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DIY Controller

2263 Views 7 Replies 3 Participants Last post by  sergiu tofanel
Hi, I'm developing an quite easy DC DC controller, for an electric motor bike.

About it, I'm just starting for a simple half bridge, and then I'll move up for more sensorial details to check while it is working...

I've got an special question, on the design, I'm using an IR2110, it is a MOSFET driver, my doubt is about the voltage, it seems to work right with 15v, but my Batteries are 36V, so what should I use for the voltage divider? a DC DC converter or just a voltage regulator? I'm afraid that the voltage regulator whaist to much power...

What does the profesional controllers use?

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I assume you are trying to provide power to Vdd, which takes a max voltage of 20V. You will have to provide some kind of voltage regulator, like the LM78xx series. In order to reduce power consumption, you could put a resistor between the +36V power node and the power input of the 78xx. Make sure the resistor is rated for the power though.
I thought about that, but there is two questions I've got...

1)About what I've read the IR2110 may consume around 2A, I'm not sure what it depends about, but in case it consume 2A and my regulator is dropping voltage from 36V to 15V, I'll be wasting (2A.21V=42W) 42W if I'm not wrong, and thats to much heat and to much waste for the battery...

2)What does use the pro Controllers?
You can use a DC to DC converter then, or build your own. Most controllers will have a separate switching power supply based on a buck converter design. the most popular controller is the SG3524 and/or its derivatives.

For your case, though, I would ditch the IR2110. I's just too much trouble to use. You can easily build your own MOSFET driver circuits that will work just fine with 36V.

Most 12V voltage regulators (12V is a good voltage to use) have a maximum voltage input of 35 or 36 volts. You should leave yourself some headroom for voltage spikes and surges, so that leaves out using the standard 78L12 type of regulator.

You can use something like a TL783. As you will notice from the datasheet, it has a maximum current output of about 700mA. This is really not a problem though. You simply want to put a large capacitor (say min. 4.7uF up to 10uF) on the output of the regulator, and also another 1.0uF to 4.7uF over at the charge pump capacitor for each drive chip. I would also recommend a couple smaller bypass caps (ceramic) over at the input to the diode (Vcc) for the charge pump. The 2A that the IR2110 requires is for a very short amount of time while it is turning the FET gate on. It is not a continuous rating, so the 700mA from the TL783 will be fine. The actual drive current(charge) will come from the caps. You may need to heatsink the TL783, (depending on the actual input voltage and current draw), so watch that.

With the IR2110 you need to be very careful that both the high side and the low side are not on at the same time, or current will shoot right through both of them. Since it takes time for the FET to turn off, you need to build in a "dead time" between turning off one gate and turning on the another. If your FETs get hotter than it seems like they should, make sure you aren't getting any shoot through. If they blow up, then you definitely need to check for shoot through. Buy extra FETs while testing just in case.

The charge pump method of building the voltage on Vb requires that at some time the Vs line will be pulled low (through the LO side FET) to charge the capacitor. Thus, if you are using PWM to drive the gates, make sure you do not leave the high side on 100 percent of the time.

When rating your FETs take your maximum current draw and multiply by 3 to get the rating of the FET you want. If you need 10 amps, then use a FET rated for 30 amps. For voltage, if you are going to be using 36V, then use a FET with a an 70 or 80 volt rating to account for voltage spikes. Make sure the FETs have good heatsinking.

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Thanks you two guys, I'll answer you in a right way as soon as I can, Noé I got just a few minutes at work.

What call my atention was about of turning on the bouth hi side and low side mosfets at the same time, If I do the half bridge they must be on at the same time! ...

Perhaps I was confused. Are you building a DC-DC converter, or a DC motor drive? Do you have a link to the circuit you are planning on using?

I am also curious as to why you need a half bridge to control a DC motor. It seems to me that a n-type MOSFET (or a gang of MOSFET's) will suffice. There is no need to reverse polarity, which is what the half-bridge and full-bridge configurations do.
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