Confusion on IR2110 high side amplitude. - Page 1
Forum section: electronics / projects

author: westlund
author_rank: Newbie
timestamp: April 05, 2019, 09:30:42 am
content: Hello,I have built a circuit for controlling an electromagnet in an active magnetic bearing. I'm able to feel the force of the EM, but I'm a bit confused on why the high side amplitude to the gate is only 7V, when the low side is 15V. I'm testing with 0V or 30V on the power side and 15V on the logic side at the moment. But I get the same result with only 7V out from HO to the gate of the high side transistor.It could be a broken component as I have already released the magic smoke one time. Or a bad component choice, or the 30V supply, but I don't see a difference between 0 and 30V on the power side. Or it might be that it supposed to be like this. I'm confused if it's supposed to be like this or if it's something broken.

author: Andy Watson
author_rank: Super Contributor
timestamp: April 05, 2019, 10:53:07 am
content: How are you driving the control signals? To operate the charge pump mechanism for the high-side supply the common, (VS - pin 5) must be pulled low. However, if I am reading your schematiic correctly, the load (coil) is in series with the with both output FETs so the lowest voltage on VS pin will include the EMF of the coil - assuming that you are driving both high and low sides simultaneously. To attain more charging potential the low-side needs to be active when the high side is not.But do you need both high and low side drivers? The voltages you are using could easily be handled by a single FET - simpler and it solves your high-side problem.

author: westlund
author_rank: Newbie
timestamp: April 05, 2019, 11:47:41 am
content: The reason for a high side FET is to use a three-level design to reduce the noise. The control signal is phase shifted 180* for one side so both will only be closed when the duty cycle is more than 50%. In this test the duty switches between values from 45% to 70%.

author: westlund
author_rank: Newbie
timestamp: April 05, 2019, 12:59:08 pm
content: I did a test where the duty was between 10-40% and the discharge at start from 15V to 7V was slower. Could figure 26 on page 24 here:an-978.pdfbe a solution?Is there any other problem you see in the circuit and is there a good way to test if the charging of the bootstrap circuit is the problem before redesigning?

author: westlund
author_rank: Newbie
timestamp: April 05, 2019, 01:09:54 pm
content: I just did a test comparing different lower duty cycles and when the magnet is connected and the duty starts at 50% it is close to 14V so much better. Thanks for the insight on how the IR2110 works. I might still need to do a redesign if we think it's needed.But what's the reason for it going to 7V instead of 0V when the charge pump is not working correctly?

author: westlund
author_rank: Newbie
timestamp: April 09, 2019, 04:17:15 pm
content: Now with the duty cycle over 50% it works better, but there is still some in the beginning of the green high side signal. So probably the bootstrap SMR circuit on the next design so the highside can charge while the low side is off.

author: westlund
author_rank: Newbie
timestamp: April 12, 2019, 04:44:14 pm
content: I have been thinking about the example in:https://www.infineon.com/dgdl/Infineon-HV_Floating_MOS_Gate_Drivers_AN978-AN-v01_00-EN.pdfpage 24, figure 26for charging the bootstrap cap.But wouldn't it blow D2 and Q1 when LO is low and HO high... or am I missing something?As I PWM HO and LO at 50%-100%(it might go under 50% sometimes) and HO is phase shifted 180deg so about half of the period will be this situation.