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M0LTE / pi-transceiver

An attempt to build a complete ham radio transceiver around a Raspberry Pi
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Power supply #33

Open gblades opened 2 years ago

gblades commented 2 years ago

With regard to the power supply and input protection I intend to use the LTC4368 that I have previously used on my inline protection board. I intend to have a P channel MOSFET on the input instead of a latching relay. It will be wired to only switch on if there is already an output on the protection board so it will latch in the same way as a relay. There will be a header for connection to a momentary switch for soft power on. The SHDN of the LTC4368 will be connected to a few inputs via diodes so that there are a few channels where between 2.5V and +VE can be connected to in order to switch off the supply. One would be the raspberry pi and others could be any other fault detection circuitry.

What are we planning to use for the 5V supply?

I'm also thinking of adding an AMS-1117-5V onto the PCB direct from the input to provide a permanent 5V supply which could be used if anyone wishes to add a little microcontroller of some sort in order to be able to remotely power on for example. The space required will be minimal and it doesn't have to be populated if not used.

What connectors do we want to use? For the input I assume screw terminals as there will be a lead to a chassis mount powerpole or similar. What power connector would people like for the 13.8V output to the PA and how many? For logic IO such as the shutdown signals I intend to use JST 2.5mm type connectors. What about the 5V output? If this direct from the 5V supply or is it going to connect back into the PSU board and fan out to where it is required?

G4CDF commented 2 years ago

I use these types of connectors: https://www.12voltplanet.co.uk/insulated-ring-crimp-terminal-red.html. These can be stacked for multiple band PAs. Bigger ones are in use on my mast winch and are rated to 200A Powerpole are too expensive for internal use

G4CDF commented 2 years ago

I thought of chocolate blocks but these can be unreliable and will take more space up with multiple bands

M0LTE commented 2 years ago

I’ve started using a lot of wago-style spring connectors. If they’re good enough for UK mains electrics, they’re good enough for us. Far prefer them to screw terminals. Does something like this exist in PCB-mount?

On Tue, 18 Jan 2022 at 15:56, Mike @.***> wrote:

I thought of chocolate blocks but these can be unreliable and will take more space up with multiple bands

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M0LTE commented 2 years ago

Like this

https://uk.farnell.com/wago/2604-1102/terminal-block-wtb-2pos-24-12awg/dp/3577796

On Tue, 18 Jan 2022 at 15:57, Tom M0LTE @.***> wrote:

I’ve started using a lot of wago-style spring connectors. If they’re good enough for UK mains electrics, they’re good enough for us. Far prefer them to screw terminals. Does something like this exist in PCB-mount?

On Tue, 18 Jan 2022 at 15:56, Mike @.***> wrote:

I thought of chocolate blocks but these can be unreliable and will take more space up with multiple bands

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gblades commented 2 years ago

They look good. https://www.rapidonline.com/phoenix-contact-1729018-mkdsn-1-5-2-2-way-screw-pcb-terminal-block-13-5a-5mm-52-3886 is the common type but a lower 13A rating. They are both a 5mm pitch so I can design for the Wago's with their two pins per contact and the others will still fit.

How many 5V and 13.8V outputs will we need and how much current would each need to handle and in total?

M0LTE commented 2 years ago

For the 5V, I’d probably allow for three positive terminals. The Pi wants 3A, and runs fine with the touchscreen on the same official 3A supply. If we can have 4A that probably makes sense. The Lime and all peripherals hang off the Pi’s USB.

I’ll let Mike speak for 13.8V.

What is going to be the ground reference for the radio? Possibly makes sense for it to be the PSU? In which case, doubling up on terminal count makes sense…

On Tue, 18 Jan 2022 at 16:12, gblades @.***> wrote:

They look good. https://www.rapidonline.com/phoenix-contact-1729018-mkdsn-1-5-2-2-way-screw-pcb-terminal-block-13-5a-5mm-52-3886 is the common type but a lower 13A rating. They are both a 5mm pitch so I can design for the Wago's with their two pins per contact and the others will still fit.

How many 5V and 13.8V outputs will we need and how much current would each need to handle and in total?

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gblades commented 2 years ago

What 5V power supply module is being used? Is it going to use one of the 13.8V outputs and then come back to the PCB and for the PCB just to act as a 5V distribution board? Or can it be piggy backed directly onto the psu pcb?

M0LTE commented 2 years ago

I am hoping that you’ll pick one and include it on this PSU board :)

On Tue, 18 Jan 2022 at 16:48, gblades @.***> wrote:

What 5V power supply module is being used? Is it going to use one of the 13.8V outputs and then come back to the PCB and for the PCB just to act as a 5V distribution board? Or can it be piggy backed directly onto the psu pcb?

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gblades commented 2 years ago

Ok no problem.

G4CDF commented 2 years ago

For the PA we will need 1 connector per band, so it is anyone's guess. Allow say 4 bands. The board can always be subpopulated. I think that any sophisticated current limiting, VSWR protection etc should be done on the RF boards if required.
Grounding issues are always going to be a problem so we need a good strategy. RF earth will have to be connected to DC earth so where does the current flow? One way is to use isolated power supplies but very expensive. The other way is to define a pseudo- common grounding point such as all the antenna connections.

gblades commented 2 years ago

I have decided to go with the LM2759 as the buck converter to generate the 5V supply. It will actually output 5.1V as that is what the Pi likes and it can supply up to 5A. Ti provide a very good web tool called WEBENCH where you can put in your power supply requirement and it generates possibly circuits which you can then filter by a particular controller chip. Have a look at https://github.com/M0LTE/pi-transceiver/tree/M7GRB/electronics/PSU%20Board as I have saved the generated schematic, efficiency graphs and the bill of materials down to specific part numbers.

M0LTE commented 2 years ago

Amazing work! Thanks! What’s next?

On Wed, 19 Jan 2022 at 21:31, Gareth Blades M7GRB @.***> wrote:

I have decided to go with the LM2759 as the buck converter to generate the 5V supply. It will actually output 5.1V as that is what the Pi likes and it can supply up to 5A. Ti provide a very good web tool called WEBENCH where you can put in your power supply requirement and it generates possibly circuits which you can then filter by a particular controller chip. Have a look at https://github.com/M0LTE/pi-transceiver/tree/M7GRB/electronics/PSU%20Board as I have saved the generated schematic, efficiency graphs and the bill of materials down to specific part numbers.

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gblades commented 2 years ago

There is still a lot of things to do. I need to put the new 5v supply into kicad, add the connectors for the wago blocks etc..., build a parts list and add the major bits onto the next order someone is making and then start on the pcb design.

gblades commented 2 years ago

I have added some of the parts to a Mouser parts list and there is a link to this in the readme.md in my branch. I haven't finished yet but the major components are there and the total cost for parts is going to be in the region £25-30+VAT

M0LTE commented 2 years ago

Great stuff, thanks Gareth 👍

On Mon, 24 Jan 2022 at 19:07, Gareth Blades M7GRB @.***> wrote:

I have added some of the parts to a Mouser parts list and there is a link to this in the readme.md in my branch. I haven't finished yet but the major components are there and the total cost for parts is going to be in the region £25-30+VAT

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