#### 1:1

Joined Jan 25, 2007
27
Hai forum member,

What does dead band control mean?
When to use it and how does it work?

Thank

#### kender

Joined Jan 17, 2007
264
AFAIK, the term "dead band" applies to switch mode power supply and motor driver sircuits. Does this sound remotely applicable to your problem? Could you give us some more context?

Joined Nov 1, 2006
133
A good place to look for definitions is Wikipedia. Deadband is the region around the setpoint of a controller such as a temperature controller, voltage regulator, etc., where it doesn't need to operate. If the conditions that are being controlled stray outside of the deadband then the controller activates & corrects them. The reason for using a deadband is to reduce the rate that the controller cycles on & off. In other words, a deadband is the acceptable range.

#### 1:1

Joined Jan 25, 2007
27
Thank,

Actually i saw this word (dead_band control) from my microcontroller datasheet.
So i was wonder that how can i use it to control my motor.

#### kender

Joined Jan 17, 2007
264
This is an interesting subject, because digital, analog and power electronics meet here. I dont have enough time to do a complete explanation today. Ill do it in the next couple of days.

Gate capacitance
It all starts with a parasitic gate capacitance of MOSFETs. Because of their construction, MOSFETs have some capacitance between the gate and the source. When a microcontroller (uC) drives a gate high (low) with a digital signal, uC charges (discharges) the parasitic capacitance and it takes time. As a result, theres a period of time, when MOSFET is only partially on.

Recall that P = I^2 * R. When MOSFET is fully off, it doesnt generate much heat, because I = 0. When the MOSFET is fully on, it also dissipates little heat, because the channel resistance R is small. But when the MOSFET is partially on, it dissipates considerable amount of heat. To reduce the heat dissipation, you want to turn the MOSFET on as quickly as possible. But the gate capacitance works against you.

One way of dealing with gate capacitance is to increase amount of current going into the gate. There is special class of digital to analog buffers called gate drivers, which are designed to source (sink) several amperes of current in a short time to charge (discharge) the gate capacitance. For a comparison, a typical uC can source or sink only about 20mA.

But gate drivers are not always a sufficient solution.

[There are some figures to illustrate the effetc of parasitic gate capacitance. At the moment, they have been pulled by me for revision. ]

The Problem
[Will be finished in the next couple of days]