[SOLVED] UC3843 boost converter (boost from 3.7 to 80v)

[TuralH]

I want to assemble a dc-dc converter that will increase the voltage from 3.7 volts to 80 volts/
I need to increase it using uc3843, but due to the fact that this PWM controller operates from 12-28 volts, I assembled another boost converter on mc34063 increased it to 27-30 volts and using LM7812 supplied 12 volts, in Ltspice the circuit works and the expected voltage is obtained at the output, but in reality and in practice will it be possible to increase the voltage using uc3843 and external NMOS from 3.7 to 80?
The duty cycle is: D≈83.76% simulated in LTspice and with 91khz of frequency. Of course there are ready-made DC-DC converters that can do this, but I would like this circuit to work too.
I will be glad for your help. Photos of the simulation are attached below.

 

[TuralH]

Frequent advice is to beware of paralleling power supplies. The risk is that one gets 'weaker', sags in voltage (for whatever reason), thus obliging the other 'strong' supplies to send current through it in reverse. This is surely counterproductive. Steering diodes are one solution although that subtracts voltage from already low 3.7V supplies.

In a reply above I jumped prematurely to the conclusion you had battery power (Li-ion type) because 3.7V is common for Li-ion cells.

Did you rule out taking 80VDC from house voltage? With a few added components? Of course that brings its own hurdles.

I assembled this circuit and I managed to achieve 80V from 3.7V to charge a 1000uF capacitor, but I would also like to assemble a circuit with cascading, can I gradually increase the voltage but the gate drive must be from one IC for mosfets

 

[D.A.(Tony)Stewart]

you cannot design anything without design specs for load regulation error and expected power-time depletion rate of cells. for 2.4Ah used at a 2A primary rate you cannot step the voltage so you might as well reconsider your power source requirements. If using batteries then you need 80/3.6=22.2 series batteries. If you need it regulated then alternatives are simpler.

 

[Easy peasy]

3.7 V x 4.5A = 16 watts, for your ave output volts of 40V ( cap charging to 80V, 2200uF ) this is 0.4A into the cap ( an average remember )

i/c = dv/dt gives us 0.5 sec approx to charge the cap - it will be a parabolic charge curve as the current drops off for constant power as the Vout goes up

you can do this with a single flyback too

 

[TuralH]

3.7 V x 4.5A = 16 watts, for your ave output volts of 40V ( cap charging to 80V, 2200uF ) this is 0.4A into the cap ( an average remember )

i/c = dv/dt gives us 0.5 sec approx to charge the cap - it will be a parabolic charge curve as the current drops off for constant power as the Vout goes up

you can do this with a single flyback too

1000uf capacitor is charging about 2-3 sec upto 80V. The only thing is that instead of mc34063 as power supply for uc3843 I used xl6009 boost converter since uc3843 works with 10V

 

[BradtheRad]

managed to achieve 80V from 3.7V to charge a 1000uF capacitor

It's hard to argue with success. Nor can my advice outdo advice you've gotten from the expert replies elsewhere. Since you say 'gradually' that's a key strategy as you're approaching high voltage levels. I was going to say put a finger on the mosfet so you can monitor its temperature (because of the watt level you're pushing through it). However we ought not poke around high voltage if we can avoid it. Consider placing a thermistor and led circuit near the mosfet.

 

[TuralH]

It's hard to argue with success. Nor can my advice outdo advice you've gotten from the expert replies elsewhere. Since you say 'gradually' that's a key strategy as you're approaching high voltage levels. I was going to say put a finger on the mosfet so you can monitor its temperature (because of the watt level you're pushing through it). However we ought not poke around high voltage if we can avoid it. Consider placing a thermistor and led circuit near the mosfet.

you are right, the power dissipationis 2-3W makes mosfet hot

 

[Easy peasy]

Nearly all mosfets require heatsink - esp if their on resistance is high and/or the gate switching is too slow in the transition.

Full details about what you were trying to achieve in post #1 would have shortened this thread - e.g. cap charging, cap size, end volts, target times ...