• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 385 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

linear regulator unstabilty and bandwidth limitations of TIP115

awadhesh baranwal
Prodigy 30 points

Dear sir 

 I am using TIP 115 PNP transistor as a linear pass element in the linear regulator. But i am getting the Bandwidth limitation with this transistor at 10KHz . actually after going through FRA instrument i saw that i am getting one pole nearby 1khz. Then i refered to the datasheet of TIP115 but i did not get any frequency information or bandwidth information from that.

Can anyone tell me about the Bandwidth information of this transistor because i have to use this transistor atleast upto 400KHz frequency.

 

waiting for reply.....    

 

 

advance me thanxs

  • 0
    TI__Mastermind 36110 points

    The frequency limitation could be caused by a number of things in the circuit.  The information you are looking for is not available. Also note that this transistor was not designed for high speed applications and will not be suitable for a linear regulator if you need a fast response time.  Your best option is to select a newer transistor that has a much more complete datasheet. 

  • 0 in reply to Matthew Day
    Prodigy 30 points

    Thank you for your valuable reply sir.

    Sir 

       actually i am making one pre regulator for the 270 volt line , but our current requirement is around 2A. so i am planning to make use of darlington PNP transistor for the linear regulator. but by using the variable reference i am planning to provide the headroom voltage not more than 10 volt because it is most power dissipating element  in linear regulator. So i am planning to use NPN transistor and op-amp as a driver for the PNP pass transistor. At the same time i am also thinking about the ripple rejection part of this regulator. my desired working frequency for this Pre regulator is atleast upto 500 KHz. 

    Can you suggest me any other best PNP pass transistor for this specification . I am again writing the specification below:---

    Transistor required -       PNP

    Current -                            2 Amp

    Vopltage-                           300 volt Minimum

    Headroom voltage -        10 volt maximum

    desired working frequency of pre regulator --  atleast upto 500Khz

    please suggest me.

    I will be highly thankful to you sir...

     

  • 0 in reply to awadhesh baranwal
    TI__Mastermind 36110 points

    I think this is a question that is better directed towards a MOSFET manufacturer.  500kHz is a very agressive spec.  I think you will find it very difficult to meet a 500kHz requirement.  Good luck with your project.

  • 0 in reply to Matthew Day
    Prodigy 30 points

    Dear sir thanks for your valuable reply.. if i dilute little bit my spec means if i am bringing my operating frequency of linear regulator upto 250 KHZ then will it be possible with any transistor configuration to achieve this desired result.

      Actually u suggested me to shift to the MOSFET. I have never tried linear regulator with MOSFET configuration becaz  i am having one doubt  that MOSFET has the Coss value and becaz of this capacitor all the high frequency input ripple can pass to the output side (load) and it will create a panic for my design.. and our regulated voltage will have a lot of ripple.

    so please give a valuable suggestion regarding my doubt  and if MOSFET is only solution then can u suggest me any best MOSFET which will fulfill my requirement..\\\

     

     

     

    thanking you and waiting for your valuable suggestion...

  • 0 in reply to awadhesh baranwal
    TI__Mastermind 36110 points

    Unfortunately I won't be able to assist you with such a design.  I suggest that you examine existing linear regulators that meet the voltage and current specs you have and compare their bandwidths to what you are trying to achive.  Again, I think you have very agressive crossover specs that can't be met.  I hope you are able to prove me wrong and meet your specs.  You must calculate your design requirements for FET or transistor characteristics and then find one that meets those requirements.  You will need to work directly with the FET and transistor manufacturers for this.  Any further assistance I can provide must be limited to Texas Instruments products.