Interactive electronics resource
AC-DC Regulator Kit Instructions
Build, understand and experiment with the AC-DC Regulator Kit. This resource brings the original kit material into the current MitchElectronics format with the schematic, circuit explanation, component and PCB information, construction guidance, troubleshooting and practical ideas where available.
Introduction
Many circuits require a voltage supply that is constant and unchanging and such circuits would include radios, calculators, computers, monitors, phones, and even cars. Batteries are a good source of constant voltage but since they are usually limited in size, weight, and power capacity the mains electricity is often used. But this source of electricity is constantly changing as it is AC (alternating current), which is not suitable for DC (direct current) circuits. Therefore, an AC-DC converter is needed to convert the alternating current into a direct current! This kit will not only do this but will also regulate this converted DC source so that it outputs a smooth constant 5V which can be used to power many projects.
Schematic
Note – This is an educational kit and can only handle up to ±16V
DO NOT CONNECT TO THE MAINS SUPPLY!
How does the AC-DC regulator work?
The AC-DC converter consists of two stages
- Rectification
- 5V Linear Regulation Input Rectification
The input is rectified via D2, D3, D4 and D5. These diodes are Schottky which reduces the voltage dropped by this stage. The typical forward voltage for a Schottky is 0.3V and with two Schottky diodes in series at any one time (D3 and D2 pair or D1 and D4 pair), the typical voltage drop would be 0.6V.
If J1 (ACIN) is positive and J2 (ACIN) is negative then
- D3 and D4 would be forward-biased
- Current enters J1 and flows through D3
- This current goes around the circuit (regulator, IC etc)
- The return path (ground), goes back to the rectifier and through D4
- The current returns to the original power source through J2
If J2 is positive and J1 is negative then
- D2 and D5 would be forward biased
- Current enters J2 and flows through D5
- This current goes around the circuit (regulator, IC etc)
- The return path (ground), goes back to the rectifier and through D2
- The current returns to the original power source through J1
Output Regulation
While the converted AC voltage source looks like a sine wave with both positive and negative peaks the resultant DC conversion looks like lots of positive bumps shown below. This cannot be used to power circuits and requires further processing to create a solid unchanging voltage.
The first step is to convert the large DC bumps from the full wave rectifier into more consistent smaller bumps. This is done using smoothing capacitors C1 and C2 which store energy during the peaks of the DC bumps and then discharge this energy back into the circuit during the dips of the DC bumps.
But this voltage will be greater than 7V on average (since this circuit has a minimum input voltage of +- 5V), and is too large to feed into common circuits. The smoothed voltage will also be slightly bumpy which will cause issues with many circuits and so it requires regulation before it can be used. To do this we use the 7805 regulator which converts the now slightly wobbly voltage into a very smooth 5V.
Try it yourself
Circuit simulation
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What you need
Component List
| Component | Quantity | PCB Reference |
|---|---|---|
| 100nF Capacitors | 2 | C1, C4 |
| 100uF Capacitor | 1 | C3 |
| 470uF Capacitor | 1 | C2 |
| 1N5817 | 6 | D1, D2, D3, D4, D5, D6 |
| 7805 | 1 | U1 |
| Red Wire | 1 | 5V |
| Green Wire | 2 | AC IN |
| Black Wire | 1 | 0V |
| AC DC PCB | 1 | — |
Inspect the board
Interactive BOM
Board reference
PCB & assembly
The PCB silkscreen and component references should be checked against the component list before soldering each part.
Before applying power
- Check every component against its PCB reference.
- Confirm the orientation of all polarised components and ICs.
- Inspect for solder bridges, unsoldered pads and clipped leads that could cause a short.
- Check that no loose wire or solder debris remains on the board.
Build with confidence
Construction tips
Recommended build order
A reliable way to assemble AC-DC Regulator Kit is to work from the lowest-profile components to the tallest. This keeps the PCB easy to access while you solder.
- Fit resistors, links and other low-profile components first.
- Fit small capacitors and diodes, checking polarity where applicable.
- Fit IC sockets and small semiconductors, observing the orientation markings.
- Fit larger capacitors, potentiometers, switches and other controls.
- Fit LEDs, connectors and the remaining taller components.
- Insert socketed ICs only after soldering around the socket is complete.
- Inspect every joint and check for solder bridges before applying power.
Electronics construction guidance
If you are new to kit construction, use the Soldering Guide alongside these instructions. Identify each component before fitting it and compare its reference with the component list and PCB silkscreen.
When it does not work
Troubleshooting
Nothing happens when power is applied
- Confirm the supply is connected to the correct input and with the correct polarity.
- Check that ICs, diodes, LEDs, transistors and electrolytic capacitors are fitted in the correct orientation.
- Compare component values and positions against the component list and PCB reference.
- Inspect for missed joints, dry joints and accidental solder bridges.
The circuit powers up but does not behave as expected
This kit is intended for low-voltage ac-to-dc rectification and regulation. If the output is stuck, unstable or outside the expected behaviour, use the schematic to trace the circuit a stage at a time rather than replacing several parts at once.
Check the components around the part of the circuit responsible for the output or timing first. A misplaced resistor, reversed semiconductor or poor connection can allow a circuit to power up while preventing it from operating correctly.
The circuit works intermittently
Intermittent behaviour is often caused by a marginal solder joint, a loose connector or a component lead that has not been fully soldered. Gently inspect the board with power removed and reflow any joint that looks dull, cracked or incomplete.
If the fault remains, compare the assembled board with the schematic and PCB reference one connection at a time.
Ready to test and experiment?
This is a low-voltage rectifier and not designed for use with the mains To use this as a PSU, be sure to use a transformer to drop the voltage to between 9V and 12V
Once the board is working, compare its behaviour with the schematic and the explanation above. Try changing only one input, control or permitted component value at a time so you can clearly see what effect that change has on the circuit.