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# The 60.0 Amp LM2940CT-9 9.0V Voltage Regulator Schematic

2017-11-29 19:38
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This is a practical application of the circuit just given. R1 should be a 6-Watt Resistor that is mountable on a heat sink. TheTIP142APNP Power Transistor is rated at 10.0 Amps, 100V. When the current draw across R1 (10 Ohms) reaches 500 ma the emitter case bias voltage reaches 5 Volts, this causes the transistor to start conducting. Essentially, the2940 Regulatoronly carries about 500ma of the load current, the remainder (4.5 Amps) is delegated to the power transistor.

To increase the power supply power rating above 6 Amps, you only need to add additional transistors. Should you use additional TIP142A PNP transistors, the power supply regulator capability will increase +6.0 Amps per transistor. You will also have to include a .1 ohm 10-watt resistor in-line with each transistor. This is more of a thermal regulator than an actual power dividing scheme. Naturally, the Power Transformer will also have to be swapped out for a transformer that is capable of supplying the additional current. To determine the fuse rating:.

F1 = Pwr (watts) / Input Voltage (120 VAC) + .4Amps

A 6-Amp 9V Power supply figures out to be 54Watts. Round this up to 60-Watts. Then divide the power (60 Watts) by the input voltage to the transformer (120-Volts). 60 divide by 120 = .4 Amps + 1.5A Inrush Current Reserve. So you need at least a 2.0 Amp fuse (I use a 2.5Amp). To explain: Since the in rush current for the transformer will equal about .9 additional amps, you have added 1.0 Amps, - Then you have reserve instantaneous current capacity, adding another .6Amps. The regulator is designed to easily handle 6.0 Ams (so The normal operation will require 1bout 2.1Amps at 120VAC line current at the power plug).

To increase the amp capacity to 35 Amps, you could use three TIP36C PNP Transistors rated at 100V 25 Amps. Since you want to run your transistors at 50% of their rated continuous power rating (this increases transistor life and regulator reliability) you will be increasing the regulators capacity to 37.5 Amps. Using 0.1 ohm transistors in -line with the transistor emitters, and keeping the Input series resistor R1 for the 2940 regulator at 10 ohms, you will be providing the 500 mA turn on trigger to activate the transistors when current draw exceeds 500mA. Don't forget to up size your rectifier bridge. It needs to be rated at 2.5 times the maximum regulator current capacity, and 2X the transformer secondary winding voltage rating.

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