Diode "polarity" question

danielzink · April 23, 2009, 03:20:45 PM

With regards to this potion of a schematic:

are the diodes oriented properly in this layout ?

Thanks, Dan

slacker · April 23, 2009, 03:28:42 PM

The diodes are the opposite way round on the layout compared to the schematic.

Andi · April 23, 2009, 03:31:28 PM

I concur.

danielzink · April 23, 2009, 03:43:12 PM

What if the transistor "numbers" were reversed ?

And why am I having such a hard time wrapping my mind around two diodes ?

Dan

anchovie · April 23, 2009, 04:18:18 PM

I think the orientation on the layout is correct. The cathodes of the diodes are connected to traces that short together two pins of the MOSFETs, just like the schematic.

This is of course on the assumption that the layout matches the pinouts of the MOSFETs correctly.

slacker · April 23, 2009, 04:27:09 PM

On the schematic the anodes are facing the gate/drain junction not the cathodes.

anchovie · April 23, 2009, 05:10:33 PM

D'oh! You're absolutely right, the dot in the MOSFET symbol threw me.

Must get more than 3 hours sleep tonight!

danielzink · April 23, 2009, 05:32:37 PM

Okay....here's why I'm confused....

I pulled this picture off the internet ...

Is it not correct ?

in the color layout picture the "band" (or - ) of D2 is connected to the gate/drain junction of Q2 as the same for D1/Q1...

Thanks, Dan

MohiZ · April 23, 2009, 05:33:08 PM

Why are the diodes labeled D1 and D2 on the schematic but D2 and D3 on the layout?

Wales · April 23, 2009, 05:40:05 PM

Quote from: danielzink on April 23, 2009, 05:32:37 PM
Okay....here's why I'm confused....

I pulled this picture off the internet ...

Is it not correct ?

in the color layout picture the "band" (or - ) of D2 is connected to the gate/drain junction of Q2 as the same for D1/Q1...

Thanks, Dan

My rule of thumb is like the photo the line on the diode on the schematic should coincide with the line on the diode.

danielzink · April 23, 2009, 06:06:22 PM

Quote from: MohiZ on April 23, 2009, 05:33:08 PM
Why are the diodes labeled D1 and D2 on the schematic but D2 and D3 on the layout?

When you're using DIY Layout creator - it labels the components as you put them in.....if I had put the one on the right in first..it would have been automatically labeled Q1...

Dan

anchovie · April 23, 2009, 06:16:40 PM

Quote from: danielzink on April 23, 2009, 05:32:37 PM
in the color layout picture the "band" (or - ) of D2 is connected to the gate/drain junction of Q2 as the same for D1/Q1...

I think you've made the same mistake that I did. In the symbol for the MOSFET, the dot with a straight line and a bent line with an arrow at the end coming from it represents just one pin of the device. It's the other two terminals that are connected (by the vertical lines at the left and right of the schematic).

danielzink · April 23, 2009, 06:19:57 PM

Quote from: anchovie on April 23, 2009, 06:16:40 PM
Quote from: danielzink on April 23, 2009, 05:32:37 PM
in the color layout picture the "band" (or - ) of D2 is connected to the gate/drain junction of Q2 as the same for D1/Q1...

I think you've made the same mistake that I did. In the symbol for the MOSFET, the dot with a straight line and a bent line with an arrow at the end coming from it represents just one pin of the device. It's the other two terminals that are connected (by the vertical lines at the left and right of the schematic).

insert cartoon lightbulb over head........

News:

Diode "polarity" question