ph2t
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Actually dude the diode on the pcb IS used for the voltage boost circuit. Trust me, I’ve done the measurements and the research for this. The DCDC convertor used is ME301 and there is a 220uH inductor on the board (axial type) also there is a 100uF 6V electrolytic cap on the board as well.
During various mods I’ve actually broken the diode on the board and substituted it with another diode no sweats. You should use a shottky based one for it’s reduced voltage drop.
The NCP1402 circuit pictured above is the one I use to convert the 1.2V rail from the NiCd and boost it to 5V. From this I’ve been able to run 5 LEDs. 2 White, 2 Blue, 2 Red and 1 Yellow. Yeah!
Fellas, to add some info:
In the receiver circuit for these cars is a DCDC convertor. The DCDC convertor is used to increase the voltage from 1.2V to 3V. The IC on the receiver pcb needs at least 2.something volts to work so that’s why it’s there.
You will notice on the unside of the pcb a little orange glass canister thingy. This is shown in the right of the picture below:
This is a diode, in particular it is probably either a gernanium (spelling?) or schottky diode. These have a lower voltage loss (as trash was eluding to earlier) than your normal silicon diodes. So instead of 0.7V, you are looking at approx 0.2V to 0.5V drop with these diodes.
Why do they use these types of diodes? We’ll it’s all about loss and minimising this. If you are using a silicon diode in the DCDC convertor circuit then you would have more loss and therefore it would be harder to maintain a higher output voltage than if you were to use a lower loss diode.
Below is a picture of a DCDC convertor circuit. This circuit is NOT the exact model of what’s on the BCG circuit but it is close.
You can see the diode in this circuit, it is this symbol
.ph2t.
Edited by – ph2t on 16 November 2003 11:34:07
Edited by – ph2t on 16 November 2003 11:36:23
just to be a bastard here betty, current actually starts at – and moves toward +. Figure that out!
Anyways to your problem:
These motors, where do they connect to? The original PCB from the toy car you pulled apart? If so my bet is that you won’t be able to run the motor in the config above? Why? Because the motor never gets to the Vcc (+ volt rail), it’s switched through two transistors, see below:
In the image above the motor changes direction depending on the current path across it. Red is one path, blue is the other…(ignore the green blocks…)
If you could find where Q6/Q7 in the diagram connect to the Vcc rail you could isolate this and run it at 6V. This way you wold still have the RF circuit and RX chip running at 3V and have the 6V source only tapped into the h-bridge(the pic above) which drives the motor direction.
ph2t.
