Using thin wire between driver pcb and mosfets

[Lucas_G]

Dear Pass Folks,

I am building a pair of Aleph 2 using the driver PCBs and Mosfet PCBs of Kristijan http://web.vip.hr/pcb-design.vip/aleph-2.html

My question is: I have just connected the driver board with the two Mosfet boards (the D-S-G-R connections).
I have used thicker wire for the D and the R and very thin (about 0.5 mm radius) wire for S and G.
Is it right that through S and G the current is very low?
Or can I expect problems by using such thin wire here?

Regards,

Lucas.

[jh6you]

I understand that the current through the D-node and S-node should be the same. Anyhow, even if the thicker the better, I have also used 0.5mm dia solid wires (length less than 200mm) without any problem.

[MBK]

Same here: only the gate current is very low, D and S currents are the same and carry the full output current. What I did was, internally, use thin wires, I believe 0.5 mm as well. I built it on proto board, and I took care that any large current does not pass through board traces but only through wires, by connecting the wires directly to D and G, routing them to PCB, and at PCB, directly soldering wires to source R and output R's. So the only current passing through traces is signal current and feedback, and supply for the input stage.

A good indication for wire gauge is the wire size of your transformer at the secondary: use the wire cross section area of your secondary if 1 PSU/channel, and 1/2 wire cross section area of secondary if 1 PSU/2 channels. No point going any thicker ;-)

You can also double up thin wires to be safe.

[Lucas_G]

Thanks JH6YOU and MBK,

I got this answer from Kristijan:


>Hello Lucas,

>You are correct.
>It is not really neccessary to use tick wires for the S and G,
>as there is not almost any current, and you can use any wire
>you would like.

>However, it is neccessary to use tick wires for the D and R
>connections, as through them running high current.

>If I can be of any further assistance to you, please feel free to
>contact me again.

>Best regards,
>Kristijan Kljucaric
>http://web.vip.hr/pcb-design.vip





----- Original Message -----
From: Lucas Guitink
To: pcb-design@vip.hr
Sent: Thursday, August 14, 2003 10:36 AM
Subject: Wire between boards


Dear Kristijan,


I am now wiring up a pair of Aleph 2 using your driver PCBs and Mosfet PCBs.

My question is: I have just connected the driver board with the two Mosfet boards (the D-S-G-R connections).

I have used thicker wire for the D and the R and very thin (about 0.5 mm radius) wire for S and G.

I saw that on de mosfet boards you too have made large connections for D and R, and small paths for S and G...

Is it right that through S and G the current is very low?

Or can I expect problems by using such thin wire here?

Regards,

Lucas.

[MBK]

Hmm, maybe I didn't get the question. Any current there is at the output definitely passes from drain to source. The Gate controls this current.

At idle, the bias current (1.5 A) will pass essentially from positive to negative rail, therefore through top D and S, bottom D and S, and both source resistors. The top source resistor has a fixed voltage across it (ca. 0.5 V). So, the source *resistor's* voltage is small, which limits the power dissipated to 0.5 x 1.5 = ca. 0.75 W, but the drain-source current, voltage and power is large: voltage is essentially rail voltage, currentis bias current, and power equals dissipated power for each half.

At positive swing, current will pass from positive rail through top D and S, to output.

At negative swing, current will pass from output trough bottom D to S and bottom source R, to negative rail.

Maybe the wires you are asking are not the ones I am thinking about...