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All components should be available at Radio Shack with the exception of the 1558 op-amp. The 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt position. 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 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 maximum DC supply voltage for the 14 is 36 and 44 respectively.
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#Power supply load tester using a 2n3055 transistor series#
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. Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. 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. 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).
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Current Boosting Using a PNP Power Transistor (MJ2955)įigure-1 shows the schematic diagram of the circuit. This problem can be solved using a pass power transistor. Overload protection remains functional even if the ADJUST terminal is disconnected.” This information proves to us that this cheap 3-terminal device is suitable for many applications but it comes with a drawback for power applications and that is the limitation of the regulator’s output current handling (1.5A in the best conditions). It includes current limiting, thermal overload protection, and safe operating area protection. The device features a typical line regulation of 0.01% and a typical load regulation of 0.1%. It requires only two external resistors to set the output voltage.
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In this article, I will discuss two methods of LM317 current boosting, using power PNP and NPN pass transistors.Īccording to the LM317 datasheet: “The LM317 device is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. However, the chip can deliver currents up to 1.5A which is not enough for some power applications. The output voltage of the regulator can be adjusted from 1.25V to 35V. LM317 is one of the most popular adjustable regulator chips.