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TDA16846
Controller for Switch Mode Power Supp...
ICs for Consumer Electronics
Controller for Switch Mode Power Supplies Supporting Low Power
Standby and Power Factor Correction
TDA16846/TDA16847

Controller for Switch Mode Power Supplies
Supporting Low Power Standby and Power
Factor Correction
TDA16846
TDA16847
Preliminary DataBipolar ICOverview
1.1FeaturesLine Current Consumption with PFCLow Power ConsumptionStable and Adjustable Standby FrequencyVery Low Start-up CurrentSoft-Start for Quiet Start-upFree usable Fault ComparatorsSynchronization and Fixed Frequency FacilityOver- and Undervoltage LockoutSwitch Off at Mains UndervoltageTemporary high power circuit (only TDA16847)Mains Voltage Dependent Fold Back Point CorrectionContinuous Frequency Reduction with Decreasing LoadAdjustable and Voltage Dependent Ringing Suppression Time
1.2Description
The TDA16846 is optimized to control free running or fixed frequency flyback converters
with or without Power Factor Correction (Current Pump). To provide low power
consumption at light loads, this device reduces the switching frequency continuously
with load, towards an adjustable minimum (e. g. 20kHz in standby mode). Additionally,
the start up current is very low. To avoid switching stresses of the power devices, the
power transistor is always switched on at minimum voltage. A special circuit is
implemented to avoid jitter. The device has several protection functions: VCC over- and
undervoltage, mains undervoltage, current limiting and 2 free usable fault comparators.
Regulation can be done by using the internal error amplifier or an opto coupler feedback
(additional input). The output driver is ideally suited for driving a power MOSFET, but it
can also be used for a bipolar transistor. Fixed frequency and synchronized operation
TDA 16846
TDA16847
The TDA16846 is suited for TV-, VCR- sets and SAT receivers. It also can be good used
in PC monitors.
The TDA16847 is identical with TDA16846 but has an additional power measurement
output (pin8) which can be used for a Temporary High Power Circuit.

Figure1Pin Configuration (top view)
1.3Pin Definitions and Functions
TDA 16846
TDA16847
1.4Short Description of the Pin Functions
TDA 16846
TDA16847
1.5Block Diagrams

TDA 16846
TDA16847
Figure3TDA16847
TDA 16846
TDA16847Functional Description
Start Up Behaviour (Pin14)
When power is applied to the chip and the voltage V14 at Pin14 (VCC) is less than the
upper threshold (VON) of the Supply Voltage Comparator (SVC), input current I14 will be
less than 100μA. The chip is not active and driver output (Pin13) and control output
(Pin4) will be actively held low. When V14 exceeds the upper SVC threshold (VON) the
chip starts working and I14 increases. When V14 falls below the lower SVC thresholdOFF) the chip starts again at his initial condition. Figure4 shows the start-up circuit and
Figure5 shows the voltage V14 during start up. Charging of C14 is done by resistor R2 of
the “Primary Current Simulation” (see later) and the internal diode D1, so no additional
start up resistor is needed. The capacitor C14 delivers the supply current until the
auxiliary winding of the transformer supplies the chip with current through the external
diode D14.
Figure4Startup Circuit
TDA 16846
TDA16847
Figure5Startup Voltage Diagram
Primary Current Simulation PCS (Pin2) / Current Limiting
A voltage proportional to the current of the power transistor is generated at Pin2 by the
RC-combination R2, C2 (Figure4). The voltage at Pin2 is forced to 1.5V when the
power transistor is switched off and during its switch on time C2 is charged by R2 from
the rectified mains. The relation of V2 and the current in the power transistor (Iprimary) isprimary: Primary inductance of the transformer
The voltage V2 is applied to one input of the On Time Comparator ONTC (see Figure2).
The other input is the control voltage. If V2 exceeds the control voltage, the driver
switches off (current limiting). The maximum value of the control voltage is the internal
reference voltage 5V, so the maximum current in the power transistor (IMprimary) is
The control voltage can be reduced by either the Error Amplifier EA (current mode
regulation), or by an opto coupler at Pin5 (regulation with opto coupler isolation) or by
the voltage V11 at Pin11 (Fold Back Point Correction).21,5VLprimaryIprimary×2C2×--------------------------------+=Mprimary3,5VR2×C2×primary------------------------------------=
TDA 16846
TDA16847
Fold Back Point Correction PVC (Pin11)11 is deviated by a voltage divider from the rectified mains and reduces the limit of the
possible current maximum in the power transistor if the mains voltage increases. I.e. this
limit is independent of the mains (only active in free running mode). The maximum
current (IMprimary) depending on the voltage V11 at Pin11 is
Off-Time Circuit OTC (Pin1)
Figure6 shows the Off-Time Circuit which determines the load dependent frequency
course. When the driver switches off (Figure7) the capacitor C1 is charged by current I1
(approx. 1mA) until the capacitor’s voltage reaches 3.5V. The charge time TC1 is
For proper operation of the special internal anti jitter circuit, TC1 should have the same
value as the resonance time “TR” of the power circuit (Figure7). After charging C1 up to
3.5V the current source is disconnected and C1 is discharged by resistor R1. The voltage1 at Pin1 is applied to the Off-Time Comparator (OFTC). The other input of OFTC is
the control voltage. The value of the control voltage at the input of OFTC is limited to a
minimum of 2V (for stable frequency at very light load). The On-Time Flip Flop (ONTF)
is set, if the output of OFTC is high 1) and the voltage V3 at Pin3 falls below 25mV (zero
crossing signal is high). This ensures switching on of the power transistor at minimum
voltage. If no zero crossing signal is coming into pin3, the power transistor is switched
on after an additional delay until V1 falls below 1.5V (see Figure6, OFTCD). As long as1 is higher than the limited control voltage, ONTF is disabled to suppress wrong zero
crossings of V3, due to parasitic oscillations from the transformer after switch-off. The
discharge time of C1 is a function of the control voltage.i.e. V1 is less than the limited control voltage.
If the control voltage is below 2V (at low output power) the “off-time” is maximum and
constantMprimary4VV113⁄–()R2C2××primary----------------------------------------------------------=
TC1C11,5V×
1mA-------------------------≈
TD1max0,47R1×C1×≈
TDA 16846
TDA16847
Figure6Off-Time-Circuit
TDA 16846
TDA16847
Figure7Pulse Diagram of Off-Time-Circuit
Figure8 shows the converters switching frequency as a function of the output power.
Figure8Load Dependant Frequency Course
TDA 16846
TDA16847
Error Amplifier EA / Soft-Start (Pin3, Pin4)
Figure9 shows the simplified Error Amplifier circuit. The positive input of the Error
Amplifier (EA) is the reference voltage 5V. The negative input is the pulsed output
voltage from the auxiliary winding, divided by R31 and R32. The capacitor C3 is
dimensioned only for delaying zero crossings and smoothing the first spike after switch-
off. Smoothing of the regulation voltage is done with the soft start capacitor C4 at Pin4.
During start up C4 is charged with a current of approx. 2μA (Soft Start). Figure10 shows
the voltage diagrams of the Error Amplifier circuit.
Figure9Error Amplifier
TDA 16846
TDA16847
Fixed Frequency and Synchronization Circuit SYN (Pin7)
Figure11 shows the Fixed Frequency and Synchronization Circuit. The circuit is
disabled when Pin7 is not connected. With R7 and C7 at Pin7 the circuit is working. C7
is charged fast by approx. 1mA and discharged slowly by R7 (Figure11). The power
transistor is switched on at beginning of the charge phase. The switching frequency is
(charge time ignored)
When the oscillator circuit is working the Fold Back Point Correction is disabled (not
necessary in fixed frequency mode). “Switch on” is only possible when a “zero crossing”
has occurred at Pin3, otherwise “switch-on” will be delayed (Figure12).
Figure11Synchronization and Fixed Frequency Circuit1,18C7×--------------≈

Partno	Mfg	Dc	Qty	Available	Descript
TDA16846	INFINEON	N/a	150	avai	Controller for Switch Mode Power Supp...