Circuit Oscillating but no output

Thread Starter

Miracletech

Joined Nov 15, 2019
124
Screenshot_2020-04-09-23-34-37.png12v to 220v.jpegthi
I am using this setting in ic 555 to build this circuit.
Please Where did I go wrong? I am using 220v-12v transformer and IRFZ44N. The circuit is oscillating but no output
 

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Thread Starter

Miracletech

Joined Nov 15, 2019
124
View attachment 203991View attachment 203994thi
I am using this setting in ic 555 to build this circuit.
Please Where did I go wrong? I am using 220v-12v transformer and IRFZ44N. The circuit is oscillating but no output
12Vdc input. I thought it was over gate resistance, but it didn't work, so I changed to bjt, didn't work. bought new transformer, didn't work. changed DC input, STILL DIDNT WORK AAAH!
 

Irving

Joined Jan 30, 2016
20
12Vdc input. I thought it was over gate resistance, but it didn't work, so I changed to bjt, didn't work. bought new transformer, didn't work. changed DC input, STILL DIDNT WORK AAAH!
What's your supply, a pp3 battery or something bigger. What transformer are you using (link to data sheet?)
 

crutschow

Joined Mar 14, 2008
24,745
What do you expect?
You are putting pulsed DC into a transformer, which means it is operating as a flyback transformer that will output short, high-voltage pulses.
Is that what you want?

If you want a square-wave output then use a push-pull driver at the 555 output and connect a large capacitor in series between the push-pull output and the transformer input to block the average DC which will otherwise saturate the core.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
124
What do you expect?
You are putting pulsed DC into a transformer, which means it is operating as a flyback transformer that will output short, high-voltage pulses.
Is that what you want?

If you want a square-wave output then use a push-pull driver at the 555 output and connect a large capacitor in series between the push-pull output and the transformer input to block the average DC which will otherwise saturate the core.
diagram sir?
 

crutschow

Joined Mar 14, 2008
24,745
A Push pull means I'm gonna use a bjt right? no FET?
FETs could be used but it is simpler to use an NPN and PNP in an emitter follower push-pull configuration.

What are you powering, and how much current will it draw from the transformer output?
The transistors will have to supply 220/12 ≈ 26 times that current.
 

Alec_t

Joined Sep 17, 2013
11,160
The post #1 circuit has no back-emf protection diode across the transformer primary, so the FET is probably fried. The 555 is lucky to have survived.
 

neonstrobe

Joined May 15, 2009
81
What do you expect?
You are putting pulsed DC into a transformer, which means it is operating as a flyback transformer that will output short, high-voltage pulses.
Is that what you want?
Not really. Though the oscillation frequency is a little low.
First, when you apply a square wave to a transformer, you will get an output voltage in proportion to the turns ratio. Only when the FET switches off will you get the flyback voltage, which, if unclamped, will generate a high voltage in both the primary and secondary windings. So that will lead to a highly asymmetrical output.
When using a 50Hz transformer intended for sinewave input, it may saturate if using a square wave at the same voltage. That will give no output when the core saturates. And if the off period is not long enough to allow de-magnetisation, the transformer will remain saturated and not give any output. THe FET could under those circumstances conduct a high current at ful voltage -- and self destruct.
Increase the operating frequency to avoid cor saturation - something like 80-100Hz minimum for a 50Hz transformer.
THirdly, the mark:space ratio in a 555 timer is not ideal. It has a longer "on" period than "off" and that will tend to increase the current and exacerbate saturation problems (if that is the problem).
And during start-up, the default output voltage is high, and for longer than normal running. That is not a good start-up condition for FETs (nor bipolars really, but especially FETs).
Then decide whether to operate the circuit as flyback or forward, but you won't get A.C. out, you need to rectify the output and add a diode clamp to the primary (leakge inductance is usually high in mains transformers which will give a voltage spike on the primary, even if the secondary is properly clamped.)
If you want A.C. then use a split transformer (dual secondaries in reverse) and drive with a 50:50 marks:space ratio and two FETs or BJTs.
 

Thread Starter

Miracletech

Joined Nov 15, 2019
124
Thank you all for your replies, but something strange happened. I changed the transistor to a D882 Bjt, and the everything works! But my question is,I don't know if if was the FET that had the fault, but it just worked immediately with the D882. I changed to a MJE13005,but it didn't still WORK. as it stands now, I am confused why the Bjt powered it. I reduced rbase to 56ohms and it kicked a few times with the others but didn't work. And also, Can I add more Bjts in parallel?
 

Thread Starter

Miracletech

Joined Nov 15, 2019
124
FETs could be used but it is simpler to use an NPN and PNP in an emitter follower push-pull configuration.

What are you powering, and how much current will it draw from the transformer output?
The transistors will have to supply 220/12 ≈ 26 times that current.
[/QU
FETs could be used but it is simpler to use an NPN and PNP in an emitter follower push-pull configuration.

What are you powering, and how much current will it draw from the transformer output?
The transistors will have to supply 220/12 ≈ 26 times that current.
FETs could be used but it is simpler to use an NPN and PNP in an emitter follower push-pull configuration.

What are you powering, and how much current will it draw from the transformer output?
The transistors will have to supply 220/12 ≈ 26 times that current.
Just a Maybe between 30-80 watts to do some small things
 

Thread Starter

Miracletech

Joined Nov 15, 2019
124
Thank you all for your replies, but something strange happened. I changed the transistor to a D882 Bjt, and the everything works! But my question is,I don't know if if was the FET that had the fault, but it just worked immediately with the D882. I changed to a MJE13005,but it didn't still WORK. as it stands now, I am confused why the Bjt powered it. I reduced rbase to 56ohms and it kicked a few times with the others but didn't work. And also, Can I add more Bjts in parallel?
If fet's work, I'm gonna use em.
 

Audioguru again

Joined Oct 21, 2019
1,302
The circuit will work a little if the output current is very low.
The circuit operates as push-pull so it needs two output devices.
Why use FET's? They produce a voltage loss of up to 20V but the BJT's have less voltage loss of up to 4V.
The horrible old circuit produces a voltage loss of up to 4V from the 555, a voltage loss of up to 25V from the 100 ohms resistor that is not even needed and a voltage loss from the 2200uF capacitor that depends if the frequency is 50Hz or 60Hz.
 

crutschow

Joined Mar 14, 2008
24,745
Note that with a 12V supply and a 12V to 120V transformer the peak-peak output will be no more than 120V for an RMS square-wave voltage of about 60V
 

Audioguru again

Joined Oct 21, 2019
1,302
I think with a 12V to 120V transformer and a 13.2V car battery the output with no load will be a 60V p-p squarewave and be almost nothing when loaded.
 
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