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ELM711 参数 Datasheet PDF下载

ELM711图片预览
型号: ELM711
PDF下载: 下载PDF文件 查看货源
内容描述: 圣诞节的LED驱动器 [Christmas LEDs Driver]
分类和应用: 驱动器
文件页数/大小: 7 页 / 38 K
品牌: ELM [ ELM ELECTRONICS ]
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ELM711  
Example Application  
This section shows how the ELM711 might be  
typically used. Basically, all that needs to be done is  
apply power to the IC and it will create a sequence of  
outputs for you. There are some concerns over the  
external connections that should be discussed first,  
however.  
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Whenever interfacing to CMOS circuitry, you need  
to protect against a problem called ‘latchup’. This may  
occur when excessive current is allowed to flow into  
one of the IC’s pins, typically an input. This can  
happen at almost any time, but generally occurs if  
there are long wires connected directly to the IC, with  
no form of current limiting. Latchup will cause  
excessive currents to flow, which may damage  
components (such as the ELM711).  
Figure 1. Typical Pushbutton Connection  
Figure 1 shows how a pushbutton will typically be  
connected to the input of the ELM711. This works well  
if the wires to the switch are short (less than about 12  
inches long). If the wires are longer than that, currents  
can more easily be induced into the wires, and into the  
ELM711 pin. Since there is no current limiting, the  
currents can possibly be large enough to exceed the  
latchup threshold, and the IC may be damaged.  
Simply adding a series resistor such as that shown in  
Figure 2 is all that is generally needed to prevent  
latchup. Note that we also show a 4.7KW pullup  
resistor connected to the switch as well. This pullup  
resistor helps to pass some of the induced currents  
around the ELM711 input, and also provides a lower  
impedance input so that the voltages caused by the  
induced currents are reduced, and less likely to  
provide false inputs. (The ELM711 input pin also uses  
a relatively long debounce time, so that it is less  
susceptible to noise.)  
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4.7KW  
4.7KW  
Figure 2. Protection for very long PB leads  
Colour  
Red  
Typical Vf  
1.8  
The ELM711 may be used to control other  
devices, but it was designed with LEDs in mind. When  
on, LEDs require a forward voltage of about 2 to 3  
volts as shown in Table 2. These voltages will remain  
fairly constant over a wide range of currents, and can  
be used in calculations as if they are constant.  
Yellow  
Green  
Blue  
1.9  
2.0  
If the ELM711 is to use a 3 to 5 volt power supply,  
it is clear that it can only be directly connected to 1 or  
possibly 2 LEDs on each output, as there isn’t enough  
voltage available to power a longer string of LEDs.  
This could result in a sparse Christmas tree unless  
something can be done.  
3.0  
White  
2.9  
Table 2. Typical LED Forward Voltage Drops  
The circuit of Figure 3 shows a transistor driving  
several LEDs from a power supply of Vp volts. As long  
as the sum of the LED voltages is less than Vp, the  
ELM711DSA  
Elm Electronics – Circuits for the Hobbyist  
< http://www.elmelectronics.com/ >  
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