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LM51581-Q1: Boost converter circuit from WBENCH deign not working

Part Number: LM51581-Q1
Other Parts Discussed in Thread: LM5158

Hi team,

Customer has some questions

I am having much difficulty getting a Boost configuration working properly. I need 50VDC output at about 200ma.  


I used a design from WBENCH with a 500khz switch frequency . I have an an electrolytic capacitor for the output at 47uf.  The feedback resistors are the right ratio but larger than specified. The inductor is one on the list provided (47uh) .


The circuit produces 50V but will not provide the specified current.  Also, the start up time is long (over 1 sec). A .1uf capacitor is used for Css .

Hiccup protection is disables as is spread spectrum.  This circuit is the last issue before the design can be produced. Volumes are 50 to 100K per year.  I am late with delivery and have a very irate customer. Please respond. I can send you the schematic (attached).



Only one of the 3 inductors is used. Also, the compensation R and C are different than in the WBENCH design but the RC constant is in the same ballpark. 


You will notice that the boost feeds a 100uf capacitor through a diode. The load is a small HV pulse transformer.  5 20usec. pulse cycles are applied followed by dead time for the remaining 15ms.  This is then repeated. All the current is supplied in the 100usec intervals. Current levels during the pulse periods are in the amperes ranges which is why the 100uf  capacitor is present.  


A design from a foreign source (which this design replaces) uses the same technique and it works,   If the real load is disconnected and I just put a resistive load across the 47uf capacitor, the 50volts drops to 20 or less so the boost is not supplying enough current although the WBENCH says that it should. The LM5158 I am using has the 3A switch and is automotive grade.

Thanks in advance for any assistance.


 Could you help?

Thanks & Best regards,