LM2940CT-15 P+ Cross Reference Replacement

The voltage regulator L7815 or 7815 it is not a good choice because the droop voltage of this I.C is (2 volt typ...2.5 volt max.) @ 1A max output current so the output regul.voltage will be (13.0 volt or 12.5 volt) that is quite far from (15.0 volt) .while the LM2940CT has a droop voltage (0.5 volt typ. 1.0 volt limited) @ 1A max output current makes the output regulated voltage (14.5 volt or 14.0 volt) .to pick up the more significant differences between them see the data sheet . use LM317 but it needs for two external Resistance R1,R2 and use this formula equation to calculate the output regulated voltage (Vo = Vref(1+R2/R1).//// apply Vref=1.25 volt. you should see the data sheet to build the circuit it's easy

Thank you for your comment, But in this case I am reparing my switching power supply, this IC located at secondary output power supply. Due to I did not have the electric diagram of this SMPS (model UT100 33 from xppower), after switching transformer has 1 schotky diod ( this diod still in good condition), I am thinking the LM2940 fail but I had tested (with pull the IC out of PCB) and measure by volmeter but not found any abnormal. Does any one has this power modul schematic?! On the primary it using 2 Ic Pwm 3843B and at output has only +5vdc, -15vdc and loss only +15vdc. I had test all semiconductors as Pwm Ic, mosfet, bridge diod but founf nothing abnormal. Please advice! Thank in advance,

I don't think there is someone has this schematic because the companies themselves that make like this commercial productions not any more offer the support as in the past where it was attached service manual catalog includes the schematic comes with sets .anyhow.since you have said your S.P.S has a double of pwm mc3843 it is there must be two of power mosfet transistors on the primary that means you have two S.P.S one for +5v d.c ,-15v d.c and the other for +15v d.c in the same PCB .here you can check which on for +15 v make some test .if you are sure that LM2940 is fail you can use LM317 instead of it

This is my power model http://uk.farnell.com/xp-power/ecm100ut33/power-supply-ac-dc-medical-3o/dp/1289215

Why can't you get one?

https://www.verical.com/pd/texas-instruments-linear-regulator-LM2940CT-15-649575?wm_ctID=250&wm_kwID=70581028&wm_mtID=1&gclid=CKTy2ZWC4sQCFdgDgQodxi0AIA

Thank you Rixter, To buy some IC like this from US is more time for import so I prefer using 7815 That I can buy easy at shop so I wonder that can I raplace by 7815 or not?! Brs

The IC 7815 may work depending on your circuit parameters, the NTE1955 would be a better substitute as its operating parameters are almost identical but with better line regulation.

Why bother repairing it?

These SMPSs aren't normally repaired. They are totally replaced, hence the standard form factor.

The whole power supply is a component.

Try it and see for yourself.

This looks like a cheap(?) Chinese junky thing. The +15 output on out 2 states 3 Amps seriously doubt either reg. would do the job. As mentioned by others the LM317 is the best option for your application.

No.

You are welcome.