General circuit description

STEVAL-ISA006V1

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General circuit description

The output of the converter is not isolated from the input. For this reason the reference ground

is common for an input and output connection terminal. The input capacitor C1 is charged from

the mains by single rectification consisting of diodes D1 and D2. Two diodes in series are used

for EMI reasons to sustain burst pulses of 2kV. Capacitor C1 together with capacitor C2 and

inductor L1 form an EMI filter. The DC voltage at C2 is then applied to the transformer primary

winding through the internal Power MOSFET switch of VIPer12 during the switching period ON

time. The snubber circuit consisting of resistor R3 and capacitor C6 reduces the voltage spike

across the transformer primary winding due to the parasitic leakage inductance. Through

rectifiers D4 and D5 and through smoothing capacitors C3 and C4, the power supply provides

two outputs from two transformer windings. The VIPer12AS is supplied by a 15V output voltage

through transistor Q2 and diode D7. The voltage feedback loop senses the 5V output through

resistor divider R5, R7. The control IC U2 compares the resistor divider output voltage to the

internal reference voltage of 2.5V and changes the cathode voltage accordingly to keep 5V

output stable. The FB pin current will decrease the peak primary current to reduce the power

delivered to the outputs.