Question

LM3172 3 2 IN OUT ADJ 1 R1 |_adj +1 V_s V Vout Ź R2 Figure 2 - A DC voltage converter which uses the LM317 device, an input voltage source V_s, and a voltage divider network.

Determine a generic (i.e. algebraic) equation (in terms of R_1, R_2, I_adj, and V_ref) for the total output voltage based on the above 5 points.

These are the only things you need to know:

1. The LM317 is a 3 terminal device. All your other components so far have had only two terminals.
2. Terminal 3 is the 'input' terminal. This is where you connect the positive terminal of your existing voltage supply V_s ( 5 V fixed voltage source on your power supply)
3. Terminal 2 is the 'output' terminal. Terminal 2 will be the positive terminal for your new voltage source
4. Terminal 1 is the 'adjust' terminal. It forces 50 μA of current into the node which connects Terminal 1 with R_1 and R_2. This 50 μA is denoted I_adj in the figure.
5. The voltage across R_1 is always 1.25 V. This voltage can be denoted as V_ref.

Hints

Hint 1: Use Kirchhoff's Current Node Law to determine the current flowing through R_2

Hint 2: Use Kirchhoff's Voltage Loop Law to determine the total voltage across both R_1 and R_2.

Upload your working here which shows the output voltage as a function of R_1, R_2, I_adj and V_ref.

Answer 1

LM3172 u + + + Ys -Sy volt metex (1) Voof acooss R, is alwoays 1.25V Tags 1.250 ER, 4 4 (2) kle are asked to find a (algebraic Equation) Indy = 50uA Rat in terms of Rig R2 , Iadj, Vref to find Vtotal output If Vref amps: RI IRI + Vref Ri - Iref = IR Voef N R, "IRE Iadj = 50 - 50uA R2 Applying kel at Node "v". Tadjie incoming current to noden Iref. is incoming current to node N. IRR is from node N. outgoing from defination of Kirchofft Current law.'s Equat to sum of leaving Currente at a Tadj + Voret = IR Current Sum of entering currente is Node. 0. enter Ri enter Leave

Now IR2 amount of current flows in R2 ver IR₂ R2 2 VR2 (Iadj + voets) R2 law :- Ri Now Buen goed is to delincent Vout" wit :- from Kirchoff's voltage » Sum of sources is equal to sum of coops around a loopi Vref VT R VR2 Vref + VR VT Vreft (Fadj + Voek ) from eq VT Vereft I adj R2 + Veref (R22) Voutput (V) expression = Vrep + Jadj R2 + Vret ) Therefore output is function of Vref, Iadj , R1, R2 terms only. 500A AS Iadj Veref = 1. a5v out pict can also be written as Vout 1.25 +(504) R2 + 1.25 (R2) RI Vout 1.95 [4 + ] + 500(R2) Summary Vout Vref [1 + R2 + Tadj R2 Ri Searranged of©.