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6.11 Auxiliary Bias Power
PFH Series modules have an Auxiliary Bias Supply pin, referenced to Vout(-). This auxiliary bias is internally over-current
protected. It is capable of providing a loosely regulated 12V bias (10V ~ 14V, with 200mA maximum current).
6.12 OPTIONAL Droop Load Share (Parallel Operation)
Droop load sharing scheme is available. The droop load share scheme senses the module's output load current, and then
intentionally lowers the output voltage reference, which then in turns reduces the regulated output voltage as shown in Figure
6-8b.
Use of OR-ing diodes (Schottky diodes or Or-ing FETs) with same forward voltage drops and same temperature rise
characteristics is required. The use of the OR-ing diodes is to prevent any negative current from flowing back into the PFH
module(s).
In steady state and near ideal sharing, each PFH Series module will provide close to 50% of the total load current. Figure 6-
8c depicts two PFH units running at 18A load, and then one of the units is turned off.
The load share accuracy is a function of the module's initial output voltage setting accuracy, load current sensing accuracy,
output wiring impedance differences, and the forward voltage drop difference of the external OR-ing diodes (or OR-ing FETs).
Dual-Packaged Schottky diodes with the same forward voltage drop and temperature characteristics will help improve the
load share accuracy.
When using droop current sharing, the RS (+) needs to be connected for local sense mode, i.e. to Vo (+) pins.
Since PFH Series modules feature hiccup OCP protection scheme, in a multiple module parallel system, start-up load
current must be the same or less than one PFH module's maximum rated current to avoid start-up problems.
It is recommended that the load is enabled after the output voltage has been established (e.g. use the Power Good feature
to enable the load). Derate load by 10% when operating in parallel.
NOTE: The Auxiliary Bias Power cannot be connected in parallel.
PFH500F-28-1Dx
Unit #1
REV 2.8 (March 30, 2020)
D1
Io1
V
Vo1
o_Load
Load
Fig. 6-8a Droop Load Share Configuration (with OR-ing Diodes)
D2
Io2
PFH500F-28-1Dx
Vo2
Io_tot
TDK-Lambda
PFH500-SERIES
INSTRUCTION MANUAL
Unit #2
21
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