Current flow controller for DC Motors

[mikebar]

Hi,

I had a crashed HDD last year. (Now I use RAID cause I am too lazy too backup '// Actually my projects never gets finished )

I found the PCB layout but seemed to have lost the schematic. Since SG3525 has complementary outputs with dead time. You need to couple (OR) both the outputs and drive the MOS.

The current sense input works on a pulse by pulse limiting followed by a soft start for persistent overload.

Thank you Sougata.
I'm sorry to strees you. Could I ask even a Paint-made schematic of what do you mean?
Maybe you mean take the signal from output A and B and connect to the input of an OR gate?
Then from the output of the OR gate, drive a logic mosfet. Correct?

I've found this info:
http://home.att.net/~wzmicro/3525.html

Is that a good application, in your opinion?

[sougata]

Hi,

My design was almost the same. I used two MOSFETs (common drain / common source) though. Reason:

• Better Current Handling
• Quicker Turn-OFFs -- Because when you use diode OR-ing you loose the low going edge that turns off the MOSFETs fast

Also I used an active Op-Amp amplifier for the current signal.

The link you posted should work absolutely fine.

[mikebar]

Hi,

My design was almost the same. I used two MOSFETs (common drain / common source) though. Reason:

• Better Current Handling
• Quicker Turn-OFFs -- Because when you use diode OR-ing you loose the low going edge that turns off the MOSFETs fast

Also I used an active Op-Amp amplifier for the current signal.

The link you posted should work absolutely fine.

Ok, I'll try it first.
Just a last question:
If I want to use an OR gate instead of the two diodes like you said, supposing that I'm feeding the chip with 24Volts, what is the output voltage level from ports A and B of the SG3525? I suppose close to 24volt as "1". So, in this case, wich kind of OR gate I should use?

[sougata]

Hi,

The SG3525 has an internal 5 volts reference but that is only for the comparator, ramp generator. It has got an internal under voltage lockout function whenever the supply drops below 8 volts (i hope i recalled correct)

The output drivers are designed to directly drive MOSFET gates so if you use a 12 volts regulator to supply the chip. You are good to go. The fast turn-off issue becomes more important when you are switching at a much higher speed. So go ahead with the circuit.

[mikebar]

Hi,

The SG3525 has an internal 5 volts reference but that is only for the comparator, ramp generator. It has got an internal under voltage lockout function whenever the supply drops below 8 volts (i hope i recalled correct)

The output drivers are designed to directly drive MOSFET gates so if you use a 12 volts regulator to supply the chip. You are good to go. The fast turn-off issue becomes more important when you are switching at a much higher speed. So go ahead with the circuit.

So, could be ok to power the chip with 12V and the motor with 24V through the MosFET?
Please note that I have to run the motor with 24V dc.

Thanks.

[sougata]

Hi,

Try out the circuit and then if you need some intelligence / monitoring hook up a PIC micro to the same. In fact with an ECCP module on any of the PICs things are easy in software too.

[mikebar]

Hi,

Try out the circuit and then if you need some intelligence / monitoring hook up a PIC micro to the same. In fact with an ECCP module on any of the PICs things are easy in software too.

Ok, I'll try it as soon I can get one SG3525 part.