Temperature detecting using a forward voltage drop across a diode

• US 5,918,982 A
• Filed: 09/11/1997
• Issued: 07/06/1999
• Est. Priority Date: 09/12/1996
• Status: Expired due to Term

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Nagata, Junichi, Ban, Hiroyuki, Hayakawa, Junji
• Primary Examiner(s): Patel, Harshad
• Assistant Examiner(s): Clark, Robin C.
• Application Number:
  US08/927,182
• Time in Patent Office: 663 Days
• Field of Search: 374/152, 374/178, 327/512, 340/598
• US Class Current: 374/178
• CPC Class Codes: G01K 7/01 using semiconducting elements having PN junctions G01K7/02, G01K7/16, G01K7/30 take precedence

Abstract

A temperature detecting circuit detects the rise of ambient temperature, using a forward voltage drop across a diode. The temperature detecting circuit comprises a temperature detecting diode whose cathode is grounded, a first constant current supply device connected with the anode of the temperature detecting diode, for supplying a constant current Ia to the temperature-detecting diode, a rectifying diode whose cathode is connected with the anode of the temperature detecting diode, a second constant current supply device connected with the anode of the rectifying diode, for supplying a constant current Ib to the temperature-detecting diode, a comparator, and a transistor. When the voltage at the anode of the temperature-detecting diode is lower than a reference voltage, the comparator produces a high-level signal indicative of overheating. In response to this, the transistor shorts the anode of the rectifying diode to ground potential to supply the constant current Ib from the second constant current supply device directly to ground potential.

Claims

1. A temperature detecting circuit for detecting the rise and ambient temperature by making use of forward voltage drop produced across a diode, said temperature-detecting circuit comprising:

a first constant current supply device connected in series with said diode, for supplying a first constant current to said diode;

a second constant current supply device connected in parallel with said first constant current supply device and in series with said diode, for supplying a second constant current to said diode;

a voltage-detecting circuit for detecting said forward voltage drop across said diode and producing an output signal indicating overheating when said forward voltage drop is smaller than a predetermined value; and

a bypass circuit for bypassing said second constant current supplied from said second constant current supply device around said diode when said voltage detecting circuit is producing said output signal.

2. A temperature detecting circuit comprising:

a temperature detecting diode having an anode and a cathode, said cathode being provided with a first potential;

a first constant current supply device having a first and a second output terminals across which a first constant current is passed, said first output terminal being provided with a second potential higher than said first potential, said second output terminal being connected with the anode of said temperature detecting diode;

a rectifying diode having a cathode connected with the anode of said temperature detecting diode;

a second constant current supply device having a first and a second output terminals across which a second constant current is passed, said first output terminal of said second constant current supply device being provided with said second potential, said second output terminal of said second constant current supply device being connected with the anode of said rectifying diode;

a comparator for comparing a voltage produced at the anode of said temperature detecting diode with a preset reference voltage and producing an output signal indicating overheating when the voltage at the anode of said temperature detecting diode is lower than said reference voltage; and

a switching device for shorting the anode of said rectifying diode to said first potential when said comparator is producing said output signal.

3. The temperature-detecting circuit as set forth in claim 2, further comprising:

a transistor for producing a reference current, said transistor having two output terminals consisting of a collector and an emitter or of a drain and a source, said two output terminals being connected in series between said first and second potentials, said transistor being constructed so that a preset constant current flows between said two output terminals,

wherein said first constant current supply device is a first transistor cooperating with said transistor for producing the reference current to form a current mirror circuit that feeds as said first constant current a current larger than said reference current by a first factor, and

wherein said second constant current supply device is a second transistor cooperating with said transistor for producing the reference current to form another current mirror circuit that feeds as said second constant current a current larger than said reference current by a second factor.

4. A temperature detecting circuit comprising:

a temperature detecting diode having a cathode and an anode, said anode being provided with a first potential;

a first constant current supply device having a first and a second output terminals across which a first constant current is passed, said first output terminal being provided with a second potential lower than said first potential, said second output terminal being connected with the cathode of said temperature-detecting diode;

a rectifying diode having an anode connected with the cathode of said temperature-detecting diode;

a second constant current supply device having a first and a second output terminals across which a second constant current is passed, said first output terminal being provided with said second potential, said second output terminal being connected with the cathode of said rectifying diode;

a comparator for comparing a voltage produced at the cathode of said temperature-detecting diode with a preset reference voltage and producing an output signal indicating overheating when the voltage at the cathode of said temperature detecting diode is higher than said reference voltage; and

a switching device for shorting the cathode of said rectifying diode to said first potential when said comparator is producing said output signal.

5. The temperature-detecting circuit as set forth in claim 4, further comprising:

a transistor for producing a reference current, said transistor having two output terminals consisting of a collector and an emitter or of a drain and a source, said two output terminals being connected in series between said first and second potentials, said transistor being constructed so that a preset constant current flows between said two output terminals,

wherein said first constant current supply device is a first transistor cooperating with said transistor for producing the reference current to form a current mirror circuit that feeds as said first constant current a current larger than said reference current by a first factor, and

wherein said second constant current supply device is a second transistor cooperating with said transistor for producing the reference current to form another current mirror circuit that feeds as said second constant current a current larger than said reference current by a second factor.