EHE003

The Ground Zero Board - EHE003

The Ground Zero board allows useful power to be extracted from extremely small or off-resonance vibration sources that produce post-rectifier open-circuit voltages as little as 350mV. A switched-capacitor charge pump boosts and stores this input to an onboard or user-supplied storage capacitor. When the capacitor voltage reaches 2.4V, the output is enabled and this voltage is applied to the load. The load is automatically disconnected when the output capacitor has discharged to approx. 1.8V. This behavior allows the EHE003 to directly power most 3.3V microcontroller circuits, with a typical operating voltage range of 1.8V ~ 3.6V, or maintain a battery- or supercap power source. Please contact Chris Ludlow at cludlow@mide.com or 781-306-0609 x227, for further information.

Your Ground Zero Board:
+ Directly powers small sensors that can perform their function
    (e.g. record or transmit a measurement) in a known amount of time and power.
+ Can be used as a battery maintainer or extender and measurement trigger source for
    devices with their own battery/supercap power source.
+ This circuit is best suited for low vibration levels (see Performance).

For the best efficiency at high vibration levels (piezo open-circuit voltages of 9V or more), use the EHE002 Pulse Power Electronics.

EHE003 Schematic

EHE003

EHE003

Example Performance Plots - Measured

EHE003

A common usage scenario is an embedded sensor with data storage/transmission capability, which takes one set of measurements each time it powers up. In this case, the measurement frequency is variable and depends on the vibration amplitude. In this case, to operate the sensor directly from the EHE003 requires:

• Estimate (or measure) the run-time and power consumption of your application within its voltage limits
• Size CPout according to worst-case usage, allowing some headroom
• Test!

If the sensor is meant to be triggered only once per power-up (e.g. it does not monitor its input voltage and initiate additional measurements when possible), the sensor should create a large load (e.g. drive an LED or GPIO pin tied to ground) after completing its tasks in order to ensure a load disconnect-reconnect cycle in high-vibration conditions.

A typical microcontroller sensor application’s load profile will be “bursty”, complicating the task of estimating the required value of CPout. However, if the load can be approximated in terms of a resistive load, the following equations can be used to estimate the required capacitance, available runtime, energy per discharge or power stored.

where Td is the runtime or discharge time in seconds, Tc is the charge time in seconds, R is the equivalent load resistance in ohms, V0 is the starting output voltage (2.4), V is the final output voltage (1.8V or the minimum operating voltage of the sensor, whichever is greater), and C is the capacitance in Farads. Likewise, the output voltage can be modeled as a simple RC time constant, V = V0e(-T/RC).