DIY Electric Car Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
3,141 Posts
Discussion Starter #1
I was searching for a high side current sensor similar to the Microchip HV7800, and found the IR25750, which has a novel way of monitoring the current in a MOSFET or IGBT by using the RdsON voltage while it is conducting. It probably works best for a MOSFET which has a relatively linear bulk resistance when turned ON, and the voltage from D-S will be proportional to current. If you know the RdsON, you can derive the current to a reasonable accuracy, maybe 10-20%, probably good enough for many purposes. For an IGBT, the VceSAT is not so linear, but a curve-fitting function might be able to derive the current, and it will also detect desaturation. Not bad for a part that costs about 50 cents, and works up to 600V.
http://www.mouser.com/ProductDetail...=sGAEpiMZZMuNY54QelN3z/7UXgInzCy0jAM0Z0Yj2J0=

I'm not sure if it would work for a high-side MOSFET or IGBT, as used in motor controls and buck switching chargers, but it might work just as well, if combined with a high-side voltage monitor such as the HV7800, which has a working voltage of up to 450V. It essentially acts as a level shifter that can measure the voltage on a shunt (up to 500mV) on the high side, and provide it on the low side, with less than 50uA current. This is also a 50 cent wonder.
http://www.mouser.com/ProductDetail...=sGAEpiMZZMuNY54QelN3z/HIFxGt7AICBG57GinpYmA=

These devices might be able to cut a good deal of cost from chargers and motor controllers, replacing relatively expensive Hall sensors and isolation amplifiers used in many designs such as the EMW charger I am working on. I am also planning to use similarly low-cost differential amplifiers to read input and output voltages. When the current drawn by such devices is under 100uA or so, true isolation may not be required. The SI8261 is another example of what is termed "opto-emulation", which provides a less expensive alternative the the HCPL-3120 gate driver.
 

·
Registered
Joined
·
732 Posts
The IR can save up to ten watts of power wasted in sense resistors.
Some controllers have IR25750-like features built in, but not the high power models I am using now.
Maybe I can combine the IR25750 device with one of the ST controllers L6598 or L6699 (positive Volt OCP inputs).
 
1 - 3 of 3 Posts
Top