基于NE555定时器的低价格电压频率转换器
基于NE555定时器的低价格电压频率转换器,NE555 V-F CONVERTER
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
z为-1V,1000Hz为-10V,转换范围的误差为0.3到3%。如果使用P1校准输入电压范围中点-5V的输出频率,那么整个范围内的转换误差小于1.3%。为改进性能,C1应该具有低耗散的特点。如果R1具有低温度系数,P1为多匝金属陶瓷电位计的话,可以减少温度影响。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).
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