AN827 APPLICATION NOTE

12/20

Pin 13 Vva-out (Error amplifier output)

To ensure system stability, the compensation network must be designed with sufficient phase margin. Addition-

ally, the system must not regulate the twice mains frequency output ripple voltage in order to avoid line current

distortion. The compensation capacitor, C10, can be calculated as follows:

Where:

R9 + R10 are the resistors from the output voltage feedback resistor divider

Ka =

for 50Hz and

for 60Hz mains frequency

, therefore use standard value 220nF

The voltage open loop gain contains two poles at the origin, causing stability problems. This can be avoided by

shifting the error amplifier pole from the origin to near the crossover frequency. This can be accomplished by

placing a resistor, R19, in parallel with the compensation capacitor, C10. The crossover frequency is calculated

as follows:

Use R19 = 120k to increase error amplifier dc gain.

Pin 14 VFEED (Error amplifier input)

This pin is the error amplifier inverting input. This pin is connected to the resistor divider connected across the

boosted output voltage to provide regulation. The boosted output voltage is specified at 400VDC. The resistor

divider network is calculated as follows:

Use R9 = R10 = 412k

Pin 15 P-UVLO (Programmable supply undervoltage threshold)

This pin may be used to modify the turn-on and turn-off power supply thresholds. This circuit does not employ

this feature and the pin is left floating. The typical turn-on threshold is 15.5V and the turn-off threshold is 10V.

Pin 16 SYNC (In/Out synchronization)

This function allows for synchronization in master or slave mode with other circuits in the system. This demo-

board does not use this function and the pin is left floating.

Pin 17 ROSC (Oscillator resistor)

C10

1

4

π f

main s

R9

R10

+

() G

ea

⋅⋅

⋅

⋅

---------------------------------------------------------------------------------

K

a

∆V

out

R9

R10

+

--------------------------

=

>

1

60

------

1

72

------

C

10

1

60

------

8

824k

-------------

162nF

=

⋅

>

f

c

P

out

V

out

∆V

ea

2

π C

out

⋅⋅

⋅

---------------------------------------------------------





1

2

π R9 R10

+

() C10

⋅⋅

----------------------------------------------------------





500

400 3.82 2

π 330πF

⋅⋅

⋅

------------------------------------------------------------





1

2

π 824k 220nF

⋅⋅

-----------------------------------------------





11.77Hz

==

=

R9

R10

+

R20

--------------------------

824k

10.6k

---------------

V

out

V

ref

-----------

1

400

5.1

----------

1

–

=

–

==