multiple output charger using flyback converter

Hi….
Im trying to design a multiple output charger using flyback converter.
I would like to know how the create feedback circuit based on the simulation circuit below….
Below is some properties of this project:
-the PWM pulse send to mosfet using microcontroller (pic16f877)
-the output voltages are 19v and 4v respectively.

If there is any sample, can you send to me….
Please inform me, if there is any mistake.
Thank you.

hi........neo

u circuit looks fine ..... jus tak the feed back of both 4 & 19v 0/p ...... for 4 volt u can give directly to adc... in 16f877a.... for 19v u need to use some opamp to scale 0 - 19 to 0 - 5 and give it to another adc input... according to the calibrated data con troll the pwm o/p in controller...... u can controll the feedback.....easily:-)

the transformer construction ( high frequency ferrite core) is a very crucial part of the SMPS design. Hope u have gone through its literature and understood the principle behind its construction before moving forward in the implementation.
:-)

IN4148 diodes are totally unsuitable.

Control can only be based on feedback from one output.

For small loads it may be better to generate an output near what is needed and use
standard 78xx regulators to get the exact output.

As pdi33 said transformer design will be a challenge.
There are many designs for single output step up or step down circuits.
If this were a practical working project I'd use two of them instead

yep, a fast recovery diode like FR106 or ultrafast diode is best suited for the application.
and just as Experimenter said, as u can use only one output for feed back, u will always need a regulator at the output of the second winding as it will not provide u with a good load regulation.
If u really want to go by Experimenters advice, search for SMPS regulators like LM2575 which can be used for step up application as well and have sufficiently high load current
capability along with high efficiency.
For a detailed reference on flyback design, i would suggest u go through the device datasheet /application notes of power integration ICs like TNY26X which have a good explaination on the design aspects.

:-)

Hi….thank u for all response….

I would like to ask what type of material/component those use in construct the transformer?

Hi,
Im trying to simulate the above circuit it proteus. The problem is I didn’t know how to set up the transformer for single input and two outputs for the circuit i shown above. Can anyone help me on this.
Thanks.

Hi,
Im trying to simulate the above circuit it proteus. The problem is I didn’t know how to set up the transformer for single input and two outputs for the circuit i shown above. Can anyone help me on this.
Thanks.

neo_himura

neo,
there are a lot of issues while dealing with a high frequency ferrite transformer. U have to select a suitable bobbin and equivalent ferrite core like EE16 /EE20 etc... Then u have to calculate the primary and secondary winding, the minimum wire gauges , the inductance etc.... I would suggest again that u refer to a good SMPS design guide before implementing it.
sorry, i have no idea how to create an equivalent model in proteus as each transformer has its own characterisitcs depending upon the input /output voltages,frequency of operation, output current etc.

[Topic moved to Electronics Discussion Forum]