Relays Vs. H-Bridge

Comparison between relays and H-Bridge circuit

Motor drivers may be implemented using H-Bridge or relays. Some comparison points between them are mentioned below:

Transistor driver is used when fast switching is required, typically relays are Used when switching frequency is less than 4 Hz.
From the power dissipation point of view, on the transistor side the motor large current passes through the switching transistor. This results in power dissipation equals to the voltage drop in the transistor multiplied by the large current pass in (power transistor is needed). On the other hand the relay contact has good conductivity this results in small power dissipation in the relay contact .the power dissipation in transistor results in the need of heat sink for temperature reduction. The relay guarantees complete input output isolation. Any fault occurs will not affect the control logic input where the some transistor faults results in collector –base short circuits so the large current may destroy the control logic circuit connected to the transistor base.
Generally using relay is simpler than transistor. On the relay’s side we are interested in the rating current pass’s in but where in the transistor side we must take into consideration the maximum current passes (the motor starting current).
Practically, transistors are preferred for small power drivers but relays is preferred for larger power driver for example in our project transistor driver circuit for turning motors(small output power).