AN10932
120 V high power factor dimmable CFL with UBA2014
Rev. 2 — 17 January 2011
Application note
Document information
Info
Keywords
Abstract
Content
CFL, high power factor, free running PFC, triac, dimmable, UBA2014
This application note describes the design of a dimmable Compact
Fluorescent Lamp (CFL) with a high power factor for use with the
UBA2014
NXP Semiconductors
AN10932
120 V high power factor dimmable CFL with UBA2014
Revision history
Rev
v.2
v.1.1
v.1
Date
20110117
20101019
20101012
Description
third version
second version
initial version
Contact information
For more information, please visit:
http://www.nxp.com
For sales office addresses, please send an email to:
salesaddresses@nxp.com
AN10932
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 17 January 2011
2 of 33
NXP Semiconductors
AN10932
120 V high power factor dimmable CFL with UBA2014
1. Introduction
This application note describes the design of a dimmable CFL with a high Power
Factor (PF) where in practice, a PF greater than 95 % is realized. An 18 W application
with the UBA2014 and SPS04N60C3 external MOSFETS is described.
A CFL dimmer which is representative of most dimmers for 120 V mains input
applications, is used as the triac wall dimmer. When using other dimmers some
component values in the application may need adjusting to ensure dimming compatibility.
The topology is based on a combined free running PFC with resonant half-bridge inverter.
OverVoltage Protection (OVP) is required and under voltage lockout (UVLO) is optional
for deep dimming.
An external no-lamp detection/protection circuit has been added to the main board for
evaluation in a laboratory set-up with different burners. This circuit is not necessary when
the lamp ballast and burner are enclosed in a CFL housing.
2. Triac dimming
2.1 Triac dimming circuit
Figure 1
shows the circuit diagram of a triac wall dimmer for 120 V (RMS) mains input.
Cfilter
Lfilter
Triac
(BT136)
Itriac
V
in
120 V RMS
Rvar
470 kΩ
R
2.7 kΩ
Diac
(DB3)
Load
C
47 nF
019aaa332
Fig 1.
Triac wall dimmer with LC filter
The triac employs forward phase-cut dimming, in which the load (i.e. incandescent lamp,
CFL etc.) is energized only during the last portion of each power-line half cycle (α to
π
and
α
+
π
to 2
π)
as shown in
Figure 2.
AN10932
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 17 January 2011
3 of 33
NXP Semiconductors
AN10932
120 V high power factor dimmable CFL with UBA2014
V
in
α
+
π
α
π
2
π
ωt
019aaa333
Fig 2.
Triac with phase-cut dimming angle
α
The capacitor (C = 47 nF) is charged via the combination of a fixed and a variable resistor
where the phase-cut dimming angle is set with the variable resistor.
When the resistance is low, the capacitor will be charged more quickly and once the break
overvoltage of the diac is reached, the triac fires immediately and current I
triac
flows. This
current continues to flow until I
triac
drops below its minimum holding current I
H
The triac is a bidirectional device that works in two quadrants as indicated in
Figure 3
so
the same process is repeated during the negative half cycle.
+I
Rated current I
L
Breakover
voltage
Minimum holding
current I
H
−V
Gate trigger voltage
+V
−I
019aaa334
Fig 3.
Typical triac V
I
characteristics
The L
filter
and C
filter
filter in the triac application (or LC filter in CFL application) can
produce ringing of the triac current when the triac latches after a step response. The triac
ringing current should remain above I
H
to keep the triac switched on.
AN10932
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 17 January 2011
4 of 33
NXP Semiconductors
AN10932
120 V high power factor dimmable CFL with UBA2014
2.2 Triac wall dimmer and CFL ballast with separate PFC
In this application, the load is a CFL ballast (i.e. a half-bridge, resonant tank and lamp)
and a separate PFC as indicated in
Figure 4.
The PFC maintains triac conduction once the triac current is greater than the minimum
hold current I
H
where an I
H
of 15 mA to 20 mA is sufficient for most triac dimmers.
AN10932
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 17 January 2011
5 of 33
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