Relay flyback diode

This short post has 2 main objective:

1. Visualization of the effect that produce the flyback diode.

2. What happen when used a different type of diode.

• Procedure of experiment and measurement.

While energize a 5 pin relay with 12VDC regulated, the low side of the coil was measured with oscilloscope probe at x10 attenuation.

Every circuit implemented on each evaluation was supported with scheme, photo of breadboard and the oscilloscope screenshot.

Was indicated the peak voltage and mark with a red circle.

• Information and list of equipment and materials

• Relay drive with a bjt transistor and pulse switch, without flyback diode

• Relay drive with pulse switch and flyback diode.

• Relay drive with bjt transistor and flyback diode.

• Module relay whit flyback diode, 3mm red led whit 1k resistor, drive with pulse switch.

Conclusion:

When a coil is energizer, all this energy is not absorber while relay is activated, that remaining energy is dropped backward to the point of control, like we see in this post, This energy is a big problem for the electronic control, that in this case, is a BJT transistor 2N2222A with a Vce = 60 vdc. This transistor was pushed as its limits while has´t a fly back diode in parallel with relay coil.

This diode is very important for improve and health of the electronic control design.