Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

12V Full bridge waveform doubt

Status
Not open for further replies.

mrinalmani

Advanced Member level 1
Joined
Oct 7, 2011
Messages
460
Helped
60
Reputation
120
Reaction score
54
Trophy points
1,318
Location
Delhi, India
Activity points
5,270
Hi
I am testing a 12V full bridge converter connected to a step up transformer. The output of the transformer is rectified using a SiC bridge diode. There's no inductor between the SiC output and the bulk capacitor.
The transformer is being driven by simple PWM. Alternate high and low FETs are on for a brief interval followed by a large deadband where all switches are off. During deadband, the current through the transformer leakage should reset to zero. But instead of stopping at 0A, it shoots negative and then snaps back to zero. The negative overshoot is significant. What could be the reason for the negative overshoot? Could this cause potential heating? Please share your opinion.
Here is an attached oscilloscope snapshot.
 

Attachments

  • Full_Bridge.png
    Full_Bridge.png
    209.7 KB · Views: 51

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
21,103
Helped
4,533
Reputation
9,078
Reaction score
4,631
Trophy points
1,393
Activity points
139,264
Hi,

I guess the problem is caused by D1.

Klaus
 

Easy peasy

Advanced Member level 5
Joined
Aug 15, 2015
Messages
3,542
Helped
1,227
Reputation
2,454
Reaction score
1,366
Trophy points
113
Location
Melbourne
Activity points
19,152
your current measuring device may be in error ... esp if it is a CT that needs resetting ....
 

BradtheRad

Super Moderator
Staff member
Joined
Apr 1, 2011
Messages
14,304
Helped
2,823
Reputation
5,654
Reaction score
2,774
Trophy points
1,393
Location
Minneapolis, Minnesota, USA
Activity points
106,693
Your waveform looks as though it goes with a modified sinewave. It has a similar dead zone between the positive and negative pulses. The dead zone involves abrupt shut-off of current.

However it's difficult to make an inductive load (or transformer) compatible with this. The transistor shuts off current but the inductor wants to continue yanking current through the wires.

I've seen a similar overshoot in my simulations of a transformer driven by pulses via an H-bridge.

It could help if you turn off current less abruptly. Or, by providing a path for transformer current during dead time. It might be a snubber network, or diode clamping, etc.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top