# H-Bridge Power Supply Erratic Behavior

Description: I have built a copper plating tank to plate circuit boards and am using a technique called Reverse Pulse Current plating to help aide in the copper plating process. What that involves is essentially flipping the current polarity of the anode/cathode at precise intervals, so I decided it would be beneficial to use an H-Bridge as my device of choice to reverse the polarity when necessary. In my circuit I control the IR2110 with an arduino and have it give a forward pulse (anode +, cathode -) of 240mS and a reverse pulse (anode -, cathode +) of 12mS.

This is the basic circuit I am using: http://2.bp.blogspot.com/-dlEcbNapBZ0/UPvnk7y2MuI/AAAAAAAAAZ4/bfSogInXgj4/s1600/IR2110+-+3.png

However: Vcc is 20V and each high side mosfet Drain is connected to it's own power supply, not +300v.

Part of the process requires that there be a different current for each pulse. To set that, I opted to buy these voltage/current regulators listed below and have one power each of the Drains of the high side mosfets.

They are switch mode power supplies, not linear.

Problem: When I connect this setup to my plating tank (which has next to zero resistance) I get a massive current draw of about 3A, despite setting a current limit through the switching power supplies to a max of 500mA. My mosfets get incredibly hot and my board I am trying to plate gets burned badly as a result of the very high current density. These switching power supplies regulate current through "fold-back voltage" which basically means the control chip regulates the voltage low enough to a point where the voltage level sustains the set current limit. I didn't think this would be a problem because my linear regulated power supplies employ the same technique, and I can connect them as separate supplies to the high side mosfet Drains and it will have no problems.

Question: What am I doing wrong by using the switching supplies vs. the linear ones? What is causing this massive current draw?

## 1 Answer

The current regulating devices in your link are rated at 5A not 0.5A but your real problem is that the IRF2110 won't work at the slow speed/rate you are using it it at I believe. It uses a technique called bootstrapping to enable the N channel MOSFET to be used as the high-side driver and this is your basic problem.

Normally folk use these devices at PWM rates over 1kHz but your rate is only about 4Hz. This means the top MOSFET won't be driven properly and will heat up as per the detail in your question.

It sounds to me like you need a H bridge that comprises N channel MOSFETs for the low side and P channel MOSFETs for the high side.