Power Supply for VFD Display

Question

I recently ordered a GP1294AI VFD display from Aliexpress. Unfortunately it did not contain the necessary power supply to power the display, but the datasheet did include the necessary schematics for a power supply.

However, the components used in the schematic are not available from European retailers. This is why I recreated the schematic using different components. I made a few adjustments and wanted to make sure I made no mistakes before starting on the PCB layout as my power electronics knowledge is limited.

• I will use a 12V supply, so I removed the USB input connector
• I will not use the aux inputs or light sensor so these were removed
• The DCDC boost converters creating 75V and 50V were designed using the online WEBENCH tool from Texas Instruments
• The circuit from the datasheet contains a seperate SMPS for generating 3V3 from 5V. I removed this one as 3V3 is already created by a linear regulator. A high-side switch enabled/disables the filament driver instead.

All feedback appreciated!

Answer 1

Few things I noticed:

• The diodes on bottom-right (VFD section) should connect to each 200R to the left, instead of having all paralleled across CLK pin.
• The connection of the PMOS that is supposed to be used to switch the V_FILAMENT is wrong. It's upside down so the body diode will always be in forward bias which means V_FILAMENT will always be present regardless of FILAMENT_EN signal status. Plus, if the FILAMENT_EN signal is a 3.3V logic signal then the Q3 can be omitted:

^{simulate this circuit – Schematic created using CircuitLab}

The circuit from the datasheet contains a seperate SMPS for generating 3V3 from 5V. I removed this one as 3V3 is already created by a linear regulator.

• It's not that simple. There must be a reason why they used a separate regulator for V_FILAMENT. For example, the current consumption could be higher than the current that the linear regulator can handle. I can see they used BL1117-33CX which is a 3V3/1A regulator, quite similar to the one you have, LM3940. They used the output for VFD as VFD_VDD but they didn't use the same voltage for V_FILAMENT. Instead, they built a 3.3V/2A synchronous buck for V_FILAMENT. So you should consider a separate regulator with similar specs anyways.

I'll update the post as I find some more things.