Voltage regulators on MiniTiouner

[G8PEF]

Hi, all

I've just built the MiniTiouner yesterday, and have a query about the voltage regulators on the board.

I'm guessing that (given the large copper land underneath them, that they need no further heatsinking - but do they need anything between the regulators and the copper? thermal compound? electrically insulating thermally conducting pad? Or are they ok just bolted straight down to the PCB?

Looking forward to testing the board and making a start on the Portsdown.

Many thanks
John

[G3GJA]

John

No further heat-sinking is needed so long as you keep the voltage from the switching regulator to 4.0v

I've built two and they both are fine as is.

Clive G3GJA

[G8PEF]

Thanks, Clive.
What about thermal compound? Is it advisable/necessary?

John

[M5TXJ]

My regulators are just bolted down with no heatsink compound, no problems.

73 Dave

[g0mjw]

John

No further heat-sinking is needed so long as you keep the voltage from the switching regulator to 4.0v

I've built two and they both are fine as is.

Clive G3GJA

That's right. The reason for the DC-DC providing a 4V input is to minimise dissipation in the linear regulators that follow it. The dissipation is so low that the PCB area is sufficient. Just bolt them down, no need for paste.

Analysis

The 3.3V tuner takes no more than 700mA. The 3.3V IO 40mA and the 1.1V digital no more than 400mA and that's with both channels working. In practice we have only 1 channel so 200mA.

Therefore, at 4V input the 3.3V tuner regulator is dropping 0.7V and so it is dissipating 0.49W. The digital 3,3V also drives the 1.1V regulator, so it passes 240mA and dissipates 0.17W. The 1.1V regulator drops 2.2V so it dissipates 0.45W. The total dissipation in the linear regulators is therefore just a bit over 1W.

The regulators have a 400mV dropout voltage, you can go below 4V, down to about 3.7V and lower the dissipation even more.

Mike

[G8PEF]

Thanks, chaps - I've now tightewned up those M3s

Mike - I powered up the board, and with an input of 13.6V (dc-dc set to about 3.9) the total current (without anything else connecte0d) is about 240mA - does that sound right?

Intertestingly, the current did vary quite markedly with changes to the input voltage, which can only be down to the operation of the dc-dc converter, as it had to 'dump' varying levels of voltage.
73
John