EHE003

The Ground Zero Board - EHE003

The EHE-003 Ground Zero Board electronics are designed to allow useful power to be extracted from extremely small or off-resonance vibration sources that produce AC peak voltages as little as 400mV. This circuit is intended for simple "one-shot" applications that wake up and perform a quick task (e.g. take a measurement, send radio packets) in a known amount of time and power.

A switched-capacitor charge pump boosts and stores this input to an onboard or user-supplied storage capacitor. When the capacitor is full (2.4V), boosting stops, the output is enabled and this voltage is applied to the load. Once the storage cap has been discharged to 1.8V, the load is disconnected and boosting resumes, recharging the storage cap for the next burst.

The 1.8-2.4v output range of the EHE003 can directly power most 3.3V microcontroller circuits, which typically have an operating voltage range of 1.8V ~ 3.6V. It can also be used to power an inductive boost converter to drive higher-voltage systems or maintain Li-Ion or thin-film batteries (4.1-4.2v). Since the load is fully disconnected between bursts, the user can employ an inductive booster without worrying about the low-voltage start-up or undervoltage behavior of the secondary booster.

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 to boostrap an inductive boost converter to deliver even higher
    voltages or charge battery/supercap supplies, without worrying about the inductive
    booster's low-voltage behavior.
+ Has 100 Ohms or lower output impedance (34 ohms typ.), regardless of input source.
+ Limits input current (0.5mA) to avoid overloading the 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

Please contact Chris Ludlow at cludlow@mide.com or 781-306-0609 x227, for further information.

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).