Electrical – Power rating of H-bridge

dc motorh-bridgemaximum-ratingspower

I am looking to build an H-bridge to control a brushed permanent magnet DC motor. The motor has the following ratings:

Full load current: 18A

Voltage: 24VDC

kW rating: 0.43kW

I am planning to use two BTN8982TA High Current PN Half Bridges by Infineon (Link to Data sheet below) to form a single H-bridge. Looking at the data sheet I can see that both the maximum voltage and current ratings are high enough to fit my application. However I am not sure if these Half bridges can handle the power ratings for my application. I cant to seem to find the maximum power ratings on the data sheet but I do have a link from the Infineon website which mentions that the half bridges can handle a total of 250W (see link below).

Can I continue to use these half bridges for my application if I was to use a heat sink and an external fan for cooling?

Also since I am using two of these half bridges to build an H-bridge does this mean that the power rating of my H-bridge is now 250W x 2 = 500W ?

Data sheet link: http://www.infineon.com/cms/en/product/power/motor-control-and-gate-driver-ics/intelligent-motor-control-ics/single-half-bridge-driver/BTN8982TA/productType.html?productType=db3a30443ef951e3013f0f6c88742068

wattage rating link: http://www.infineon.com/cms/en/product/evaluation-boards/DC-MOTORCONTR_BTN8982/productType.html?productType=5546d4624ad04ef9014b07c0c07922e0

Best Answer

The power rating of the motor is for the input power it can handle, 18A*24v =432 watts.

The power rating for the H bridge is for the loss power its packages can dissipate, which has nothing to do with 432 watts directly.

There are two main loss mechanisms in the switches of the H bridge

1) Voltage drop across the FET resistance when conducting with a low voltage drop, conduction losses
2) Momentary high power dissipation as they commute, switching losses

Look at the datasheet static RON specs to see what the conduction losses will be at your currents. Look at the data sheet dynamic switching specs to see what the losses will be at your current, voltage and PWM frequency. Add those together to get the total losses. Look at the datasheet to see what the thermal resistances are, to see whether you need a heatsink, to keep the junctions cool enough, at that power.

Generally, if the H bridge is over rated for the current, and for the voltage, and you use a PWM frequency within its suggested range, then you will be able to handle the loss dissipation, and you will probably need a heatsink. Whether it needs to be fan-blown or not depends on how big you can tolerate it being.

If you don't want to do the loss sums, then start with a humungeous heatsink, and reduce the size while checking the temperature.