Re: LM317LZ Regulator Circuit on ProgRock

Robin Midgett

Thanks for all the inputs.
3.73V & 5.20V is what I ended up with, operating conditions, I'm satisfied.
No, my meter(s) aren't out of calibration...they agree on the measurements.

On Sun, Sep 24, 2017 at 5:50 AM, Hans Summers <hans.summers@...> wrote:
Hi Alan, all

The LM317 components were chosen to produce a "3.3V" voltage somewhat on the high side, because it helps get a little more power output out of the Ultimate3S PA circuit. 

In the QCX transceiver kit the "3.3V" for the Si5351A comes from two 1N4148 in series to 5V! A little approximate... but it does work just fine!

73 Hans G0UPL 

On Sep 24, 2017 11:02, "Alan G4ZFQ" <alan4alan@...> wrote:

Put the circuit under load, maby a 1000ohm resistor to gnd, and make your measurements again

Actually I think if you use the formula in the LM317 PDF using the typical Adjustment Pin Current of 50uA the voltage calculates to 5.15V.
So the Robin's measured LM317 voltage is not so far out.
The nominal 3.3 is not so easy to calculate but assuming no base current in Q1 and a 0.6V drop in the b-e junction I make it 3.6.
Maybe it will be a little lower, 3.6 volts is the maximum recommended for the Si5351. I think Hans designs it like this.

73 Alan G4ZFQ

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