# How to calculate values for my variable DC power supply

I am making a variable DC power supply via Multisim and the values are given to me is V1=7, V2=15, Imax(load)=209mA (both V1 and V2 is DC value which is on U1.)

I am using resistors, an LM317 voltage regulator, and a variable resistor to change my voltage to my V1 to V2 and 2 capacitors.

The issue I am facing that I am not able to get calculate correct values for me to work for resistors, capacitors and Imax(load). but This what I have done fo far:

• VPeak=Vrms*sqrt(2)
• CS=5Io(maybe I max)/Vp100
• R1=250 as a constant
• R2=R1*(Vout-1.25)/1.25
• CF=1uF Tant capacitor as a constant I tried to apply ohms law to get desired Imax(load)=209mA on RL, but my DC value decreases and it does not even reach to the required mA, (I applied ohms law when my variable resistor is at 100%). This is the circuit I have drawn so far in Multisim, feel free to improve it and tell me what I have done wrong.

• This is not a workable regulator schematic with a resistance in the zener shunt path. Zener diode shunt regulators without the potentiometer are theoretically possible but generally not advisable today. At the least use a a linear regulator IC. Nov 24, 2020 at 4:52
• This circuit will not regulate well at all, and your question needs a lot of work. Where is V2 on the schematic? V1 is shown as 240 Vac, not 7(?). What is the desired output voltage range? What are the max and min output currents? Nov 24, 2020 at 5:01
• @AnalogKid 240 is my Vrms, The V1= 7V is DC V which is U1; also if you don't mind can you clarify, I am taking Analogue circuit this semester and I am not that well versed and how should I improve it Nov 24, 2020 at 5:05
• Where are V1 and V2? You state V1 = 7V and V2 = 15V, but V1 in your schematic is 240V AC (mains input I guess). What is the output that you want to achieve? consider using a series transistor to do the regulation, using a shunt method for any significant current will be very inefficient. Try an NPN transistor, collector to C1+, emitter to output. Resistor from C1+ to the NPN base, vener of a voltage a little higher then you need going from NPN base to ground. Nov 24, 2020 at 5:16
• @user1582568 240 is my Vrms, The V1= 7V is DC V which is U1; also if you don't mind can you clarify, I am taking Analogue circuit this semester and I am not that well versed and how should I improve it Nov 24, 2020 at 6:03