PTV12020L Buck Converter Troubleshoot

Thread Starter

DocQBN

Joined Jan 2, 2017
32
Hi, I currently trying to troubleshoot this device. At the moment I am able to get 0.8 to 1.8 volts with the potentiometer which is not an issue. The current on the other hand is the issue. The current maxes out at 4amps and I need it to be in the 8-10 amp range. The current is following the voltage so 1.8v = 4a, 1.6 = 3.8a etc....

I have it set up such that:
Pin 1+2 = Vout -
Pin 3+4 = Vout +
Pin 5+6 = Vin w/ 560uF metal and 22uF metal capacitor in parallel (I'm using a 12V/3A wall wart as a Vsupply)
Pin 7 = I initially had it connected to Pin 4, but removed it during troubleshooting w/ no resolve
Pin 8 = I have a 10k rotary potentiometer connected to GND
Pin 9 = I had this pin connected to Pin 6, but removed it while troubleshooting w/ no resolve
Pin 10+11: GND
Pin 12: I initially had this connected as an on/off, but removed it during troubleshooting w/ no resolve.


I noticed the emphasis on using a 22uF ceramic capacitor in the schematic, but it's all I have. I wouldn't imagine this would be the root of my issue.

I'm puzzled why it's maxing at 4 amps when the device is capable of 16 amps.

Thank you.
 

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DickCappels

Joined Aug 21, 2008
10,152
Some general partially rhetorical questions things first:

What is the voltage at pin your measurement point and at Vin when loaded to 4 amps?

Is the sum of resistances of your load and wiring, from the ground pin to the Vo Sense point low enough (1.8V/8 amps = 0.225 ohms)?

Is VoAdjust (pin 4) connected directly to GND on pin 7 (-not pin 1)? If connected anywhere else, a ground loop could increase the output resistance of the regulator.

Is anything getting unreasonably hot (thermal limit concern),
 

Thread Starter

DocQBN

Joined Jan 2, 2017
32
I measured 12.6 volts at Vin and 1.815 volts on the Vout

At my potentiometers lowest resistance I am getting 2 ohms.

My VoAdjust (Pin 8 w/ Potentiometer) is connected to Pin 2 GND.
The VoSense (Pin 7) is connected directly to Pin 4 with a small piece of breadboard wire. I recently cut this though during my troubleshooting phase. Currently, it is open.

Everything is cool to the touch, not even noticeably warm.

I going to try removing the potentiometer GND from pin 2 to pin 11 to see if that helps. If that doesn't help, I will see if I can find something of lower resistance.
 

Thread Starter

DocQBN

Joined Jan 2, 2017
32
Some general partially rhetorical questions things first:

What is the voltage at pin your measurement point and at Vin when loaded to 4 amps?

Is the sum of resistances of your load and wiring, from the ground pin to the Vo Sense point low enough (1.8V/8 amps = 0.225 ohms)?

Is VoAdjust (pin 4) connected directly to GND on pin 7 (-not pin 1)? If connected anywhere else, a ground loop could increase the output resistance of the regulator.

Is anything getting unreasonably hot (thermal limit concern),
I reconnected VoSense (Pin 7) to Vin (Pin 4) as well as Pin 9 to Pin 5 (I had previously said Pin 6 but that was a mistake it was Pin 5).
I tried moving the potentiometer GND to Pin 11 w/ no resolve. I removed the potentiometer and put in place a resistor 0.41ohm 5% (YellowBrownSilverGold) read 1.8v @ ~4.17 A. I tried several other resistors with the same result. I finally just put a wire instead and still got 1.8v @4.17 A.
 

DickCappels

Joined Aug 21, 2008
10,152
Ohms law: 1.8 volts/0.47 ohms = 3.83 amps. You need a lower total resistance in order to get more current with that voltage.

If you want 10 amps you will need a total load resistance of 1.8V/10A = 0.18 ohms. That is close to the resistance of the test leads on one of my DVMs.

Be sure to include the resistance of your current meter which I assume you have in the circuit.
 

Thread Starter

DocQBN

Joined Jan 2, 2017
32
Ohms law: 1.8 volts/0.47 ohms = 3.83 amps. You need a lower total resistance in order to get more current with that voltage.

If you want 10 amps you will need a total load resistance of 1.8V/10A = 0.18 ohms. That is close to the resistance of the test leads on one of my DVMs.

Be sure to include the resistance of your current meter which I assume you have in the circuit.
I'm currently using a piece of wire instead of a resistor. It's the lowest resistance that I am able to get. I am able to get 1.8 volts with it but still limited in current. My DMM isn't accurate enough to measure how much resistance the wire has. I'd imagine it would be somewhere around 0.02ohms as the piece of wire is about 1 in long.

Another thought I had was, it was being limited by the power supply so I hooked it up to a computer power supply with enough amperage and it still did not push more than 4 amps.
 
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