Testing the LTC3703 Buck.

[bigkahoonaa]

I'm looking for a Switching-Mode Power Supply (SMPS) controller, and the LTC 3703 seems promising.  It's from Linear Technology:

 

I think I can program pins Mode, Fset, IMAX, INV, Run/SS, with a micro controller. Big drawback is it's only available in surface mount and not DIP.

[Boss]

You didn't mention what you want to do with it. Yeah surface mount pins are too much fun to hand solder

[bigkahoonaa]

Seems like many post on this site ask about changing generated voltage to something the batteries can take.  I'm trying to see how easy/hard it would be to make a buck converter, Vin from 15 to 100.  Nice thing sbout this one is you can simulate how it will work:

SwCAD III

PS forgive my dyslexia - it's an LTC3703 and not TLC3703

[TomW]

Big;

Fixed the dyslexia error

T

[bigkahoonaa]

Thansk T

A bit of info on how the chip works:

V1 = chip and MOSFET power supply (in this configuration)

V2 = voltage from generator.

Vout = output voltage to batteries.

Mode = pulse skip mode when > 0.8V or continuous operation when < 0.8V

Fset = PWM frequency for the MOSFETs (Q1 and Q2).

COMP = loop compensation (?)

FB = Feedback Input.  Needed to control Vout.

IMAX = Max current.  Float = no control.  Setting R1 limits Amps.

INV = Buck/Boot mode.  Buck at < 2V and boost at > 2V. May need reconfiguration for boost.

Run/SS = chip on/off.  Off < 0.9V and soft start >0.9V.

GND = ground

BGRTN = Bottom gate (Q2) return.

BG = Bottom gate (Q2) driver.

DRVcc = bottom gate (Q2) power supply (10V in this configuration).

Vcc = chip power (10V).

SW = Switch Node Compensation (?)

TG = top gate (Q1) driver.

BOOST = Top Gate (Q1) Drive Supply (10V in this configuration).

Vin = Input Voltage Sense Pin.

Output voltage is controlled by the R4 and R6 voltage divider.

Big

[Opera House]

What is wrong with the older technology chips like the like TL494 and SG35XX chips with leads.  Everyone here should be using larger inductors and slower switching speeds to minimize problems.  Those who work with these know they can be a pack of hidden troubles.  Slow things down and the people here stand a chance.

[s4w2099]

This applies if you are trying to match a wind genny or high volt solar panel array. Correct me if I am wrong but I think that this circuit will end up stalling your wind generator, or it will drag your solar panel array volts down.

The voltage feedback is in the output and the circuit will increase the PWM if the voltage is under the set point. For battery charging maybe you would like 14.4V at the output of the converter. If the battery is discharged its voltage will not go to 14.4V so easily. The buck converter will try to increase the PWM at this point as it sees a lower voltage than 14.4V in its output.

With higher PWM it will be drawing more power from the mill making possible stall. In the other hand if battery is too charged the effect will be the opposite. PWM will be small to keep the battery volts at 14.4V and the mill will be very unloaded causing overspeed.

I know that a similar circuit will work well for matching the loads and prevent these problems. I dont know if this IC can be configured to take volts from the input and keep those constant instead of trying to keep the output constant.

[Opera House]

Chips like I mentioned have two inputs so the boost can be inhibited if the input voltage falls below a certain level.  The second input is usually used in other applications for a current limit.

[s4w2099]

true Opera House. I am talking about the presented circuit in particular. I think tl494 would be a better deal for this application combined with a half bridge driver like the IR21834.

I just got used to the tl494 maybe there are better chips out there for this purpose.