‘Ask the Experts’ Tutorial: The Linear Regulator

In advance of the upcoming “Ask the Experts” session on Planet Analog on Wednesday, April 23, at 1:00 p.m. EDT, Planet Analog brings you this series of brief daily “nuggets” to fuel your quest for a deeper understanding of this topic, and as a preparation for you to ask questions during our session next week. Here is the first nugget.

The Linear Regulator (Excerpts from a Texas Instruments Application note)

    We see a tremendous need in today’s electronic design for battery powered equipment, especially in the past decade and with the advent of the Internet of Things (IoT). This quest has created unique requirements for a voltage regulator that, in many instances, cannot be met by industry standards like the LM340 or the LM317 (Bob Dobkin’s design still is used widely in so many designs around the world).

    These regulators use an NPN Darlington pass transistor (Figure 1), and can be referred to in this document as NPN regulators . The demand for higher performance is being met by the newer lowdropout (LDO) regulators.

    Figure 1: The NPN regulator (Image courtesy of Texas Instruments)

    Figure 1: The NPN regulator (Image courtesy of Texas Instruments)

    The NPN Darlington pass transistor with PNP driver used in an NPN regulator requires that at least 1.5V to 2.5V be maintained from input-to-output for the device to stay in regulation. This minimum voltage “headroom” (called the dropout voltage ) is:


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Stay tuned to Planet Analog daily for these nuggets. Please register on Planet Analog if you have not done so already and click on this link to enter our chat room. You can begin to ask questions immediately today in advance of the actual chat on Wednesday, April 23, at 1:00 p.m. EDT. Your questions will be answered during the chat for all to see.

9 comments on “‘Ask the Experts’ Tutorial: The Linear Regulator

  1. etnapowers
    April 16, 2014

    The circuit proposed is really interesting, I guess that the drop should be acceptable depending on the input voltage range. For high voltage applications this circuit should be really useful to provide high currents to the load with a negligible voltage drop and a good efficiency of voltage conversion.

  2. Steve Taranovich
    April 16, 2014

    @etnapowers—you are correct about a better pass transistor with low impedance at high currents. Stay tuned for later today when the LDO regulator  is posted using MOSFETs

  3. etnapowers
    May 8, 2014

    @Steve, really nice post, thank you. The MOS pass transistor is easy to drive through the gate terminal and the CMOS technology is very good to be integrated.

  4. Steve Taranovich
    May 8, 2014

    @etnapowers–Don't forget to sign up and participate in our May 21 session on Precision voltage and current referencesat 10 AM PDT.


    Sign in link:

  5. etnapowers
    May 12, 2014

    Thank you very much Steve for this , will you deal Reference circuits built in different technologies?

  6. Steve Taranovich
    May 12, 2014

    @etnapowers we can discuss any aspect of question about references that you want to present

  7. chirshadblog
    May 13, 2014

    @etnapowers: True but what about durability? Also the compatibility factor ? 

  8. etnapowers
    May 14, 2014

    Thank you for this Steve, I'm thinking to solution for a pass transistor easy to drive and having a low drop at the same time, I wonder if CMOS technology is the best solution for this aspect.

  9. etnapowers
    June 11, 2014

    @chirshadblog: I think that the durability of this solution is quite good , the compatibility factor is not so easy to evaluate, I can tell that this might be a problem to be solved by the designer.

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