Relay diode

[GatorGnet]

I wanted to see if I am connecting the diode correctly from the relays to the transistors. This is not the real layout so no comments on the crude layout! haha

**broken link removed**

 

[ericgibbs]

I wanted to see if I am connecting the diode correctly from the relays to the transistors. This is not the real layout so no comments on the crude layout! haha

hi gator,
Look at this.

 

[GatorGnet]

That helps a lot. Although, would it be okay to keep the ground on the other pin and the + voltage on the transistor? Not a huge deal if it is not.

 

[Boncuk]

Hi Gator,

here is a schematic containing two possible ways to connect transistor and relay to a PIC.

Decide what suits your needs best.

(Observe the L/H relay pulled in at 5.31V and the R/H relay remaining open at 3.73V)

Boncuk

 

[GatorGnet]

How does the diode not create a short when power is applied to the coil?

 

[Boncuk]

How does the diode not create a short when power is applied to the coil?

As you see one coil terminal is always connected to the positive power rail.

When Q1 conducts it "switches" ground to the second relay terminal, thus activating it.

The diode parallel with the relay is a "free wheeling diode" and should be there to protect Q1.

When the relay is deactivated the coil generates reverse voltage (back EMF) higher than the supply voltage. This voltage is shorted out by the protection diode.

Connecting the anode of the diode to +5V and the cathode to the collector of Q1 it creates a short when power is applied to the coil.

Boncuk