 as shown in Figure 3(b).
Figure 4 is a circuit diagram of the comparator 13 which is of low power consumption. An N channel MOS transistor 40 determines whether or not the input voltage level at the terminal B is higher than that at the terminal C. The output of the comparator 1 3 is stored by a latching circuit 41. A signal E derived from the output terminal of the latching circuit 41 is used as a control signal to the transistor 28 of the control circuit 12 and this measure decreases power dissipation. The READ IN action of the latching circuit 41 is made by a timing signal S from the divider circuit 4.
Figures 5(a) and 5(b) illustrate the signals of the comparator shown in Figure 4 and the relation between the output voltage B of the control circuit 12 and the reference voltage C.
The power source circuit 2 may be used in a temperature compensated multiplex drive system for a liquid crystal display device of an electronic timepiece such as that shown in Figure 1. Figure 6 shows the relation between driving voltage and temperature in the case of two dividing drive according to 1/2 bias driving method. It is known that cross-talk phenomenon is produced when the voltage applied to a non-selective point of the liquid crystal display device -- that is a point which is not required to produce a display at any given instant -- exceeds the threshold voltage of liquid crystal material of the liquid crystal display device, as the voltage is applied to the non selective point in the case of a time sharing system.Also the liquid crystal display device cannot produce a good contrast display since the voltage applied to a selective point - that is a point of the liquid crystal display device which is required to produce a display at any given instant - is below the saturation voltage Vsat of the liquid crystal material in the case of a low driving voltage.
Curve 1 of Figure 6 shows the voltage 2E when the liquid crystal material at a selected point begins to saturate. Curve 2 shows the variation of the reference voltage Eo depending upon the temperature when the liquid crystal material on the non-selective point begins to produce crosstalk phenomenon. The cross-talk phenomenon occurs at a temperature of about 400C when the reference voltage Eo is equal to a battery voltage of 1.5V.
As will be appreciated from Figure 6, the reference voltage Eo needs to have negative temperature characteristics because the threshold voltage of the liquid crystal material also has negative temperature characteristics so that the liquid crystal display device will produce a display with a good contrast over a broad temperature range. The reference voltage generating circuit 14 of the power source circuit produces the reference voltage as a function of the threshold voltage Vth of the transistors 24, 25, 26 and it is known that the temperature characteristic of the threshold voltage of MOS transistors is also negative.
Figure 7 shows the temperature characteristic of the threshold voltage of the reference voltage.
The temperature coefficient of the threshold voltage of a single MOS transistor is --2mv/OC and so the threshold voltage of three MOS transistors in series such as the transistors 24, 25, 26 is about 6mv/CC. Accordingly, the operational temperature range of the electronic timepiece of Figure 1 with a multiplex drive system is enlarged.
the threshold voltage of the MOS transistors 24, 25, 26 may be ion implantation technology and the reference voltage may be controlled by the fabrication process requirements. The major proportion of the electronic timepiece may be fabricated on a single IC chip as it consists of MOS transistors. The power source circuit described above has low power dissipation and this enables an electronic timepiece in which it is used also to have lower power dissipation and to be driven by low voltage which is below the battery voltage.
The power source circuit produces a constant or substantially constant voltage in spite of variation of the battery voltage so that instability of the oscillation frequency of an oscillator circuit of an electronic timepiece and the variation of display contrast of a liquid crystal display device thereof due to variation of battery voltage are eliminated.

Claims (10)

1. A power source circuit comprising: a reference voltage generating circuit connected to receive a battery voltage and to produce a reference voltage which is less than the battery voltage; a control circuit connected to receive the battery voltage; and a comparator circuit for comparing the reference voltage with the output voltage of the control circuit, the output signal of the comparator circuit being connected to the control circuit to control operation thereof so that the output voltage of the control circuit is substantially constant and substantially independent of fluctuations of the battery voltage.
2. A power source circuit as claimed in claim 1 in which the reference voltage generating circuit has negative temperature characteristics.
3. A power source circuit as claimed in claim 1 or 2 in which the reference voltage generating circuit comprises a plurality of MOS transistors connected in series so that the reference voltage is equal or substantially equal to the sum of the threshold voltages of said MOS transistors.
4. A power source circuit as claimed in any preceding claim in which a latching circuit is provided for storing the output signal of the comparator circuits.
5. A power source circuit as claimed in any preceding claim in which the control circuit includes time constant means.
6. A power source circuit substantially as herein described with reference to and as shown in the Figures 2 to 7 of the accompanying drawings.
7. An electronic timepiece including timekeeping circuitry and a power source circuit as claimed in any preceding claim arranged to drive the timekeeping circuitry.
8. An electronic timepiece as claimed in claim 7 in which the power source circuit is fabricated on a single integrated circuit chip with the timekeeping circuitry.
9. An electronic timepiece as claimed in claim 7 and substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.
10. In an electronic timepiece having a battery, an oscillator circuit, a divider circuit and a time counter, the improvement comprising a power source circuit having a reference voltage generating circuit producing a reference voltage below a voltage of the battery and a comparator for comparing an output voltage of the reference voltage generating circuit with an output voltage of a control circuit which is controlled by the output of the comparator, whereby an output voltage of the control circuit is adjusted into constant voltage.
GB7924512A 1978-07-19 1979-07-13 Voltage regulation Expired GB2026739B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP8805978A JPS5515056A (en) 1978-07-19 1978-07-19 Electronic watch

Publications (2)

Publication Number Publication Date
GB2026739A true GB2026739A (en) 1980-02-06
GB2026739B GB2026739B (en) 1982-12-22

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ID=13932264

Family Applications (1)

Application Number Title Priority Date Filing Date
GB7924512A Expired GB2026739B (en) 1978-07-19 1979-07-13 Voltage regulation

Country Status (3)

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JP (1) JPS5515056A (en)
GB (1) GB2026739B (en)
HK (1) HK884A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3239432A1 (en) * 1981-12-08 1983-06-16 Intersil Inc., 95014 Cupertino, Calif. MONOLITHIC VOLTAGE DIVIDER
EP0257404A2 (en) * 1986-08-28 1988-03-02 International Business Machines Corporation Power conversion with reduced switching loss
US7469174B2 (en) * 2005-07-15 2008-12-23 Mitsubishi Denki Kabushiki Kaisha Vehicle-borne electronic control device

Families Citing this family (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56144381U (en) * 1980-03-31 1981-10-30
JPS576384A (en) * 1980-06-13 1982-01-13 Hitachi Ltd Power source circuit and electronic watch using this
US4436648A (en) * 1980-12-22 1984-03-13 Bell Telephone Laboratories, Incorporated Electrically conducting thermoplastic material, its manufacture, and resulting article
JPS57137874A (en) * 1981-02-20 1982-08-25 Hitachi Ltd Electronic watch
EP0083336B1 (en) * 1981-07-13 1986-11-05 ADLER-NIETZHOLD, Brunhilde Electronic apparatus
JPS60174888U (en) * 1984-04-27 1985-11-19 カシオ計算機株式会社 Small electronic equipment with solar battery

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5228366A (en) * 1975-08-28 1977-03-03 Shimauchi Seiki Kk Voltage detection circuit
JPS53845A (en) * 1976-06-25 1978-01-07 Matsushita Electric Ind Co Ltd Power source
JPS533864A (en) * 1976-06-30 1978-01-13 Seiko Instr & Electronics Ltd Electronic watch

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3239432A1 (en) * 1981-12-08 1983-06-16 Intersil Inc., 95014 Cupertino, Calif. MONOLITHIC VOLTAGE DIVIDER
EP0257404A2 (en) * 1986-08-28 1988-03-02 International Business Machines Corporation Power conversion with reduced switching loss
EP0257404A3 (en) * 1986-08-28 1989-06-14 International Business Machines Corporation Power conversion with reduced switching loss
US7469174B2 (en) * 2005-07-15 2008-12-23 Mitsubishi Denki Kabushiki Kaisha Vehicle-borne electronic control device

Also Published As

Publication number Publication date
GB2026739B (en) 1982-12-22
HK884A (en) 1984-01-13
JPS5515056A (en) 1980-02-01

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Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19920713