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Registered Member #4465
Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145
The PTB48560x is a series of 30-W rated isolated DC/DC converters, designed to operate from a standard 48Vdc telecom supply. This model (PTB48560B) has a adjust output voltage that can be set to intermediate bus voltages of 1.8 - 3.3 V. The input Voltage: 36 V to 75 V 30-W Total Output Power Output Voltage: 1.8V up to 3.3 V Up To 88% Efficiency Overcurrent Protection
I was quite lucky to find those converters on sales, at 4 euro per item. The major problem I ran into was the board is a 4-layer with lots of tiny traces. The trick was to get the circuit diagram of the DC_DC supply and based on that diagram to hack the PCB to get the desired output voltage. I took pictures o the front and bottom traces of the PCB.
L393= LM393 257021=UCC25702 Advanced Voltage Mode Pulse Width Modulator IC T1IG= TL331IDBVRG4 SINGLE DIFFERENTIAL COMPARATOR 8101= MOC8101 VBGI= TLV2371ID single supply operational amplifier Y2W= BZX84-C12 Voltage regulator diode 7464= Si7464DP N-Channel 200-V Fast Switching MOSFET 7840= SI7840DP N-Channel 30-V Fast Switching MOSFET S15L30C= STPS15L30CDJF Low drop power Schottky rectifier B4H= Low drop power Schottky rectifier diode W2X=PMBT4401 NPN Switching Transistor 40 V 600 mA 4NCU= LM4040C50IDBZR 5V Precision Micropower Shunt Voltage Reference 8K= N channel MOSFET transistor KJC= BAW56W DUAL SURFACE MOUNT SWITCHING DIODE KJG= BAV99W DUAL SURFACE MOUNT SWITCHING DIODE W5C = PMBD7000 two high-speed switching diodes YJ03= NPN bipolar transistor 702= 2N7002 N-channel Trench MOSFET 60 V, 300 mA E:A= ? (That’s seems to be some kind of under/overvoltage safety circuit) HHS3= ADT6501-ADT6504 ? Micropower Temperature Switches RLB= ? 3-terminal adjustable shunt regulator
So, in order to lower the input voltage, all that's needed is to change R11 or add another resistor in parallel, and the 91k up to 100k resistor will do the trick. For this setup the minimum input voltage is about 20Vdc.
To adjust the output voltage we need to add supplementary turns to the secondary transformer and a new resistor R51. At 5V one turn is necessary and for 12V 4 to 5 turns to be added. The value for 5Vdc output R51= 31.5k and for 12Vdc output the resistor value R51= 5.3k. For the 12Vdc output, in order to minimize power wasted in PCB, we need also to change the R25 and R46 and to take out the R33.
See the final hacked version of the PCBs:
I have done tests on 12Vdc output using a 10 ohms load. At this power level some of the PCB components temperature reaches up to 90°C. See the attached thermal pictures of the board at start-up and later on, after 15 minutes on a 10 ohms load.
The wide output voltage adjust range and the wide input voltage range makes the PTB48560 series of converters an attractive product as a stand-alone dc/dc converter. Now the output voltage can be adjusted to any value within the applicable adjust range. In this case the Auto-Track features are simply not used. Final products:
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Reverse engineer of PTB48560B 30W DC-DC isolated converter in order to change its output voltage.
