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•新特器件应用
萦嗓型焚疙灯 (CFL) 态系~a 锡蕃
11
L6567 羔级在悉用
d
句真…
山东省格沂沂克电子股份公司
刘玉 2在
国营第 8072 厂
高洪民
Principle and App Ji cation of CFL Higb Voltage Driver L6S67
Li u Yujun
Gao Hongmin
摘要 :ST 公司新推出的 CFL 高压丰桥驱动器 L6567 可为 CFL 灯丝预热、点火和稳压工作提供所
必需的控制功能。文章在介摇了 L6567 的功能特点和工作原理的基础上，重点介绍了 L6567 在
CFL 镇琉器中的应用电路与设计方法。
1
关键词 :CFL 镇就器;二手桥驱动器;变频;
L6567
分类号 :TM571
文章编号 :1006 一 6977(2倪沁)10 一俱到08 忡。3
文献标识码 :B
L6567 采用 B∞
引言
1 、手
FS l!
脱线技术，可专门用作
'
Ii4I CI
<:1
挝W
小型荧光灯(Compact Fluorescent Lamp ，简写
驱动 CFLo L6567 的浮
为 CFL) 的镇流器与灯管通常是有机地结合在一个
置电源电压高达 570V ，
整体中，在不损坏其中部件的情况下一般是可拆卸
地参考电源电压为
RS 事
的。而 CFL 中的镇流器的塑壳内部空间非常有限，
18V; 驱动器掠电流为
CP
散热能力很差，因此对电子镇流器的要求非常高。
3位nA，灌电流为吨郎 '1
虽然目前 CFL 在世界范围内得到广泛应用，然而迄
7伽埠。 L6567 内置可变频率振荡器，可对 CFL 预籍
今为止， CFL 驱动器专用 IC 却并不是很多。 ST 公
和点火时间进行蝙程。 L6567 能使 CFL 功率挫立主
，司最近推出了 L6567 型高压学桥驱动器 IC ，该 IC
线电源电压的变化，并具有欠压锁定和电容性模式保
只需外加少量的外部元件，就可组成性能先进的
护等特征。对于半桥拓朴中的两只外接功率 MOS
CFL 电子镇流器。
FET ， L6567 可提供电平移位和驱动等控制功能。
2
L6567 的引脚功能及特点
L6567 采用 14 脚 DIP 封装，因 1 所示为其引脚
排列。表 1 给出了 L6567 各引脚的功能说明。
-
...
、þ".".' ....-嘟
旷
---二工工， τ
3
[!I部，ND
T司 RItEF
PGNDI'f
L6567 的弓!脚排列
L6567 的工、作原理
3.1 IC 启动
图 2 所示是 L6567 的内部握图及外部连接电
..................唱--.咱....
工 J二
....…-
...............~....~…
PLLEN2 两个管脚接地可将器件设置为四倍额，这
其他片选可用于选择 1/0 及岛。口。
样，其运行速度将达到MHz。片选 cso 选通 2 片
参考文献
FLASH 存储器AMD29F040- 郁，寻址范围为 512k
1. 80296SA MicrocontrolIer User' 's Ma.nual
TEL Corporation.
宇空间，设置为一个等待状态。起始地址 F∞∞旺f 用
于存放用户程序;片选臼1 选通 2 片E制628512-
IN
50.哥址 512k字空间，设置为一个等待状态。起始地
2. Migrating from the 8XC196NP or 8XC196NU
to 802销商A INTEL co叩oration.
址翩翩H 用来存放数据，如果要使数据在掉电时
3. 起秀蒋-对江椅二单片叔.8XC196 原理Z也应用
不丢失，可使用后备电池翩翩路为朋4部512 供
电 s 如果存储器存取时间小于 35阳，则无需等待。这
样可提高主蜒的效率二但是器件价格将有被大提高。
,
东南大学出版社二
牧稿日期手创阳 ....04-06
咨询编号 z∞1∞2
毡 ，卢"，-"""
吃
t 龟争一
Z芳:雪飞子可导:-:~
沪二主专三、予建运毒草鼻、z 哼.~~伊'..，，，.........-，吐
带凑型荧光灯 (αL) 高压扭动器1.:6567 原理反应用
_.....,.
袋 1 - 1.6567 曹11.功能'
"号
弓 IJ部符号
-说明
8
CP
与 RREF 共同决定预热和点火时间
RS
RREF
流经Ræum-电流监控输入
高端开关M克FET 源极
9
10
未连接
11
$ND
CF
RHV
CI
信号地，在 IC 内部连接到 PGND
序号
弓i 脚符号
1
2
FS
离端驱动器浮置电摞
G1
离揭开关栅极题动输出
3
g
4
N.C.
Vs
5
6
7
G2
PGND
说明
地电平控制与驱动电压
12
低端开关栅极驱动输出
13
功率地
14
电流设定参考电阻
PJ
品'
频率设定电容
启动电阻，尔后用作检测电源电压
频率偏移定时电容
路。在 L6567 通电后，经整施的主线电压通过电阻
预热过
Rhv 及外部连接电路施加到 L6567 的脚 13 ，在脚 13
程结束后，
上产生的电施经 IC 内的二极管从脚 5(Vs ) 流出并
频率向 fM剖
对外部电容 G 充电。当 Vs 脚电压达到门限值 Vg.
偏移。一旦
LOWl( 最大值为 6V) 后， IC 外部低端 MOSFET(T2)
输出频率接
导通，丽高端 MOSF盯(T l)保持截止，连接于脚 1
近于 L 和
与脚 3 之间的外部自举电容Gxx.t被充电。当 Vs 脚
G:.串联电路
电压达到上限门限值 VSlGH ì( 典型值为 11. 7V)时，
的固有频率 (fo) ， 则 LC 电路发生谐振。于是在c.
振荡器开始工作。
两端产生一个 600-1200V 的离压脉冲使灯管击穿
3.2 预热模式
丽点燃。点火时间 T1GN
L6567 振荡器被启动后，首先输出一个高频
血皿，尔后很快使频率降低到设定的预热频率 fPRE
,
;":'9-
F
&x
FMlft ←一一一斗
|
i
预热
固3
点火
j 稳态点燃 T
启动到稳态的事率变化图
= (15/16)~醋，频率偏移斜
率由脚 14 上的电容 G 决定。
3.4 稳压工作与前锻模式
事
上。 IC 脚 14 上的外接电容 G 用于决定频率下降的
灯点火后， L6567 将在最低颜率 fMJN 上稳压工
速率(dF/dt) 。脚 10 上的外接电阻 RREF 和脚 8 上的
作。国 3 为 IC 从启动到进入稳定工作状态的频率
电容 G 用于共同设定预热时间 TPREo 预戴电流则由
变化曲线。随着输出频率的变化?扼流圈 L 的阻抗
检割电器i Rsam町来调节，并由马RJNT 及负载元件 L
相应改变，灯电流也随之变化。血副主要由Rm:F 和
和巳共同决定。一旦在预棋期间旗率达到 FM剖，振
G 决定。且有 fM 剧 =O.lfMAXO
为防止在离主线电压上灯的功率太大 j
荡器则停止振荡。
L6567可执行前馈校正功能。如果 13 蹄内部的电距
3.3 点火模式
检测到超过Rm:F 所设定的电流值，则摄荡器定
时电容G 上的充电电施将增大，这将导致频率
升高，振流圈 L 阻挠增大，从而使灯功率相应减
小。脚 8上的电容 G 和内部电随可用来撑除高
压前模载波。
L6567 脚 9 内比较器的门限电压 VCM拙的典
型值是 2如山。如果脚 9 上的电压 VRS 小于
飞'O.im ， IC 则转入容性模式保护控制功能，这样可
防止 MOSFET 出现硬开关，从丽实现零电压开
关。
无论任何时刻， L6S67 的稳态工作频率均由
fM刷、前馈模式频率 fFF 和容性模式保护频率
图2
M仰的内部结构严图
fCMP 三者中最大的一千决定。
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褒z
类别
滤被元件
镇流器元件
4 典型应用电路
元件参鼓选取
兀件
数值或蜜号
R
470
c
3.3，æ'， 4∞v
L
820禹王， 14OmA
01- 剖
L6567 的典型应用如图 4 所示。民主v 和连接在
IC 脚 5 与脚 7 之间的电容G.r，∞为启动元件。一旦 IC
驱动 Q1 和 Q2 ， 脚 3 与脚?之间的阻尼电容和电荷
[)F(活N
泵电容与脚 5 与脚 7 之间的两只二极管组成的辅助
Cfls(2 只〉
0.1段，却OV
电流源便为脚 5 补给工作电班，同时也对 G∞充
4.A腊
3页)()PF.4(泊V
电。 IC 开始工作后，民w 用作栓测母线目:离压，
Laoæ
Q1、æ
3. 1mB
SfP2NB5O
RæUN-r用作监控开关与负载电碟。脚 10 上的Rau与
乌烟黯
47OpF. 到)()V'
句VtRGE-PUMP
6船pF， 50V
比4剧lE-l'UMP
BA516,1Ñ4148
和点火时间 TJ:ìN. RæUN-r .... I..æc.岱和 G刷p 等决定预
G町.4mr
0.1声，如V
热频率 fi咽. R.m用于决定死区时间 T町，脚 14 上
属M. Rm2
22OkO
的电容 G 决定频率扫描速率 df/巾。该电路的电子
马 '4
RREF
O.l ,æ', 50V
G
0.1卢
IC
1.6567
整流金桥
.
L6567 典型应用电路
•
3OkO
脚 12 上的 G 决定灯点燃工作频率邸，Ravl/G:
决定前馈频率 fF霄，忌由和 G 决定好颈热时间 TPRE
镇流器负载为 15W。
Rw 、 G 、 G 、 G 、Ra.tF 和RsmmT 这六个元件，对
L6567 的正常工作和电子镇流器的性能具有决定性
的影响。图 4 电路中各元件的参数选择如表 2 所
列。
'
收稿日期 :2'∞ -03-22
咨询编号 :001003
…到E啤圄噩噩-团噩噩E噩噩噩·.1
大型科提川
崎且代号阶 778'
t
《北京电子》象志是以促进中国电子锚息产业发展，编宵电子市场为宗旨的大型科技月梢。
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《北京电子'为大 16 开本，每JiI' 25 日躏踵，国内外公开a行。订价每.6 元，余年订价 72 元，全国备地邮局均可宵躏.也
可向本刊..部直撞在就订筒。
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器件的应朋友，〉握
紧;奏型聚光生了高压驱动器 IJ6567 及其典型应用
口毛兴式
L656751 脚功能
L6567 是 ST 摄电子公司新推出的紧 i奏型荧光奸
(CFU 高压驱动器 I C.只需要很少量的外部元件即可
组成高性能的 CFL 电子镇流器。
一、 L656751 剧功能、主要参数及特点
1. 6567 采用 14 脚。 IP 封装，外形如因 l 所示 e 国 2
Fs
CI
G
、
..•
S
卢嘈
会
RHV
CF
•••
1 ①1.6567 外型
SGNO
N.C.
是
S
为 L6567 引脚排列，尺寸为
能如表所列。
、
由
DmR
Z0.× 1p〈 5mmeL6567 引脚功 PGND
CP
βr、
i
λL6567 的 Vs 导通门限\伊
寻 i 脚排序及符号
电压是 11.7 土 1V ，最高电源电压为 18V 。流入 V s
脚的、
限制电流是 200mA ，流入脚 13(RHV) 的最大电流为
3mA. 脚 8(CP) 、脚 9(R s ) 、脚 10(RREF) 和脚 14(CI)上
的最高电压均为 5V L6567 的结温为 -40~+150C 。
0
L6567 内置可变频率振荡器，为 CFL 预热、点火
和稳态操作提供所需要的功能，同时为半桥拓扑结构
中的两只外接功率 MOSFET 提供电平移位和驱动功
能。 L6567 、能控制 CFL 功率不受 AC 输入电压波动影
响，使光输出稳定.
筑，大卫
蜘号
符号
1
2
3
4
5
6
7
Fs
Cl
SI
Nc
Vs
~;~D
8
Cp
9
10
Rs
RREF
11 一
8G NI)
: 12
, 13
‘ 14
G2
CF
RHV
CI
功
能
高精湛动器悬浮电源
高端 Jf 关 (MOSFET) 栅极驱动输出
高端Jf关 (MOSFET)i~在极
未连接
电源电压
J
低端 ff 关栅极稳功输出
功率地
预热定时兀件，同时用作滤除 RHV
脚检测电压纹波
电流监测输入
电流设定基准电阻
信号地，内与 PGND 相连接
频率设定电容
IC 启动电阻，同时检测电源电压
频率偏移定时电容
用 L6567 驱动与控制的 15W 、 CFL 电子镇流器电
路如图 3 所示.
l!电路组成
01-04 为桥式整流器 ;Cl 、L1组成滤波器 ;QL
Q2 为 L6567 驱动的半桥高/低开关 (MOSFET);L2 和
C4 等组成 LC 串联谐振电路 ;C7 为自举电容 ;C5 是阻
尼电容与 C6 和 05.D6 组成电荷泵电路 ;R3 与 C8 为
L6567 的 V s 启动元件 ;R2 为电流检测电阻。
2. 工作原理
'
AC 输入电压经桥式整流器 D1-D4 整流和 C l.
L1谴波，输出约 300V 的平滑 oc 电压。通过 R3 的电
流经 L6567 脚 13 流入和脚 5 流出 .xt C8 充电 e 当 C8
二、典型应用电路
上的充电电压经约1. 8μs 线性升高到 IC 脚 5(Vs ) 的
Ll
R3
01
Rl
.
...,‘
470
220V 土 20%
'
CF I.
C3
。3
0.1μF
r~. ，2，~?V
<
15W
，，~-'
二
叫
f
4 巳 F势，.豆且
!tf:巨二茅(;尊 ‘之J
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; ~.飞苦、￡牛，
.'
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夕，制
飞gj ，
1.30
F
.: .'
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、
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匾画圈圈画噩噩噩画回国运基4hι
门限电压〈约 1 1. 7V) 后 .L6567 被启动，并首先输出一
,
E
每
向 f2 偏移。当频率接近于 L2 和 C4 等组成的 LC 串联
4'
f
对较小。在预热时间结束之后 .L6567 振荡器频率由 fl
1|
'.
叮"?
,
t
哑。
二
'一句
多，故扼流圈 L2 的阻挠较大，通过灯丝的加热电流相
…卜
;ETfrz22TJZi在523:24gij等 MPPfJE 霆
谐振电路的固有频率时，则发生谐振，在 C4 上产生一
l kHV
10
个足够高的脉冲电压，使灯管击穿而燃点，并在频率
穗态工作前馈校正频率与电流关系曲线
f2 上工作。 L6567 软启动过程频率变化曲线如图 4 。
出低电平 .Q1 与 Q2 均截止。
1
HkHz)
3. 主要元件选取
④
fl
Ql 和 Q2 选用 STP2NB50 型附FET.R3 承受
较高的电压，在 IC 脚 Vs 启动过程中，流过阳的电流
'\
较大，功耗达 0.3W 左右，制用 2 支 1/2W 的圳。
协一一一口三牛一一
预热;点火;然点
的电阻串接使用. L1 =O. 6--1mH. L2 =3. 5mH. 当L1
不用时， Cl 的电容量宜适当增大。 L2 的电感值因所选
。
11
12
磁芯材料及型号不同而存在差异.如果 L2 电感量偏
- \(s)
软启动频率与时间关系曲线
大，灯电流则偏小，灯光则比额定状态变暗。 C4 宜选用
预热频率 fl 由 L2 、 C4.CFL 和 R2 等数值共同决
定， IC 脚 8 上的电容 C11 和脚 10 上的电阻 R4 则决定
预热时间。当 Cp=O. !t-tF 和 R4=30kO 时，预热时间 tl
=0.7s. 预热电琉为 2白mA 。点火时间为 05/16) • tl ，二 4
町.'"
与预热时间相近。通常工作频率 f2 约为 40k叮z. 主要 4
金属化聚丙烯电容器.若通电后灯管不能击穿，只在灯
丝部位发亮，则说明 C4 容量偏大。灯管功率不同，或
虽功率相同但型号不同f 与之匹配的启动电容 C4 的
数值也不一样，具体在调试中选定.
'"
ι.
由 R4 和 IC 脚 12 上的电容 CI0 的数值决定~ 'IC.M 9 、
上的电容 C9 则决定 fl 偏移.
至 f2'的斜率 (dfldt) 。
_.._-'
，".‘… 4. 印制板电路设计锦
叶
三』二、人
j
s
，，-… 4 吨，
L6567 还具有前馈校正‘
功能二在稳态工作条件下，一
'
旦直梳总线电压升高.则通
过 R3 被 IC 脚 13 检测.脚
13 内部连接一支高压传感
也阻，当该电阻上的电流增
大时 .IC 脚 12 上的振荡器
也容 C10 上的充电电流也
随之士曹大，从而导致顿率升
43mrn
命高，如自 5 所示 e 其结果是使
L2 的阻扰增大，灯电流减
小，从而保持灯功率恒定。
在 L6567 进入稳态工
作后， C5 、 C6 和 C5h 组成
的电荷菜为 IC 脚 5 提拱工
作电波.同时也对 C3 充屯 r
lC 脚') ( V
⑥」
, ) T 11: I 让 i走{豆约
1.2Tn!\ 俨?可飞、 litji 艺 U~ 降气:
10V 以 FH、J
.IC rHX IH [~ (1
t 2 ; 1)
锁电路则使脚 2 手u 脚 6 均输
电子制作
2000 年第 9 期
•
19 •
节吁-由市市市事市南市市市市市事甲宁市啕 +F-，，:;s---.
叫‘协也飞
''1
，电画
市市市明市市可←V可~寸--节市~叮【~可-甲
户"
~..; CFL 与镇流器是F 体化的，在不损坏内部部件的
间很小，在设计印板电路时，元件要合理排布.困 6 为
情况下，一般是不可拆卸的.容纳镇流器的塑壳内部空
参考印制板图 (2
I
、
1) o.
‘
\
.,
'
• 20.
2000 年第 9 期
占
电子制作
,
,
,
L6567
HIGH VOLTAGE DRIVER FOR CFL
■
BCD-OFF LINE TECHNOLOGY
■
FLOATING SUPPLY VOLTAGE UP TO 570V
■
GND REFERRED SUPPLY VOLTAGE UP TO
18V
■
UNDER VOLTAGE LOCK OUT
■
CLAMPING ON Vs
■
DRIVER CURRENT CAPABILITY:
30mA SOURCE
70mA SINK
■
MULTIPOWER BCD TECHNOLOGY
SO14
PREHEAT AND FREQUENCY SHIFT TIMING
DESCRIPTION
The device is a monolithic high voltage integrated circuit designed to drive CFL and small TL lamps with a
minimum part count.
It provides all the necessary functions for proper preheat, ignition and steady state operation of the lamp:
♦ variable frequency oscillator;
DIP14
ORDERING NUMBERS:
L6567D
L6567
♦ settable preheating and ignition time;
♦ capacitive mode protection;
♦ lamp power independent from mains voltage variation.
Besides the control functions, the IC provides the level shift and drive function for two external power MOS
FETs in a half-bridge topology.
BLOCK DIAGRAM
Vhv
Rhv
Cp/Cav
RHV
CP
13
8
5
VS
PREHEATING
TIMING
FEED FORWARD
CS
Cf
CF
12
CI
14
LEVEL
SHIFTING
HIGH
SIDE
DRIVER
1
FS
2
G1
3
S1
6
G2
7
PGND
11
SGND
Vhv
Cboot
VS
T1
Chv
L
Lamp
VCO +
FREQ. SHIFTING
Ci
LOW
SIDE
DRIVER
LOGIC
BIAS
CURRENT
GENERATOR
VOLTAGE
REFERENCE
to
comp.
C
9
T2
CL
MAINS
Chv
Rshunt
RS
10
Ref
RREF
D96IN441B
March 2001
This is preliminary information on a new product now in development. Details are subject to change without notice.
1/15
L6567
PIN FUNCTION
N°
Pin
Description
1
FS
Floating Supply of high side driver
2
G1
Gate of high side switch
3
S1
Source of high side switch
4
NC
High Voltage Spacer. (Should be not connected)
5
VS
Supply Voltage for GND level control and drive
6
G2
Gate of low side switch
7
PGND
8
CP
First timing (TPRE TIGN), then averaging the ripple in the representation of the HVB (derived
through RHV).
9
RS
R SHUNT: current monitoring input
10
RREF
Reference resistor for current setting
11
SGND
Signal Ground. Internally Connected to PGND
12
CF
13
RHV
14
CI
Power Ground
Frequency setting capacitor
Start-up supply resistor, then supply voltage sensing.
Timing capacitor for frequency shift
PIN CONNECTION (Top view)
FS
1
14
CI
G1
2
13
RHV
S1
3
12
CF
N.C.
4
11
SGND
VS
5
10
RREF
G2
6
9
RS
PGND
7
8
CP
D96IN440
2/15
L6567
ABSOLUTE MAXIMUM RATINGS
Symbol
VS
Parameter
Low Voltage Supply
Value
Unit
18 (1)
V
VRHV
Mains Voltage Sensing
VCP
Preheat/Averaging
5
V
VCF
Oscillator Capacitor Voltage
5
V
VCI
Frequency Shift Capacitor Voltage
5
V
VRREF
Reference Resistor Voltage
5
V
VRS
Current Sense Input Voltage
-5 to 5
V
transient 50ns
-15
V
VG2
Low Side Switch Gate Output
18
V
V S1
High Side Switch Source Output: normal operation
-1 to 373
V
-1 to 550
V
-1 to 391
V
0.5sec mains transient
-1 to 568
V
with respect to pin S1
Vbe to V S
V
391
V
568
V
18
V
VS +2VBE (2)
0.5sec mains transient
VG1
VFS
High Side Switch Gate Output: normal operation
Floating Supply Voltage: normal operation
0.5sec mains transient
VFS/S1
Floating Supply vs S1 Voltage
∆VFS/∆T
VFS Slew Rate (Repetitive)
-4 to 4
V/ns
∆V S1/∆T
VS1 Slew Rate (Repetitive)
-4 to 4
V/ns
3 (3)
mA
200 (4)
mA
IRHV
Current Into RHV
IVs
Clamped Current into VS
Tstg
Storage Temperature
-40 to 150
°C
Tj
Junction Temperature
-40 to 150
°C
NOTES: (1) Do not exceed package thermal dissipation limi ts
(2) For VS ≤ VS high 1
(3) For VS > VS high 1
(4) Internally Limited
Note: ESD immunity for pins 1, 2 and 3 is guaranteed up to 900 V (Human Body Model)
3/15
L6567
ELECTRICAL CHARACTERISTCS
(VS = 12V; RREF = 30KΩ; CF = 100pF; Tj = 25°C; unless otherwise specified.)
Symbol
Parameter
Test Condition
Min.
Typ.
Max.
Unit
10.7
11.7
12.7
V
12
13
14
V
9
10
11
V
1.5
1.65
1.8
V
1
6
V
50
250
µA
1.2
mA
VS - SUPPLY VOLTAGE SECTION
VS high 1
VS Turn On Threshold
VS high2
VS Clamping Voltage
V S low 2
VS Turn Off Threshold
VS HYST
Supply Voltage Hysteresis
V S low 1
VS Voltage to Guarantee
VG1 =”0”and VG2 = ”1
VS = 20mA
ISSP
VS Supply Current at Start Up
VS = 10.6V Before turn on
ISOP
VS Supply Operative Current
VS = VShigh 1
OSCILLATOR SECTION
fosc min
Minimum Oscillator frequency
IRHV = 0mA; CI = 5V
41.7
43
44.29
kHz
fosc 600m
Feed Forward Frequency
IRHV = 600mA
47.88
50.4
52.92
kHz
fosc 1mA
Feed Forward Frequency
IRHV = 1mA
79.8
84
88.2
kHz
fosc max
Maximum Oscillator Frequency CI = 0V
96.75
107.5
118.25
KHz
∆ICF/∆VCI
Oscillator Transconductance
17.5
µA/V
1.12
sec
9
PREHEAT/IGNIT ION SECTION
P.H.T.
Preheat Time
Cp = 150nF
0.88
1
P.H.clocks
Number of Preheat Clocks
16
IGN.clocks
Number of Ignition Clocks
15
RATE OF FREQUENCY CHANGE SECTION
ICIP charge
CI Charging Current During
Preheat
106
118
130
mA
ICII charge
CI Charging Current During
Ignition
1
1.2
1.4
mA
CI Discharge Current
-52
-47
-42
mA
CI Low Voltage Threshold
10
100
mV
ICI disch
VTH CI
RS - THRESHOLD SECTION
VCMTH
VPH
Capacitive Mode Voltage
Threshold
Preheat Voltage Threshold
0
20
40
mV
-0.64
-0.6
-0.56
V
1.05
1.4
1.75
µs
G1 - G2 DELAY TIMES SECTION
G1DON
4/15
On Delay of G1 Output
L6567
ELECTRICAL CHARACTERISTCS (Continued)
Symbol
G2DON
Parameter
Test Condition
On Delay of G2 Output
IRHV = 1mA; Cl = 5V
G1 DON + G1ON Ratio between Delay Time +
------------------------------------------- Conduction Time of G1 and G2
Cl = 0V
G2 DON + G2ON
Min.
Typ.
Max.
Unit
1.05
1.4
1.75
µs
0.87
0.77
1.15
1.30
LOW SIDE DRIVER SECTION
Ron G2 so
G2 Source Output Resistance
VS = 12V, V = 3V
80
190
Ω
Ron G2 si
G2 Sink Output Resistance
VS = 12V, V = 3V
65
125
Ω
Ron G1 so
G1 Source Output Resistance
VS = 10V, V = 3V
80
190
Ω
Ron G1 si
G1 Sink Output Resistance
VS = 10V, V = 3V
65
125
Ω
HIGH SIDE DRIVER SECTION
IFSLK
Leakage Current of FS PIN to
GND
VFS = 568V; G1 = L
VFS = 568V; G1 = H
5
5
µA
µA
IS1 LK
Leakage Current of S1 PIN to
GND
VS1 = 568V; G1 = L
VS1 = 568V; G1 = H
5
5
µA
µA
BOOTSTRAP SECTION
Boot Th
BOOTSTRAP Threshold
VS = 10.6V before turn on
5 (*)
V
AVERAGE RESISTOR
R AVERAGE
Average Resistor
27
38.5
50
kΩ
(*) Before starting the first commutation; when switching 6V is guaranteed.
General operation
The L6567 uses a small amount of current from a supply resistor(s) to start the operation of the IC. Once start
up condition is achieved, the IC turns on the lower MOS transistor of the half bridge which allows the bootstrap
capacitor to charge. Once this is achieved, the oscillator begins to turn on the upper and lower MOS transistors
at high frequency, and immediately ramps down to a preheat frequency. During this stage, the IC preheats the
lamp and after a predetermined time ramps down again until it reaches the final operating frequency. The IC
monitors the current to determine if the circuit is operating in capacitive mode. If capacitive switching is detected,
the IC increases the output frequency until zero-voltage switching is resumed.
Startup and supply in normal operation
At start up the L6567 is powered via a resistor connected to the RHV pin (pin 13) from the rectified mains. The
current charges the CS capacitor connected to the VS pin (pin 5). When the VS voltage reaches the threshold
VS LOW1 (max 6V), the low side MOS transistor is turned on while the high side one is kept off. This condition
assures that the bootstrap capacitor is charged. When VS HIGH1 threshold is reached the oscillator starts, and
the RHV pin does not provide anymore the supply current for the IC (see fig.1).
5/15
L6567
Figure 1. Start up
VSHIGH1
VSLOW1
VS
TDT
0
VG
low side mosfet
0
VG-VS
high side mosfet
0
CF
0
TIME
Oscillator
The circuit starts oscillating when the voltage supply VS has reached the VS HIGH1 threshold. In steady state
condition the oscillator capacitor CF (at pin 12) is charged and discharged symmetrically with a current set mainly by the external resistor RREF connected to pin 10. The value of the frequency is determined by capacitor CF
and resistor RREF. This fixed value is called FMIN. A dead time TDT between the ON phases of the transistors
is provided for avoiding cross conduction, so the duty cycle for each is less than 50%. The dead time depends
on RREF value (fig. 7).
The IC oscillating frequency is between FMIN and FMAX = 2.5 · FMIN in all conditions.
Preheating mode
The oscillator starts switching at the maximum frequency FMAX. Then the frequency decreases at once to reach
the programmed preheating frequency (fig.2). The rate of decreasing (df/dt) is determined by the external capacitor CI (pin 14). The preheat time TPRE is adjustable with external components (RREF and CP). The preheat
current is adjusted by sense resistance RSHUNT. During the preheating time the load current is sensed with the
sense resistor RSHUNT (connected between pin 9-RS- and pin 7-PGND-). At pin 9 the voltage drop on RSHUNT
is sensed at the moment the low side MOS FET is turned off. There is an internal comparator with a fixed threshold VPH: if VRS > VPH the frequency is decreased and if VRS < VPH the frequency is increased. If the VPH threshold is reached, the frequency is held constant for the programmed preheating time TPRE.
TPRE is determined by the external capacitor CP (pin8) and by the resistor RREF: CP is charged 16 times with a
current that depends on RREF, and these 16 cycles determine the TPRE.
So the preheat mode is programmable with external components as far as TPRE is concerned (RREF &CP) and
as far as the preheating current is concerned (choosing properly RSHUNT and the resonant load components:
L and C L).
The circuit is held in the preheating mode when pin 8 (CP) is grounded.
In case FMIN is reached during preheat, the IC assumes an open load. Consequently the oscillation stops with
the low side MOS transistor gate on and the high side gate off. This condition is kept until V
S undershoots VS LOW1.
6/15
L6567
Figure 2. Preheating and ignition state.
FREQUENCY
F MAX
F MIN
preheating
state
ignition
state
burning state
TIME
Ignition mode
At the end of the preheat phase the frequency decreses to the minimum frequency (FMIN), causing an increased
coil current and a high voltage appearing across the lamp. That is because the circuit works near resonance.
This high voltage normally ignites the lamp. There is no protection to avoid high ignition currents through the
MOS transistors when the lamp doesn’t ignite. This only occurs in an end of lamp life situation in which the circuit
may break. Now the lowest frequency is the resonance frequency of L and CL (the capacitor across the lamp).
The ignition phase finishes when the frequency reaches FMIN or (at maximum) when the ignition time has
elapsed. The ignition time is related to TPRE: TIGN = (15/16) · TPRE. The CP capacitor is charged 15 times with
the same current used to charge it during TPRE.
The frequency shifting slope is determined by CI.
During the ignition time the VRS monitoring function changes in the capacitive mode protection.
Steady state operation: feed forward frequency
The lamp starts operating at FMIN, determined by RREF and CF directly after the ignition phase. To prevent too
high lamp power at high mains voltages, a feed forward correction is implemented. At the end of the preheat
phase the RHV pin is connected to an internal resistor to sense the High Voltage Bus. If the current in this resistor
increases and overcomes a value set by RREF , the current that charges the oscillator capacitor CF increases
too. The effect is an increase in frequency limiting the power in the lamp. In order to prevent feed forward of the
ripple of the VHV voltage, the ripple is filtered with capacitor CP on pin 8 and an integrated resistor RAVERAGE.
Figure 3. Burn state
FREQUENCY
feed forward mode
FMIN
Irhv
7/15
L6567
Capacitive mode protection
During ignition and steady state the operating frequency is higher than the resonance frequency of the load
(L,CL,RLAMP and RFILAMENT), so the transistors are turned on during the conduction time of the body diode in
order to maintain Zero Voltage Switching.
If the operating frequency undershoots the resonance frequency ZVS doesn’t occur and causes hard switching
of the MOS transistors. The L6567 detects this situation by measuring VRS when the low side MOS FET is turned
on. At pin 9 there is an internal comparator with threshold VCM TH (typ~20mV ): if VRS < VCM TH capacitive mode is
assumed and the frequency is increased as long as this situation is present. The shift is determined by CI.
Steady state frequency
At any time during steady state the frequency is determined by the maximum on the following three frequencies:
fSTEADY STATE= MAX {FMIN, fFEED FORWARD, fCAPACITIVE MODE PROTECTION}.
IC supply
At start up the IC is supplied with a current that flows through RHV and an internal diode to the VS pin whichcharges the external capacitor CS. In steady state condition RHV is used as a mains voltage sensor, so it doesn’t
provide anymore the supply current. The easiest way to charge the CS capacitor (and to supply the IC) is to use
a charge pump from the middle point of the half bridge.
To guarantee a minimum gate power MOS drive, the IC stops oscillating when VS is lower than VS HIGH2. It will
restart once the VS will become higher than VS HIGH1. A minimum voltage hysteresis is guaranteed. The IC restarts operating at f = FMAX ,then the frequency shifts towards FMIN. The timing of this frequency shifting is TIGN
(that is: CP capacitor is charged and discharged 15 times).Now the oscillator frequency is controlled as in standard burning condition (feed forward and capacitive mode control). Excess charge on CS is drained by an internal clamp that turns on at voltage VS CL .
Ground pins
Pin 7(PGND) is the ground reference of the IC with respect to the application. Pin 11( SGND) provides a local
signal ground reference for the components connected to the pins CP, CI, RREF and CF.
Relationship between external components and sistem working condition
L6567 is designed to drive CFL and TL lamps with a minimum part count topology. This feature implies that each
external component is related to one or more circuit operating state.
This table is a short summary of these relationships:
FMIN ---> RREF & CF
FFEED FORWARD ---> CF & IRHV
TPRE & TIGN ---> CP & RREF
FPRE ---> RSHUNT, L, CL, LAMP
TDT ---> RREF
df/dt ---> CI
Some useful formulas can well approximate the values:
1
F MI N ≅ --------------------------------8 ⋅ RR E F ⋅ CF
15
If IRHV is greater than: I R HV ≥ -------------- , the feed forward frequency is settled and the frequency value is fitted by the
R R EF
followi ng expression:
IR H V
F F E ED FOR W AR D ≅ --------------------121 ⋅ CF
8/15
L6567
Other easy formulas fit rather well:
TDT ≅ 46.75 · 10^-12 · RREF
TPRE ≅ 224 · CP · RREF
As far as df/dt is concerned, there are no easy formulas that fit the relation between CF, RF, and CI. CI is charged
and discharged by three different currents that are derived from different mirroring ratios by the current flowing
on RREF. The voltage variations on CI are proportional to the current that charges CF, that is to say they are
proportional to df/dt.
The values obtained in the testing conditions (CI = 100nF) are:
during preheating and working conditions the typical frequency increase is ~ 20KHz/ms, the typical decrease is
~-10Khz/ms;
During ignition the frequency variation is ~ -200Hz/ms.
If slower variations are needed, CI has to be increased.
Due to these tight relationships, it is recommended to follow a precise procedure: first RHV has to be chosen
looking at startup current needs and dissipation problems. Then the feed forward frequency range has to be
determined, and so CF is set.
Given a certain CF, RREF is set in order to fix FMIN. Now CP can be chosed to set the desired TPRE and TIGN.
The other external parameters (RSHUNT and CI) can be chosen at the end because they are just related to a
single circuit parameters.
9/15
L6567
Figure 4. IC Operation
START
VS>VSLOW1
N
Y
NO OSCILLATION
LOW SIDE MOS ON
HIGH SIDE MOS OFF
VS>VSHIGH1
N
Y
START OSCILLATION
F=FMAX
T=T0
VS>VSHIGH2
N
Y
N
VS>VSHIGH2
T>T0+TPRE+TIGN
Y
Y
T=T 0+TPRE
N
Y
VRS<VCMTH
N
PREHEATING MODE
N
N
IGNITION MODE
F>FMIN
INCREA SE
FREQUENCY
F>FMIN
N
Y
Y
DECREA SE
FREQUE NCY
DECR EASE
FREQUENCY
FEED FORWARD MODE
ACTIVATED
OPEN LOAD DETECT ION: STOP
LOW SIDE MOS ON
AND HIGH SIDE MOS OFF
N
VS>VSHIGH2
Y
STOP OSCILLATION
LOW SIDE MOS ON
HIGH SIDE MOS OFF
N
Y
RESTART WITH
F=FMAX
FREQUENCY SHIFTS IN T=T IGN
TOWARDS BURNING STATE CONDITION
(F=MAX{FMAX,FFEEDFORWARD,FCAPACITIVEMODE })
10/15
Y
VRS<V CMTH
BURNING MODE
VS>VSHIGH1
Y
Y
VRS>V PH
N
N
Y
F>F MIN
Y
DECREA SE
FREQUE NCY
F>F FEEDFORWARD
N
INCR EASE
FREQUENCY
INCREASE
FREQUE NCY
L6567
Figure 8. Frequency vs IRHV @ CF = 82pF
Figure 5. Working frequency vs IRHV
@ RREF = 30Kohm
120.00
1 6 0 .0 0
15 0 .0 0
C f= 47pF
R re f= 30Ko hm
14 0 .0 0
1 2 0 .0 0
C f= 82pF
10 0 .0 0
Cf= 100 pF
9 0 .0 0
8 0 .0 0
Cf= 120 pF
7 0 .0 0
fr e q u e n c y [k H z ]
Cf= 6 8p F
11 0 .0 0
fr eq u e n cy [kH z]
100.00
Cf= 56p F
13 0 .0 0
R r ef= 20 K
R r ef= 22 K
R re f= 24K
Cf=15 0pF
6 0 .0 0
80.00
60.00
R re f=2 7K
Cf=1 80 pF
5 0 .0 0
R re f= 30 K
Cf=22 0pF
4 0 .0 0
R re f= 33K
3 0 .0 0
Rr ef= 36 K
40.00
2 0 .0 0
R re f= 39 K , 4 3 K, 4 7K , 5 1K
1 0 .0 0
0 .0 0
0.2 0
0.20
0.4 0
0 .6 0
0 .8 0
1 .00
0.40
1 .20
0 .60
0.80
Irh v [m A ]
1.00
1.20
Irh v [m A ]
Figure 6. Frequency vs CF @ RREF=30Kohm
Figure 9. Frequency vs IRHV @ CF=100pF
10 0.0 0
1 60 .0 0
150.00
140.00
R ref= 30K ohm
130.00
8 0.0 0
1 20 .0 0
fr e q u e n c y [k H z ]
110.00
fre q u e n c y [k H z ]
100.00
90.00
80 .0 0
70.00
R re f= 2 0 K
R r ef = 2 2 K
6 0.0 0
Rr ef = 2 4 K
R re f = 2 7 K
60.00
R re f = 3 0 K
50.00
R re f = 3 3 K
4 0.0 0
R re f = 3 6 K
I=1m A
40 .0 0
R re f = 3 9K ,4 3 K
I= 0 .7 5 m A )
30.00
20.00
I=0.5m A
10.00
0 .0 0
40 .0 0
2 0.0 0
0 .2 0
60 .0 0
0 .4 0
0 .6 0
0 .8 0
1 .0 0
1 .2 0
Ir h v [m A ]
80 .0 0 1 00 .0 0 1 2 0.00 14 0 .0 0 16 0.0 0 1 80 .0 0 20 0.0 0 2 20 .0 0 2 4 0.00
C f [p F ]
Figure 10. Frequency vs IRHV @ CF=120pF
Figure 7. TDT vs RREF @ CF = 100pF
80 .0 0
T d t [ca lc u late d da ta]
2.40
Td t [m e as u re d d a ta]
2.00
fre q u e n c y [k H z ]
T d t [u s ]
60 .0 0
1.60
R r ef = 20 K
R re f = 2 2 K
R r e f = 24 K
40 .0 0
R re f = 2 7 K
R re f= 3 0 K
1.20
R r e f = 33 K
R re f = 3 6 K
R re f = 3 9 K
R r e f= 43 K , 4 7 K , 5 1 K
0.80
20 .00
30 .00
4 0.0 0
R re f [ K o h m ]
50.00
6 0.0 0
20 .0 0
0 .20
0 .40
0.60
0.80
1.00
1.20
Ir h v [m A ]
11/15
L6567
Figure 11. Frequency vs IRHV @ CF= 150pF
Figure 13. FFEED FORWARD: measurements and
calculations
80.00
120000.00
c a lc u latio ns ( 1/12 1 )*Ir hv /C f
110000.00
Cf= 8 2pF
m eas u re m en ts
100000.00
Cf= 1 00p F
90000.00
F req . fe ed for wa rd [H z]
fre q u e n c y [k H z ]
60.00
R ref= 20 K
40.00
R ref= 22 K
Rr ef= 24 K
R re f= 27K
80000.00
C f= 12 0 pF
70000.00
Cf= 1 50p F
60000.00
50000.00
40000.00
30000.00
R re f= 30K
R r ef= 33K
Rr ef= 36 K
R r ef= 39K
20000.00
10000.00
20.00
Rr ef=4 3 K, 47K , 51 K
0.00
0. 4 0
0 .6 0
0 .8 0
Irh v [ m A ]
0.20
0.40
0.60
0.80
Ir h v [m A ]
1.00
1.20
Figure 12. FMIN: measurements and calculations
1 00 .0 0
m eas ura m ents
Fm in= 1/(8 *C f*R ref)
F m in [KH z ]
80 .0 0
60 .0 0
40 .0 0
C f= 82pF
C f=100p F
C f=120pF
20 .0 0
C f=15 0pF
0 .0 0
20 .0 0
30 .0 0
R re f [K o hm ]
12/15
4 0 .0 0
50 .0 0
1 . 00
1 .2 0
L6567
mm
DIM.
MIN.
a1
0.51
B
1.39
TYP.
inch
MAX.
MIN.
TYP.
MAX.
0.020
1.65
0.055
0.065
b
0.5
0.020
b1
0.25
0.010
D
20
0.787
E
8.5
0.335
e
2.54
0.100
e3
15.24
0.600
F
7.1
0.280
I
5.1
0.201
L
OUTLINE AND
MECHANICAL DATA
3.3
0.130
DIP14
Z
1.27
2.54
0.050
0.100
13/15
L6567
mm
DIM.
MIN..
TYP.
A
a1
inch
MAX.. MIN..
TYP.. MAX..
1.75
0.1
0.25
b
0.35
b1
0.19
a2
0.069
0.004
0.009
0.46
0.014
0.018
0.25
0.007
0.010
1.6
C
0.063
0.5
c1
0.020
45° (typ.)
D (1)
8.55
8.75
0.336
0.344
E
5.8
6.2
0.228
0.244
e
1.27
e3
0.050
7.62
0.300
F (1)
3.8
4
0.150
0.157
G
4.6
5.3
0.181
0.209
L
0.4
1.27
0.016
0.050
M
S
0.68
0.027
8° (max.)
(1) D and F do not include mold flash or protrusions. Mold flash or
potrusions shall not exceed 0.15mm (.006inch).
14/15
OUTLINE AND
MECHANICAL DATA
SO14
L6567
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. N o license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics
2001 STMicroelectronics - All Rights Reserved
STMicroelectronics GROUP OF COMPANIES
Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain
- Sweden - Switzerland - United Kingdom - U.S.A.
http:/ /www.st.com
15/15
AN1234
APPLICATION NOTE
L6567: DESIGN HINTS
An integrated ballast design has been made with L6567 IC. The chosen topology is an half bridge inverter. L6567 provides all the necessary functions for driving the external power mosfets and for preheat, ignition and steady state operations control of the lamp. The minimum part count required makes
L6567 optimal for compact fluorescent lamp driving.
The design is intended for 15W CFL (or similar one) and for 220V±20% mains.
Introduction
The circuits to drive CFL have usually the following block diagram:
Figure 1. Block Diagram
INPUT
FILTER
HALF
BRIDGE
INVERTER
D00IN1101
There are three sections: an EMI filter, a diode bridge rectifier that gives the rectified mains, (then smoothed by
a filtering capacitor), and a half bridge inverter.
There is usually no voltage pre regulator for the High Voltage Bus (HVB), so the bus voltage will depend on the
mains. A key point of L6567 is the load current regulation according to the bus value, that means that the power
in the lamp is constant, not depending on mains value.
The high frequency inverter topology is a very efficient one, because of the zero voltage switching principle, that
let the mosfet switching losses to be held to the minimum: just the turn on one. The “capacitive mode” protection
implemented in L6567 helps preventing mosfet hard switching.
L6567 is able to control a preheat time to make lamp ignition easier and lamp life longer.
The main phases of circuit working are described in the following sections: start up, preheat, ignition and steady
state condition. The circuit schematic we will refer to is shown below:
March 2001
1/9
AN1234 APPLICATION NOTE
Figure 2. Application Schematic
RHV
L
13
D1
D2
CHB
Q1
220V
50-60Hz
D3
D4
CHB
CSNUBBERCHARGEPUMP
CBOOT
1
DCHARGE PUMP
CLAMP
RSHUNT
CF
3
LCHOKE
C
14
L
LAMP
R
CI
2
CCHARGE
DCHARGE
PUMP
PUMP
12
L6567
11
5
RREF
CVCC
10
6
Q2
CP
7
8
9
D00IN1102
The way to get the right components value will be shown in the last paragraph.
Start up
As soon as the mains is applied a high voltage appears across the filtering capacitor C and the half bridge inverter (Q1 and Q2). L6567 is powered through RHV: the current flows from HVB to C VCC through RHV and
L6567. When CVCC voltage reaches VSLOW1 (max. 6V) the low side mosfet Q2 is turned on while the high side
mosfet Q1 is turned off, in order to charge the bootstrap capacitor (CBOOT). When CVCC voltage reaches
VSHIGH1 (typ. 11.7V) the oscillator starts and the RHV pin is no more involved in providing C VCC charge: it is
provided by the charge pump connected to the half bridge midpoint (pin 3 OUT). A high voltage capacitor is
needed and it is used both for the charge pump and for snubber function.
Preheat phase
A preheat sequence is done to assure a longer lamp life: a small current is delivered to the lamp cathodes to
warm them, in order to make ignition easier.
We refer to a very simple lamp model: before ignition no current flows in the lamp, and the only conductive paths
are the electrodes, that can be seen as two small resistors (see fig. 3.A). After ignition, current flows between
the electrodes, and the lamp can be seen as a resistor connected between them. The value of this resistance
can be evaluated as the ratio between the nominal lamp power and the nominal voltage (squared) across the
lamp. The equivalent load connected to the midpoint of the half bridge is shown in fig. 3.B (the filaments resistances have been disregarded).
Figure 3. Lamp equivalent load
LCHOKE
LAMP
LCHOKE
RLAMP FILAMENT
CLAMP
CLAMP
RLAMP FILAMENT
(A)
2/9
LCHOKE
RLAMP
CLAMP
D00IN1103
(B)
AN1234 APPLICATION NOTE
We will have two different transfer functions (= VLAMP/VHALF_BATTERY) :
Figure 4. Transfer functions
VLAMP/VHB
B
A
C
freq.
D00IN1104
The preheat phase is typically in the “A” part of the upper characteristic: here we have a few Khz resonant frequency (See fig 3.A), small gain, so the voltage across the lamp is much smaller than the ignition one. The
frequency of the oscillator is decided according to the current we want to flow in the lamp cathode.
There is a pretty simple way to determine the needed preheat current when it is not specified by lamp characterization: if R0 is the filament resistance at room temperature , we have to warm the filament so that after preheat time R(TPRE)~3R0 (as a rule of thumb). Moreover we have to do it with a current that allow us to use
reasonable preheat time : the end customer will not wait for a long time before the lamp being on , but TPRE has
not to be so short to be out of control.
We can force a fixed DC current in the filament and we can measure the voltage across it: when it is three times
the initial one, we have reached the needed preheat time.
A simple set up is shown in fig. 5.
Figure 5. Preheat Time and Current Measurements set up
LAMP FILAMENT
UNDER TEST
∆V
I
~1MΩ
+
40V
R (to set I)
VZ20V
D00IN1105
3/9
AN1234 APPLICATION NOTE
We have measured different lamp types with the following results:
Thin cathode lamps
Thick cathode lamps
Philips 11W
Sylvania 15W
R0 [ohm]
Current mA
3R0 time [s]
15
200
1.4
230
1
250
0.7
300
0.3
525
3.5
775
1.2
300
2.5
390
1.5
510
0.42
12
Light of America 27W
Light of America 42W
1.7
3
Typical preheat times are nearly 1s (0.5-1.5s).
When we have set the right IPRE - TPRE values, we have to use them taking into account the model of fig.4. Here
we have a resonant circuit, and in “A” zone we are far from the resonant frequency: the current wave form is
not sinusoidal, but is nearly triangular. Using the rms. current value times RSHUNT you have the voltage that is
compared to pin 9 internal threshold. Setting RSHUNT we set the preheat current and, as a consequence, the
preheat frequency. The preheat time is set by C P capacitor, connected to pin 8.
Ignition phase
After preheat time has elapsed L6567 oscillator sweeps down toward lower frequency, using the “B” part of fig.
4 characteristic. In this way the gain increases, and the voltage across the lamp and across C LAMP capacitor
increases too. When the frequency approaches the resonant frequency the voltage gain is very high, and the
voltage across the lamp will reach the ignition one: the lamp strikes on and the load will look like model B in fig.3:
that means we are now in “C” part of fig. 4 lower characteristic, with a lower gain and not so near to the new
resonant frequency.
If the lamp doesn’t ignite the oscillation frequency could cross the resonant frequency and go to the left side of
the upper characteristic. The frequency range lower than the resonant frequency is dangerous for mosfet
switching: they switch in capacitive mode, that means there is no more zero voltage switching, and the mosfet
switch with the full HVB across source and drain. We don’t have this problem with L6567: the IC provides a capacitive mode protection, sensing RSHUNT voltage, and forcing the frequency towards higher values until we are
at frequency higher than the resonant one. The ignition frequency sweep lasts the time needed to reach the set
working frequency or , maximum, 15/16TPRE. The sweep rate is set by CI capacitor (pin 14).
Burn phase
When the lamp is properly ignited we are in the burn phase. The minimum oscillator frequency (F MIN) is set by
RREF and CF (pin 10 and 12). There are two main control functions performed by L6567: there is the capacitive
mode protection that has already been enabled in the ignition phase, and there is the feed forward control. This
second function mainly sets the working frequency in the burn phase. L6567 checks the rectified mains value
(sensing RHV current) and changes the working frequency to maintain constant lamp power. There is also the
filtering action of CP to avoid the 100Hz mains ripple. Without feed forward frequency sweep the high voltage
bus voltage variations would be applied to the half bridge inverter, and as a consequence to the lamp: sudden
4/9
AN1234 APPLICATION NOTE
increase and decrease of lamp power could cause a shortening of lamp life. With feed forward control the lamp
works at nearly the same power level regardless the mains variation. Another feature of L6567 is the chance to
set the dead time value with the resistor RREF at pin 10.
Setting components
In this application there are components typical of nearly every ballast application, to which general rules apply:
Mosfets have to be chosen taking care of the High Voltage Bus value as far as VDSMAX is concerned, and using
the lower RDSON for thermal consideration. With 220V mains 500V mosfet class is ok, and R DSON times max.
current has to be a withstandable dissipated power. Considering the high dV/dt due to the switching, NB mos
are safer than NA type.
After choosing the lamp, PLAMP and VLAMP set a constrain to LCHOKE value: L has to be the main components
as far as ILAMP setting:
P LAM P
VL
V HB – V LAM P
I L AMP = ------------------ = I L = ------------------------------------------------ = -----------------------------------------------V LAM P
X L ( f = f W O RKING )
X L ( f = f W O RKING )
That means:
( V HB – V L AM P ) ⋅ V LAM P
L = -----------------------------------------------------------------2 ⋅ π ⋅ f WO RKING ⋅ P LA MP
CLAMP has the aim to prevent V IGNITION across the lamp to be reached during preheat, so:
VCLAMP = IPRE ⋅ XCLAMP(f = fPRE) << VIGNITION
CHB capacitors are the half battery capacitors, the bigger they are the smaller the ripple of the voltage across
the resonant load, 100nF is the commonest value.
CBOOT capacitor has to be chosen according to the mos type: as a rule of thumb you can use:
Q to t_gate
C BO O T >>C MO S_equ. ~ ----------------------V G ATE
(see AN994 for further details)
Mosfet have no big equvalent capacitors in this kind of application, and a 100nF capacitor is often used.
The charge pump components have no special requirements, except the capacitor connected to the OUT node
that has to withstand a voltage swing equal to the High Voltage Bus value, and so it has to be properly rated
(i.e. 500V).
The remaining six parts: RSHUNT, RHV, RF, CI, CP, CF are strictly related to the IC working. L6567 is able to set
really a big deal of application parameters with a very few number of external components, namely the six key
components listed below. As a logical consequence, the same component is not related to a single application
characteristic, but to two or more.
5/9
AN1234 APPLICATION NOTE
The table below summarize these relationships (see L6567 datasheet for further details):
characteristic
components
burn phase minimum freq.
FMIN
RREF &CF
feed forward freq.
FFF
CF & RHV
T PRE&TIGN
CP & RREF
F PRE
RSHUNT & load
TDT
RREF
dF/dT
CI
preheat and ignition time
preheat freq.
dead time
freq. sweep rate
start up current
RHV
There are key part (i.e. RREF) that are related even to three parameters (i.e. FMIN, TPRE, TDT).
The suggested order to set parameters is the following:
•
Set RHV considering start up current and dissipation problem;
•
Set CF to have the feed forward frequency range: FFF=IRHV/(k1 ⋅ CF);
•
Set RREF to fix the minimum working frequency: F MIN = k2 ⋅ RREF ⋅ CF;
•
Set CP to fix the preheat time: TPRE = k3 ⋅ CP ⋅ RREF;
•
Now we have two parameters that are related just to a parameter: RSHUNT to the preheat current (and frequency) and CI that is related to the frequency sweep rate.
•
At the end we have two parameters that are related to parts already choosen:
TDT = k4 ⋅ RREF and TIGN = k5 ⋅ TPRE.
We can see a numerical example.
RHV choice
We begin from the start up current required to charge CVCC: it has to be greater than the IC consumption before start
up (Iq = 250µA), and the greater it is the shorter the start up time is. The problem is the dissipation: the greater the
current, the greater the dissipation on RHV. We have to make a compromise between these two settlements, starting
from reasonable current value. We can start from: ISTART_UP = 700µA and CVCC = 100nF. We get:
V ⋅ C VCC
Q
T START _UP = ----------------------------- = ----------------------------I START _UP
I START_UP
If we consider VLOW1 and VHIGH1 (max. 6V and 12.7V) we have T1~0.9µs and T2~1.8µs, that are reasonable
time for this kind of application. It means that the IC starts working after ~2µs.
We can use the max. rms. mains value to calculate the Rc- value. If the mains is 220V±20% we have:
310 V
R HV = -------------- ~443k Ω
0.7A
We have to check if this value gives dissipation problems: it is safer to use the peak mains voltage, so:
2
V M AX 370 V 2
P DISS = --------------- ~ ------------------ ~0.3W
R HV 440 kΩ
It is cheaper to use 1/4watt resistors, so we can choose two 220Kohm resistors.
6/9
AN1234 APPLICATION NOTE
CF choice
We can choose CF in order to set the feed forward frequency range. A useful formula that fits pretty well the
L6567 behavior is:
I RHV
F FF = ----------------k1 ⋅ C F
Where k1~121 (see in L6567 datasheet the fitting between calculations and measurements). It is useful to use
the datasheet characterization to select the proper frequency range. An example is the graph in fig. 6.
We have to choose the desired frequency range vs. the IRHV
range, as done in fig.6, and we have the C F characteristics.
If the frequency ranges from 40 to 60 kHz a good capacitor
value is 100pF.
Figure 6. Freq. vs. IRHV @ different CF
f
(KHz)
140
D00IN1106
47pF
56pF
RREF=30KΩ
When we measure the frequency on the board we have to
measure the mosfets gate on-off frequency (i.e. pin 6). We
don’t have to put the probe on CF. On CF we will see a triangular waveform (see L6567 datasheet characterisation) but
with a wrong frequency: the probe capacitor is some pF (i.e.
8pF), that is not negligible compared to a 100pF capacitor.
68pF
120
82pF
100
100pF
80
120pF
150pF
60
180pF
40
RREF choice
Cf=220pF
After choosing CF value we can set the F MIN value with the
formula:
20
0
0.2
0.4
0.6
0.8
1.0
FMIN = (8 ⋅ RREF ⋅ CF)-1
Irhv(mA)
If FMIN is 40 kHz, we get RREF=31250ohm, that may mean a RREF commercial value of 30Kohm.
CP choice
We fix CP value setting the preheat time:
TPRE = 224 ⋅ CP ⋅ RREF
We look in the preheat current-time table shown before a good setting for a 15W lamp. We choose the following
preheat condition: IPRE~250mA and TPRE~0.6-0.7ms. We get CP~100nF.
RSHUNT choice
RSHUNT sets the preheat current and (as a consequence) the preheat frequency.
We have already chosen IPRE (~250mA) from the lamp filament characterization table. This value is a DC one,
so it is also the rms. one. During preheat we work in a strongly inductive mode (see fig. 4, range A), so the current is nearly triangular shaped. With this approximation we are allowed to use the following formula:
I PP
I RM S = ---------12
L6567 compares the peak current times RSHUNT with an internal threshold (~600mV typ.):
VR
SHUNT
I PP
= -------- ⋅ R SHUNT
2
7/9
AN1234 APPLICATION NOTE
At the end we get:
R SHUNT ~V R
SHUNT
0.577
⋅ -------------------------I PRE_RMS
And we have a 1.3-1.4 ohm shunt resistor.
CI choice
CI value is the main factor that sets the frequency sweep rates during preheat, ignition and feed forward phase.
The suggested value is 100nF (see datasheet characterization).
Dead time and ignition time
There are formulas that relate TDT and TIGN to external parts:
TDT = 46.75-12 ⋅ RREF
15
15
T IG N = ------ ⋅ T PRE = ------ ⋅ 224 ⋅ C P ⋅ R RE F
16
16
All these parts have already been set, as a consequence we have T DT~1.4µs and TIGN~0.6s.
Usually these are not key parameters, and these values are reasonable. If this is not the case we have to iterate
the process, changing the order in which we set the external parts (starting from the most critical ones).
With the above calculations we get the following part list:
Filtering parts
R
47 Ω
C
3.3µF 400V
L
820µH 140mA
Rectifier bridge
Ballast parts
8/9
DF06N
CHALF_BATTERY (2)
100nF 250V
L
3.1mH
CLAMP
3.9nF 400V
Mosfets (2)
STP2NB50
RSHUNT
1.3 Ω
CSNUBBER-CHARGE_PUMP
470pF 500V
CCHARGE_PUMP
680pF 50V
Charge pump diodes (2)
BAS16,1N4148
CVCC
100nF 50V
RHV1 RHV2
220KΩ
CP , C I
100nF 50V
RREF
30KΩ
CF
100pF
IC
L6567
AN1234 APPLICATION NOTE
Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.
The ST logo is a registered trademark of STMicroelectronics
2001 STMicroelectronics - All Rights Reserved
STMicroelectronics GROUP OF COMPANIES
Australia - Brazil - China - Finland - France - Germany - Hong Kong - India - Italy - Japan - Malaysia - Malta - Morocco - Singapore - Spain
- Sweden - Switzerland - United Kingdom - U.S.A.
http://www.st.com
9/9