TM 11-6625-2965-14&P
following formula:
g.The output impedance (Zout) should be less than 0,020 ohms.
h.Using formula of Step f, calculate output impedance at frequencies of 50kHz and 500kHz. Values should be less than 0.5 ohm and 3.0 ohms, respectively.
Figure 5-10. Output Impedence, Test Setup
5-40 Temperature Coefficient. Definition: The change in output voltage per degree Centigrade change in the ambient temperature under conditions of constant input ac line voltage, output voltage setting, and load resistance.
5-41 The temperature coefficient of a power supply is measured by placing the power supply in an oven and varying it over any temperature span
within its rating. (Most 
power supplies are rated for operation from 0°C to 55°C. ) The power supply must be allowed to thermally stabilize for a sufficient period of time at each temperature of measurement.
5-42 The temperature coefficient specified is the maximum temperature-dependent output voltage change which will result over any 5°C interval. The differential voltmeter or digital voltmeter used to measure the output voltage change of the
supply should be placed outside the oven and should have a long term stability adequate to insure that its drift will not affect the overall measurement accuracy.
5-43 To check the temperature coefficient, proceed as follows:
a . Connect test setup shown in Figure 5-5.b. Turn CURRENT controls fully clockwise
and adjust front panel VOLTAGE controls until the front panel voltmeter indicates 10Vdc.
c.Insert the power supply into the temper- ature-controlled oven (differential voltmeter and load resistance remain outside oven). Set the temperature to 30°C and aIlow 30 minutes warm- up.
d.Record the differential voltmeter indica-
tion.
e . Raise the temperature to 40°C and allow 30 minutes warm-up.
f. The differential voltmeter indication should change by less than 90mV from indication recorded in Step d.
5-44 Output Stability.
Definition: The change in output voltage for the first eight hours following a 30 minute warm-up period. During the interval of measurement all parameters, such as load resistance, ambient temperature, and input line voltage are held constant.
5-45 This measurement is made by monitoring the output of the power supply on a differential voltmeter or digital voltmeter over the stated measurement interval; a strip chart recorder can be used to provide a permanent record. A thermometer should be placed near the supply to verify that the ambient temperature remains constant during the period of measurement. The supply should be put in a location immune from stray air currents (open doors or windows, air conditioning vents); if pos- sible, the supply should be placed in an oven which is held at a constant temperature. Care must be taken that the measuring instrument has a stability over the eight hour interval which is at least an order of magnitude better than the stability specification of the power supply being meas- ured. Typically, a supply may drift less over the eight hour measurement interval than during the ½ hour warm-up period.
5-46 Stability measurement can be made while the supply is remotely programmed with a fixed wire-wound resistor, thus avoiding accidental changes in the front panel setting due to mechanical vibration or “knob-twiddling. “
