spänningsregulator
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EagleSpirit
- Inlägg: 1288
- Blev medlem: 27 maj 2003, 23:15:48
- Ort: Västerås
- Kontakt:
De ritningar jag har sett så har det varit tantaler. Men det går säkert lika bra med polyester, kanske bättre. Jag tror att det bara är o kika i databladet på den aktuella regulatorn.EagleSpirit skrev:måste det vara tantaler? jag har lärt mig att det ska vara polyester? ja såklartdet funkar men frågan är om kondingarna hjälper något?
Mikael
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matseng
- Inlägg: 2360
- Blev medlem: 16 september 2003, 17:18:13
- Ort: Dubai, United Arab Emirates
- Kontakt:
Här är från databladet för LM350 (justerbar linjär stabb) Tantal eller keramisk, 0.01u eller 1u.... I de flesta fall verkar det väldigt okritiskt särskilt om man inte ska massproducera något som har speciella krav och has snabba förändringar i strömbehovet.
EXTERNAL CAPACITORS
An input bypass capacitor is recommended. A 0.1µF disc or 1µF solid tantalum on the input is suitable input by passing for almost all applications.
The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used by the above values will eliminate the possibility of problems.
In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25µF in aluminium electrolytic to equal 1µF solid tantalum at high frequencies.
Ceramic capacitors are also good at high frequencies, but some types have a large decrease in capacitance at frequencies around 0.5MHz. For this reason, 0.01µF disc may seem to work better than a 0.1µF disc as a bypass.
Although the LM350 is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can cause excessive ringing. This occurs with values between 500pF and 5000pF. A 1µF solid tantalum (or 25µF aluminium electrolytic) on the output swamps this effect and insures stability.
EXTERNAL CAPACITORS
An input bypass capacitor is recommended. A 0.1µF disc or 1µF solid tantalum on the input is suitable input by passing for almost all applications.
The device is more sensitive to the absence of input bypassing when adjustment or output capacitors are used by the above values will eliminate the possibility of problems.
In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25µF in aluminium electrolytic to equal 1µF solid tantalum at high frequencies.
Ceramic capacitors are also good at high frequencies, but some types have a large decrease in capacitance at frequencies around 0.5MHz. For this reason, 0.01µF disc may seem to work better than a 0.1µF disc as a bypass.
Although the LM350 is stable with no output capacitors, like any feedback circuit, certain values of external capacitance can cause excessive ringing. This occurs with values between 500pF and 5000pF. A 1µF solid tantalum (or 25µF aluminium electrolytic) on the output swamps this effect and insures stability.
