There are few professional designs in the audio business and in the ventilation flow control business who completely skip that extra 68V supply - I haven't checked the data-sheet what it says but they don't bother with that extra voltage. Some designs use a SN75468/9 IC (75469 in case of CMOS and 75468 if TTL is used) instead of transistors and no pull-up resistors, just hook the 68V signal to the common pin on the SN75468/9.
For all of the designs I've seen there is not one that uses a 1M resistor on the keep alive cathode, only on the anode, they all just ground the keep alive cathode pin directly. Some designs uses a voltage between 50-80V for the 68V voltage. Some designs uses a voltage doubler/tripler to supply all voltages from a low voltage AC transformer, so maybe use a switcher with say 62.5V DC output and the quadruple that to 250V DC if there is the possibility of hooking into the circuit before rectification/smoothing? /Martin On Friday, 31 October 2025 at 06:57:04 UTC+1 Richard Scales wrote: > Does anyone have any experience in driving these panaplex-like bargraph > displays? > > I have some IGT2-203R and am using a well publicised circuit from here: > https://stromrichter-org.translate.goog/attachment.php?aid=4116&_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp > > [image: Pic1.jpg] > > I have made various changes, I'm using an Arduino Nano for the controller, > an HV module for the 245V and I changed out the R2/D2 combination for an > LR8 HV regulator as I found that R2 was getting a lot warmer that I would > like. > > Now I am looking at the anode supply which is controlled by R8+R18 (I am > only using one channel so don't have R7/R17. > > It seems that when Q8 is off, the Anode is connected to the 245 supply > via 36K for current limiting purposes - that's all good. When Q8 is on, > then the anode is fed from what is now the voltage divider combination of > R8+R18 (98V) - also good. > > However, that combination of 24K+36k is drawing about (245/60)mA - 4mA - > the power being almost 1W - so they get a little warm. I have over > specified and used 5W parts. > > What I have works just fine, and, in fact I even doubled up on the > resistors to share the load even further but I wonder if there is perhaps > a better way which might not generate quite so much heat? > > It might seem overkill but I could make 98V using another LR8 and then use > high side drivers to 'switch' between the two (like a couple of Opto > Couplers or a bunch of 42/92 transistors). > > ... or am I being over cautious? > > - Richard > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/5dceb9ad-7758-4247-a9cd-770115891ad2n%40googlegroups.com.
