MR2920 Datasheet, PDF (18/19 Pages) Shindengen Electric Mfg.Co.Ltd – Provision for Standby mode operation Partial Resonance Power Supply IC Module

5.4 Selection of Constants for Peripheral Components
5.4.1 Values of Constants for MR2900 Peripheral Components (see 4. Standard Circuit on P12)
Component
Constant
C107
C108
This is the power supply voltage rectification condenser.
If this value is small operation at start-up readily becomes intermittent, and if it is too large start-up time
becomes excessive.
A value of between 47μF and 100μF is appropriate.
This condenser determines the resonance frequency. Select the value on the basis of noise and efficiency etc.
A value of between 820pF and 2200pF is appropriate for autosensing power supplies of between 75W and
150W capacity.
C109
This condenser is incorporated to deal with noise at pin 2. A value of approximately 4700pF is appropriate.
Also beneficial in gain phase adjustment, however frequency response deteriorates if the value is too large.
C111
This is the partial resonance adjustment condenser. Adjust so that turn-on occurs at the resonance trough.
Turn-on occurs earlier if this value is small, and later if it is large.
A value of between 10pF and 33pF is appropriate.
R102
This is the current limiting damper resistor for C108. A value up to a few ohms is appropriate.
Select the value on the basis of noise and efficiency etc.
R103
This is the over-current detection resistor. It determines the droop point.
Calculate the resistance value as follows.
[0.60 (over-current threshold voltage) / Droop point collector current at minimum input]
R104
Adjust on the basis of droop characteristics. Set to a value slightly higher than the droop point set with R103.
A value of a few tens of kohms is appropriate.
R105
This resistor compensates for droop due to input voltage. Adjust on the basis of droop characteristics.
A value of approximately 50kohms is appropriate.
R106
This resistor limits current at the Z/C pin. A value of approximately 20kohms is appropriate.
D102
D106
This corresponds to the body diode for the main switching device (ultra high-speed IGBT).
Select a high-speed diode in the 900V, 1A class.
This is a Zener diode to compensate for droop due to input voltage.
Select a diode for a Zener voltage at least equal to that found with the following equation.
Zener voltage
= 1.3
×150
×
NC
NP
(assume an initial compensation voltage of 150V)
R105 and D106 are additional components for autosensing input specifications.
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