7805 Psu | Electronic Project Circuits

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Uninterruptible Alarm Power Supply by 7805

Although this Power Supply was designed for the Modular Burglar Alarm – it has other applications. It provides an output of 12-volts – at a current of up to 1-amp. In the event of a mains failure – the back-up battery takes over immediately. And when mains power is restored – the battery recharges automatically.
The 7805 needs the larger heatsink because it has to dissipate a lot of energy – especially when called upon to recharge a flat battery. Its heatsink is at 9v1 – and must NOT be connected to ground. The 7812 never has to dissipate more than 2-watts – so its heatsink can be smaller.
Many of the components, which are shown lying flat on the board, are actually mounted standing upright. The links are bare copper wire on the component side of the board. The heatsinks are folded strips of aluminium, about 2mm thick. Use a well-insulated panel mounted fuse holder for the mains supply to the transformer – and fit it with a 1-amp fuse.
Use a genuine alarm type back-up battery. They are maintenance-free. Their terminals can be held at 13v8 for many years – with no apparent ill effects. They have a life expectancy of about five years. However, they tend not to recover from a very deep discharge. If you wish – you can use a smaller or larger capacity battery.

Read More Source: http://uk.geocities.com/ronj_1217/al1/psu.html
Thank you.

Be the first to comment - What do you think? Posted by admin - March 20, 2008 at 11:02 am

Categories: Electronic Control, Power supply Tags: 7805, 7805 psu, alarm power supply circuit

6V backup battery power supply regulator with IC 7805

This is circuit power supply, 6V backup battery power supply regulator with IC 7805.

For inportant circuit, Because this circuit with backup system by Baterry 6V.
Detail read in circuit.

Be the first to comment - What do you think? Posted by admin - September 10, 2007 at 11:19 pm

Categories: Battery, Power supply Tags: 6v power supply battery backup, 7805 psu

Logic PSU with Overvoltage Protection by IC 7805

Circuit : Andy Collinson
Email: anc@mitedu.freeserve.co.uk

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

overvoltage_circuit

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.