A converter using a self-protected switching transistor. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic ballasts. A converter using a "self-protected" switching transistor. Encyclopedia of radio electronics and electrical engineering

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Much more stable characteristics have a converter using "self-protected" switching transistor. On fig. 3.73 shows a converter circuit with collector current protection of the key transistor.

Converter using "self-protected" switching transistor
Rice. 3.73. Converter circuit with collector current protection

The sawtooth voltage from the resistor R3, proportional to the current of the primary winding of the transformer, is applied to the base of the auxiliary transistor VT2. As soon as the voltage across the resistor R3 reaches the opening threshold of the transistor VT2 (about 0,6 V), it will open and limit the base current of the transistor VT1, which will interrupt the process of energy accumulation in the transformer. Maximum current of the primary winding of the transformer

turns out to be little dependent on the parameters of a particular instance of the transistor. Naturally, the current limiting value calculated by formula (2) must be less than the current determined by formula (1) for the worst value of the static current transfer coefficient.

Author: Koryakin-Chernyak S.L.

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