VIPER53 Ver la hoja de datos (PDF) - STMicroelectronics

Número de pieza

componentes Descripción

Fabricante

VIPER53

OFF LINE PRIMARY SWITCH

STMicroelectronics 

VIPer53DIP / VIPer53SP

Figure 14: Off Line Power Supply With Auxiliary Supply Feedback

F1

AC IN

C1

T1

R1

D1

C2

U1

VIPer73

R3

VDD

OSC

15V

C4

TOVL

R4

DRAIN

COMP SOURCE

R6

1k

R5

C5

C11

10nF

C6

C7

R2

C3

D2

D3

T2

L1

D4

C8 C9

DC OUT

C10

PRIMARY REGULATION CONFIGURATION

EXAMPLE

The schematic on figure 14 delivers a fixed output

voltage by using the internal error amplifier of the

device in a primary feedback configuration. The

primary auxiliary winding provides a voltage to the

VDD pin, and is automatically regulated at 15 V

thanks to the internal error amplifier connected on

this pin. The secondary voltage has to be adjusted

through the turn ratio of the transformer between

auxiliary and secondary.

The error amplifier of the VIPer53 is a

transconductance one: its output is a current

proportional to the difference of voltage between

the VDD pin and the internal trimmed 15 V

reference, i.e. the error voltage. As the

transconductance value is set at a relatively low

value to control the overall loop gain and insure

stability, this current has to be integrated by a

capacitor (C7 in the above schematic). When the

steady state operation is reached, this capacitor

blocks any DC current from the COMP pin and

imposes a nil error voltage. Therefore, the VDD

voltage is accurately regulated to 15 V.

This results in a good load regulation, which

depends only on transformer coupling and output

diodes impedance. The current mode structure

takes care of all incoming voltage changes, thus

providing at the same time an excellent line

regulation.

The switching frequency can be set to any value

through the choice of R3 and C5. This allows to

optimize the efficiency of the converter by adopting

the best compromise between switching losses,

EMI (Lower with low switching frequencies) and

transformer size (Smaller with high switching

frequencies). For an output power of a few watts,

typical switching frequencies are comprised

between 20 kHz and 40 kHz because of the small

size of the transformer. For higher power, 70 kHz

to 130 kHz are generally chosen.

The value of the compensation resistor R5 sets the

dynamic behavior of the converter. It can be

adjusted to provide the best compromise between

stability and recovering time with fast load

changes.

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