How to properly model an linear power supply with LDO in LTspice?

I've build the following linear power supply:

Before building it I tried to model it in LTspice. I couldn't find an LTspice model of L4941BV LDO (datasheet [PDF]) or a suitable replacement. Thus I used the following "naive" model:

R1, R2, L1 and L2 are measured resistance and inductance of a transformer windings. V1 is 50Hz, amplitude: 310 V. Here is Vout:

My idea was following. Let's say that all extra voltage turns into heat, and also account for ~10 mA quiescent current of LDO itself. In other words assume that this circuit's output power is ~0.95W.

Naturally this model turns out to be inadequate. It predicts PF 0.442 and efficiency 32%. The real device can produce up to 217 mA before a noticeable ripple (60 mV) will be observed. Under these circumstances it's measured PF is 0.925, consumed power - 2.75 W and efficiency - about 39.5%.

I tried to play with values used in the model but didn't come even close to observed PF and efficiency. Thus it looks like a less naive model is required.

The problem is I have no clue how to make an accurate model of an LDO. Could you please explain how it can be done or at least suggest some literature on the subject.

• I'm quite confused here, what you have built is not even near an LDO, it's not regulating anything at all, just a plain old unregulated AC-DC converter. Did you forget to show your "naive" version?
– pipe
Jun 25 '20 at 11:39
• Maybe replace the current sink with a ~30 ohm resistor and see if you can get the PF and voltages to agree with reality. Speaking of reality, in reality you would want a lot more voltage at the input of the regulator to account for mains variations. That particular regulator is a lateral PNP type that has an Iq spike near dropout, though not as severe as some, so it’s not as simple to accurately model as, say, a modern CMOS type. Jun 25 '20 at 11:44
• You can use "NCP1117ST50T3G" spice model.Its output voltage 5V fixed like L4941BV and 1A. you can find model in the link .mouser.com.tr/ProductDetail/ON-Semiconductor/… Jun 25 '20 at 11:52
• @GuneyBoss The LM1117 types have much higher (like 5x higher) dropout voltage than the OP's regulator. They're really semi-LDO types. Jun 25 '20 at 12:14
• @GuneyBoss At OP's 200mA operating current, the typical dropout of the NCP1117 is about 950mV compared to 150mV for the L4941. Jun 25 '20 at 14:03