too much voltage in the output of step up boost converter

[Rishles69@]

I have made a simple step up boost converter using a 555 timer for my audio amplifier. Its working pretty well, but the problem is the voltage uncontrollably increasing at its output stage. I tried loading it even with a 100ohm resistor, still nothing. this converter I have made is capable of delivering up to 3 amps. 555 timer circuit creates 34khz...

[Andy Chee]

If you want to reduce voltage, you can reduce the duty cycle.

Ideally you want to use feedback to regulate the voltage, for example, notice the output voltage from the following schematic feeds back to the controller chip:

[Rishles69@]

is there any way to add a similar feedback circuit to this 555 timer ?. does increasing the frequency of my 555 timer do the job?. I don't think a boost made with this ic(lm2587) can power my amplifier. the amplifier i made is a classAB amplifier which will take 2 Amps at its full power also the circuit shown can only produce 20v where my amplifier needs +-25v. is it possible to add a mosfet to switch pin for more power?

[Andy Chee]

I recommend playing with TI's webbench to find a suitable circuit topology and part number.

https://webench.ti.com/power-designer/switching-regulator?powerSupply=0

Webench doesn't allow for multiple output rails.  But if you just design for a 50V 2A output, flyback, then you can use a similar transformer winding and rectifier scheme as the circuit I posted, to generate the dual rails.

[Rishles69@]

that ic (lm2587s) in not available here. and without the option to connect a mosfet to the ic's output i don't think its going to last very long. the amplifier i made can do 70 watt RMS to 4 ohm load.
does increasing the frequency of the 555 timer do the job to some extend? is there any way to add a feedback circuit to this ne555?. the circuit i made is capable of handle the amplifier. but when its on idle or the amplifier is not playing a music, the voltage rises, and the driver transistors of the amplifier starts to get overheat.

[Andy Chee]

How about the TL494 chip?  If you cannot obtain it from your supplier, you can surely obtain one from a scrap e-waste AT/ATX computer power supply.

You can use the TL494 to control the MOSFET in your design.  Or even better, rewind your transformer for push-pull operation.

I would abandon the 555 for this power supply project.

https://www.onsemi.com/pdf/datasheet/tl494-d.pdf

[Rishles69@]

The circuit should be very small and adjustable, also it should be very efficient more than 70%. i already had made one with tl494 and the voltage is not very stable as it should be because the voltage drop significantly. later i made another boost converter using 3525A which was very powerful and stable. and now it is used to run a 500w RMS 3.1 amplifier i made. but the problem is these circuits are too large for my new project... the 3525a can hold 10Amps 80volts for a pretty long time.

[Andy Chee]

i already had made one with tl494 and the voltage is not very stable as it should be because the voltage drop significantly.

I think that's because you didn't use the feedback on the TL494.  Try it again with feedback.

Another simple chip to try is the MC34063A.  If your supplier doesn't have this part, you can also get it from e-waste mobile phone chargers that plug into car cigarette lighter.

[MrAl]

is there any way to add a similar feedback circuit to this 555 timer ?. does increasing the frequency of my 555 timer do the job?. I don't think a boost made with this ic(lm2587) can power my amplifier. the amplifier i made is a classAB amplifier which will take 2 Amps at its full power also the circuit shown can only produce 20v where my amplifier needs +-25v. is it possible to add a mosfet to switch pin for more power?

Hello,

The mechanism behind voltage regulators is they have some sort of negative feedback that adjusts the output to some set level.  This is done by comparing the output voltage to a reference voltage and developing a signal that can control the switching circuit.

To get this to happen with a 555 timer, you would have to incorporate the modulation input which in a regular 555 is pin 5.  A voltage at this pin would change the duty cycle and maybe the frequency too, but you could look into that. It has to be set up such that a higher voltage at the output reduces the duty cycle, and a lower voltage at the output increases the duty cycle.  The frequency may not matter as much but something to pay attention too also.

To start, I would look up "555 timer as voltage regulator" on Google.  You should get some idea circuits to start with.

[DavidAlfa]

No so feedback, the output voltage will heavily change with load.
Why the gate potentiometer? If that's your workaround to reduce the output, its totally wrong, you must adjust the PWM duty not the mosfet condictivity.

As they already told you, the proper circuit for this is the TL494 / KA7500.
If it wasn't stable, it problably was due a poor circuit design. Specially with flying wires like that.

A TL431 might do the job. Add a optocoupler to provide isolation. Adjust the ref pin resistors to limit the voltage.

[Rishles69@]

"Why the gate potentiometer? If that's your workaround to reduce the output, its totally wrong, you must adjust the PWM duty not the mosfet conductivity.", yeah, a piss-poor connection. I was too much urged to test my amplifier so i did that. I didnt had time to find proper value for the potentiometer, also the whole circuit is made with calculation from ohio(no calculation was done properly) even the transformer winding the mosfet can get really hot within a less amount of time while operation

[alligatorblues]

I have made a simple step up boost converter using a 555 timer for my audio amplifier. Its working pretty well, but the problem is the voltage uncontrollably increasing at its output stage. I tried loading it even with a 100ohm resistor, still nothing. this converter I have made is capable of delivering up to 3 amps. 555 timer circuit creates 34khz...

There's a very annoying aspect of audio amp  design. There's always one thing at the end that doesn't fit right.

[Rishles69@]

speakers, every time, to be honest... I remember wasting one whole day just to find 50w 8ohm speaker. at last i went to a shop. the shop was actually only for speakers. i asked them for a 6 inch 50 watt 8 ohm speaker, after a long waiting they found one from an old stock. on that speaker, no specs were marked they told me it was for 40watt continuous and also told me something very interesting "this speaker is made for both 4ohm and 8ohm". Wait WTF.! how is that even possible, My bad, i forgot to bring my multimeter the check the actual resistance. they didnt had the multimeter. i brought it home, checked it with my multimeter and its 4ohm. My bad... anyway i hooked it to my 100w amplifier. to be honest, for some thing that cost about 300 rupees it actually sound pretty well. it had a slight coil rub. any way it blew up within a month. WHY? the coil wasn't aligned properly. the coil is half burnt 

[Rishles69@]

is it a good idea to go with this IR2153 it is pretty cheap and available everywhere https://pdf1.alldatasheet.com/datasheet-pdf/view/68074/IRF/IR2153.html , also is there any idea of the operating frequency of this?
it als has a feed back circuit for it

[Andy Chee]

IR2153 does not have feedback.  You will have the same uncontrollable increasing voltage problem that you had before with the 555.

[tooki]

that ic (lm2587s) in not available here.

Yes it is. You can get it from Digi-Key, which officially sells to India.

[Rishles69@]

https://www.homemade-circuits.com/smps-2-x-50v-350w-circuit-for-audio/  transformer will be modified to handle 80volts, 20amps this circuit have a feedback...

[dmulligan]

is there any way to add a similar feedback circuit to this 555 timer ?

Yes it's possible though not necessarily recommended.

https://youtu.be/-kGhAGvmLJk?si=8ZIJjuhmN2-i8YFJ

[Rishles69@]

is it possible to replace the 2n7000 with tl431 ? what about the potentiometer value...

[Rishles69@]

i think my intrusive thoughts started to win...

[Rishles69@]

i think this circuit is working pretty well... is the any way to add a mosfet to the coil? (transformer)

[Rishles69@]

i think this circuit is working pretty well... is the any way to add a mosfet to the coil? (transformer)

is it possible to add another mosfet to the output of the ic (which already equipped with a mosfet) for more amperes? this circuit is pretty stable...