HA16107P Datasheet, PDF (34/40 Pages) Hitachi Semiconductor – PWM Switching Regulator for High-performance Voltage Mode Control

HA16107P/FP, HA16108P/FP
Application
1. Use of Error Amplifier for Flyback Transformer Primary-Side Control
In this example, the fact that the transformers winding ratio and voltage ratio in Figure 4 are mutually proportional is
made use of in a flyback transformer type AC-DC converter. As fluctuation of output voltage V₂ also appears in IC
power supply voltage V₃, this is divided by a resistance and amplified by an error amplifier. An advantage of this
method is that a photocoupler need not be used, making it possible to configure a power supply with a small number of
parts (this example cannot be applied to a forward transformer).
Commercial AC input
•V₁(input voltage)
Start-up
resistance
N₁
V₃(IC power supply voltage) ^{To switch element}
N₂
Output
V₂(output voltage)
N₃
R₁
R₄
C₁
14
R₂
− ^R3
15
E/O
+ _{Error amp.}
11 _2.5V
Flyback
transformer
R₂
R₁ + R₂
× V₃ =
1
2
Vref
Where
V₃
=
N₃
N₂
×
V₂,
Figure 4 Error Amplifier Peripheral Circuitry Diagram
<Determining External Constants around Error Amplifier>
1. Detrrrmining DC Characteristics
In Figure 4, the relational expression in the box is satisfied, and therefore parameters are determined based on this.
The absolute value of the number of transformer windings is determined based on the equation N₁:N₂:N₃ = V₁:V₂:V₃,
taking primary inductance into consideration.
Next, IC operating voltage V₃ is made around 11V to 18V, taking the UVL voltage into consideration. If V₃ is too
large, the power consumption of the IC will increase, causing heat emission problems. If V₃ is too small, on the
other hand, there will be problems with defective power supply start-up.
2. Determining Error Amplifier Gain vs. Frequency Characteristic
Taking the configuration in Figure 4, the error amplifier gain characteristic with respect to fluctuation of output
voltage V₂ is as shown in Figure 5.
G₁
f₁ f_AC
G_{2 R6 ≠ 0}
R₆ = 0
f₂
f_OSC Frequency f (Hz)
Figure 5 Error Amplifier Characteristic
Rev.4.00 Jun 15, 2005 page 34 of 39