Elenco Variable Voltage Power Supply Kit - Manual (Page 11)

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1. AC voltage is supplied to the rectifier stages by the . . .
r A. step up transformer.
r B. step down transformer.
r C. 1 to 1 transformer.
r D. AC to DC transformer.
2. The secondary windings of the transformer are . . .
r A. 90
O out of phase.
r B. 180
O out of phase.
r C. 270
O out of phase.
r D. 320
O out of phase.
3. Diodes allow current to flow . . .
r A. when the anode is more negative than the
cathode.
r B. when the cathode is more positive than the
anode.
r C. in one direction.
r D. when a negative or positive voltage is on the
anode.
4. What circuit is more efficient for rectifying AC to DC?
r A. Hartley oscillator.
r B. Half wave.
r C. Schmitt trigger.
r D. Full wave.
5. The DC voltage is smoothed by using a . . .
r A. half-wave rectification circuit.
r B. small value capacitor with a high voltage value.
r C. Large value capacitor.
r D. 90
O out of phase rectification circuit.
6. An inefficient rectification circuit usually contains . . .
r A. large gaps between cycles.
r B. twice the AC voltage needed.
r C. more diodes.
r D. all of the above.
7. The maximum current that a diode can handle is
determined by . . .
r A. the transformer’s current rating.
r B. the amount of AC ripple.
r C. three times the diode rating.
r D. peak current rating.
8. The LM317 will shut down when . . .
r A. the output voltage is too high.
r B. no current is being drawn.
r C. the junction overheats.
r D. the output voltage drops to 1.25V.
9. The LM317 regulator contains . . .
r A. a pass transistor.
r B. a constant current source.
r C. a differential amplifier.
r D. all of the above.
10. The LM317 is . . .
r A. a positive voltage regulator.
r B. a 6.25V regulator.
r C. a 2.5V regulator.
r D. a negative voltage regulator.
LED Not Lit
1) Check transformer and line cord.
2) Check for 20VDC at the cathode of D1.
3) LED in backwards or defective.
No Output Voltage
1) Check AC voltage across points P1 & P2 or
P2 & P3. It should read about 18VAC.
2) Measure voltage at the output of D1 and D3.
It should read about 20VDC. If not, then
check D1, D3, C1, U1, R2, R3, D7, and D8.
Poor Regulation
1) Check AC ripple at the input of the regulator.
It should be less than 2.5V.
2) If ripple is higher, check diodes D1, D3, and
the filter of capacitor C1.
QUIZ
TROUBLESHOOTING GUIDE
Consult your instructor or contact ELENCO ® if you have any problems. DO NOT contact your place of purchase
as they will not be able to help you.
Copper Side of PC Board