Basic UPS Power Supply circuit and Description

Description

This circuit is a simple form of the commercial UPS, the circuit provides a constant regulated 5 Volt output and an unregulated 12 Volt supply. In the event of electrical supply line failure the battery takes over, with no spikes on the regulated supply.

Circuit diagram

Notes:
This circuit can be adapted for other regulated and unregulated voltages by using different regulators and batteries. For a 15 Volt regulated supply use two 12 Volt batteries in series and a 7815 regulator. There is a lot of flexibility in this circuit.
TR1 has a primary matched to the local electrical supply which is 240 Volts in the UK. The secondary winding should be rated at least 12 Volts at 2 amp, but can be higher, for example 15 Volts. FS1 is a slow blow type and protects against short circuits on the output, or indeed a faulty cell in a rechargeable battery. LED 1 will light ONLY when the electricity supply is present, with a power failure the LED will go out and output voltage is maintained by the battery. The circuit below simulates a working circuit with mains power applied:

Between terminals VP1 and VP3 the nominal unregulated supply is available and a 5 Volt regulated supply between VP1 and VP2. Resistor R1 and D1 are the charging path for battery B1. D1 and D3 prevent LED1 being illuminated under power fail conditions. The battery is designed to be trickle charged, charging current defined as :-
(VP5 - 0.6 ) / R1
where VP5 is the unregulated DC power supply voltage.
D2 must be included in the circuit, without D2 the battery would charge from the full supply voltage without current limit, which would cause damage and overheating of some rechargeable batteries. An electrical power outage is simulated below:

Note that in all cases the 5 Volt regulated supply is maintained constantly, whilst the unregulated supply will vary a few volts.

Standby Capacity
The ability to maintain the regulated supply with no electrical supply depends on the load taken from the UPS and also the Ampere hour capacity of the battery. If you were using a 7A/h 12 Volt battery and load from the 5 Volt regulator was 0.5 Amp (and no load from the unregulated supply) then the regulated supply would be maintained for around 14 hours. Greater A/h capacity batteries would provide a longer standby time, and vice versa.

author: Andy Collinson
e-mail: anc@mitedu.freeserve.co.uk
web site: http://www.zen22142.zen.co.uk

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Parts of the UPS Uninterruptible Power Supply

Uninterruptible Power Supply

UPS is basically composed of three main components, namely:

1) Rectifier-Charger

This section is used to transfer circuit and battery charging. Rectifier-charger circuit block is going to supply the power needed by the inverter under full load and at that time to maintain the charge in the battery. Besides these blocks must have the ability to drain the power output of 125-130%.

Characteristics of the batteries also need to be taken into account in its charger circuit design because if a rechargeable battery with a current that exceeds the capacity limit will be able to shorten the life of the battery. Usually for a battery charging current to the UPS is 80% of current conditions issued by the batteries at full load.

Limitation of a UPS system is good by the standards of NEMA - National

Electical Manufacturer Association - is able to provide 100% power continuously (continuous load) and 2 hours at 125% load without a decrease in performance (damage). The battery can still be categorized as unfit for use if the condition is still capable of providing 100% power for 1 hour if the time of filling for 8 hours (determined by the manufacturing

battery).

2) Inverter

The quality of the inverter is a determinant of the quality of power generated by a UPS system. Inverter function to change the DC voltage of the rectifier-charger circuit into AC voltage signal in the form of a sine wave formation and after going through the filter circuit. The resulting output voltage must be stable both voltage amplitude and frequency, low distortion, there are no voltage transients.

In addition, the inverter system needs a feedback circuit (feedback) and the regulator circuit to maintain constant voltage to be obtained.

3) Switch Shifters (Transfer switches)

Transfer switch is divided into two types, namely electromechanical and static. Electromechanical switch uses relays to get one of the supply voltage terminal and the other from the UPS system. Static switch system using semiconductor components, such as SCR.

The use of SCR would be better because of the removal operation is performed with the SCR takes only 3 to 4 ms, while the electromechanical switch is about 50 to 100 ms.

The use of UPS is done by connecting the UPS to the AC input and output PLN UPS to the load. Most UPS are used to supply the computer, because if the source of PLN suddenly dies, then the data being processed is not lost but is still in the back-up by UPS, so theres still time to save data.

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