A4WP Charger - Power Transmitting Unit PTU

- the A4WP charger pad is known as the power transmitting unit or PTU. It contains all the elements required to transfer power to compatible receiving devices.

The A4WP wireless charger or pad is known as the power transmitting unit, PTU.

This power transmitting unit is the key controller and power source for the wireless charging system.

The A4WP charger or power transmitting device contains all the electronics to enable power to be taken from the mains of other power supply and convert it into a format where it can be picked up by the receiver unit to enable it to be charged.


A4WP PTU basics

The A4WP power transmitting unit or charging pad has a number of basic building blocks within it.

The A4WP wireless charger consists of a number of blocks that provide the functionality required to meet the specification set down by the Alliance for Wireless Power.

The power transmitter unit, PTU for an A4WP charger showing the different circuit blocks required within the wireless charging system.
A4WP power transmitter unit block diagram

The A4WP charger / power transmitter unit, PTU contains two main areas. One comprises the areas used for the power transfer, and the second is associated with the signalling.

The signal for the power is generated at a frequency of 6.78 MHz which is in the HF portion of the radio spectrum, in a band reserved for Industrial, Scientific, and Medical applications. Traditionally this band has been widely used for industrial inductive heating.

Also generated, is a signal in another ISM band, but at 2.4 GHz. This link is used for the data transfer for control between the A4WP power transmitting unit and the receiving unit.

Both signals are generated and amplified to the required level before being applied to the transmit resonator.

By Ian Poole


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