30.09.2015

Smps circuit diagram working

A 100kHz oscillator within IC1 (UC3524) generates pulses, which are processed by the pulse width modulator (within IC1)used to drive the power switching transistors. The pulse width and therefore the output voltage is controlled by the error amplifier in IC1. Over current protection is provided to ensure that the supply is shut down in the event of too high a current demand at the output.
Each pulse of current in the power switching transistors produces a voltage pulse across the sensing resistor R12. The push pull switching transistors create an AC waveform across the transformer primary winding, and the secondary winding feeds a conventional full wave rectifier and LC low pass filter to supply the load with a stable 5V at the output terminals. The oscillator within IC1 produces narrow 100kHz (approx) pulses that are used as clock pulses for the Switch Logic within IC1. The pulse width modulator comprises the comparator within IC1 and the switching logic, which consists of a bistable and two three input NOR gates.
The error amplifier compares a stable reference voltage on pin 1 (set by Vr1 supplied from an internally regulated 5V from pin 16) with a sample of the load voltage developed across the opto-isolator emitter resistor, R11.
The facilities of the UC3524 that are used in this circuit are shown in more detail in Fig.
Output Q provides an input to NOR gate a, and output Q (the opposite of Q) provides an input to NOR gates b.
The third input to each of the NOR gates is provided by the comparator output, which is a series of variable width low state pulses, produced by comparing the DC error voltage from the error amplifier in IC1 with the ramp produced by the oscillator timing capacitor C2. As each NOR gate output goes high, only when all of its three input signals are low, alternate high state pulses, whose width depends on the value of the error voltage, are fed to the bases of the internal transistors Qa and Qb. The internal drive transistors Qa and Qb each produces a series of pulses at its collector, and an a series of anti-phase pulses at its emitter.
Because the transformer primary centre tap is connected to the main (+VIN) supply, it will always be at the supply potential. Because of the push pull design used by this circuit, it is a simple matter to arrange for such a circuit to have multiple outputs. The total current supplied to the multiple outputs however, must not exceed the maximum current rating of the SMPS. Current limiting, which is capable of completely shutting down the circuit under extreme overload conditions is provided by the action of IC2 and the shut down transistor between pins 9 and 10 within IC1. Every time either transistor conducts, the resulting large emitter current produces a voltage pulse across R12.
If the peak voltage of any of these pulses applied to the non-inverting input of IC2 exceeds the stabilised DC voltage at the inverting input, a positive pulse will be produced at the output, and therefore at the base of Qc within IC1. The action of the current limit circuit is not absolutely instant however, due to the presence of C4 on the shut down compensation pin (9) of IC1. I've drawn an awful lot over the years (gosh, come to think of it, I'm coming up on my 10th anniversary of getting a soldering tool :), from Doom levels to mechanical contraptions to metal-melting devices to electronic circuits. Useful for electronics hobbyists, this linear workbench desktop power supply circuit converts a high input voltage (12V) from the SMPS of a PC into low output voltage (1.25 to 9 volts).
Connect a standard digital voltmeter in parallel with the output leads to accurately set the desired voltage with the help of variable resistor VR1.
3.provide s1 on the in put side of the yellow wire by which you will not load the cap c1 and the led if at all you want the led to be on continuously when the pc is on provide S1 before D1. Recent Questionsinverter power consump in watt at charging time Here is more info hope it helps what ic can be used to start and stop a buzzer in 3 minutes In the schematic universal-triac-control-with-optocoupler, the PNP transistor 2SB328 is shown as NPN. Grid tie (also known as grid-intertied or utility-interactive) systems are intended to operate in parallel with an electric utility.


Such configuration is the most common, simplest and less expensive than other types of grid-interactive residential PV setups. Here is a simplified schematic of a basic grid tie solar power system that illustrates its operation.
Several strings of solar panels are paralleled in the combiner that includes fuses or circuit breakers.
Besides a manual disconnect switch there should be a DC ground fault interrupter (GFI) - a device that opens the circuit when it detects a specified leakage current to earth. A voltage from the PV array is converted to AC by a special utility interactive DC-AC inverter.
To extract the maximum power out of the PV panels, they have to operate near peak power point of their volt-amp curve. By the way, in practice, the solar inverters often have several built-in fused pairs of DC inputs that make an external combiner unnecessary. The circuit uses push pull power switching driving a high frequency transformer, which fully isolates the output circuit from the input. The width of the processed drive pulses controls the length of time for which the power switching transistors conduct, and therefore the amount of power delivered to the transformer.
This measures the difference between a sample of the output voltage, fedback via the opto-isolator, and a reference voltage set by Vr1. The amplitude of these pulses is proportional to the current being delivered to the transformer by the switching circuit. The logic rule for a NOR gate is that its output will be high, only when all its three inputs are low. The lower the value of the error voltage (due to a higher value of "sample" voltage at pin 1) the narrower the pulses produced. The collector voltages of Tr3 and Tr4 will also be at +VIN during the periods when both transistors are turned off. A sample of the load voltage is fed back to the LED within opto-isolator IC3 via the LED current limiting resistor R13.
Different (higher or lower) voltages can be obtained by using a transformer similar to the one illustrated in Fig.
Each supply line will have its own rectifier and filter system, and may also include some extra point of load regulation. This will cause the collector voltage of this transistor to fall, also reducing the error amplifier output that is controlling the pulse width modulator. This capacitor tends to integrate the voltage changes on the collector of the shut down transistor so that very rapid (cycle by cycle) variations of the output voltage during current limiter action are avoided. An adjustable three-pin voltage regulator chip LM317T (IC1) is used here to provide the required voltages.
Currently, an average net cost of an installed batteryless on-grid PV generators for homes is under $7 per watt.
It is desirable although not required to have a separate overcurrent interrupter for each string.
Such a device operates as a pulse-width modulated switch mode power supply SMPS with AC output (read more).
If the peak value of any of these pulses exceeds the DC voltage set by Vr2 (Current limit) then the output from IC2 will cause pulse width modulator input to reduce the width of the pulse being produced by the modulator at that time, momentarily reducing the output voltage. The higher the output voltage, the brighter the glow from an LED sealed within the secondary side, and the larger the DC output voltage derived from pin 4 of IC3 in the primary side of the device.
The ramp waveform produced as C2 charges is also used as an input to the inverting input of the comparator in IC1.


These narrower pulses, when used to turn on the power switching transistors TR3 and Tr4, will lead to a reduction in power in the transformer and a reduction in load voltage.
A voltage sample will normally be taken from only one of the outputs to provide feedback to the pulse width modulator however, as controlling the power applied to the transformer primary will control all the voltage outputs. This action has the effect of reducing the width of the pulse presently being produced, thus instantly reducing output voltage. Switch on S1 and set the required voltage through preset VR1 and read it on the digital voltmeter.
Then open the cabinet of your PC and connect the input line of the gadget to a free (hanging) four-pin drive power connector of the SMPS carefully. During the daylight hours, the system generates some power, offsetting the consumption of electricity from the utility and cutting electric bills. Most inverters come configured for negative ground, although some panels manufacturers recommend positive ground for higher efficiency. Grid tie inverters for solar applications normally use maximum power tracking algorithm that helps to extract maximum power from the panels (see: I-V characteristics of solar panels). If there is a difference, the width of the pulses produced by the pulse width modulator is increased or decreased to correct the error.
If the over current condition disappears, the output voltage will be restored to its normal level, but if the load current remains high, the current limiter will continue to reduce the pulse width, dependent on the amount of over current, even down to zero in the case of a short circuit output. If the current overload disappears, the pulse width modulator will return to normal operation. The main disadvantage of such systems is that normally they do not provide any back-up power during blackouts even if sun is shining and the PV array is producing enough energy.
The combiner frame or the PV arrays grounding conductor should also bonded to an earth rod. Although it includes internal disconnect switch, the utility companies usually require an additional manual AC disconnect. Since sunlight intensity varies during the day, it may not be simple to size your system and find the required amount of the panels. If not, subsequent pulses will be further reduced until the output voltage falls (if necessary) to zero. Diode D2 prevents the output voltage from rising above the input voltage when a capacitive or inductive load is connected at the output.
If the PV panels are producing more electricity than you are using, the system will feed the surplus of the energy back to the utility. A manual DC disconnect switch is required at the place where the cables from the solar array enter the house. A grid tie inverter should meet certain power quality and synchronization requirements, and provide anti-islanding protection. They either provide isolation in a high-frequency converter stage or don't have a transformer at all. Since it is hard to find UL listed single-pole breakers rated for 600VDC, installers often use a breaker with multiple poles connected in series. To reduce the possibility of a fire and to protect the system from a damage caused by lightings it is desirable to have a voltage-clamping device, such as a metal oxide varistor (MOV) across the DC buss. In order to allow the current flow back into the power lines, its output voltage has to be just slightly higher than the utility voltage.




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