Open Dots 101

Open Dots™ is a conductive, wire-free power technology employing pads with conductive stripes, and devices with contact points that touch the conductive stripes.

The basic principle of operation of the Open Dots™ standard is shown in figure 1. A pattern of connection points on the bottom of an Open Dots™ device makes contact randomly with metal strips on the Open Dots™ pad.

DotsOnPad

Figure 1

 

The contact strips on an Open Dots™ pad are alternately connected to plus and minus. By the nature of the geometry of the contact points on the device (power receiver), at least one contact will be connected to plus, and at least one contact will be connected to minus no matter where the device rests on the pad.

 

Because it is not possible to know which contact(s) will land on a positive strip and which contact(s) will land on a negative strip, a four-way bridge rectifier is used to right the random polarity. The contact points connect to the signals A, B, C, and D in the diagram, and the output of the rectifier is labeled “+” and “-“.

The Open Dots™ standard calls for a potential of 15V to 20V on the pad electrodes. Thus, the output of the four-way bridge rectifier is approximately 15V to 20V. For many applications, such as for cell phones, the rectifier output is regulated down to 5V with a switching regulator.

 

The entire signal path is shown below. A power supply provides power for the system. The power is conditioned by a sensing circuit and brought to the pad electrodes. The contact points make direct electrical connection to the pad electrodes. The contact signals are brought through a rectifier to provide a positive and negative power signal into the device-side regulator. Finally, the regulated output powers a device.

 

The pad voltage is 15V for pads that can supply up to 50W, and 20V for pads that can supply up to 160W. Thus a device resting on the pad can determine if it is on a low-power pad or a high-power pad.