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Showing posts from January, 2009

Current Expanded Regulated Power Supply

Actually, this is ordinary regulated power supply, but the current expander using a transistor make this power supply become powerful.

Based on the datasheet, the stabilizer IC’s can deliver up to 1A output current. For example 78xx series regulators are available in different voltage ratings, but in any case the current should not exceed 1A.

The transistor Q1 (2N 29055) used here has 5A current capacity. The resistor R1 is used to keep the current through regulator IC below 300mA. When the current through R1 increases the base current of Q1 (2N 29055) also increases & the load required load current flows through this transistor. By this way a current greater than the capacity of the regulator IC can be delivered to the load. The C1 is used to filter the ripples off the rectifier output.
Notes:Assemble the circuit on good quality PCB.T1 can be a 230V primary,15V/1A secondary, step down transformer.If 1 A bridge is not available, make one using four 1N 4007 diodes.The series regulat…

9V Regulated Power Supply

Here is 9V Regulated Power Supply schematic diagram:


You can use this power supply for your electronics project which only require electric current about 500mA. This is cheap circuit which will give you stabilized output voltage.

If you want to change the output voltage, you should change the IC type.
For example, you need 5V output, then change the IC from 7098 with 7805 dan change the output of transformer from 16V AC become 9VAC or 12V AC.

High and Low Voltage Cutout with Delay and Music Power Supply

This simple circuit will protect the costly equipment from high as well as low voltages and the voltage surges (when power resumes). It also gives a melodious tune when mains power resumes. When mains voltage is normal, the DC voltage at the cathode of zener diode D4 is less then 5.6V. As a result transistor T1 is in ‘off’ state. The DC voltage at the cathode of zener diode D5 is greater than 5.6V and as a result transistor T2 is in ‘on’ state. Consequently, relay RL1 gets energised, which is indicated by lighting up of green LED. Under high mains voltage condition, transistor T1 switches to ‘on’ state because the voltage at cathode of zener diode D4 becomes greater than 5.6V. Consequently, transistor T2 switches to ‘off’ state, making the relay to de-energise Under low mains voltage condition, transistor T1 switches to ‘off’ state and as a result transistor T2 also switches to ‘off’ state, making the relay to de-energise.

Read more explanation here

Over / Under Voltage Cut-Out Power Supply

This circuit is not really simple, but will save your money :).

This over/under voltage cut-out will save your costly electrical and electronic appliances from the adverse effects of very high and very low mains voltages. The circuit features auto reset and utilises easily available components. It makes use of the comparators available inside 555 timer ICs. Supply is tapped from different points of the power supply circuit for relay and control circuit operation to achieve reliability. The circuit utilises comparator 2 for control while comparator 1 output (connected to reset pin R) is kept low by shorting pins 5 and 6 of 555 IC. The positive input pin of comparator 2 is at 1/3rd of Vcc voltage.

Read more explanation here

Low-cost 12V - 50W off-line switching power supply

This is a simple low-cost 12 Volt 50W off-line switching power supply, which can be used for home projects or to learn operation of flyback converters. It can work over a universal AC line input range 90-264 VAC and provides a 12VDC output at more then 4A load. Line and load regulation is better then 0.5%. The unit has overcurrent, overtemperature and overvoltage protections as well as passive inrush current limiting. Output ripple are approximately 0.2 V. If you need to get lower ripple, you may put an additional output LC filter.

Complete explanation, visit this site

Basic Regulated Power Supply (IV)

This page come from my.integritynet.com.au, will show you about how to make a variable regulated power supply.

This type of regulation is ideal for having a simple variable bench power supply. Actually I think this is quite important because one of the first projects a hobbyist should undertake is the construction of a bench supply. While a dedicated supply is quite handy e.g. 12V, it's much handier to have a variable supply on hand. There have been many times I have had to "smoke test" a project. This means I have started out at the minimum voltage on my supply (about 3V), seen nothing untoward happening and then slowly winding up the voltage to say 15V (this would only be where the project design called for 15V). By the way, this is the recommended way to test a project after having double checked parts placement against circuit drawings and parts placement guide (if any). Always start out at minimum voltage and look for signs of distress among components (usually resis…

Basic Regulated Power Supply (III)

Let's look at the very common LM340-X series or the equivalent 78XX series. Firstly they come in a variety of voltage ranges from 5, 12 and 15V for LM340-XX and 78XX. They also come in a variety of current ratings and package sizes. Common packages are TO-92, TO-5, TO-220 and TO-3. The first two, TO-92 and TO-5 are generally unavailable to the hobbyist because suppliers like to keep reduced stock lines and so tend only to stock the TO-220 and TO-3 types. In fact you can pay more for a TO-92 type (rated at 100 ma) than you would for a TO-220 type (rated at 1.5A) When you have a requirement for a project of say 12V, or even 5V if it's a digital project, then these are the types you use. LM340-5, LM340-12 or 7805 or 7812 are the types. There are of course negative voltage regulators with the numbers LM320-XX or 79XX which are substantially the same as those discussed here excepting they are negative. We will not consider them further. Assume your project calls for a basic fixed …

Basic Regulated Power Supply (II)

To regulate small amounts of current the cheapest approach is to use a zener diode. Higher currents can be obtained from higher power zeners but I prefer to use dedicated I.C.'s in these cases. In one instance you can use a zener diode in conjunction with a pass transistor to extend the range of the zener regulator.


As with our previous design example in Part - 1 we had a small unregulated bench supply of 500 ma for our projects. Now we have decided that it should become a well regulated, well filtered supply giving us 13V dc. By using a series pass transistor we are extending the useful range of the zener diode as well as reducing Vo ripple. This is called "electronic filtering". There is one large handicap with this circuit though. Under over-current conditions Q1 will most likely be destroyed long before F1 blows. Of course I have very cynical (practical?) friends who will tell you that if you buy up Q1 types at 5c each then in fact they are cheaper than most fuses any…

Basic Regulated Power Supply

The ac from the transformer secondary is rectified by a bridge rectifier D1 to D4 which may also be a block rectifier such as WO4 or even four individual diodes such as 1N4004 types. (see later re rectifier ratings). The principal advantage of a bridge rectifier is you do not need a centre tap on the secondary of the transformer. A further but significant advantage is that the ripple frequency at the output is twice the line frequency (i.e. 50 Hz or 60 Hz) and makes filtering somewhat easier. As a design example consider we wanted a small unregulated bench supply for our projects. Here we will go for a voltage of about 12 - 13V at a maximum output current (IL) of 500ma (0.5A). Maximum ripple will be 2.5% and load regulation is 5%. Now the rms secondary voltage (primary is whatever is consistent with your area) for our power transformer T1 must be our desired output Vo PLUS the voltage drops across D2 and D4 ( 2 * 0.7V) divided by 1.414. This means that Vsec = [13V + 1.4V] / 1.414 …

12V / 20 mA max Transformerless Power Supply (input 230V)

If you are not experienced in dealing with it, then leave this project alone. Although Mains equipment can itself consume a lot of current, the circuits we build to control it, usually only require a few milliamps. Yet the low voltage power supply is frequently the largest part of the construction and a sizeable portion of the cost.

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device. (E.g. MOC 3010/3020) If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator. C1 should be of the 'suppressor type'; made to …

5V / 100mA max Transformetless Power Supply (input: 110V AC)

This is transformerless power supply schematic diagram. Please take a note that this circuit running ONLY for input voltage 110V AC.

I use this power supply for applications that doesn't use too mucho power. It can provide power to circuit that uses less than 100mA without any problem. The disadvantage of this circuit is the danger of an electrical shock, so it cannot be used if the circuit is in contact with the user.

The voltage supplied by this is determined by the zener diode.

The version of the transformerless power supply that uses a bridge rectifier provides more current than the first one because it rectifies both phases of the AC voltage.

Unregulated Power Supply

This is a very basic AC to DC rectifier power supply. The transformer is chosen according to the desired load. For example, if the load requires 12V at 1amp current, then a 12V, 1 amp rated transformer would do. However, when designing power supplies or most electronic circuits, you should always plan for a worst case scenario. With this in mind, for a load current of 1 amp a wise choice would be a transformer with a secondary current rating of 1.5 amp or even 2 amps. Allowing for a load of 50% higher than the needed value is a good rule of thumb. The primary winding is always matched to the value of the local electricity supply. Notes:
An approximate formula for determining the amount of ripple on an unregulated supply is: where I load is the DC current measured through the load in amps and C is the value of the capacitor in uF.The diagram below shows an example with a load current of 0.1 amp and a smoothing capacitor value of 1000uF. The calculated value of ripple is (0.1 * 0.007) /…