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ELM341SM 参数 Datasheet PDF下载

ELM341SM图片预览
型号: ELM341SM
PDF下载: 下载PDF文件 查看货源
内容描述: 低功率恒温器 [LOW POWER THERMOSTAT]
分类和应用:
文件页数/大小: 4 页 / 32 K
品牌: ELM [ ELM ELECTRONICS ]
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ELM341  
Example Application  
Figure 1 shows the ELM341 in an example heating  
below. Take into account it’s value when determining  
the setpoint, though.  
control circuit.  
A
closed contact output occurs  
whenever the temperature measured by RTEMP falls to  
a value less than that determined by RSET. It is  
anticipated that this type of circuit could possibly be  
used to control temperatures over the range of -40°C  
to +40°C.  
For this design, RSET was selected to be equal to  
the resistance of RTEMP at 10°C, so that the relay  
contact closes for any measured temperatures less  
than 10°C. The resistance value was determined from  
specs given by the manufacturer, but could have been  
determined experimentally as well.  
Power for the control circuit is from a 3V battery,  
while the output relay is powered from a 12V supply.  
The output relay type is not important, as long as  
consideration is given to the coil drive requirements,  
and the capabilities of the ELM341. In this example, a  
relay with a 400W coil resistance was chosen so that a  
2N3904 could drive it directly. For further reductions in  
current requirements, consideration could be given to  
using a power MOSFET transistor instead of this  
bipolar one.  
An LED has been provided for visual feedback of  
the circuit operation. It is connected to the  
‘measurement in progress’ output, so that it is  
energized each time a measurement is being made.  
Typically, this would be for about 25mS every 2  
seconds.  
Current requirements for this entire circuit have  
been measured to be about 2µA minimum and 23µA  
average, at room temperature and the relay de-  
energized, even with the LED blinking. Measurement  
times, and thus current consumption, vary with  
Temperature measuring is performed by RTEMP,  
which is  
a negative temperature coefficient type  
thermistor. It has a resistance of 10KW at 25°C, and  
this value decreases with increasing temperature. This  
value was chosen both because it is commonly  
available, and because it limits the 0.1µF integrating  
capacitor currents to less than 1mA over the typical  
range of operation (keeping the thermistor self-heating  
to a minimum).  
temperature, so this should only be used as  
guideline. With a 5V supply, these values escalate to  
about 8µA and 70µA, respectively.  
a
Just a reminder that consideration must be given  
to the fact that the pin 7 output is in a tri-state (open  
circuit) mode just prior to making a measurement. This  
mode lasts for approximately 300µs, sufficient to  
possibly affect some output circuits. It is generally not  
sufficient for an electromechanical relay to drop out,  
however, especially with a ‘kick-back’ diode across the  
coil.  
If the thermistor is mounted any appreciable  
distance from the ELM341, consideration must be  
given to cabling effects such as capacitive and induced  
currents. Generally the integrated circuit can be  
adequately protected by mounting a small value (220W)  
resistor physically close to the ELM341 as shown  
+12V  
3V  
12V Relay  
To the  
1N4001  
heating  
control  
1
8
7
6
5
1.5KW  
see text  
2
3
2N3904  
4
RTEMP  
560W  
10KW  
RSET  
@25°C  
18KW  
10KW  
LED  
0.1µF  
Figure 1. Backup Heating Control Thermostat  
ELM341DSB  
Elm Electronics – Circuits for the Hobbyist  
< http://www.elmelectronics.com/ >  
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