H-Bridge
Many microcontrollers feature onboard PWM generators, and when combined with an external amplification and switching circuit (commonly referred to as an ’H-bridge’), are sufficient to power a motor. The H-bridge used is the Signal LLC 50V-20A High Power H-Bridge with Aluminum Plate Heat Sink for Bidirectional DC Motor Control.
Key specs
| Quantity | Value | Units |
|---|---|---|
| input voltage (DC) | 9-50 | V |
| max continuous load current @ 60 Hz PWM | 20 | A |
| max continuous load current @ 20 KHz PWM | 2 | A |
| max peak current | 50 | A |
Key documentation
- Si20HPB4-50V-20A-AP1 product page
- Si20HPB4-50V-20A-AP1 spec sheet (February 2010)
- Wikipedia: H-bridge
Notes
- The maximum sustainable current through this device is limited by the PWM carrier frequency.
- 20 KHz seems too high for the motor (which can draw up to 4A of current).
- 1 KHz seems to be the best PWM carrier frequency.
Testing
- The output of the H-bridge should not be measured when an inductive load (such as a motor) is attached.
- The inductance acts as a lowpass filter on the signal.
- Signals with high harmonic frequency content (such as PWM signals) will be distorted upon measuring.
- Measure the H-bridge output by applying a resistive load, such as a 360 Ohm, 15W resistor (heat sink necessary), and scoping the two terminals of the resistor.
- In the lab, input signals exceeding 1 KHz were distorted by the H-bridge circuit, apparently because of slow rise and fall times of its transistors.
- While high PWM frequency is optimal, 1 KHz signals seem to drive the motor well.