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Half-Wave Rectifiers - Practical Demonstration


In our previous tutorials about diode, we have discussed how a diode operates theoretically. A diode can be used as rectifier in which it could be a half-wave or a full-wave rectifier. A rectifier converts an AC voltage into a DC voltage, so it is usually found in a DC power supply. If you want to build a basic half-wave power supply, this tutorial will guide you on how to build it.

Warning! If you’re planning to build a power supply, make sure that all conductors, especially on the primary side of the transformer, are safely insulated since we’re dealing with high-voltage here.

Parts and Materials

So in order to build a half-wave power supply, we need the following parts and materials:

1. Electrical Plug and Zip-Cord

The electrical plug and the zip-cord allows the power supply to be connected to the wall outlet where we will be getting our AC source. There are different types of plug so be sure the one that you will use matches the wall outlets available at your location. Also consider if the plug and the zip-cord can withstand the voltage from the wall outlet and the current that the load will draw.

2. Switch

The switch makes it easier to turn ON or OFF the power supply without disconnecting the plug from the wall outlet. The same with the electrical plug and zip-cord, you need to make sure the voltage and current rating of the switch meets the requirement. The wiring also depends on the type of switch that you will use.

3. Fuse and Holder

The fuse serves as a protection in case there’s an overcurrent event that will happen. Under normal operating conditions, the fuse just act like a normal conductor. But if the current flowing through the circuit exceeds the current rating of the fuse, the wire inside the fuse melts and causes the circuit to be opened. This prevents the current to flow again.

When selecting a fuse, be sure to get a slow-acting or a slow-blow type fuse since the transformer and capacitor filters may initially draw high surge current that causes the fuse to blow when it’s a fast-acting type. To determine the current rating of the fuse that you’re going to use, divide the power rating of the transformer by the voltage of the AC source.

4. Stranded Electrical Wire

The stranded electrical wire is going to be used to connect the switch, fuse, transformer, and the rectifier circuit. The size of the wire depends on the current required.

5. Transformer

A transformer is a passive electrical device that can be used to step up or step down a voltage. In a DC power supply, most of the time a transformer is used to step down an AC voltage. Also, the transformer isolates the circuit on the secondary side from the AC source.

6. Diode

The diode here functions as the half-wave rectifier that converts the AC voltage into a pulsating DC voltage. You can use a general purpose diode like a 1N4007 if the current required is less than 1A.

7. Electrolytic Capacitor

Since the output of the half-wave rectifier is still a pulsating DC voltage, the electrolytic capacitor here is used to filter the output of the rectifier and produce a smooth DC voltage. For smoother output, please use at least 1000uF capacitor. The voltage rating depends on the output voltage from the rectifier.

8. Zener Diode

The Zener diode is used as a voltage regulator to have a steady DC output voltage even if there’s a variation with the input voltage or the load’s resistance. The voltage rating of the Zener diode depends on what voltage you want your power supply to output.

9. Resistor

The resistor here is just used as a dummy load and is not really required. We’re just going to use it to experiment.

Instructions on How to Build

1. Assemble the parts on the primary side of the transformer (plug, zip-cord, switch, and fuse) first as shown in the diagram and do a safety check before connecting or soldering it to the transformer.

2. After connecting all the parts, turn ON the switch and measure the resistance between the prongs of the plug using an ohmmeter. The ohmmeter should display infinite resistance. If it shows continuity, there’s a short between the two power conductors which is dangerous.

3. The switch and fuse holder are usually mounted to the power supply case, so you also need to check if there’s a short between the prongs of the plug and the casing.

4. Solder the wire connected to the other end of the fuse and the wire connected to the switch to the terminals of the transformer.

Instruction number 5 to 10 is for a specific transformer VPS24-5400 from Triad Magnetics. But some of the tips here are still applicable even if you use a different transformer.

5. The connection to the transformer depends on what type of power transformer you are using. In our case, we’re using the VPS24-5400 power transformer from Triad Magnetics. It’s a 130VA transformer which can accept around 230VAC input when its primary windings are connected in series or 115VAC if connected in parallel and can have an output of 24VAC when the secondary windings are connected in series or 12VAC if connected in parallel.

6. Since we want to have approximately 12VAC on the secondary side from a 120VAC input, we are going to have a parallel connection on both sides of the transformer.

7. So according to the datasheet, to have a parallel connection on the primary side, we need to connect terminal 6 to 2 and terminal 5 to 1 and use terminals 6 and 1 as our input terminals. So we are going to connect or solder the stranded wires from the fuse and switch to terminals 6 and 1.

8. After soldering the wires from the fuse and switch to the input terminals of the transformer, check the continuity of the primary windings by measuring the resistance across the prongs of the plug. When the switch is OFF, there should be infinite resistance or no continuity. When the switch is ON, the ohmmeter should measure a small amount of resistance. If there’s no continuity, check the connections if they’re really connected and check the fuse if it’s good or blown.

9. On the secondary side, we need to connect terminal 12 to 8 and terminal 11 to 7 to have a parallel connection. Then terminals 12 and 7 are going to be our output terminal on the secondary side which will be connected to the rectifier circuit.

10. Now solder the wires to terminal 12 and 7 and check the continuity of the secondary winding. If there’s continuity, next thing to do is to connect the plug into a wall outlet, turn ON the switch, and measure the AC voltage across the secondary side. You should be able to measure approximately 12VAC. Now, turn OFF the switch and disconnect the plug from the outlet.

11. Next thing to do is to breadboard the parts on the secondary side of the transformer (rectifier diode, capacitor filter, zener voltage regulator circuit, load) as shown in the circuit diagram. Since this is just a prototype, we’ll just put the power supply circuit on a breadboard. If you still don’t know how to use a breadboard, you can check our tutorial about breadboards here. You can always transfer this circuit to a PCB if you are already sure of the value of the components.

12. Check if all devices are connected properly. Check the polarity of the rectifier diode, electrolytic capacitors, and the Zener diode. If they’re all connected correctly, you can now connect the wires from the secondary side of the transformer to the input of the rectifier diode.

13. Connect again the plug into the wall outlet and turn ON the switch. Check if there’s a DC voltage across the output of the rectifier or the capacitor filter and across the load. The voltage across the capacitor filter should be closed to the secondary voltage of the transformer and the voltage across the load should be the same or approximately equal to the Zener diode voltage rating.

So that’s how you build a basic DC power supply with a half-wave rectifier. If you have any questions, leave it in the comments below and if you’ve found this interesting or helpful, give it a like and subscribe to our channel!

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