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Self-made power supply with overload protection circuit

Published on Apr 18 2011 // Protection Circuits

In the cable television system, according to the size, are equipped with varying amounts of power supply to a trunk amplifier or line amplifier provides a 60V AC voltage. However, many rural radio and television stations have adopted a simple power supply fuse protection, this protection method of the large current of several amperes responsive, while over ten amps less able to maintain long-term overload current is not blown. But at this time due to power supply transformer rated power and will be burned, this often happens, this not only caused economic losses also affect the user’s viewing.
  I refer to the relevant information, a trial has overload protection, sound and light alarm function of power supply, add a little cost can effectively solve the burning problem of power supply. Has been used in the project, nearly a hundred units, has never occurred in the power supply overload and burn accidents.
  One circuit. Electrical power supply as shown in diagram see attached. Sample set in the transformer primary circuit. When the cable television system circuit is overloaded, the sampling resistor R10 R11 on the AC voltage rise, the D1, C1 rectifier filter produces a DC voltage, the R2 limit after the optocoupler IC1 the foot of the light-emitting diode is IC1’s follow on-foot. foot potential rise, fed by R3 to the voltage comparator IC3 four feet. feet because the voltage comparator IC3 the inverting input of B, the IC3 potential instant pin down, the R7 is fed to the IC2 (NE555) of feet, at this time constitute a pulse-initiated NE555 monostable circuit.feet usually pick high, when the negative pulse input, IC2 conduction, pin output high voltage, so that transistor V1, V2 turn, led the relay KA action, cut off its contacts J and 220V power transformer primary connection , turn the alarm buzzer and red light, audible alarm signal. At this point, two output sockets to stop power supply 60V AC output voltage, two green signal lights be turned off.
  NE555 temporary state as td = 1.1RTCT, the local RT = 100kO, CT = 100µF, so td = 11 seconds. Then every 11 seconds, IC2 will automatically detect potential feet, until the user troubleshooting. feet high recovery potential before automatic return to normal power supply. As IC3 (LM339) voltage comparator four largest offset voltage of only 2mV, so long as the potentiometer RP determine the reference voltage, its response was very sensitive, and reliable.
  Second, the testing method. OK to install correctly, it will take 220V power supply device, the output power slide resistance termination, the control current meter readings, adjust the potentiometer RP, you can overload the current point needed to produce a protective action.
  If there is no protection action, you should check IC2 foot is in the protection from 0V up to 15V; IC3 foot is in the protection from 15V down to 1V; IC1 foot is in the protection from 0V to rise to 5 ~ 8V, so from the back to front, section examination can detect the problem.

Self-made power supply with overload protection circuit.