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. Here is the LM338 Adjustable DC power supply circuit, 1.2V to 30V. It can provide a current maximum to 5A and 10A. If you have used LM317 or LM350. They are similar, so easy to use with a few components. But LM338 has higher a current than LM317. You can look at a datasheet below more spec.  Table of Contents LM338 Datasheet and PinoutThe LM138/LM238/LM338 are adjustable 3-terminal positive voltage regulators capable of supplying in excess of 5A over a 1.2V to 32V output range. They are exceptionally easy to use and require only 2 resistors to set the output voltage. The careful circuit design has resulted in outstanding load and line regulation comparable to many commercial power supplies. The LM338 or LM138 family is supplied in a standard 3-lead transistor package. LM338 features
Schematic DiagramLook at the Schematic Diagram inside LM338.  It has a lot of transistors, Zener diodes, resistors, and capacitors. We cannot learn all about it. But I think we can do it. LM338 Basic circuit Voltage CalculatorLook at a basic circuit. We use only 2 resistors can set the constant output voltage.  Vout = 1.25V x {1+R2/R1} + Iadj x R2 Some said Iadj is very low current(approx 50uA only). Vout = 1.25V x {1+R2/R1} Which is better? For example: Is it easy? If you have voltages choice with most resistors. In local stores near you. Look at the Resistors list (without calculating):You don’t have a calculator, right or too little time or really slow brain. See below, I have an easy solution. For you (me too) choose the right resistor according to the voltage we need. 1.43V : R1 = 470Ω, R2 = 68Ω For example, you need 20V 5A power supply. You look at 20.00V : R1 = 220Ω, R2 = 3.3K. Read next: Simple transformerless power supply circuit Protection DiodesYou do not want to see this IC damage, right? As it is expensive. Read now to keep it is healthy. In the circuit diagram above. We use the external capacitors with any IC regulator. Sometimes, we need to add the protection diodes to prevent low current parts in the regulator. When these capacitors(like 20uF) discharge. It will have low enough internal series resistance to deliver 20A spikes when shorted. Although this surge is short. But it has enough energy to  Look at n the circuit diagram. We connect the output capacitor(C1) to the regulator. Then, We use D1, D2 1N4002 to absorbs this current spike to protects the regulator circuits. The discharge current depends on 3 factors.
In the LM138. this discharge path is through a large junction. It can tolerate a 25A surge with no problem. This is not true of other types of positive regulators. Note: For output capacitors of 100 uF or less at the output of 15V or less, there is no need to use diodes. The bypass capacitor(C2) on the adjustment terminal can dis- The Discharge occurs when either the input or output is shorted. Internal to the LM138 is a 50X resistor. which limits the peak discharge current. No protection is needed for output voltages of 25V or less and 10 mF capacitance. So, In-the circuit shows an LM138 with protection diodes included for use with outputs greater than 25V and high values of output capacitance. It is easy, right? 1.25V to 30V, 5A Variable power supply using LM338We may have many ways such as: to modify the LM317 Variable Regulator 0-30V 1A. By adding the power transistor MJ2955 in a circuit. As following Adjustable Voltage and current regulator IC power supply . Or You may build the Variable dc regulator 0-30V 5A circuit, as well. But these methods. Rather cumbersome and wasting too much money. However, we can build this circuit easily and cheaply, By using the packages IC No. LM338 only one, Similar to the LM317 IC number, but it can supply up to 5A, like the circuit shown in Fig. How this circuit worksThe transformer T1 converts the AC 220V to 24 Vac, so be rectified the current by the bridge diode rectifier BD1 – 10A 400V. Until DCV has come out that the filter capacitor C1 is equal to 35 volts. The IC1 is the heart of the operation of this circuit. By the voltage output value obtained from the IC depends on the voltage value at the Adj pin of IC1, or can be varied by adjusting the VR1. However, the output voltage will be approximately equal to 1.25+1.25VR1/R1  Parts you will needIC1: LM338K, LM338P The BuildingYou must solder all devices in the PCB to completely, for the IC LM338K should install with a large heat sink. and all device has the poles. Caution connected the correct, especially electrolytic capacitor.  Figure 2 The PCB layout and components layout
Related: Dual 15V Power Supply Schematic With PCB, +15V -15V 1A 1-20V, 10A Adjustable DC Power Supply1.2V-20V 10A adjustable dc power supply using LM338 If you want Variable Regulated Power Supply high current more than 10A up. I would recommend this circuit. Because build easy, use LM338 and LM107 again. The normal LM338 has the current about 5A. Then, must use 2 pcs. It causes more current up to 10A. The VR1 adjusts an output voltage of 1.2V to 20V to cover usual usability. This idea can protect all errors with two LM338.  See other LM338 circuitsI want you to get the most out. The LM338 is very usable. Because we can use it in many circuits as follows. Of course, we would like to focus on simple circuits as the main. 0 to 22V Adjustable voltage regulatorHow to start the output voltage at “zero”. In normal it will begin at 1.2V. But we can use other negative voltage to offset this voltage to the zero. We use the LM113 Zener regulator IC, 1.2V.  Recommended: 0-30V dual regulator using LM317 and LM337 Precision Current LimiterThis is a simple constant current regulator. It will limit the output current by adjusting R1. Iout = Vref / R1  5A current Regulator circuitThe current will get a constant current of 5A. We use only one resistor to control the output current. R1 = 0.24 ohms at 2 watts. We need to use the right power of Resistor, too.  Adjustable Current Regulator circuitIf you want to adjust the output current. We adjust R2 to set the current from 0A to 5A. This circuit uses LM117 to set the current at Adj of LM338. Check out these related articles, too:
If you want to see examples of projects. Using LM338 to multiple connections in parallel. To boost the higher current. Learn next: 0-30V 20A High current power supply Project using LM338 Sharing is caring! Related PostsGET UPDATE VIA EMAILI always try to make Electronics Learning Easy. Thank you!You have successfully joined our subscriber list. |
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