Few confusing things on a circuit that needed to be understood

Thread Starter

liamneeson248

Joined Jan 11, 2016
36
There are a few things about this circuit that i am having problem to understand, this is an open source BLDC motor driver circuit.
This circuit have both sensor-less and sensor circuit but it is upto us what option to use, in my case i am going to use the sensor-less option because my motor does not have place to put hall effect sensor in it so i am using the back emf to make my programming a little bit smarter.

1-Why have they used N-Channel mosfet for both High and Low Side switching?
2-Why the VS(6) pin of IR2101 is attached to the output of the bridge?
3-Why are they using 74HC08 from arduino output to the Mosfet driver High Side input? why not just simple put it directly to the driver High side?
4-Why is shunt resistor used in this circuit?
5-What is the circuit with LM358? what does it do here?
6-What output does the LM339 is going to give when there is a BACK EMF detected?
7-I have studied that we need bootstrap circuit if we want to use N-Channel Mosfet for High side switching but if we are driving it via driver do we still need a bootstrap circuit or not?
 

Thread Starter

liamneeson248

Joined Jan 11, 2016
36
N channel Mosfets can be used for both hi and lo side when a charge pump of some kind is used, the Ir2101 IC for e.g. provides this.
See http://tahmidmc.blogspot.com/2013/01/using-high-low-side-driver-ir2110-with.html
Here is a bootstrap calc https://www.silabs.com/support/isolation-bootstrap-calculator
The bottom Mosfet has to be turned on for the charge pump to work for the top one..
Max.
so the ir2101 already have bootstrap circuit? or do i need to add the circuit myself even after mosfet?
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
The LM358 circuit is a current detector for the bridge Mosfets via the two .04Ω resistors, with feedback to the Micro.
The bootstrap cap and rectifier need to be added.
Max.
 

Thread Starter

liamneeson248

Joined Jan 11, 2016
36
The LM358 circuit is a current detector for the bridge Mosfets via the two .04Ω resistors, with feedback to the Micro.
The bootstrap cap and rectifier need to be added.
Max.
isn't the 1uF capacitor is doing the same thing?
are you talking about adding UF4007 on HIGH Side out from mosfet? according to the Tahmid's Blog i already have a capacitor from VB to VS
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
The LM358 is a separate issue for the current sense.
The charge pump components are shown on the schematic, VD4/6 and C32/34.
Max.
 

Thread Starter

liamneeson248

Joined Jan 11, 2016
36
The LM358 is a separate issue for the current sense.
The charge pump components are shown on the schematic, VD4/6 and C32/34.
Max.
so please make it clear? do my schematic already have bootstrap circuitry in it? or do i need to add something else too? i am sorry its just bootstrap is something that i could not get my head around.
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
The schematic looks complete with the Bootstrap already in place, I just though you were asking if you needed to add any thing else.
The AN 978 explains a lot.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
I see it is just the signal input for HI side input, it does not affect the charge pump components, per-se.
With the IR1220, 5v can be used for the HI in.
Max.
 

bertus

Joined Apr 5, 2008
20,540
Hello,

The W-L V-L and U-L signals come direct from the ATMEGA:

Liam mega signals dcHib1Q png (PNG-afbeelding, 3353 × 2157 pixels).png

The 74HC08 combines the signals PD7, PB0, PB1 and PB2 for the high side driver.

Bertus
 

MaxHeadRoom

Joined Jul 18, 2013
20,707
I am not familiar with the Atmega so I am not sure why they would need to multiplex the PWM signals.
With the regular Pic, the PWM has 6 outputs for feeding the IR2110 directly.
Max.
 
Last edited:

bertus

Joined Apr 5, 2008
20,540
Hello,

It looks like that the 74HC08 is used to create the dead time.
It mixes the PB2 signals with the other signals from the ATMEGA.

Bertus
 

bertus

Joined Apr 5, 2008
20,540
Hello,

The dead time is to prevent that both fets are on in the half-bridge.
When both fets would be on a massive current will flow thruogh the fets distroying them.

Bertus
 

Thread Starter

liamneeson248

Joined Jan 11, 2016
36
Hello,

The dead time is to prevent that both fets are on in the half-bridge.
When both fets would be on a massive current will flow thruogh the fets distroying them.

Bertus
Yes i know about the dead time and i know it is necessary in BLDC motor control, but i want to know how to generate it, i am using arduino for motor control, all the mosfet driver circuit is correct and checked but i have few more things like dead time generation and back emf check circuit to make which will help it run.
 
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