Description
This
regulated power supply can be
adjusted from 3
to 25
volts and is current limited to 2 amps as shown, but may be increased
to 3 amps or more by selecting a smaller current sense resistor (0.3
ohm). The 2N3055 and 2N3053
transistors
should be mounted on suitable heat sinks and the current sense resistor
should be rated at 3 watts or more. Voltage regulation is controlled by
1/2 of a 1558 or 1458 op-amp. The 1458 may be substituted in the
circuit below, but it is recommended the supply voltage to pin 8 be
limited to 30 VDC, which can be accomplished by adding a 6.2 volt zener
or 5.1 K resistor in series with pin 8. The maximum DC supply voltage
for the 1458 and 1558 is 36 and 44 respectively. The power transformer
should be capable of the desired current while maintaining an input
voltage at least 4 volts higher than the desired output, but not
exceeding the maximum supply voltage of the op-amp under minimal load
conditions. The power transformer shown is a
center tapped 25.2 volt AC / 2 amp unit that will provide
regulated outputs of 24 volts at 0.7 amps, 15 volts at 2 amps, or 6 volts at 3 amps. The 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt
position. All components should be available at
Radio Shack with the exception of the 1558 op-amp.
Circuit diagram
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