Method and apparatus for power control of solar powered display devices

• US 5,196,781 A
• Filed: 02/12/1991
• Issued: 03/23/1993
• Est. Priority Date: 09/14/1990
• Status: Expired due to Term

• Current Assignee: Weiss Instruments, Inc.
• Original Assignee: Weiss Instruments, Inc.
• Inventors: Jamieson, Robert S., Weiss, John
• Primary Examiner(s): HICKEY, ROBERT
• Application Number:
  US07/655,217
• Time in Patent Office: 770 Days
• Field of Search: 323/906, 323/284, 323/285, 320/61, 320/1
• US Class Current: 320/102
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: Y02B 10/70 Hybrid systems, e.g. uninterruptible or back-up power supplies integrating renewable energies
• CPC Class Codes: Y10S 136/291 Applications
• CPC Class Codes: Y10S 136/293 Circuits
• CPC Class Codes: Y10S 320/18 Indicator or display
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

An automatic power control device comprising a passive, non-linear voltage detector controlling a series bipolar transistor regenerative latch circuit, acts to connect the load to a power source only when the voltage obtainable from the power source is sufficient to prevent improper ambiguous operation of the load, and further acts to disconnect the load from the power source when its voltage declines to that range which could result in ambiguous and/or erroneous operation. An electronic thermometric digital display instrument is shown, powered solely by a miniature solar panel. The instrument is amply powered, and the display is legible, even in dim light. Operation at lower levels of light is available with an economical auxiliary battery that is cut out of the circuit at when the light is as little as 5 lux.

Claims

1. A lower power latch circuit for connecting and disconnecting a source of d.c. electric power to and from a load, said source and said load each having first and second means for connections of opposite electric polarity, said source having an output voltage subject to variation, said latch circuit comprising:

first and second bipolar transistors (Q1, Q2) of opposite polarity types, each having emitter, base and collector connections and each having its base connected to the collector of the other, whereby between the respective emitters of said transistors a regenerative latch unit is constituted;

a substantially resistive voltage divider (D1, D2, D3;

R1, R2, R3, Rt) connected between said first and second connection means of said d.c. power source and having a tap connection, which is connected to the base of said first transistor, the emitter of said first transistor being connected to said first connection means of said d.c. power source, the emitter of said second transistor being connected to said first connection means of said load, and the second connection means of said load being connected to the second connection means of said d.c. power source, with the particular electric polarities of said first and second source and load connections and the particular conductivity types of said first and second transistors being suited to each other for operation of said latch unit as a series latch circuit, whereby the voltage divider provides by said tap connection a control of said latch which avoids unstable operation of said latch during relatively low voltage output of said d.c. source.

2. The latch circuit of claim 1, wherein a capacitor (C1) is connected between said first and second connection means of said d.c. power source for providing additional turn-on power to said latch unit and thereby producing rapid latching.

3. The latch circuit of claim 2, wherein said capacitor is an electrolytic capacitor.

4. The latch circuit of claim 1, wherein said resistive voltage divider contains at least one diode for taking advantage of the non-linear conduction characteristic of a diode.

5. The latch circuit of claim 4, wherein the portion of said divider connected between the emitter and base of said first transistor comprises at least one diode (D1, D2) connected for forwardly biased operation.

6. The latch of claim 4, wherein the portion of said divider connected between said tap connection and said second connection means of said d.c. source and of said load comprises a reversely biassed diode (D3).

7. The latch circuit of claim 1, wherein there is connected between said first and second connection means of said load a current leakage path allowing enough leakage therethrough to prevent a current leaking through said latch unit in its unlatched state from causing voltage across said load to increase.

8. The latch circuit of claim 7, wherein said low level leakage diode is a reverse biassed germanium diode.

9. The latch circuit of claim 2, wherein a second capacitor (C2) is connected between the emitter of said second transistor and said second connection means of said d.c. source and of said load, whereby premature unlatching consequence of a transient load condition is preventable.

10. The latch circuit of claim 2, wherein voltage limiting means are connected between said first and second connection means of said load so that said latch circuit may be used with a d.c. voltage source of variable voltage output and a load which is optimally driven at a voltage which, when present, remains within a limited voltage band.

11. The latch circuit of claim 10, wherein said voltage limiting means is a light-emitting diode.

12. The latch circuit of claim 11, wherein said d.c. power source is a solar power panel and said load includes a driver circuit (U1) for a visual display.

13. The latch circuit of claim 12, wherein said load also includes means for measuring a physical condition connected to said driver circuit for display of a physical condition measurement in said visual display.

14. The latch circuit of claim 12, wherein said display driver circuit is part of an integrated circuit which also includes a sample and hold circuit for making intermittent measurements of said physical condition, and wherein a second capacitor (C2) is connected across said load to prevent said intermittent measurements from producing premature unlatching of said latch circuit.

15. A d.c. power supply powered at least in part by a solar panel and capable of powering, unattended in varying light conditions, a load which includes a driver unit (U1) which is optimally driven by a voltage which, when present, remains within a limited voltage band, comprising:

a solar panel having positive and negative output connections;

a first capacitor (C1) having a first terminal connected to a first terminal of said solar panel and also directly connected to a first connection means of a load, said capacitor having a second terminal connected to a second output terminal of said solar panel;

a first transistor (Q2) having a substantially switchable conduction path connected between said second terminal of said first capacitor and a second means of connection of said load and having a control electrode;

voltage detection means (U2, Q1, R, R2, R3, Rt, D1, D2, D3, R4) for detecting a voltage lying above a first lower predetermined voltage value and for producing, at an output connected to said control electrode of said first transistor (Q2), an output signal for turning on said transistor after said voltage exceeds a second higher predetermined voltage value, which voltage to be detected is a voltage that rises and falls with a voltage contemporaneously present between said first and second terminals of said capacitor;

voltage limiting means (D4) for defining an upper limit of said limited voltage band, and

means interconnecting said transistor (Q2) and said voltage detector (U2, Q1) for accelerating turn-on of said transistor and for keeping said transistor turned on, after being turned on, during continued presence of said output signal of said voltage detector.

16. The d.c. power supply of claim 15, wherein said voltage detection means comprises a second transistor (Q1) of a polarity type opposite to that of said first transistor (Q2) and a resistive voltage divider (D1, D2, D3, R4;

R1, R2, R3, Rt) having a tap connection connected to a control electrode of said second transistor and being connected between said first and second terminals of said first capacitor, said means for keeping said first transistor turned on being the connection of said switchable conduction path of said first transistor (Q2) between said tap of said voltage divider and said second connection of said load while said second transistor (Q1) has a switchable conduction path interposed between said control electrode of said first transistor and said second terminal of said first capacitor (C1).

17. The power supply of claim 16, wherein said first polarity connection for said load is connected to the negative output connection of said solar panel, said second polarity connection for said load is connected to the emitter of said first transistor (Q2), the positive output connection of said solar panel is connected to the emitter of said second transistor (Q1) is of the NPN polarity type and said second transistor is of the PNP polarity type.

18. The power supply of claim 16, wherein said first capacitor is an electrolytic capacitor.

19. The power supply of claim 16, wherein said voltage divider contains at least one diode for taking advantage of the non-linear conduction characteristic of a diode.

20. The power supply of claim 16, wherein the portion of said divider connected between the emitter and base of said second transistor (Q1) comprises at least one diode (D1, D2) connected for forwardly biassed operation.

21. The power supply of claim 16, wherein the portion of said divider between said tap connection and said first one of said output connections of said solar panel comprises a reversely biassed diode (D3).

22. The power supply of claim 16, wherein a diode (D5), for allowing current leakage of a very low level to prevent current leaking through said said transistors in their non-conducting states from causing the voltage across said load to increase, is connected between said first polarity load connection and said load connection for a polarity opposite to said first polarity.

23. The power supply of claim 22, wherein said low level leakage diode is a reverse biassed germanium diode.

24. The power supply of claim 16, wherein a capacitor (C2) is connected between the emitter of said first transistor (Q2) and said load connection of said first polarity for preventing premature unlatching of the power supply from the load in consequence of a transient load condition.

25. The power supply of claim 16, wherein voltage limiting means (D4) are connected between the emitter connection of said first transistor (Q2) and said load connection of first polarity.

26. The power supply of claim 25, wherein said voltage limiting means is a light-emitting diode.

27. The power supply of claim 16, wherein said load includes a driver circuit for a visual display and means for measuring a physical condition connected to said driver circuit for display of a physical condition measurement.

28. The power supply of claim 27, wherein said display driver circuit is part of an integrated circuit which also includes a sample and hold circuit for making intermittent measurements of said physical condition, and wherein a second capacitor (C2) is connected across said load to prevent said intermittent measurements from producing premature unlatching of said latch circuit.

35. The power supply of claim 16, powered exclusively by said solar panel.

36. The power supply of claim 16, powered exclusively by said solar panel.

37. The power supply of claim 16, further comprising:

an auxiliary battery for assistance at low light levels, said battery having a first terminal connected to said first output connection of said solar panel, said first a battery terminal being of the same polarity as said first solar panel output connection, said battery having a second terminal connected through a first auctioneer diode (D7) to a circuit point to which said emitter of said second transistor (Q1) is connected,

a second auctioneer diode (D6) being interposed in circuit between the second output connection of said solar battery and said circuit point to which said emitter of said second transistor is connected,

the voltage of said battery and the resistance value of at least said second auctioneer diode being so chosen that in darkness greater than a first threshold light level said latch unit is unlatched, in a band of light levels just above said first threshold light level both said solar panel and said auxiliary battery supply power to said load and at light levels above a second threshold light level only said solar panel supplies power to said load.

38. The power supply of claim 37, wherein a current limiting means (R5) is interposed in series with said first auctioneer diode (D7) between said auxiliary battery and said circuit point to which said emitter of said second transistor (Q2) is connected.

39. The power supply of claim 37, wherein said first polarity connection for said load is connected to the negative output connection of said solar panel, said second polarity connection for said load is connected to the emitter of said first transistor (Q2), the positive output connection of said solar panel is connected through said second auctioneer diode (D6) to the emitter of said second transistor (Q1) said second transistor (Q1) is of the PNP polarity type, and said first transistor (Q2) is of the NPN polarity type.

40. The power supply of claim 37 wherein said first capacitor (C1) is an electrolytic capacitor.

41. The power supply of claim 37, wherein said resistive voltage divider contains at least one diode for taking advantage of the non-linear conduction characteristic of a diode.

42. The power supply of claim 37, wherein the portion of said divider connected between the emitter and base of second transistor (Q1) comprises at least one diode (D1, D2) connected for forwardly biassed operation.

43. The power supply of claim 37, wherein the portion of said divider between said tap connection and said first one of said output connections of said solar panel comprise a reversely biassed diode (D3).

44. The power supply of claim 37, wherein a resistive leakage path is connected between said first polarity load connection and said load connection for a polarity opposite to said first polarity to prevent current leaking through said first transistor (Q2) in its nonconductive state from causing the voltage across said load to increase.

45. The power supply of claim 37, wherein said low level leakage diode is a reverse biassed germanium diode (D5).

46. The power supply of claim 37, wherein a second capacitor (C2) is connected between the said load connections of first and second polarity for preventing premature unlatching of the power supply from said load in consequence of a transient load condition.

47. The power supply of claim 46, wherein voltage limiting means are connected between the said load connections of first and second plurality.

48. The power supply of claim 37, wherein said voltage limiting means is a light-emitting diode.

49. The power supply of claim 37, wherein said load includes a driver circuit for a visual display and means for measuring a physical condition connected to said driver circuit for display in said liquid crystal display of a physical condition measurement.

50. The power supply of claim 49, wherein said display driver circuit is part of an integrated circuit which also includes a sample and hold circuit for making intermittent measurements of said physical condition, and wherein a second capacitor (C2) is connected across said load to prevent said intermittent measurements from producing premature unlatching of of the power supply from the load.

61. The d.c. power supply of claim 15 powered by said solar panel, with economical battery assistance at low levels of light, and capable of unattended supply of power to a load in widely varying light conditions, further comprising:

a battery having positive and negative output connections, said first capacitor (C1) having its first terminal connected to respective first output connections of said solar panel and of said battery which are of the same polarity and are also directly connected to said first connection means of a load;

a first auctioneer diode (D6) connected between a second output connection of said solar panel and said second terminal of said first capacitor (C1);

a second diode (D7) connected between a second output connection of said battery and said second terminal of said first capacitor (C1);

said means for accelerating turn-on of said transistor including a first resistive path (R6) connected between said control electrode of said transistor and said second terminal of said capacitor for

said voltage detection means (U2) having a second resistive path (D9, D9) connected between an input of said voltage detection means and said second terminal of said first capacitor for setting said second predetermined voltage.

62. The power supply of claim 61, wherein a current limiting means (R5) is interposed in series with said second auctioneer diode (D7) between said battery and said capacitor (C1).

63. The power supply of claim 61, wherein said second resistive path includes at least one diode.

64. The power supply of claim 67, wherein said third resistive path includes a reverse-biased germanium diode.

65. The power supply of claim 61, wherein a voltage-limiting means (D4) is connected between said first and second connection means of said load.

66. The power supply of claim 65, wherein said voltage-limiting means is a light-emitting diode.

67. The power supply of claim 61, wherein said load is incorporated in an integrated circuit which includes a sample-and-hold circuit for performing intermittent operations, wherein a second capacitor (C2) is connected across said load to prevent said intermittent operations from prematurely turning off said transistor and wherein

a third resistance path (R7) is connected between said first and second connection means of said load for rapidly diminishing electric charge stored in said second capacitor to a value insufficient to power an ambiguous operation of said load when said output signal of said voltage direction means (U2) terminates.

29. A method of powering by solar energy an electronic instrument having a visual display without the provision of an auxiliary battery, comprising:

charging a first capacitor, which is permanently connected to a solar panel, by electric current produced by said solar panel;

operating a regenerative bipolar transistor latch unit connected in series with power input connections of said instrument and in series with said solar panel, under control of a substantially resistive voltage divider connected in parallel with said first capacitor and having a tap connection to which a control connection of said latch unit is connected, said latch unit comprising first and second bipolar transistors of opposite polarity types, each having a base electrode connected to a collector electrode of the other, said second transistor having an emitter electrode connected to a first polarity power input connection of said instrument and said first transistor having an emitter electrode connected to a corresponding output connection of said solar panel and having a base electrode connected, for operation as a control electrode of said latch unit, to said tap connection of said voltage divider, and

limiting the voltage of power supplied to said input connections of said instrument by means of a voltage limiter diode.

30. The method of claim 29, wherein said voltage limiter diode is a light-emitting diode.

31. The method of claim 29, in which advantage is taken of the non-linear conduction characteristics of diodes for controlling said latch unit by providing at least one diode in said voltage divider.

32. The method of claim 29, wherein a second capacitor connected in parallel to said power inputs of said instrument is charged through said latch unit, whereby transient changes in the amount of current delivered to said power input connections of said instrument are prevented from prematurely unlatching said latch unit.

33. The method of claim 29, wherein a slight but inevitable leakage current through said latch unit in its unlatched condition is prevented from building excessive potential across said power input connections of said instrument by means of a current leakage path connected across said power input connections.

34. A method of charging a storage battery over a wide range of light conditions by means of a solar panel assembly, comprising:

charging a first capacitor which is permanently connected to a solar panel assembly by electric current produced by said solar panel assembly, and

operating a regenerative bipolar transistor latch unit connected in series with said storage battery and with said solar panel, under control of a substantially resistive voltage divider connected in parallel with said first capacitor and having a tap connection to which a control connection of said latch unit is connected, said latch unit comprising first and second bipolar transistors of opposite polarity types, each having a base electrode connected to a collector electrode of the other, said second transistor having an emitter electrode connected to a first polarity power input connection of said instrument and said first transistor having an emitter electrode connected to a corresponding output connection of said solar panel and having a base electrode connected, for operation as a control electrode of said latch unit, to said tap connection of said voltage divider.

51. A method of powering by solar energy, economically assisted by a battery, an electronic instrument having a visual display, comprising:

charging a first capacitor (C1) by electric current produced by said solar panel or said battery or both, said capacitor (C1) having a first terminal which is connected to a first terminal of a solar panel through a first auctioneer diode (D6) and is connected to a first terminal of a battery through a second auctioneer diode (D7), said capacitor having a second terminal connected to second terminals respectively of said solar panel and said battery both of the same polarity;

operating a regenerative bipolar transistor latch unit connected in series with power input connections of said instrument and in series through said auctioneer diodes respectively with said solar panel and said battery, under control of a substantially resistance voltage divider connected in parallel with said first capacitor and having a tap connection to which a control connection of said latch unit is connected, said latch unit comprising first and second bipolar transistors of opposite polarity types, each having a base electrode connected to a collector electrode of the other, said second transistor having an emitter electrode connected to a first polarity power input connection of said instrument and said first transistor having an emitter electrode connected to a corresponding output connection of said solar panel and having a base electrode connected, for operation as a control electrode of said latch unit, to said tap connection of said voltage divider, and

limiting the voltage of power supplied to said input connections of said instrument to a voltage band lying between an upper limit set by means of a voltage limiter diode connected between said first and a second terminal of said instrument and a lower limit set by said voltage divider including any extension thereof connected to said battery (R5).

52. The method of claim 51, wherein said voltage limiter diode is a light-emitter diode.

53. The method of claim 51, in which advantage is taken of the non-linear conduction characteristics of diode for controlling said latch unit by providing at least one diode in said voltage divider.

54. The method of claim 51, wherein a second capacitor (C2) connected in parallel to said power inputs of said instrument is charged through said latch unit, whereby transient changes in the amount of current delivered to said power input connections of said instrument are prevented from prematurely unlatching said latch unit.

55. The method of claim 51, wherein a slight but inevitable leakage current through said latch unit in its unlatched condition is prevented from building excessive potential across said power input connections of said instrument by a current leakage path connected across said power input connections of said instrument.

56. A low-power latch circuit for connecting and disconnecting a source of d.c. electric power to and from a load, said source and said load each having first and second means respectively for connections of opposite electric polarity said source having an output voltage subject to variation and having a first capacitance (C1) connected between its said first and second connection means, said latch circuit comprising:

a transistor (Q2) having a switchable conduction path connected between said first connection means of said source and said first connection means of said source and having a control electrode, said second connection means of said source and of said load being connected together;

voltage detection means (U2) for detecting a voltage lying above a first lower predetermined voltage and providing an output signal when a second higher predetermined voltage is exceeded, which voltage to be detected is a voltage present between said first and second connection means of said source and having an output for said output signal connected to said control electrode of said transistor for turning on said transistor after said second predetermined voltage is exceeded, a first resistive path (R6) being connected between said control electrode of said transistor and a said connection of said source for providing turn-on bias for said transistor during presence of said output signal of said voltage detection means and

a second resistive path (R5, D9) connected between an input of said voltage detection means and said first connection means for setting said second predetermined voltage.

57. The latch circuit of claim 56, wherein said second resistive path includes at least one diode.

58. The latch circuit of claim 56, further comprising:

a second capacitance (C2) connected between said first and second connection means of said load, and

a third resistance path (R7) connected between said first and second connection means of said load for rapidly diminishing electric charge stored in said second capacitor to a value insufficient to power an ambiguous operation of said load when said output signal of voltage detection means (U2) terminates.

59. The latch circuit of claim 56, wherein a voltage-limiting means (D4) is connected between said first and second connection means of said load, whereby power is deliverable to said load at a voltage not less than said second predetermined voltage and not more than a value set by said voltage limiting means.

60. The latch circuit of claim 59, wherein said voltage-limiting means is a dark light-emitting diode.

68. A method of powering by solar energy, with economical assistance of a battery at low light levels, an electronic instruments having a liquid crystal display, comprising:

charging a first capacitor by said battery during essentially total darkness, by said battery and said solar panel together from a first threshold light level in a band lying between 2 and 8 lux up to a second threshold light level in the band between 30 and 40 lux and exclusively by said solar battery at above said second threshold light level;

supplying voltage present across said capacitor to a voltage detector (U2) for providing an output signal to a control electrode of a transistor (Q2) having its switched path connected between a terminal of said capacitor and a terminal of said load, for turning on said transistor when a predetermined voltage is reached in said voltage detector where said voltage is reduced by a diode chain (D8, D9);

as soon as said transistor is turned on, keeping said transistor turned on, by means of a resistance path (R6) between said control electrode of said transistor and an electrode of said transistor connected to said capacitor, until a voltage above or near said predetermined voltage no longer is present as aforesaid in said voltage detector;

limiting the availability to said load of power from said battery by provision of auctioneer diodes (D6, D7) through which said solar panel and said battery are respectively connected to said first capacitor, and

preventing leakage current through said transistor, when said transistor is turned off, from accumulating a charge in said load, by providing a leakage path resistance across said load.

69. The method of claim 68 wherein said leakage path is provided by a reverse-biassed germanium diode (D5).

70. The method of claim 68, in which voltage across the load is limited so as to supply only a narrow band of power supply output voltage to the load, with the lower limit being set by resistance elements (R5, D8, D9) and the voltage detector and the upper limit of said narrow band being set by voltage limiting means connected across the load.

71. The method of claim 68, in which intermittent operations that may occur in said load are prevented from prematurely turning off said transistor by the provision of a second capacitor (C2) connected across said load.