Linear Regulator made by JACKY CHEN

Technical Review of Linear Regulator Operation & Performance 1.Dropout Voltage 4.Efficiency7.Transient Response 2.Quiescent current & Ground current 5.Load Regulator 8.Frequency Response 3.LDO Topology 6.Line Regulation 9.Range of ESR

1.Dropout Voltage Dropout voltage is the input-to-output voltage difference at which the circuit cease to “regulate” against further reductions in input voltage.

Pinch off Regulation Un-regulation

2.Quiescent Current & Ground Current Quiescent current or ground current is the difference between input and output currents. Quiescent consists of bias current & drive current of pass element. –Bias current Band-gap reference. Sample resistor. Error amplifier.

3.LDO Topology 4 functional blocks.

Darlington The Darlington needs at least 1.6V dropout to regulate.

NPN The base volt of the NPN must always higher than the emitter volt.

PNP The big advantage of PNP is its very little dropout voltage.

PMOS & NMOS MOSFET is voltage controlled device,so,very low quiescent current is obtained.

Summary PNP bipolar good for low dropout application,but it got high quiescent current and low efficiency. NMOS most advantage because of its low on resistance.gate drive difficulties make it less than ideal. PMOS has been highly developed,and now the performance level exceeding most bipolar devices.

4.Efficiency Power dissipation & efficiency :

5.Load Regulation Load regulation is a measure of the circuit ability to maintain the o/p under varying load condition.

Load Regulation Since load regulation is steady-state parameter,all frequency components are neglected. The load regulation is limited by the open loop current gain of the system.

6.Line Regulation Line regulation is a measure of the circuit ability to maintain the o/p under varying line input voltage.

Line Regulation Since line regulation is steady-state parameter,all frequency components are neglected. Increase dc open loop gain increase line regulation.

7.Transient Response Transient response is the maximum allowable o/p volt variation for a load current step change. The transient response is a function of output Cap value(Co),the ESR,the bypass Cap(Cb),and maximum load current Io(max).

8.Frequency Response The essential elements of a linear regulator

The first Pole:Po is The Second Pole:Pb is

In addition,another pole exist from the input impedance Of the pass element,and the o/p impedance of the error Amplifier.Rpar,Cpar.

Summary

9.Range of ESR A LDO needs would require an o/p cap and an o/p ESR to stabilize the control loop. The linear regulator is unstable Because the phase shift at unit gain is –180,to make it stable A zero must be added.

With External Compensation The zero produced by the ESR locates before the UGF,so,the phase shift at UGF will be around –90.