sr086 Supertex, Inc., sr086 Datasheet - Page 6

• Manufacturer Part Number: sr086
• Description: Adjustable Off-line Inductorless Switching Regulator
• Manufacturer: Supertex, Inc.

Line Transformer
During initial testing it is tempting to use an isolation
transformer or a variable transformer on the AC line. However,
the high inductance of the transformer (frequently in the
mH’s) interferes with the normal operation of the SR086 and
should not be used. This is not a concern with the normal
inductance of the AC line or for AC line fi lters.
The SR086 draws current from the AC line in short, high
current pulses. The transformer’s high inductance tends to
limit the current pulse. Furthermore, inductive kickback on
the falling edge of the current pulse can create high voltage
spikes which must be absorbed by the transient protector.
EMI Capacitor
The use of a small-value capacitor from circuit common to
earth ground prevents the SR086 from operating and should
not be employed.
EMI
The SR086 circuit as depicted on Page 1, (Typical Application
Circuit), meets FCC Class B and CISPR 14-1 (household
appliances) requirements for conducted emissions, for
combined loads of less than 20mA (I
Fuse
Although the average current drawn from the AC line is
low, the RMS current is fairly high due to the current being
drawn in short, high-current pulses. Since a fuse is basically
a resistor with a power dissipation given by I
must be sized for the RMS current, not the average current.
For a 1.0W load and 120VAC the RMS current is 700mA
and for a 0.5W load at 230VAC it is 360mA
OUT
+ I
REG
RMS
RMS
).
.
2
R, the fuse
RMS
,
6
Load
Total load on the SR086 is the total load current drawn from
V
V
load is calculated as follows:
I
P
UPS
The SR086 will not operate from uninterruptable power
supplies having a square wave output. This type of output is
usually referred to as ‘modifi ed sine wave’.
LOAD
OUT
OUT
LOAD
, it also includes the current drawn from V
= I
(I
= V
OUT
OUT
OUT
) and, since the linear regulator is supplied from
+ I
(I
REG
OUT
+ I
REG
)
REG
SR086
(I
REG
). Total