Quote:
Originally posted by johnrtse
This H-bridge concept has me intrigued. I am building a multi-cell Dragster right now and was planning to do the std. transistor mod, but had some reservations about having the weight of an extra cell in there just to power the pcb (this thing will be plenty heavy enough!).
I'll be watching this post closely, wild!
John
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Well, I finally got to do some rough testing and the good news is that the H-bridge actually switches back and forth, the bad news is that the thing is SO inefficient that it doesn't work.
I used a simple 4 transistor H-bridge, a pair of 2n2222a NPN and a pair of 2n2907a PNP. check this page for details.
http://library.solarbotics.net/circu...arHbridge.html
I didn't use inverters or buffers on the input so my bridge is what they call the "Bolt Light" check this page for some data on it
http://library.solarbotics.net/circu...varH_test.html
I used a 1.5v pager motor for the tests. and Power supply Vcc set to 1.506v
Vcc = input voltage
Vnl = Voltage "No Load" (no motor)
Vm = Voltage across motor
Im = Amps at motor.
First I took some measurements with just the motor connected to the power supply.
Vnl = Vcc = 1.506v
Vm = 1.488v
Im = 42mA
Second I used the simple transistor switch from my page, with a 1k resistor at the base. again Vcc = 1.506v and I used a 1.5v AA for the input signal.
Vnl = 1.487v
Vm = 1.28v
Im = 51mA
Third the "Bolt Light" H-bridge Vcc = 1.506v
Vnl = .7v
Vm = .038v
Im = 5.8mA
needless to say that with this numbers the motor didn't move. inverting the input signals did invert the Vnl voltage from +.7v to -.7v so the H-bridge was at least switching. Invreasing Vcc didn't have an effect on Vnl. I don't know why this is so, I'll have to leave it to the experts.
