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H-Bridge Contoller

Hello,

I am trying to cycle an h-bridge from forward to reverse at a frequency of anywhere between 1 and 500Hz. I am using a function generator to trigger the bridge, and I have separated a square wave output of the bridge into a negative and positive component using diodes. The H-bridge schematic that I am using is from Eugene Blanchard's website, it uses MOSFET switching transistors. Anyway, I need to trigger the bridge using the function generator, and I can't devise a way to trigger one leg of the bridge using the negative f.g. output. Can anybody tell me how to modify the bridge to accept this input? Or invert the f.g signal to a positive value? Thanks in advance!

-- JJ

Reply to
James
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Are you using it as a pwm fwd/reverse speed control, or just as an onfwd-off-onreverse switch/relay?

Reply to
BobG

The H-Bridge is used as a relay to cycle a low resistance load from 8 to -8V, in a square wave type signal. During testing I am using a 0.5 and a 2 Ohm power resistors to simulate different amounts of load. I can create two pulsed signals using the f.g. and diodes to trigger the bridge, but one logical input signal has a negative sign, which is not activiating one side of the bridge. The "off" time for the bridge should be negligible, I am trying to switch directly from fwd to reverse. I can supply a schematic of the bridge if necessary. thanks!

Reply to
James

just as an switch/relay as you said, basically I am driving a low resistance load that needs to be cycled from 8 to -8 V, with about 10 Amps of current. The load has negigible capacitance, and I am using a 2 Ohm and 0.5 Ohm power resistors. to simulate the load during testing. I have a f.g. that can provide two logical input pulses via a square wave and diodes, but the only problem is that one of the logical inputs is negative, which is causing me problems. Also, I may have to vary the driving voltage from 1 to 8V. do you need a schematic?Thanks for the interest.

Reply to
James

Schematic would help. If you have N chan mosfets on the top and the bottom, the 'top' one needs to get its gate really pulled up to turn on. Or you could have a 'complementary' rig where the top gate (P chan) get pulled down to turn on, and the bottom is N chan and the gate gets pulled up to turn on. What volts from the f.g. and what batt volts on the bridge?

Reply to
BobG

The schematic can be found here

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As far as the voltages are concerned, I can put 0 to 8 DC volts on the bridge, and from 0 to

10 volts peak to peak on the f.g., which is used to activate inputs A and B. C and D are connected as shown in note #4. Anyway, basically what I need is to either activate B using a negative voltage, or invert the sign of the voltage that is going to B. I hope this makes everything clearer.
Reply to
James

Looks like you put a pos pulse on A to put out pos volts, or you put the pos pulse on B to put out neg volts. Need to have the jumpers in the 2-3 position. So you need a spdt switch from the fg to A and B or an inverter from A to B, so they are opposite from each other.

Reply to
BobG

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