H-bridge A simple, reversible motor drive circuit, based (to some degree) on a simple conceptual schematic (see diagram on right). A basic H-bridge has 4 switches, relays, transistors, or other means of completing a circuit to drive a motor.  In this diagram, the switches are labeled A1, A2, B1, B2.  Since each of the four switches can be either open or closed, there are 24 = 16 combinations of switch settings.  Many are not useful and in fact, several should be avoided since they short out the supply current (e.g., A1 and B2 both closed at the same time).  There are four combinations that are useful: Closed switches Polarity Effect A1 & A2 forward motor spins forward B1 & B2 reverse motor spins backward A1 & B1 brake motor acts as a brake None free motor floats freely As was alluded to above, more-sophisticated H-bridge designs can avoid "smoke" conditions that short out the supply current (tho' many BEAM applications do not require this). For details on H-bridge drivers in use in BEAM, see the BEAM Reference Library's Circuit collection page on H-bridges here.

Legalities    Page author: Eric Seale   This page was last updated on This work is licensed under a Creative Commons License.