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Floating 9V Supply For DVM Modules(TLC555)

2017-08-09 23:11  
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This article briefly describes Floating 9V Supply For DVM Modules (TLC555). This principle is easy to understand, but also very practical. Depth understanding of circuit elements, you can better grasp this principle. In this circuit, you can learn about and purchase these components: TLC555.

Most commercialDVMmodules with anLCDreadout are 9-V powered and based on an ICL7106 or similar A-D converter chip. These modules are typically used in laboratory power supplies and other test and measurement equipment where a drop-in solution needs to be found to realize a voltmeter readout. Particularly in power supply units, theLCDmodule will need to ‘float’ relative to thePSUsupply rails, and this inevitably requires a separate 9-volt power supply. In some cases, batteries may be used but these have distinct advantages. The alternative, a 9-V converter effectively powered by thePSUand yet ?oating, is shown here.


Figure 1 

It is built from the ubiquitous TLC555, LMC555 or 7555) timer IC acting in astable multivibrator con?guration producing a 70-kHz square wave fed into a simple rectifier. In essence, capacitors C5 and C6 afford the above mentioned electrical isolation between thePSUsupply rails and theLCDmodule. The old, bipolar NE555 IC should not be used here because it presents a too heavy loads on the converter’s own supply voltage. Depending on the exact type and brand of theCMOS555 you’re using, resistor R6 may need to be redimensioned a bit to ensure a supply voltage of about 10 volts at pins 8 and 4 of the chip. At an output voltage of 9.5 V, the maximum output current of the converter s about 1 mA.



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