XNOX_Rambo said:Have you considered this (from the datasheet)?:
"The LM117 is capable of providing extremely good load
regulation but a few precautions are needed to obtain maximum
performance. The current set resistor connected between
the adjustment terminal and the output terminal (usually
240Ω) should be tied directly to the output (case) of the
regulator rather than near the load. This eliminates line
drops from appearing effectively in series with the reference
and degrading regulation. For example, a 15V regulator with
0.05Ω resistance between the regulator and load will have a
load regulation due to line resistance of 0.05Ω x IL. If the set
resistor is connected near the load the effective line resistance
will be 0.05Ω (1 + R2/R1) or in this case, 11.5 times
worse."
E-design said:Change the 220R to 120R. The 220R is only valid for premium devices and not commercial ones. Look carefully at the datasheet and you will notice that the commercial device needs about twice the current into the ADJ terminal and hence 1/2 the resistance as generally quoted in the datasheets. With a 220R in place regulation will suffer.
Here is my the reasoning posted on this subject in the past: It is regarding a LM338 device but the principle is the same for the 317.
----------------------------------------------------
The adjustment pin current may vary anything from 45uA to 100uA
according to the datasheet. This output current combines with the
current through the voltage divider on the output formed by the 240
Ohm resistor and the adjustable resistor. This causes a error term in
the Vout formula .....+( IadjR2). To minimize this error the quiesent
operating current ( 1 to 3mA ) of the device is directed to the output
requiring a min. load current tot be present for the device to operate
within specs. If the load current is too small the output voltage will
increase.( Error term comes into play ). The required min load current
for the LM138 is 3.5mA to 5mA and for the LM338 3.5mA to 10mA.
At the min. voltage output of 1.25V the bottom resistor equals zero.
The top resistor is now responsible for the min. load current. Taking
the worst case, to get 10mA flowing through R1, R=V/I then
R1=1.25/10mA = 125 Ohm ( Closest standard value - 120 Ohm ). By using
a 330 Ohm the min load current of 3.8mA is lower than the worst case
of 10mA for the 338. For the 5mA of the 138/238 a value of 250 Ohm is
required ( Closest standard value - 240 Ohm ).
---------------------------------------------------------
E-design said:Why the 0.22R at the output?
Also I have seen these type of regulators go into some sort of burst-HF-oscillation under certain load conditions if you don't put some capacitance on the input Pin 3 when you have series resistance in this path, like you have. Put a scope on Pin 3 and monitor under various loads and you might see the oscillation. Putting a low value cap 0.1uF to 1uF directly on Pin 3 ->GND normally prevents this.
papyaki said:Hi,
Max current flowing through R1 = Vbe/R1 = 0.7/22 = 31.8mA. Hfe of 2N2955 is 70max @ Ic=4A so Ib (base current) must be equal to Ic/hfe = 4/70 = 57mA. Ib flows through R1. I think you need to reduce R1 value to 10ohms, allowing 2n2955 and LM317 to both work properly.
E-design said:Change the 220R to 120R. The 220R is only valid for premium devices and not commercial ones. Look carefully at the datasheet and you will notice that the commercial device needs about twice the current into the ADJ terminal and hence 1/2 the resistance as generally quoted in the datasheets. With a 220R in place regulation will suffer.
XNOX_Rambo said:Eh...
Semiconductor - you say you have Vin = 23.97V and Vout = 23.86V.
In the datasheet they specify that Vin-Vout = 5V, i.e. you must have a 5V higher
input voltage than output voltage. All linear regulators "use" some voltage, the
"dropout voltage".
Good luck!
/Rambo
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