Amplifier circuit with a stabilized bias in its output stage

• US 5,467,058 A
• Filed: 08/26/1994
• Issued: 11/14/1995
• Est. Priority Date: 09/01/1993
• Status: Expired due to Term

• Current Assignee: Yamaha Corporation
• Original Assignee: Yamaha Corporation
• Inventors: Fujita, Shinichi
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/296,712
• Time in Patent Office: 445 Days
• Field of Search: 330/263, 330/265, 330/267, 330/268, 330/266
• US Class Current: 330/267
• CPC Class Codes: H03F 1/307 in push-pull amplifiers
• CPC Class Codes: H03F 3/3076 with symmetrical driving of the end stage

Abstract

An amplifier circuit with a stabilized bias in its output stage includes a push-pull type output-circuit having a first transistor and second transistor connected to each other in Darlington connection, a third transistor and a fourth transistor respectively operating complementarily with the first transistor and the second transistor. The third transistor and fourth transistor are connected to each other in Darlington connection, and the second transistor and fourth transistor are connected in series as output stage transistors between terminals of a DC power supply source. The amplifier circuit further includes a current detection circuit having current detection resistance inserted between either the first transistor or the third transistor and the DC power supply source and detecting idling current of either the first transistor or the third transistor by means of terminal voltage of the current detection resistance, and a biasing circuit responsive to output of the current detection circuit for controlling the idling current of either the first transistor or the third transistor in a negative feedback fashion.

Claims

1. An amplifier circuit comprising:

a push-pull type output circuit including a first transistor and a second transistor connected to each other in Darlington connection, a third transistor and a fourth transistor respectively operating complementarily and connected to each other in Darlington connection, and said second transistor and said fourth transistor being connected in series as output stage transistors between terminals of a DC power supply source;

current detection means comprising current detection resistance inserted between either said first transistor or said third transistor and said DC power supply source and detecting idling current of either said first transistor or said third transistor on the basis of terminal voltage of said current detection resistance; and

biasing means responsive to output of said current detection means for controlling the idling current of either said first transistor or said third transistor in a negative feedback fashion.

2. An amplifier circuit comprising:

a push-pull type output circuit including a first transistor and a second transistor of opposite polarities connected to each other in Darlington connection, a third transistor and a fourth transistor respectively operating complementarily with said first transistor and said second transistor and connected to each other in Darlington connection, and said second transistor and said fourth transistor being connected in series as output stage transistors between terminals of a DC power supply source;

current detection resistance inserted between either said first transistor or said third transistor and said DC power supply source;

error amplifying means for amplifying an error between terminal voltage of said current detection resistance and reference voltage; and

biasing means responsive to output of said error amplifying means for controlling the idling current of either said first transistor or said third transistor in a negative feedback fashion.