ถ้าหา LM7806 ไม่ได้ ใช้แบบนี้มีพื้นที่ใส่อุปกรณ์เพิ่มก็น่าจะได้ใช่ไหมครับ
Another simpler method is to use a zener diode to raise the ground terminal voltage, then the output is
V = Vzener + 5VThe BZY88/BZX55 series 0.5W zeners come in a range of values between 2.7V and 5.1V giving 7.7-10.1V from the regulator.
The resistor R1 is present to produce enough current to make sure the zener is well on, and many regulators will work fine without it (Iq is enough).
Text-book method shown is with a two-resistor potential divider on the output. Voltage across R1 is 5V, which produces a current of 5/R1 amps. This, plus the regulator's current from the "common" terminal (quiescent current Iq), flows through R2 producing a voltage across R2 of R2(5/R1 + Iq) volts. This voltage across R2 is added to the 5V across R1 to give the raised output voltage.
Formula for the output voltage V is
V = 5 + R2(5/R1 + Iq)which rearranges to
V = 5(1 + R2/R1) + (Iq * R2)
Iq is typically about 4mA (.004A), so if R1 is 240 ohms and R2 is 150 ohms,
V = 5(1 + 150/240) + (.004 * 150) = 8.7V
To minimise the effect of Iq variations between regulators, the divider current needs to be significantly higher than Iq, so R1 should preferably be under 330 ohms.
Check the output with a multimeter, as small changes in Iq from one regulator to another have a significant effect. Or use a 220-ohm preset potentiometer for R2 and adjust as required.
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