BPU-S4 The BPU-S4 is a high power brushless PWM servo amplifier in a Eurocard 3U form factor. It is ideally suited to torque control applications or for velocity control using a digital position controller. This amplifier can be configured for external sinusoidal commutation or for self commutation using either voltage or current supplied analog Hall effect sensors. This unit is similar to the BPU-S3 but in a smaller form factor due to a lower maximum voltage rating. Look to the BPU-S5 if digital Hall effect sensors are required.

The BPU-S4 is a double card unit, consisting of separate Power and Personality Modules. The Personality Module adds digital status reporting capability, inputs for Hall effect sensors, and allows future amplifier reconfiguration with modules under development at Western Servo Design. Hall effect commutation or external sinusoidal commutation may be selected "on the fly" via digital switching. When using external sinusoidal commutation, the amplifier receives two 120 out of phase sinusoidal command inputs. The optimal third phase is derived by the amplifier. This eliminates "cogging" and greatly enhances low speed operation. An optional backplane is available to allow quick and easy access to motor, power, control and other I/O signals.


  • Eurocard 3U Form Factor
  • Accepts Digital or Analog Hall Effect Sensors
  • Two Commutation Modes: Hall Effect and External Sinusoidal Input
  • High Speed Commutation Mode selection using Digital Switching
  • 4 Digital Status Outputs plus Global Fault
  • Travel Limits and Amp Enable Inputs
  • Protected from Over Current, Over Voltage, and Under Bias Conditions
  • Current Monitor Output
  • PWM Frequency: 20kHz or 80kHz
  • Bus Voltage: 30 - 170 VDC
  • Continuous Current: 5, 8 or 12 Amperes
  • Full Isolation between Input and Output Circuits
  • Designed for Three-Phase Wye or Delta Wound Motors
  • Advanced Design, Superior Quality and High Reliability
  • One Year Parts and Labor Warranty


Standard Models: 10/10 17/15 17/30
Max Bus Voltage 100 VDC 170 VDC 170 VDC
Peak Output Current* 10 A for 0.5 Sec 15 A for 0.5 Sec 30 A for .5 Sec
Continuous Output* 5 A 8 A 12 A
Command Input Voltage:

Hall Commutation

Sinusoidal Commutation


0 to 10V

0 to 5V


0 to 10V

0 to 5V


0 to 10V

0 to 5V

Command Input Impedance 10 kOhm 10 kOhm 10 kOhm
Minimum Load Inductance 0.2 mH 2 mH 2 mH
Switching Frequency 80 kHz 20 kHz 20 kHz
Torque Gain:

Hall Mode

Sinusoidal Mode


1.0 A/V

2.0 A/V


1.5 A/V

3.0 A/V


3.0 A/V

6.0 A/V

Bandwidth 13 kHz 4 kHz 2 kHz
Weight 0.96 Lb (435 g)
Recommended Chassis CHU-S3 or CHU-S6 Eurocard
Available Accessories ACC-V1F Backplane,  ACC-V3A PMAC Interface Board, PSU-S1 Power Supply

*All ratings with forced air cooling to maintain 40C heat sink temperature. Failure to keep constant air flow to the heat sink will reduce the output current capacity and may result in damage to the unit.

Ordering Information

Product Order Number
BPU-S4-10/10 Amplifier 100 VDC/10A Peak WS-007-0010
BPU-S4-17/15 Amplifier 170 VDC/15A Peak WS-007-0011
BPU-S4-17/30 Amplifier 170 VDC/30A Peak WS-007-0012
ACC-V1F Backplane WS-914-0005

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