Need electrical help with DC to DC converter please

[ort5]

Hello,

I have a Tyco QW050b1 DC to DC converter that I'm trying to use for my headlight (datasheet here: http://www.part-datasheets.com/data/qw050b1.pdf )

I'm having trouble with the remote switching option, and I could use some help. The datasheet says the following:

Remote On/Off
Negative logic remote on/off turns the module off during
a logic high and on during a logic low . To turn the
power module on and off, the user must supply a switch
to control the voltage between the on/off terminal and
the VI(–) terminal (Von/off). The switch can be an open
collector or equivalent (see Figure 15). A logic low is
Von/off = 0 V to 0.7 V. The maximum Ion/off during a logic
low is 1 mA. The switch should maintain a logic-low
voltage while sinking 1 mA.
During a logic high, the maximum Von/off generated by
the power module is 15 V. The maximum allowable
leakage current of the switch at Von/off = 15 V is 50 μA.
If not using the remote on/off feature, short the ON/OFF
pin to VI(–).


I was just going to use a switch in series with the headlight power leads, so I planned to not use the remote on/off feature. When I take the advice of the datasheet, it says to short the ON/OFF pin to VI(-). The problem is that the unit will not turn on if I do this (if there is a load on it). I have to apply power to the unit first (with the load), and then short the ON/OFF pin to VI(-). However, I can't just plain short it. I have to sort of make a very light contact between the two pins such that I get a tiny spark. Otherwise, it won't turn on. It works well with frayed wires contacting each other. After a few tries, this usually turns it on. Then I can just twist the wires together and it stays on. I tried a regular pushbutton switch and it doesn't work. Any ideas? How can I simulate this "light contact with spark" effect using a switch? I measured the voltage between the two pins and it's only around 3.5V.

If I have no load on the converter, then it does turn on with the ON/OFF pin shorted to VI(-). It makes a very high pitched switching sound and puts out approx 14V. If I try to apply my headlight load, it just immediately turns off. This is perhaps because the inrush current of the light is too high, but I'm not sure.

I'm open to any suggestions you may have.

Other useful data:
56V battery voltage
35W headlight rated for 12V
Converter puts out 12V and is good for 50W

Thanks,
Dave

 

[rkosiorek]

these are really easy to use.

you need to make a few connections o make it go.

1. short the Sense(+) to the Vout(+)
2. short the Sense(-) to the Vout(-)
3. connect one end of a swith to the Vin (-)
4. connect the other end of the switch to the On/Off pin.
5. connect the battery to the Vin(+) and the Vin(-)

NOTES:
a. closing the switch will short the On/Off to the Vin(-) and turn the unit on.
b. on most of these the Vin(-) is isolated from the Vout(-) and they should not be shorted together.

Suggestion:
most HID or Halogen lights are actually meant to work on 13.8V. they will look rather dim if you are only using 12V. you can adjust this upward abit though. connect a 10K variable resistor between the Sense+ and the trim pin. now you can adjust the voltage upward to about 13.2 volts or so.

rick

 

[ort5]

these are really easy to use.
you need to make a few connections o make it go.

1. short the Sense(+) to the Vout(+)
2. short the Sense(-) to the Vout(-)
3. connect one end of a swith to the Vin (-)
4. connect the other end of the switch to the On/Off pin.
5. connect the battery to the Vin(+) and the Vin(-)

NOTES:
a. closing the switch will short the On/Off to the Vin(-) and turn the unit on.

rick

Thanks for the help Rick. The problem is that I have it wired exactly as you indicated, and it doesn't work. The problem is that it seems that just shorting the ON/OFF pin to Vin(-) doesn't work. I have to sort of "tease" the wires together so they just barely contact for it to turn on. After it's on, I can directly short them. Perhaps this means I need a resistor in series? It's hard to explain...

 

[marty]

Good chance that I am wrong. Not a expert with these things. I copy from:
http://www.part-datasheets.com/data/qw050b1.pdf
Output Overvoltage Protection
The output overvoltage protection consists of circuitry
that monitors the voltage on the output terminals. If the
voltage on the output terminals exceeds the overvoltage
protection threshold, then the module will shut
down and latch off. The overvoltage latch is reset by
either cycling the input power for one second or by toggling
the on/off signal for one second.

Try a smaller, lower watt bulb and see if it works?
Good place to learn about light bulbs http://www.donsbulbs.com

 

[ZapPat]

I think your problem is that the inrush current when the bulb is cold is too high and this trips the overcurrent protection feature, which on these units I believe turns them off until power is cycled. When you use your jittery contact technique to get it to work, I guess that you might be pre-warming the bulb during the first contacts, then OC protection isn't triggered the last time you leave it on. After all, you have a 35W nominal bulb on a 50W converter, so it is kind of close. Inrush current for filament bulbs can be quite high I believe.

Solution 1: Add a small switch and a resistor in series between the trim and sense-, and use this switch as a dimmer, or low beam since the voltage will be lowered at the output. If you turn it on with low beam on, then switch to high it might work. You are going to have to read about triming the voltage down in the datasheet.

Solution 2: Switch to using LEDs instead of inefficient halogens - they don't have inrush current.

Also make sure you have a good quality (low ESR) smallish (1-10uF) capacitor across the unit's input in case you have a long cable run going to it. This in itself might solve some odd problems with this kind of switching converter.

 

[trappermike]

Why not try to make the DC regulators work? They convert any DC voltage into whatever output you want,12v,6v etc.? They are $1 each per amp output.
Ex.- MC4812 (12v output),$1 each.
Just need to know how to wire them in....(I don't know how) :?

 

[ZapPat]

Why not try to make the DC regulators work? They convert any DC voltage into whatever output you want,12v,6v etc.? They are $1 each per amp output.
Ex.- MC4812 (12v output),$1 each.
Just need to know how to wire them in....(I don't know how) :?

Two problems with these regulators, mike.

First prob: You are talking about linear voltage regulators, and these DC converters are switch mode converters (PWM buck specificaly). Linear regulators work by acting a bit like a variable resistor, adjusting themselves to make sure their output is at the specified voltage. The problem is that your linear regulator will be using a proportion of energy equivalent to the input voltage minus the output voltage times the current being used by your load. So if you drop 48V to 5V like this, you are wasting almost 90% of your energy in your regulator itself! Of course, this makes it heat up, which you would have to deal with too. Switching converters are usually about 85%-90% efficient, and can output much larger currents because they obviously won't heat up anything close to the linear regulator.

Second prob: It's hard to find linear regulators rated over 50V.