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UC1848_14 PDF预览

UC1848_14

更新时间: 2024-11-24 02:58:43
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德州仪器 - TI /
页数 文件大小 规格书
9页 361K
描述
Average Current Mode PWM Controller

UC1848_14 数据手册

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UC1848  
UC2848  
UC3848  
Average Current Mode PWM Controller  
BLOCK DIAGRAM  
FEATURES  
Practical Primary Side Control of  
Isolated Power Supplies with DC  
Control of Secondary Side Current  
Accurate Programmable Maximum  
Duty Cycle Clamp  
Maximum Volt-Second Product Clamp  
to Prevent Core Saturation  
Practical Operation Up to 1MHz  
High Current (2A Pk) Totem Pole  
Output Driver  
Wide Bandwidth (8MHz) Current Error  
Amplifier  
Under Voltage Lockout Monitors VCC,  
VIN and VREF  
Output Active Low During UVLO  
Low Startup Current (500µA)  
Precision 5V Reference (1%)  
UDG-93003-1  
DESCRIPTION  
The UC3848 family of PWM control ICs makes primary output driver. The current error amplifier easily interfaces  
side average current mode control practical for isolated with an optoisolator from a secondary side voltage sens-  
switching converters. Average current mode control in- ing circuit.  
sures that both cycle by cycle peak switch current and  
A full featured undervoltage lockout (UVLO) circuit is con-  
maximum average inductor current are well defined and  
tained in the UC3848. UVLO monitors the supply voltage  
will not run away in a short circuit situation. The UC3848  
to the controller (VCC), the reference voltage (VREF),  
can be used to control a wide variety of converter topolo-  
and the input line voltage (VIN). All three must be good  
before soft start commences. If either VCC or VIN is low,  
gies.  
In addition to the basic functions required for pulse width  
modulation, the UC3848 implements a patented tech-  
nique of sensing secondary current in an isolated buck  
derived converter from the primary side. A current wave-  
form synthesizer monitors switch current and simulates  
the inductor current down slope so that the complete cur-  
rent waveform can be constructed on the primary side  
without actual secondary side measurement. This infor-  
mation on the primary side allows for full DC control of  
output current.  
the supply current required by the chip is only 500µA and  
the output is actively held low.  
Two on board protection features set controlled limits to  
prevent transformer core saturation. Input voltage is mon-  
itored and pulse width is constrained to limit the maxi-  
mum volt-second product applied to the transformer. A  
unique patented technique limits maximum duty cycle  
within 3% of a user programmed value.  
These two features allow for more optimal use of trans-  
formers and switches, resulting in reduced system size  
and cost.  
The UC3848 circuitry includes a precision reference, a  
wide bandwidth error amplifier for average current con-  
trol, an oscillator to generate the system clock, latching  
PWM comparator and logic circuits, and a high current  
Patents embodied in the UC3848 belong to Lambda  
Electronics Incorporated and are licensed for use in ap-  
plications employing these devices.  
4/96  

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