Re: LG 42PC1RR-ZL y sus problem
Here is a not so brief explanation of the common technique used to regulate the output voltage of an SMPS. Also, study the datasheet of the TL431. Some monitor service manuals have at least a casual description of it's operation; the words, typos, and errors in this description are mine.
TL431A analysis
The TL431A is a common component in many SMPS power supply. It is has been described as a programmable zener diode, and is often used as such. In extremely simple terms, the TL431A conducts cathode to anode whenever the reference input is over 2.5 volts. Thus it is possible to create a zener of up to 36 volts by the use of a TL431A and two resistors.
One example of using it to control the output voltage of a SMPS is seen in the power supply of an Acer AL1916WX. In this application the design is more complex, however the design itself is straightforward. Resistor R824 forms a voltage divider with the parallel combination of R822 and R823. As the voltage at the reference input (R) of IC803 reaches 2.5 volts current flows from the filtered 5 volt supply, through R519, through the LED of IC801 which is in parallel with R820, into the cathode of IC803 and out the anode. The light from the LED of IC801 causes the photo transistor half of IC801 to conduct. This raises the voltage on pin 2 of IC802, reducing the width of the drive pulses to Q804.
One additional feature is R830, D806 and C827. They serve to reduce the rise rate of the power supply at initial power up. Another feature was not implemented in this version of the supply. ZD801, ZD802, R825, R826, C824, and Q802 limit the output voltages independent of the TL431.
PlainBill
Originally posted by Th3_uN1Qu3
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TL431A analysis
The TL431A is a common component in many SMPS power supply. It is has been described as a programmable zener diode, and is often used as such. In extremely simple terms, the TL431A conducts cathode to anode whenever the reference input is over 2.5 volts. Thus it is possible to create a zener of up to 36 volts by the use of a TL431A and two resistors.
One example of using it to control the output voltage of a SMPS is seen in the power supply of an Acer AL1916WX. In this application the design is more complex, however the design itself is straightforward. Resistor R824 forms a voltage divider with the parallel combination of R822 and R823. As the voltage at the reference input (R) of IC803 reaches 2.5 volts current flows from the filtered 5 volt supply, through R519, through the LED of IC801 which is in parallel with R820, into the cathode of IC803 and out the anode. The light from the LED of IC801 causes the photo transistor half of IC801 to conduct. This raises the voltage on pin 2 of IC802, reducing the width of the drive pulses to Q804.
One additional feature is R830, D806 and C827. They serve to reduce the rise rate of the power supply at initial power up. Another feature was not implemented in this version of the supply. ZD801, ZD802, R825, R826, C824, and Q802 limit the output voltages independent of the TL431.
PlainBill
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