According to abbreviationfinder, TV stands for Television.
Power supply operation
The power supply of this TV is based on a principle. Switched sources or pulsating sources are sources that have become widespread in practically all modern TVs, due to their greater efficiency compared to linear sources. However, not all pulsating fonts are the same.
Pulsating fonts can be divided into three groups
- Pulse sources that vary their frequency (frequency modulation)
- Pulse sources that vary amplitude (amplitude modulation)
- Pulsating sources that vary the width of the pulse (pulse width modulation)
A characteristic of this switched source is that its oscillation frequency is fixed, at 75 KHz. Other pulse sources change the frequency and thus guarantee regulation. In this source the regulation is going to be maintained by varying the width of the pulse, not its frequency. This is done by the control IC. In principle, this type of source increases its efficiency, since the transformer works at a fixed frequency and can be designed to transfer the maximum of energy with the minimum of losses. Additionally, this frequency of 75 KHz is higher than that used by the switched sources of other televisions, and this avoids having to use large capacitors to filter the voltages obtained in the secondary windings.
It is connected to the AC, from 85 to 240 V AC. It has a general switch SW601, it passes through fuse F601, line filter L601, to the diode bridge VD603 ~ VD606, there it is rectified and filtered with the C607. The DC level at this point corresponds to the AC level that has entered. This DC level across the 5-7 primary winding is applied to the Drain of the MOSFET. From this DC through R600 the control IC N601 (pin 8) is fed. This is to boot the integrated.
Inside the control IC there is a 9 ma current source terminated at pin 8, which is responsible for putting this IC to work. The moment the TV is switched on, there is no voltage, because all the capacitors are discharged. When the rectified DC voltage appears and is applied to pin 8, it is going to activate a 9 ma current source that exists inside the IC and is terminated at this pin. This source is going to be connected until an internal capacitor that exists inside the control IC called the VCC Capacitor is charged. This Capacitor will charge to the 13 volt level. When this internal C reaches 13 volts, the 9 ma source is disconnected and the IC begins to oscillate. This source is designed in such a way that it is reconnected if the voltage on this VCC Capacitor for any reason drops from 13V to 6.5 volts. It is important to remember this characteristic, since while the TV works, the voltage in this Capacitor will be stable, but when any protection is activated, or when the TV is switched to Stand-By mode it will be seen later that this voltage will drop and cause the 9 ma source is activated again. When the IC oscillates, an output pulse appears on pin 5 and this output will control the switching work of the MOSFET. When the MOSFET is switched, it causes the DC that is in its drain to appear alternately in it, and a pulsating waveform will be produced. When the MOSFET is conducting, energy is stored in the primary winding of the T601. When it is not conducting, there is no current flow in the primary, but there is energy stored in it. It is necessary to transfer this energy for secondary winding. To achieve this, a current conduction is required. This is achieved by the network formed VD612 and the parallel R604B and R604, which in turn serves to protect the MOSFET against excessive voltage spikes.
In the secondary, the voltages that appear in its different windings will depend on the ratio of turns that exists between these windings and the primary winding. There is an auxiliary winding in the transformer between pins 1 and 3, which fulfills the function of forming the supply voltage necessary to supply the control IC through the network formed by the diode VD610 and the Capacitor C613. When in normal operation, a stable voltage appears on pin 6 that is in the range of 13 volts. This voltage is what the integrated one needs to work when the TV is in normal operation.
Control Pins
Control IC pin 3
Regulation is achieved by optoelectronics. On pin 3 of the control IC. A sample is taken from the output of the B + in the secondary through the voltage divider formed by R639, VR601 and R640. The voltage from this divider is injected to pin 2 of the TL431LP programmable reference regulator. Pin 1 of this regulator is connected to the cathode of the optoelectronic LED and 3 to ground. The anode of the photodiode is connected to the 8 volt source through R641. Assuming an increase in the voltage at the output, the voltage at pin 2 will increase, so it puts point 1 more to ground, resulting in greater current flow through the photodiode. If this happens, the phototransistor conducts more, the one that puts more voltage on pin 3 of the control IC. This higher voltage causes the output waveform on pin 5 of the control IC to vary so that the width of the pulse in the non-conduction time is greater, causing the MOSFET to be longer without conducting, which causes that the output voltage drops, compensating for the initial increase that occurred in the B +. In this way regulation is obtained. If a decrease in B + is assumed, the opposite occurs.
The grounds are different at the source, because a part of it is not isolated from the power line, this is known as the hot zone, here the primary and auxiliary windings are included. The earth of the hot zone is not the same as that of the cold zone, this can be seen in the electrical diagram with different symbols. The control IC also has pins 1 and 2, which we will explain their purpose below:
Control IC pin 2
Pin 2 (current sensor) contains a comparator circuit that controls a protection that has an internal reference of 1 volt with respect to the voltage reaching pin 2. As can be seen in the diagram, the voltage reaching pin 2 depends on the current that flows through the R609, which due to its characteristics of very low ohmic resistance and great stability, is a sensing resistance of the current that flows through the MOSFET. The resistors R615 and R610 together with C611 make up a network that will eliminate the peaks and interferences that may exist unrelated to the actual current that is flowing through the MOSFET. In normal operation, the voltage on pin 2 of the control IC is below 1 volt, so the internal comparator is not going to trip the protection. If for any reason, the voltage drop across the sensing resistor exceeds 1 volt, the comparator acts to trip the overcurrent protection. This causes the control IC to be disabled, ceasing to oscillate, thus protecting the source and the TV.
Control IC pin 3
Pin 1 is called the degauss pin. Through this pin, through an internal comparator, the zero crossing will be detected. The comparator will internally have a comparison reference between 20 and 50 millivolts and performs a comparison of the current that is injected to the IC through this pin. If the current is greater than a certain level, an overvoltage protection is activated. If the current falls below a level, a circuit is activated that tells the control IC that it should go to work in Stand-By mode which is a work mode in which it drops when the TV is turned off from normal operation using the Remote Control.
