AN993 Datasheet, PDF (6/27 Pages) STMicroelectronics – Electronic ballast with PFC using L6574 and L6561

L6574 ballast driver
AN993
Figure 3. Connection of a typical application
+
HVBus
CSupply
D1
D2
Rpre.
Ref.
C1
CSnub
CBoot
R1
D3
R2
12
2
16 15
7
14
6
11
L6574
5
8
9
43
1
10
C2
R3
Rign. Cf
Cpre R4
Rgh
Rgl
Qh
L_ballast
Ql
Cb
R5
R6 ^LAMP
D4
Cres
C3
Rcs
R9
R7
C4
R8
AM01311v1
Table 1. Description of device pins
Number
Name
Function
Preheat timing capacitor. The capacitor C_pre sets the preheating and the frequency
shift time, according to the relations: t_pre= K_pre· C_pre and t_SH= K_FS· C_pre (typ. K_pre=
1.5 s/ ∝F, K_FS= 0.15s/∝F). This feature is obtained by charging C_pre with two different
1
C_pre
currents. During t_pre, this current is independent of the external components, so C_pre
is charged up to 3.5 V (preheat timing comparator threshold). During t_SH, the current
depends on the value of R_pre (that is, on the difference between f_pre and f_ign). In this
way t_SH is always set at 0.1t_pre. In steady state the voltage at pin 1 is 5 V (see
Figure 5).
Maximum oscillation frequency setting. The resistance connected between this pin
2
R_pre
and ground sets the f_pre value, fixing the difference between f_pre and f_ign(f_pre> f_ign). At
the end of the start-up procedure, the effect current drown from R_pre is over. The
voltage at this pin is fixed at V_REF = 2 V.
3
CF
Oscillator frequency setting. The capacitor C_F, along with to R_pre and R_ign, sets f_pre
and f_ING. In normal operation this pin shows a triangular wave.
4
Minimum oscillation frequency setting. The resistance connected between this pin
R_ign
and ground sets the f_ign value. The voltage at this pin is fixed at V_REF = 2 V.
5
OPout
Out of the operational amplifier. To implement a feedback control loop this pin can be
connected to the R_ign pin by means of appropriate circuitry.
6
OPin- Inverting input of the operational amplifier.
7
OPin+ Non-inverting Input of the operational amplifier.
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Doc ID 5656 Rev 10