Class-D amplification combined with switched-mode power conditioning-the route to long battery life

Class-D amplification is the acknowledged means by which amplifier power demand can be reduced in battery-powered audio products. However, it is also well known that the switching action of the class-D amplifier is a potential source of electromagnetic interference and therefore designers of audio consumer products are naturally concerned that the adoption of this form of amplification will jeopardise the ability of their product to comply with EMC regulations. We show that when properly screened, class-D amplifiers can be used within a few inches of a sensitive AM broadcast receiver. Furthermore, the cost of the screening can be defrayed by including switched-mode power management circuits within the screened environment. This reduces the power consumption, allows the use of a single cell as a power source, and reduces the total ownership cost and the size and the weight of the product.