L4950

The L4950 has the following features including VERY  LOW  VOLTAGE  DROP  (0.75Vmax);OVER FULL TEMPERATURE RANGE;OUTPUT CURRENT UP TO 500mA;OVERVOLTAGE AND REVERSE VOLTAGE PROTECTIONS;REVERSE VOLTAGE PROTECTION;SHORT CIRCUIT PROTECTION AND THERMAL SHUT-DOWN (with hysteresis);LOW START UP CURRENT.

The L4950  devices are a monolithic integrated circuit in Versawatt package specially designed to provide a stabilized supply voltage for automotive and industrial electronic systems. Thanks to their very low voltage drop, in automotive applications the L4950 devices can work correctly even during the cranking phase, when the battery voltage could fall as low as 6V. Furthermore, they incorporate a complete range of protection circuits against the dangerous overvoltages always present on the battery rail of the car.The block diagram shows the basic structure of the devices:the reference, the error amplifier, the driver, the power PNP, the protection and reset functions.

The internal antisaturation circuit allows a drastic reduction in the current peak which takes place during the start up.Since the purpose of a voltage regulator is to supply and load variations, the open loop gain of the regulators must be very high at low frequencies.This may cause instability as a result of the various poles present in the loop. To avoid this instability dominant pole compensation is used to reduce phase shift due to other poles at the unity gain frequency. The lower the frequency of these others poles at the unity gain frequency. The lower the frequency of these other poles, the greater must be capacitor esed to create the dominant pole for the same DC gain.Where the output transistor is a lateral PNP type there is a pole in the regulation loop at a frequencybtoo low to be compensated by a capacitor which can be integrated. An external compensalion is therefore necessary so a very high value capacitor must be connected from the output to ground.