555 timer voltage increase

Discussion in 'General Electronics Chat' started by darshelectro, Jan 22, 2007.

  1. darshelectro

    Thread Starter New Member

    Jan 22, 2007

    I'm trying to increase the voltage from a 9volt battery by connecting it to a 555 timer then through a audio transformer.

    The problem is the voltage does not increase.

    The 555 timer works, using 619 Kohm resistors for R1 and R2 and 0.1uf capacitor i get 85 ms on and 42 ms off.

    The voltage goes up and down on pin 3. The transformer i'm using is shown on the website below,


    it is the LT700
    primary 1.2kΩCT
    secondary 3.2Ω

    I have reversed the transformer, so the output of the 555 timer is connected to the secondary. This should increase the voltage on the primary.

    The reason i'm using this transformer is because it is small.And the reason why i'm doing this is becasue i want to see it working.

    When i connect the volt meter to the any of the three wires that come out of the transformer on the primary, i get nothing.

    Can anybody tell me what i'm doing wrong.
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    A post of your circuit would help. One guess is that the 555 can't source enough current into the 3.2 ohm load of the transformer secondary.
  3. hgmjr


    Jan 28, 2005
    I looked at the datasheet for the LT700 and it seems to have the resistance of 12K ohms on the primary and 32 ohms on the secondary.

    Still I believe beenthere has nailed the primary (no pun intended) reason you are encountering a snag is due to the inability of the 555 timer to deliver 9 volts across the 32 ohms. That would require a current of around 281 milliamps. The other problem is that the 9 volt battery is not likely to last very long with that kind of current draw. You can use a transistor driver between the 555 timer and the 32 ohm secondary but the battery is not going to last very long.

    The LT44 would have been a better choice since its secondary is 1K ohms. The 555 would be able to deliver 9 millamps without too much trouble.

    hgmjr (1100)
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
  5. darshelectro

    Thread Starter New Member

    Jan 22, 2007
    I must have misread the label because i thought it read 3.2 ohm, looking at it it say 32 ohms. Thanks very much.