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Solomon e National Semiconductor Corporation Semiconductor Drive, Santa Datahseet, California TWX National does not assume any responsibility for use of any circuitry described; no circuit patent licenses are Implied, and National reserves the right, at lm3305h time without notice, to change said circuitry.

Table of Contents 1. Information is also supplied on heat sink selection and design, power transformer and filter specification, and on various extended use applications for the basic three-terminal and dual tracking regulators. If a system supply already exists and regulation is required at a current range or voltage listed in Figure 1. Make initial selection from Figure 1. If a higher current is required, refer also to Section 7, Applications, for current booster circuits. For small systems using only one regulator or if a system supply does not yet exist, Section 8, Power Supply Design, provides the information necessary to specify transformer output voltage and current, diode characteristics, and filter capacitance.

For applications other than simple three-terminal regulation listed in Section 1. For voltage regulation at other than the voltages listed in Figure 1. Refer to the data sheets on these parts and to the National Semiconductor Linear Applications Handbook. Ordering information is covered in Appendix 2.

Test methods and circuits are covered in Appendix 4. A cross-reference listing the National Semiconductor part number most closely matching other manufacturers’ part numbers is in Appendix 6. In the past, one used bulky, high power regulators or regulators made up of many discrete components to regulate a line which supplied all areas of an electronic system. Unfortunately, the impedance of this line and associated connectors caused voltage drops which varied throughout lm305u system.

Also, any common impedance in the line between chasses or cards could allow unwanted coupling between critical parts of the system. These older systems often required considerable bypassing or decoupling which caused degraded local regulation.

LM305H View Datasheet(PDF) – National ->Texas Instruments

More recently, simple three-terminal regulators supplying one to three amps have been placed on individual cards within a system. These, however, are often larger in capacity and price than is necessary for one-per-card use. If used to supply several cards and fully loaded, some of the same old problems recur.

The newest regulator designs emphasize low-current ranges and small, low-power, three- lead packages. These regulators are available in a variety of positive and negative voltages-at current ranges of mA to 3 A, some in packages as small as the TO plastic small-signal transistor. With this variety to choose from, it is now possible to select the regulator for each application, and reduce cost significantly over competing approaches. All devices with KC package designation are supplied in aluminum TO Some voltage options are rated only to mA.

Adjustable voltage regulators can regulate voltages to infinity- 1. All include short-circuit protection, automatic thermal shutdown, on-chip pass transistors, and internal references. The LM1 27 series are dual tracking regulators with provision for external boost while using the internal circuitry for current limiting in the boosted mode Figure 1. The LM series are essentially a pair of three-terminal regulators, one positive and one negative, while the others are single three-terminal positive or negative regulators.


With the exceptions to be noted, all listed regulators operate simply without the need for external components. Normal catasheet are as indicated in Figure 1. If the regulator is located more than two inches from the supply filter capacitor, a supply bypass capacitor is required to maintain stability much as is the case with op-amps.

This should be an 0. The LM series alone of all the group requires an output capacitor to insure stable operation. With this exception, no output capacitor is required for stability; however, transient response and noise rejection can be improved by adding an output capacitor.

Basic Fixed Voltage Dual Tracking Regulator In addition to datasjeet normal fixed-voltage application, the three-terminal regulators may be used in the following circuits discussed in Section 7: Special applications for the tracking regulators are discussed in Section 7, as follows: High current boosted operation Foldback current limiting Electronic shutdown Positive current dependent simultaneous current limiting 1.

The variable eatasheet are most useful for providing non-standard voltages, switching regulators, or in programmable-voltage high current supplies with foldback current-limiting.

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Fairly complex external circuit Practical with some performance loss Practical with external circuit Complex external circuit Single capacitor Simple external circuit Simple and effective with two resis- tors Uses: No short circuit protection on switching transistor Possible easy with LM Internal not programmable for all three-terminal regulators.

Programmable for LM1 Simple external circuit Practical Self-oscillating or driven modes. Short circuit protection, but must be added for external pass transistor Practical Requires 2 resistors lm305n. Note that accuracy specifications are over the full temperature range, including drift. Near zero to max ratedOU T. Tj, maximum operating junction temperature. Convection is the effective method of heat transfer from case to ambient and heat sink to ambient.

Radiation is important in transferring heat from lk305h fins. Surface emissivity and area. Temperature difference between radiating and adjacent objects or space. A simplified heat transfer circuit for a cased semiconductor and heat sink system is shown in Figure 4. The circuit is valid only if the system is in thermal equilibrium constant heat flow and there are, indeed, single specific temperatures Tj, To, and Tx no temperature distribution in junction, case, or heat sink.

Nevertheless, this is a reasonable approximation of actual performance. Semiconductor-Heat Sink Thermal Circuit Datasheef junction-to-case datadheet resistance 6jc specified in the regulator data sheets depends upon the material and size of the package, die size and dtasheet, and quality of the die bond to the case or lead frame. The heat sink to ambient thermal resistance flsA depends on the quality of the heat sink and dwtasheet ambient conditions. Where the upper curve slope is zero, the limit is the arbitrary power dissipation rating instead of Eqn 4.

Although this protects the device, prolonged operation at such temperatures can adversely effect device reliability see Appendix 5, Reliability. JC must De met. See Section 7, Applications, for boost circuits. The total thermal resistance is that from lm05h to case plus that from case to ambient or sink to ambient neglecting that from daatasheet to sink, which is small.


Insure datadheet no-load Vin max does ml305h exceed the value listed on the data sheets or in the table of Section 2. The LMP is also a possibility as seen from this figure, although a marginal one on the basis of Iout max. If not already elim- inated in step a above, the LMH would also drop out at this time. If extended periods of short circuit operation are expected, calculate “‘ja TOT f rom Eqn 5. Further selection will depend upon hermeticity and mounting re- quirements. This list is only representative.

PO BoxW. Wakefield Lmm305h ‘ All values are typical as given by mfgr. The required S a was determined in Section 5. Even though many heat sinks are commercially available, it is om305h more practical, more daatasheet, or more economical to mount the regulator to chassis, to an aluminum or copper fin, to an aluminum extrusion, or to a custom heat sink.

In such cases, design a simple heat sink. It may be determined from the nomogram of Figure 6. Symmetrical Fin Shapes The procedure for use of pm305h nomogram of Figure 6.

For other conditions, t; must be modified as follows: Horizontal mounting – multiply h c by 0. Horizontal mounting where only one side is effective – multiply 7 by 0. For non-symmetrical fins where the regulator is mounted at the bottom of a vertical fin – multiply T by 0.

LMT operating conditions are: Accordingly, using a fin of 4. Some of the circuits which are practical and useful are described in this section. Pertinent equations are in- cluded rather than providing fixed component values as the circuits are equally applicable to all regulators within a family.

Basic Regulator Connection Normal connections are indicated in Figure 7. Progressively larger values are required of ceramic, solid tantalum and aluminum electrolytic capac- itors because the effective series resistance ESR increases respectively in each type capacitor. The others are stable when operating into a resistive load.

Transient re- sponse of all the regulators is improved when pm305h capacitors are added. To minimize high-frequency noise, an 0. High Current Ln305h with Short Circuit Limit During Output Shorts This current boost circuit takes advantage of the internal current limiting characteristics of the regulator to provide short-circuit current protection for the booster as well.

Some suggested transistors are listed below. Equivalent of Power PNP Transistor The minimum input-to-output voltage differential of the regulator circuit is increased by a diode drop plus the Vri drop. Variable Output Regulator 7. Nstart with an arbitrary value for R. Determine R 2 and R3 from Eqn 7. Variable Output Voltage of 0. A 0- to volt supply can be built using a volt supply and a conventional op-amp.

For higher output voltages, a high-voltage op-amp, such as LIV, is required. N and V dropoutprovided that the amplifier can source the current required to raise Vq to Vo – Vreg- Example: Transistor Q conducts full load current, and therefore requires a power device with adequate heat sink.