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Dell SE197FPf Monitor 12v Conversion

My other monitors are a different model, and have a slightly different main PCB inside, but the process is mostly the same for converting these to 12v supply.

Main PCB
Main PCB

In this monitor type, there is only a single board, with all the PSU & logic, instead of separate boards for each function.

PSU Closeup
PSU Closeup

This monitor is slightly different in it’s power supply layout. The mains supply provides only a single 12v rail, which is then stepped down by a switching converter to 5v, then by smaller linear regulators to 3.3v & 1.8v for the logic. This makes my life easier since I don’t have to worry about any power conversion at all.

PCB Reverse
PCB Reverse

Here’s the backside of the PCB, the mains PSU section is in the centre.

Attachment Points
Attachment Points

Here’s the pair of 12v supply wires soldered onto the main board, onto the common GND connection on the left, and the main +12v rail on the right. I’ve not bothered with colour coding the wiring here, just used whatever I had to hand that was heavy enough to cope with a couple amps.

12v Socket
12v Socket

A small mod later with a cone drill & the 12v input socket is mounted in the LCD frame.

Casing Mod
Casing Mod

Some light removal of plastic & the back cover fits back on. Current draw at 13.8v is ~2A.

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Rigol DS1054Z DC Power Supply – Linear Post Regulation

Finally, here’s the last part of the Rigol 12v DC Power Supply project, the linear post regulation section to remove some of the ripple.

I have made a couple of layout adjustments since the last post about this part of the project – a little more filtering on the DC outputs. As usual the Eagle project files are at the bottom of the post for those who might find them useful.

Updated PCB
Updated PCB
Updated Schematic
Updated Schematic

 

Completed PCB
Completed PCB

Here’s the completed PCB, partially installed in the back of the scope. The missing regulator is the 5v one, since I already have a source of clean 5v from my original attempt at the supply, it’s not a problem not using a linear after the switcher. The filtering is the same on all channels, input from the switchers is on the right, outputs to the scope on the left.

PCB Bottom
PCB Bottom

Here’s the bottom of the PCB, with the common mode input chokes. The design of this board has allowed me to remove a couple of the switching modules as well, as I can use a single bipolar supply to run both sets of bipolar regulators on this board. This should help remove some of the noise also.

The ripple level has now dropped to lower than it was originally on the mains supply! Current draw at 13.8v DC is about 1.75A.

Scope Ripple
Scope Ripple

[download id=”5589″]

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Rigol DS1054Z 12v Power Supply Noise Filtering

Since I fitted my scope with a SMPS based 12v input supply, there has been a noise problem on very low volts/div settings, this noise isn’t present on the mains supply, so I can only think it’s coming from the switching frequencies of the various DC-DC modules I’ve used.

Scope Ripple
Scope Ripple

Because of this I’ve designed a linear post-regulation stage for the supply, to remove the RFI from the DC rails.
This board takes the outputs from the DC-DC converters, removes all the noise & outputs clean DC onto the mainboard of the scope.

As the scope internally uses regulation to get the voltages lower, I’ve found that I don’t have to match the outputs of the mains supply exactly, for the +/-17.5v rails, 12v is perfectly fine instead.

Scope Linear PSU
Scope Linear PSU

Here’s the PCB layout, with the 6  common mode filters on the input (left), linear regulator ICs in the centre & the output filters on the right.

Scope Linear PSU
Scope Linear PSU

Here’s the schematic layout, as usual the Eagle Project files are in the link below, I’ll update when I have built the board & tested!

[download id=”5589″]

73s for now 🙂