Monday, July 4, 2011

H Bridge

H-bridge is a circuit configuration that allows the designer to apply the voltages in both directions. H-bridge also allows higher voltage and current to be applied to the load while controlling the direction through a low voltage signal. The illustration below shows the flow of the H-bridge.

H Bridge

Figure 1: H-bridge circuit diagram

Above Figure 1 is the diagram for the H-bridge. Switches that are used to control the logic level are SW1, SW2, SW3, and SW4. D1, D3, D4, and D5 diodes are used to protect the reverse flow. The circuit in Figure 1 shows that the supplies to the load a well as the control are tied together. However, this can be separated if the load requires additional current and voltage. Both Figure 1 and Figure 2 shows the supply voltage in 2 different direction.

Figure 2: Q3 low Q2 high

Figure 3: Q4 low Q1 high

The circuits below will show the H-Bridge implementation using 2 switches instead of 4.

Figure 4: Controlling with 2 input

Figure 5 shows when SW5 and SW6 are low.

Figure 5: SW5, SW6 low

In order for the H-Bridge to work, either one of the switch SW5 or SW6 has to be high while the other switch has to be low.

Figure 6: SW5 high, SW6 low

Figure 7: SW5 low, SW6 high


The discussion above shows the implementation of the H-bridge to control direction. This can be used to control motor in both direction by controlling the switches. The proteus simulation above is used to test, debug as well as simulate the concept of the circuit to make sure that the circuit is workable.