CA1226622A - Current overload detector - Google PatentsCurrent overload detector
- Publication number
- CA1226622A CA1226622A CA000450648A CA450648A CA1226622A CA 1226622 A CA1226622 A CA 1226622A CA 000450648 A CA000450648 A CA 000450648A CA 450648 A CA450648 A CA 450648A CA 1226622 A CA1226622 A CA 1226622A
- Prior art keywords
- voltage drop
- 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.)
- 230000015556 catabolic process Effects 0.000 claims description 4
- 238000000034 methods Methods 0.000 description 1
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
A voltage drop develops across a thermistor connected between a power source and a load in pro-portion to the current draw. A zoner diode becomes conductive in the reverse direction when the voltage drop increases to a threshold, thereby connecting the voltage drop to a light emitting diode (LED).
For detecting excessive current draw, the LED is normally off.
This invention relates to the detection of current overloads by solid state means.
historically, power systems utilized fuses or circuit breakers for protection against faults in wiring or loads. Both means isolate faults by mock-animally breaking contact with the power source.
Both means are dependent on a thermal reaction to circuit overload currents, thus are slow and tempt erasure dependent. The thermal element of a fuse is destroyed in the isolation process, while circuit breakers are large and heavy as compared to circuit i components.
Therefore, it is an objection of this invention to protect power sources and distribution equipment from faults in wiring or loads using solid state means that are space and weight efficient. It is a further object to provide for protection with-out necessarily disconnecting the faulty circuit or load. It is another object to detect current over-load conditions.
In accordance with a particular embodiment circuit for providing an indication of an excessive current drain on a DC source by a load and for limit-in the current drain on the source by the load includes a thermistor connected between the source and the load for providing a voltage drop indicative of the current drain and for limiting the current drain, wherein the resistance of the thermistor in-creases in proportion to the current there through.
A light emitting diode (LED) is connected in forward bias across the thermistor for providing the indict-lion of excessive current drain when energized. A
zoner diode is connected in reverse bias in series with the LED across the thermistor so that the LED
is energized when the voltage drop is at least the reverse breakdown voltage of the zoner diode.
According to the invention, a power source is connected to a load by a thermistor. Under normal operating conditions the voltage drop across the thermistor is small. When the load draws excess current (fault), such as in a short circuit, the voltage drop across the thermistor increases, non-linearly. In response to a threshold voltage drop across the thermistor, a zoner diode becomes conduct-ivy in the reverse direction (reverse breakdown) and flows current to an indicator, such as an LED.
The foregoing and other objects, features and advantages of the present invention, will become more apparent in the light of the following detailed description of the invention.
Figure 1 is a schematic of a prior art current overload detector circuit.
Figure 2 is a schematic of the current over-load detector circuit of this invention.
Figure 1 shows a prior art current overload detector circuit. A resistor 10 is connected between a source 12 and a load 14. As load current increases, the voltage drop across the resistor 10 increases, linearly, according to Ohm's law (E = IT). A-t a threshold voltage drop, a zoner diode 16 connected in reverse bias across the resistor 10 becomes conductive and flows current through a series-connected light emitting diode 18. Illumination of the LED is indict-live of a current overload. This basic concept is disclosed in I. S. Patent No. 4,418,342 (Aschoff, 1983). In Figure 2 therein, the elements are a nests-ion 1, a zoner diode 8', and an LED 6'.
Consider the following example. The load 14 draws 1.0 - 2.0 milliamps under normal operating condo-lions. It is desirable to indicate a current overload at currents above 2.0 milliamps. The combination of a 12 volt zoner diode and a 6000 ohm resistor will :~266Z2 illuminate the LED at exactly 2.0 milliamps (discount-in forward thresholds in the LED). However, the voltage drop will fluctuate from 6.0 to 12.0 volts under normal operating conditions. Such a wide range of voltages may be highly undesirable. Furthermore, the 6000 ohm resistor will consume as much as 0.024 watts of power under normal operating conditions, and more under fault conditions.
Suppose, however, that a 4000 ohm resistor were used. Power consumption would be reduced by one-third and there would be less voltage fluctuation (4 to 8 volts) under normal operating conditions.
However, the zoner diode would not reach reverse breakdown until 3.0 milliamps of current were drawn by the load. Thus, there would be a 'dead band" of non detection between 2.0 and 3.0 milliamps.
With a 2000 ohm resistor, the voltage flue-tuition at normal operating current would be 2.0 to 4.0 volts, but the dead band would be between 2.0 and 6.0 milliamps.
As is readily concluded from the above examples, there is a tradeoff involved in the use of a resistor as the voltage drop means in the current overload detector circuit. The present invention overcomes these limitations.
Figure 2 shows the current overload detector circuit of this invention. A nonlinear resistive element, such as a thermistor 20 is connected between a source 22 and a load 24. The resistance of the thermistor 20 increases in proportion to the current there through. As in the circuit of Figure 1, at a threshold voltage, a threshold conductivity means, such as a zoner diode 26 connected in reverse bias across the thermistor 20, becomes conductive and flows current through a series connected indicator means, such as a forward-biased LED 28. Illumine-lion of the LED 28 is indicative of a current overload.
~Z2~;~22 Consider the following example. The thermistor has a resistance related linearly to current, as follows:
1000 ohms at 1.0 milliamps, 2000 ohms at 2.0 milliamps, and 3500 ohms at 3.5 milliamps. In the normal operate in range of 1.0 to 2.0 milliamps, the voltage drop would be 1 volt and 4 volts, respectively. A fault would be indicated at about 3.5 milliamps, which is substantially lower than either a 1000 ohm or a 2000 ohm resistor would result in. Thus, using a thermistor produces an acceptable dead band (2.0 to 3.5 milliamps), while normal operating current voltage drop fluctuations are greatly reduced. Power loss is commensurately mini-mixed.
The operating characteristics of the therms-ion of this example are simply meant to illustrate the concept of this invention. It is well within the scope of one skilled in the art to select an approp-rite nonlinear resistive element depending on the particular load, acceptable voltage fluctuations, and acceptable dead band.
Although the invention has been shown and described with respect to an exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the invention.
a thermistor connected between the source and the load for providing a voltage drop indicative of the current drain and for limiting the current drain, where-in the resistance of the thermistor increases in pro-portion to the current there through, a light emitting diode (LED) connected in forward bias across the thermistor for providing the indication of excessive current drain when energized, and a zener diode connected in reverse bias in series with the LED across the thermistor so that the LED is energized when the voltage drop is at least the reverse breakdown voltage of the zoner diode.
Priority Applications (2)
|Application Number||Priority Date||Filing Date||Title|
|Publication Number||Publication Date|
|CA1226622A true CA1226622A (en)||1987-09-08|
Family Applications (1)
|Application Number||Title||Priority Date||Filing Date|
|CA000450648A Expired CA1226622A (en)||1983-04-18||1984-03-28||Current overload detector|
Country Status (10)
|JP (1)||JPS59198837A (en)|
|AU (1)||AU571210B2 (en)|
|CA (1)||CA1226622A (en)|
|DE (1)||DE3414536A1 (en)|
|ES (1)||ES531669A0 (en)|
|FR (1)||FR2544563A1 (en)|
|GB (1)||GB2139437B (en)|
|IL (1)||IL71529A (en)|
|IT (1)||IT1209530B (en)|
|SE (1)||SE8401957L (en)|
Families Citing this family (2)
|Publication number||Priority date||Publication date||Assignee||Title|
|AU2039695A (en) *||1994-06-07||1995-12-14||Honeywell Inc.||Led indicator with low operating voltage and high over-voltage tolerance|
|US6795321B2 (en)||2001-07-20||2004-09-21||Power Integrations, Inc.||Method and apparatus for sensing current and voltage in circuits with voltage across an LED|
Family Cites Families (10)
|Publication number||Priority date||Publication date||Assignee||Title|
|GB971286A (en) *||1962-04-20||1964-09-30||Brookhirst Igranic Ltd||Improvements in or relating to operation and fault indication for unidirectional conducting devices|
|DE1297198B (en) *||1962-09-28||1969-06-12||Siemens Ag||Circuit arrangement for electrical circuits|
|GB1217673A (en) *||1966-12-12||1970-12-31||Essex Internat Inc||Component failure detection system|
|DE2331732B2 (en) *||1973-06-22||1976-01-02||Robert 7995 Neukirch Buck|
|US3925709A (en) *||1973-08-13||1975-12-09||Westinghouse Electric Corp||Overcurrent protection circuit for AC systems|
|DE2411633C3 (en) *||1974-03-12||1981-06-19||Brown, Boveri & Cie Ag, 6800 Mannheim, De|
|US3919565A (en) *||1974-04-08||1975-11-11||Ibm||Overcurrent sense circuit|
|DE2529883B1 (en) *||1975-07-04||1976-05-06||Grundig Emv||Circuitry for UEberlastungsschutz|
|US4220900A (en) *||1978-06-16||1980-09-02||Sky-Top Sunroofs Ltd.||Motor control system for a linearly reciprocating load device such as automotive vehicle closure including sun roof|
|DE2935807A1 (en) *||1979-09-05||1981-04-02||Bbc Brown Boveri & Cie||Overload protection circuit - has PTC resistor in series with load and shunted by overload warning lamp|
- 1984-03-28 CA CA000450648A patent/CA1226622A/en not_active Expired
- 1984-04-02 GB GB08408405A patent/GB2139437B/en not_active Expired
- 1984-04-06 AU AU26611/84A patent/AU571210B2/en not_active Ceased
- 1984-04-09 SE SE8401957A patent/SE8401957L/en not_active Application Discontinuation
- 1984-04-10 JP JP7168384A patent/JPS59198837A/en active Pending
- 1984-04-12 IL IL7152984A patent/IL71529A/en not_active IP Right Cessation
- 1984-04-17 ES ES531669A patent/ES531669A0/en not_active Expired
- 1984-04-17 DE DE19843414536 patent/DE3414536A1/en not_active Withdrawn
- 1984-04-17 FR FR8406035A patent/FR2544563A1/en not_active Withdrawn
- 1984-04-18 IT IT2061184A patent/IT1209530B/en active
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