Voltage regulator question lm1084 & 7805

Discussion in 'General Electronics Chat' started by bytraper, May 17, 2011.

  1. bytraper

    Thread Starter Active Member

    Sep 28, 2010

    Is there any penalty for using a lm1084 to drop the voltage from 36v to 12v for one set of chips and then feeding the 7805 from the output of the 1084 to power the 5v chips?

    The thing is I need 12v for the full bridge driver chip, but only 5v for the logic chips.

    These will be running off 12v 24v and 36v batteries, so is his the best way to go about this?
  2. SgtWookie


    Jul 17, 2007
    Well, you're going to dissipate ~2/3 of the power in the LM1084 for the full bridge driver IC. I hope it doesn't require much current.

    You don't mention what the current requirement is for either the full bridge driver IC, nor the 5v logic IC's, so it'll be mighty difficult to determine what might be best.

    If you are going to be running off 12v to 36v, you would be better off to use a switching supply with a wide input voltage range. The LT1084 has a minimum dropout of around 1v from input to output; so if your input voltage is 12v, your output will be ~11v max.
  3. bytraper

    Thread Starter Active Member

    Sep 28, 2010
    Hey Sarge,

    The HIP4081a takes 2.5A peak. The LM/LV1084 gives out 5A (but I do like the LT1084 giving 7.5A), and the 5v chips don't take much, there's a LM393, a LM339, 74HC02, and 74HC04. So no more than probably 0.5A.

    I would have liked to use 48V as an input as well, but I couldn't find a switching regulator to drop from 48v to 12v and still give decent current. All i've really been able to find is lenear regulators,

    By the way Sarge, do you want me to send you a few of these HIP4081a's so you can have a look over them? You seem to get a few questions about them and it might help others you answer.