ZXBM200X Ver la hoja de datos (PDF) - Zetex => Diodes

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ZXBM200X

ZXBM200x SERIES OF VARIABLE SPEED 2-PHASE FAN MOTOR CONTROLLER

Zetex => Diodes 

Applications Note AN36

Issue1 - JULY 2002

MOSFET Power Transistors

Power MOSFET devices are becoming

increasingly popular and as regard the

ZXBM200x provide a very good method of

driving the motor phase windings. Figures 9

and 10 illustrate the methodology of the

driver circuit.

Figure 9

MOSFET Output Drive Stage

Figure 10

MOSFET Output Drive Stage Using Active Clamping.

The components in Figures 9 & 10 have a very

similar topography to that of the Bipolar drive

with again two variants, one with the direct

Zener clamping and the second having active

clamping.

The main difference arising in the active

clamping circuit in Figure 10 is the need for a

diode in series with the active clamp Zener

diode. This prevents the Zener being forward

biased and thus detracting from the gate

drive when the MOSFET is turned on. In the

active clamp circuit there is also no need for

any drain to source negative voltage

protection as this will be achieved by the

inherent body diode of the MOSFET.

When using MOSFET devices it is a

compromise between the Voltage rating and

the RDS(on) of the MOSFET with a higher

voltage rating producing a higher RDS(on).

The aim therefore should always be to use the

lowest voltage rating to suit the application

as this will give the lowest full-speed RDS(on)

related dissipation. The disadvantage is that

there will be a slightly higher dissipation

when using active clamping as this will be

working harder to maintain a lower voltage

when the fan is running at near to full speed.

The latest generation of N channel trench

MOSFETS from Zetex provide suitable

solutions with the ZXMN6A11G and the

ZXMN10A11G, 60V and 100V devices

respectively, having been used in the

applications described.

Reverse Supply protection

An increasingly common requirement for

modern systems is for components and

modules to have a degree of reverse supply

protection. This is particularly so for

Automotive applications. To achieve this a

supply blocking diode is required in the Fan

electronics.

For the best performance from the

ZXBM200x device it is best to provide

separate diodes for the device and the

winding supplies. This is illustrated in the full

applications circuit in Figure 17. The main

reason for this is that having blocked the

reverse path to the power supply for the

switching currents, high voltages can be

experienced at the winding high end. This

energy manifests itself as excessive voltages

and these are required to be kept away from

the device supply.

AN 36 - 8

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