Egodriver Double voltager

[teknoman2]

Last month I was trying to add a voltage doubler circuit to the egodriver,

so I drew it and made the board.

Today I just finished it and I took the DM to measure my ic voltages,

when I turn on the voltage doubler, pin 8 of opamp is 7.5v (instead on my switch pin is 15v)

and when is off is 8.05v using and 8.05v battery.

I believe when its off everything works well but when is on something going wrong.

Here my schematic.

Where is my mistake ?

[RobA]

Pin 6 on the charge pump shouldn't be connected to ground for supply inputs greater than 3.5V.

From the spec sheet.

The voltage regulator portion of the TC1044S is an integral part of the anti-latch-up circuitry. Its inherent voltage drop can, however, degrade operation at low voltages. To improve low-voltage operation, the "LV" pin should be connected to GND, disabling the regulator. For supply voltages greater than 3.5V, the LV terminal must be left open to ensure latch-up-proof operation and prevent device damage.

Edit: if you are using the MAX1044, it's not quite as severe, but you should still leave the LV pin disconnected.

[RobA]

Also, I think your caps need to be bigger, around 10µF and preferably low ESR type electrolytics. I don't know if these are your issues, but they could be part of the problem.

[teknoman2]

My caps are 10uF so thats not the problem,

I just leave opened pin 6 and I have 9.5 when its off and 7.8 when its on (battery voltage 8.0v)

Any other suggestions?

[RobA]

Which charge pump are you using?

[teknoman2]

Which charge pump are you using?

I am using max 1044.

http://datasheets.maximintegrated.com/en/ds/ICL7660-MAX1044.pdf

[RobA]

Well, the Max chip is supposed to be OK when the LV pin is connected at high voltage. Other charge pumps can be damaged. I'd guess that's not the problem.

If your circuit is pulling too much current, the output voltage will drop. The Max1044 is limited to about 20mA and a bit less with the boost pin used. This can be even lower if your caps have high ESR. Can you check to see how much current you are drawing through the circuit?

[RobA]

As a note, I don't think the circuit should be pulling too much current. It's just that if something else is wrong and it is, then that could show up on the charge pump output.

[teknoman2]

Well, the Max chip is supposed to be OK when the LV pin is connected at high voltage. Other charge pumps can be damaged. I'd guess that's not the problem.

If your circuit is pulling too much current, the output voltage will drop. The Max1044 is limited to about 20mA and a bit less with the boost pin used. This can be even lower if your caps have high ESR. Can you check to see how much current you are drawing through the circuit?

How can I check the current draw?

Here is my board if anything helps.

[RobA]

If your multimeter has a current setting, you can use that. If not, then you can put a really small resistor, 10Ω or so, in series with the power input and just measure the voltage drop across it and then use Ohm's law.

I've got to be away from the computer for a while, but I'll look at the board in a bit.

[RobA]

I just looked at your schematic again and realized that you have a 100Ω on the input. You can just measure the voltage drop across that and use Ohm's law.

[teknoman2]

I measured across 100R resistance 7.49v so my current draw is 74.9mA.

My battery has 7.91v

Is that normal?

[RobA]

I measured across 100R resistance 7.49v so my current draw is 74.9mA.

My battery has 7.91v

Is that normal?

Is that measured from one side of the resistor to the other? Or, is that the voltage from ground to the output side of the resistor?

If it's across the resistor (leads on either side of the resistor), that seems really high for this circuit. If it's from ground to the output side, then you are at about 4mA and that seems reasonable. If you really are at 75mA draw, I'd suspect a short somewhere.

If it is at 75mA, then I doubt if the MAX1044 can supply that much current especially in the boost mode.

I was just looking at your schematic again and I thought that it would probably be good if you had the 9V/18V switch setup as a DPDT that in addition to the voltage switching it would cut the power to the charge pump. That way, in 9V mode it wouldn't need to power the charge pump and the charge pump wouldn't be putting noise on the power rails.

If you have the charge pump socketed, try taking it out and measuring the current draw when in 9V mode.

[teknoman2]

Thank you again for your time,

my values are measured from ground to the output of the resistor , so my current draw as you said 4mA
is normal.

In my board I am using an SPDT ON-ON do you believe is the cause of my issue?

I will take out the charge pump and I will measure the current draw in 9v.

[RobA]

No, I don't think the switch is your problem. I just thought it would be a nice addition to the way your circuit is setup now.

With only a 4mA draw, the charge pump should be OK at delivering the doubled voltage and you should be seeing something around 15V on the power supply.

Perhaps the charge pump is damaged or there is an issue with one of the caps. Or, since you are seeing 15V at the pin to the switch (is this both the input and output of the switch?) there is a solder bridge or something like that. It doesn't seem likely though because the voltage is right with the charge pump out of the circuit.