升压控制器形式负降压稳压-Step-Up Controlle

2011-05-27 23:09:20来源: 互联网
Positive step-down switching regulators are common, but the complementary negative step-down function (converting a negative voltage to a smaller negative voltage) is rare by comparison.

Figure 1 shows a negative step-down switching regulator that delivers 1A at -7.5V from -15V, with efficiency better than 90%. The IC is a step-up switching controller referenced to the negative rail.


Figure 1. This negative step-down circuit regulates -15V down to -7.5V.

When the power switch (Q3) turns on, the current in L1 increases as long as VOUT is less negative than VIN. When this inductor current reaches the limit set by R6, Q3 turns off. Q3's drain flies high and is clamped to the positive supply rail (ground) by the catch diode (D2). Inductor current then decreases until Q3 turns on again. The output capacitor (C3) integrates inductor current to produce the output voltage.

Output voltage is referenced to the positive supply rail, and Q4 reflects the error signal from the positive rail to the negative rail. When the error signal falls below the feedback threshold, the power switch turns on and initiates another switching cycle.

D1, Q1, Q2, and R1-R4 form a startup circuit that holds IC1 in shutdown until VIN reaches approximately -11V. This action ensures that Q4 has sufficient voltage compliance to regulate the feedback loop. The minimum input voltage necessary to maintain a regulated output voltage is VOUT +(-VFB), where VFB is the feedback threshold voltage (1.5V in this case). Efficiency varies with load current as shown in Figure 2.


Figure 2. Conversion efficiency for the Figure 1 circuit rises with load current.

The MAX1771 controller IC used in this circuit operates in the pulse-frequency modulation (PFM) mode. The MAX668 controller IC, which operates in the pulse-width modulation (PWM) mode, could be used in a similar circuit to step-down a negative voltage. PWM controllers offer the advantage of fixed-frequency operation. The MAX668 controller offers the further advantage of coming in a smaller package than the MAX1771 PFM controller.

A similar version of this article appeared in the September 6, 1999 issue of EE Times magazine.

关键字:形式  降压

编辑:神话 引用地址:http://www.eeworld.com.cn/mndz/2011/0527/article_9214.html
本网站转载的所有的文章、图片、音频视频文件等资料的版权归版权所有人所有,本站采用的非本站原创文章及图片等内容无法一一联系确认版权者。如果本网所选内容的文章作者及编辑认为其作品不宜公开自由传播,或不应无偿使用,请及时通过电子邮件或电话通知我们,以迅速采取适当措施,避免给双方造成不必要的经济损失。
论坛活动 E手掌握
微信扫一扫加关注
论坛活动 E手掌握
芯片资讯 锐利解读
微信扫一扫加关注
芯片资讯 锐利解读
推荐阅读
全部
形式
降压

小广播

独家专题更多

富士通铁电随机存储器FRAM主题展馆
富士通铁电随机存储器FRAM主题展馆
馆内包含了 纵览FRAM、独立FRAM存储器专区、FRAM内置LSI专区三大部分内容。 
走,跟Molex一起去看《中国电子消费品趋势》!
走,跟Molex一起去看《中国电子消费品趋势》!
 
带你走进LED王国——Microchip LED应用专题
带你走进LED王国——Microchip LED应用专题
 
电子工程世界版权所有 京ICP证060456号 京ICP备10001474号 电信业务审批[2006]字第258号函 京公海网安备110108001534 Copyright © 2005-2016 EEWORLD.com.cn, Inc. All rights reserved