Power amplifier
View Patent ↗A power amplifier for driving a load connected to an output terminal having an output transistor connected in parallel with a corresponding current detection path between the output terminal and a power supply. The detection path includes a switching device and a resistor connected in series, the switching device is turned on only during an on-state period of the corresponding output transistor, and the presence or absence of over-current generation is detected at the output transistors on the basis of a sensing signal obtained from a point connecting the switching device and the resistor. When over-current is detected, the operation of the output transistors is stopped to protect the amplifier.
1. A power amplifier for driving a load connected to an output terminal, comprising:
an output transistor connected between said output terminal and a power supply, said output transistor supplying a driving signal to said load;
an amplifier driver for driving said output transistor;
a current detection path comprising a switching device and a resistor connected in series and said path disposed in parallel with said output transistor between said power supply and said output terminal; and
an over-current detector for controlling said switching device so as to turn on during an on-state operating period of said output transistor and detecting over-current flowing to said output transistor on the basis of a sensing signal obtained from a point connecting said switching device and said resistor of said current detection path;
wherein the sensing signal and a signal for turning on or off the switching device are input to a first AND gate;
the over-current detector is configured to control said output transistor on the basis of the output signal of the AND gate;
wherein the power amplifier further comprises a second AND gate configured to output the signal for turning on or off the switching device to the first AND gate; and
wherein inputs to the second AND gate comprise:
a first signal provided from a pre-drive;
a gate signal obtained by delaying the first signal with a first delay circuit; and
a delayed gate signal obtained by delaying the gate signal by a second delay circuit.
2. A power amplifier according to claim 1 , further comprising a switch controller for controlling said switching device of said current detection path;
said switch controller sets said switching device into a conduction state after a predetermined delay period from start of on-state operation of said output transistor disposed in parallel with said current detection path; and said over-current detector judges whether or not over-current flows on the basis of a sensing signal obtained during a conduction state of said switching device from a point connecting said switching device and said resistor.
3. A power amplifier according to claim 1 , wherein: said amplifier driver drives said output transistor on and off with a pulse-shaped driving signal in accordance with a pulse width modulated signal.
4. A power amplifier according to claim 1 , wherein:
said output transistor comprises a high-voltage output transistor disposed between a high-voltage power supply and said output terminal and a low-voltage output transistor disposed between a low-voltage power supply and said output terminal;
a high-voltage current detection path is disposed between said high-voltage power supply and said output terminal and a low-voltage current detection path is disposed between said output terminal and said low-voltage power supply,
said high-voltage current detection path and said low-voltage current detection path respectively comprise said switching device and said resistor; and
on the basis of a sensing signal obtained by controlling the switching devices of said high-voltage current detection path and said low-voltage current detection path to turn on, generation of said over-current in a corresponding output transistor is detected.
5. A power amplifier according to claim 4 , wherein:
said amplifier driver comprises a high-voltage amplifier driver for driving said high-voltage output transistor and a low-voltage amplifier driver for driving said low-voltage output transistor;
a common power supply as a high-voltage amplifier driver power supply is connected to said high-voltage amplifier driver and said low-voltage amplifier driver;
a boot capacitor can be connected between said output terminal and a boot terminal to which a predetermined power supply is connected; and
a driving signal output from said output terminal via said high-voltage output transistor is stepped up in voltage in accordance with a holding voltage of said boot capacitor charged via said boot terminal.
6. A power amplifier according to claim 4 further comprising a switch controller for controlling said switching device of said current detection path;
said switch controller sets said switching device into a conduction state at a timing of a predetermined delay period from start of on-state operation of said output transistor disposed in parallel with said current detection path; and said over-current detector judges whether or not over-current flows on the basis of a sensing signal obtained during a conduction state of said switching device from a point connecting said switching device and said resistor.
7. A power amplifier according to claim 4 , wherein: said amplifier driver drives said output transistor on and off with a pulse-shaped driving signal in accordance with a pulse width modulated signal.