Short Circuit Condition

When a converter is in current limit mode the output voltages will drop as the

output current demand increases. If the output voltage drops too low, the

magnetically coupled primary side voltages will also drop, thereby shutting

down the PWM controller.

Following a time-out period, the PWM will restart, causing the output voltage to

begin ramping to its appropriate value. If the short-circuit condition persists,

another shutdown cycle will be initiated. This on/off cycling is referred to

as "hiccup" mode. The hiccup cycling reduces the average output current,

thereby preventing internal temperatures from rising to excessive levels. The

UEP is capable of enduring an indefinite short circuit output condition.

Thermal Shutdown

These UEP converters are equipped with Thermal Shutdown Circuitry. If envi-

ronmental conditions cause the internal temperature of the DC/DC converter

rises above the designed operating temperature (typically 118°C case), a

precision temperature sensor will power down the unit. When the internal

temperature decreases below the threshold of the temperature sensor the unit

will self start.

Output Overvoltage Protection

Output voltages are monitored for an overvoltage condition via magnetic

coupling to the primary side. If the output voltage should rise to a level which

could be damaging to the load circuitry, the sensing circuitry will power down

the PWM controller causing the output voltages to decrease. Following a

time-out period the PWM will restart, causing the output voltages to ramp to

their appropriate values. If the fault condition persists, and the output voltage

again climbs to excessive levels, the overvoltage circuitry will initiate another

shutdown cycle. This on/off cycling is referred to as “hiccup” mode.

Temperature Derating Curves for UEP-3.3/4500 Output Models

17.5

15

12.5

10

7.5

5

2.5

0

–40

0

40

45

50

55

60

65

70

75

80

85

90

95

100

Single Output UEP Models

Ultra-High Density, 2" x 1", 1.2-6 Amp,15-30 Watt DC/DC’s

MDC_UEP Models.A02 Page 6 of 11

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Typical Performance Curves