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參數(shù)資料
| 型號： | ISL6740 |
| 廠商： | Intersil Corporation |
| 英文描述： | Flexible Double Ended Voltage and Current Mode PWM Controllers |
| 中文描述： | 靈活的雙端電壓和電流模式PWM控制器 |
| 文件頁數(shù)： | 22/29頁 |
| 文件大?。?/td> | 639K |
| 代理商： | ISL6740 |
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22
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 below.
The circuit provides feed forward compensation for a 2:1
input voltage range. Resistors R100 and R101 set the input
voltage divider to generate a 1.00 volt signal at the input
voltage that corresponds to maximum duty cycle (V
IN
minimum). Resistors R109, R110, and R111 form a voltage
divider from VREF to create reference voltages for the
amplifiers. The first stage uses U100A, R102, R103, R104,
and C100 to form a unity gain inverting amplifier. Its output
varies inversely with input voltage and ranges from 1 to 2V.
The bandwidth of the circuit may be controlled by varying the
value of C100. The gain of the first amplifier stage is:
where:
V
A
= Output voltage of U100A
V
D
= The input divider voltage
The second stage uses U100B, R105, R106, R107, and
R108 to form a summing amplifier which offsets the first
stage output by 0.8V (the value of CT 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 CT, and offset by the valley voltage.
Since the peak-to-peak CT 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 (EQ.
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 ISL6740EVAL2 demonstration
platform implements this design and is available for
evaluation. The input voltage range was increased to 36V -
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.
+
-
+
-
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 V
ERROR
U100A
U100B
FIGURE 18. VOLTAGE FEED FORWARD CIRCUIT
V
A
V
D
3.00
+
–
=
V
(EQ. 25)
ISL6740, ISL6741
相關PDF資料 |
PDF描述 |
|---|---|
| ISL6740IB | Flexible Double Ended Voltage and Current Mode PWM Controllers |
| ISL6740IV | Octal Buffers/Drivers With 3-State Outputs 20-SSOP -40 to 85 |
| ISL6741 | 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) |
| ISL6845IB | Improved Industry Standard Single Ended Current Mode PWM Controller |
| ISL6845 | Improved Industry Standard Single Ended Current Mode PWM Controller |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| ISL6740AIVZA | 功能描述:IC REG CTRLR PWM VM 16-TSSOP 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(shù):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) |
| ISL6740AIVZA-T | 功能描述:IC REG CTRLR PWM VM 16-TSSOP 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(shù):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) |
| ISL6740EVAL1 | 功能描述:EVALUATION BOARD 1 ISL6740 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:- 產品培訓模塊:Obsolescence Mitigation Program 標準包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓撲結構:升壓 頻率 - 開關:3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| ISL6740EVAL2 | 功能描述:EVALUATION BOARD 2 ISL6740 RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 過時/停產零件編號 系列:- 標準包裝:1 系列:- 傳感器類型:CMOS 成像，彩色（RGB） 傳感范圍:WVGA 接口:I²C 靈敏度:60 fps 電源電壓:5.7 V ~ 6.3 V 嵌入式:否 已供物品:成像器板 已用 IC / 零件:KAC-00401 相關產品:4H2099-ND - SENSOR IMAGE WVGA COLOR 48-PQFP4H2094-ND - SENSOR IMAGE WVGA MONO 48-PQFP |
| ISL6740EVAL2Z | 功能描述:EVALUATION BOARD 2 ISL6740 RoHS:是 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - DC/DC 與 AC/DC（離線）SMPS 系列:- 產品培訓模塊:Obsolescence Mitigation Program 標準包裝:1 系列:True Shutdown™ 主要目的:DC/DC，步升 輸出及類型:1，非隔離 功率 - 輸出:- 輸出電壓:- 電流 - 輸出:1A 輸入電壓:2.5 V ~ 5.5 V 穩(wěn)壓器拓撲結構:升壓 頻率 - 開關:3MHz 板類型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
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