Digital amplifier

• US 7,268,621 B2
• Filed: 12/20/2005
• Issued: 09/11/2007
• Est. Priority Date: 12/21/2004
• Status: Expired due to Fees

• Current Assignee: Yamaha Corporation
• Original Assignee: Yamaha Corporation
• Inventors: Noro, Masao, Kanoh, Masaya
• Primary Examiner(s): NGUYEN, PATRICIA T
• Application Number:
  US11/313,066
• Publication Number:
  US 20060133002A1
• Time in Patent Office: 630 Days
• Field of Search: 330/251, 330/207.P, 330/10
• US Class Current: 330/251
• CPC Class Codes: H03F 1/52 Circuit arrangements for protecting such amplifiers monitoring arrangements G01R31/28; increasing reliability in communication systems, e.g. using redundancy H04B1/74
• CPC Class Codes: H03F 2200/351 Pulse width modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers

Abstract

A threshold value adjustment circuit for adjusting a predetermined threshold value is provided in a stage followed by a protection circuit which starts protection operation when a load current flowing into an MOSFET exceeds the threshold value. A voltage proportional to a drain current and generated between the opposite ends of a current detection resistor Rd inserted between the high-side MOSFET and a positive power supply +V, and an output of an output voltage detection circuit for detecting the voltage amplitude of an analog signal from a low pass filter for modulating an output of a class D amplifier stage are inputted to the threshold value adjustment circuit. The threshold value adjustment circuit adjusts the threshold value in such a manner that a limit current of the MOSFET is set as the threshold value when the output voltage is large, and protection operation is started in response to a lower current than the limit current when the output voltage is small.

Claims

1. A digital amplifier comprising:

a class D amplifier stage that includes a first switching device and a second switching device connected in series with each other;

a low pass filter connected to an output of the class D amplifier stage;

a current detection unit that detects a pulse current flowing into at least one of the first switching device and the second switching device;

an output voltage detection unit that detects a voltage of an analog signal outputted from the low pass filter; and

a protection unit that performs protection operation on the basis of the current value detected by the current detection unit and the output voltage detected by the output voltage detection unit, the protection unit starting protection operation in response to a low current value when the output voltage is low, the protection unit starting protection operation in response to a high current value when the output voltage is high.

2. A digital amplifier according to claim 1, wherein the current detection unit detects a voltage generated between opposite ends of a resistor inserted in series with the first or second switching device.

3. A digital amplifier according to claim 1, wherein the current detection unit detects a voltage generated between opposite ends of the first or second switching device when the switching device is on.

4. A digital amplifier according to claim 1, wherein the protection unit includes:

a switching element that is activated when the current value detected by the current detection unit exceeds a predetermined threshold value; and

a threshold value adjustment circuit that changes the threshold value in accordance with the output voltage detected by the output voltage detection unit.

5. A digital amplifier according to claim 1, wherein the current value detected by the current detection unit and the output voltage detected by the output voltage detection unit are inputted in the protection unit, and the protection unit performs protection operation when the current value exceeds a threshold value corresponding to the output voltage.

6. A digital amplifier according to claim 1, further comprising a switching element for disconnecting the output low pass filter and a load from each other in accordance with an output of the protection unit.

7. A digital amplifier according to claims 1, further comprising a unit for controlling amplitude of an input signal in accordance with an output of the protection unit.