Identify chip on Chinese 12v speed controller

[Matchless]

I needed a small 12V DC motor speed controller and found one on ebay for a fraction of the cost for all the parts. I ordered it thinking even if it is not good I could use the hardware and build one with a 555.
When it arrived I noticed a small 8 pin IC with the numbers ground off! I traced out the circuit and also measured the PWM output on pin 4 as 15khz and could see the duty cycle changing when adjusting the pot.

I have since looked at many datasheets, but have not found anything that matches how this one is connected.

Does anyone have any idea what PWM chip was used or is it a microcontroller?

[Pedram]

i'm sure it's a microcontroller. because most PWM controllers can work with 12V.
 it's probably a PIC.

[mikerj]

The power pins are correct for a 12C/12F PIC, but pin 4 is the MCLR pin and on all the devices I have used that can only be configured as a digital input (if not configured for Reset).

[Matchless]

The unknown U1 chip is powered with 5V.  Thanks for your replies, hopefully someone can shed some light on this.
I wonder what the purpose is for removing the markings as the transistor and regulator still has its markings.

[cypherpunks]

No idea about the part, but I'm surprised they left opportunities for cost saving on the table.

The one that jumps out at me would be to put the CW and CCW LEDs in antiparallel and use a single 2K2 instead of R1 and R2.

Another hack I've done would be to eliminate R5 and install the "On" LED in place of D2.   There's plenty of drop there, and the supply current of the chip is probably about right to light the LED.

I admit to confustion about what Z1 and R3 are doing in the circuit.  Connecting the top of the pot to pin 5 suggests that IC1 is not a microcontroller.  If it was one with an ADC, the pot would go to +5V, and if it was one without, there would be an external timing capacitor attached to that net, not to pin 2.

Anyway, power/ground are reversed for a 555, correct for an PIC but I can't find one that allows output on pin 4, ATtiny85 has GND on pin 4.

I can find at least one PIC that allows pin 4 to be an output: PIC12F1612 allows pin 4 to be an open-drain output.  I suppose you could go through the rest of their 8-pin product line looking for something.

[Matchless]

cypherpunks, thanks for the feedback.
Unfortunately that PIC is not on my programmer list, otherwise I may have tried to read it.
I have looked at many possible 8 pin chips, but could not find any with a similar pin out yet, especially one that puts out a logic level pulse for the IRL2203N.

I am still hopeful that someone will know what is used here.

[Stonent]

Could be just some kind of 8051 clone. They tend to make their way into the really cheap stuff.

[IconicPCB]

Arrrr....

Isn't this unethical ... I mean reverse engineering Chinese designs?

[bktemp]

The design looks weird: Why does the 7805 needs a heatsink? For a typical microcontroller a 78L05 should provide enough power.
It seems to be a more powerful mosfet driver, otherwise the low value for R4 makes no sense since the output of a typical microcontroller can only supply a few 10mA.

Why does it have a 5.1V zener diode at the output of P1 when its supply voltage is only 5V?
Using a 50V rated cap at the output of the 5V regulator is also odd.
D1 should be at the output (drain) of the mosfet, not at the soure.

Either it was designed by somebody without much experience, or they used the next best parts they could get.

[sunnyhighway]

Would the TC643 make any sense?

http://www.datasheets360.com/pdf/1024631978325838882

[Kjelt]

Would the TC643 make any sense?

Close but no sigar, the gnd is not properly connected.

My best bet is to look at http://www.onsemi.com  they have hundreds of this kind of ic's.

[dannyf]

The design looks weird:

Witout knowing what the chip is, it is without basis to say that the design looks weird.

Why does the 7805 needs a heatsink?

High power dissipation because of high output current from the driver?

For a typical microcontroller

You are assuming that it is a microcontroller.

It is unlikely a microcontroller. Looks to be a specialty chip, a gate driver with built-in oscillator (IRF has a few such beasts).

[bktemp]

Why does the 7805 needs a heatsink?

High power dissipation because of high output current from the driver?

The gate  of a mosfet is basically a capacitor. The IRL2203N has a quite large gate charge of max. 60nC, but it is driven only at 5Vpp. Assuming a switching frequency of 10kHz, this gives a power consumption of <10mW. Therefore no need for a 7805 with a heatsink, even if the supply voltage is 24V and my calculation is an order of magnitude off.

For a typical microcontroller

You are assuming that it is a microcontroller.

It is unlikely a microcontroller. Looks to be a specialty chip, a gate driver with built-in oscillator (IRF has a few such beasts).

Guessing from the regulated 5V supply it looks like it is one, but as I said, the gate resistor has a too low value to make sense for a microcontroller output pin.
Non of those gate drivers needs a well regulated 5V supply. Almost all mosfet drivers are happy with a wide supply voltage range. Some of them have even a build in zener diode across Vcc, therefore no need for an additional regulator unless you need a wider input voltage range.

[Matchless]

Thanks for all the replies, but I still have not identified a likely match. 

This makes me sure that as per Murphy's Law this will be the part that will fail first!

Any other suggestions wil be appreciated.

[SteveC]

Hi,

Did you ever find out what this chip was?  I have recently bought an identical unit to power a 12V motor with a max run current of around 60mA.  Start current is around 300mA.  The controller ran fine for a few hours, then died.  At first I thought it was the mosfet, as the motor still ran but with no control.  I tried a possible substitute as I could not get the right type quickly and cheaply, but it did not fix the issue.  Then I realised the 7805 was putting out 9.6V, enough to possibly fry the unidentified chip. Why the 7805 was putting out 9.6V I have no idea unless it got fried somehow.  I replaced the 7805 and it now works.  As the 7805 only provides VCC for the chip, the chip must have an over voltage protection inbuilt.  I am powering the unit with 12.5V from a 3 cell RC Lipo battery.

Considering these units are dirt cheap, I will order a few more.  The supplier is sending me a replacement free of charge.

[Matchless]

No I never did unfortunately, but repaired it by replacing D1 and T1. Its since been working perfectly as a variable 12V DC motor speed control between 800 to 14000 RPM.

Never connect it without a fuse, only then you can make a mistake and reverse the power leads without blowing D1 and damaging T1!

[SteveC]

Thanks.  The more I think about it, I suspect the chip provides a ref voltage to the pot, if that is too high as it was in my case with the 7805 gone, then control would be lost.  The reason I did not suspect the 7805 at first with 9.6V out was that without the circuit at the time the 7805 could have been set uo to provide the 9.6V.  I'm using it as a motorised star tracker for astro photography.  Apparently there are pwm chips that are only available in China, maybe this is one of them.  I have actually asked the supplier for a full sepc including chip detals, doubt I'll get them though.