[time-nuts] FE-5680A Voltage?

[Robert LaJeunesse]

Looking at the LM2596 datasheet the switch transistor saturation voltage is 1.5V max at 3A (1.16v typ). That and an educated guess of about 0.25V for inductor loss combine to set the minimum difference between input and output. The 1.23V reference is about +/-3% accurate, so after setting the "buckboard" to 15.00V out (at 25C) expect it to shift at most 0.5V over time and temp. Add that to the minimum in-out difference and now you are at a minimum safe input of 2.25V above the nominal 15V output, or 17.25V in.  An old 19V 3A laptop supply might be a good supply to use for this, if you were local I'd hand you one.

As for efficiency, that just tells you the amount of heat the regulator, plus inductor, plus diode, etc. will throw off. FWIW the datasheet Figure 5 indicates you should expect about 88% or better efficiency for 15V out and at least 2V higher input voltage. (Doing some switching power supply design for a living does help with my understanding of them, but not ever enough!)

Bob LaJeunesse



>________________________________
> From: Bob Stewart <bob at evoria.net>
>To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Sent: Thursday, September 12, 2013 9:28 PM
>Subject: Re: [time-nuts] FE-5680A Voltage?
> 
>
>I hadn't given it any thought.  I saw some ad that said 1.5 volts so I assumed that.  But, after looking through the datasheet I see an  efficiency figure of  73 percent for the adjustable one, so that does imply a need for about 20.5 volts.  OTOH, it says the feedback voltage is 1.23V, so I dunno.  And I'm certainly not pretending I have any electrical design skills.   I'll find out.  =)
>
>Bob
>
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>