Thread: [Sproggy PSU] T6 replacement

You can try using MAX1771. It's DC-DC step-up controller,so it can work with voltages below 12v. Use bootstraped mode,as shown in datasheet.Every one of it can supply about 1A without overloading the circuit.
I also used Sproggy's DC-DC PSU,I got all the parts,including T6.The problem was that 12v section couldn't supply enough current for Hard-Disk spin-up,which requires about 2.5A at startup for about 3 sec. After searching the web and consulting with engineers in my work I decided to go with MAX1771. If you look on his datasheet you'll see that the only problem is that you need powerful chokes and diode (about 3A - to be safe),and powerful MOSFET,probably with heatsink on it,depends how much current you'll use.

While back when i designed my DC-DC converter i used the LM2587 Flyback regulator with 1:1 transformer which was available as a sample from coilcraft. After testing the design it was clear that it could handle power load of up to 2 Amps. I ran some tests using a 6Gig Fujitsu HD and a 12x CD-ROM. The test system was P166 based.
Considering the input voltage which can be 8-15 volts the flyback regulations is most suitable design you can use.
MAX1771 is a Step-up regulator .... which means it will work if the input voltage is less then the output voltage. However Maxim claims that Max1771 will operate from 5 to 16 volts... i havent tested this but as far as i know this only can be achived using Flyback regulations. MAX1771 might have integrated Step-up and Step-down regulators in which case it will work as long as the input voltage is less then or above the output voltage... but what if the input voltage is +12 (+-0.5v)?
Dima have you tested the MAX1771 IC ? what was the results like ....


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Fosgate

Ok,to understand what I'm gonna say here you need to look on its datasheet.
There are two possible modes for operating MAX1771: bootsrapped and non-bootstrapped.Bootstarpped mode is more effective in our case,cause we need to suck more current.Use the circuit as shown at figure 2a.For input I'm using 5v,which is taken from MAX787 output (up to 5A!).Also,you can use bigger inductor,about 47uH,that can handle 2A at least.Now,R-slnsl,that in figure is 40mOhm,determines the maximum output current.I'm using 20mOhm,and output current that I get is 1.2A. I'm using two MAX1771,so I have 2.4A for +12v,it's enough for me.
One more thing,I tested the circuit also with 12v input instead of 5v,it worked pretty well and gave me about 1.7A,but the MOSFET became very hot.After checking the currents I came to conclusion that I need more powerful MOSFET that can handle about 3A.After checking the prices I discovered that it's a quite expensive (about 6$ here),and you also need 2 ot these for more current,so I decided to use 5V as input (MAX787 is free!).
I also checked the circuit in figure 6.If the input voltage is more than 12v (situation when the engine is running - voltage raises to about 15-16v),more powerful MOSFET required.
So after all,I decided to stay with bootstrapped mode with 5v input.
Fosgate,when I used LM2587 circuit with T6,I could only get about 0.8A,without using -12V output.How did you managed to get 2A from it?

Dima my design of the DC converter was bit different from Sproggy's. I'm using another transformer from Coilcraft it was 1:1 ratio and was only used for +12 volt. For -12 i was using an inverting step-up convertor from Maxim. Im pretty sure you have the schematic of my design if not i can send it to you, it in Protel format. Its pretty much a standard design from the datasheet of LM2587... nothing special ... with Big heatsink and a fan on it it can handle power output up to 2 amps without any problem ... and it doent get hot at all (well there is a fan on it with a heat sink). Thats about it i guess.
I might play around with Max1771, see if its any better ... it sayes its pretty efficient.
Anyway i will keep you posted.
By the way what MOSFET did you use with MAX1771 Dima?



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Fosgate