How to make a 12v to 5v Regulator

So let’s say you have this digital camera that can take pictures and videos as well, cool eh? But there’s a catch, its battery drains electricity charge fast. The solution, use an external battery, but the hassle of using external batteries is that most of the batteries are 12 volts. So you have to reduce the power voltage as your device gains charge from the higher voltage battery.

This project is also helpful in cars. We can use a USB adapter and convert a 12 volt to a 5 volt transformer. This are great when you charge devices that only requires a little let say like 5 volts digital cameras, cellular phones and tablets. If you need 5 volts for anything other than USB, simply skip the steps about adding the USB ports.

Here are the things that you will need:

• a fuse holder
• a 0.5 amp fast blowing fuse (you can use a higher rated one if you use a different transistor that can take higher amperage. Because we put the fuse on the 12v side, (which can vary from 11.5-12.5 volts, we have to use a  value 2.5x smaller than what we want on our USB side. So, if you want 1.5 amps for your USB ports, then you select a 0.6amp fuse, if you want 2.5 amps at 5v, you select a 1 amp fuse, if you want 3.75 amps, you select a 1.5 amp fuse, etc.)
• 2 different colors of wire (so that you don't get confused later on)
• a L7805CV voltage regulator, part number 497-1443-5-ND from Digikey (search for 296-11414-5-ND if you want higher AMP output, like 2 amps since it is a max of 3 amps along with a 1-1.2 amp fast blowing fuse, and LT1084CT-5#PBF-ND if you want 2 ports at 2 amps each, along with a 1.5-1.75 amp fast blowing fuse.)
• a 220uf 16v Capacitor, part number P5139-ND from Digikey.
• female USB ports times the number of ports you want (2-3 would be normal, you can expect most devices to use up to 0.5A each, except for tablets that can use 1-2 amps), Digikey number AE9923-ND
• if you choose to add an LED, you need an LED and an appropriate resistor for 5V. This depends on your LED's rating. Any LED will do, here are the values for the most common LEDs : 1.2v = 220ohm, 1.6v = 180ohm, 2v = 180 ohm, 2.2v = 150ohm. If you have a strange LED or want to make it brighter, please use this resistor calculator.

Conclusion

It is always helpful when you have a simple 12v to 5v converter, when you are on the road for a little vacation, charging small devices as never been so easy.

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DC – DC Buck Converter

A buck converter is a voltage step down and current step up converter. It is used in SMPS circuits where the DC output voltage needs to be lower than the DC input voltage. The DC input can be derived from rectified AC or from any DC supply. It is useful where electrical isolation is not needed between the switching circuit and the output, but where the input is from a rectified AC source, isolation between the AC source and the rectifier could be provided by a mains isolating transformer.

The basic operation of the buck converter has the current in an inductor controlled by two switches. All the components are considered to be perfect in the idealized converter. The switch and the diode have zero voltage drop when on and zero current flow when off and the inductor has zero series resistance. Further, it is assumed that the input and output voltages do not change over the course of a cycle.

The switching transistor between the input and output of the Buck Converter continually switches on and off at high frequency. The circuit uses the energy stored in the inductor to maintain a continuous output, during the on periods of the switching transistor, to continue supplying the load during the off periods. The circuit operation depends on what is sometimes also called a Flywheel Circuit. This is because the circuit acts rather like a mechanical flywheel that, given regularly spaced pulses of energy keeps spinning smoothly at a steady rate.

Here's the full article.

How to repair/troubleshoot your SMPS?

A switched-mode power supply or SMPS or sometimes called the switcher, is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently. An SMPS transfers power from a source, like any other power supplies, like mains power, to a load, such as a personal computer, while converting voltage and current characteristics.

So what if your SMPS got broke? With a little electronics know-how and some guides, it should be simple.  Knowledge is power. Don’t forget that the SMPS repairing guide is packed with invaluable step-by-step instructions presented by a reputable and highly experienced electronics engineer.

Some say that it’s extremely difficult to repair a switch more power supply. No! It’s not. The first thing to do is to take a closer look at the SMPS structure. It would be best to look at the generic block diagram of a SMPS. The image below is a simple structure.

Safety is our primary concert.

SMPS are dangerous circuits, so before starting to troubleshoot, safety should come first. Just reminders, half of the components are directly connected to the mains voltage, so voltage shock would be painful. A large storage capacitor is charged at high voltage and can be dangerous even when the mains supply is disconnected. The capacitors could stay charged for a long time since not all SMPS include bleeding resistors or even some might be broken. If you don’t know exactly what you’re doing, might as well call an experienced technician.

It’s good to do a visual inspection

It is always good to do a visual inspection. First, disconnect the SMPS and make sure all capacitor are discharged. Burned resistor can be spotted by their black colour and bad smell. It is important to always check the ferrite transformer, if it looks burned and smells badly, we can give it up because it may sometime have shorted turns and it will be a nightmare to repair or find a replacement part. If the transformer if faulty, it would be best to replace the whole SMPS and will save us a lot of time.

No output, good fuse

SMPS can fail in many different ways, but the most common would be no output power at all. With this, start by checking the input fuse. If the fuse is good but there is no output, probably all the semiconductors are good and it could be easy to fix.

No output, blown fuse

If the fuse is open, then something went really wrong in the circuit. Although don’t replace the fuse yet, as it would just blow again; you have to fix first a short circuit somewhere. Typical problems are blown up power transistors or rectifier diodes, especially on the primary side.

SMPS partially working

There are times when the SMPS is only partially working; it may start for a fraction of a second then shuts down or it may pulsate trying to start every few seconds and shutting down after a fraction of second, or it may producing a wrong output voltage. Probably all power semiconductors are good, so the first thing to check are the capacitors.

Check the capacitors

Often the cause of SMPS problems is the electrolytic capacitors. In what we call cheap designs, where thermal dissipation is a bit too close to the limit, and a choice of components a bit too cost-oriented, electrolytic capacitors are oftentimes real time-bombs that will eventually fail or sometimes explodes. The liquid electrolyte inside these components tends to evaporate and dry out completely altering the characteristics.

Here's the full article.

How Do Voltage Regulators Work?

Linear and switching are the two types of voltage regulators. It generates a fixed output voltage of a preset magnitude that remains constant despite everything on the changes to its load conditions or input voltage.

An active (BJT or MOSFET) pass device is employed by a linear regulator which is controlled by a high gain differential amplifier. A precise reference voltage and the output voltage are compared by the linear regulator. To maintain a constant output voltage, it adjusts the pass device.

Switching regulator on the other hand converts dc input voltage to a switch voltage applied to a power MOSFET or BJT switch. To keep the output remains constant regardless of input voltage or load current changes, the filtered power switch output voltage is fed back to a circuit that controls the power switch on and off times.

What are some of the switching regulator topologies?

The three common topologies are: buck (step-down), boost (step-up) and buck-boost (step-up/step-down). Some other topologies include the flyback, SEPIC, Cuk, push-all, forward, full-bridge and half-bridge topologies.

How does switching frequency impact regulator designs?

Higher switching frequencies mean the voltage regulator can use smaller inductors and capacitors. It also means higher switching losses and greater noise in the circuit. What losses occur with the switching regulator? Losses occur as a result of the power needed to turn the MOSFET on and off, which are associated with the MOSFET's gate driver. Also, MOSFET power losses occur because it takes a finite time to switch to/from the conduction to nonconduction states. Losses are also due to the energy needed to charge and discharge the capacitance of the MOSFET gate between the threshold voltage and gate voltage.

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What is a DC-DC converter?

Think of a DC-to-DC converter as an elevator. The elevator takes a person from one floor to another. Like an elevator, the DC-to-DC converter converts a source of direct current (DC) from one voltage to another level. It’s a class of power converter.

We can see this kind of electronic circuits and are important on portable electronic devices such as cellular phones and laptop computers, which are supplied primarily with power from batteries. This kind of devices often contain several sub-circuits, each with its own voltage level requirement different from that supplied by the battery or an external supply or sometimes higher or lower that the supply voltage. Additionally, the battery voltage declines as its stored energy is drained. Switched DC to DC converters offer a method to increase voltage from a partially lowered battery voltage thereby saving space instead of using multiple batteries to accomplish the same thing.

There are also other examples converters that are used on railway or transit applications. Such converters are important to provide the ultra-wide input range, robust filtering, rugged packaging and high reliability required for railway/transit applications.

The output voltage is regulated in most DC to DC converters. But there are some exceptions which include high-efficiency LED power sources, which are a kind of DC to DC converters that regulates the current through the LEDs, and simple charge pumps which double or triple the output voltage.

DC to DC converters developed to maximize the energy harvest for photovoltaic systems and for wind turbines are called power optimizers.