[sdiy] 7915 regulators

[Scott Gravenhorst]

According to the datasheet:

(T=25 deg C) Load regulation:

    Output Current         typ     max
5ma <= Iout <= 1.5A         15     100
250ma <= Iout <= 750ma      5      50

So it seems from this that the mfr expects a load of at least 5 ma.
To achieve this, your load needs to be 3000 ohms or less for a regulator
operating at 15 volts output.  10K won't draw enough current to put
the regulator in this range.  



Seb Francis <seb at is-uk.com> wrote:
>Hi,
>
>Slightly OT .. does anyone have the experience that 7915 
>regulators are very poor under low loads? I've just built a 
>simple bench power supply (I wanted it to be kind of a worst-case 
>PSU, hence using cheap fixed voltage regulators). The 7815 & 7805 
>give near enough perfect voltage with only the load of a DVM. But 
>with -30V in, the 7915 gives out -22V with no load, and -17V with 
>a 10K load. My friendly local electonics shop was kind enough to 
>test their entire stock of 6 to try and find a good one, but they 
>were all the same, giving out <-20V with -30V in and no load. 
>Should I put some kind of load across the output? I've seen a few 
>78/9XX-based PSU circuits where a single indicator LED is across 
>the -ve rail output - I always thought it was just a arbitrary 
>choice to place the LED across this rail. BTW, the 7915 in 
>question (and the 78XXs) are all manufactured by ST, although 
>they all come from different locations (Morocco, China, 
>Malaysia!) Perhaps I should try and get some NS or ON versions of 

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