Hex file too big for chip

[Ian Rogers]

Hi Ian,
The current sense op amp (Pins 5, 6, 7) will not be a problem as both inputs will be very close to ground. The voltage sense op amp (Pins 1, 2, 3) will have the output voltage scaled down by R9 and R10 1.8K/(1.8K + 10K) = 1.8/11.8 = 0.1525. So when thye output is at 20 volts the input to pin 3 of the op amp will be 20 * 0.1525 = 3.05 volts.

Les.

So if I use a MCP6244 ( 1,8 ~ 5v device ) I'll be okay?? I haven't got the 15v device listed!!

Both have a specific +0.3vdd maximum on all out / inputs...

Nice little circuit.... I'm converting the code to C and using a small LCD for the readout...

I have a TIP107 ( Darlington ) and all the other components.... I've always wanted to build one of these!!!!

 

[Les Jones]

Hi Ian,
I've just had a look at the data sheet on the MCP6244 and it looks like it should be OK. I was concerned that the that the inputs would have to work a to close to ground but the data sheet says that the inputs and output can be used up to either power rail. I have not looked at the code to see how it works but I suspect that the output of the voltage sense op amp is fed to the ADC in the PIC. (The op amp will output 3.6 volts to the PIC when the output voltage is set to 20 volts.) I think the TIP107 should be OK as long as the PWM fequency is not too high. Just out of interest I have recently bought**broken link removed** regulator / display modules from ebay. It performs a similar function to the unit being discussed.

Les.

 

[Ian Rogers]

Awww!! But I want to make one!! Doubt I could do it for that price.... I think the micro cost that!!!

I was going to jack it up slightly to 24v... The TIP107 is good for 1Mhz I was thinking of running at 40~50Khz ( that's what LM2675's run at!! )... I can ditch the 10000uf cap as the 24v supply I have is regulated ( I just hope it isn't running at 50Khz LOL )

We'll see.... Boards done ( except for the current sense resistor ( 0.01r seems awfully low )..

 

[Ian Rogers]

Whoops... May have misread!!! I have a TIP42C ( This runs at 1Mhz ) No spec for the darlington... Ah well easy enough to change at the moment.... I may have to boost the NPN as I don't think 100mA will be enough for the TIP42C it has a min gain of 20... --- 2A... I'll have to swap it out...

If the darlington works, I can leave it!!