Thank
you, Tony.
?
Here¡¯s
the problem I encountered with the unmodified LM317A_TRANS
while hoping to use the DC current source I1 to create a
programmable current source. See ProgCurrSource.asc.
?
The drop
across Rc leaves only 12.5mV across Rs, leading to a 10mA
current through RL. There are no AC currents flowing through
either ADJ or through Rc, and there is no DC current through
ADJ.
?
The PSRR
at the OUT2 terminal below 100Hz is a measly 25dB. At OUT1,
the same PSRR is 55dB.
?
With
LTspice 17.1.14, simulating with .ac dec 100 10 10000 yields
the following errors, although it also obviously produces
the above results:
?
Questionable
use of curly braces in "b¡ìe_abmgate yint 0
v={if(v(a)>{{vthresh}},{{vdd}},{{vss}})}"
???
Error: undefined symbol in:
"if([v](a)>((vthresh)),((vdd)),((vss)))"
Questionable
use of curly braces in "b¡ìe_abmgate yint 0
v={if(v(a)>{{vthresh}},{{vdd}},{{vss}})}"
???
Error: undefined symbol in:
"if([v](a)>((vthresh)),((vdd)),((vss)))"
u2:_u1_u12:dd1:
Emission coefficient, N=2.6437e-312, too small, limited to
0.1
u2:_u1_u11:dd1:
Emission coefficient, N=2.6437e-312, too small, limited to
0.1
u1:_u1_u12:dd1:
Emission coefficient, N=2.6437e-312, too small, limited to
0.1
u1:_u1_u11:dd1:
Emission coefficient, N=2.6437e-312, too small, limited to
0.1
Direct
Newton iteration for .op point succeeded.
?
?
?
?
?
On 04/04/2025 23:51, Christopher Paul via
groups.io wrote:
There
are at least two unencrypted models I saw today:
LM317_TRANS (No note on PSRR) and a more extensive model
LM317A_TRANS, which states:
?
* Model
Usage Notes:
*
* A.
Features have been modelled
*?????????
1. Startup Response
*?????????
2. Peak Current Limit
*?????????
3. Dropout Voltage vs Output Current?
*?????????
4. Line & Load Transinet (sic) Response
*
* B.
Features haven't been modelled
*?????????
1. Quiescent Current vs Input Voltage
*?????????
2. Temperature dependent characteristics
*?????????
3. PSRR Response
?
If the
more extensive model says no to PSRR, I don¡¯t hold out
hope for the less extensive one.
The notes in the LM317A model are nonsense.
PSRR is modelled, although it doesn't quite stack up with the
datasheet, which states 68dB (typ) - the model delivers -55dB.
For comparison, for the LM317, the datasheet figure is 57dB
and the model delivered 62dB. The model behaviour overall is
better than for the LM317, which doesn't model the output
capacitor effect on PSRR. In the LM317A, it is modelled. The
LM317A PSRR figure for when a 10uF capacitor is hung on the
ADJ pin can't be achieved.
What doesn't seem to be modelled is the effect of the load
current on PSRR. Maybe this is what the notes were supposed to
cover.
The two transistor level models don't model current limiting
correctly - it kicks in at ~800mA with some foldback, whereas
the two TI behavioural models limit at ~2.2A, but with no
foldback. None of them will have limiting modelled fully,
because it is determined by Tj in the actual device. The
LM317A behavioural model doesn't implement
temperature-dependent limiting at all, whereas the LM317
version does, but the analysis explodes at 75?C.
Conclusion: all the models are flawed, but the TI LM317A model
is the most reliable. I modified it so the inherent PSRR was
68dB, as per the TI datasheet Figure 10, and it showed the
additional 10uF capacitor on the ADJ pin lowers this to 85dB,
although Figure 10 suggests it should be closer to 82dB. These
are close enough.
I didn't test the other characteristics.
--
Regards,
Tony
John Woodgate