Stable current generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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Devices are commonly called stable current generators. whose output current is practically independent of the load resistance. It can be used, for example, in ohmmeters with a linear scale.
On fig. 1 shows a schematic diagram of a stable current generator based on two silicon transistors. The value of the collector current of the transistor V2 is determined by the ratio
Ik=0,66/R2.
Ris.1
For example, with R2 equal to 2,2 k0m. the collector current of the transistor V2 will be equal to 0,3 mA and remains almost constant when the resistance of the resistor Rx changes from 0 to 30 k0m. If necessary, the direct current can be increased to 3 mA, for this the resistance of the resistor R2 must be reduced to 180 ohms.
A further increase in current while maintaining high stability of its value both with a change in load and with an increase in temperature is possible only when using a three-transistor generator shown in Fig. 2. In this case, transistors V2 and V3 should be of medium power, and the voltage of the second power source should be 2 ... 3 times the supply voltage of transistors V1, V2. The resistance of the resistor R3 is calculated using the above formula, but is additionally adjusted to take into account the variation in the characteristics of the transistors.
Ris.2
Transistors BC 108 can be replaced by KT315G. VS107 - KT312B, BD137 - KT602B or KT605B, 2N3055 - KT803A.
Literature
- "Elektrotehnicar", 1976, No. 7-8
Publication: N. Bolshakov, rf.atnn.ru
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