LM196 datasheet(9/14 Pages) NSC

9 / 14 page

Typical Performance Characteristics (Continued)

Load Transient Response

TLH9059 – 9

With no adjustment pin bypass For output volt-

ages other than 5V multiply vertical scale by

VOUT 5

Typical Applications (Continued)

TLH9059 – 10

Regulation can be improved by adding an LM336 reference diode to increase the effective reference

voltage to 375V Load and line regulation are improved by 31 including thermal effects

FIGURE 3 Improving Regulation

TLH9059 – 11

R3 is selected to supply partial load current Therefore a minimum load

must always be maintained to prevent the regulated output from rising un-

controlled R3 must be greater than (VMAX b VOUT)IMIN where VMAX is

worst-case high input voltage and IMIN is the minimum load current R3

must be rated for at least (VIN b VOUT)2 R3 watts Regulator power dissipa-

tion will be reduced by a factor of 2–3 in a typical situation where minimum

load current is 12 full load current Regulator dissipation will peak at

VIN e

(R3)(IOUT)

VOUT

and will be equal to

PMAX e

(R3)(IOUT)2

Assuming (R3)(IOUT) s VMAX b VOUT

A few words of caution (1) R3 power rating must be increased to (VMAX)2

R3 if continuous output shorts are possible (2) Under normal load condi-

tions system power dissipation is not changed but under short circuit condi-

tions

system power dissipation increases by (VIN)2 R3 watts over the al-

ready high power of a shorted regulator The LM196 will not be harmed and

neither will R3 if it is rated properly but the raw supply components must be

able to withstand the overload also Thermal shutdown of the LM196 will

probably occur for sustained shorts somewhat alleviating the problem

FIGURE 4 Reducing Regulator Power Dissipation

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