INFO: Chronos Warning: Driving Induction Load [25077]

This article applies to:
Chronos

Detail
Warning: Improper use of Chronos may void your warranty.

1. Failure to use a flyback protection diode while driving an inductive load like a motor can cause physical damage to Chronos that is not covered by the warranty.
2. The motor must be switched on and off using a separate transistor. A single Chronos digital output cannot provide enough current to start the motor. Failure to use an external transistor could mean the motor takes longer to turn on, if it turns on at all.
3. Chronos guarantees 100mA for the digital outputs and the 5V pin on the Primary and Auxiliary connectors. All are shared. Typically, Chronos boxes are around 150mA. Each Digital Output is limited to ~20mA.

A 3V regulator will work, but if the motor is rated to operate up to 3.6V and you may find it easier to use a 3.3V regulator.

The power lost to heat in a linear regulator may make the motor start more slowly. PST recommends a switching regulator such as the OKI-78SR series. They are through-hole which will be easier to deal with.

Consult the datasheet of whatever regulator is chosen to determine bypass capacitors C1 and C2.

Example

Motor M1 is the motor selected for this example. The motor (M1) used in this example is https://www.precisionmicrodrives.com/product/312-101-12mm-vibration-motor-3mm-type.

Diode D1 is basically any diode, but 1N4001 is often recommended for flyback protection. It must be oriented in the reverse-biased condition as shown or damage will result to Chronos that is not covered by the warranty.

Transistor Q1 is basically any n-Channel enhancement mode MOSFET. n-FETs go on the low side of the motor with the Source connected to Ground. If a p-FET is chosen the schematic will be different; we prefer n-FET because a logic ‘1’ will turn the motor on. It is possible to use an NPN or PNP BJT to switch the motor if they are biased correctly, but the MOSFET is less complicated.

All Aux connections are on the Chronos Auxiliary I/O. The I/O Expansion Kit for Chronos can also be used for this purpose, if purchased.

If you have any questions or concerns about your configuration, please contact Product Service & Support.

See Also:
INFO: Powering Devices With Chronos [29142]
INFO: Connecting third-party switches to Chronos [30394]