TOP255 is like other IC in the TOPSwitch-HX family,TOP252-TOP262 are also have some highlight feature:Enhanced EcoSmart™, Integrated Off-Line Switcher with Advanced Feature Set and Extended Power Range.With some utilities,TOP252-TOP262 is exactly choice of almost IC in electronic technology,beside,Lower System Cost, Higher Design Flexibility make this IC more convenience to circuit as bring comfortable for users and technicians.And then TOPSwitch-HX cost effectively incorporates a 700 V power MOSFET, high voltage switched current source, PWM control, oscillator, thermal shutdown circuit, fault protection and other control circuitry onto a monolithic device.
2.Type packet and output voltage
TOP252-TOP262 is not easy to understand IC in electronic technology so it have specific function.So about type packet and output voltage,TOP252-TOP262 have 3 type:PN/GN packet,EN/EG packet and MN packet.On the other hand,Y Package Option for TOP259-261 is used to improve noise-immunity on large TOPSwitch-HX Y package parts, the F pin has been removed (TOP259-261YN are fixed at 66 kHz switching frequency) and replaced with a SIGNAL GROUND (G) pin. This pin acts as a low noise path for the C pin capacitor and the X pin resistor. It is only required for the TOP259-261YN package parts.
Output voltage with each packet of TOP252-TOP262 is showed in the table to follow:
DRAIN (D) Pin:(highlight: as a pass to connect for the current pass and go to another Pin)High-voltage power MOSFET DRAIN pin. The internal start-up bias current is drawn from this pin through a switched highvoltage current source. Internal current limit sense point for drain current.
CONTROL (C) Pin:(highlight: exactly control the pulse generator,adjust cycle and treat errors output voltage)Error amplifier and feedback current input pin for duty cycle control. Internal shunt regulator connection to provide internal bias current during normal operation. It is also used as the connection point for the supply bypass and auto-restart/ compensation capacitor.
EXTERNAL CURRENT LIMIT (X) Pin (Y, M, E and L package):(common: used to reduce the current limit externally to a value close to the operating peak current.This pin can also be used as a remote ON/OFF input) Input pin for external current limit adjustment and remote ON/OFF. A connection to SOURCE pin disables all functions on this pin.
VOLTAGE MONITOR (V) Pin (Y & M package only):(highlight: is usually used for line sensing and support to rectify current) Input for OV, UV, line feed forward with DCMAX reduction, output overvoltage protection (OVP), remote ON/OFF and device reset. A connection to the SOURCE pin disables all functions on this pin.
MULTI-FUNCTION (M) Pin (P & G packages only): This pin combines the functions of the VOLTAGE MONITOR (V) and EXTERNAL CURRENT LIMIT (X) pins of the Y package into one pin. Input pin for OV, UV, line feed forward with DCMAX reduction, output overvoltage protection (OVP), external current limit adjustment, remote ON/OFF and device reset. A connection to SOURCE pin disables all functions on this pin and makes TOPSwitch-HX operate in simple three terminal mode (like TOPSwitch-II).
FREQUENCY (F) Pin (TOP254-258Y, and all E and L packages):(highlight: in the TOP254-258 Y and E/L packages set the switching frequency in the full frequency PWM mode to the default value of 132 kHz when connected to SOURCE pin.In the P, G and M packages and the TOP259-261 Y packages, the frequency is set internally at 66 kHz in the full frequency PWM mode) Input pin for selecting switching frequency 132 kHz if connected to SOURCE pin and 66 kHz if connected to CONTROL pin. The switching frequency is internally set for fixed 66 kHz operation in the P, G, M package and TOP259YN, TOP260YN and TOP261YN.
SIGNAL GROUND (G) Pin (TOP259YN, TOP260YN & TOP261YN only): Return for C pin capacitor and X pin resistor.
SOURCE (S) Pin: (highlight: output pass for the current after going through Pin of Mosfet) Output MOSFET source connection for high voltage power return. Primary side control circuit common and reference point.
4.Application in circuit with simple explainations
In a example of a High Efficiency, 65 W, Universal Input Power Supply using TOP260EN to show the executed process of this IC.Each circuit have many and many elements so we will find out of specific feature in this ciruit.Starting with the input source,the current is usually high voltage and alternative current then the inductor L1, capacitor C1 is designed to filter and lesson sensitivity, on the other hand,resistor R1 and R2 will make the voltage is 4.4 MΩ for the current transmit.After that,the current will be converted from AC to DC by the rhombus diode form BR1.Moreover,capacitor C2 is the hulk filter capacitor that ensures low ripple current before transmit to the switch stage.
In the next stage,resistor R3 and R4 is clamped to set a 4MΩ norm to prevent the increase input voltage and resistors R5, R6 and R7 provide power limiting, maintaining relatively constant overload power with input voltage.So the incorporation R3-R7 will make TOPSwitch-HX stop switching until the voltage returns to normal, preventing device damage if the DC input rail rises above 450 VDC.
Then the current continuously go to primary coil and pass to the D pin of Mosfet of TOP260EN.So for the current can go through the TOP,the pulse generator of Mosfet will act by create pulse to connect between Pins.If the generator is ON,the G pin like a gate will close and allow the current go through but if the generator is OFF,the G will cut and the current can't go,will be keep in the primary coil and can impact harm to D pin as well as leak the voltage.Hence,high efficiency network is clamped consist of diode D1, zener VR1, capacitor C5 together with resistors R8 and R9 to protect the D pin and get the best out of voltage for the transformer.When the generator acts with high variable intensity frequency,the current can transmit to secondary coil by the pulse transformer.
In this point,the current will follow by two secondary coil called easily: output coil and feedback coil.In the output coil,the current will be rectified by diode D2 and filtered by capacitors C13 and C14. Ferrite Bead L3 and capacitors C15 form a second stage filter and effectively reduce the switching noise before going to the output.In addition,in the feedback coil,the current will be also rectified and filtered by diode D4 and capacitor C10 but zener diode VR2 will protect voltage if the feedback loop break due to a defective component.For the execute Feedback process,resistor R19 and R20 are formed to sense the output voltage.So resistor R16 will limit the LED current and set the overall control loop DC gain.C8, C9 and R15 are set to connect with control Pin and help to make the low frequency pole and zero to further shape the control loop response.Finally,optocoupler U2 will support for control pin by sending the signal feedback if the output voltage is over so control Pin can control the cycle of frequency as pevent the damaged device.The difference of the Mosfet of TOP252-TOP262 is extract the problem follow another way: if the current voltage is over and drop to VR3 then the VR3 link R13 to V-pin and trigger the problem.
So that is all about TOP252-TOP262 with family,and then we think this IC is so neccessary and people should know more information.Thanks for your attention.