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Ultimately, the solution system cost is significantly lowered. Also able to function in a traditional way constant output voltage regulation levelany intermediary solutions can be easily implemented. This flexibility makes it ideal to optimally cope with a wide range of applications.
This application note will discuss on the design of power factor correction circuit with MC with traditional boost constant output voltage regulation level operation and follower boost variable output voltage regulation level operation.
For derivation of the 15n245 equations related to the IC please refer to MC data sheet. R6 R7 D5 Introduction The MC is an active power factor controller that functions datashee a boost pre—converter which, meeting international standard requirement in electronic ballast and off—line power supply application.
MC is designed to drive a free running frequency discontinuous mode, it can also be synchronized and in any case, it features very effective protections that ensure a safe and reliable operation. This circuit is also optimized to offer extremely compact and cost effective PFC solutions. It does not entail the need of auxiliary winding for zero current detection hence a simple coil can be used instead of a transformer if the MC Vcc is drawn from the load please refer to page 19 of the data sheet.
Typically, continuous mode is more favorable for high power application for having lower peak current. On the other hand, for less than W application, discontinuous mode offers smaller inductor size, minimal parts count and lowest?
For critical conduction mode, the inductor current must fall to zero before start the next cycle. This operation results in higher efficiency and 1 February, — Rev. Secondly, since there are no dead—time gaps between cycles, the fatasheet line current is continuous thus limiting the peak switch to twice the average input current.
The converter works right on critical conduction mode, which results in variable frequency operation. Assuming the inductance and the on—time over each line half—cycle are constant, di is actually the peak current, ILpk, this is because the inductor eatasheet begins charging at zero current.
Regulated DC Output Voltage: In practice, t on tends to increase at the ac line zero crossings due to the charge on output capacitor Cout. On—time By solving inductor equation 1on—time required to charge the inductor to the correct peak current is: Off—time The instantaneous switch off—time varies with the line and load conditions, as well as with the instantaneous line voltage.
Off—time is analyzed by solving equation 1 for datashert inductor discharging where the voltage across the inductor is Vo minus Vin.
The off—time is at a minimum at ac line crossings. This equation is used to calculate t off as Theta approaches zero. Inductor 1j5245 Summary The required energy storage of the boost inductor is: Typically, the PFC converter is designed to operate above the audible range after accommodating all circuit and component tolerances. Higher frequency operation that can significantly reduce the inductor size without negatively impacting efficiency or cost should also be evaluated.
The minimum switching dayasheet occurs at the peak of the ac line voltage. As the ac line voltage traverses from peak to zero, t off approaches zero producing an increase in switching frequency. Both t on max and t off max will be individually calculated and added together to obtain the maximum conversion period, ttotal. This is required to obtain the inductor value. Then an inductor is what it needs.
Dattasheet auxiliary winding will have the low frequency —Hz variation on its peak—rectified voltage. The auxiliary winding capacitor must be large to minimize the droop in the Vcc of the controller. Datsheet auxiliary turn number can be approximated with below equation: As a rule of thumb, can start with 1? Selection of Semiconductors Maximum currents and voltages must first be determined for over all operating conditions to select the MOSFET and boost rectifier.
This implying the need of devices with at least V breakdown voltage. High voltage diodes with recovery 1n52455 of ns, or less should be used for the boost rectifier. Then there is no risk to have the power switch ddatasheet at start—up because of the in—rush current.
In the same way, in an overload case, the power MOSFET is kept off as long as there is a direct output capacitor charge current, i.
SemeLAB – datasheet pdf
This is one of the major advantages compared to MC and competition. Current Limiting for Start—up Inrush Initially Vo is zero, when the converter is turned on, the bulk capacitor will charge resonantly to twice Vin. The voltage can be as high as V if Vin happens to be at the peak high—line V condition V. The peak resonant charging current through the inductor will be many times greater than normal full load current. The boost shunt switch cannot do anything to prevent this and could be worse if turned on during start—up.
The inrush current and voltage overshoot during the start—up phase is intolerable. A fuse is not suitable, as it will blow each time the supply is turned on. There are several methods that may be used to solve the start—up problem: Start—up Bypass Rectifier This is implemented by adding an additional rectifier bypassing the boost inductor. The bypass rectifier will divert the start—up inrush current away from the eatasheet inductor as shown in Figure 3. The dataasheet capacitor charges through Dbypass to the peak AC line voltage without resonant overshoot and without excessive inductor current.
Dbypass is reverse—biased under normal operating conditions. If load overcurrent pulls down Vo, Dbypass conducts, but this is probably preferable to having the high current flowing through boost inductor.
A 31 Designing the Current Sense Circuit The inductor current is converted into a voltage by inserting a ground referenced resistor, RCS in series with the input diode bridge. Therefore a negative voltage proportional to the inductor current is built. datqsheet
The current sense resistor losses, PRcs: The MC Zero Current Detection uses the current sensing information to prevent any power switch turn on as long as some current flows through the inductor.
Rectifier bypass of start—up inrush current 2.
General Semiconductor Datasheets |
External Inrush Current Limiting Circuit For low power system, a thermistor in series with the pre—converter input will limit the inrush current. Concern is the thermistor may not respond fast enough to provide protection after a line dropout of a few cycles. A control circuit is necessary. This method can function on a cycle—by—cycle basis for protection after a dropout. Load Overcurrent Limiting If an overcurrent condition occurs and exceeds the boost converter power limit established by the control circuit, Vo will eventually be dragged down below the peak value of the AC line voltage.
If this happens, current will rise rapidly and without limit through the series inductor and rectifier. This may result in saturation of the inductor and components will fail. The control circuit holds off the shunt switch, since the current limit function is activated.
It cannot help to turn the switch ON — the inductor current will dataeheet even more rapidly and switch failure will occur. Typically, a power factor correction circuit is connected to another systems like switched mode power supply or electronic ballast.
These downstream converters typically will have current limiting capability, eliminating concern about load faults. However, a downstream converter or the bulk capacitor might fail. Hence there is a possibility of a short circuit at the load. If it is considered necessary to limit the current to a safe value in the event of a downstream fault, some means external datashest the boost converter must be provided.
(PDF) 1N5245 Datasheet download
The number of turns required for a selected core size and material is: The required air gap to achieve the correct inductance and dagasheet is: To determine the output capacitor As rule of thumb, for 80W output, start with mF, V capacitor.
The on resistance, Rds on 1.
Design of regulation and overvoltage protection circuit The output voltage regulation level can be adjusted by Ro, Ro C. Designing the oscillator circuit For traditional boost operation, CT is chosen with below equation: Datasheer the current sense resistor losses, PRcs: Overcurrent protection resistor, ROCP can be determined with below equation: This provide current limit at 3.
A 85 Figure 4. F V nF 10nF ? F V 1nF 50V 0. To determine the output capacitor As rule of thumb, for 80W output, start with ? A Use W resistor. Datqsheet V nF pF ? SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
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