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MM5314 Clock Chip and B7971 Nixie Tubes

Discussion in 'General Electronics Discussion' started by Dkuriloff, Feb 5, 2010.

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  1. Dkuriloff


    Jan 18, 2010
    I found a circuit which can be modified to drive the B7971 giant 7 segment Nixie tubes using the MM5314N Clock IC but need help with mods.

    Here is the article and schematic:

    Here is the data sheet for the MM5314N:

    1. Power Supply Mod:

    Modify the power supply to the chip using a 6.3 - 0 - 6.3 V AC out center tap transformer, a full wave bridge rectifier, 1500µf, 35V filter cap and a 7812 regulator. This will give a regulated 12 v DC supply for Vss. The center tap is left unconnected. This is better than the 9v, unregulated supply in the schematic and may fall shy of the 11v minimum required for the IC. Can a 22 µF, 400v cap be used to filter the mains for the HV side of the circuit instead of the 15µF, 150V as in the schematic, since this is what I have on hand? Can a smaller 1 watt bleeder resistor be used say 2.2k instead of 220K in the schematic? Why was such a high value chosen in the first place?

    2. Transistor Substitution Mod:

    MPSA42 (NPN) will replace of the UL624. MPSA92 (PNP) will replace the SA480. Adjustment of the multiplex frequency may be necessary. For the MPSA92s, Q8- Q13, there is a pull-up resistor from the transistor bases to “ground” in the schematic. A question was raised by Alan 'A.J.' Franzman: “I've just realized another possible mistake in the schematic, but I'm not quite sure if it's wrong or not. You may need to build a temporary breadboard version of the circuit (or at least most of it) to find out. Each of transistors Q8-Q13 is shown with a 2.2M ohm resistor going to 0 V DC. I believe these may need to go to the "+150 V DC" high voltage line instead, but because the resistors are of such high value and the transistor base inputs are capacitively coupled, the circuit may work either way.”

    Does anyone have an opinion and can connecting the transistor base to HV damage the IC? Should I put series diodes with the IC outputs to prevent stray voltages?

    3. Mutiplex Timing adjustment on pin 23:

    3000 µF is appears to be wrong, based on Figure 3 from the MM5314N.
    datasheet (it's WAY off the chart!) If the author needed to use that value to get the chip to work, it was probably because of the chip not functioning correctly due to supply voltage being too low. Either .01 µF with the recommended 220K ohm resistor from 0 V to pin 23, or if I use the 100K ohm resistor as shown in the schematic, will increase the capacitor to .022 µF. It seems from the article that the values were based on needing a higher frequency to allow pulses from the IC to get through series capacitors connected to the digit enable outputs. Can anyone shed more light on this issue?

    Since .5 µF is no longer a common capacitor value, I will substitute .47 or higher 250 v nonpolarized mylar caps.

    4. Fixing “Inter-digit Ghosting”

    All of the above was devised to prevent flickering and display ghosting. I noticed that when the same IC was used for Numitron tubes that every segment of the Nixie tube needed a diode.


    Perhaps the inter-digit blanking circuit in figures 9 and 10 of the MM5314 data sheet should be used? *The example given was for the 28 pin version of the clock chip MM5309 and shows the circuit connected to pins 26 and 28. Can I assume that this same circuit will work if connected to pins 23 and 1 respectively?

    Any help much appreciated!


    Direct email is kuriloff at NYHNI dot org.
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