Pulse width modulation driving apparatus for light emitting diode

• US 6,989,701 B2
• Filed: 12/31/2003
• Issued: 01/24/2006
• Est. Priority Date: 12/31/2002
• Status: Expired due to Fees

• Current Assignee: Hon Hai Precision Industry Co., Ltd.
• Original Assignee: Hon Hai Precision Industry Co., Ltd.
• Inventors: Lee, Ching Yen, Lin, Jyh Chain
• Primary Examiner(s): Lam, Tuan T.
• Assistant Examiner(s): Nguyen, Hai L.
• Application Number:
  US10/750,121
• Publication Number:
  US 20040155600A1
• Time in Patent Office: 755 Days
• Field of Search: 327172-176, 327 50- 52, 327/56, 327/63, 327/68, 327/90, 327/164, 327/514, 327/515, 327/108, 327/109, 372/38.02, 345/39
• US Class Current: 327/175
• CPC Class Codes: H04B 10/502 LED transmitters
• CPC Class Codes: H04B 10/524 Pulse modulation

Abstract

A PWM driving apparatus for an LED includes a sawtooth wave generator (1) for generating a sawtooth wave signal, a comparator (2), an FET (3), a first resistor (4), a second resistor (5), a power supply (7), and a light emitting diode array (8). A modulation signal provided by a modulation signal source (6) and the sawtooth wave signal are fed to the comparator, an output of the comparator is connected to a gate terminal of the FET, the power supply is connected to a source terminal of the FET through the first resistor, and a drain tenninal of the FET outputs a driving current through the second resistor to the light emitting diode array.

Claims

1. A pulse width modulation driving apparatus for a light emitting diode, comprising:

a sawtooth wave generator for generating a sawtooth wave signal;

a comparator;

a field effect transistor having a gate terminal, a source terminal, and a drain terminal;

a power supply;

a first current limiting resistor and a second current limiting resistor; and

at least one light emitting diode serving as a load;

wherein a modulation signal and the sawtooth wave signal are input to the comparator, an output of the comparator is connected to the gate terminal of the field effect transistor, the first resistor is connected between the power supply and the source terminal of the field effect transistor, and the drain terminal of the field effect transistor outputs a driving current through the second resistor to the load.

2. The pulse width modulation driving apparatus as described in claim 1, wherein the field effect transistor is an N-channel enhancement-type field effect transistor.

3. The pulse width modulation driving apparatus as described in claim 1, wherein the field effect transistor is a P-channel enhancement-type field effect transistor.

4. The pulse width modulation driving apparatus as described in claim 1, wherein the field effect transistor is an N-channel depletion-type field effect transistor.

5. The pulse width modulation driving apparatus as described in claim 1, wherein the field effect transistor is a P-channel depletion-type field effect transistor.

6. A pulse width modulation driving apparatus assembly, comprising:

a field effect transistor defining a gate terminal, a source terminal, and a drain terminal;

a power supply and a first current limiting resistor connected to the source terminal;

a light emitting diode array and a second current limiting resistor electrically connected to the drain terminal;

a comparator connected to the gate terminal; and

a modulation signal source and a wave generator respectively connected to input terminals of the comparator;

wherein an equivalent driving current is provided on the drain terminal, which is proportional to an amplitude of a signal derived from the modulation signal source.

7. A method of providing a light emitting diode array with a linearly adjusted driving current, comprising steps of:

providing a field effect transistor defining a gate terminal, a source terminal and a drain terminal;

electrically connecting a light emitting diode array and a current limiting resistor to the drain terminal;

electrically connecting a comparator to the gate terminal; and

electrically connecting a modulation signal source and a wave generator to input terminals of the comparator, respectively;

electrically connecting a power supply and another current limiting resistor to the source terminal; and

comparing the signals respectively from the modulation signal source and the wave generator in the comparator, and outputting a positive high level signal so as to turn on the field effect transistor;

wherein providing a driving current provided on the drain terminal for activating said light emitting diode array is changed linearly corresponding to a linear change of signals generated from the modulation signal source.

8. The method as described in claim 7, wherein the comparing step further comprises the steps of:

outputting a positive high level signal when a modulation signal is lower than a wave signal generated by the wave generator, and outputting a zero level signal when a modulation signal is equal to or higher than a wave signal generated by the wave generator.