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參數資料
| 型號： | ISL6741 |
| 廠商： | Intersil Corporation |
| 英文描述： | Flexible Double Ended Voltage and Current Mode PWM Controllers(靈活的雙端電壓和電流模式PWM控制器) |
| 中文描述： | 靈活的雙端電壓和電流模式PWM控制器（靈活的雙端電壓和電流模式的PWM控制器） |
| 文件頁數： | 22/29頁 |
| 文件大?。?/td> | 635K |
| 代理商： | ISL6741 |
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22
FN9111.4
July 13, 2007
Adding Line Only Regulation - Feed Forward
Output voltage variation caused by changes in the supply
voltage may be virtually removed through a technique known
as feed forward compensation. Using feed forward, the duty
cycle is directly controlled based on changes in the input
voltage only. No closed loop feedback system is required.
Voltage feed forward may be implemented as shown in
Figure 18..
The circuit provides feed forward compensation for a 2:1
input voltage range. Resistors R
100
and R
101
set the input
voltage divider to generate a 1V signal at the input voltage
that corresponds to maximum duty cycle (V
IN
minimum).
Resistors R
109
, R
110
, and R
111
form a voltage divider from
VREF to create reference voltages for the amplifiers. The
first stage uses U
100A
, R
102
, R
103
, R
104
, and C
100
to form
a unity gain inverting amplifier. Its output varies inversely
with input voltage and ranges from 1V to 2V. The bandwidth
of the circuit may be controlled by varying the value of C
100
.
The gain of the first amplifier stage is:
where:
V
A
= Output voltage of U
100A
V
D
= The input divider voltage
The second stage uses U
100B
, R
105
, R
106
, R
107
, and R
108
to form a summing amplifier which offsets the first stage
output by 0.8V (the value of C
T
valley voltage). The signal
applied to the V
ERROR
input now matches the offset and
amplitude of the oscillator sawtooth so that the duty cycle
varies linearly from 100% to 50% of maximum with a 2:1
input voltage variation.
Other duty ranges are possible, but are still limited to a 2:1
ratio. The voltage applied to V
ERROR
must be scaled to the
peak-to-peak voltage on C
T
, and offset by the valley voltage.
Since the peak-to-peak C
T
voltage is 2.00V nominal, the
voltage at the output of U100A must be divided by 2.0V to
obtain the desired duty cycle. For example, if an 80% duty
cycle was required at the minimum operating voltage, the
output of U100A must be 1.60V (80% of 2.00V). From
(Equation 25), the divider voltage must be set to 1.4V for the
input voltage that corresponds to the 80% duty cycle.
It should be noted that the synchronous rectifiers (SRs),
being driven from the transformer secondary, are only gated
on during the ON time of the primary FETs. Conduction
continues through the body diodes during the OFF time
when operating in continuous inductor current mode. This
mode of operation usually results in significant conduction
and switching losses in the SR FETs. These losses may be
reduced considerably by either adding schottky diodes in
parallel to the SR FETs or by driving the SR FETs directly
with a control signal.
Adding Regulation - Closed Loop Feedback
The second Typical Application schematic adds closed loop
feedback with isolation. The ISL6740EVAL2Z demonstration
platform implements this design and is available for
evaluation. The input voltage range was increased to 36V to
75V, which necessitates a few modifications to the open loop
design. The output inductor value was increased to 4.0
μ
H,
schottky rectifier CR4 was added to minimize SR FET body
diode conduction, the turns ratio of the main transformer was
changed to 4:3, and the synchronous rectifier gate drives
were modified. The design process is essentially the same
as it was for the unregulated version, so only the feedback
control loop design will be discussed.
The major components of the feedback control loop are a
programmable shunt regulator and an opto-coupler. The
opto-coupler is used to transfer the error signal across the
isolation barrier. The opto-coupler offers a convenient means
to cross the isolation barrier, but it adds complexity to the
feedback control loop. It adds a pole at about 10kHz and a
significant amount of gain variation due the current transfer
ratio (CTR). The CTR of the opto-coupler varies with initial
tolerance, temperature, forward current, and age.
FIGURE 18. VOLTAGE FEED FORWARD CIRCUIT
+
-
+
-
1.5V
0.8V
R102
100k
R101
2k
R100
69.8k
+VIN
VREF
R109
3.48k
R110
698
R111
806
R104
100k
R106
100K
R105
100k
R107
100k
R108
100k
R103
49.9k
C100
1nF
to VERROR
U100A
U100B
V
A
V
D
3.00
+
–
=
V
(EQ. 25)
ISL6740, 1SL6741
相關PDF資料 |
PDF描述 |
|---|---|
| ISL6845IB | Improved Industry Standard Single Ended Current Mode PWM Controller |
| ISL6845 | Improved Industry Standard Single Ended Current Mode PWM Controller |
| ISL6845IRZ-T | Improved Industry Standard Single-Ended Current Mode PWM Controller |
| ISL6845IU | Octal Buffers/Drivers With 3-State Outputs 20-SO -40 to 85 |
| ISL6845IBZ | Improved Industry Standard Single-Ended Current Mode PWM Controller |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ISL6741IB | 功能描述:電流型 PWM 控制器 CUR PWM MODE CNTRLR 16LD N RoHS:否 制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| ISL6741IB-T | 功能描述:IC REG CTRLR PWM CM 16-SOIC RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:500kHz 占空比:100% 電源電壓:8.2 V ~ 30 V 降壓:無 升壓:無 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:0°C ~ 70°C 封裝/外殼:8-DIP（0.300"，7.62mm） 包裝:管件 產品目錄頁面:1316 (CN2011-ZH PDF) |
| ISL6741IBZ | 功能描述:IC REG CTRLR PWM CM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:275kHz 占空比:50% 電源電壓:18 V ~ 110 V 降壓:無 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:-40°C ~ 85°C 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) |
| ISL6741IBZ-T | 功能描述:IC REG CTRLR PWM CM 16-SOIC RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:275kHz 占空比:50% 電源電壓:18 V ~ 110 V 降壓:無 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:-40°C ~ 85°C 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 包裝:帶卷 (TR) |
| ISL6741IV | 功能描述:IC REG CTRLR PWM CM 16-TSSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,500 系列:- PWM 型:電流模式 輸出數:1 頻率 - 最大:500kHz 占空比:100% 電源電壓:8.2 V ~ 30 V 降壓:無 升壓:無 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:是 工作溫度:0°C ~ 70°C 封裝/外殼:8-DIP（0.300"，7.62mm） 包裝:管件 產品目錄頁面:1316 (CN2011-ZH PDF) |
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