Power Circuit Write-Up

Parts:

• D1 1N4001 1A 100V
  
• D2 1N4001 1A 100V
  
• Zener Diode 5V1 400mW
  
• 25V 33uF Capacitors x2
• Voltage Reg. LM317T
• R1 resistor 1KR 0.5W
  
• R2 resistor 330R 0.5W
  
• R3 resistor 100R 0.5W
  
• LED 2.V 30mA
  
• Jumper Wires x3
• Red Wire 12V
  
• White Wire 5V
• Black Wire Earth
• Vero Board
  

Whats its used for: Anything requiring a 5V Vs when only a 12V Vs is available up to 30V.

How it Works: This circuit only needs a voltage regulator and 3 resistors to work which means that everything else is there for protection.

With a 12V Vs connect the positive wire to the Red wire on the Vero Board and the Earth wire of the Vs to the Black wire on the Vero Board. Current will pass through the first 1N4001 Diode ,which has a forward bias voltage of 0.7V giving us 11.3V, a Zener Diode and a 33uF Capacitor , both of which function as protectors for the Voltage Regulator, current then hits the IN terminal of the voltage regulator. There is also an additional 1N4001 Diode in Reverse Bias providing extra protection to the Voltage Regulator.

In order to calculate the resistors needed I remembered that because the outut voltage was going to be 5V I could use any Resistors as long as their ohm values had a ratio of 1:3 for R1 and R2 and used the formula Vout = Vref ( 1 + R3/R2 ) and ended up with 1KR and 330R resistors for my ADJ circuit. Now getting 5V out of the OUT Terminal of the Voltage Regulator, current goes through a 33uF capacitor then my Red LED protected by a 100R Resistor ( R3 ) will light up. At the end of the circuit is 3 wires. My 12V out, my 5V out and my Earth coloured Red, White and Black.

Testing: With a Voltmeter. As long as you are getting 5V out of the 5V output and 12V out of your 12V output your circuit is working as it should.

Problems: At first I realised my 1N4001 Diode in reverse bias didnt have a drill hole underneath it which I promptly included. Secondly I was only getting 3.3V from my OUT terminal of the VReg. After much fault finding and help from Carl it was discovered that I was using the wrong resistors for R1 and R2 in the wrong format. After switching to a 1KR for R1 and using the 330R for R2 i rearranged them in the format you can see in the picture. At this point i was still getting 3.3V. For a reason unknown to me the placement of my 5V out wire was affecting my readings as when I relocated it to right in front of the VReg I got 5V and my LED lit up.

Reflection: If I was to do this again I would double check my resistor calculation so as to not have the problems I had and after having learnt how to fault find properly double check the R1 and R2 resistor layout to make sure it would work properly.