eldenh
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Tue Oct 27, 2020 5:59 pm

It looks like I mislabeled the terminals. The central terminal of Q101, Q104 and Q110 are at 59v.
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kiev
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Tue Oct 27, 2020 8:05 pm

Q104 and Q103 are the upper FETs in the H-bridge. The ODD numbered side feeds the -1 terminal of TR103; the EVEN numbered side feeds the -2 terminal.

So the question is what does it take to boot strap IC101 the switching regulator controller to start switching Q110?

The datasheet indicates it uses a 26V supply and start up threshold of 11V.

In the pictures you can see the bottom layer has a HV resistor divider network. It is self-switched by Q109 to create a voltage labelled as "Vsub" on the top layer in a little box with 2 vias over by IC101. It is carried around on internal traces.

This Vsub provides the "collector" voltage to pin 10, and passes thru R125, 51Ω, to provide the Vcc for IC101 on pin 11. Ground is pin 6 and it connects to the HV(-) terminal.

So check the voltage at Vsub with respect to HV(-) , IC101 probably won't start switching until it hits 11V.

There are 2 more HV resistor divider networks on the bottom layer, appear to be associated with IC102 op amp, and somewhere else--there are some internal traces.

[edit]
So the HV resistor divider networks: the first one drops the HV(+) across R117-120 for a total of 204kΩ and feeds a zener diode ZD101 (can't read the marking) on the base of Q109 ; the second one drops across R121-124 for 188kΩ to the collector of Q109. i think the action here is to self start Q109 to provide the power supply Vsub. There is a diode D101 (blocking diode?) on the emitter of Q109 before the Vsub via.

Vsub is the voltage on C122, 47uF 35V.

The third divider drops 900kΩ across R139-141 and runs to some internal plane on vias. It is also dropped across 130Ω R142 to feed ?

There is an ON/OFF pin 13 of IC101, but i'm not finding the source--it is carried on an internal trace...
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eldenh
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 10:58 am

Kenny, it looks like you stayed up late working on this! I decided I would have to take the PC board off the check on the back side too. After examining it, I chose to power up again with 59v. I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.
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kiev
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 1:45 pm

Continuation,

i found the ON/OFF.

IC101 has an internal reference voltage regulator, +5V output on pin 14. The board vias and traces that i couldn't seem to follow are coming from that pin.

When the Vcc on pin 11 is greater than 11V, but less than 26V, the internal reference 5V is created and available on pin 14. On this board they have connected pin 14 to the ON/OFF control pin 13, so it should start right up given a proper Vcc.
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kiev
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 2:19 pm

eldenh wrote:... I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.


i tried to measure mine in-circuit--it was breaking over at about -0.5V, and had about 1V of forward drop. So your's is probably okay.

2.5V should be enough to turn on Q109, but i'm not seeing how it could create 11 to 26V for the chip supply.

Need to get this drawn up and look at the datasheets...

[edit] i'm seeing a faint impression of "182" on the zener, maybe that's the Vz = 18.2V

Q109 turns on at about 0.6 according to datasheet, so my measurement was likely just biasing that junction in the device and not the zener. if i have time i will remove it and test it separately, but it doesn't matter unless it is shorted the Q109 will be turned on if HV is high enough.
Last edited by kiev on Fri Oct 30, 2020 7:47 am, edited 6 times in total.
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eldenh
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 2:32 pm

Can anyone determine the correct voltage for ZD101?
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coulomb
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 5:48 pm

kiev wrote:
eldenh wrote:... I found that the ZD101 is at 2.56v and the output from D101 is 1.37v which is what i'm finding pin 11, VCC, of IC101. Since the spec sheet calls for 11.5 to 24v, it seems that ZD101 may be defective.


i tried to measure mine in-circuit--it was breaking over at about -0.5V, and had about 1V of forward drop. So your's is probably okay.

My understanding is that zener diodes below about 3.3 V are really useless, and even 5.1 V is a bit dodgy. So I doubt that it's a less than 1 V zener. More likely, the rest of the circuit is loading it down.

I think to get the voltage to IC101 up with 59 V applied (and I think it's worth a bit of effort doing this), some of the resistor chains will have to be temporarily shorted. But there seem to be three separate chains, so some tracing will likely be needed.

To find the voltage of ZD101, I think applying about 12 V limited to about 25 mA directly across it with nothing else powered should be fairly safe. But the rest of the circuit could well load it down too much. But it might give you an idea, like oh it's more than 5 V. I wonder if it might be compared with Vref to generate a sort of "power good" or "DC-DC operating OK" signal, or at least one input into the power good logic.

eldenh
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 6:40 pm

ZD101 is connected to the HV+ by about 205k. It appears the voltage out of Q109 is connected to VCC of IC101 by a diode. The spec sheet lists max VCC of 26v and recommended 11.5 to 24 with 15 normal. Without proper test equipment, I've been making do with a 12v battery and a 58.7v bicycle battery charger.
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coulomb
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Wed Oct 28, 2020 9:08 pm

eldenh wrote:ZD101 is connected to the HV+ by about 205k.

Ah, That's probably R117-R120 (51 kΩ x 4 = 204 kΩ). Perhaps consider shorting one or two of these temporarily.

It appears the voltage out of Q109 is connected to VCC of IC101 by a diode.

OK. So perhaps Q109 turning on, perhaps partially, is what "bootstraps" IC101. IC101 gets its power from the "logical OR" of Q109 or another path via another diode. That other path is probably one of the secondary windings of TX105, suitably rectified and filtered. So once IC101 is driving the MOSFET and transformer (probably actually a multi-winding inductor), it can power itself from the HV source. At that point, something will likely happen to turn off Q109. Perhaps there is a capacitor in the base circuit of that transistor that turns it off after a few hundred milliseconds.

Without proper test equipment, I've been making do with a 12v battery and a 58.7v bicycle battery charger.

Hopefully, that's a dumb battery charrger that doesn't need to see an actual battery there. Elcon charrgers for example won't turn on their output relay unless a battery is detected. An actual current limited power supply would be much better, since it can be programmed not to supply more than a few watts of power, which hopefully reduces the chances of something burning up. But of course, you have to work with what you have.

kiev
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Re: Gen1 DCDC Converter Troubleshooting and Repair

Thu Oct 29, 2020 5:33 am

coulomb wrote:
It appears the voltage out of Q109 is connected to VCC of IC101 by a diode.

OK. So perhaps Q109 turning on, perhaps partially, is what "bootstraps" IC101. IC101 gets its power from the "logical OR" of Q109 or another path via another diode. That other path is probably one of the secondary windings of TX105, suitably rectified and filtered. So once IC101 is driving the MOSFET and transformer (probably actually a multi-winding inductor), it can power itself from the HV source. At that point, something will likely happen to turn off Q109. Perhaps there is a capacitor in the base circuit of that transistor that turns it off after a few hundred milliseconds.


Mike, you are a really smart guy with a great ability to explain the details without a board or schematic in hand. As always, i appreciate your observations and analysis.

After reading what you wrote i went back to look at the board and you are spot on. The resistor chains and Q109 on the bottom layer can only get so far on generating a startup voltage even with a 360V supply, in fact it may function just as a "Pre-charge" circuit for filling the Vsub reservoir of capacitor C122. Vsub is the supply voltage created on the "hot side" secondary by the switching action of Q110, and it is used as the Vcc for the IC101 chip.

Here is a simulation run with a 15V zener and no load on the test point that would be pin 11. The voltage can be adjusted by changing the zener value--it's going to level off at a little below the zener.

Image

And this is with a bit of load added to represent the drain on Vcc at pin 11,
Image
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