CD4094 Shiftregister

Discussion in 'General Electronics Chat' started by hadeedunhaad, May 6, 2011.

  1. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    I wanna use CD4094 shift register in my circuit. But when i trigger ( strobe, data & clk) the chip with 5V (mC) while its supply voltage is 12V it doesn't work. Is it necessary to use both supply and triggers at the same voltage level ?:confused: It works fine when i do so. I'm selected this chip as i wanna drive my loads in 12volts.

    Should i have to use some voltage steppers like MOSFET and all ? isn't there any other way around ?

    Any help would be greatly appreciated.

    Thank you all in advance.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Yes, logic input levels and chip Vcc have to be the same.

    This is a case where we need to see a schematic to be able to tell what you are doing.
  3. atferrari

    AAC Fanatic!

    Jan 6, 2004
    Do you actually understand what is a logic 1 and what is a logic 0 in that context?

    Think of them as related to the VDD and VSS values.

    Look for that and you will understand why you are not getting the results you expect.

    May I know why do you need to use 12V?
  4. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    Thank you all for the reply. yeah i understood why i'm not getting the results.

    I hope the question was quite clear and i don't find the relevance of the schematic in this case.

    I wanna drive my output in 12V as i'm driving devices which will be pulling current of about 0.8 A and i don't wanna give all this load to my poor 7805 which will have a tough time.

    So here in this case i guess i will have to step up the 5volts into 12volts, right ? So for that I will have to go for an FET with low side switching ?
    As for some reason which i read earlier (cant remember now) the normal transistor wont work in this case.

    Do i make some sense ? Or is there some simple way out ?

    concept of the circuit

    12v----->7805----->AT89C2051---(only triggering sig)--->CD4094( supply to this chip is straight from 12v and not through 7805)
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    You can run the 4094 on 5V, then use a logic-level N-channel MOSFET to switch the low side of your 12V load. Here is a link to Fairchild devices. Notice that Rds(on) is specified at different Vgs voltages. Choose a part which is spec'ed for Vgs=4.5V or less.
    Other companies make logic level MOSFETs. This is just an example.
    Note that a 4094 will provide relatively slow gate rise and fall times. If you are running at high speed, you will need a different arrangement.
  6. hadeedunhaad

    Thread Starter New Member

    Apr 22, 2011
    thank you very much for your advice,
    but I can't use the mosfet to drive the loads as there are too many 7 segments.:( And its very expensive to dedicate one mosfet for a segment.

    Yes i'm using them to run the whole bunch of 7segments. But it seems to be working fine, no flickers nothing, steady and stable. I'm having these outputs keeping everything at 5volts. Until my 12v issue isn't solved i'll keep it remain same for my further testings.