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.

 

[std_match]

I think the uc3843 requires minimum 9V DC in to start, so it seems to be a bad choice for this application.

 

[TuralH]

I think the uc3843 requires minimum 9V DC in to start, so it seems to be a bad choice for this application.

yes, You are right, for uc3843 starting i use mc34063 for boosting from 3.7 to 27-30v and with lm7812 make 12v for VCC, but 3.7v i supplied inductor of uc3843 for boost from 3.7 to 80v

 

[Easy peasy]

3.7 VDC to 80VDC needs 2 or 3 stages to get you there, 1st you need a small converter that will run off 3.7VDC to get you up to 12V say to run a proper control IC,

a small self oscillating flyback can do this,

then you need to look at a cascaded boost ( 2 fets 2 diodes - same gate drive ) to go from 3.7 to 17V, and thence to 80V, 17 being the geometric mean of 17 & 80,
thus the boost in each case is 4.7 x - a much more manageable figure, 4.7 = D/( 1-D ) therefore D still needs to be > 82.5% on the gate of each fet to achieve your ends . . . .

goooooooooooooood luck !

 

[TuralH]

3.7 VDC to 80VDC needs 2 or 3 stages to get you there, 1st you need a small converter that will run off 3.7VDC to get you up to 12V say to run a proper control IC,

a small self oscillating flyback can do this,

then you need to look at a cascaded boost ( 2 fets 2 diodes - same gate drive ) to go from 3.7 to 17V, and thence to 80V, 17 being the geometric mean of 17 & 80,
thus the boost in each case is 4.7 x - a much more manageable figure, 4.7 = D/( 1-D ) therefore D still needs to be > 82.5% on the gate of each fet to achieve your ends . . . .

goooooooooooooood luck !

thank You for Your help and advice. I tried to do a gradual increase, but as I connected the second converter, the voltage of the first dropped to 3V (but it should have been 12V) did you have any experience? For example, I did this, connected two mc34063 in series, but nothing worked, can you send a source or an approximate circuit