If you had a separate accurate voltage reference available, you could determine if your DMM is “telling the truth.” This is but one example of why you might want an accurate voltage reference. You apply power and look at the data ... Hmmmm, the numbers don’t look quite right. Your specific application will determine if you need to use a device with a low temperature coefficient. It seems to work quite well. For example, if the supply is 7.5V, the 5.000V reference could be off as much as 600 µV(500 µV from the initial .01% tolerance plus another 100 µV from the supply being 1V from the ideal 6.5V); 1% resistors and a 0.5% TL431 are used to keep the 6.5V supply between 6.3V and 6.7V.
Use a small tip on your iron and solder the X60008. For instance, with a 9V supply and a 1N751A which has a Iz of 20 mA, the resistor value is (9-5.1)/20 mA = 195 ohms. I need to be able to measure small currents.Thanks a lot! In other words, even though the temperature, applied voltage, and load current may be constant, all voltage references will slowly drift over time. Slide the power switch to the OFF position. This device provides 5.000V within 2.5 mV (.05% accuracy) and has a low temperature coefficient of 5 ppm/°C, an aging rate of 15 ppm/1,000 hours, and a supply current of 3 mA. This device costs about a dollar and is a “shunt” reference similar in general concept to a zener except that it isn’t nearly as picky as to the current flowing through it.
However, the following discussion of various reference voltage parameters applies equally well to using a voltage reference as a circuit element. Leaving the soldering iron on a pad too long can result in the reference voltage permanently shifting to an out-of-spec value. However, I was pleasantly surprised when I measured the first couple of prototypes and found that the 5V reference voltage was within .01% with a battery voltage all the way down to 6.7V! Now we are getting somewhere! 11 0 obj<> Increased battery run-time can be achieved by applying power, letting the unit stabilize, making your measurement, and then turning the power off. Just click the link below to review your options, then click SUBSCRIBE to make a selection and place your order. Finally, put your meter across the + and – output terminals and you should see 5.000V displayed.
For instance, pressing down on the board and causing it to flex can cause stress. To find maximum voltage that this circuit can measure hit and trial method is used. However, it is common to have a gain of 10 or so in such practical circuits because the voltage difference may be so small, for example: If shunt resistor is 0.1 Ohms (very common) and the current is 1A, this will result in 1 x 0.1 = 0.1v across shunt resistor, this will mean 0.1v output of the differential amplifier when unity gain is used, so it is 0.1v per 1 A. All Rights Reserved | endobj But if that’s not you, then get the Online Only Edition and save a few trees and some cash. endobj The LED should light up; if not, look for proper polarity of all the diodes including the LED. Easy! Unfortunately, changes in ambient temperature will cause a change in the reference voltage, regardless if the device is a zener or a precision reference. This will extend the meter movement’s range to higher voltages. Shown is the complete design of the R-2R circuit with op-amps feeding comparators and an analog multiplexer. When you subscribe to Nuts & Volts — Print Edition, unlike other magazines, you also get full access to our Digital Edition at no extra charge.
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FIGURE 6. Finally, solder the battery holder wires to the PCB. This is a little unconventional but no big deal, and as can be seen in Figure 7, results in a compact assembly. 22 0 obj<> Some readers prefer a paper copy they can hold in their hands or keep on their bench. Simulation is performed for various voltages between 220 r.m.s to 440v. If you have an adjustable temperature soldering iron, don’t turn it up beyond 600°F. endobj Since the actual voltage reference IC is surface mount, this pretty much dictated that everything be soldered on the component side of the board. Mechanical stress on the die inside the X60008 package can cause a voltage shift in the reference voltage. This photo shows the 9V battery and holder supporting the PCB. This means that the series-limiting resistor shown in Figure 1 must be sized to guarantee that this current will, indeed, flow. So far, accuracy has been stated as a percentage of the nominal voltage with no additional qualifying conditions. You may be asking, what is the advantage of using a zener if an accurate supply voltage and a precision resistor are needed to get the precise desired current flowing through the device? I purposely left off the four PCB pads associated with the unused IC leads; this minimizes the number of leads that need to be soldered, which lowers the amount of thermal stress that the die is exposed to. It is stressful to the IC die to have one lead at an elevated temperature and other leads at a lower temperature. Schematic of the battery-powered, .01% accurate, 5.000V reference. FIGURE 7. endobj 8 0 obj<> These manufacturers also have application notes available that delve into the details of voltage references and will help insure that you have the knowledge to apply them properly.
After all the components are in place and their leads cut off flush with the bottom of the board, insert the two leads of the battery holder through the holes in the PCB. FIGURE 4. 3- put the probes as the figure to close the circuit. �x&�s��p��Q`b@!���@7�H���|sNz����{�J� ��C����`�7{ʒa�PS���H3cuǎ�X� ��Ι����Έl�řad���2:;!��I3�������X�Q����B� � /iqǂk/��Ϋ�{7GK?�=1�L�?vI(9�X��/��0��MĀ���R��1�e���8���5c�LlY}x�&"z��6�x�m*�4.�9�Ț��'N�����"-��x�=]�DP;NE���P $�YHZ8�[ub�8�/��(�*��\���ow�({'��!����I ��*d�k_�u٬������I��gYV��590 ���!vOH^@ӻS9Ve_rF3�T��������;���O�",eK3�HjA�8���Ԏ��s&B ��u�>���Y�4�D?��x�9���������1�S�_�%��~$�q��x���2����w�WrJ���{�h����)ISE,~��X�0�t�0d����� �,p��%zf�G�X(���!BQ̴�o�m��)�)��k�7;��
If you aren’t confident in your soldering ability, you may want to have someone help you who is more skilled. Note that the value of R1 will be different if anything other than a high impedance is placed across the zener.
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