Increasing the supply voltage of the output stages of transmitters. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / RF power amplifiers
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When building radio transmitters with low-voltage autonomous power supply (radio intercoms, burglar alarm transmitters, etc.), developers are forced to use expensive and, as a rule, extremely scarce low-voltage transistors (for example, KT925.KT927) to provide the required power indicators of the output stages.
Attempts to achieve the required power through the use of available high-power transistors such as KT904, KT907 do not give the desired result, since the latter must be used at higher supply voltages (20-24 V).
The proposed method allows using the available element base to build a simple and stable transmitter with the required power performance. This is ensured by increasing the supply voltage through the use of a capacitive doubler.
The above diagram of a typical FM transmitter for the 27 MHz band with the proposed supply voltage doubler is quite simple and does not require explanation. We only note that with the indicated ratings of capacities C 12 and C 13, the current consumed by the transmitter can be 0,2-0,3 A at a supply voltage of 20 V.
The no-load current of the converter is determined by the frequency of the multivibrator (DD1.1, DD1.2), the values of the elements R8C10, R9C11 and is 5-10 mA.
If it is necessary to use the transmitter in low power mode (with a supply voltage of 12 V), the converter is turned off by applying a low level to pin 2 of DD 1.1.
Author: Sh. Mnatsakanyan; Publication: N. Bolshakov, rf.atnn.ru
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