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AndrejkaB
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Добрый день, уважаемые!
Хотел попросить помощи в связи с проблемным прибором Fluke 96 (Series 2)
Устройство не включается - не работает вторичный преобразователь, который формирует напряжения -30В, -5В, +5В
Данный преобразователь запитан напрямую через ключ MOSFET от батареи 4,8V или от 8V, которое идет от другого преобразователя напряжения сети.
При подаче питания слышно что на короткий промежуток преобразователь возбуждается, потом лабораторный БП переходит в режим ограничения тока на уровне 3,3V. Спасибо за подсказки.
Прилагаю схему, а также короткое описание работы на английском.
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This self oscilating flyback converter consists of:
1. Converter-switch
2 - 8. Sense-resistors
9. thyristor switch
10. start-up resistor
11. windings
Separate secondary circuits for -30V, -5V, and +5V
The main regulating component is operational amplifier LM358. This op-amp compares
the produced secondary +5V voltage with reference voltage, produced by zener diode.
If the secondary +5V increases the fault signal generated by the op-amp will produce
a current that causes an extra voltage drop over R2508. Because of this, thyristor
"9" will fire earlier. The switching frequency of the flyback converter increases and
the secondary +5V voltage decreases.
When the ScopeMeter is switched on (RSSLSTN is "active low"), V2544 connects the
inverting input of LM358 to ground. When the ScopeMeter starts up, capacitor C2509
causes the reference voltage and therefore the output voltage, to rise slowly,
limiting the inrush current drawn from the batteries or line voltage.
Undervoltage detection and protection circuit
When the flyback converter is oscillating, capacitor C2532 is charged every period
via R2543 and V2516. During normal operation C2532 is discharged by V2517, which is
driven via R2541, V2511, R2529, and V2509. If, for example, the secondary +5V voltage
cecomes too low, C2532 is not discharged by V2517. this will activate RESPOW signal,
and the power will be switched off completly, preventing further damage of circuits.
R2542, C2531, and diode V2508 will reset C2532 during the startup of the power supply
(the voltage across C2532 will become zero). This is necessary because V2517 cannot
be driven via V2541, just after the Scopemeter is switched on.
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