INSTRUCTION MANUAL
PFE500F
Series
TDK-Lambda
<Page>
●
Selection Method of External Resistor
(1) Calculating Resistance Value for External Resistor
Resistance can be calculated by the formula below.
(Formula 1-2)
R : Resistance Value for External resistor
Vin : Input Voltage converted to DC value
=Input Votlage (rms) x
2
Irush : Input surge current value
(2) Required Surge Current Rating
Sufficient surge current withstand capability is required for external resistor.
Required Surge Current Rating can be selected by I
2
t. (Current squared multiplied by time)
(Formula 1-3)
I
2
t : Current-squared multiplied by time
Co : Boost Voltage Bulk Capacitance
Vin : Input Voltage converted to DC value
=Input Voltage (rms) x
2
R : Resistance Value for External Resistor
2. Output Voltage Adjustment Range (TRIM terminal)
Output voltage can be adjusted within the range below by connecting fixed and variable resistors or applying
external voltage.
However, take care not to exceed the output voltage range shown below because OVP function will activate.
In the PFE1000F Series, be careful not to drop from the following range, because a Low Voltage Protection
(LVP) function will be activate.
Output Voltage Adjustment Range : +/-20% of the typical voltage rating
When increasing or decreasing output voltage, it must not exceed maximum output current and power.
Even if the output voltage is adjusted using external circuit shown in Fig. 2-1, remote sensing can be done.
For details on Remote Sensing function, refer to “9. Remote Sensing”.
Output Voltage Adjustment using Fixed and Variable Resistors
External resistor (R1) and variable resistor (VR) values, as well as, circuit connection is shown below.
For this case, remote programming of the output voltage can be done through the remote programming resistor
VR.
Be sure to connect the remote programming resistor bS and +V terminals.
External Resistor : Tol/-5% or less
Variable Resistor : Total Tol/-20% or less
Remain Resistance 1% or less
11/21
R=
Vin
Irush
(
W
)
I
2
t=
Co
×
Vin
2
2
×
R
(A
2
s)
R1
VR
Table 2-1 External Resistor and Variable Resistor Value
(For +/-20% Output Adjustment)
18k
12V
10k
18k
28V
20k
18k
48V
50k
unit
：
[
W
]
√
√
