TL5001A: inverter

Hi JB,

Thank you for posting and for considering our solution.  I think the driver logic inverting FET Q42 should be used with its source pin to IC GND node (which is also your -100V rail in the configuration), and R76 be inserted between the drain of Q42 and the gate o Q43.  Do you agree?

Thanks,

Youhao 

Hello Youhao. I don't understand issue you see with Q42. Q42/R76 limits current at 9 mA. Thus, voltage at Q43's gate is always between V20 node (28Vdc) when TL5001 internal switch is open and V20-Vz(D34) = 28 - 15 = 13V.

Example:

M1 acts as a current limiter. For simulation, V1 takes values between 0 and 100V (and not 35V, I haven't modified schematic).

Best regards,

JB

Hi JB,

Very sorry my bad:  I thought M1 was a regular NFET just by seeing the symbol.  I should have done this yesterday:  I just checked the datasheet online and realized M1 is a depletion mode FET, which we do not use often in our regular work. 

Then, your circuit should work.  I just recommend to things:

• reserve an RC snubber across D35 in case it is needed after testing, then you can avoid doing a new PCB.
• Add a RC branch in parallel with R78 (like seen in the datasheet example circuit, which I copy and pasted below).  This is a voltage mode controller and it need this RC to help stabilize the loop with a Type-3 compensation.

Again, sorry for the confusion and good luck in your project.

Thanks,

Youhao

Bad news, Youhao.

I have wired a test and TL5001 doesn't start.

Green is GND, white is +15V and I expect between black and green around -100V.

I have simplified my test and I have removed D3, R9, Q3 and Q4. Now, I have put a 15V power supply between green and white and another floating power supply (15V also) between pin 2 of TL5001 and black. Same result.

I'm trying to simulate this circuit in PSpice (trial version) as PSpice has a TL5001 model as you doesn't provide model for this chip, but if you have an idea...

Best regards,

JB

Hi JB,

Sorry to hear.  It seems a problem in the gate drive circuit.  The 10k (R3) does not allow the PFET's inherent gate capacitor to be discharged in time.  I remember you have an earlier circuit that can turn-off the PFET quickly.   I checked the PFET's datasheet it has >1nF inherent gate capacitance. 

Before you do anything else, would you check if the TL5001 output is switching? 

Thanks,

Youhao

Hi Youhao,

I will check asap and will try to reduce R3.

Thanks a lot,

JB

Hi Youhao,

I have reduced R3 until 1,8kR without difference. TL5001A doesn't start and SCP is around 2,5V. Thus controller triggers a short circuit condition.

Best regards,

JB