Components:
• Input/output Wires
• Jumper Wires
• 2x 1N Diodes
• 1x Zener Diode
• 2x 33uF 25V Capacitors
• 1x 317T 12- 5V Voltage Regulator
• 1x Red LED
• 1x 150Ω Led Resistor (1W Carbon) (R3)
• 1x 330Ω Resistor (1W Carbon) (R2)
• 1x 1000Ω Resistor (1W Carbon) (R1)
Calculations:
150Ω Led Resistor (R3)
(Vs-V led)/I
(12-1.8)/0.07=145Ω
Preferred Value of 150Ω for R3
For my R2 and R1 resistors used, I chose them based on the rule that the R1 is to be three times larger than R2. According to the LM317 resistor values, with 330Ω and 1000Ω I should obtain 5.04V. This is very close to my output which is 5.14V.
How It Works: My circuit is designed to have an input of 12V which is then regulated down to 5V by use of a 317T Voltage Regulator, with a 12V bypass wire. The complete run through as to how 12V goes in and 5V comes out is as follows. A 12V input voltage is run through the positive rail and the earth wire is run through the negative rail. The 12V first runs into a jumper wire leading up to the 12V bypass rail, ending at an output wire. The 12V also continues past the first jumper and through a 1N diode and onto a Zener diode which is also bridged to the negative rail. Alongside the Zener diode is a 33uF capacitor, also bridged down to the negative rail. Now the 12V will lead into the input leg of the Voltage Regulator therefore jumping my positive rail down to the output leg of the Voltage Regulator. This point in the circuit will now show 5V as the voltage has now been stepped down by use of the regulator. The Regulator still has a third leg, the adjust, which is bridged to a resistor (R1) which is bridged to earth. The resistor (R2) is bridged to R1 except it is jumped at the other end back up to positive rail. These two resistors provide current reduction for the Voltage Regulator. R1 and R2 can be any sized resistors as long as R1 is three times larger than R2. After the resistor (R2), back on the positive rail, now flows onto another 33uF capacitor (used as a filter), then onto a jumper which connects a diode, in reverse bias, from the positive rail after the regulator back around to the positive rail before the regulator. This is used to stop the 12V getting from the input to the output rail.
Back at the positive rail after the regulator and capacitor, a resistor (R3) is placed before a red Led, and then bridged to earth. This Led is used as an indicator to us that the circuit has power to it at that point. After R3 is the output wire which is measured at 5.14V, very close to the 5V rating.
Test Procedure: This circuit has a simple test procedure to see if it is working. A 12V supply with a positive and negative lead is attached to the positive and negative input wires. Then a multimeter is used at the output wires, with the black lead on the negative output, and the red lead on the 12V bypass output. The reading on my multimeter was as expected, 11.97V. Whilst leaving the black lead on the negative output change the red lead to the 5V output wire. My reading at that point was 5.14V which is very close to the 5V mark and acceptable as a finished 12-5V Voltage Regulator.
Problems: The only problem that I encountered was after I had completed my circuit; I tested the voltage with my voltmeter at the 5V output and obtained a reading of 11.97V. I removed my 317T Regulator only to find that it was in working condition. After visually inspecting my board further, I noticed that my diode going across the voltage regulator was placed along the same rail without having a drill hole placed between it. Meaning that it was allowing the 12V from the input to link up with the output rail, resulting in my 12V reading I obtained at my 5V output. To fix this problem I drilled a hole under the diode and retested my 5V output to get a reading of 5.14V
Reflection: If I had the opportunity to do this circuit again, I would place the diodes across the rails so that I do not have to drill holes under them, also to use the diodes as jumpers at the same time. Simply to limit the jumper wires as much as possible and keep the board clean.
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