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Base Board - why no 87L05 ?
Posted by: Killom ()
Date: May 27, 2013 04:01PM

Hey Folks,

Im going to build me this Base Board.

http://www.lancos.com/e2p/siprog_base.png

But why I shouldn't replace the 2936Z with an 87L05 ? I've got a bunch of these LM87's but not a single LM2936Z ...

I would prefer to use available resources.

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Re: Base Board - why no 87L05 ?
Posted by: RG ()
Date: September 02, 2013 06:46PM

Killom Wrote:
-------------------------------------------------------
> Hey Folks,
>
> Im going to build me this Base Board.
>
> http://www.lancos.com/e2p/siprog_base.png
>
> But why I shouldn't replace the 2936Z with an
> 87L05 ? I've got a bunch of these LM87's but not a
> single LM2936Z ...
>
> I would prefer to use available resources.


Hello Killom,

the answer is given in IC's datasheets. I presume you are meaning LM78L05.

Few general characteristics from datasheets are:

LM78L05 is 3-Terminal Positive Regulator with fixed output voltage 5V and max. output current 100 mA, output voltage tolerances of ±5% over the temperature
range

LM2936-5.0 is Ultra-Low Quiescent Current 5V Regulator with max. output current 50 mA, with dropout voltage typically 200 mV @ IO = 50 mA, output voltage tolerance ±3% over line, load, and temperature

In the SiProg circuit is used LM2936-5.0 due to the smaller input voltage sufficient for stabilize the output voltage in the right level.

Minimum input voltage on pin Vin for stable output voltage 5 Volt on pin Vout from datasheets:

LM78L05 = +7V
LM2936-5.0 = +5.5V

Because the power from a serial port is very limited, usage of each Volt is "good" for programming of an integrated circuit.

Practical example (values are only for illustration):
-initial conditions are max. serial port voltage +10 Volt with internal resistance 150 ohm

1.we have one uC with supply current 20 mA
-input voltage on pin Vin of the regulator is +7 Volt
-output voltage on pin Vout is +5 Volt on both regulators (LM78L05 , LM2936-5.0)

2.we have another uC with supply current 30 mA
-input voltage on pin Vin of the regulator is now ONLY +5,5 V
-output voltage on Vout pin is +5 Volt ONLY on LM2936-5.0
-output voltage on Vout pin is roughly +3 Volt on LM78L05 - INsufficient programming voltage for for stable function of some uC's

Unce more, the values are ONLY for illustration, not specifically for serial port smiling smiley

Best regards

Sonix

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