LM138/LM338
5-Amp Adjustable Regulators
General Description
The LM138ries of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 5A over a 1.2V to 32V output range.They are exceptionally easy to u and require only 2resistors to t the output voltage.Careful circuit design has resulted in outstanding load and line regulation —comparable to many commercial power supplies.The LM138family is supplied in a standard 3-lead transistor package.
A unique feature of the LM138family is time-dependent cur-rent limiting.The current limit circuitry allows peak currents of up to 12A to be drawn from the regulator for short periods of time.This allows the LM138to be ud with heavy tran-sient loads and speeds start-up under full-load conditions.Under sustained loading conditions,the current limit de-creas to a safe value protecting the regulator.Also in-cluded on the chip are thermal overload protection and safe area protection for the power transistor.Overload protection remains functional even if the adjustment pin is accidentally disconnected.
深圳桔钓沙
Normally,no capacitors are needed unless the device is situ-ated more than 6inches from the input filter capacitors in which ca an input bypass is needed.An output capacitor can be added to improv
e transient respon,while bypass-ing the adjustment pin will increa the regulator’s ripple re-jection.
Besides replacing fixed regulators or discrete designs,the LM138is uful in a wide variety of other applications.Since the regulator is “floating”and es only the input-to-output differential voltage,supplies of veral hundred volts can be regulated as long as the maximum input to output differential is not ,do not short-circuit output to ground.The part numbers in the LM138ries which have a K suffix are packaged in a standard Steel TO-3package,while tho with a T suffix are packaged in a TO-220plastic package.The LM138is rated for −55˚C ≤T J ≤+150˚C,and the LM338is rated for 0˚C ≤T J ≤+125˚C.
Features
n Guaranteed 7A peak output current n Guaranteed 5A output current n Adjustable output down to 1.2V n Guaranteed thermal regulation
n Current limit constant with temperature n P +Product Enhancement tested n
Output is short-circuit protected
Applications
n Adjustable power supplies n Constant current regulators n Battery chargers
Connection Diagrams
(See Physical Dimension ction for further information)
(TO-3STEEL)Metal Can Package
DS009060-30
Bottom View
Order Number LM138K STEEL or LM338K STEEL
See NS Package Number K02A
(TO-220)Plastic Package
DS009060-31
Front View
Order Number LM338T See NS Package Number T03B
May 1998
LM138/LM3385-Amp Adjustable Regulators
©1999National Semiconductor Corporation
查询LM338K供应商笋干炒腊肉
Absolute Maximum Ratings(Note1)
If Military/Aerospace specified devices are required, plea contact the National Semiconductor Sales Office/ Distributors for availability and specifications.
(Note4)
Power Dissipation Internally limited Input/Output Voltage Differential+40V,−0.3V Storage Temperature−65˚C to+150˚C Lead Temperature
Metal Package(Soldering,10conds)
Plastic Package(Soldering,4conds)
300˚C
260˚C ESD Tolerance TBD Operating Temperature Range
LM138−55˚C≤T J≤+150˚C LM3380˚C≤T J≤+125˚C
Electrical Characteristics
Specifications with standard type face are for T J=25˚C,and tho with boldface type apply over full Operating Tempera-ture Range.Unless otherwi specified,V IN−V OUT=5V;and I OUT=10mA.(Note2)
Symbol Parameter Conditions LM138Units
Min Typ Max
V REF Reference Voltage3V≤(V IN−V OUT)≤35V, 1.19 1.24 1.29V
10mA≤I OUT≤5A,P≤50W
V RLINE Line Regulation3V≤(V IN−V OUT)≤35V(Note3)0.0050.01%/V
0.020.04%/V V RLOAD Load Regulation10mA≤I OUT≤5A(Note3)0.10.3%
0.30.6%
Thermal Regulation20ms Pul0.0020.01%/W I ADJ Adjustment Pin Current45100µA ∆I ADJ Adjustment Pin Current Change10mA≤I OUT≤5A,0.25µA
3V≤(V IN−V OUT)≤35V
∆V R/T Temperature Stability T MIN≤T J≤T MAX1% I LOAD(Min)Minimum Load Current V IN−V OUT=35V 3.55mA I CL Current Limit V IN−V OUT≤10V
DC58A
挥舞的近义词0.5ms Peak712A
V IN−V OUT=30V11A V N RMS Output Noi,%of V OUT10Hz≤f≤10kHz0.003
属猪和属狗相配吗%
Electrical Characteristics(Continued)
Symbol Parameter Conditions LM338Units
Min Typ Max
∆V R/T Temperature Stability T MIN≤T J≤T MAX1% I LOAD(Min)Minimum Load Current V IN−V OUT=35V 3.510mA I CL Current Limit V IN−V OUT≤10V
DC58A
0.5ms Peak712A
V IN−V OUT=30V1A V N RMS Output Noi,%of V OUT10Hz≤f≤10kHz0.003%糯米的功效与作用禁忌
Typical Performance Characteristics
(Continued)
确认英文
Application Hints
In operation,the LM138develops a nominal 1.25V reference voltage,V REF ,between the output and adjustment terminal.The reference voltage is impresd across program resistor R1and,since the voltage is constant,a constant current I 1then flows through the output t resistor R2,giving an out-put voltage of
Temperature Stability
DS009060-38
Output Impedance
DS009060-39
Minimum Operating Current
DS009060-40
Ripple Rejection DS009060-41Ripple Rejection DS009060-42
Ripple Rejection
DS009060-43
Line Transient Respon DS009060-44Load Transient Respon
DS009060-45
4
Application Hints
(Continued)
Since the 50µA current from the adjustment terminal repre-nts an error term,the LM138was designed to minimize I ADJ and make it very constant with line and load changes.To do this,all quiescent operating current is returned to the output establishing a minimum load current requirement.If there is insufficient load on the output,the output will ri.External Capacitors拘谨的反义词
An input bypass capacitor is recommended.A 0.1µF disc or 1µF solid tantalum on the input is suitable input bypassing for almost all applications.The device is more nsitive to the abnce of input bypassiing when adjustment or output capacitors are ud but the above values will eliminate the possiblity of problems.
The adjustment terminal can be bypasd to ground on the LM138to improve ripple rejection.This bypass capacitor prevents ripple from being amplified as the output voltage is incread.With a 10µF bypass capacitor 75dB ripple rejec-tion is obtainable at any output level.Increas over 20µF do not appreciably improve the ripple rejection at frequen-cies above 120Hz.If the bypass capacitor is ud,it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current paths and damaging the device.
In general,the best type of capacitors to u are solid tanta-lum.Solid tantalum capacitors have low i
mpedance even at high frequencies.Depending upon capacitor construction,it takes about 25µF in aluminum electrolytic to equal 1µF solid tantalum at high frequencies.Ceramic capacitors are also good at high frequencies;but some types have a large decrea in capacitance at frequencies around 0.5MHz.For this reason,0.01µF disc may em to work better than a 0.1µF disc as a bypass.
Although the LM138is stable with no output capacitors,like any feedback circuit,certain values of external capacitance can cau excessive ringing.This occurs with values be-tween 500pF and 5000pF.A 1µF solid tantalum (or 25µF aluminum electrolytic)on the output swamps this effect and insures stability.
Load Regulation
The LM138is capable of providing extremely good load regulation but a few precautions are needed to obtain maxi-mum performance.The current t resistor connected be-tween the adjustment terminal and the output terminal (usu-ally 240Ω)should be tied directly to the output of the regulator (ca)rather than near the load.This eliminates line drops from appearing effectively in ries with the refer-ence and degrading regulation.For example,a 15V regula-tor with 0.05Ωresistance between the regulator and load will have a load regulation due to line resistance of 0.05Ωx I L .If the t resist
or is connected near the load the effective line resistance will be 0.05Ω(1+R2/R1)or in this ca,11.5times wor.邀请函英语
Figure 2shows the effect of resistance between the regula-tor and 240Ωt resistor.
With the TO-3package,it is easy to minimize the resistance from the ca to the t resistor,by using 2parate leads to the ca.The ground of R2can be returned near the ground of the load to provide remote ground nsing and improve load regulation.
Protection Diodes
When external capacitors are ud with any IC regulator it is sometimes necessary to add protection diodes to prevent the capacitors from discharging through low current points into the regulator.Most 20µF capacitors have low enough internal ries resistance to deliver 20A spikes when shorted.Although the surge is short,there is enough energy to damage parts of the IC.
When an output capacitor is connected to a regulator and the input is shorted,the output capacitor will discharge into the output of the regulator.The discharge current depends on the value of the capacitor,the output voltage of the regu-lator,and the rate of decrea of V IN .In the LM138this dis-c
harge path is through a large junction that is able to sustain 25A surge with no problem.This is not true of other types of positive regulators.For output capacitors of 100µF or less at output of 15V or less,there is no need to u diodes.
The bypass capacitor on the adjustment terminal can dis-charge through a low current junction.Discharge occurs when either the input or output is shorted.Internal to the LM138is a 50Ωresistor which limits the peak discharge cur-rent.No protection is needed for output voltages of 25V or less and 10µF capacitance.Figure 3shows an LM138with protection diodes included for u with outputs greater than 25V and high values of output capacitance.
DS009060-6
FIGURE 1.
DS009060-7
FIGURE 2.Regulator with Line Resistance in Output Lead
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