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3

IRPLMB1E

5. Circuit Description

The schematic for MINIBALLAST1 is shown in figure

5.1. The BOM with the components values is shown

in table 5.2.

The ballast incorporates a fuse, EMI filter, input recti-

fier, bus capacitor, half-bridge, control and output

stage. The output stage is the classical resonant

circuit consisting of an inductor, LRES, and a capaci-

tor, CRES. The circuit is built around the IR2520D

Ballast Control IC. The IR2520 provides adjustable

preheat time, adjustable run frequency to set the lamp

power, high starting frequency (about 2.5 times fmin)

to avoid lamp flash, capacitive mode protection for

open filament condition and current crest factor

protection for failure to strike or no lamp conditions.

The AC line input voltage is rectified to provide a bus

voltage of approximately 300 volts. The start up

resistor, Rsupply (in the reference design we have 2

resistors, Rsupply and Rsupply 2 in series), is sized

such that they can supply the micro-power current

during under-voltage lockout (UVLO). When VCC

exceeds the UVLO+ threshold, the IR2520 begins to

oscillate and the charge pump circuit (CSNUB, DCP1

and DCP2) supplies the current to VCC that causes

the internal 15.6V zener clamp to regulate.

The IR2520 Ballast Control IC controls the frequency

of the half-bridge programming the right parameters

on the lamp to provide lamp preheat, lamp ignition,

running mode, low AC line protection and lamp/

ballast fault protection.

1

2

3

4

VCC

COM

VCO

LO

VS

HO

VB

8

7

6

5

FMIN

MHS

CBS

CVCC

RFMIN

F1

CBUS

RSUPPLY

DCP2

DCP1

LRES

CRES

CSNUB

CVCO

BR1

LF

CF

MLS

CDC

LAMP

Fig. 5.1) MINIBALLAST1 Circuit Diagram