Turning on transistors in a chain. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Radio amateur designer
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Many transistors are designed for maximum collector voltages up to 30-50 V, and if necessary, to have a transistor amplifier with an output voltage amplitude of about 300 V, you can use the circuit for switching transistors in a chain, as shown in the figure.
The current flowing into the base circuit of the input transistor T1 flows through the resistor R11 and causes an increase in the voltage drop across the resistor RL. At the same time, the voltage drop across each of the transistors connected in series decreases. This causes an increase in current in the base circuits of all transistors.
Resistors R12 - R21 are calculated in such a way that the base currents of all transistors are always equal. In this case, the following equation will be valid for the output collector current: IL=(Bn)Ib.in,
where IL - current through the resistor R1; B is the current gain of an individual transistor; n is the number of transistors in the chain; Ib.in - base current of the input stage (T1).
If the input base current T1 stops, then each transistor goes into the off state and the voltage drop on the voltage divider chain in the base circuits equalizes. As a result, the circuit shown in the figure is equivalent to a single transistor circuit with parameters:
U'k.max=n*Uk.max;
B'=(Bn)
In this example, 10 transistors are taken with Uk.max=35V and V=60. Without the feedback resistor R11, which serves to stabilize the mode, the circuit is equivalent to a single-transistor circuit with U'k.max=350 V and B'=50.
At the given values, the gain of the circuit is 10, the maximum amplitude of the output voltage is 300 V.
Literature
- Radio und Fernsehen, 1965, No. 10.
Publication: N. Bolshakov, rf.atnn.ru
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