Transistor Basics is a free introductory textbook on transistors and their basic applications. See the editorial for more information.... 
Home Grounded Emitter and Grounded Collector Transistors Testing Transistors Equal Voltage Method  
Search the VIAS Library  Index  
Equal Voltage MethodAuthor: Leonard Krugman The equal voltage method is a quick way of determining the input or output resistance of a system when the equipment is limited. This connection is illustrated in Fig. 418 (A).
Figure 418 (B) illustrates the equal voltage method for measuring a negative resistance. In this case, a calibrated resistor R_{1} having a larger absolute value than that of the negative resistance is connected in series with r_{1}. Again resistor R is adjusted until V = V_{1}, for which R  R_{1} = r_{1}. For example, suppose a pointcontact transistor is operating in its negative resistance region. When a resistor R = 2,000 ohms is placed in series with the input, it brings the circuit into its positive input region (stable operation). When the connection of Fig. 418 (B) is set up, R = 1,225 causes V to equal V_{1}. Then r_{1} = R  R _{1} = 1,225 2,000 = 775 ohms.
Fig. 418. Equivalent voltage method of measuring system input or output resistance. Notice that this latter arrangement requires that R be greater than the absolute value of r_{1}. If the only calibrated resistors available are low in value, the parallel method illustrated in Fig. 418 (C) can be used. The procedure is the same as before except that when V = V_{1}, R is equal to R_{1} and r_{i} in parallel, which in terms of the inputresistance becomes: For the same transistor measured above, if R_{1} = 500 ohms, R is adjusted to 1,408 ohms, at which time V = V_{1}. Then r_{i }= = 775 ohms.


Home Grounded Emitter and Grounded Collector Transistors Testing Transistors Equal Voltage Method 