Category: LCD Television Repair and Service
Contents of this article
- NCP1207 AC-DC Converter
- NCP1396 Resonant mode controller
- SG6961 PFC Controller
- Power supply schematic diagram
LG 42LG5000
NCP1207 AC−DC Converter
The NCP1207 is a controller dedicated for driving the current−mode free running quas −resonant Flyback offline converter. This converter is designed for consumer products like notebooks, offline battery chargers, consumer electronics (DVD players, set−top boxes, TVs), etc. The growing interest for EMI pollution reduction, efficiency improvement, and maximum safety has been taken into account while designing the NCP1207. By implementing the NCP1207 one can build a power supply that can meet all those requirements. This can be achieved with help of the following NCP1207 main features:
# Current−Mode Control: Cycle−by−cycle primary current observation is helping to prevent any significant primary overcurrent which would cause transformer’s core saturation and consequent serious power supply failure.
# Current−Mode Control: Cycle−by−cycle primary current observation is helping to prevent any significant primary overcurrent which would cause transformer’s core saturation and consequent serious power supply failure.
# Critical Mode Quasi−resonant Operation: Prevents the converter operation in Continuous Conduction Mode inany input and output condition. It is provided by the zero crossing detection of the auxiliary winding’s voltage.
# By addition of the reasonable delay the switch turn−on instant can be shifted to the minimum (valley) of drain voltage. This improves EMI noise and efficiency.
# Dynamic Self−Supply: Ensures IC proper operation in applications where the output voltage varies during operation like battery chargers. The DSS also supplies the IC when the overvoltage event is being latched and converter operation is stopped.
# Overvoltage Protection: By sampling the plateau voltage on the auxiliary winding, the NCP1207 enters into latched fault condition whenever the overvoltage is detected. The controller stays fully latched until the VCC decreases below 4.0 V, e.g. when the user unplugs the power supply from the mains outlet and re−plugs it. The OVP threshold can be adjusted externally.
# Over−Load Protection: by continuously monitoring the feedback loop activity, NCP1207 enters hiccup operation as soon as the power supply is overloaded. As soon as overload condition disappears, the NCP resumes operation.
NCP1396A Resonant Mode Controller
The NCP1396 A/B offers everything needed to build a reliable and rugged resonant mode power supply. Its unique architecture includes a 500 kHz Voltage Controlled Oscillator whose control mode brings flexibility when an ORing function is a necessity, e.g. in multiple feedback paths implementations. Thanks to its proprietary high--voltage technology, the controller welcomes a bootstrapped MOSFET driver for half--bridge applications accepting bulk voltages up to 600 V. Protections featuring various reaction times, e.g. immediate shutdown or timer--based event, brown--out, broken opto--coupler detection etc., contribute to a safer converter design, without engendering additional circuitry complexity. An adjustable deadtime also helps lowering the shoot--through current contribution as the switching frequency increases.
Applications
# Flat Panel Display Power Converters
# High Power AC/DC Adapters for Notebooks
# Industrial and Medical Power Sources
# Offline Battery Chargers
# Flat Panel Display Power Converters
# High Power AC/DC Adapters for Notebooks
# Industrial and Medical Power Sources
# Offline Battery Chargers
PIN COFIGURATION
1 CSS - Soft--start Select the soft--start duration
2 Fmax - Frequency clamp A resistor sets the maximum frequency excursion
3 Ctimer - Timer duration Sets the timer duration in presence of a fault
4 Rt - Timing resistor Connecting a resistor to this pin, sets the minimum oscillator frequency reached for VFB = 1 V
5 BO - Brown--Out Detects low input voltage conditions. When brought above Vlatch, it fully latches off the controller.
6 FB - Feedback Injecting current in this pin increases the oscillation frequency up to Fmax.
7 DT - Dead--time A simple resistor adjusts the dead--time width
8 Fast - Fault Quick fault detection Fast shut--down pin. Upon release, a clean startup
sequence occurs. Can be used for skip cycle purposes
9 Slow - Fault Slow fault detection When asserted, the timer starts to countdown and shuts down the controller at the end of its time duration.
10 GND - Analog ground --
11 Mlower - Low side output Drives the lower side MOSFET
12 VCC - Supplies the controller The controller accepts up to 20 V
13 -- -- --
14 HB - Half--bridge connection Connects to the half--bridge output
15 Mupper - High side output Drives the higher side MOSFET
16 Vboot - Bootstrap pin The floating VCC supply for the upper stage
2 Fmax - Frequency clamp A resistor sets the maximum frequency excursion
3 Ctimer - Timer duration Sets the timer duration in presence of a fault
4 Rt - Timing resistor Connecting a resistor to this pin, sets the minimum oscillator frequency reached for VFB = 1 V
5 BO - Brown--Out Detects low input voltage conditions. When brought above Vlatch, it fully latches off the controller.
6 FB - Feedback Injecting current in this pin increases the oscillation frequency up to Fmax.
7 DT - Dead--time A simple resistor adjusts the dead--time width
8 Fast - Fault Quick fault detection Fast shut--down pin. Upon release, a clean startup
sequence occurs. Can be used for skip cycle purposes
9 Slow - Fault Slow fault detection When asserted, the timer starts to countdown and shuts down the controller at the end of its time duration.
10 GND - Analog ground --
11 Mlower - Low side output Drives the lower side MOSFET
12 VCC - Supplies the controller The controller accepts up to 20 V
13 -- -- --
14 HB - Half--bridge connection Connects to the half--bridge output
15 Mupper - High side output Drives the higher side MOSFET
16 Vboot - Bootstrap pin The floating VCC supply for the upper stage
SG6961 PFC CONTROLLER
Description
The SG6961 is an 8-pin boundary mode PFC controller IC intended for controlling PFC pre regulators. The SG6961 provides a controlled on-time to regulate the output DC voltage and achieve natural power factor correction. The maximum on-time of the external switch is programmable to ensure safe operation during AC brownouts. An innovative multi-vector error amplifier is built in to provide rapid transient response and precise output voltage clamping. A built-in circuit disables the controller if the output feedback loop is opened. The startup current is lower than 20|JA and the operating current is under 4.5mA. The supply voltage can be up to 20V, maximizing application flexibility.
PIN CONFIGURATION
1 INV - lnverting Input of the Error Amplifier. INV is connected to the converter output via a resistive divider. This pin is also used for over-voltage clamping and open-loop feedback protection.
2 COMP - The Output of the Error Amplifier. To create a precise clamping protection, a compensation network between this pin and GND is suggested.
3 MOT - Maximum On Time. A resistor from MOT to GND is used to determine the maximum on-time of the external power MOSFET. The maximum output power of the converter is a function of the maximum on time.
4 CS - Current Sense. lnput to the over-current protection comparator. When the sensed voltage across the sense resistor reaches the internal threshold (O.8V), the switch is turned off to activate cycle-by-cycle current limiting.
5 ZCD - Zero Current Detection. This pin is connected to an auxiliary winding via a resistor to detect the zero crossing of the switch current. When the zero crossing is detected, a new switching cycle is started. If it is connected to GND, the device is disabled.
6 GND - Ground. The power ground and signal ground. Placing a O.1pF decoupling capacitor between VCC and GND is recommended.
7 GD - Driver Output. Totem-pole driver output to drive the external power MOSFET. The clamped gate output voltage is 16.5V.
8 VCC - Power Supply. Driver and control circuit supply voltage.
2 COMP - The Output of the Error Amplifier. To create a precise clamping protection, a compensation network between this pin and GND is suggested.
3 MOT - Maximum On Time. A resistor from MOT to GND is used to determine the maximum on-time of the external power MOSFET. The maximum output power of the converter is a function of the maximum on time.
4 CS - Current Sense. lnput to the over-current protection comparator. When the sensed voltage across the sense resistor reaches the internal threshold (O.8V), the switch is turned off to activate cycle-by-cycle current limiting.
5 ZCD - Zero Current Detection. This pin is connected to an auxiliary winding via a resistor to detect the zero crossing of the switch current. When the zero crossing is detected, a new switching cycle is started. If it is connected to GND, the device is disabled.
6 GND - Ground. The power ground and signal ground. Placing a O.1pF decoupling capacitor between VCC and GND is recommended.
7 GD - Driver Output. Totem-pole driver output to drive the external power MOSFET. The clamped gate output voltage is 16.5V.
8 VCC - Power Supply. Driver and control circuit supply voltage.
POWER SUPPLY SCHEMATIC DIGRAM
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