Revisiting VFD PSU – Part III

It is time to test our revisited VFD PSU in real life. We are going to build a quick prototype using a PCB from MVFD 16S7D Panel with minimum components loaded. All we need to solder is a VFD controller IC2 (instead of HT16515 we are going to use PT6315 as they are pin-to-pin compatible), a 82k resistor R14 to keep controller’s oscillator running, a decoupling 100n capacitor C11 and CTRL connector along with VFD glass VFD1. The PCB is then connected with the PSU to provide filament (~2.5ADC), high voltage (-24VDC) and logic voltage supply (+5VDC) as shown on the picture below.

VFD_PSU_EXP01 VFD Driver Soldered

VFD_PSU_EXP01 VFD Driver Soldered

To drive the VFD controller our specifically designed Arduino compatible VFD Serial Backpack is used. The backpack is programmed with a slightly modified Magictale VFD Demo lib published in VFD driver demo article. The backpack is simply attached to the VFD panel, it gets power from it and at the same time communicates with PT6315.

VFD_PSU_EXP01 Backpack Attached

VFD_PSU_EXP01 Backpack Attached

The prototype works smoothly, in our experiment it jumpstarted immediately without any troubleshooting. The brightness of the VFD is much better than the original MVFD 16S7D panel. Also there is no brightness gradient, thanks to the pulse filament drive.

VFD_PSU_EXP01 With Serial Backpack

VFD_PSU_EXP01 With Serial Backpack

However, nothing can be perfect. This solution exhibits a ghosting effect when some segments are faintly glowing while they actually must be completely dark as it is shown on the picture below. The reason for this is absence of cut-off voltage which we hopefully can solve by adjusting some components of the PSU but this will be our next exercise.

VFD_PSU_EXP01 Ghost Effect

VFD_PSU_EXP01 Ghost Effect

Despite of a couple of annoying issues such as ghosting effect and a bit excessive current consumption of the whole prototype (250mA) we managed to prove that the new PSU is generally functional and has some improvements over the old design. And most importantly, it is very cheap and doesn’t have fancy chips which could potentially become obsolete in nearest future without any hope to be replaced with something similar.

UPDATE: R9 = 2.1K, R10 = 9.1K to cancel ghosting effect.