Dynamic Power Boost Circuit for Audio Amplifier Rail Limits
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Solution Overview
Problem
Conventional power amplifiers are limited by voltage swing and load impedance, which restricts the maximum output power and introduces distortion, especially in audio amplification systems, and existing solutions like bridging or switching power supplies have limitations and complications.
Innovation Solution
A power boost circuit that temporarily increases the power supply voltage by drawing current from a reservoir capacitor when the amplifier output approaches the rail voltage, allowing independent boosting of positive and negative supply rails to achieve a larger peak-to-peak voltage swing without requiring a bridged amplifier or switching power supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the amplifier output voltage approaches the power supply rail voltage, then the maximum output power is limited, but increasing the power supply voltage would require a switching power supply or bridged amplifier configuration which adds complexity
Solution Approach 1:
The reservoir capacitor is pre-charged to the power supply rail voltage before the amplifier needs to deliver high power. When the amplifier output approaches the rail voltage, the capacitor is already ready to provide the additional voltage boost without requiring a switching power supply or complex bridged configuration.
Solution Approach 2:
The reservoir capacitor acts as an intermediary energy storage element between the power supply and the amplifier output. It temporarily stores energy and releases it when needed to boost the output voltage beyond the rail voltage, avoiding the need for complex power supply circuits.
2Power
If the load impedance is reduced to increase output power, then the current requirement increases and distortion increases, but maintaining higher load impedance limits the available power
Solution Approach 1:
The invention dynamically changes the effective power supply voltage parameter based on the amplifier output level. When high power is needed, the reservoir capacitor boosts the supply voltage, allowing the amplifier to maintain low distortion while delivering high power to higher impedance loads.
3Power
If a bridged amplifier configuration is used to double the output voltage swing, then the output power increases, but the current requirement per amplifier doubles and the load impedance seen by each amplifier is halved
Solution Approach 1:
The reservoir capacitor is pre-charged to the power supply rail voltage, ready to provide additional voltage when needed. This allows a single amplifier to achieve high power output without the current demands of a bridged configuration.
Solution Approach 2:
The invention extracts the voltage boosting function from the amplifier circuit itself and places it in the power supply section using the reservoir capacitor. This separates the voltage generation from the current amplification, allowing the amplifier to operate at lower current levels.
4Power
If a switching power supply is used to raise the power supply voltage, then the voltage swing capability increases, but high frequency operation and interference risks increase
Solution Approach 1:
The reservoir capacitor provides periodic voltage boosting only when the amplifier output approaches the rail voltage, rather than continuously switching at high frequency. This reduces electromagnetic interference while still providing the necessary voltage swing capability.
Solution Approach 2:
The invention replaces the electronic switching mechanism with a passive capacitor discharge mechanism. The capacitor naturally discharges through the amplifier when voltage is needed, eliminating the high-frequency switching and associated electromagnetic interference.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables a voltage swing of up to three times the supply voltage, increasing output power to approximately 27 Watts into an 8Ω load while reducing distortion and heat dissipation, and is suitable for applications requiring occasional peak voltage swings.
Implementation Method 1
The power boost circuit tracks the output signal from the amplifier and temporarily boosts the power supply input voltage signal feeding the amplifier, by drawing current from a reservoir capacitor when the output signal from the amplifier approaches the power supply rail voltage
Data Source
AI summary
A dynamic power supply for N amplifiers includes first and second power boost circuits which temporarily boost the positive or negative power supply rail, respectively. A control circuit monitors amplifier output signal levels and provides power boost control signals to the power boost circuits, which temporarily raise the positive supply voltage above the nominal voltage level in tandem with the highest output signal from the N amplifiers and lower the negative supply voltage below the nominal voltage level in tandem with the lowest output signal level from the N amplifiers. The power boost circuits each may be coupled to a reservoir capacitor from which current is drawn to provide the power boost. When inactive, the reservoir capacitors charge up from the respective power supply rails. The dynamic power supply is well suited for audio amplification systems.