Transformer power supply question

Discussion in 'The Projects Forum' started by DougB, Sep 29, 2010.

  1. DougB

    Thread Starter New Member

    Sep 11, 2010
    Have a few schematics for a power supply for a CCD camera I am building. I prefer one because it solves a Thermal Electric cooler(TEC) power supply issue I was having by using a PWM. I have a few questions with regards to transformer requirements for the power supplies.

    The camera requires a linear regulated and very quiet +/- 15VDC supply. This is done on one schematic by using LM7815 and LM7915 regulator and on the other by using a LM7915 and a LM317 along with an assortment of capacitors/resistors. Either way I don't think it is much of an issue. Difference is one uses a 28V CT transformer and the other a 36V CT transformer. They are both 1 amp transformers. The load is about 40 mA on the positive side and 20 mV on the negative side. I already have a 28V CT transformer. Will this supply me with the +/- 15 volts I need. (14.75 will probably do). I should say that I believe both are working in similar cameras although they are slightly different from each other with respect to the sensor they have on board.

    Second question has to do with the PWM. The developer of this cct uses an unregulated 12VDC via a 12V transformer at the input to the PWM cct. The input range of this particular PWM is 6-36 VDC . Output is required to be no more than 7 VDC at about 3 amps. I also know that he has a few variable trimming capacitors in the cct which are supposedly used to calibrate the supply to the TEC. I have a 16V transformer. In the overall scheme of things is this a significant problem?
  2. AlexR

    Well-Known Member

    Jan 16, 2008
    Given that your loading is very light, the 28V-CT transformer should be fine. A 14V per side AC voltage translates into a peak rectified voltage 19.8 Volt per side which gives plenty of head-room for the regulators to regulate it down to 15Volt.

    As for your second question, without seeing the circuit its impossible to say whether using a 16 volt transformer will work or whether your circuit will end up toast.