High voltage

Thread Starter


Joined Jan 22, 2007
This is my first time using audio transformers, and i want to make sure i get my calcs correct.

Could you tell me how you would work out what the voltage output on the secondary side will be , if 9 volts from an ac supply was applied on the primary side of the transformer.

More detail:

The 9 volt supply is from a 9volt DC supply. A 555 timer with and transistor on the output will allow the transformer to operate, as the 555 timer will generate square wave. I need a output voltage above 150 Volts and below 230 Volts. I have attached a sample drawing of the circuit.

Below is my calculation:

Primary side:
9 volt supply, resistance 75 ohms, therefore current 0.12 amps.

Is/Ip = (Zp/Zs)^(1/2)

Is= Secondary current, Ip=Primary current , Zp= primary impedance, Zs= Secondary Impedance

Is/Ip = (1200/8)^(1/2)

Is/Ip = 12.2 * Ip

Is= 12.2*0.12 = 1.2 amps

Secondary voltage = (V=I*R) = 1.2* 1 = 1.2 Volts , should be over 150 Volts

The electronic guy has told me that this circuit does produce volt over 150 Volts, as he is away and i am trying to get my head around this, do you know where i have gone wrong?

If so can you correct my mistake?



Joined Apr 20, 2004
Working off the turns ratio, the voltage step-up is 150 (1200/8). With 9 volts driving the primary, that will give you 1350 volts out. For 150 volts, the turns ratio should be more like 16.66.


Joined Oct 11, 2004
Could it be that he has used an output transformer for matching the 1200Ω output impedance of an amplifier to an 8Ω loudspeaker?

If so the transformer will have a turns ratio of 12.2:1