Gate driver for large PWM module? - Page 1
Forum section: electronics / projects

author: Halvmand
author_rank: Regular Contributor
timestamp: May 26, 2017, 02:47:33 pm
content: I've taken home from work a "variator" from a scissor lift. The variator is basically just an PWM controller for the lifts motor.To my luck the power section is totally separate from the rest of the electronics in the box. Now i have the bare module which works fine.I've checked it with a small motor and a homemade PWM driver made from op amps.These tests was all performed with my bench supplies, so low currents and low chance of fire and death.Now, the module is rated to 300A 24V. And before I connect it to two big lead acid batteries and an 1.8 kW motor I was wondering if I need a gate driver to feed the six mosfets the PWM signal?I can't trace the original control board to se if there is a driver. There is only two quad op amps in the vicinity of the connector that drives the gates.The mosfets is IRF 64-2092pbf.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 26, 2017, 03:08:30 pm
content: Pic of the board.

author: Leon23
author_rank: Contributor
timestamp: May 26, 2017, 03:42:37 pm
content: There seem to be a SO8 package device on your pictures. It looks like it could be the gate driver?

author: Halvmand
author_rank: Regular Contributor
timestamp: May 26, 2017, 04:03:22 pm
content: unfortunately that's an LM335 temp sensor.I was a bit trigger happy when I made the post. Meanwhile I've consulted the bible. And me and The Art of Electronics agree on a gate driver is necessary since the combined gate charge vill be pretty high, and i don't know how much current my TL074 op amp will provide.

author: DBecker
author_rank: Frequent Contributor
timestamp: May 26, 2017, 07:06:25 pm
content: The gate charge per device will be 40-75nC, and you'll want to drive the gate at 10V-15V. A gate driver will be easier to design with and much more robust than pushing an opamp to the edge.If you have a design choice, use an inverting gate driver. And for a one-off, just spend a few extra cents and buy the highest current gate driver that fits your requirements. The MIC4451 used to be the go-to part. Use individual gate resistors to set the turn-on/off time.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 27, 2017, 11:16:41 am
content: Thanks for the component advice DBecker.If I can get the MIC4451, can I just connect the PWM output from the opamp to the input of the driver? Of course staying within the driver parameters.

author: DBecker
author_rank: Frequent Contributor
timestamp: May 27, 2017, 01:18:31 pm
content: A real gate driver such as the MIC4451 supports logic-level inputs, although it will also work with higher voltage inputs.If you already have full gate voltage swings you can design around a basic gate driver such as a ZXGD300x, but it's a little more complex to design with.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 27, 2017, 01:58:53 pm
content: Variator means something totally different.What you have here is a teardown of a so called motor driver or motor controller - most likely a brushed DC motor driver.Designing it to work again is much more than just a gate driver and a FET, because it's not just a PWM module, but a motor controller, which is more complex. For example, it most likely needs an active current limit or current mode control. Luckily, there is a lot of information and it's not an impossible task now that you know the right search terms.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 27, 2017, 06:05:26 pm
content: Quote from: Siwastaja on May 27, 2017, 01:58:53 pmActually it is called a variator here in Denmark. I gues it's just a specific specefic term for a lift motor controller.But yes. you are correct on all points.It's for a brushed DC motor driving the hydraulic pump.Thanks for posting. Current management totally slipped my mind.It has a current transformer on the power section on the control board. It might be salvageable, but it may be easier to go another route.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 27, 2017, 06:12:25 pm
content: DBecker:It's just a "for fun project" so the MIC4451 looks like the chip to go with. By the datasheet it looks easy to work with and claim to be able to take some abuse, which it probably will.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 29, 2017, 10:00:23 pm
content: Thanks again for the help guys.I have drawn op a shematic of the control board I designed based on your input.Would somebody take a look at my control board circuit? It's IC1D and IC4 whose supposed to limit the current if to high.My concern is if it will oscillate when the current limiting circuit starts limiting, since the op amp IC1D is configured as a comparator. I have tried to make the output swing not to aggressive by adding C10 and R12. I haven't decided on the values yet.Am I on the right track?

author: Halvmand
author_rank: Regular Contributor
timestamp: May 29, 2017, 10:04:50 pm
content: Picture not as pdf.

author: Halvmand
author_rank: Regular Contributor
timestamp: May 31, 2017, 09:32:19 am
content: Bump

author: Halvmand
author_rank: Regular Contributor
timestamp: May 31, 2017, 02:25:32 pm
content: New revision.

author: CopperCone
author_rank: Super Contributor
timestamp: June 07, 2017, 12:28:37 am
content: If you want a high current gate driver thats blazing fast, look at IXYS parts. To me thats the analog devices or LT of power drivers.