Method and apparatus for low cost, current and voltage sense circuits with voltage drop

• US 20050017706A1
• Filed: 08/19/2004
• Published: 01/27/2005
• Est. Priority Date: 07/20/2001
• Status: Active Grant

• Current Assignee: Arthur B. Odell, Balu Balakrishnan
• Original Assignee: Arthur B. Odell, Balu Balakrishnan
• Inventors: Balakrishnan, Balu, Odell, Arthur B.
• Granted Patent: US 7,005,914 B2
• Time in Patent Office: Days
• US Class Current: 323/320
• CPC Class Codes: G01R 19/0084 measuring voltage only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G01R 19/16523 using diodes, e.g. Zener diodes
• CPC Class Codes: G01R 19/16571 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current G01R19/16514, G01R19/16519, G01R19/16528, G01R19/16533, G01R19/1659 take precedence; measuring currents by using elements sensitive to the magnetic field generated G01R15/14; measuring earth resistance G01R27/18; testing for leakage or short circuits in electrical apparatus G01R31/52
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence

Abstract

Methods and apparatuses to sense current and voltage in circuits with voltage drop. In one aspect of the invention, a sense circuit includes a series combination of a diode and a resistor in the path of the current to be sensed, the voltage across this series combination coupled to drive a light emitting diode (LED).

Claims

1. A circuit, comprising:

a first diode;

a first resistor coupled to the first diode, a first current to be directed through the first diode and the first resistor, a first voltage being the sum of the voltages developed across the first resistor and the first diode; and

a light emitting diode (LED) coupled to the first diode and the first resistor such that the first voltage is to be applied across the LED to sense the first current.

2. The circuit of claim 1 wherein the LED is included in an optocoupler.

3. The circuit of claim 2 wherein the optocoupler is coupled to provide feedback from an output of a power supply, the optocoupler coupled to provide the feedback to a power supply controller included in the power supply.

4. The circuit of claim 3 wherein the power supply is a switched mode power supply.

5. The circuit of claim 1 wherein the first diode comprises a PN junction diode.

6. The circuit of claim 1 further comprising a second resistor coupled to the LED, the first diode and first resistor coupled to the LED and the second resistor.

7-34. -34. (canceled).

35. A method, comprising:

sensing a current representative of a load current supplied by an output of a circuit with a current sense circuit comprising a diode and a resister;

passing the current through the diode and the resistor; and

coupling the sum of the voltages developed across the resistor and the diode across a light emitting diode (LED) such that the LED is turned on when the current exceeds a current sense threshold of the current sense circuit.

36. The method of claim 35 wherein the LED is included in an optocoupler.

37. The method of claim 36 wherein the optocoupler is coupled to provide feedback from an output of a power supply, the optocoupler coupled to provide the feedback to a power supply controller included in the power supply.

38. The method of claim 37 wherein the power supply is a switched mode power supply.

39. The method of claim 35 wherein forward voltage drop of the diode has a temperature coefficient that is substantially similar to the forward voltage drop of the LED.

40. The method of claim 35 further comprising:

sensing at the output of the circuit using a voltage sense circuit coupled across the output of the circuit and to the LED;

turning the LED on when the voltage at the output of the circuit exceeds a sense voltage of the voltage sense circuit.

41. The method of claim 40 further comprising changing the sense voltage of the voltage sense circuit as a function of the load current with a compensation circuit.

42-43. -43. (Canceled).