Studying example circuits using tny274 tny275 tny276 tny277 tny278 tny279 tny280

AUTH ELECTRONIC 17/08/2020

1. What are some applications of TNY274 TNY275 TNY276 TNY277 TNY278 TNY279 TNY280

TNY274 TNY275 TNY276 TNY277 TNY278 TNY279 TNY280 are usually used power supply circuit of chargers, adapters, cameras, portable audio devices, etc. They are also used in PC board, auxiliary supplies,  decoders, industrial systems, metering, etc. 

2. Output table and how to replace TNY274 TNY275 TNY276 TNY277 TNY278 TNY279 TNY280 in a electronic circuit

3. Packet and Pin Functional Description

TNY274 to TNY280 IC has 7 pins and have 2 types of package. P package and G package. 

G Packet example

P packet example

DRAIN (D) Pin: This pin is the power MOSFET drain connection. It provides internal operating current for both start-up and steady-state operation

BYPASS/MULTI-FUNCTION (BP/M) Pin: This pin has multiple functions, it connects to a capacitor or other components to choose functions of TNY274.

ENABLE/UNDER-VOLTAGE (EN/UV) Pin: This pin has dual functions: enable input and line under-voltage sense. During normal operation, switching of the power MOSFET is controlled by this pin. MOSFET switching is terminated when a current greater than a threshold current is drawn from this pin. Switching resumes when the current being pulled from the pin drops to less than a threshold current. A modulation of the threshold current reduces group pulsing. The threshold current is between 60 µA and 115 µA. The EN/UV pin also senses line under-voltage conditions through an external resistor connected to the DC line voltage. If there is no external resistor connected to this pin, TinySwitch-III detects its absence and disables the line under-voltage function

SOURCE (S) Pin: it's S pin of Mosfet inside TNY274. 

4. Studying example circuit using TNY274 TNY275 TNY276 TNY277 TNY278 TNY279 TNY280 in a real pulse power supply circuit

In this example circuit , we use TNY278PN to convert 220VAC to 12VDC output. Let's study how TNY278PN works in this pulse power supply circuit. 

First start with 220VAC input voltage, it goes through input protection block including F1 fuse and RV1 varistor, then it is converted to DC Voltage by bridge rectifier D1 D2 D3 D4 diodes. This DC voltage will be flattened by L1 coil, C1 C2 capacitors. And the positive pole of this 300V DC voltage goes to input primary coil 1,3 of T1 pulse transformer, the rest of primary coil connects to D pin of TNY278. This D pin is also D pin of the Mosfet inside TNY278. The S pin of TNY278 connects to the negative pole of 300V DC voltage. Let's see, there are two secondary coils of T1 pulse transformer. The first coil 6,8 connects to D7 diode. We see in this diagram below. 

In the primary coil side, the mosfet switches on and off at a certain frequency, then we can see voltage of primary coil will variability, therefore it appears a induction voltage at secondary coil. The output of secondary coil will be converted to DC voltage by D diode and flatted by C capacitor.Iin the same way, the output voltage of 6,8 secondary coil will be converted to DC voltage by D7 diode and flatted by C10 C11 capacitors and L2 coil. 

At primary coil side,you can recognize the circuit designer used a drain protection block to protect D pin of TNY278 from opposite voltage generated from 1,3 primary coil. To stable output voltage there is a voltage feedback system, it measures the variation of output voltage and feedback this value to EN/UV pin of TNY278, therefore the pulse generator inside TNY278 will change pulse width and frequency to Mosfet inside TNY278, and it leads to the output voltage will be stable. Let's go in detail in this circuit, the output voltage of 4,5 secondary coil will be converted to DC voltage by D6 diode and flatted by C6 capacitor. Then it connects to the PC817 opto, this PC817 opto is used to isolate output circuit from power circuit of primary side. Using a voltage divider circuit to divide the output voltage 12VDC to smaller voltage at Vr4. ( voltage of R4 resistor) . When 12VDC output volatage varition then Vr4 will be varition, that makes PC817 ON and OFF, lead to EN/UV pin will receive ON and OFF signal.  The TNY278 will understand how the 12VDC output is high or low depends on this signal. 


 

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