Generate high voltage using LM555 with a transformer

high voltagetransformervoltage

I'm a French student (please forgive my bad English spelling) who works on a system of portable echograph (you can find the information of the project on the wiki of echopen). Could you help me please?

I would like to generate a tension of 100V. First, I took a transformer from a system which is used to transform 230v to 12v. I tested it with a frequency generator to determine the inductance of the coil and the transformation coefficient:

L1 = 11.13mH
L2 = 31.89 mH

I saw that at 13kHz the voltage was higher.
I transformed 15Vpp to 110V and I wanted to integrate it into a system which used 10v.
So, I used a LM555 component to have a oscillating circuit.

The circuit I used:
Oscillating circuit

My observation and problem:

  • I want to use a MOSFET to control the 10v but the voltage is dropping
  • The generating voltage from the transformer is not enough maybe I
    need two elevation stages
  • When I plug the transformer, the square wave signal is distorted
  • I can't have more than 50V from the transformer (I have more using
    the frequency generator)

You can find my work on this page

Edit: I forgot to tell, I can't have more than 50V from the transformer using the oscillating circuit, with the frequency generator I have 100V from 15Vpp (the problem is the tension dropping with a load resistance I suppose the frequency generator don't have power enough)

Edit 2 (02/31/2015) : this circuit works thanks a lot to everybody and especially "jp314", I have 130V from 12v!

Best Answer

You need to determine how much power you need to transfer. From your wiki, I think you need plenty of peak power, and this circuit won't do that.

You don't actually need a transformer -- a flyback converter (boost DC/DC converter) will work, although you will need a high duty cycle to get 230 V from 12 V at high power. At low power, you can use discontinuous conduction, and simpler control (maybe even a 555).

To get started, use a single inductor between supply (12V) and a switch transistor (rated at > 230 V). drive the transistor on with the 555 for a time so that Ipeak = Vsupply*T_on/L, and Ipeak reaches the peak you need (related to the power you need). Then turn off the transistor, and the collector voltage will spike up (because of the inductance) to a high value -- use your D1 & C7 to rectify that. If you limit may duty cycle from the 555 to < 90 %, your circuit won't run away. Regulated the output by masking pulses when VOUT > 230 V.