Demonstration
board overview
UM2076
10/43
DocID029457 Rev 1
1.
STEVAL-ISF003V1 board (without modifications) with SCRs in the OFF state (SW2
HVDC switch in OFF position) and the J1 bypass mode jumper is unplugged (PTC not
connected).
2.
Same as 1, but the following circuits used for demonstration purposes and which
consume undesired power in standby are disconnected:
HV Capacitor Discharge circuit: R5 and R6 are disconnected from the DC bus
D6 HVDC LED: D1 is disconnected from the DC bus
D14 POWER_ON LED: R44 is disconnected
3.
Same as 2, but the J1 bypass jumper is plugged (PTC connected) to simulate the
losses for a conventional solution using only one PTC (EPCOS B59107J0130A020).
Table 2: "Comparison of standby losses"
gives the experimental results for the above
cases with 230 and 120 V line voltages and a 2-mF HV output capacitor connected to the
demonstration board. The test results clearly show that the mixed SCR/Diode bridge
rectifier is the only solution with power consumption lower than 0.5 W, as currently required
by European directive 2005/32/EC.
The losses on this demonstration board are mainly due to:
resistors R54, R55 and R56 to discharge the HV output capacitor
resistors R7 and R9 and the current source to control HVDC LED indicating HVDC
voltage
resistors R6 and R9 to accelerate the HV output capacitor discharge time connected
to the demonstration board output
the other R24, R25 and R28 resistor divider circuit to sense the HVDC voltage
The HVDC voltage is monitored to ensure proper soft-start operation and avoid the DC
capacitor charging too long (e.g., a load is kept connected to the DC bus before start-up).
In standard circuits, such a voltage sensor is often required (e.g., to start the PFC or the
DC/DC supplies).
The losses for a 230 V rectified voltage are:
140 mW for the discharge circuit
500 mW for the HVDC LED circuit
180 mW for the acceleration circuit to discharge the HV output capacitor connected to
the demonstration board output
52 mW for the HVDC sense.
Table 2: Comparison of standby losses
case
SCR
status
PTC
status
circuits
power consumption (mW)
Power
LED
HVDC
LED
HV capacitor
discharge
circuit
V
AC
=230
V
RMS,
C
HVout
=2 mF
V
AC
=120
V
RMS,
C
HVout
=2 mF
1
OFF
OFF
connected
270
200
2
OFF
OFF
disconnected
200
140
3
OFF
ON
disconnected
500
200
