HA17431_15 Datasheet, PDF (16/21 Pages) Renesas Technology Corp – Shunt Regulator

HA17431 Series
In Figure 3, the following formulas are obtained:
Gain
G₁ = G₀ ≈ 50 dB to 60 dB (determined by shunt regulator)
G₂ =
R₅
R₃
Corner frequencies
f₁ = 1/(2π C₁ G₀ R₃)
f₂ = 1/(2π C₁ R₅)
G₀ is the shunt regulator open-loop gain; this is given by the reciprocal of the reference voltage fluctuation
ΔVref/ΔV_KA, and is approximately 50 dB.
3. Practical Example
Consider the example of a photocoupler, with an internal light emitting diode V_F = 1.05 V and I_F = 2.5 mA, power
supply output voltage V₂ = 5 V, and bias resistance R₂ current of approximately 1/5 I_F at 0.5 mA. If the shunt
regulator V_K = 3 V, the following values are found.
R₁ =
5V – 1.05V – 3V
2.5mA + 0.5mA
= 316(Ω) (330Ω from E24 series)
R₂ =
1.05V
0.5mA
= 2.1(kΩ) (2.2kΩ from E24 series)
Next, assume that R₃ = R₄ = 10 kΩ. This gives a 5 V output. If R₅ = 3.3 kΩ and C₁ = 0.022 μF, the following
values are found.
G₂ = 3.3 kΩ / 10 kΩ = 0.33 times (–10 dB)
f₁ = 1 / (2 × π × 0.022 μF × 316 × 10 kΩ) = 2.3 (Hz)
f₂ = 1 / (2 × π × 0.022 μF × 3.3 kΩ) = 2.2 (kHz)
R03DS0086EJ0400 Rev.4.00
Jan 10, 2014
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