AND8019/D

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3

Regulation

To measure line regulation, hold the load constant and

vary the input over the desired range taking measurements

at convenient intervals. The change in output voltage for a

fixed load, across the range of input voltages is the line

regulation.

Load regulation is measured in a similar manner. The line

is held constant and the output voltage is measured as the

load is varied from minimum to maximum.

Ripple

The scope should be connected as described in the

Measurement Techniques section, and should be ac coupled.

Peak–to–peak ripple is the measurement from the lowest

point to the highest point on the trace. If a peak–to–mean

measurement is desired, set the scope input to ground, move

the trace on top of the center graticule line of the scope, and

then set the scope coupling back to ac. The voltage from the

lowest point on the trace and the highest point on the trace,

to the center graticule line are the peak–to–mean

measurements.

Efficiency

Efficiency is defined as:

The output power is the output voltage multiplied by the

output current. The input power must be read from a quality

wattmeter with a wide bandwidth due to the harmonic

content of the input current waveform. There is no accurate

method of measuring the input power by the use of DVM’s

or oscilloscopes.

Most wattmeters will also measure power factor, line

voltage and line current.

Transient Loads

Rapid changes in the load of a power converter cause the

output voltage to increase or decrease for a short period of

time. If the circuit that will be attached to this converter is

sensitive to small excursions in voltage, it is highly

recommended to test the unit under similar transients. The

following exercise will test the unit for a transient from

250 mA to 1.0 A and from 1.0 A to 250 mA. If the actual load

transient is different, the loads should be modified to reflect

those conditions.

Response to load transients can be observed by causing a

step load change and synching the oscilloscope to this event.

The best way to do this is to replace the switch on the 500 mA

load (10

W resistor) with a FET. An ON Semiconductor

MTD3302 transistor, driven by a pulse generator with a

0 volt to 10 volt pulse will make a simple electronic switch.

Figures 8 and 9 show the transient response to an output load

change of 10% to 100% load.

Observing the output voltage on an oscilloscope during

this event will allow measurement of the level of

perturbation as well as the duration.

Converter Test Data

Parameter

Conditions

Data

Line Regulation

85 V

Load Regulation

0 A

Combined Line/

Load Regulation

85 V

0 A

Output Ripple

Input Power

7.75 watts

7.88 watts

Power Factor

–0.57

–0.49

Efficiency

h = 66%

h = 64%

Troubleshooting

Symptom

Solution

Unit does not

turn on, does not

draw current

1. Assure that ac source and meter are

properly connected by measuring the

voltage at the input connector.

2. Measure the voltage across C2. If it is

not approximately equal to the peak input

voltage, check for wrong or defective

components (R6, R7, D1–D4).

3. Observe voltage at pin 1 of U1. This

voltage needs to exceed 8.5 volts for

unit to start, and remain greater than

7.5 volts for unit to operate. If not in this

range check for shorts, and assure that

pin 5 is greater than 50 volts, otherwise

replace chip.

4. Measure the voltage at pin 2 of U1.

It should measure less than 4.5 volts for

PWM to be active. If it is, and the output

is not switching, the NCP1000 may be

defective.

Unit does not

turn on, draws

excessive current

1. Check for obvious shorts on the board

and remove if found.

2. Disconnect all leads and measure

resistance across C2. If no short is found,

check test setup. If a short is found,

isolate it by removing components and

testing (D1–D4, C2, U1).

not regulate

1. Assure that the input voltage and output

current are in the specified ranges.

2. Measure voltage across C8. It should be

at least twice the output voltage. If not,

check D6, L2 and C8.

3. Check the voltage at pin 2. If it is greater

than 4.5 volts the opto may be shorted,

if 0 the opto may open or C4 may be

shorted.

4. Measure voltage at pin 8 of U3 and

measure voltage drop across R3. If: