+5V and -5V Dual Regulated Power Supply

Thread Starter

Charlie Magne Aguda Ü

Joined Oct 24, 2017
33
I'm trying to simulate a power supply circuit that i have found online in multisim. The problem is that the -5 terminal is showing wrong value. What do you think is the problem here? (I'm a Beginner :) ) I have attach some screenshot and the file from my circuit in multisim.
 

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Thread Starter

Charlie Magne Aguda Ü

Joined Oct 24, 2017
33
Hello,

As @Alec_t said, the regulator might need a minimum load.
On the positive you have a 1K resistor, on the negative not.

Bertus
What should i add to fix this problem? i try adding a 1k resistor on the negative side but it's still the same output. i really don't know what to do here now. i did also try to add those missing decoupling capacitors, still no effect
 

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dl324

Joined Mar 30, 2015
10,523
What should i add to fix this problem? i try adding a 1k resistor on the negative side but it's still the same output.
Try increasing the load to 10mA. That seems to be a common requirement; even if not stated. You just need to dig it out of the datasheet.

EDIT: I just checked a datasheet and it seems that 5mA should be sufficient. But, I've had LM317 that wouldn't regulate unless the load was more than 10mA (which is the minimum stated in the datasheet). It was an out of spec part, but what could I do? Complain??

I'm surprised that MultiSim cares about minimum regulator load.
 

Alec_t

Joined Sep 17, 2013
11,145
I too would query the accuracy of your Multisim model. The 7905 output tolerance specified by Texas Instruments is ±4%, which your model clearly exceeds.
That said, the LTspice model gives Vout = -5.3V, which is also outside the TI spec :confused:.
 
Last edited:

absf

Joined Dec 29, 2010
1,943
What should i add to fix this problem? i try adding a 1k resistor on the negative side but it's still the same output. i really don't know what to do here now. i did also try to add those missing decoupling capacitors, still no effect
What are the voltages before entering 7805 and 7905? I guess it was too high...

My simulation with proteus shows reasonable voltages at the outputs even without the 1K resistors.

+_- 5V psu.PNG
Allen
 

JoeJester

Joined Apr 26, 2005
4,259
That's one way to do it. Not a good way, but still, one way.

Any particular reason you want to drive those 5 volt regulators with 22V?
 
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