Signal Consulting, LLC 

Model Si21HFHB-50V-20A-AP1

50V, 20A, High-Frequency H-Bridge with Optically Isolated Forward, Reverse, Brake and PWM Control Inputs and with Aluminum Plate Heat Sink  





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Si21HFHB-50V-20A-AP1 Features:

Max. Continuous Load Current: 20A with the plate mounted on a large metal frame.
Max. Load Current for 2 sec: 50A with board mounted on a large metal frame.

Overall Dimensions:  4.0"x 3.3”x1.4”, (102 x 83 x 36 mm).

Board Isolation:    All Control Lines are Optically Isolated from the Motor-Power Circuits.

Typical Operating Temperature:  450C at 20A with the board mounted on a 4.0” x3.3” x0.062" Aluminum plate and exposed to air at 250C.

Voltage Requirements: A Single DC Source (unregulated and unfiltered). Any voltage from 9V to 50 Volts ( from Pin +P to Pin -P).

Control Type: Active High, (0 to 5V)
Typical Power Efficiency: 98.5% at full-load (50V and 20A).

Load Isolation: The Load Must be Isolated for the Power Source.
Components Type: 100% Solid State, NO Relays

PWM Control Input: The VPC input can be Pulse-Width Modulated in the  0-20kHz frequency range.
A bicolor LED is used to monitor the load voltage (Forward = Red, Reverse = Green).

On Board: 
Filter Capacitors.
VTS diodes.
Snubber Circuit.


    For Details, Download the  Si21HFHB-50V-20A-AP1-1   Manual


The Si21HFHB-50V-20A-AP1 is an  efficient 50V,20A high-frequency and high-power H-bridge with an integrated (4"x3.3"x0.062") Aluminum Plate Heat Sink that works over a wide range of source voltages (9V to 50V) at high continuous load currents (+/-20A max.). Higher current values can be attained with more efficient heat sinks. The motor or load action (as shown on the truth table below) is controlled by the voltages applied to pins: Brake (VB,C), PWM (VP,C), Forw (VF,C), Rev (VR,C) (relative to pin Com, the common negative terminal) on the Control connector (shown on the application drawing below). These control pins are optically isolated from the rest of the power circuit, requiring a minimum input current of 1.5 mA at 3.5V and max. input current of 7mA at approx. 9V. An external resistor (connected in series with each control input) can be used when higher control voltages are required (1k Ohm for 12V, 2.2k Ohm for 24V).

 Truth Table for the Control Connector Inputs

The PWM input can be left in a continuously oscillating state (Don’t’ care State) but the static control inputs (Brake (VB,C), Forw (VF,C), Rev (VR,C)) must be applied one at a time with a minimum of 1ms delay between command changes. This 1ms delay is required for the H-bridge to disengage from the previous command state and to acquire the new command state. WARNING: Permanent Damage May Occur if this Condition is Violated.

oltage Requirement: The Si21HFHB-50V-20A will work with any DC source in the 9V to 50V range. In addition, the power filters are included on this board. Consequently, only unregulated DC input power is required in most applications. Furthermore, the control circuit is optically isolated from the power circuit; rejecting unwanted power glitches.

 Frequency Response of the Si21HFHB-50V-20A-AP1

The PWM (VP,C) input can be Pulse Width Modulated (PWM, with duty-cycle of 0% to 100%) over a wide range of carrier frequencies, as shown on the graph. This plot was obtained with the board mounted on a 4.0” x 3.3” x 0.062” Aluminum Plate, placed on a nonmetallic bench top and exposed to 25 degree C air. Improved performance (25A) can be achieved with the board mounted on a metal frame. Please click on this link and read the Board Mounting Instructions and Heat Sink Selection Guide

A Typical Motor Control Application of the Si21HFHB-50V-20A-AP1

In this bi-directional speed control application, the motor speed is controlled using the duty-cycle of the PWM (VP,C) input; while the direction of rotation is controlled, using the static signals Forw (VF,C) (Forward) and Rev (VR,C) (Reverse). After a Forward or Reverse command is removed (by placing the Forw (VF,C) and Rev (VR,C) inputs in the Low state), a Brake command can be applied (by placing the Brake (VB,C) input in the High state) to short circuit the DC Motor or Load.

Warning:  The connecting wires to the Load and the Power Supply must be heavy gauge copper wire (#12 AWG or heavier) to handle the rated current level. In addition, these heavy gauge wires act as a heat sink, protecting the board from overheating.

 Typical Applications: Power Driver for Variable-Speed Bidirectional DC Motors, Peltier Effect TE Cells, Heat Pumps, PPDT Solid State Relays.

Si21HFHB-50V-20A-AP1, 50V 20A High-Frequency H-Bridge with Aluminum Plate Heat Sink
Price  $169.00

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Availability: We usually ship in 2-3 business days.



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