Current detecting circuit

• US 6,701,262 B2
• Filed: 08/22/2001
• Issued: 03/02/2004
• Est. Priority Date: 08/23/2000
• Status: Expired due to Fees

• Current Assignee: Autonetworks Technologies, Ltd. (Sumitomo Corporation), Sumitomo Electric Industries Limited (Sumitomo Corporation), Sumitomo Wiring Systems Limited (Sumitomo Corporation)
• Original Assignee: Autonetworks Technologies, Ltd. (Sumitomo Corporation), Sumitomo Electric Industries Limited (Sumitomo Corporation), Sumitomo Wiring Systems Limited (Sumitomo Corporation)
• Inventors: Mizuno, Fumiaki, Isshiki, Isao
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): Charioui, Mohamed
• Application Number:
  US09/933,723
• Publication Number:
  US 20020026287A1
• Time in Patent Office: 923 Days
• Field of Search: 702/57, 702/58, 702/60, 702/64, 702/65, 702/117, 702/124, 702/126, 702/189, 702/198, 324/433, 324/537, 323/283, 307/10.1, 307/10.6
• US Class Current: 702/60
• CPC Class Codes: H02H 1/0092 concerning the data processing means, e.g. expert systems, neural networks
• CPC Class Codes: H02H 3/087 for dc applications

Abstract

In a current detecting circuit, a virtual earth generating circuit 7 generates a low voltage V_SS lower by a predetermined potential difference than a battery voltage V_BT outputted from anon-vehicle battery 1. A CPU 5 operates while the low voltage V_SS is used as an earth potential and the voltage V_BT higher by the predetermined voltage value than the low voltage V_SS is used as a power-supply voltage. A/D conversion input terminals 53 and 54 of the CPU 5 are connected to the battery 1 side of a current detecting resistor 3 and the load 4 side of the resistor 3. The voltages on the battery 1 side and the load 4 side of the resistor 3 to be inputted to the terminals 53 and 54 are detected by an A/D converter 60. A load current I_LD is calculated based on the detected results and the resistor 3 resistance.

Claims

1. A current detecting circuit for use in a current supply circuit for supplying a load current from a power supply portion to a load when a switching unit interposed between said power supply portion and said load is turned on, said current detecting circuit comprising:

a voltage generating circuit for generating and outputting a second voltage which is lower by a predetermined voltage value than a first voltage outputted from said power supply portion;

a current detecting resistor interposed between said power supply portion and said load and having a predetermined resistance value;

an analog-digital conversion circuit which operates on the basis of a potential difference between said first voltage and said second voltage to thereby convert analog values into k-bit digital values, where k is an integer not smaller than 2; and

an arithmetic circuit for calculating at least one of said load current and a value corresponding to said load current on the basis of the digital values which are obtained by the analog-digital conversion of voltages respectively on one and the other ends of said current detecting resistor by said analog-digital conversion circuit when said switching unit is turned on.

2. A current detecting circuit according to claim 1, wherein:

said analog-digital conversion circuit comprises;

a divisional voltage output circuit for successively selectively outputting summation values which are obtained by adding said second voltage to various voltage values which are obtained by multiplying a divisional voltage by m, m is an integer from 0 to n-1, said divisional voltage being obtained by dividing a potential difference between said first voltage and said second voltage into n-1 parts, where n is an integer satisfying n-2^k;

a comparator circuit for comparing said voltage on said one end of said current detecting resistor with each of said summation values which are successively selectively outputted from said divisional voltage output circuit and for comparing said voltage on the other end of said current detecting resistor with each of said summation values which are successively selectively outputted from said divisional voltage output circuit; and

said arithmetic circuit calculating the at least one of said load current and the value corresponding to said load current on the basis of results of said comparison in said comparator circuit.

3. A current detecting circuit according to claim 2, wherein:

said arithmetic circuit uses in the calculation the summation value at which an inequality relation between the analog value of the voltage on the one end of the current detecting resistor and the summation values successively selectively outputted is changed over in the comparison result by the comparator circuit, as the digital value of the voltage on the one end of the current detecting resistor,

said arithmetic circuit uses in the calculation the summation value at which an inequality relation between the analog value of the voltage on the other end of the current detecting resistor and the summation values successively selectively outputted is changed over in the comparison result by the comparator circuit, as the digital value of the voltage on the other end of the current detecting resistor; and

the arithmetic circuit calculates voltage drop over the current detecting resistor on the basis of a difference between the digital value of the voltage on the one end of the current detecting resistor and the digital value of the voltage on the other end of the current detecting resistor.

4. A current detecting circuit according to claim 1, wherein said analog-digital conversion circuit forms a part of a CPU integrated on a semiconductor wafer;

said CPU has a power-supply input terminal and a ground terminal; and

said first voltage is applied to said power-supply input terminal and said second voltage is applied to said ground terminal.

5. A current detecting circuit according to claim 1, wherein said current detecting resistor is formed from a semiconductor switching device constituting said switching means;

and said predetermined resistance value is a resistance value of ON-state resistance generated when said semiconductor switching device is turned on.