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SMPS charger,how to implement

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freeman3020

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Hi all

I want to design charger with smps transformer
I will use tl494 for pwm and mosfet driver for primary side of transformer for range 150 to 240 v AC
I have some questions here , in secondary side I will get constant voltage let say 14.5 volt to charge 12 volt battery,this method use feedback from output voltage
As i know 12 volt charger output over 14 volt then after connect to battery it will decrease depend on battery voltage, and increase constantly to 14.7 then the charger will disconnect (I assume one stage charger)
here i'm confusing if I used feedback from output the pwm will set to pulse width that output 14.5 ,it's mean feedback will compensate drop voltage

I asked to use correct feedback for smps charger?????
 

you need to regulate the current, then when the voltage gets up to the "charged" voltage, just keep the thing regulating to that voltage.
 

treez said:
you need to regulate the current, then when the voltage gets up to the "charged" voltage, just keep the thing regulating to that voltage.
Click to expand...

how to regulate current,if there isn't load ,if I connect battery current also decrease until battery fully charged?
 

Hi,

First read about charging method and decide which one you want to use.

Maybe you use CCCV.....then at first you need to keep current constant...

Klaus
 
current source on no load.....you need OV protection...VOUT limit
 

KlausST said:
Hi,

First read about charging method and decide which one you want to use.

Maybe you use CCCV.....then at first you need to keep current constant...

Klaus
Click to expand...

I know cccv method, how to set current before battery, it's same voltage sense,

battery will draw more current if it's empty and not take a lot if it's charged ,how to regulate charger
 

you have 2 error amplifierss, one on current , one on voltage...you make the voltage one take over when you get up to a certain voltage.
 

treez said:
you have 2 error amplifierss, one on current , one on voltage...you make the voltage one take over when you get up to a certain voltage.
Click to expand...

please explain it,

i want to ask if i made isolated auxiliary turns on transformer and set it to fixed voltage let's say 5 volt ,then use high ampere secondary for charging ,did the voltage on load drop in each output?
 

Be careful charging batteries with say a flyback and an auxiliary coil, because f the battery is dea flat, then your auxiliary volts may not be high enough because it is coupled to the secondary.
What power level are you here?
You can design it using the PI Expert software of power integrations if you want.
If low power then just use a flyback....they have excellent app notes too
 

treez said:
Be careful charging batteries with say a flyback and an auxiliary coil, because f the battery is dea flat, then your auxiliary volts may not be high enough because it is coupled to the secondary.
What power level are you here?
You can design it using the PI Expert software of power integrations if you want.
If low power then just use a flyback....they have excellent app notes too
Click to expand...

i will not use flyback , i will use push-pull in primary side , output will be 20A , i meant to use 2 secondary one for voltage feedback and one for charging
 
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With push pull the off state voltage of the fets is very high....hence also the switching losses are high.

You coudl do a two transistor forward, much less off state fet voltage......much simpler transformer aswell.

- - - Updated - - -

The push pull converter is basically just two interleaved Single transistor forward converters. (without a reset winding)

- - - Updated - - -

Nobody really uses one transistor forwards, and henceforth, nobody really uses push-pulls
 

regardless to using topology,

suppose i want to make 1 stage charger, in iron normal transformer, if I put 220 to primary I will get 14.5 to secondary , when put this output to battery the voltage decrease under load and over the time the voltage will increase during charging.

in smps we use pwm with duty cycle , so how to set this duty cycle to get 14.5 volt, if I use feedback from voltage the feedback will compensate voltage under load, so battery will not charge or will be in floating mode
 

The error amplifier sets the duty cycle via the PWM comparator.

- - - Updated - - -

In current mode control, it is as discussed...here is an ltspice simulation you can investigate and look how the duty cycle is created in a flyback in this case.

- - - Updated - - -

LTspice is a free download....just change the .txt to .asc and run the sim
 

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