Rainbow Electronics MAX13256 - Manual (Page 11)

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MAX13256
36V H-Bridge Transformer
Driver for Isolated Supplies
Output-Voltage Regulation
For many applications, the unregulated output of the
MAX13256 meets the output-voltage tolerances. This
configuration represents the highest efficiency possible
with the device.
For applications requiring a regulated output voltage, Maxim
provides several solutions. In the following examples, assume
a tolerance of Q10% for the input voltage.
When the load currents on the transformer’s secondary
side are low, the output voltage can strongly increase.
If operation under low load currents is expected, output-
voltage limiting should be used to keep the voltage within
the tolerance range of the subsequent circuitry. If the min-
imum output load current is less than approximately 5mA,
connect a zener diode from the output node to ground as
shown in
Figure 6 to limit the output voltage to a safe value.
Example 1: +24V to Isolated, Regulated +3.3V
In Figure 6 , the MAX13256 feeds approximately +4.4V to the
input of an LDO through a TGMR-502V6LF 4:1 transformer
and 4-diode bridge rectifier (see
Figure 3C ). From this, a
MAX604 LDO produces a regulated +3.3V output at up
to 500mA.
Example 2: +24V to Isolated, Regulated +12V
In the circuit of Figure 7 , the MAX13256 feeds approxi-
mately +14.2V through a 1.5:1 transformer and a 4-diode
bridge rectifier (see
Figure 3C ). From this, a MAX1659
LDO produces a regulated +12V output at up to 350mA.
Figure 6. +24V to Isolated, Regulated +3.3V
Figure 7. +24V to Isolated, Regulated +12V
MBRS140 x 4
GND
ST2
ST1
EN
CLK
+24V
TGMR-502V6LF
4:1
+
+3.3V
-
10µF
V DD
10µF
1µF
MAX13256
MAX604
MBRS140 x 4
GND
ST2
ST1
EN
CLK
+24V
1.5:1
+
+12V
-
10µF
V DD
1.0µF
1µF
MAX13256
MAX1659