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The wiring example of a small transistor power supply comes from the Siemens Wiring
Examples (Schaltbeispiele) from 1970.
It is a textbook, a classic example of the connection of a transistor regulated and
controllable source. The power supply allows setting the output voltage from 0.7V to 8V
and regulating the current limit up to 2A.
Fig.1
The resistor R1 (330Ω) sets the maximum output current to approx. 2A. If in
series with we also add a potentiometer to the resistor R1, which will increase the
resistance R1, we will achieve the possibility set even lower current limits.
We use a potentiometer P (2.5kΩ) to regulate the output voltage from
0.7V to 8V. A BDY39 transistor is required place on a heat sink with a temperature
resistance of less than 2.5 K / Watt. Diodes in bridge it is good to choose the
connection with as little as possible Uf.
It is of course possible to use a classic integrated diode bridge, but integrated
diodes in the bridge they usually have large Uf
Tthe bridge then has an unnecessary power loss and heats up. The diodes must be
dimensioned for current over 2A.
The transformer should provide at full load the output, secondary voltage min. 7V.
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