Half bridge Electronic Converter Tips Needed

[stuartiannaylor]

Hi,

Trying to get started with a microcontroller and half bridge circuit for an electronic transformer application for halogen lamps (12V ac output).

All the examples seem to use chips like the IR2161.

I just wondered if anyone has any circuits where something like a pic using pwm and a half bridge circuit instead of a custom chip. I am struggling with the feedback circuit but any application notes would be greatly appreciated.

Stuart

 

[stuartiannaylor]

Hi I am not doing very well! Lol. Its probably my ignorance of the power side of electronics. Apologies if my terminology is incorrect. Is everybody stumped or is it my description?

What I want is a rough application note or any circuits tips on how to provide approx 30Khz Half Bridge and feed back circuit for 220Vac to 12Vac.

Basically an electronic transformer?

 

[stephen the obdurate]

A half bridge is easy using two outputs from a microcontroller. You just make sure that you don't turn both halves on at the same time. It's important to check the processor initial output levels so you don't have a problem on power up.


The low side can be an NMosfet driven directly from the processor. Most microprocessors have a strong pull down so you can use a pull up resistor to the gate turn it on. Any logic level NMosfet will work.

You can use a driver chip for the high side as you suggested. There are lots to choose from.

One problem with driving a lamp is the huge inrush, of 10 to 15 (or more!) times the final current. This is fast but if you have any overcurrent circuit protection it may trigger on the inrush.

An IR3310 (replaced with a 90A IR3316?) is a nice 100 A high side switch with protection but It won't drive two 55W 12V headlight bulbs due to the inrush and sometimes won't drive a single bulb if the bulb is cold.

Added after 26 minutes:

A half bridge is easy using two outputs from a microcontroller. You just make sure that you don't turn both halves on at the same time. It's important to check the processor initial output levels so you don't have a problem on power up.

The low side can be an NMosfet driven directly from the processor. Most microprocessors have a strong pull down so you can use a pull up resistor to the gate turn it on. Any logic level NMosfet will work.

You can use a driver chip for the high side as you suggested. There are lots to choose from.

One problem with driving a lamp is the huge inrush, of 10 to 15 (or more!) times the final current. This is fast but if you have any overcurrent circuit protection it may trigger on the inrush.

An IR3310 (replaced with a 90A IR3316?) is a nice 100 A high side switch with protection but It won't drive two 55W 12V headlight bulbs due to the inrush and sometimes won't drive a single bulb if the bulb is cold.

I don't understand where the 220VAC comes in. Are you trying to drive a 12V load directly from 220VAC?. You don't need a half bridge for this. A half bridge commonly has an output that is pulled high (usually to 12VDC or more) or to ground.

If you want to power the halogen lamps directly from the 220VAC you could use a simple mosfet to ground and a circuit that shuts off the output when the circuit reaches the target current. There should be some low side drivers that provide the protection though I'm not sure they would recover fast enough once they reached overcurrent,

The inrush here could be a big problem. Once the bulb is warm it won't have significant inrush, but when it's cold the inrush could trigger the control circuit so the bulb never comes on.