LM5027A

更新时间： 2024-11-26 11:36:39

品牌	Logo	应用领域
美国国家半导体 - NSC		/
页数	文件大小	规格书
28页	565K
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Evaluation Board evaluation board is designed to provide

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National Semiconductor

Application Note 2067

Terry Allinder

LM5027A Evaluation Board

June 15, 2010

Introduction

Theory of Operation

The LM5027A evaluation board is designed to provide the

design engineer with a fully functional power converter based

on the Active Clamp Forward topology to evaluate the

LM5027A controller. The evaluation board is provided in an

industry standard quarter-brick footprint.

Power converters based on the Forward topology offer high

efficiency and good power handling capability in applications

up to several hundred Watts. The operation of the transformer

in a forward topology does not inherently self-reset each pow-

er switching cycle; a mechanism to reset the transformer is

required. The active clamp reset mechanism is presently find-

ing extensive use in medium level power converters in the 50

to 200W range.

The performance of the evaluation board is as follows:

Input Operating Range: 36 to 78V (100V peak)

Output Voltage: 3.3V

The Forward converter is derived from the Buck topology

family, employing a single modulating power switch. The main

difference between the topologies are, the Forward topology

employs a transformer to provide input / output ground isola-

tion and a step down or step up function.

Output Current: 0 to 30A

Measured Efficiency: 90.5% @ 30A, 92.5% @ 15A

Frequency of Operation: 250 kHz

Board Size: 2.3 X 1.45 x 0.5 inches

Load Regulation: 1%

Each cycle, the main primary switch turns on and applies the

input voltage across the primary winding, which has 12 turns.

The transformer secondary has 2 turns, leading to a 6:1 step-

down of the input voltage. For an output voltage of 3.3V the

required duty cycle (D) of the main switch must vary from ap-

proximately 60% (low line) to 25% (high line). The LM5027A

limits the PWM duty cycle output to a maximum of 70% (typ-

ical). The maximum duty cycle limits the voltage stress on the

Active Clamp Forward converter MOSFETs. The clamp ca-

pacitor along with the reset switch reverse biases the trans-

former primary each cycle when the main switch turns off.

This reverse voltage resets the transformer. The clamp ca-

pacitor voltage is Vin / (1-D).

Line Regulation: 0.1%

Line UVLO, Hiccup Current Limit

A 70% Maximum Duty Cycle

The printed circuit board consists of 6 layers of 2 ounce cop-

per on FR4 material with a total thickness of 0.050 inches.

The unit is designed for continuous operation at rated load at

<40°C and a minimum airflow of 200 CFM.

Feedback from the output is processed by an amplifier and

reference, generating an error voltage, which is coupled back

to the primary side control through an optocoupler. The

LM5027A voltage mode controller pulse width modulates the

error signal with a ramp signal derived from the input voltage.

Deriving the ramp signal slope from the input voltage provides

line feed-forward, which improves line transient rejection. The

LM5027A also provides a controlled delay necessary for the

reset switch. The evaluation board can be synchronized to an

external clock with a recommended frequency range of 275

to 300 kHz.

301263

www.national.com

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与LM5027A相关器件

型号	品牌	获取价格	描述	数据表
LM5027A_15	TI	获取价格	Voltage Mode Active Clamp Controller
LM5027AMH/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller
LM5027AMHX/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller 20-HTSSOP -40 to 125
LM5027ASQ/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller
LM5027ASQX/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller
LM5027MH	NSC	获取价格	Voltage Mode Active Clamp Controller
LM5027MH/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller
LM5027MH/NOPB	NSC	获取价格	IC SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO20, ROHS COMPLIANT, TSSOP-20, Sw
LM5027MHX	NSC	获取价格	Voltage Mode Active Clamp Controller
LM5027MHX/NOPB	TI	获取价格	Voltage Mode Active Clamp Controller 20-HTSSOP -40 to 125

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