FUNDAMENTALS
KEEPING IT MORE REGULAR
There's a range of other options with voltage regulators which are worth exploring. - by Daniel Koch
In last month’s FUNdamentals, we presented several ways of deriving a fixed, clean, regulated voltage for your project when the power supply voltage is greater than your circuit requires; and spoke of some reasons why this may be the case. This month, we look at some different methods to regulate the voltage, as well as covering some devices that step the voltage up.
1 Vin
Vout LM294OCT-5-0
0.47µF
GND
+
22µF
MORE ON VOLTAGE REGULATORS Last month we covered the traditional, low-cost regulators that require the supply voltage to be at least 2.5V greater than the output voltage. However, this is not always practical. Take, for example, producing a 5V USB supply from four AA batteries, totalling 6V when new. This would be impossible with a 7805; however, there is another three-pin, fixed regulator that can help us. The LM2940CT-5.0 is a member of a family of regulators referred to as “low-dropout” regulators, meaning that the difference between the input and the output voltage can get quite low before the devices “drop out”. The LM2940CT-5.0 only requires an input 0.5V higher than the output, making them perfect for our scenario above [1]. diyodemag.com
The LM2940CT-5.0 even has the same layout as the 78XX series, with input on the left, ground in the middle, and output on the right (when viewed from the front). The manufacturer’s datasheet for the Texas Instruments product does recommend using both an input and an output capacitor, however. The family of regulators are also of interest to the maker because there is a 3.3V variant, the LM3940. The low dropout regulators are anywhere between three and ten times the price of the 78XX series though – depending on the item chosen, and the supplier – so they are not always ideal if their particular attributes are not essential. ››
Issue 004 October 2017
23