General description
UM0527
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The converter is based on push-pull topology. The PWM controller works in voltage mode.
The power components used for the low voltage side are switches 5 - 8 and a transformer.
The energy recovery circuit includes L1, D1, L2, D2, C1 and R1. It works as both a clamp
and a snubber. Power components on the secondary side are limited to rectifier diodes D3 -
D6 and a small voltage smoothing capacitor. The output voltage is limited with direct control
loop without insulation. An internal soft-start circuit is used to limit the voltage rise rate on
the output of the DC/AC converter. The soft-start circuit is controlled from the microcontroller
by an additional transistor. The PWM controller is powered from the main UPS power supply
section. The output converter voltage range is battery voltage dependent and has been set
to achieve maximum efficiency.
Table 1.
DC/DC specification
DC/DC converter
120 Vac version
230 Vac version
Output voltage
130 – 190 V
250 - 360 V
Output power
450 W
450 W
Efficiency
> 80%
> 80%
Frequency
40 kHz ± 10%
40 kHz ± 10%
PWM controller U1
SG3525
SG3525
Power switches 5 – 8
STP75NF75
STP75NF75
Push-pull transformer T11
EE42
EE42
Rectifiers diodes D1 – D4
STTH803
STTH8R06
