SWITCH-MODE POWER SUPPLIES AND SYSTEMS Silesian University of Technology Faculty of Automatic Control, Electronics and Computer Sciences Ryszard Siurek Ph.D., El. Eng. Lecture No 2

Power supply status indications  Optical indication (usually different colour LEDs) - green - normal operation - red-failure (protection circuit activation) - yellow-warning (e.g. mains voltage decay and battery operation) and battery operation)  Contact indication (rely) - contacts closed-normal operation - contacts open-power failure  Power Fail Signal or PF U OUT PF t t tttt UUUU  t > 1ms  U < 5%Uo „1” „0”

 Power Good Signal UUUU U OUT t t PG  U < 5%Uo „0” „1”

Output voltage hold-up time 95% Uo U OUT Uo U IN tp tp – hold-up time (up to several ms) t t

Power Supply protection Overcurrent protection 1.Constatnt current (CC) limiting 2.Power limiting I SC U OUT I OUT power limiting switch-off constant current

3. Output current fold-back 4. Power supply switch-off (fuses 5. Thermal protection nominal working point resistive load non-linear load possible start-up operating point U OUT I OUT I SC

Over-voltage protection U OUT Uo U OUTmax t switch-off UM UM - voltage monitoring circuit U OUT power supply switching-off switch-off regulated voltage level 2 U OUT FS1 FS2 FS – feedback loop (voltage regulation) U OUT typical implementation crowbar type overvoltage protection - activates overload or short-circuit protection circuit

Power leads voltage drop compensation Ro rsrs rsrs +S -S Uo  Us Uo Io Is = 0 Power Supply U1 Feedback circuit controls voltage across +S & -S U1 = Uo + 2  Us

Parallel operation of power supplies Increasing of the the total output power Power Supply # 1 Power Supply #2 I1I1I1I1 I2I2 U0U0 U 01 U 02 U 01 = U 02 ~ I0I0 I0I0 I 1max I 1, I 2 I 1max I1I1 I2I2 2I 1max Power Supply # 1 100% load I 1max = I 2max Parallel connection with non-balanced output currents Overload protection circuit with current (power) limitation is required U 01 > U 02

I1I1I1I1 I2I2I2I2 U0U0 U 01 U 02 U 01 > (<) U 02 (may slightly differ) I0I0 I0I0 I 1max I 1, I 2 I 1max I1I1I1I1 I2I2 2I 1max I 1max = I 2max Parallel connection with current share facility (balanced output currents) CS CS CS - current share Power Supply # 1 (master) forces adequate changes of U O2 to keep I 2 close to the actual value of I 1 additional connection Power Supply # 1 Power Supply # 2

Paralleling of power supplies for redundancy (output voltage security) I1I1 I2I2 U0U0 U 01 U 02 U 01 = U 02 ~ I0I0 I 0 < I 1max, I 2max I 1max = I 2max D1D1 D2D2 U IN1 U IN2 Redundancy Redundancy n + x - „n” modules necessary to supply load current - „x” modules which can fail simultaneously - „x” modules which can fail simultaneously Power Supply # 1 Power Supply # 2