Method and apparatus for sensing current and voltage in circuits with voltage across an LED

• US 20070120594A1
• Filed: 01/29/2007
• Published: 05/31/2007
• Est. Priority Date: 07/20/2001
• Status: Abandoned Application

• Current Assignee: Arthur Odell, Balu Balakrishnan
• Original Assignee: Arthur Odell, Balu Balakrishnan
• Inventors: Balakrishnan, Balu, Odell, Arthur
• Application Number:
  US11/699,658
• Publication Number:
  US 20070120594A1
• Time in Patent Office: Days
• US Class Current: 327/589
• 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 circuit includes a transistor coupled to a voltage reference. A light emitting diode (LED) is coupled to be driven by the transistor in response to a voltage across an output of the circuit. A first diode is coupled to the LED. A first resistor coupled to the first diode and the LED. The LED is coupled to be driven in response to a voltage drop across the first diode and the first resistor to sense a first current directed through the first diode and the first resistor.

Claims

1. A circuit, comprising:

a transistor coupled to a voltage reference;

a light emitting diode (LED) coupled to be driven by the transistor in response to a voltage across an output of the circuit;

a first diode coupled to the LED; and

a first resistor coupled to the first diode and the LED such that the LED coupled to be driven in response to a voltage drop across the first diode and the first resistor to sense a first current directed through the first diode and the first resistor.

2. The circuit of claim 1 wherein the transistor is coupled to drive the LED in response to the voltage across the output of the circuit exceeding a sense voltage.

3. The circuit of claim 1 wherein the transistor comprises a bipolar transistor having a base coupled to the voltage reference, the bipolar transistor to drive the LED when the voltage across the output exceeds a sense voltage.

4. The circuit of claim 1 wherein the voltage reference is provided by a Zener diode coupled to the output of the circuit.

5. The circuit of claim 1 wherein a sense voltage includes a sum of the voltage reference provided by a Zener diode coupled to the output of the circuit and a forward base emitter voltage of bipolar transistor having a base coupled to the voltage reference.

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

7. The circuit of claim 1 wherein an optocoupler including the LED 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.

8. The circuit of claim 7 wherein the power supply is a switched mode power supply.

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