A simple 5 Volt regulated PSU featuring overvoltage protection.

Description:
A simple 5 Volt regulated PSU featuring overvoltage protection.

Notes
The 5 volt regulated power supply for TTL and 74LS series integrated circuits, has to be very precise and tolerant of voltage transients. These IC's are easily damaged by short voltage spikes. A fuse will blow when its current rating is exceeded, but requires several hundred milliseconds to respond. This circuit will react in a few microseconds, triggered when the output voltage exceeds the limit of the zener diode.

This circuit uses the crowbar method, where a thyristor is employed and short circuits the supply, causing the fuse to blow. This will take place in a few microseconds or less, and so offers much greater protection than an ordinary fuse. If the output voltage exceed 5.6Volt, then the zener diode will conduct, switching on the thyristor (all in a few microseconds), the output voltage is therefore reduced to 0 volts and sensitive logic IC's will be saved. The fuse will still take a few hundred milliseconds to blow but this is not important now because the supply to the circuit is already at zero volts and no damage can be done. The dc input to the regulator needs to be a few volts higher than the regulator voltage. In the case of a 5v regulator, I would recommend a transformer with secondary voltage of 8-10volts ac.

By choosing a different regulator and zener diode, you can build an over voltag trip at any value. I have a simulated transient graph of this over voltage protection circuit in the Design section

Circuit Modification
I have a circuit modification from one of my viewers in Sweden, Ulf Kylenfall. The modified circuit is shown below and the electrolytic capacitor is moved to a position directly after the rectifier bridge and before the fuse.

With the original circuit, the thyristor had to [rapidly] discharge the capacitor in its effort to protect the downstream circuitry. This current surge may otherwise destroy the thyristor depending on what quality that has been used for the capacitor.

With the modified circuit, shown above, the fuse needs to blow in such a short time that the integrated energy dissipation over the thyristor is within its limits. Moving the capacitor to a position before the fuse ensures this. (Provided that a sufficiently fast-blow fuse has been used).

Thank you Ulf, for highlighting this design problem, and your solution to improve the circuit, kind regards Andy Collinson.
this circuit by :  Andy Collinson.

5Vdc 2A circuit with LM317

The electronic circuit  for DC voltage 5-12 Volts or -12Volts regulator isolated from double LM317 IC-12V. Power supply for 4V to 6V, current 0.3A. 

 

 

 

 

Details of this circuits.

 

A power supply of  low voltage 5V. function of regulation by LM317  When +5VDC want but the total of the input voltage is 5.1V only slightly.

Heavy possible that we see in this fuel system low-voltage devices to regulation by the LM317.

The circuitry by low job control have low voltage drop in the circuit a lot. The important point for this new type of circuit use IC LM317 very popular. Then make sure that no heavy equipment safely. If the circle of thinking, the use of LEDs ensures that a voltage regulated then mainly in the direction of the work of the racetrack. Normally, this route, the input voltage of 5.1V to 12V. Q1 TIP42 also improve current tallly carry up to 2A. Completion of this course is really useful, a friend of the joy of the Lord Mail.

Applications
1.Flyback controller
2. Multiple-output regulator
3. Simply promoting regulator
4. Forward Converter

5V Dc converter using ADP2303 ADP2302

A very simple and high efficient DC-DC 5 volts power supply circuit can be constructed using ADP2302 or ADP2303 nonsynchronous step down regulator , designed by Analog Devices .
Both of this circuits support a wide input voltage range from 3 volts up to 20 volts .
The difference between this two fixed frequency , current mode control, step down regulators is that ADP2302 support a maximum load current of 2A and the ADP2303 regulator support a maximum load current of 3A .

This schematic circuit is a step down dc converter that will provide a 5 volts output voltage at a maximum 2A load , from a 12 volts input voltage .
The output voltage of the ADP2302 , ADP2303 can be set down to 0.8 V for the adjustable version, while the fixed output version is available in preset output voltage options of 5.0 V, 3.3 V, and 2.5 V.
This circuit use a 700 kHz operating frequency that allows small inductor and ceramic capacitors to be used, providing a compact solution.
For this DC DC converter circuit we will use the ADP2303ARDZ-5.0 which is the ADP2303 fixed voltage 5 volts version .


The recommended vales for the Shotky diodes that can be used for this project are : Vishay SSB43L or SSA33L , ON Semiconductor MBRS330T3 , Diodes Inc. B330B .
If you need to choose another part for the coil , please read the datasheet to see the recommended parts .

5V DC power supply

A regulated 5 volt DC supply is essential for powering micro-controller and TTL based circuits. The output of most wall-warts and adapters is to rippled and impure for use in digital circuits. Lets build an inexpensive power supply using some discrete components and a fixed voltage regulator IC.

You will need:

• a step down transformer [12V]
• four silicon diodes [1N4007]
• a resistor [47Ω]
• capacitors [2 x 220µF, 0.3µF and 0.1µF]
• three terminal voltage regulator IC [LM7805]
• a small general propose PCB, some wires, and a suitable output port (I use a
• audio connector).

The circuit of the supply is as given below:

  

The circuit consists of three main blocks, the rectifier, filter and regulator. The rectifier is used to transform the mains AC voltage to a suitable DC voltage. The output of the rectifier is however an impure DC signal so we use a filter to clean the signal and finally a regulator to deliver precisely 5 volts, irrespective of the load connected to the output.

Rectifier

It consists of a transformer and a diode bridge. The diodes are standard silicon 1N4007 diodes. We have chosen a 12V transformer because the regulator IC needs at-least 7.5V of input voltage to function properly.

Filter

We use a pi-filter here. The two 220µF capacitors and resistor form the filter. Pi-filters are great for light load applications like digital circuits. Be sure to check the polarity of the capacitors before connecting them. The resistor shown above is one rated to dissipate up-to 5W of power across it. You may use smaller 3W resistors, but availability may be an issue. Don't use the tiny 0.25 W or 0.5W ones though.

Regulator

The voltage is regulated by three terminal voltage regulator IC – LM7805. This regulator provides stable 5V DC output against large fluctuations in input voltage and load. It also has internal protection circuits which 'brownout' the device when overloaded. To decide the pin-outs, hold the regulator with its face towards you and legs pointing upward, the pin to the right is the input, middle pin is ground and left most pin is output.

Questions and suggestions are welcome, please use the comment form below.

5V DC power supply

Summary of circuit features

• Brief description of operation: Gives out well regulated +5V output, output current capability of 100 mA
• Circuit protection: Built-in overheating protection shuts down output when regulator IC gets too hot
• Circuit complexity: Very simple and easy to build
• Circuit performance: Very stable +5V output voltage, reliable operation
• Availability of components: Easy to get, uses only very common basic components
• Design testing: Based on datasheet example circuit, I have used this circuit succesfully as part of many electronics projects
• Applications: Part of electronics devices, small laboratory power supply
• Power supply voltage: Unreglated DC 8-18V power supply
• Power supply current: Needed output current + 5 mA
• Component costs: Few dollars for the electronics components + the input transformer cost

Circuit description

This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily available, but usually their voltage regulation is very poor, which makes then not very usable for digital circuit experimenter unless a better regulation can be achieved in some way. The following circuit is the answer to the problem.
This circuit can give +5V output at about 150 mA current, but it can be increased to 1 A when good cooling is added to 7805 regulator chip. The circuit has over overload and therminal protection.

    

The capacitors must have enough high voltage rating to safely handle the input voltage feed to circuit. The circuit is very easy to build for example into a piece of veroboard.

Component list

7805 regulator IC
100 uF electrolytic capacitor, at least 25V voltage rating
10 uF electrolytic capacitor, at least 6V voltage rating
100 nF ceramic or polyester capacitor

Modification ideas

More output current

If you need more than 150 mA of output current, you can update the output current up to 1A doing the following modifications:

• Change the transformer from where you take the power to the circuit to a model which can give as much current as you need from output
• Put a heatsink to the 7805 regulator (so big that it does not overheat because of the extra losses in the regulator)

Other output voltages

If you need other voltages than +5V, you can modify the circuit by replacing the 7805 chips with another regulator with different output voltage from regulator 78xx chip family. The last numbers in the the chip code tells the output voltage. Remember that the input voltage muts be at least 3V greater than regulator output voltage ot otherwise the regulator does not work well.