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How does a shunt regulator work?

Latest Updated:11/01/2007

Question:

Using a film capacitor is recommended as an external capacitor for a 3-terminal regulator. Can any other capacitor be used?

Answer:

Any capacitor can do as long as it has good temperature characteristics and frequency characteristics.
Some capacitors have poor temperature characteristics and frequency characteristics.
Therefore, be careful about the characteristics of the capacitor to be used.

1. Some electrolytic capacitors substantially decrease in capacitance at a low temperature (0 °C or lower).
The specified capacitance must be secured at the temperature at which you use the capacitor.
2. Generally, the capacitance of an electrolytic capacitor is measured at a frequency as low as 100 to 120 Hz. If the frequency rises, the capacitance of some electrolytic capacitors substantially drops.

The 3-terminal regulator oscillates in the vicinity of 1 to 3 MHz.
Therefore, the specified capacitance must be secured at 1 to 3 MHz.
If a capacitor with poor frequency characteristics is used, oscillation must be suppressed
by connecting a capacitor with good high-frequency characteristics in parallel.

Particular caution is required regarding the characteristics of electrolytic capacitors.
In addition, some ceramic capacitors also have poor characteristics. Exercise care in selecting capacitors.
Generally, the characteristics of a tantalum capacitor are stable.
Therefore, use of a tantalum capacitor is recommended in the Data Sheet.
Note that oscillation could also occur when using a capacitor with low ESR (equivalent series resistance) or ESL (equivalent series inductance). It is therefore very important to sufficiently evaluate your system with the capacitor to be used, because the ESR and ESL are affected by temperature and frequency.

Suitable Products
CMOS Operational Amplifiers
Bipolar Operational Amplifiers
3 Terminal Regulators