The reference voltage sources, usually built on the parametric principle on the basis of voltage and current, such as a precision Zener diodes, FETs, etc., To ensure stability over temperature and time the output parameter is necessary, that through these elements proceeded a certain operating current. The desired mode is established by means of the ballast resistors and stabilization of the supply current.
Fig. 1
In Fig. 1 shows a diagram of the source of the bipolar reference voltage based on the stabilization of the static resistance of a precision silicon Zener diode VD1 (see Mackinaw L. B. Source reference voltages. - RF patent №2251139, bull. No. 12, 2005). The device covered by the negative feedback through the operational amplifier DA2. A variable resistor R6 sets the desired value of the output positive relative to the common wire voltage. To the negative output voltage is positive (in absolute value) inverting repeater at the shelter DA1 must have a gain, is strictly equal to unity. This is achieved by the variable resistor R2.
Since operational amplifiers DA1, DA2 eat bipolar voltage at the time of turning on the Zener diode VD1 may be included in a direct - diode - direction, and then the polarity of the output voltage of the shoulders of the source will change to the opposite. Diode VD2, flowing from the output of op-amp DA2 only a positive voltage, eliminates the possibility of polarity reversal.
Fig. 2
As shown by the measurements, the sample source has a temperature and time stability, practically corresponding to the characteristics of the Zener diode VD1. With the said scheme bipolar output voltage it was used to power desethylatrazine DACS and ADCS.
In Fig. 2 shows a diagram similar to the operating reference voltage source with the application for use as a standard element of a field effect transistor VT1. It is known that the characteristics mentioned in the scheme of the transistor when the drain current of about 200 μa is thermostable point. The desired value of current is set by selection of the resistor R3. The stability of the output voltage of the source turned out to be almost the same as that of the Zener diode.
The load capacity of both sources does not exceed 20 mA.
Such devices may find application in laboratory practice. The use of more advanced element base (precision Zener, Oh with less drift of the zero-voltage and high gain) will improve the options described sources.
Author: L. Mackinaw, Chernogolovka, Moscow region; Publication: www.radioradar.net