基于NE555定时器的低价格电压频率转换器
技术分类： 模拟设计 | 2008-02-29
来源：EDN | 作者：Gyula Diószegi and János Nagy, Divelex Ltd, Budapest, Hungary
NE555定时器和Miller积分器结合组成电压到频率转换器，价格低于50美分。
1971年，Signetics——Philips的前身——生产了NE555定时器，目前制造商每年仍生产超过十亿件产品。通过给NE555增加一些器件，可以构造价格低于50美分的简单电压频率转换器。电路包括NE555定时器和基于TL071的Miller积分器（图1）。应用中输入电压为0到-10V，产生0到1000Hz的输出频率范围。C1的电流为输入电压的函数：IC=–VIN/(P1+R1)。
C1的电压达到VCC的2/3时，定时器的内部放电晶体管打开，C1的电压回到VCC的1/3，比较器的低阈值。到电压的1/3处，放电晶体管关闭，C1再次开始充电。C1充电时，NE555的输出为高，而C1放电时，NE555的输出为低。输入电压和C1充电时间的乘积为常数。因为放电时间小于充电时间，下面的公式计算了输出频率fOUT~VIN/(P1+R1)×C1×1/3VCC。
P1校准了输出频率和输入电压的关系。因为放电时间约为30µs，电压频率转换的精度随频率的增加而降低。如果设定100H
英文原文：
NE555 timer sparks low-cost voltage-to-frequency converter
The combination of an NE555 timer and a Miller integrator yields a voltage-to-frequency converter that costs less than 50 cents.
Gyula Diószegi and János Nagy, Divelex Ltd, Budapest, Hungary; Edited by Charles H Small and Fran Granville -- EDN, 2/21/2008
In 1971, Signetics—later Philips—introduced the NE555 timer, and manufacturers are still producing more than 1 billion of them a year. By adding a few components to the NE555, you can build a simple voltage-to-frequency converter for less than 50 cents. The circuit contains a Miller integrator based on a TL071 along with an NE555 timer (Figure 1). The input voltage in this application ranges from 0 to –10V, yielding an output-frequency range of 0 to 1000 Hz. The current of C1 is the function of input voltage: IC=–VIN/(P1+R1).