IR2161 datasheet(8/20 Pages) IRF

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IR2161(S)&(PbF)

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Halogen Convertor Controller

Functional Description

Under-voltage Lock-Out Mode (UVLO)

The under-voltage lockout mode (UVLO) is defined as the

state the IC is in when VCC is below the turn-on threshold.

To identify the different modes of operation, refer to the

State Diagram shown on page 7 of this data sheet. The

IR2161 under voltage lock-out is designed to maintain an

ultra low supply current of less than 300uA, and to guaran-

tee the IC is fully functional before the high and low side

output drivers are activated. Figure 1 shows a simple VCC

supply arrangement that will work effectively, also when

the convertor is being dimmed from a conventional triac

based wall dimmer

Figure 1, Halogen Convertor.

The start-up capacitor (C

VCC) is charged by current through

supply resistor (RS) minus the start-up current drawn by

the IC. This resistor is chosen to provide sufficient current

to supply the IR2161 from the DC bus. In a Halogen conver-

tor it is important to consider that the DC bus is completely

unsmoothed and has a full wave rectified shape. C

VCC should

be large enough to hold the voltage at Vcc above the UVLO

threshold for one half cycle of the line voltage as it will only

be charged at the peak. A charge pump consisting of two

diodes (DCP1 and DCP2) connected to CSNUB is recom-

mended to supply VCC as this allows RS to be a large value

since it is only needed at startup. IF RS is required to supply

the circuit without a charge pump it needs to be a relatively

low value and consequently dissipates 1 to 2W, which is

undesirable.

An external 16V zener diode DZ has been added to avoid

the need for the internal zener to dissipate power (it should

be rated at 1.3W). The resistor RD in series with CD is

necessary if the convertor is required to operate from a

triac based (leading edge) phase cut dimmer. When the

triac fires at a point during the mains half-cycle the high dv/

dt allows a large current to flow through this path to instantly

charge C

VCC to the maximum Vcc voltage.

The external zener (DZ) will prevent possible damage to

the IC by shunting excess current to COM.

Once the capacitor voltage on VCC reaches the start-up

threshold the IC turns on and HO and LO begin to

oscillate.

The supply resistor (RS) and RD/CD must be selected such

that enough supply current is available over all ballast

operating conditions. A bootstrap diode (DB) and supply

capacitor (CB) comprise the supply voltage for the high

side driver circuitry. To guarantee that the high-side supply

is charged up before the first pulse on pin HO, the first

pulse from the output drivers comes from the LO pin. During

under voltage lock-out mode, the high and low-side driver

outputs HO and LO are both low.

Soft Start Mode

The soft start mode is defined as the state the IC is in at

system switch on when the lamp filament is cold. As with

any type of filament lamp, the Dichroic Halogen lamp has a

positive temperature coefficient of resistance such that the

cold resistance (at switch on when the lamp has been off

long enough to cool) is much lower than the hot resistance

when the lamp is running. This normally results in a high

inrush current occurring at switch on. Under worst-case

conditions this could potentially trigger the convertors shut

down circuit. To overcome this problem the IR2161

incorporates the soft start function.

When the IC starts oscillating the frequency is initially very

high (about 130kHz). This causes the output voltage of the

convertor to be lower since the HF transformer in the system

has a fixed primary leakage inductance that will present a

higher impedance at higher frequency and thus allowing

less AC voltage to appear across the primary. The reduced

output voltage will naturally result in a reduced current in

the lamp which eases the inrush current thus avoiding

tripping of the shutdown circuit and will ease the stress on

the lamp filament as well as reducing the current in the half

bridge MOSFETs (M1 and M2).

The frequency sweeps down gradually from 130kHz to the

OUTPUT

VCC

COM

CSD

RCS

CVCC

CCS

IR2161 Datasheet(PDF) 8 Page - International Rectifier

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