Where is the power to the regulator for the +5v isolated supply coming from ? That source needs to be isolated as well.
On Saturday, June 17, 2023 at 9:01:46 AM UTC-7 Max DN wrote: > That was a mistake, I have corrected the schematic, attached. Grahame > pointed it out too. Apologies. > > What I don't understand is: is it even possible to connect IsolatedGnd to > GridGround? There is 1.2k Volt differential. I see Sgiteach does it but > Grahame is using two different transformers for the highvoltage supply vs > heater supply and then he connects IsolatedGnd to GridGround, I'm trying to > do that from the same core, maybe isn't possible? What I don't understand > is that if I connect the heater secondary (AC voltage) to GridGround, it > works all fine. > > If I connect a resistor between IsolatedGnd and GridGround it gets hot > very quickly, rightly so... > > I must be missing something very simple here... > > > Il giorno sabato 17 giugno 2023 alle 15:54:35 UTC+1 gregebert ha scritto: > >> I see a +5 v supply going to the filament supply, but there is no mention >> of that being isolated like the 12V_isolated supply. I suspect there is >> missing isolation somewhere. The filament is biased near the cathode >> voltage, which is several hundred volts negative. >> >> On Saturday, June 17, 2023 at 12:07:20 AM UTC-7 Max DN wrote: >> >>> Hello, >>> >>> Reposting with a new title for good order, as I didn't get a reply >>> before, probably because this post was comingoled in another post. >>> >>> I have built a Scope Clock based on David Forbes design. I hand wound >>> the transformer. >>> >>> All secondaries, including for the heater are on the same core, so the >>> voltage for the heather output depends on duty ratio, frequency and load on >>> the other secondaries. >>> >>> I noticed that even if I’m careful with the winding ratio, it’s >>> difficult to get an exact 6.3VAC RMS under load and the output voltage >>> would also depend on the overall load on the primary, being the regulated >>> secondary winding on the same core (SMPS regulated to +250VDC). >>> >>> So now I’m thinking to use a +6.3VDC power supply that I had designed on >>> the same board. I have rectified one of the secondary voltage to about >>> +12VDC, then I stepped it down to +6.3VDC regulated. The step-down power >>> supply works well this way. >>> >>> However when I connect the ‘IsolatedGround’ from the 6.3VDC power supply >>> to the Cathode PIN of the CRT (internally connected on this tube), the >>> power consumption increases and the focus pot gets hot very quickly, taking >>> the a full 600mA load. >>> >>> So, clearly something isn’t right in this last step, given the huge >>> voltage differential between CATHODE and IsolatedGround. >>> >>> My schematic attached. >>> >>> >> Any suggestions on how to connect the +6.3VDC isolated power supply >>> to the Cathode pin of the CRT welcome. I’m sure I’m missing something >>> obvious. >>> >>> >> Also, any tips on what RMS voltage I should read (with and without >>> load) if I power the heater straight from the secondary. This works well >>> when connected to the Cathode pin of the CRT, I can even read 6.2VRMS but a >>> test light bulb of 6.2V 500mA got quickly very dark when receiving 5.7V >>> under 450mA load, not good. >>> >>> So, not testing it on the CRT again until I get this right. I manage to >>> get a green dot on the CRT, which is a good sign. But I need to get the >>> heater voltage right before I plug the CRT in again. >>> >>> Thank you >>> >> -- 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 on the web, visit https://groups.google.com/d/msgid/neonixie-l/b57c020d-0c02-4171-bf9d-9a53b297e2e8n%40googlegroups.com.
