Transistor Red Saturable-Core Oscillator

TM 11-6665-209-40

d. High Voltage Power Supply Circuits. The high-voltage power supply circuits con-

sist of a transistorized, saturable-core, square wave "oscillator"; a half-wave doubler rec-

tifier; a "filter circuit" and a regulator circuit. (Fig. 1-3)

(1) Transistor Red Saturable-Core Oscillator.

(a) Nine volts DC is supplied by BT101 (which consists of six type BA-30, 1.5

volt dry cells in series) to the transistor regulator circuit consisting of Q103 a n d

Q104, the action of which will be described in paragraph (2) below. The

regulator output supplies the transistor oscillator. When range switch S102 is

turned to the ON position, this voltage is applied through T101 and Q101 a n d

Q102. Because of the small differences between Q101 and Q102 the forward

bias supplied by R103 favors one transistor. For example, assume it to be tran-

sistor Q101. This transistor thus passes more current than Q102 causing the

dot end of winding "A" to become more negative with respect to its center-tap.

(b) Because of transformer action, the dot end of winding "B" also becomes

more negative than its center-tap, increasing the forward bias of Q101 and

bringing it further into conduction. Action is cumulative and Q101 is thus rapidiy

switched into full conduction. When this occurs the full voltage is applied across

winding "A" causing a magnetizing current to flow which is a function of the

inductance of this winding and time. An induced voltage is presented in the

other windings of the transformer. When the current flowing in winding "A"

cannot produce more flux due to saturation of the transformer core, the voltage

induced in winding "B" (and in the secondary winding) begins to fall off. This

reduction of base drive to Q101 lowers its conduction and thus reduces the

current through winding "A". Decreasing current causes a collapsing magnetic

field which induces a voltage of opposite polarity in winding "B" (and in all

other windings). The dot end of winding "B" thus becomes more positive lower-

ing the conduction of Q101, while the terminal 6 end becomes more negative

and brings Q102 into conduction. This is again a cumulative action, and, as

before, switching occurs rapidly. Circuit actions are repetitive, and the core

saturation time is the total time taken to go from positive core saturation

through zero into negative core saturation, or vice versa. The resultant

waveshape is very nearly a square, the degree of vertical rise and fail times be-

ing limited by the transistor characteristics and transformer loading.

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