Buck Converter Output Smoothing

[M1ASR]

Hi, Looking at the photo of G4KLB's transmitter on the Wiki pages, there look to be filtering on the output of the buck converters. Has anyone got any info on the configuration and component values ? Thank you for reading.

Graham M1ASR

[g0mjw]

I think he just used the same inductors that we use in the Minitiouner (28C0236-0JW-10) and a large capacitor, exact value probably unimportant and I would not be surprised if it was based on what was available rather than a specific design. 1000uF or more. I am not sure this additional filtering is really needed though. Why are you including it?

Mike

[M1ASR]

Hi Mike,

I was just wondering about ripple on the output of the buck converter supplying the Filter Modulater. I’m not worried about the Rpi, just the FM. I’m just about to start construction and was going to include filtering if ripple was an issue. I have all the parts ready to go.

Graham

[G8GKQ]

Hi Graham

As long as you are using the 7805 linear regulator to supply the filter modulator board, there should be no need for additional filtering.

Dave

[M1ASR]

Thank you for your replies, I’ll feed the FM with 9V, which should help cooling of the onboard 7805 also and drop the extra filtering idea.

[g0mjw]

You could go a bit lower than 9V , 7V is the minimum, 7.5V should be fine.

Mike

[M5TXJ]

Hi Graham,

I'm running the FM and the LO filter direct from a buck regulator at 8V with no issues.

73 Dave

[G4KLB]

The above reply's are all correct, the parts I used are as listed above, this was a prototype so extra precautions were taken.
I like to use the additional filtering wherever there isn't a linear regulator downstream.

[M1ASR]

Thank you all understood.

73 Graham M1ASR

[pa2mrx]

I`m currently putting my Portsdown together.

I measured the outputs of my buck converters. Build into a circuit board case with the extra filtering on the output.
Small spikes at 20µS interval, about 20mV.
Got 4 buck converters with different output voltages to supply my portsdown,..all measure the same "dirt".

If no problems, I let it as it is.



73
Frank