Datasheet

SLUU087B
6
10-Watt Flyback Converter Using the UCC3809
Peak current mode control responds immediately to line voltage changes and also provides over current
protection to the switching device. A discontinuous current-mode controlled flyback converter does not have a
right half plane zero and does not have the subharmonic-loop instability problems usually seen in the large
duty–ratio continuous–inductor current topologies. Although this converter does have peak-current limit, and
survives a momentary short circuit on the output, an extended short circuit results in power supply failure.
4 UCC3809EVM–052 Operating Instructions
J1
J2
J3
J4
J5
DUT
OUTPUT
VOLTAGE DMM
INPUT
CURRENT DMM
OUTPUT
CURRENT DMM
INPUT POWER
SUPPLY
OUTPUT
ELECTRONIC
LOAD
–
–
–
+
+
+
INPUT
VOLTAGE DMM
+–
+
–
–
+
NOTES: 1. Source power should be able to supply a minimum of 0.5 A at 75 V.
NOTES: 2 Load should be able to sink up to 3 A with adequate power rating. Resistive loads with adequate ratings may be used.
Figure 2. Connection Diagram for the UCC3809EVM–052
1. Connect a dc power supply, capable of supplying up to 75 V at 0.5 A, to terminals J1 and J2. Note
that the positive terminal is connected to J1, the negative terminal is connected to J2. The power
supply should be set to its minimum-output voltage level and current limited to 0.5 A.
2. Connect the load to J3 and J4. This load should be capable of handling 3 A at 3.3 V. The positive
terminal is connected to J3, the negative terminal is connected to J4.
The output load should never exceed 3 A.
Do not short the output terminals, power converter failure results.
3. Turn on the electronic load.
4. Turn on the input power supply. Starting with the input dc power supply at its minimum setting,
slowly increase the voltage to the EVM operating range, 32 V to 75 V. The converter actually
begins regulating when the dc supply is at approximately 24 V.
The input voltage to the EVM should be no greater than 75 V at any time.