On 11/21/2012 04:49 AM, secretsather wrote: > Hi all, > > I'm new to this group, and I would appreciate if somebody could help me or > point me in the right direction. > > I'm a newbie when it comes to electronics, but I'm building my first Nixie > clock, and experiencing some problems with it. > > it's before work right now, so I will post a schematic if needed when I get > home, but I will describe my set up. > > I'm using a 555 Nixie driver to obtain 185 volts. Basically, I have an ATMega > 328 hooked up to 595 shift registers, and those are hooked up to transistor > Darlington arrays (SN75468N Texas Instruments) > > I'm able to successfully program the Atmega328, and get it to work with the > shift registers. I can even cycle the numbers on the nixie tube. But here's > my problem: > > when the 555 Nixie driver comes up to voltage the entire circuit is only > drawing 5 Milliamps. When I hooked the first Nixie tube up (the first hour > tube which will only display a 0,1,or 2) the whole circuit was drawing a half > of an amp, and the LM 7805, which regulates the voltage for the low voltage > part of the circuit was getting hot as a result. > > i then put a base resistor between the shift registers and the SM 75468 N of > 680 ohms, just to try. when I plugged the circuit in after that, it was only > drawing 100 mA. > > so I guess my question is this: what the heck is going on? I thought the > transistor array, according to the data sheet, has a built in 2.2 K resistor, > so why would putting an additional 680 ohms on the base of the Darlington > array make that much of a difference? > > just to clarify, the SN75468n is similar to the uln2003. Also, my common pin > on the transistor array is floating, I didn't hook it to anything. > > How is it possible that the base of these transistor arrays are sinking so > much current? Or do you think I may have a problem elsewhere in my circuit? > If so, why would putting an additional resistor between the shift registers > and the array make such a difference? > What resistors do you have around of the transistors? If you do not have an resistors in front of the base of the transistor, it will draw as much current as you can supply.
I'd be happy to send you the eagle files that I use for my nixie tubes for you to compare against. Also, did you built the HV supply yourself? Michael- -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
