H bridge problem  - Page 1
Forum section: electronics / projects

author: Unknown
author_rank: Unknown
timestamp: April 28, 2015, 08:37:29 pm
content: Hi,i have an exsisting board with a SK85MH10T h-bridge controlled by two IR2183 that i have to troubleshoot. The diode of the bootstrap circuit is a UF1002, the capacitor value is 1 uF and the resistors on the gates are 12 ohm. On the motor terminal there are two RC circuit and two 1.5KE51CA to smooth voltage spikes.The power supply of the h-bridge is 24V (with one 2200 uF cap close to the bridge) and 12V for the driver. I'm controlling the drivers with a MCU powered at 3.3V that generates a 10 KHz PWM signal on the high mosfet on one side and turns on the bottom mosfet on the other side . The problem i'm having is that when i connect a motor to the h-bridge and little by little i increase the duty cycle at about 20% of the DC the motor stops to accelerate and slowly stops itself. If i change the motor and use a small fan there is no problem.After some research i found some possible causes:1) The IR2183 has a min logic level of 2.7V for a '1' and maybe is too high for a 3.3V MCU2) the bootstrap circuit is wrong, i tried with a 10uF cap but same result.3) the IR2183 is not capable of driving the SK85MH10T4) the fact that the board has an awful layout and massive ground loops.In my opinion is n.4 but i would like other opinions before i make a new board.

author: owiecc
author_rank: Frequent Contributor
timestamp: April 28, 2015, 08:48:45 pm
content: Please add a schematic and some measured waveforms. Do you start up the bootstrap circuit correctly? You need to charge the caps in the high side gate drivers before starting PWM.

author: Unknown
author_rank: Unknown
timestamp: April 28, 2015, 09:29:16 pm
content: Quote from: owiecc on April 28, 2015, 08:48:45 pmI attached the schematic, tommorow i can post some waveforms. Right now i simply start with the pwm.

author: Unknown
author_rank: Unknown
timestamp: April 30, 2015, 09:34:46 am
content: Update:When the motor stops running the MCU reset itself.If i force a 50% dutycylce from an external source the motor starts spinning then it stops then it starts spinning again ... any help?The fact that the mcu reset itself may be a grounding problem?

author: H.O
author_rank: Frequent Contributor
timestamp: April 30, 2015, 10:29:05 am
content: Does the MCU reset when the motor stops or does the motor stop because the MCU resets?Can obviously be a number of things....To me it sounds like voltage rail buckling under load.Is the 12V for the driver chips derived from 48V supply for the motor? If so (or, actually, no matter from where it's derived) have you monitored the 12V rail of the driver chips? Is it stable as the motor accelerates? Have you measured the voltage between the MCU GND pin and the driver chip GND pin(s)?

author: Unknown
author_rank: Unknown
timestamp: April 30, 2015, 10:51:44 am
content: Without the motor but with a smaller load like a fan the MCU doesn't have any problem. The 12V and 3V3 rails are stable. Like i said before this is an existing board but the layout is awful, there is no proper ground plane and the return path of every signal is terrible, forming enormous loops.

author: pelule
author_rank: Frequent Contributor
timestamp: April 30, 2015, 08:44:18 pm
content: n1) The IR2183 has a min logic level of 2.7V for a '1' and maybe is too high for a 3.3V MCU"may also the cause. The 3.3V Logic output high level is defined with min. 2.4V. The IR2183S input high level should be min. 2.7V, thus there may a big chance of input signal oscillation t the HIN/LIN pins just supressed by the IR2183S dead time logic. Check the MCU high level output (if > 2.7V) and if not, put a pull-up (~10k) to the pins to drag the level close to 3.3V.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 01, 2015, 06:59:18 am
content: check gnd connection, if all ok, check C21-25 they must be very close to the mcu.

author: Unknown
author_rank: Unknown
timestamp: May 01, 2015, 09:17:16 am
content: From the MCU ground and driver ground there is 13 mV, beetwen the mosfet ground and power supply ground there is 122 mV !! Another strange thing is that the pwm and other input signal from the MCU to the drivers are 3.5V but the supply of the micro is 3.3V.

author: owiecc
author_rank: Frequent Contributor
timestamp: May 01, 2015, 09:27:47 am
content: Measure the output voltages of the H-bridge at light load and close to when the motor stops. Then you will know what to do next.

author: Unknown
author_rank: Unknown
timestamp: May 01, 2015, 09:53:20 am
content: Quote from: owiecc on May 01, 2015, 09:27:47 amI will have access to the board after the weekend. Do you have any idea of what is the problem?

author: owiecc
author_rank: Frequent Contributor
timestamp: May 01, 2015, 01:06:39 pm
content: Quote from: exapod on May 01, 2015, 09:53:20 amLack of waveforms is the problem. We can play the guessing game all day long but without any real data it is hard to tell. So many things can be wrong. After you post the data finding the problem should be quite straight forward.

author: nuno
author_rank: Frequent Contributor
timestamp: May 01, 2015, 08:17:06 pm
content: You don't tell enough, but by the components let's assume you're trying to power a 200W+ motor on an electric vehicle. For that you need to do current control; without it your motor current will rise to levels where several things can happen, from fried FETs due to repetitive avalanche/self turn-on/... to huge transients going to the rest of the circuit to the power supply dropping voltage to a level so low the rest of the circuit stops working or works badly. I would fix this first.

author: eneuro
author_rank: Super Contributor
timestamp: May 01, 2015, 09:40:51 pm
content: Quote from: exapod on April 28, 2015, 08:37:29 pmAny reason to power up MCU with 3.3V-why not to use 5V powered MCU, especially when you are using not optoisolated gate drivers?Did you tested this circuit with another 5Vcc MCU?10KHz PWM quite slow and within human hearing range200W @ 24V means less than 10A which is nothing in the case of bulky mosfets.Anyway, did you checked gate driver Vcc while increasing duty cycle-maybe this 1uF bootstrap caps are too small and 10kHz is too slow to powerup high side gate drivers ?Quote from: exapod on April 30, 2015, 09:34:46 amI never used SK85MH10T, but in your schematics it look slike you connected its NC pins 17-20 to GND-only speculating and I wonder if it might be any issue thereHowever I'd rather try first test it with 5Vcc MCU and see what happends...