IRPLMB1E datasheet(12/13 Pages) IRF

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IRPLMB1E

10. Design Procedure to adapt the design

to different lamps types

The design with the IR2520D is very simple because

it only has 2 control pins: VCO (0-5VDC oscillator

voltage input) and FMIN (minimum frequency set-

ting). To modify the design for a higher lamp power,

you will need to modify RFMIN, CVCO, LRES and

CRES. Make sure that FETs and inductors are rated

to the current you need with the new lamp and that

VCC is stable. To modify the design to a lower lamp

power, you will need to decrease RFMIN and only in

some case to modify also CVCO, LRES and CRES.

In most cases you can use FETs and inductors with

lower current ratings.

Pin FMIN is connected to ground through a resistor

(RFMIN). The value of this resistor programs the mini-

mum frequency (fmin) of the IC and the starting fre-

quency of the IC (2.5xfmin). The IR2520 will work in

run mode at the minimum frequency unless non-

ZVS is detected. Generally, to work with constant fre-

quency, the minimum frequency needs to be chosen

above the resonant frequency of the low-Q R-C-L

circuit. In this case, one can increase the value of

RFMIN to decrease the frequency and increase the

lamp power, or, decrease the value of RFMIN to in-

crease the run frequency and decrease the lamp

power.

Pin VCO is connected to ground through a capacitor

(CVCO). The value of this capacitor programs the

time the frequency needs to ramp down from 2.5

times fmin (fmax) to fmin.

One can increase the capacitor value to increase the

preheat time, or, decrease the capacitor value to de-

crease the preheat time.

The suggested design procedure is as follows:

Use the BDA software to calculate LRES

and CRES.

Select the input configuration without PFC,

select the IR2156 IC and select single lamp

current mode configuration. Select the new

lamp in the database or add the lamp pa

rameters by hand selecting the “Advanced”

option.

Calculate the operating point and chose the

right values of L and C that satisfy:

1.1)

Run frequency (best working range) 40-

50KHz

1.2)

C as small as possible to minimize

losses (suggested value 4.7nF)

1.3)

L values you have available

While measuring LO, apply 15V from pin

VCC to pin COM and adjust the value of

RFMIN to obtain the right minimum fre-

quency (it is suggested set fmin = run fre-

quency obtained with the BDA software).

Increase RFMIN to decrease the minimum

frequency or decrease RFMIN to increase

the minimum frequency.

Apply the AC input and check preheat, igni-

tion and run states of the lamp.

3.1) If the lamp ignites during preheat, the pre

heat current is too small or the starting volt

age across the lamp is too big, increase

the value of CRES to decrease the voltage

across the lamp during preheat and startup

while increasing the preheat current. LRES

may need to be decreased to maintain the

same power and the same frequency.

3.2) If the IC works at a frequency > fmin, in

crease CRES or LRES to decrease the reso

nant frequency avoiding hard-switching, or,

decrease the value of the snubber capaci

tor CSNUBBER (a CSNUBBER minimum

value of 680pF is suggested to make sure

VCC stays above the UVLO-).

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