APPLICATIONNOTES BPC SERIES POWER

APPLICATION
NOTES
BPC SERIES POWER RESISTOR APPLICATIONS
BI Technologies offers the BPC Series of noninductive, planar, thick film, power resistors for
current limiting, power supply circuits and snubber
circuits. Manufactured using 96% alumina substrates
with ruthenium oxide resistors, the BPC Series
power resistors are capable of withstanding a 20X
overload for 8 ms and offer excellent performance
and high reliability. BPC Series power resistors are
available in 3, 5, 7.5 and 10 watt power ratings as
shown below.
Model
Power Rating, Watts
Dimensions, mm
Length
Width
Thickness
Range
Standard Tolerance
Operating Temperature Range
Operating Voltage, Maximum
Temperature Coefficient of Resistance
BPC3
3
BPC5
5
BPC7
7
BPC10
10
27.7
10.2
2.54
27.7
12.7
2.54
27.7
19.1
2.54
27.7
25.4
2.54
3 to 200 KΩ
200 mΩ to 200 KΩ
±10% (Standard), ±1%, ±2%, ±5% (Optional)
-55°C to +125°C
300 Vac, 500 Vdc
±100 ppm/°C, Max.
±250 ppm/°C for values below 1Ω
WHY USE BI TECHNOLOGIES BPC SERIES
POWER RESISTORS
• Vertical mounting means power is dissipated above
board level – enhancing board cooling due to
natural convection flow
• Planar thick film cermet resistor offers very low
inductance for high frequency operation
• 20X rated power surge capability
• Small footprint requires only 1/3 of the board area
used by a typical wirewound resistor
• Low operating temperature at board surface means
high temperature solder is not required
• Large surface area to thickness ratio – maximizes
power dissipation, minimizes hot spots
5-16
INRUSH CURRENT SUPPRESSION
The BPC may be used to limit inrush current when a
power supply is switched on. In Figure 1 is a typical
PFC circuit in which two BPC 10 resistors in series
function as inrush current suppression circuit which
operates principally at switch-on
BPC 10
BPC 10
5Ω
5Ω
C T HM31
Vo
400 VDC
EMI Filter
L1
HM00
CT
HM31
+
Load
Co
AC Line
5
Gate
Driver
PFC PWM
FIGURE 1. Typical PFC Circuit
SNUBBER CIRCUIT
STARTUP CIRCUIT
EMI Filter
The BPC may be used in series with a capacitor in a
snubber circuit to filter spikes in the rising and falling
edges of square waves. In Figure 2 a 500Ω BPC 3 is
used.
Figure 2 also includes a startup circuit that provides
18 volts to the PWM while the power supply is
turning on. In this case, a 50KΩ BPC 5 is utilized.
BPC 3
500Ω
BPC 5
50KΩ
To Output
Circuitry
AC Line
18V
+
PWM
47µF
FIGURE 2. Typical startup and snubber circuits
5-17
APPLICATION
NOTES
INRUSH CURRENT LIMITING
This resistor limits the amount of current allowed to
surge into the system at turn-on. Power resistors in
this circuit must be able to withstand a 20 X nominal
surge for 8 ms. This is typically a 15Ω, 7 to 10 watt,
10% resistor. A typical location of this resistor is
shown in Figure 3. This resistor carries the main
current load.
*
+
+
AC Input
DC
Circuitry
*
EMI/RFI Filter
* Other Power
Resistors
Inrush Power
Resistor
BPC 7, BPC 10
FIGURE 3. Circuit showing a BPC resistor in an inrush application
OTHER SNUBBER CIRCUITS
In these applications the power resistor bleeds the
current of the magnetics to prevent inductive spikes.
This resistor will experience voltage spikes at 2 X the
switchmode switching frequency. This is typically a
500 Ω to 1K Ω, 3 watt to 5 watt, 2% to 5% resistor.
Circuit configurations are found in Figure 4.
1,000 pF
1,000 Vdc
Ceramic
L101
FBL-00-103
FBL-00-103
BPC 5
500 Ω
5%, 5W
Snubber Circuit 1
BPC 3
1K Ω
2%, 3W
FBL-00-256
240 pF
20%, 1kV
Ceramic
Snubber Circuit 2
FIGURE 4. Snubber circuits found in power supplies.
5-18
APPLICATION
NOTES
BIASING (CURRENT CONDITIONING)
These resistors do not experience surges or spikes.
This is a steady state application. In these
applications the resistor values vary considerably
from 200 Ω to 20K Ω, 3 watt to 5 watt, 2% to 5%.
An example is shown in Figure 5.
BPC 5
Biasing
Resistor
PRELOADING 1
To DC Section
This resistor experiences a steady state condition.
The typical resistor is 3 Ω to 1K Ω and needs 10%
tolerance. The preloading is usually a function of the
circuit. An example is shown in Figure 6.
+
FIGURE 5. Cicuit from a high current, power
supply which uses a BPC resistor for biasing.
5
10K Ω
Sensing
Resistor
0.1 Ω
180 Ω
470 pF
1,000 V
Ceramic
1,500 µF
35 V
+
BPC 3
650 Ω
3W
+
4.7 µF
Output
Preload Resistor
From Switching
Circuitry
BPC
Power Resistor
FIGURE 6. Part of proprietary power supply showing two power resistors.
5-19
APPLICATION
NOTES
CURRENT LIMITING
BPC resistors have uses as current limiters in highvoltage power supplies. An example of a highvoltage power supply, which is used to drive a laser,
is shown in Figure 7 and the BPC resistor is
highlighted.
0.01µF (5 KV)
1,800 pF
47K
1,800 pF
(10 KV)
BPC5
5W
High Voltage Diodes
Laser
+
Vsw
Switching
Regulator
Vin
+
Vfb
Vin
+
FIGURE 7. Laser power supply showing a BPC5 for circuit limiting.
5-20
APPLICATION
NOTES
PRELOADING 2
Another example of preloading is in a Battery
Charger circuit as shown in Figure 8 where a resistor
is used as a dummy load to prevent overcharging the
battery.
BPC 10
3.65 M
6.8 V
7.5 Ω
10W
BPC 10
1M
8M
TIP121
1M
+
1A
Solar
Array
300 K
Si9405
12 V
5 Ahr
1M
Load
+
VN2222
1.2 V
FIGURE 8. Shunt battery charger using a BPC10.
5
Vertical Mounting:
Enhances board
cooling due to
natural convection
airflow.
Planar, Thick Film
Cermet Resistor:
Virtually eliminates
inductance for high
frequency designs
compared with
wirewound alternatives.
Automated Laser
Trimming:
Assures accurate
and stable
resistance values.
Large surface Area
to Thickness Ratio:
Maximizes power
dissipation and
minimizes hot spots.
Robust Leads:
Are firmly attached to
both sides for superior
mechanical integrity.
Built-in Standoffs
Low Operating
Temperature:
At board surface means
high temperature solder
is not required.
Vertical Mounting:
Minimizes required
board area. Uses only
1/3 the board area versus
a typical wirewound resistor.
Model BPC5 (5 watt)
5-21
APPLICATION
OVERLOAD CHARACTERISTICS - INRUSH
APPLICATIONS
20X Nominal
Power Rating
Power
Nominal
Power Rating
0
8
Time (milliseconds)
SIZE COMPARISON
1"
1"
W
10 bound
e
Wir
0.10"
0.312
" DIA
.
5-22
NOTES