Does anyone have a simple circuit for 13.8v step down converter to 5v ?

Or recommend one

Thanks bton-fm, Appreciated

Minor changes - connect your 100nF caps right at the legs of the regulator, and use a couple of 4µ7 or 10µ electrolytic capacitors in place of the 10nF.

The 78L05 is only good to 100mA. If you need more current, you'll need a 7805 (good to an amp, but will need a small TO220 heatsink at more than about ½A. If you go for the heavier current device, you'll need the same capacitors to keep RF (in particular) out of the regulator.

LeeCavanagh wrote: ↑Mon Jan 25, 2021 1:06 pm Thanks bton-fm, Appreciated

What are you trying to power with this? I presumed it was a PLL?

Albert H wrote: ↑Mon Jan 25, 2021 3:31 pm Minor changes - connect your 100nF caps right at the legs of the regulator, and use a couple of 4µ7 or 10µ electrolytic capacitors in place of the 10nF.

That's how I normally do it with the legs soldered to the middle leg if its a 7805 on a tuner can or as close as possible if it's on a PCB. I guess it depends what it's powering to what the decoupling values are?

Bton-FM wrote: ↑Mon Jan 25, 2021 6:37 pm

LeeCavanagh wrote: ↑Mon Jan 25, 2021 1:06 pm Thanks bton-fm, Appreciated

What are you trying to power with this? I presumed it was a PLL?

Oh, a tiny pll which only gives out 100mw

I did consider using a cigarette lighter to usb charger which i have spare, that give out 5v more than enough amps too

LeeCavanagh wrote:I did consider using a cigarette lighter to usb charger which i have spare, that give out 5v more than enough amps too

Most of the time they give out a load of noise too. They can be used, but should be shielded.

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Be REALLY careful with the filtering on the supply if you use the 5V adaptor. They frequently put out ~100kHz ripple, which can appear as spurs on your carrier!

do not forger electrolyte capacitor