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US 3,992,678 AGranted
Protective circuit for transistor amplifier
AssigneeSony Corporation
InventorTadao Suzuki
Life of this patent
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Abstract
A protective circuit for a transistor amplifier is provided which measures the load impedance and actuates a protective means across an input terminal of the transistor amplifier when a measured value of said load impedance becomes lower than a predetermined value, to protect the transistor amplifier from overload. The protective circuit is applicable for a class B push-pull amplifier and, particularly effective to protect the overload even when the load of the amplifier has a reactance component. Various modifications such as relay type protective circuits are also disclosed.
Claims7
A protective circuit for a transistor amplifier comprising:
- a. a DC voltage source;
- b. a first transistor having first, second and third electrodes, said first electrode supplied with an input signal to be amplified and said second electrode connected to said voltage source;
- c. a first resistor with one side connected to said third electrode;
- d. a load connected between the other side of said first resistor and a reference point;
- e. a first capacitor;
- f. first circuit means including a first diode and a second resistor connected in series between one side of said first capacitor and said one side of said first resistor to supply a first DC voltage of one polarity proportional to a voltage across said first resistor to said first capacitor;
- g. second circuit means including a second diode and a third resistor connected in series between said one side of said first capacitor and said reference point to supply a second DC voltage of the other polarity proportional to a voltage across said load to said first capacitor;
- h. voltage detecting means for detecting the output voltage across said first capacitor and producing a control signal when the voltage becomes a predetermined value;
- i. switching means controlled by said control signal so as to cut off operation of said first transistor, and wherein said voltage detecting means includes a second transistor having first, second and third electrodes, said first and second electrodes being connected across said first capacitor, said third electrode producing said control signal when the voltage across said first capacitor becomes a predetermined value;
- and said switching means includes at least one further transistor controlled by said control signal, a relay coil connected as the load for said further transistor, a relay switch controlled by said relay coil and connected between said third electrode of said first transistor and said load so as to cut off the operation of said first transistor.
7 more elements
A protective circuit for a transistor amplifier comprising:
- a. a DC voltage source;
- b. a first transistor having first, second and third electrodes, said first electrode supplied with an input signal to be amplified and said second electrode connected to said voltage source;
- c. a first resistor with one side connected to said third electrode;
- d. a load connected between the other side of said first resistor and a reference point;
- e. a first capacitor;
- f. first circuit means including a first diode and a second resistor connected in series between one side of said first capacitor and said one side of said first resistor to supply a first DC voltage of one polarity proportional to a voltage across said first resistor to said first capacitor;
- g. second circuit means including a second diode and a third resistor connected in series between said one side of said first capacitor and said reference point to supply a second DC voltage of the other polarity proportional to a voltage across said load to said first capacitor;
- h. voltage detecting means for detecting the output voltage across said first capacitor and producing a control signal when the voltage becomes a predetermined value;
- i. switching means controlled by said control signal so as to cut off operation of said first transistor, and wherein said voltage detecting means includes a second transistor having first, second and third electrodes, said first and second electrodes connected across said first capacitor, said third electrode producing said control signal when the voltage across said first capacitor becomes a predetermined value, and said switching means comprises a relay coil connected between said voltage source and said third electrode of said second transistor, and a relay switch controlled by said relay coil and connected between said load and said first resistor to cut off said first transistor from said load during overload condition.
6 more elements
A protective circuit for a transistor amplifier comprising:
- a. a DC voltage source;
- b. a first transistor having first, second and third electrodes, said first electrode supplied with an input signal to be amplified and said second electrode connected to said voltage source;
- c. a first resistor with one side connected to said third electrode;
- d. a load connected between the other side of said first resistor and a reference point;
- e. a first capacitor;
- f. first circuit means including a first diode and a second resistor connected in series between one side of said first capacitor and said one side of said first resistor to supply a first DC voltage of one polarity proportional to a voltage across said first resistor to said first capacitor;
- g. second circuit means including a second diode and a third resistor connected in series between said one side of said first capacitor and said reference point to supply a second DC voltage of the other polarity proportional to a voltage across said load to said first capacitor;
- h. a second transistor having first, second and third electrodes, said first electrode supplied with an input signal to be amplified and said second electrode connected to receive a bias of opposite polarity to that supplied to said second electrode of said first transistor;
- i. a fourth resistor with one side connected to said third electrode of said second transistor and its other side connected to said load;
- j. a second capacitor;
- k. third circuit means including a third diode and a fifth resistor connected in series between one side of said second capacitor and said load;
- l. fourth circuit means including a fourth diode and sixth resistor between said one side of said second capacitor and said reference point;
- m. voltage detecting means for detecting the output voltage across said first and second capacitors and producing a control signal when the voltage has predetermined values, switching relay means controlled by said control signal so as to cut off operation of said first and second transistors and wherein said voltage detecting means includes a third transistor having at least input and output electrodes, said input electrode connected to receive the voltage across said first capacitor and said output electrode producing said control signal when said output voltage becomes a predetermined value, a fourth transistor having at least input and output electrodes, said input electrode connected to receive the voltage across said second capacitor and said output electrode producing said control signal when said output voltage becomes a predetermined value.
10 more elements
Dependencies are inferred from the claim text.