PLC810PG
Applications Example
Circuit Description
Figures 4, 5, and 6 show the schematic of a typical 280 W LCD
TV power supply application using HiperPLC and TinySwitch-III.
The PSU contains PFC + LLC stage using a PLC810PG which
provides the high power outputs, plus a standby power supply
using a TNY275PN.
The design has 4 outputs: 12 V and 24 V, 5 V main and 5 V
standby. The 5 V main and 5 V standby are provided by the
TinySwitch-III flyback circuit. See the Typical Application
section of the TinySwitch-III data sheet found on the Power
Integrations website for a description of a TinySwitch-III flyback
converter.
The PSU has a standby input signal, which enables the main
converter (PLC810PG).
EMI Filtering and Rectification
Capacitors C42, C1, C5, C3, C4, C2, C6 and common mode
chokes L1 and L2 perform EMI filtering. Diode bridge BR1
rectifies the input AC with D14 and D15 providing a separate
full-wave rectified signal for the brownout circuit.
Inrush Limiting
Thermistor RT1 provides inrush limiting. It is bypassed by a
relay (RL1) which is driven by the power supply remote-on
signal. The use of a relay increases efficiency by approximately
1%. Diode D3 provides an inrush path to the bulk capacitor C9
that bypasses the PFC inductor L4 to prevent it from saturating.
PFC Stage
The main PFC inductor L4, MOSFET Q2, boost diode D2, and
bulk cap C9, form a PFC boost converter. Capacitor C8 and
R5 damp reverse recovery ringing on D2. Inductor L4 uses a
small low cost Sendust core. Two key advantages of this
continuous mode PFC design are that the low ripple current
allows the use of:
1. High B
SAT
material (such as low-cost Sendust), allowing fewer
turns which saves copper cost and reduces size.
2. Low-cost magnet wire rather than Litz wire.
Diode D2 is a low-cost silicon ultrafast PFC boost diode.
Components Q1, Q3, C10 and R7 form the gate drive circuit.
See description under “Recommended PFC Gate Drive Circuit“.
PFC Current sense resistors R6 and R8 are clamped by D3 and
D4 to protect the current sense input of the controller IC during
inrush. Capacitor C11 is positioned close to the PFC MOSFET
and diode to limit the size of the high frequency loop around
components Q2, D2 and C9. This reduces EMI. Low-loss film
capacitor C7 functions as the input capacitance to the PFC
boost converter, and also filters EMI.
LLC Stage
LLC Input Stage
MOSFETs Q10 and Q11 form the LLC half-bridge. They are
driven directly by the PLC810 via gate resistors R56 and R58.
Capacitor C39 is the primary resonating capacitor, and should be
a low-loss type rated to tolerate the highest RMS current seen at
maximum load. Transformer T2 has a large built-in leakage
inductance which acts with C39 to form the series resonant tank.
Capacitor C40 is used for local bypassing, and is located directly
adjacent to Q10 and Q11. Resistor R59 provides primary current
sensing to the controller for overload protection.
LLC Outputs
The secondary ouputs of transformer T2 are rectified and filtered
by D9, D10, C38, C39 and C53 to provide the +12 and +24 V
outputs.
Switched +5 V Main Output
MOSFET Q12 is used to switch the output of the +5 V logic
supply. The AC signal from one side of the 12 V output rectifier
is used to drive Q12 via R60, R61, D11, and C43. Capacitor
C44 provides filtering near the output connection.
Bias Regulator / Remote On/Off and Brownout
Shutdown Circuit
Components Q4, U1, C17, and associated components constitute
the bias regulator and provide the remote on-off function.
Darlington transistor Q4, R14, and VR2 form a simple emitter
follower voltage regulator that is switched via optocoupler U1.
Capacitor C17 limits the rate of rise of the bias voltage. Transistor
Q5 and R20 quickly discharge C17 when optocoupler U1 is
turned off.
On the secondary, optocoupler U1 is turned on via Q8 when the
standby signal is high. This turns on the PFC LLC stages.
A brownout shutdown circuit is provided to actively shutdown
the PSU when the output turns off due to a brownout condition.
This circuit operates by sensing the AC input voltage together
with the presence of the GATEL signal from the LLC controller.
During a brownout condition, the PFC output voltage will drop
until the VFB pin voltage drops to INH, turning off the LLC
stage. If at this point the AC voltage is below 82 VAC, the
brownout circuit will turn off the PLC810 via the bias regulator,
preventing the PFC from charging up the bulk capacitor again,
restarting the LLC, and repeating the cycle (and creating output
voltage glitches).
Resistor R24, R26, R28-30, C21, VR4, and Q7 are used to
sense the AC input voltage. The voltage threshold of this circuit
is set below the turn-on threshold of the standby/primary bias
converter. Sufficient AC voltage turns on Q7, discharging
capacitor C22, which is charged via R15. Components R32,
R35, and Q9 sense the switching GATEL signal. Transistor Q9
discharges capacitor C22 when the switching signal is present.
10
Rev. F 08/09
www.powerint.com
POWERINT [ POWER INTEGRATIONS, INC. ]
