[SI-LIST] Re: Regarding Output Voltage Rise time of linear Regulators.

A linear voltage regulator cannot adequately be modeled as a resistor. 
By definition, it has an output impedance approaching zero.  Thus, upon
power up there will be a current surge into the downstream caps.  Some
regulator designs deal with this with a soft-start feature, others go
into current limit.  In the first case, you get to pick dV/dt.  For the
second, model the regulator as a constant current source that ramps the
cap voltage linearly with time until the regulation range is reached.  If
the regulator lacks either strategy, current is limited only by the
supply impedance behind the regulator or by the ESR of the caps and
connections.  It has to be able to grunt the energy surge without damage,
usually relying upon a large pass transistor and the thermal mass of the
heat sink, which is crude design.

Orin Laney

On Fri, 27 Feb 2009 14:26:45 +0530 "Vivekkumar M-TLS,Chennai"
<Vivekkumarm@xxxxxx> writes:
> Dear All,
>  
> We need to find the output Voltage regulation time of linear 
> regulators.
> Generaly when using LDO's(Linear Dropout Regulators) the Output 
> Voltage
> regulation time is given by the manufacturer himself. But in the
> scenario when data is not avaliable in the spec, please can any one
> confim if the following method is acceptable:
>  
> (Input Voltage - Output Voltage)/Load Current =  Series pass 
> resistance
> Value.
>  
> Let this resistance value be Rs.
>  
> We will have adjustable resistors which provides a feedback of the
> output voltage. Let them be Ra,Rb.
>  
> Hence using Thevenin's theorem,
>  
> The effective resistance would be Rs + (Ra II Rb) = Reff.
>  
> The Effective output capacitance will be the total capacitance added 
> at
> the LDO output. = Cout.
>  
> Hence the Regulation time ( Load changing from 10% to 90%) = t 
> 5*Reff*Cout.
>  
>  
> Requesting everyone to give their comments on this.Your immediate
> response will be sincerely appreciated.
>  
> Regards
> Vivek
>  
>  
> 
> 
> DISCLAIMER:
>
-------------------------------------------------------------------------
----------------------------------------------
> 
> The contents of this e-mail and any attachment(s) are confidential 
> and intended for the named recipient(s) only.
> It shall not attach any liability on the originator or HCL or its 
> affiliates. Any views or opinions presented in 
> this email are solely those of the author and may not necessarily 
> reflect the opinions of HCL or its affiliates.
> Any form of reproduction, dissemination, copying, disclosure, 
> modification, distribution and / or publication of 
> this message without the prior written consent of the author of this 
> e-mail is strictly prohibited. If you have 
> received this email in error please delete it and notify the sender 
> immediately. Before opening any mail and 
> attachments please check them for viruses and defect.
> 
> ------------------------------------------------------------------
> 
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject 
> field
> 
> or to administer your membership from a web page, go to:
> http://www.freelists.org/webpage/si-list
> 
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> 
> 
> List technical documents are available at:
>                 http://www.si-list.net
> 
> List archives are viewable at:     
>                 http://www.freelists.org/archives/si-list
> or at our remote archives:
>                 http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
>                  http://www.qsl.net/wb6tpu
>   
> 
> 
> 
____________________________________________________________
Want more out of life?? Fast track your career with an online degree.
http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTKL6eppq2tZJzHeJZQquwZ7qi3LeD9a55J16MWYUufi9MWdy0puBS/
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field


List technical documents are available at:
                http://www.si-list.net

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu

Other related posts: