[PIC] PWM for currrent and voltage control

[Pulsetronics]

Hi Guys, I want to vary the charging current of my Battery charger from 5A - 30A. I have knowledge on PWM but I need more explanation on how to use it to control current via microcontroller. My battery charger system uses a 1000W 12v Transformer with mosfet as rectifier. How can I vary my current. Thanks

 

[Easyrider83]

You should use buck converter with adjustable backfeed as loop, controlled by MCU. PWM can be used as a DAC.
Or you can use PWM to drive mosfet directly and calculate PWM duty based on current and voltage feedback, converted by ADC.
The first one methode is more difficult, but gives you h/w independed circuit with protection from mcu stuck.
Second one requers very high speed PWM, so the MCU's frequency should be very high to realise necessary PWM accuracy.
For 6 bit PWM working on 300kHz your MCU frequency should be about 40Mhz.

 

[FvM]

MOSFETs as (synchronous) rectifier don't provide a pwm control option because the substrate diodes are still forward biased when the MOSFETs are turned off. You need an additional MOSFET switch for pwm control.

 

[Easyrider83]

Well, try to find in google "Digitally Adjustable Boost Converter"
Like TPS61045 or similar. It has digital input with 6 bit DAC.

 

[Pulsetronics]

I don't want to use boost converter. I already have my transformer, so if I control my PWM duty cycle how will it affect the charging current

 

[Easyrider83]

The current will pulsate, sure :lol:
You also can use opto-triac to control mains voltage, but this is not a true way.

 

[TechGuy]

How about you slightly alter your battery charger that you already have adding a current sensor to it https://www.digikey.com/product-detail/en/MAX4372FEUK+T/MAX4372FEUK+TTR-ND/807299 then feed that voltage to the ADC of the micro then you can generate a pwm in relation of that voltage (current) the only thing is, you need to close that loop controlling your charger output with the pwm generated from the microcontroller.!!

 

[D.A.(Tony)Stewart]

What crest factor are hoping to achieve ?
This is peak/avg ratio?
What efficiency?
What kind of transformer 50/60Hz? Lam. Core?

This is important in determining how and what commutation rate it can support. Without this info, design is impossible.

 

[FvM]

Provided you want to use an existing transformer with Vpk > Vbat, a buck PFC circuit would be the best solution **broken link removed**

 

[Pulsetronics]

Guys check out my circuit.
Will I be able to control current this way for my charger

 

[FvM]

I already told in post #3 why this synchronous rectification circuit doesn't provide PWM control. The substrate diodes will pass the input voltage independent of the gate signal. By controlling the gates with wrong waveform, you can at best short the transformer output.

 

[sahu]

Guys check out my circuit.
Will I be able to control current this way for my charger

View attachment 112931

if u want ac controled o\p then u can use SCR OR TRIAC .for controled input for transformer . as use in inverter .
if u want dc controlled o\p then u can use High-Power CC/CV Battery Charger Using an Inverse SEPIC (Zeta) Topology
AN1467 form microchip download