The Output of LM317AH is decreasing in Simualtion

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Shanzay Jmail

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I was trying to simulate varaible DC power supply but The output of Regulator is decreasing gradually from 11.9 (Vin) to 1.6 (Vout) Why it's happening??
 

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Hi,

D2 and D3 cause short circuit. --> Remove them.

You can easily find out when you look at currents and voltages. This is what a simulation is used for.

Klaus
 

You are missing the resistor that sets the output voltage. There should be potential divider formed across Vout and GND with the ADJ pin at its center.

Add a resistor between Vout and ADJ and take note of the minimum load current requirement. Typically it shouldn't be more than about 270 Ohms.
Also note that if the simulation is accurate, the diodes will be overloaded at power-up and at quite a low DC output currents.

Brian.
 



By the way 1N914 are small signal diodes, low current capability. Sure thats what you want.

FW Bridge config (as Klaus pointed out) normally done this way -




Regards, Dana.
 
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Disconnect the center tap of the transformer secondary.
 
as above - also you generally need a resistor from o/p to adj -> READ THE DATA SHEET ...!
 

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